Surface Structures, Particles, and Fibers of Shape-Memory ...downloads.hindawi.com/journals/apt/2020/7639724.pdf · 7/1/2019 · Review Article Surface Structures, Particles, and

Review ArticleSurface Structures Particles and Fibers of Shape-MemoryPolymers at Micro-Nanoscale

Liangliang Cao123 Liwei Wang4 Cihui Zhou123 Xin Hu 123 Liang Fang 123

Yaru Ni123 Chunhua Lu 123 and Zhongzi Xu123

1State Key Laboratory of Materials-Oriented Chemical Engineering College of Materials Science and EngineeringNanjing Tech University Nanjing 210009 China2Jiangsu Collaborative Innovation Center for Advanced Inorganic Function Composites Nanjing Tech UniversityNanjing 210009 China3Jiangsu National Synergetic Innovation Center for Advanced Materials (SICAM) Nanjing Tech UniversityNanjing 210009 China4Beijing Institute of Space Launch Technology Beijing 100076 China

Correspondence should be addressed to Xin Hu xinhunjtecheducn Liang Fang lfangnjtecheducn andChunhua Lu chhlunjtecheducn

Received 1 July 2019 Accepted 6 December 2019 Published 8 January 2020

Academic Editor Behnam Ghalei

Copyright copy 2020 Liangliang Cao et al shyis is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work isproperly cited

Shape-memory polymers (SMPs) are one kind of smart polymers and can change their shapes in a predened manner understimuli Shape-memory eect (SME) is not a unique ability for specic polymeric materials but results from the combination of atailored shape-memory creation procedure (SMCP) and suitable molecular architecture that consists of netpoints and switchingdomains In the last decade the trend toward the exploration of SMPs to recover structures at micro-nanoscale occurs with thedevelopment of SMPs Here the progress of the exploration in micro-nanoscale structures particles and bers of SMPs isreviewedshye preparationmethod SMCP characterization of SME and applications of surface structures free-standing particlesand bers of SMPs at micro-nanoscale are summarized

1 Introduction

Shape-memory polymers (SMPs) are capable to be deformedand xed into temporary shapes as well as to recover towardtheir originalpermanent shapes upon external stimuli in-cluding heat light pH electric eld and magnetic eld[1ndash4] In the last two decades SMPs have attracted greatattention from both academic and industrial elds becausethey can be used in biomedical devices aerospace smarttextile soft actuators exible electronics and so on [5ndash12]Shape-memory eect (SME) is not a unique ability forspecic polymeric materials but results from the combi-nation of suitable molecular architecture and a tailoredshape-memory creation procedure (SMCP) [13 14] In

addition the shape of SMPs can be programmed on-de-mand shyese two features oer SMP advantages over othershape-changing polymers such as smart hydrogels [15ndash17]and liquid crystal elastomers [18ndash20]

shye molecular architecture of SMPs mainly consists oftwo elements ie netpoints and switching domains whichare responsible for permanent shape and temporary shaperespectively [1 4] Switching domains are usually contrib-uted by glass transition meltcrystallization reversibleconnection supramolecular bonding and so on [21] Net-points can be either chemical crosslinking in the form ofcovalent bonds or physical crosslinking [21] More specif-ically chemical crosslinking determines the permanentshape of thermoset SMPs and the domains having higher

HindawiAdvances in Polymer TechnologyVolume 2020 Article ID 7639724 16 pageshttpsdoiorg10115520207639724

transition temperature (Ttrans) in thermoplastic SMPs ieglass transition temperature (Tg) or melting temperature(Tm) act as physical netpoints [22]

e molecular mechanisms of thermoset SMPs withinSMCP and recovery modules are illustrated in Figure 1External force is first applied to deform an SMP specimeninto a temporary shape at deformation temperature (Tdeform)that is higher than Ttrans (Tg or Tm) of switching domainsleading to the orientation of polymer chains Subsequentlyby cooling below Tg (Figure 1(a)) or crystallization tem-perature Tc (Figure 1(b)) of the switching domains thetemporary strain is stored via the solidification of switchingdomains When the specimen is reheated beyond theswitching temperature (Tsw) that is dominated by Ttransrecovery process occurs via entropy-driven recoiling of theoriented polymer chains If Ttrans Tg the strain-inducednonequilibrium state is retained via the vitrification of theamorphous phase (Figure 1(a)) If Ttrans Tm the crystal-lization of switching domains limits the flexibility of ori-ented polymer chains as shown in Figure 1(b)

e quantification of SMCP ie how efficient a defineddeformation can be obtained is typically characterized bymeasuring the shape-fixity ratio Rf using the followingequation [13]

Rf εu(N)

εm (1)

where εu(N) and εm are strains after releasing stress at Tlow intheNth cycle and deformed strain respectively e recoveryfrom the fixed shape to the permanent one during applyingexternal stimuli is of the most importance to evaluate SMEStress-free recovery ie no external load is applied is themost common method to quantify shape recovery Shaperecovery ratio Rr is typically characterized by the ratio of thestrain during the present Nth cycle εmndashεp(N) and the strainobtained during SMCP in the previous (N minus 1) cycleεmndashεp(N minus 1) as shown in equation (2) An additionalcharacteristic of SME is switching temperature Tsw which isdefined as the temperature where the highest recovery rate isobtained [13]

Rr εm minus εp(N)

εm minus εp(N minus 1) (2)

With the development of SMPs the trend toward theexploration of the ability of SMPs to recover structures atmicro-nanoscale occurs Several approaches focused on theindentation of SMP films in some cases in combinationwith the subsequent removal of the topmost polymer layers[23ndash27] Temporary cavities are generated onto SMP sur-faces by indentation techniques which can be erased uponannealing However the minimization in surface energymay also enable polymers to reach smooth surface [28] erecovery of the indented nanostructures to permanentsmooth surface thus may not be unique for SMPs Anotherwidely reported manner for demonstrating SMEs at micro-nanoscale is to incorporate permanent micro-nano-structures onto SMP substrates using molding replication aswell as to deform them into either flat surface or other

structures with different features [29ndash43] Furthermorefree-standing SMP matrices with all dimensions at micro-scale are also of increasing interest [44ndash48] ese free-standing particles or fibers may behave differently fromindented and micro-nanostructured SMP surfaces becausethe underlying bulk material may to some extent contributeto their shape-memory functionality e SMCP may in-volve distortion eg of pillars during which their defor-mation is transferred into the bulk phase Accordingly theunderlying matrix may contribute to or even dominate theswitching of surface structures In contrast free-standingSMP particles of fibers at micro- or nanoscale exclude thecontributions of underlying bulk materials

In this review the recent progress in the development ofmicro-nanoscale structures and particles of SMPs is dis-cussed We try to summarize the preparation methodSMCP characterization of SME and applications of SMPsurface structures particles and fibers at micro-nanoscaleWe hope that this short review can be beneficial for de-veloping miniature SMP devices that can be used greatly inoptical biomedicine and smart surface areas

2 Surface Structures of SMPsat Micro-Nanoscale

21 Preparations of Permanent SMP Surface Structures atMicro-Nanoscale e reported SMP systems as well as theprepared features and aspect ratio (AR) of the micro-nanostructured surfaces are briefly summarized in Table 1Based on feature dimensions permanently 2D 25D and 3Dstructures on SMP surface can be considered [49] Typically2D structures present elongated features in surface planesuch as groove patterns while 25D structures presentuniformly spacing features with the same geometry in thevertical direction such as cylindrical pillar arrays e fea-tures with variable geometry in the vertical direction can beconsidered as 3D structures such as microprism andmicrolens arrays [49]

For the reported SMP-structured surfaces 2D and 3Dstructures have a small AR (le1) [32 33 50ndash55] while 25Dstructures possess a relatively high AR (ge1) [29ndash31 56] emain method to create permanent SMP-structured surface isto enable the replication of polymer or prepolymer surfacefrom master molds (Table 1) As shown in Figure 2(a) amold with pre-defined microstructures is placed against theSMP surface at a high temperature under load allowing thesufficient filling of materials into mold cavities eembossed specimens are subsequently cooled down in thepresence of the load A structural replication of SMP surfacefrom the master mold is achieved after the mold is releasedis method is quite efficient for thermoplastic SMPs withgood flowing capability at the high temperature [55 57] Forexample the 25D pillar arrays with AR 4 of a thermo-plastic polyurethane (Tecoflex having a wide range of Tgending at 120degCndash140degC) were successfully fabricated at 200degC[57]

After the formation of covalent network the mobility ofcrosslinked polymers into mold cavities is limited ere-fore to facilitate chemically crosslinked SMPs to fully

2 Advances in Polymer Technology

replicate the master mold prepolymers (polymer and curingagent) are typically used instead [32 50 53 56] As shown inFigure 2(b) after imprinting the mold against premixedprepolymers extra thermal curing or photocuring step isperformed to generate chemical networks of SMPs in moldcavities Crosslinked poly(ε-caprolactone) (c-PCL) is thewidely reported thermosetting SMP system to produce SMP-microstructured surfaces the network of which is generatedthrough either thermal curing or photocuring [32 50 56]Via crosslinking tetra-branched PCL with acrylate end-groups in the presence of linear PCL telechelic diacrylate 2Dgroove patterns of c-PCL with Tsw 33degC were generated[32] With the aid of benzoyl peroxide as the cuing agentallyl alcohol-plasticized PCL was crosslinked at 130degCthereby generating 25D pillar arrays with AR 3 andTsw 37ndash46degC [56] Finally as an instance PCL networkswith Tsw 40degC were prepared by photocuring PCL trime-thacrylate in the presence of diethoxyacetophenone asphotoinitiator [50]

Utilization of precursors is another approach to effi-ciently create 25D SMP microstructures having high AR[30 31] As shown in Figure 2(c) instead of placing a moldagainst SMP surface precursors with low viscosity arepoured into the mold before thermal treatment is performedto cure the materials Because polymer microstructures withhigh AR possess large surface area and adhesion force theyare liable to mechanical instabilities such as lateral andground collapses [31] e critical aspect ratio (ARc) forlateral and ground collapses can be calculated using theEquations as follows

ARc 049π13E13S12

W13d16 1 minus v2( )112

ARc 0284 1 minus v2

1113872 111387316 Ed

W1113888 1113889

23

(3)

where E W v and d stand for Youngrsquos modulus adhesionwork Poissonrsquos ratio and diameter of the pillar respectivelywhile s is pillar-to-pillar spacing [31] An epoxy-based SMPas an instance resulted from the thermal curing of diglycidyl

ether of bisphenol A (DGEBA) and poly(propylene glycol)bis(2-aminopropyl ether) and decylamine has been used tocreate pillar arrays with AR 2ndash4 [31] For such pillarshaving diameter of 10 μm the ARc for lateral collapse in-creased from 49 for s 5 μm to 120 for s 30 μm while theARc for ground collapse remained as 280 [31]

Last but not the least nanoimprint lithography (NIL)offers a simple approach to fabricate nanostructures onto theSMP surface by creating a polymer sacrificing layer ontowhich SMP precursors can be poured and cured before thesacrificing layer is removed afterwards [51] As an examplepolyacrylic acid (PAA) nanopatterns on silicon wafers werefirst created via thermal embossing NIL e curing of ac-rylate-based SMPs precursors on nanostructured PAA layerwas then performed After dissolving the sacrificing PAAlayer the SMP-nanostructured surfaces with identical 2Dgroove pattern having the height of 20ndash194 nm were ob-tained [51]

22 SMCP of SMP Surface Structures at Micro-NanoscaleIn comparison with the macroscale SMCP at micro-nanoscale is challenging In brief the demonstrated ap-proach to program SMPs micro-nanostructured surface isapplied to a vertical load to compress the structures withARlt1 or a shearing force to tilt the structures with ARlt1using a flat or structured plate During SMCPs permanentSMPs-micro-nanostructured surfaces are deformed intotemporary structures having required features relative to theapplications Permanently flat SMP surfaces are usuallydeformed into temporarily 2D groove patterns for cellculture [32 50 55 58] As an instance permanently flatsurface of NOA-63 (a polyurethane with ends linked bythiol-based crosslinker) was compressed by an epoxy em-bosser at 90degC for 1min before 5min of cooling at 20degCunder the compression [58] e microstructures can beeasily erased ie recover to the previously flat surfaces uponheating above Ttrans

Permanent 2D and 3D structures with ARlt1 are typi-cally deformed into flat surfaces or other features viacompression or imprinting for applications in the fields of

Heating and stretching

Heating again Coolin

g

(a)



g

(b)

Figure 1 Schematic illustration of the molecular mechanisms of SMPs having chemically crosslinked netpoints during SMCP and recoverymodules In system (a) Ttrans Tg and in system (b) Ttrans Tm

Advances in Polymer Technology 3

Tabl

e1

Materialsystemswith

theirsw

itching

temperaturesandcuring

metho

dsaswella

sstructural

featuresg

eometriesand

aspect

ratio

sof

repo

rted

SMP-micro-nano

structured

substrates

Materialsystem

T sw

Curingmetho

dsStructural

dimensio

nsandfeatures

Geometries

AR

Ref

Polymers

Polyno

rbornenep

ristinefullerenes

NA

3Dnano

lens

arrays

H250nm

1[55]

D250nm

S250nm

Tecoflex72Dcycloaliphatic

polyetherurethaneblock

copo

lymer

51NA

25D

pillararrays

H100μm

5[57]

D20

μmS

20μm

Prepolym

ers

PCLtrim

ethacrylatedietho

xyacetop

heno

ne40

Photo

3D3μm

times1μm

[50]

Hexnu

ts10

μmtimes1μm

Boom

erangs

NOA-63a

polyurethane

which

isend-lin

kedby

athiol-b

asecrosslink

erusingph

otoinitia

tedthiol-e

necrosslink

ing

Altered

Photo

2DHsim92μm

006

[58]

Groovepatte

rns

Wsim140μm

Ssim140μm

Tetra-branched

PCLwith

acrylate

end-grou

ps33

ermo

2Dgroo

vepatte

rns

H150nm

015

[32]

Linear

PCLtelechelic

diacrylates

W1μm

S2μm

Poly(ethylene-co-vinyl

acetate)d

icum

ylperoxide

63Ph

oto

3DFo

rmicroprism

05

[53]

Microprism

array

microlens

arraysw

hite-ligh

tho

logram

transmiss

iongrating

H72

μmW

150μm

Linear

PCL

37ndash4

6

ermo

25D

H15

μm3

[56]

Allyla

lcoh

olPillararrays

D5μm

Benzoylp

eroxide

S5μm

Precursors

Bispheno

ladiglycidyl

ether(BADGE)

poly(propylene

glycol)bis(2-am

inop

ropyle

ther)

decylamine

60

ermo

25D

pillararrays

H4μm

4[30]

D1μm

S1or

2μm

Bispheno

ladiglycidyl

ether(BADGE)

poly(propylene

glycol)bis(2-am

inop

ropyle

ther)

decylamine

60

ermo

25D

pillararrays

D10

μm2ndash

3[31]

S5ndash

30μm

Diglycidyletherof

bispheno

lan

epoxymon

omerm

-xylylenediam

inen-octylamine

78

ermo

25D

pillayarrays

H10

μm1

[40]

W10

μmS

5102

030

μmDiglycidyle

ther

ofbispheno

lan

epoxymon

omer

poly(propylene

glycol)bis(2-am

inop

ropyle

ther)

neop

entylg

lycold

iglycidyle

ther

35ndash6

5

ermo

3Dpyramids-term

edmicrotip

sH

12ndash21μm

07

[52]

W17ndash3

0μm

S100μm

Methylm

ethacrylatepo

ly(ethyleneglycol

dimethacrylate)p

hotoinitiator

95Ph

oto

Groovepatte

rns

H194nm

02

[51]

W834nm

S834nm

Hheigh

tW

widthD

diameterS

spacing


micro-optical devices dry adhesion or microchannels[29 33 50ndash53] By compressing against a flat quartz sub-strate at 105degC for 5min 3D microprism arrays of cross-linked poly(ethylene-co-vinyl acetate) (cPEVA) weredistorted during SMCP before the sample was cooled downto room temperature in the presence of the compressionforce [53] Similarly the programming of 2D groovenanopatterns of an acrylate-based SMP into flat surface wascarried out using NIL with a flat wafer at 180degC for 30min[52] Besides the SMCP of microstructures into flat surfacescan be directly performed for certain applications in dryadhesion Uniformly spaced microscale 3D pyramids-sha-ped microtips of thermoset epoxy-based SMP were placedagainst a mating substrate at the temperature above its Tgresulting in the collapse of microstructures into flat surfacesas shown in Figure 3 e contact with the substrate wasmaintained after cooling below its Tg [52] In addition toprogramming micro-nanostructured substrates into flatsurfaces they were also deformed into different features[33 50] e c-PCL surfaces with 3D hexnuts and boo-merang structures at microscale were mechanically de-formed to cubic and cylindrical arrays at 130degC using asecond replica mold and subsequently cooled to minus 78degCunder the load [50] Furthermore the c-PCL films withpermanent 2D linear and L-shaped channel patterns as apotential application in microfluidic control were over-written above Tm for 5min by the same structures orientedperpendicular to the permanent ones before the temporaryshapes were fixed at 4degC for 10min [33]

e permanent 25D structures having a high ARgt1 aretypically inclined and compressed to control the adhesionability and contact angle of the surface as well as to governcell behaviors [29ndash31 57] Pillar arrays of a thermoplasticelastomer (Tecoflex 72D) having a high AR 5 were heatedabove Ttrans A glass plate was utilized to press smoothlyagainst the pillars before pulling it manually along specificdirections (Figure 4) [57] In the presence of the glass platethe sample was cooled down below Ttrans to fix the defor-mation A tilting angle of 45deg was typically obtained Similarcreation procedures were performed to shear epoxy-based

SMP pillar arrays with AR 2ndash3 at 80degC along the latticevector and diagonally along the lattice In addition to tiltingtwo sets of identical pillar arrays with a high ARwere pressedagainst each other at 80degC (above Tg) and subsequentlycooled down to room temperature to fix the deformed shape(Figure 5) [30] e deformed scenario including inter-digitation indenting and interweaving highly depended onload pillar geometries (diameter spacing AR) and elasticmodulus of the material at Tdeform

23 Recovery Manner and Quantification of SMP SurfaceStructures at Micro-Nanoscale e incorporation of dif-ferent stimuli resources multiple shape transitions andreversibility into SMP structures at micro-nanoscale resultsin more functions and thereby explores more potentialapplications In addition similar to SMCP at micro-nanoscale the quantification of SMEs at micro-nanoscale isalso challenging New evaluation methods are requiredbased on offline microscopic approaches and measurementparameters

To date the research on SMP-micro-nanostructuredsurfaces mainly focuses on the area of direct thermally-in-duced one-way dual-shape memory effect ie upon heatingthe programmed temporary shape recovers to the perma-nent shape directly which cannot return to the temporaryshape again without another SMCPs [30 32 52] Recentlystudies on indirect thermally-induced one-way dual-shapememory effect [55] direct thermally-induced one-waymultiple-shape memory [3] and direct thermally-inducedtwo-way reversible multiple-shape memory effect [54] havebeen involved as well erefore in this context we presentthese recent developments of SMP-micro-nanostructuredsurfaces before the discussion of quantifying the SMEs

Instead of heating the recovery of deformed nanolensarrays of polynorbornene with 01 wt fullerene was trig-gered by absorbing electromagnetic energy which wasgenerated by microwave irradiation [55] e fullerene as athermal conductive filler played a role in absorbing mi-crowave and reinforcing the nanostructures simultaneously

Polymer

Mold

Thigh

Tlow

(a)

Prepolymer

Mold

Tlow

Thigh

Curing

(b)

MoldCuring

Precursors

Tlow Tlow Tlow

(c)

Figure 2 Schematic illustration of preparation methods of permanent SMP-structured surfaces from (a) polymers (b) prepolymers(polymer + curing agent) and (c) polymer precursors


realizing the indirect thermally-induced one-way dual-shapememory effect of microstructured surfaces

Nafion is a perfluorosulphonic acid ionomer having abroad Tg from 55 to 130degC which has been reported pre-senting dual- triple- and at least quadruple-shape memoryeffects [3] Its triple-shape memory effect has also beenachieved in the nanostructured surfaces [51] As shown inFigure 6 the permanent Nafion film with groove patterns

(H 194 nm s 834 nm Figure 6(a)) were programmedinto grid-like patterns at 90degC for 3min (Figure 6(b)) beforeanother silicon wafer (s 150 nm) was pressed againstNafion sample oriented 45deg with respect to the previousgroove patterns at 60degC for 30min (Figure 6(c)) Uponheating at 60degC for 80min the second temporary shape(pattern with s 150 nm) almost disappeared (Figure 6(d))Subsequently annealing Nafion film at 90degC for 10 s the

(a) (b)

Figure 3 Schematic illustration of the programming of SMP microtips against flat substrate and the subsequent recovery is figure wasmodified from [52]

Heat to T gt Ttrans

OriginalTecof lexpattern

Hot plate

(a)

Apply deformation force at T gt Ttrans

Glass slide

(b)

Cool at T lt Ttranswhile maintaining deformation

DeformedTecoflexpattern

(c)

Reheat at T gt Ttrans

RecoveredTecoflexpattern

(d)

Figure 4e inclining deformation of Tecoflex SMP pillar arrays during SMCP and the subsequent recoveryis figure wasmodified from[57]


Test shear

adhesion

Test normaladhesion

Apply a loadat T gt Tg

Cool down below Tg

(a) (b)

(c) (d)

Figure 5 (a) Schematic diagram of pressing identical pillar arrays against each other as well as the adhesion measurements (bndashd) reepossible deformation modes between two identical pillar arrays after SMCP (b) interdigitation (c) indenting and (d) interweaving isfigure was modified from [30]

0 300 6000

25

50

75

Ver

tical

dim

ensio

n (n

m)

Lateral dimension (μm)

00 05 10 15 20 25

ndash100

ndash50

0

50

100

150


Ver

tical

dim

ensio

n (n

m)

00 05 10 15 20 25

ndash100

ndash50

0

50

100

150


Ver

tical

dim

ensio

n (n

m)

0

00 05 10 15 20 25

ndash100

ndash50

50

100

150


Ver

tical

dim

ensio

n (n

m) S1 S2

S1 S2

S3

S1 S2

S3

00 05 10 15 20 25

ndash100

ndash50

0

50

100

150


Ver

tical

dim

ensio

n (n

m)

00 05 10 15 20 25

ndash100

ndash50

0

50

100

150


Ver

tical

dim

ensio

n (n

m)

S1 S2

S3

S4

(a)

(c)

(d) (e)

(b)

Figure 6 Topographic AFM images of multipattern memory effect in Nafion films programmed by TE-NIL is figure was modified from [51]


permanent groove patterns were obtained again(Figure 6(e))

e two-way multiple-shape memory effect of thethermosetting copolyester poly(octylene adipate)-co-poly(octylene diazoadipate) sub-microstructured surfaceshas been reported [54] When the temporary flat surfaceswere heated to an intermediate temperature of 50degCpartial melting of crystals allowed the shape recoverytoward the permanent boomerang patterns increasing thefeature height Cooling from the intermediate tempera-ture to 20degC resulted in the recrystallization and reversiontoward the temporary flat surfaces erefore the featureheight was reduced again Variations in one heating andcooling cycle (20ndash50degC) caused the height change in therange of 60ndash70 nm

Furthermore the full recovery of pillar arrays havinghigh AR has been reported to be dependent on the adhesionenergy between neighboring pillars which was affected bypillar spacing [30 31] Upon heating simultaneous anduniform recovery of inclined pillar arrays can be achieved onthe square lattice with s 30 μm However at the hexagonallattice with s 10 μm the recovery was localized because thepillars were in lateral contact Similarly if two identical setsof pillar arrays were pressed against each other only whenthe adhesion energy between interweaved or indented pillarswere small and the full recovery of pillar arrays can beachieved erefore the collapsed pillar arrays with α 2cannot recover at all while at α 3 pillars partially recov-ered upon heating

e full quantification of SME of micro-nanostructuredpolymer surfaces ie the determination of Rr Rf and Tsw isa challenge To date most research is limited in the eval-uation of Rr based on the height variation of the verticallydeformed 2D and 3D structures or the angle change of theinclined 25D structures [32 33 51 57]e recovery ratio of2D groove patterns made of acrylate-based SMP wasquantified using the following equation

Rr Hrecovered

Hpermanent (4)

whereHrecovered andHpermanent are recovered and permanentheights of the grooves which can be obtained from thecross-section profile of the atomic force microscopy (AFM)topography images [51] e full-pattern recovery wasachieved for all patterns having different Hpermanent from 20to 179 nm [51] suggesting that the size limitation of SME onstructured surfaces could be reduced down to sub-100 nme recovery of 25 D pillar arrays made of a shape memorythermoplastic elastomer (Tecoflex 72D) was quantified asfollows

Rr θtemporary minus θrecoveredθtemporary minus θpermanent

(5)

where θ represents pillar tilting angles in original(θpermamemt 90deg) deformed (θtemporarysim44deg) and recovered(θrecoveredsim75deg) positions measured from electronic scan-ning microscopy images [57] A partial recovery ieR 67 was obtained after the first deformation because the

overload applied for the tilting could result in the permanentdeformation [57] In addition to direct measurements of thegeometry variation during recovery the transmittance ofcPEVA film varied during recovery which was related to theheight variation of the microprism arrays was also used toindirectly evaluate the recovery ratio ie Rr IrecoveredIor-iginal [53] Here Irecovered and Ioriginal stand for the lighttransmittance through the recovered and original films Rr of100 was observed suggesting a complete microstructurerecovery [50]

24 Applications of SMP Surface Structures at Micro-Nanoscale Upon applying the stimuli the temporarilydeformed structures recover to their permanent shapesvarying surface topography and thereby changing surfaceproperties erefore SMP-micro-nanostructured surfacecan be used for cell culture substrates switchable valves andchannels in microfluidics dry adhesion as well as micro-optics

Cell culture substrates with defined structures arepowerful tools to direct cell alignment adhesion andtraction forces SMP-structured substrates that enable theswitch of surface structures have been reported as a newapproach to provide dynamic topography to control cellbehavior [32 50 56 58] e recovery force generatedduring the change in surface topography can be controlledmore simply and precisely to examine cell behaviors bymimicking natural cellular environments [56] It wasdemonstrated that the recovery of 2D groove patterns madeof polyurethane-based SMP toward flat surfaces decreasedthe alignment of C3H10T12 mouse embryonic fibroblastswhile the cell viability was not affected by the topographyvariation [58] Similar results were also reported for humanmesenchymal stem cells that switched from highly aligned tostellate-shaped morphology in response to the topographyrecovery from 2D groove patterns to flat surfaces [50]Furthermore 25D pillar arrays of allyl alcohol-plasticizedcrosslinked PCL-Fe3O4 nanocomposites which can recoverfrom a fully titled state at 32degC to the permanent 90deg at 41degCeffectively influenced the adhesion spread and alignment ofrat bone marrow mesenchymal stem cells as well [56] erecovery force and the variation in cell contact area providecomplex mechanical environmental conditions for cells andtrigger the process named as signal transduction activatingmany signaling pathways and affecting their behaviors [56]

SMP-microstructured surfaces can also find themselvesin the application of switchable and dry adhesions[30 52 57 59] To mimic the ability of attachment pads oflizards that can switch the reorientation of setae shaft angleand adjust the adhesive contact through a noncovalentinteractions 25D pillar arrays with a AR 5 were producedfrom Tecoflex and programmed into tilted positions of 45deg[57]e adhesion force presented by the permanent verticalpillars was the highest (297 kPa) while that of the temporarydeformed pillars was neglected After the full shape recoveryof the pillars to the titled positions at 75deg the adhesion forcewas restored (118 kPa) suggesting that SMP microstruc-tures enabled a switchable adhesion e interlocking


adhesion mechanism was also achieved by deforming twosets of identical 25D SMP pillar arrays with high AR againsteach other [30] e pillar-pillar adhesion forces in bothnormal and shear manners were higher than the forcesbetween pillars and flat surface as well as flat surface againstflat surface More importantly the SMP offered an easydetachment ie P and S dropped significantly to 4 and8N cmminus 1 because of the shape recovery and the modulusdrop via heating to 80degC In addition 3D microtip arrays ofSMP were pressed against a glass substrate directly while thefixation of the microstructures provided a strong dry ad-hesion of 184N cmminus 1 which reduced to sim3times10ndash3N cmminus 1

after the recovery at 90degC [52]Surface topography plays a dominant role in deter-

mining surface wettability SMP-microstructured surfacethus enables the control of topography variation therebytuning wettability [31 54] e deformed and originalre-covered SMP 25D pillar arrays presented distinct watercontact angle and droplet sliding angle Recently thepolymer-microstructured surface having reversible SME hasbeen used to demonstrate the modulation of wettingproperties [54] e elbow boomerang and cubic structuresin their programmed states displayed the glycerol contactangle of sim80deg at room temperature [31] By increasing thetemperature to 50degC the structure height was increased econtact angle thus was increased to 96degsim105dege cooling ofthe microstructured surface to 20degC decreased the reversibletopography and accordingly reduced the contact angle backto 83degsim88deg

e applications of SMPs for flexible programmable andshape-memorizing micro-optical devices have also been dem-onstrated [29 51 53] e cPEVA film having microprismarrays that acted as a retroreflector for light that entered fromthe flat side of the film was programmed into flat surface thateliminated such reflection mechanism and thus made the filmtransparent [53] e transmittance was increased from lt08for the originalrecovered microprism arrays to gt60 for thetemporary state as shown in Figure 7 An alternative approachto harass the microprism arrays for the purpose of tuning thetransmittance was to stretch the films As the strain increasedfrom 0 to 400 the transmittance increased from 08 to18 Furthermore the deformed SMP-microstructured sur-faces were heated by the arrays of transparent-resistivemicroheaters selectively triggering the local recovery of thesurface structures and providing additional capabilities in user-definable optics [53]

3 SMP Particles at Micro-Nanoscale

31 Preparation of SMP Particles at Micro-Nanoscaleepreparation of polymer particles at micro-nanoscale is aroutine topic of polymer science and technology [60ndash64]Here we only focus on the reported preparation method forpolymer particles at micro-nanoscale with SME Whenmixing polymer droplets as one phase in an immisciblesecond phase polymer micro-nanoparticles can be foundA PPDL-PCL multiblock copolymer comprising poly(ε-caprolactone) (PCL) and poly(ω-pentadecalactone) (PPDL)segments was dissolved in methylene chloride and the

solution was dispersed in aqueous solutions of differentstabilizers [45 46] e shear forces during the dispersiondetermined the particle size and microparticles can beachieved by solvent evaporation using magnetic stirring for3 h Spherical particles of photocrosslinked polymer net-works with six-arm poly(ethylene glycol)-poly(ε-capro-lactone) were also prepared using the oil-in-water emulsiontechnique [65] Electrospraying technique was also used tocreate microparticles of SMPs consisting of poly(ε-capro-lactone) (PCL) and poly(p-dioxanone) (PPDO) segments[66] e applied high electric field deforms the liquidmeniscus at the nozzle tip e liquid meniscus forms aconical jet and further breaks into droplets due to electro-static force Processing parameters can be easily optimized tocontrol the size and distribution of droplets

Nonspherical SMP particles were prepared using tem-plating methods as well [47 67] A general techniqueParticle Replication in Nonwetting Templates (PRINT) wasintroduced to fabricate monodisperse particles havingcomplex shapes [68 69] e only difference between theldquoPRINTrdquo process and the imprint lithography that can beused to create permanent or temporary structures on SMPsurface is that the precursors do not wet the substrate eprecursors thus dewet from the substrate and accumulate inmold cavities Particles with complex shapes can be achievedafter curing and being isolated Poly(ε-caprolactone) (PCL)-and poly(octylene adipate-co-meso-25-diazoadipate)-basedSMP particles were created using this method and theshapes included cubes cylinders boomerangs andH-shapes[67] A similar approach was also reported [47] Instead ofautonomous dewetting the remaining crosslinked film onthe mold surface was removed using a tweezer [47] ecube-shaped microparticles of poly(ethylene-co-(vinyl ace-tate)) were transferred to a glass slide

32 SMCPofSMPParticlesatMicro-Nanoscale Because it isa big challenge to program a single SMP particle practicallythere is a need to achieve SMCP onto multiple SMP mi-croparticles simultaneously Lendlein and coworkers sug-gested an approach by embedding free-standing SMPparticles in the matrix consisting of water-soluble polymers[45 46] As shown in Figure 8 the subsequent deformationusually stretching of the polymer matrix with embeddedSMP particles varied their original spherical shape totemporary ellipsoid shape e deformed particles can beremoved by dissolving the polymer matrix in water To datethis approach has been used by different groups as SMCP fordifferent polymer particles [65 70] Poly(vinyl alcohol)(PVA) is soluble in water and has a high melting temper-ature which is one candidate matrix material for SMCP ofpolymer particles Pristine PVA however is brittle to behandled at room temperature Plasticizer (usually glycerol)should be used to reduce the modulus of PVA during SMCP[45 46]

Compression of SMP particles into temporary-compressedflat particles was widely used as well [47 66 71] For sphericalSMP particles Zhang et al applied a pressure of 100 or 02MPafor 10min to compress heated SMP particles into either a


cylinder (100MPa) or a partial sphere geometry (02MPa)[66] e temperature was decreased by maintaining thepressure constante SMCP was finished by finally removingthe pressure Liu et al performed the similar SMCP onmicrocuboids using microscopy glass slides [47] e micro-cuboids on the first glass slide were heated and covered by thesecond glass slide Foldback clips were mounted on the two

glass slides for compression After cooling the SMCP wasfinished by removing the clips and the top cover slide

33 Recovery Manner and Quantification of SMP Particles atMicro-Nanoscale Similarly characterization of shapevariation of SMP particles at micro-nanoscale also depends

0 20 40 60 80Compression strain ()

0

20

40

60

80

100Tr

ansm

ittan

ce (

)

(a)

0

20

40

60

80

100

82 4 60 10Number of cycles

Tran

smitt

ance

()

25 compressive strain


(b)

Original shape Compressed shape Recovered shape

(c)

Figure 7 Transmittance variable soft films based on shape-memory polymers with programmable microprism arrays is figure wasmodified from [53]

PVA filmwith SMP

micromatrices

Thighstretching

Tlowshape

fixation

Collection ofprogrammed

matrices

Dissolutionof PVA film

Figure 8 Schematic diagram of SMCP of SMP microparticles to a prolate ellipsoid shape followed by subsequent particle collection isfigure was modified from [45]


on microscopic techniques ie scanning electric micros-copy (SEM) [45ndash47 66] optical microscopy (OM)[45ndash47 66 67 72] or atomic force microscopy (AFM)[47 66] e in situ heating and observation can be easilyachieved using OM and AFM At each temperature imagescontaining one or multiple particles are recorded e ge-ometries of the particles are analyzed for quantitativecharacterization of SME For spherical SMP particles thatwere stretched changes in AR can be used to quantitativelydescribe the shape recovery of microparticles as follows[45 46]

ARrAR ARprogrammed minus ARrecovered

ARprogrammed minus ARoriginal (6)

where RrAR represents recovery ratio of the aspect ratioARoriginal corresponds to the permanent spherical shape(AR 1) ARprogrammed is AR of the temporary prolate el-lipsoidal shape and ARrecovered is AR of the same particleafter shape recovery respectively Zhou et al preparedpolymer microparticles that can reversibly switch theirshapes based on the polymer network containing six-armPEG-PCL e particles were deformed at 60degC using thePVA film Reversible shape change between spherical andellipsoid was found between 43deg and 0degC [65]

e height variation during recovery is used to evaluatethe SME of temporarily compressed SMP particles in-cluding both spherical shape and cuboid shapee recoveryratio (Rr) can be defined by equation (7)

Rr Hr minus Hp

Hi minus Hp (7)

where the initial programmed and recovered height of theparticles are Hi Hp and Hr respectively [47] Liu et alreported that the recovery ratio of microcuboids was relatedto the deformation ratio ey deformed microcuboids witha height of 10 μm into temporary height of 27 and 56 μmrespectively [47] e Rrs were 42plusmn 1 and 88plusmn 1 for theone with high and low deformation respectively Zhanget al compressed SMP microparticles into one free-stranding macroscopic film that disintegrated after shaperecovery [66] Smart macroscopic films that can disintegrateon demand can be envisioned

34 Applications of SMP Particles at Micro-NanoscaleNaturally occurring particles at micro-nanoscale includingcells bacteria and viruses usually have nonspherical andvariable shapes and can adjust their biological functionsNowadays more and more research studies were focused onthe physicochemical properties of these stimuli-responsivemicro- and nanoparticles such as size shape swellinguniformity surface morphology and rigidity [73ndash80] Greatadvances in polymer microparticles have been made espe-cially in its application in drug delivery [74 81 82]

e shape-switching property of SMPs can potentiallyprovide the functions of drug delivery and medical im-aging for their ability to deliver the medical molecules tothe targeted locations e shape switch under thermal

stimuli often exhibit one-way characters which is an ir-reversible shape changing process that the particle shapeswitches from a temporary shape to a permanent shapeunder transition temperature (Ttrans) [83ndash85] To dateSMPs with two-way effect have aroused increasing re-search interest in the reversible shape switch under theenvironment stimulus [11 86ndash92] However two-wayshape memory effect (2W-SME) materials often sufferconstant stress under the cooling-heating cycles and aredifficult to be carried out [86ndash88] Microparticles based onbiocompatible and biodegradable network of six-armpoly(ethylene glycol)-poly(3-caprolactone) (6A PEG-PCL) were developed [65] ese polymeric microparticlescould reversibly switch their shapes from spherical toelliptical both extracellularly or intracellularly in with theincreasing and decreasing temperature from 43degC to 0degCe shape changing is under the mechanism of reversible2W-SME which should be attributed to the reversiblecrystalline and melting under the thermal stimuli ephagocytosis property could be controlled by tuning theaspect ratio of the particle

Zhu and coworkers investigated the relationship betweensurface textures of polymer microparticles and their drugrelease property [72] Poly(DL-lactic-co-glycolide) (PLGA)and PLGA-b-poly(ethylene glycol) (PLGA-b-PEG) micro-particles with uniform size and tunable surface structures weresynthesized via the process combining the advantages of in-terfacial instabilities of emulsion droplet and polymer-blending strategy utilizing microfluidic technology Solventremoval from the emulsion droplets is responsible for theinterfacial instabilities and the appearance of proportions esurface roughness of the particles could be adjusted by reg-ulating the ratio of PLGAb-PEG and PLGA in the blendwhich determines the efficiency of drug loading and releasekinetics of encapsulated hydrophobic paclitaxel e particleswith various roughness performed well cell viability andbiocompatibility showing the great potential in the area offields of drug delivery and other biomedical applications

Entanglement-based thermoplastic shape memory mi-croparticles composed of poly(DL-lactic acid) (PDLLA) andgold nanoparticles (AuPDLLA hybrid microparticles)were developed (Figure 9) [70] e shape-memory effect ofthe microparticles were indicated by their capability ofkeeping anisotropic shape at 37degC and recovery to a sphericalshape at a temperature ranges from 37 to 45degC By carefullyregulating the stretching temperature the property of shapememory and anisotropy could be imparted in the particlese light-responsive nature of the gold nanoparticles en-capsulated in the matrix provides the microparticles ex-cellent spatiotemporal control of shape recovery for thephotothermal heating is shape memory system indicatedpromising potential for shape-switching drug deliveryvehicles

4 SMP Fibers at Micro-Nanoscale

Another candidate SMP objects at micronanoscale to achievethe cyclic thermomechanical test could be SMP micronanofibers which can be produced by electrospinning [93ndash96]


or wet spinning [97 98] e shape-memory effect of fiberwoven is usually investigated and the woven can be used insmart textiles [99 100] or biomedical fields [101 102] Al-though the SME of SMP woven is determined by knittedmicronanofibers physical entanglement and chemical con-nection play important roles as well erefore the SME of asingle micronanofiber is discussed here

Regarding to the cyclic thermodynamic test the usage ofatomic force microscopy (AFM) due to its high spatialresolution and force-sensing capabilities to obtain themodulus of polymer micronanofibers via the manner ofthree-point bending test has been fully developed in thesedecades [103ndash105] is method enables an AFM cantilevertip to manipulate only a single polymer fiber which sus-pends over a small trench by applying a known force on itsmidpoint Furthermore with the combination of a hot stageAFM can also allow a real-time investigation of polymerstructures and properties while changing the temperaturewhich is also required for the cyclic thermodynamic test[106 107] Fang et al reported an AFM-based method thatcan apply the cyclic thermomechanical test onto single free-suspended polymer micronanofibers of aliphatic poly-etherurethane while unambiguously quantifying the fullspectrum of their SMEs [48] An AFM cantilever was used toprogram and fix a single free-suspended PEU fiber at thescale of asymp1 μm to a temporarily vertically bended shapeSubsequently the stress-free and constant-strain recoveriesof such programmed PEU microfiber were characterized inthe real-time manner to thoroughly quantify the importantcharacteristics of SMEs while the temperature-memoryeffects (TMEs) of a single PEU microfiber were also ex-amined More importantly this method was further mod-ified to be performed onto PEU fibers at the scale ofasymp100 nm as well as to quantify their real-time constant-strain recoveries e restoration of the original free-sus-pended shape with programming strains of 10plusmn 1 and21plusmn 1 were realized upon heating [48]

Very recently Poulin et al developed shape memorynanocomposite fibers to use as untethered high-energymicroengines [108] Fibers were twisted at the temperatureabove Tg and the mechanical deformation was stored viarapid quenching Upon heating the fibers generated agravimetric work capacity that is 60 times higher than that ofnatural skeletal muscles due o high torque with large anglesof rotation

5 Summary

e development of surface structures particles and fibersof SMPs at micro- and nanoscale expands the applicationfields of SMPs in cell culture substrates switchable valvesand channels in microfluidics dry adhesion optical devicesdrug delivery carriers etc e research to date has con-firmed that SME of polymers with suitable chemicalstructures can be achieved at nanoscale and is similar to thatat macroscale Different shape-memory effects includingtemporary memory effect reversible shape-memory effectand multishape effect can also be realized e preparationsof permanent surface structures particles and fibers ofSMPs are determined by conventional approaches whileSMCPs should be concerned to create temporary shapes oflarge amount of polymer surface structures and particles atmicro- and nanoscale simultaneously e observation andcharacterization of SME are still limited by microscopytechniques e recovery of structures is relatively easy torecord e force variation during recovery now is still a bigchallenge is field is still in progress especially SMPparticles New functions should be included in SMP particlesto satisfy different requirements

Conflicts of Interest

e authors declare that they have no conflicts of interest

Acknowledgments

is work was supported by the National Natural ScienceFoundation of China (nos 21604037 and 51503098) ePriority Academic Program Development of the JiangsuHigher Education Institutions (PAPD) is appreciated

References

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[2] Y Liu H Lv X Lan J Leng and S Du ldquoReview of electro-active shape-memory polymer compositerdquo Composites Sci-ence and Technology vol 69 no 13 pp 2064ndash2068 2009

[3] T Xie ldquoTunable polymer multi-shape memory effectrdquoNature vol 464 no 7286 pp 267ndash270 2010

Polymer chain

Gold nanoparticlesPolymer entanglements asphysical crosslinks

65degC

90degC

37degC

37degC

hυheat

hυheat

Shape memory effect

No shape memory effect

Step 1programming

Step 2application

Step 3triggeredrecovery

Figure 9 e structure of entanglement-based polymer microparticles and the their photothermal actuation is figure was modified from [70]


[4] Q Zhao H J Qi and T Xie ldquoRecent progress in shapememory polymer new behavior enabling materials andmechanistic understandingrdquo Progress in Polymer Sciencevol 49-50 pp 79ndash120 2015

[5] K Hearon M A Wierzbicki L D Nash et al ldquoA pro-cessable shape memory polymer system for biomedicalapplicationsrdquo Advanced Healthcare Materials vol 4 no 9pp 1386ndash1398 2015

[6] B Q Y Chan Z W K Low S J W Heng S Y ChanC Owh and X J Loh ldquoRecent advances in shape memorysoft materials for biomedical applicationsrdquo ACS AppliedMaterials amp Interfaces vol 8 no 16 pp 10070ndash10087 2016

[7] A Biswas A P Singh D Rana V K Aswal and P MaitildquoBiodegradable toughened nanohybrid shape memorypolymer for smart biomedical applicationsrdquo Nanoscalevol 10 no 21 pp 9917ndash9934 2018

[8] Y Liu H Du L Liu and J Leng ldquoShape memory polymersand their composites in aerospace applications a reviewrdquoSmart Materials and Structures vol 23 no 2 Article ID023001 2014

[9] J Hu and S Chen ldquoA review of actively moving polymers intextile applicationsrdquo Journal of Materials Chemistry vol 20no 17 pp 3346ndash3355 2010

[10] D J Maitland M F Metzger D Schumann A Lee andT S Wilson ldquoPhotothermal properties of shape memorypolymer micro-actuators for treating strokerdquo Lasers inSurgery and Medicine vol 30 no 1 pp 1ndash11 2002

[11] M Behl K Kratz U Noechel T Sauter and A LendleinldquoTemperature-memory polymer actuatorsrdquo Proceedings ofthe National Academy of Sciences vol 110 no 31pp 12555ndash12559 2013

[12] H Gao J Li F Zhang Y Liu and J Leng ldquoe researchstatus and challenges of shape memory polymer-basedflexible electronicsrdquo Materials Horizons vol 6 no 5pp 931ndash944 2019

[13] T Sauter M Heuchel K Kratz and A Lendlein ldquoQuan-tifying the shape-memory effect of polymers by cyclicthermomechanical testsrdquo Polymer Reviews vol 53 no 1pp 6ndash40 2013

[14] C Liu H Qin and P T Mather ldquoReview of progress inshape-memory polymersrdquo Journal of Materials Chemistryvol 17 no 16 pp 1543ndash1558 2007

[15] S Sun and P Wu ldquoA one-step strategy for thermal- and pH-responsive graphene oxide interpenetrating polymerhydrogel networksrdquo Journal of Materials Chemistry vol 21no 12 pp 4095ndash4097 2011

[16] S Jin M Liu S Chen and C Gao ldquoSynthesis character-ization and the rapid response property of the temperatureresponsive PVP-g-PNIPAM hydrogelrdquo European PolymerJournal vol 44 no 7 pp 2162ndash2170 2008

[17] P Gupta K Vermani and S Garg ldquoHydrogels fromcontrolled release to pH-responsive drug deliveryrdquo DrugDiscovery Today vol 7 no 10 pp 569ndash579 2002

[18] Y Yu M Nakano and T Ikeda ldquoDirected bending of apolymer film by lightrdquo Nature vol 425 no 6954 p 1452003

[19] J-A Lv Y Liu J Wei E Chen L Qin and Y Yu ldquoPho-tocontrol of fluid slugs in liquid crystal polymer micro-actuatorsrdquo Nature vol 537 no 7619 pp 179ndash184 2016

[20] Y Yu and T Ikeda ldquoSoft actuators based on liquid-crys-talline elastomersrdquo Angewandte Chemie International Edi-tion vol 45 no 33 pp 5416ndash5418 2006

[21] J Hu Y Zhu H Huang and J Lu ldquoRecent advances inshape-memory polymers structure mechanism

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[22] Q Zhao M Behl and A Lendlein ldquoShape-memory poly-mers with multiple transitions complex actively movingpolymersrdquo Soft Matter vol 9 no 6 pp 1744ndash1755 2013

[23] T Altebaeumer B Gotsmann H Pozidis A Knoll andU Duerig ldquoNanoscale shape-memory function in highlycross-linked polymersrdquo Nano Letters vol 8 no 12pp 4398ndash4403 2008

[24] N Liu Q Xie W M Huang S J Phee and N Q GuoldquoFormation of micro protrusion arrays atop shape memorypolymerrdquo Journal of Micromechanics and Microengineeringvol 18 no 2 Article ID 027001 2008

[25] N Liu W M Huang S J Phee H Fan and K L Chew ldquoAgeneric approach for producing various protrusive shapes ondifferent size scales using shape-memory polymerrdquo SmartMaterials and Structures vol 16 no 6 pp N47ndashN50 2007

[26] J T Fulcher Y C Lu G P Tandon and D C Fosterldquoermomechanical characterization of shape memorypolymers using high temperature nanoindentationrdquo PolymerTesting vol 29 no 5 pp 544ndash552 2010

[27] B A Nelson W P King and K Gall ldquoShape recovery ofnanoscale imprints in a thermoset ldquoshape memoryrdquo poly-merrdquo Applied Physics Letters vol 86 no 10 Article ID103108 2005

[28] Z Fakhraai and J A Forrest ldquoMeasuring the surface dy-namics of glassy polymersrdquo Science vol 319 no 5863pp 600ndash604 2008

[29] J Li J Shim J Deng et al ldquoSwitching periodic membranesvia pattern transformation and shape memory effectrdquo SoftMatter vol 8 no 40 pp 10322ndash10328 2012

[30] C-M Chen C-L Chiang C-L Lai T Xie and S YangldquoBuckling-based strong dry adhesives via interlockingrdquoAdvanced Functional Materials vol 23 no 30 pp 3813ndash3823 2013

[31] C-M Chen and S Yang ldquoDirected water shedding on high-aspect-ratio shape memory polymer micropillar arraysrdquoAdvanced Materials vol 26 no 8 pp 1283ndash1288 2014

[32] M Ebara K Uto N Idota J M Hoffman and T AoyagildquoShape-memory surface with dynamically tunable nano-geometry activated by body heatrdquo Advanced Materialsvol 24 no 2 pp 273ndash278 2012

[33] M Ebara K Uto N Idota J M Hoffman and T AoyagildquoRewritable and shape-memory soft matter with dynamicallytunable microchannel geometry in a biological temperaturerangerdquo Soft Matter vol 9 no 11 pp 3074ndash3080 2013

[34] Y Jiang U Mansfeld L Fang K Kratz and A LendleinldquoTemperature-induced evolution of microstructures on poly[ethylene-co-(vinyl acetate)] substrates switches their un-derwater wettabilityrdquoMaterials amp Design vol 163 Article ID107530 2019

[35] J K Park and S Kim ldquoDroplet manipulation on a structuredshape memory polymer surfacerdquo Lab on a Chip vol 17no 10 pp 1793ndash1801 2017

[36] Y Wang H Lai Z Cheng et al ldquoGecko toe pads inspired insitu switchable superhydrophobic shape memory adhesivefilmrdquo Nanoscale vol 11 no 18 pp 8984ndash8993 2019

[37] W L Lee and H Y Low ldquoGeometry-and length scale-de-pendent deformation and recovery on micro-and nano-patterned shape memory polymer surfacesrdquo ScientificReports vol 6 p 23686 2016

[38] T Lv Z Cheng E Zhang H Kang Y Liu and L JiangldquoSelf-restoration of superhydrophobicity on shape memorypolymer arrays with both crushed microstructure and


damaged surface chemistryrdquo Small vol 13 no 4 Article ID1503402 2017

[39] Z Cheng D Zhang T Lv et al ldquoSuperhydrophobic shapememory polymer arrays with switchable isotropicaniso-tropic wettingrdquo Advanced Functional Materials vol 28no 7 Article ID 1705002 2018

[40] T Lv Z Cheng D Zhang et al ldquoSuperhydrophobic surfacewith shape memory micronanostructure and its applicationin rewritable chip for droplet storagerdquo ACS Nano vol 10no 10 pp 9379ndash9386 2016

[41] S Schauer T Meier M Reinhard et al ldquoTunable diffractiveoptical elements based on shape-memory polymers fabri-cated via hot embossingrdquo ACS Applied Materials amp Inter-faces vol 8 no 14 pp 9423ndash9430 2016

[42] C A Tippets Q Li Y Fu et al ldquoDynamic optical gratingsaccessed by reversible shape memoryrdquo ACS Applied Mate-rials amp Interfaces vol 7 no 26 pp 14288ndash14293 2015

[43] A Espinha M C Serrano A Blanco and C Lopezldquoermoresponsive shape-memory photonic nano-structuresrdquo Advanced Optical Materials vol 2 no 6pp 516ndash521 2014

[44] K Uto and M Ebara ldquoMagnetic-responsive microparticlesthat switch shape at 37degCrdquo Applied Sciences vol 7 no 11p 1203 2017

[45] C Wischke and A Lendlein ldquoMethod for preparationprogramming and characterization of miniaturized partic-ulate shape-memory polymer matricesrdquo Langmuir vol 30no 10 pp 2820ndash2827 2014

[46] C Wischke M Schossig and A Lendlein ldquoShape-memoryeffect of micro-nanoparticles from thermoplastic multi-block copolymersrdquo Small vol 10 no 1 pp 83ndash87 2014

[47] Y Liu M Y Razzaq T Rudolph L Fang K Kratz andA Lendlein ldquoTwo-level shape changes of polymericmicrocuboids prepared from crystallizable copolymer net-worksrdquoMacromolecules vol 50 no 6 pp 2518ndash2527 2017

[48] L Fang O E C Gould L Lysyakova et al ldquoImplementingand quantifying the shape-memory effect of single polymericmicronanowires with an atomic force microscoperdquoChemPhysChem vol 19 no 16 pp 2078ndash2084 2018

[49] S Tawfick M De Volder D Copic et al ldquoEngineering ofmicro- and nanostructured surfaces with anisotropic ge-ometries and propertiesrdquoAdvancedMaterials vol 24 no 13pp 1628ndash1674 2012

[50] D M Le K Kulangara A F Adler K W Leong andV S Ashby ldquoDynamic topographical control of mesen-chymal stem cells by culture on responsive poly(ϵ-capro-lactone) surfacesrdquo Advanced Materials vol 23 no 29pp 3278ndash3283 2011

[51] Z Wang C Hansen Q Ge et al ldquoProgrammable pattern-memorizing polymer surfacerdquo Advanced Materials vol 23no 32 pp 3669ndash3673 2011

[52] J D Eisenhaure T Xie S Varghese and S Kim ldquoMicro-structured shape memory polymer surfaces with reversibledry adhesionrdquo ACS Applied Materials amp Interfaces vol 5no 16 pp 7714ndash7717 2013

[53] H Xu C Yu S Wang V Malyarchuk T Xie andJ A Rogers ldquoDeformable programmable and shape-memorizing micro-opticsrdquo Advanced Functional Materialsvol 23 no 26 pp 3299ndash3306 2013

[54] S A Turner J Zhou S S Sheiko and V S AshbyldquoSwitchable micropatterned surface topographies mediatedby reversible shape memoryrdquo ACS Applied Materials ampInterfaces vol 6 no 11 pp 8017ndash8021 2014

[55] S Jeon J Jang J Youn J-H Jeong H Brenner andY S Song ldquoFullerene embedded shape memory nanolensarrayrdquo Scientific Reports vol 3 no 1 p 3269 2013

[56] W Li T Gong H Chen LWang J Li and S Zhou ldquoTuningsurface micropattern features using a shape memory func-tional polymerrdquo RSC Advances vol 3 no 25 pp 9865ndash98742013

[57] S Reddy E Arzt and A del Campo ldquoBioinspired surfaceswith switchable adhesionrdquo Advanced Materials vol 19no 22 pp 3833ndash3837 2007

[58] K A Davis K A Burke P T Mather and J H HendersonldquoDynamic cell behavior on shape memory polymer sub-stratesrdquo Biomaterials vol 32 no 9 pp 2285ndash2293 2011

[59] S Kim M Sitti T Xie and X Xiao ldquoReversible dry micro-fibrillar adhesives with thermally controllable adhesionrdquo SoftMatter vol 5 no 19 pp 3689ndash3693 2009

[60] Q Xu M Hashimoto T T Dang et al ldquoPreparation ofmonodisperse biodegradable polymer microparticles using amicrofluidic flow-focusing device for controlled drug de-liveryrdquo Small vol 5 no 13 pp 1575ndash1581 2009

[61] J Guan A Chakrapani and D J Hansford ldquoPolymer mi-croparticles fabricated by soft lithographyrdquo Chemistry ofMaterials vol 17 no 25 pp 6227ndash6229 2005

[62] S Mawson M Z Yates M L OrsquoNeil and K P JohnstonldquoStabilized polymer microparticles by precipitation with acompressed fluid antisolvent 2 Poly(propylene oxide)- andpoly(butylene oxide)-based copolymersrdquo Langmuir vol 13no 6 pp 1519ndash1528 1997

[63] C Amiet-Charpentier J P Benoit P Gadille and J RichardldquoPreparation of rhizobacteria-containing polymer micro-particles using a complex coacervation methodrdquo Colloidsand Surfaces A Physicochemical and Engineering Aspectsvol 144 no 1ndash3 pp 179ndash190 1998

[64] N Bock M A Woodruff D W Hutmacher andT R Dargaville ldquoElectrospraying a reproducible method forproduction of polymeric microspheres for biomedical ap-plicationsrdquo Polymers vol 3 no 1 pp 131ndash149 2011

[65] T Gong K Zhao WWang H Chen L Wang and S Zhouldquoermally activated reversible shape switch of polymerparticlesrdquo Journal of Materials Chemistry B vol 2 no 39pp 6855ndash6866 2014

[66] Q Zhang T Sauter L Fang K Kratz and A LendleinldquoShape-memory capability of copolyetheresterurethane mi-croparticles prepared via electrosprayingrdquo MacromolecularMaterials and Engineering vol 300 no 5 pp 522ndash530 2015

[67] S M Brosnan A-M S Jackson Y Wang and V S AshbyldquoShape memory particles capable of controlled geometricand chemical asymmetry made from aliphatic polyestersrdquoMacromolecular Rapid Communications vol 35 no 19pp 1653ndash1660 2014

[68] J P Rolland B W Maynor L E Euliss A E ExnerG M Denison and J M DeSimone ldquoDirect fabrication andharvesting of monodisperse shape-specific nano-biomaterialsrdquo Journal of the American Chemical Societyvol 127 no 28 pp 10096ndash10100 2005

[69] Y Wang T J Merkel K Chen C A Fromen D E Bettsand J M DeSimone ldquoGeneration of a library of particleshaving controlled sizes and shapes via the mechanicalelongation of master templatesrdquo Langmuir vol 27 no 2pp 524ndash528 2011

[70] Q Guo C J Bishop R A Meyer et al ldquoEntanglement-basedthermoplastic shape memory polymeric particles withphotothermal actuation for biomedical applicationsrdquo ACS


Applied Materials amp Interfaces vol 10 no 16 pp 13333ndash13341 2018

[71] L M Cox J P Killgore Z Li et al ldquoInfluences of substrateadhesion and particle size on the shape memory effect ofpolystyrene particlesrdquo Langmuir vol 32 no 15pp 3691ndash3698 2016

[72] M Hussain J Xie Z Hou et al ldquoRegulation of drug releaseby tuning surface textures of biodegradable polymer mi-croparticlesrdquo ACS Applied Materials amp Interfaces vol 9no 16 pp 14391ndash14400 2017

[73] V Kozlovskaya B Xue and E Kharlampieva ldquoShape-adaptable polymeric particles for controlled deliveryrdquoMacromolecules vol 49 no 22 pp 8373ndash8386 2016

[74] J A Champion Y K Katare and S Mitragotri ldquoParticleshape a new design parameter for micro- and nanoscaledrug delivery carriersrdquo Journal of Controlled Release vol 121no 1-2 pp 3ndash9 2007

[75] E Eyiler and K B Walters ldquoMagnetic iron oxide nano-particles grafted with poly(itaconic acid)-block-poly(N-iso-propylacrylamide)rdquo Colloids and Surfaces APhysicochemical and Engineering Aspects vol 444 pp 321ndash325 2014

[76] B Malile and J I L Chen ldquoMorphology-based plasmonicnanoparticle sensors controlling etching kinetics with tar-get-responsive permeability gaterdquo Journal of the AmericanChemical Society vol 135 no 43 pp 16042ndash16045 2013

[77] S Shi Q Wang T Wang S Ren Y Gao and N Wangldquoermo- pH- and light-responsive poly(N-iso-propylacrylamide-co-methacrylic acid)-Au hybrid microgelsprepared by the in situ reduction method based on Au-thiolchemistryrdquo De Journal of Physical Chemistry B vol 118no 25 pp 7177ndash7186 2014

[78] Y Pei A B Lowe and P J Roth ldquoStimulus-responsivenanoparticles and associated (reversible) polymorphism viapolymerization induced self-assembly (PISA)rdquo Macromo-lecular Rapid Communications vol 38 no 1 Article ID1600528 2017

[79] L Y T Chou F Song andW C W Chan ldquoEngineering thestructure and properties of DNA-nanoparticle superstruc-tures using polyvalent counterionsrdquo Journal of the AmericanChemical Society vol 138 no 13 pp 4565ndash4572 2016

[80] S P Meaney B Follink and R F Tabor ldquoSynthesischaracterization and applications of polymer-silica core-shell microparticle capsulesrdquo ACS Applied Materials amp In-terfaces vol 10 no 49 pp 43068ndash43079 2018

[81] J Wang J D Byrne M E Napier and J M DeSimoneldquoMore effective nanomedicines through particle designrdquoSmall vol 7 no 14 pp 1919ndash1931 2011

[82] L Tao W Hu Y Liu G Huang B D Sumer and J GaoldquoShape-specific polymeric nanomedicine emerging oppor-tunities and challengesrdquo Experimental Biology and Medicinevol 236 no 1 pp 20ndash29 2011

[83] L Peponi I Navarro-Baena A Sonseca E GimenezA Marcos-Fernandez and J M Kenny ldquoSynthesis andcharacterization of PCL-PLLA polyurethane with shapememory behaviorrdquo European Polymer Journal vol 49 no 4pp 893ndash903 2013

[84] H Zhang H Wang W Zhong and Q Du ldquoA novel type ofshape memory polymer blend and the shape memorymechanismrdquo Polymer vol 50 no 6 pp 1596ndash1601 2009

[85] B Alvarado-Tenorio A Romo-Uribe and P T MatherldquoMicrostructure and phase behavior of POSSPCL shapememory nanocompositesrdquo Macromolecules vol 44 no 14pp 5682ndash5692 2011

[86] H Qin and P T Mather ldquoCombined one-way and two-wayshape memory in a glass-forming nematic networkrdquo Mac-romolecules vol 42 no 1 pp 273ndash280 2009

[87] J Li W R Rodgers and T Xie ldquoSemi-crystalline two-wayshape memory elastomerrdquo Polymer vol 52 no 23pp 5320ndash5325 2011

[88] T Chung A Romo-Uribe and P T Mather ldquoTwo-wayreversible shape memory in a semicrystalline networkrdquoMacromolecules vol 41 no 1 pp 184ndash192 2008

[89] K Wang Y-G Jia C Zhao and X X Zhu ldquoMultiple andtwo-way reversible shape memory polymers design strate-gies and applicationsrdquo Progress in Materials Science vol 105Article ID 100572 2019

[90] M Behl K Kratz J Zotzmann U Nochel and A LendleinldquoReversible bidirectional shape-memory polymersrdquo Ad-vanced Materials vol 25 no 32 pp 4466ndash4469 2013

[91] M Saatchi M Behl U Nochel and A Lendlein ldquoCopolymernetworks from oligo(ε-caprolactone) andn-butyl acrylateenable a reversible bidirectional shape-memory effect athuman body temperaturerdquo Macromolecular Rapid Com-munications vol 36 no 10 pp 880ndash884 2015

[92] A Biswas V K Aswal P U Sastry D Rana and P MaitildquoReversible bidirectional shape memory effect in polyure-thanes through molecular flippingrdquoMacromolecules vol 49no 13 pp 4889ndash4897 2016

[93] A Shirole J Sapkota E J Foster and C Weder ldquoShapememory composites based on electrospun poly(vinyl alco-hol) fibers and a thermoplastic polyether block AmideelastomerrdquoACS AppliedMaterials amp Interfaces vol 8 no 10pp 6701ndash6708 2016

[94] D Kai M J Tan M P Prabhakaran et al ldquoBiocompatibleelectrically conductive nanofibers from inorganic-organicshape memory polymersrdquo Colloids and Surfaces B Bio-interfaces vol 148 pp 557ndash565 2016

[95] M Bao X Lou Q Zhou W Dong H Yuan and Y ZhangldquoElectrospun biomimetic fibrous scaffold from shapememory polymer of PDLLA-co-TMC for bone tissue en-gineeringrdquo ACS Applied Materials amp Interfaces vol 6 no 4pp 2611ndash2621 2014

[96] A Iregui L Irusta O Llorente et al ldquoElectrospinning ofcationically polymerized epoxypolycaprolactone blends toobtain shape memory fibers (SMF)rdquo European PolymerJournal vol 94 pp 376ndash383 2017

[97] S Aslan and S Kaplan ldquoermomechanical and shapememory performances of thermo-sensitive polyurethanefibersrdquo Fibers and Polymers vol 19 no 2 pp 272ndash280 2018

[98] Q Meng J Hu Y Zhu J Lu and Y Liu ldquoPolycaprolactone-based shape memory segmented polyurethane fiberrdquo Journalof Applied Polymer Science vol 106 no 4 pp 2515ndash25232007

[99] Q Meng J Hu and Y Zhu ldquoShape-memory polyurethanemultiwalled carbon nanotube fibersrdquo Journal of AppliedPolymer Science vol 106 no 2 pp 837ndash848 2007

[100] S Mondal and J L Hu ldquoWater vapor permeability of cottonfabrics coated with shape memory polyurethanerdquo Carbo-hydrate Polymers vol 67 no 3 pp 282ndash287 2007

[101] E Niiyama K Tanabe K Uto A Kikuchi and M EbaraldquoShape-memory nanofiber meshes with programmable cellorientationrdquo Fibers vol 7 no 3 p 20 2019

[102] M Tomohiro Y Kim T Aoyagi and M Ebara ldquoe designof temperature-responsive nanofiber meshes for cell storageapplicationsrdquo Fibers vol 5 no 1 p 13 2017

[103] M K Shin S I Kim S J Kim S-K Kim and H LeeldquoReinforcement of polymeric nanofibers by ferritin


nanoparticlesrdquo Applied Physics Letters vol 88 no 19 ArticleID 193901 2006

[104] S Shanmugham J Jeong A Alkhateeb and D E AstonldquoPolymer nanowire elastic moduli measured with digitalpulsed force mode AFMrdquo Langmuir vol 21 no 22pp 10214ndash10218 2005

[105] B A Samuel M A Haque B Yi R Rajagopalan andH C Foley ldquoMechanical testing of pyrolysed poly-furfurylalcohol nanofibresrdquo Nanotechnology vol 18 no 11 ArticleID 115704 2007

[106] J K Hobbs and R A Register ldquoImaging block copolymercrystallization in real time with the atomic force micro-scoperdquo Macromolecules vol 39 no 2 pp 703ndash710 2006

[107] L Li C-M Chan K L Yeung J-X Li K-M Ng and Y LeildquoDirect observation of growth of lamellae and spherulites of asemicrystalline polymer by AFMrdquo Macromolecules vol 34no 2 pp 316ndash325 2001

[108] J K Yuan ldquoShape memory nanocomposite fibers foruntethered high-energy microenginesrdquo Science vol 365no 6449 pp 155ndash158 2019


CorrosionInternational Journal of

Hindawiwwwhindawicom Volume 2018

Advances in

Materials Science and EngineeringHindawiwwwhindawicom Volume 2018


Journal of

Chemistry

Analytical ChemistryInternational Journal of


ScienticaHindawiwwwhindawicom Volume 2018

Polymer ScienceInternational Journal of



Advances in Condensed Matter Physics


International Journal of

BiomaterialsHindawiwwwhindawicom

Journal ofEngineeringVolume 2018

Applied ChemistryJournal of


NanotechnologyHindawiwwwhindawicom Volume 2018

Journal of


High Energy PhysicsAdvances in

Hindawi Publishing Corporation httpwwwhindawicom Volume 2013Hindawiwwwhindawicom

The Scientific World Journal

Volume 2018

TribologyAdvances in



ChemistryAdvances in


Advances inPhysical Chemistry


BioMed Research InternationalMaterials

Journal of


Na

nom

ate

ria

ls


Journal ofNanomaterials

Submit your manuscripts atwwwhindawicom

transition temperature (Ttrans) in thermoplastic SMPs ieglass transition temperature (Tg) or melting temperature(Tm) act as physical netpoints [22]

e molecular mechanisms of thermoset SMPs withinSMCP and recovery modules are illustrated in Figure 1External force is first applied to deform an SMP specimeninto a temporary shape at deformation temperature (Tdeform)that is higher than Ttrans (Tg or Tm) of switching domainsleading to the orientation of polymer chains Subsequentlyby cooling below Tg (Figure 1(a)) or crystallization tem-perature Tc (Figure 1(b)) of the switching domains thetemporary strain is stored via the solidification of switchingdomains When the specimen is reheated beyond theswitching temperature (Tsw) that is dominated by Ttransrecovery process occurs via entropy-driven recoiling of theoriented polymer chains If Ttrans Tg the strain-inducednonequilibrium state is retained via the vitrification of theamorphous phase (Figure 1(a)) If Ttrans Tm the crystal-lization of switching domains limits the flexibility of ori-ented polymer chains as shown in Figure 1(b)

e quantification of SMCP ie how efficient a defineddeformation can be obtained is typically characterized bymeasuring the shape-fixity ratio Rf using the followingequation [13]

Rf εu(N)

εm (1)

where εu(N) and εm are strains after releasing stress at Tlow intheNth cycle and deformed strain respectively e recoveryfrom the fixed shape to the permanent one during applyingexternal stimuli is of the most importance to evaluate SMEStress-free recovery ie no external load is applied is themost common method to quantify shape recovery Shaperecovery ratio Rr is typically characterized by the ratio of thestrain during the present Nth cycle εmndashεp(N) and the strainobtained during SMCP in the previous (N minus 1) cycleεmndashεp(N minus 1) as shown in equation (2) An additionalcharacteristic of SME is switching temperature Tsw which isdefined as the temperature where the highest recovery rate isobtained [13]

Rr εm minus εp(N)

εm minus εp(N minus 1) (2)

With the development of SMPs the trend toward theexploration of the ability of SMPs to recover structures atmicro-nanoscale occurs Several approaches focused on theindentation of SMP films in some cases in combinationwith the subsequent removal of the topmost polymer layers[23ndash27] Temporary cavities are generated onto SMP sur-faces by indentation techniques which can be erased uponannealing However the minimization in surface energymay also enable polymers to reach smooth surface [28] erecovery of the indented nanostructures to permanentsmooth surface thus may not be unique for SMPs Anotherwidely reported manner for demonstrating SMEs at micro-nanoscale is to incorporate permanent micro-nano-structures onto SMP substrates using molding replication aswell as to deform them into either flat surface or other

structures with different features [29ndash43] Furthermorefree-standing SMP matrices with all dimensions at micro-scale are also of increasing interest [44ndash48] ese free-standing particles or fibers may behave differently fromindented and micro-nanostructured SMP surfaces becausethe underlying bulk material may to some extent contributeto their shape-memory functionality e SMCP may in-volve distortion eg of pillars during which their defor-mation is transferred into the bulk phase Accordingly theunderlying matrix may contribute to or even dominate theswitching of surface structures In contrast free-standingSMP particles of fibers at micro- or nanoscale exclude thecontributions of underlying bulk materials

In this review the recent progress in the development ofmicro-nanoscale structures and particles of SMPs is dis-cussed We try to summarize the preparation methodSMCP characterization of SME and applications of SMPsurface structures particles and fibers at micro-nanoscaleWe hope that this short review can be beneficial for de-veloping miniature SMP devices that can be used greatly inoptical biomedicine and smart surface areas

2 Surface Structures of SMPsat Micro-Nanoscale

21 Preparations of Permanent SMP Surface Structures atMicro-Nanoscale e reported SMP systems as well as theprepared features and aspect ratio (AR) of the micro-nanostructured surfaces are briefly summarized in Table 1Based on feature dimensions permanently 2D 25D and 3Dstructures on SMP surface can be considered [49] Typically2D structures present elongated features in surface planesuch as groove patterns while 25D structures presentuniformly spacing features with the same geometry in thevertical direction such as cylindrical pillar arrays e fea-tures with variable geometry in the vertical direction can beconsidered as 3D structures such as microprism andmicrolens arrays [49]

For the reported SMP-structured surfaces 2D and 3Dstructures have a small AR (le1) [32 33 50ndash55] while 25Dstructures possess a relatively high AR (ge1) [29ndash31 56] emain method to create permanent SMP-structured surface isto enable the replication of polymer or prepolymer surfacefrom master molds (Table 1) As shown in Figure 2(a) amold with pre-defined microstructures is placed against theSMP surface at a high temperature under load allowing thesufficient filling of materials into mold cavities eembossed specimens are subsequently cooled down in thepresence of the load A structural replication of SMP surfacefrom the master mold is achieved after the mold is releasedis method is quite efficient for thermoplastic SMPs withgood flowing capability at the high temperature [55 57] Forexample the 25D pillar arrays with AR 4 of a thermo-plastic polyurethane (Tecoflex having a wide range of Tgending at 120degCndash140degC) were successfully fabricated at 200degC[57]

After the formation of covalent network the mobility ofcrosslinked polymers into mold cavities is limited ere-fore to facilitate chemically crosslinked SMPs to fully




ARc 049π13E13S12

W13d16 1 minus v2( )112

ARc 0284 1 minus v2

1113872 111387316 Ed

W1113888 1113889

23

(3)








g

(a)



g

(b)



Tabl

e1

Materialsystemswith

theirsw

itching


metho

dsaswella

sstructural

featuresg

eometriesand

aspect

ratio

sof

repo

rted

SMP-micro-nano

structured

substrates

Materialsystem

T sw

Curingmetho

dsStructural

dimensio

nsandfeatures

Geometries

AR

Ref

Polymers

Polyno

rbornenep

ristinefullerenes

NA

3Dnano

lens

arrays

H250nm

1[55]

D250nm

S250nm



copo

lymer

51NA

25D

pillararrays

H100μm

5[57]

D20

μmS

20μm

Prepolym

ers

PCLtrim

ethacrylatedietho

xyacetop

heno

ne40

Photo

3D3μm

times1μm

[50]

Hexnu

ts10

μmtimes1μm

Boom

erangs

NOA-63a

polyurethane

which

isend-lin

kedby

athiol-b

asecrosslink

erusingph

otoinitia

tedthiol-e

necrosslink

ing

Altered

Photo

2DHsim92μm

006

[58]

Groovepatte

rns

Wsim140μm

Ssim140μm

Tetra-branched

PCLwith

acrylate

end-grou

ps33

ermo

2Dgroo

vepatte

rns

H150nm

015

[32]

Linear

PCLtelechelic

diacrylates

W1μm

S2μm


acetate)d

icum

ylperoxide

63Ph

oto

3DFo

rmicroprism

05

[53]

Microprism

array

microlens

arraysw

hite-ligh

tho

logram

transmiss

iongrating

H72

μmW

150μm

Linear

PCL

37ndash4

6

ermo

25D

H15

μm3

[56]

Allyla

lcoh

olPillararrays

D5μm

Benzoylp

eroxide

S5μm

Precursors

Bispheno

ladiglycidyl

ether(BADGE)

poly(propylene

glycol)bis(2-am

inop

ropyle

ther)

decylamine

60

ermo

25D

pillararrays

H4μm

4[30]

D1μm

S1or

2μm

Bispheno

ladiglycidyl

ether(BADGE)

poly(propylene

glycol)bis(2-am

inop

ropyle

ther)

decylamine

60

ermo

25D

pillararrays

D10

μm2ndash

3[31]

S5ndash

30μm

Diglycidyletherof

bispheno

lan

epoxymon

omerm

-xylylenediam

inen-octylamine

78

ermo

25D

pillayarrays

H10

μm1

[40]

W10

μmS

5102

030

μmDiglycidyle

ther

ofbispheno

lan

epoxymon

omer

poly(propylene

glycol)bis(2-am

inop

ropyle

ther)

neop

entylg

lycold

iglycidyle

ther

35ndash6

5

ermo

3Dpyramids-term

edmicrotip

sH

12ndash21μm

07

[52]

W17ndash3

0μm

S100μm

Methylm

ethacrylatepo

ly(ethyleneglycol

dimethacrylate)p

hotoinitiator

95Ph

oto

Groovepatte

rns

H194nm

02

[51]

W834nm

S834nm

Hheigh

tW

widthD

diameterS

spacing








Polymer

Mold

Thigh

Tlow

(a)

Prepolymer

Mold

Tlow

Thigh

Curing

(b)

MoldCuring

Precursors

Tlow Tlow Tlow

(c)






(a) (b)


Heat to T gt Ttrans


Hot plate

(a)


Glass slide

(b)



(c)



(d)



Test shear

adhesion

Test normaladhesion


Cool down below Tg

(a) (b)

(c) (d)


0 300 6000

25

50

75

Ver

tical

dim

ensio

n (n

m)


00 05 10 15 20 25

ndash100

ndash50

0

50

100

150


Ver

tical

dim

ensio

n (n

m)

00 05 10 15 20 25

ndash100

ndash50

0

50

100

150


Ver

tical

dim

ensio

n (n

m)

0

00 05 10 15 20 25

ndash100

ndash50

50

100

150


Ver

tical

dim

ensio

n (n

m) S1 S2

S1 S2

S3

S1 S2

S3

00 05 10 15 20 25

ndash100

ndash50

0

50

100

150


Ver

tical

dim

ensio

n (n

m)

00 05 10 15 20 25

ndash100

ndash50

0

50

100

150


Ver

tical

dim

ensio

n (n

m)

S1 S2

S3

S4

(a)

(c)

(d) (e)

(b)







Rr Hrecovered

Hpermanent (4)



(5)






















0

20

40

60

80

100Tr

ansm

ittan

ce (

)

(a)

0

20

40

60

80

100


Tran

smitt

ance

()



(b)


(c)


PVA filmwith SMP

micromatrices

Thighstretching

Tlowshape

fixation


matrices









Rr Hr minus Hp

Hi minus Hp (7)













5 Summary




Acknowledgments


References




Polymer chain


65degC

90degC

37degC

37degC

hυheat

hυheat

Shape memory effect


Step 1programming

Step 2application























































































































Advances in



Journal of

Chemistry















Journal of





Volume 2018









Journal of


Na

nom

ate

ria

ls






ARc 049π13E13S12

W13d16 1 minus v2( )112

ARc 0284 1 minus v2

1113872 111387316 Ed

W1113888 1113889

23

(3)








g

(a)



g

(b)



Tabl

e1

Materialsystemswith

theirsw

itching


metho

dsaswella

sstructural

featuresg

eometriesand

aspect

ratio

sof

repo

rted

SMP-micro-nano

structured

substrates

Materialsystem

T sw

Curingmetho

dsStructural

dimensio

nsandfeatures

Geometries

AR

Ref

Polymers

Polyno

rbornenep

ristinefullerenes

NA

3Dnano

lens

arrays

H250nm

1[55]

D250nm

S250nm



copo

lymer

51NA

25D

pillararrays

H100μm

5[57]

D20

μmS

20μm

Prepolym

ers

PCLtrim

ethacrylatedietho

xyacetop

heno

ne40

Photo

3D3μm

times1μm

[50]

Hexnu

ts10

μmtimes1μm

Boom

erangs

NOA-63a

polyurethane

which

isend-lin

kedby

athiol-b

asecrosslink

erusingph

otoinitia

tedthiol-e

necrosslink

ing

Altered

Photo

2DHsim92μm

006

[58]

Groovepatte

rns

Wsim140μm

Ssim140μm

Tetra-branched

PCLwith

acrylate

end-grou

ps33

ermo

2Dgroo

vepatte

rns

H150nm

015

[32]

Linear

PCLtelechelic

diacrylates

W1μm

S2μm


acetate)d

icum

ylperoxide

63Ph

oto

3DFo

rmicroprism

05

[53]

Microprism

array

microlens

arraysw

hite-ligh

tho

logram

transmiss

iongrating

H72

μmW

150μm

Linear

PCL

37ndash4

6

ermo

25D

H15

μm3

[56]

Allyla

lcoh

olPillararrays

D5μm

Benzoylp

eroxide

S5μm

Precursors

Bispheno

ladiglycidyl

ether(BADGE)

poly(propylene

glycol)bis(2-am

inop

ropyle

ther)

decylamine

60

ermo

25D

pillararrays

H4μm

4[30]

D1μm

S1or

2μm

Bispheno

ladiglycidyl

ether(BADGE)

poly(propylene

glycol)bis(2-am

inop

ropyle

ther)

decylamine

60

ermo

25D

pillararrays

D10

μm2ndash

3[31]

S5ndash

30μm

Diglycidyletherof

bispheno

lan

epoxymon

omerm

-xylylenediam

inen-octylamine

78

ermo

25D

pillayarrays

H10

μm1

[40]

W10

μmS

5102

030

μmDiglycidyle

ther

ofbispheno

lan

epoxymon

omer

poly(propylene

glycol)bis(2-am

inop

ropyle

ther)

neop

entylg

lycold

iglycidyle

ther

35ndash6

5

ermo

3Dpyramids-term

edmicrotip

sH

12ndash21μm

07

[52]

W17ndash3

0μm

S100μm

Methylm

ethacrylatepo

ly(ethyleneglycol

dimethacrylate)p

hotoinitiator

95Ph

oto

Groovepatte

rns

H194nm

02

[51]

W834nm

S834nm

Hheigh

tW

widthD

diameterS

spacing








Polymer

Mold

Thigh

Tlow

(a)

Prepolymer

Mold

Tlow

Thigh

Curing

(b)

MoldCuring

Precursors

Tlow Tlow Tlow

(c)






(a) (b)


Heat to T gt Ttrans


Hot plate

(a)


Glass slide

(b)



(c)



(d)



Test shear

adhesion

Test normaladhesion


Cool down below Tg

(a) (b)

(c) (d)


0 300 6000

25

50

75

Ver

tical

dim

ensio

n (n

m)


00 05 10 15 20 25

ndash100

ndash50

0

50

100

150


Ver

tical

dim

ensio

n (n

m)

00 05 10 15 20 25

ndash100

ndash50

0

50

100

150


Ver

tical

dim

ensio

n (n

m)

0

00 05 10 15 20 25

ndash100

ndash50

50

100

150


Ver

tical

dim

ensio

n (n

m) S1 S2

S1 S2

S3

S1 S2

S3

00 05 10 15 20 25

ndash100

ndash50

0

50

100

150


Ver

tical

dim

ensio

n (n

m)

00 05 10 15 20 25

ndash100

ndash50

0

50

100

150


Ver

tical

dim

ensio

n (n

m)

S1 S2

S3

S4

(a)

(c)

(d) (e)

(b)







Rr Hrecovered

Hpermanent (4)



(5)






















0

20

40

60

80

100Tr

ansm

ittan

ce (

)

(a)

0

20

40

60

80

100


Tran

smitt

ance

()



(b)


(c)


PVA filmwith SMP

micromatrices

Thighstretching

Tlowshape

fixation


matrices









Rr Hr minus Hp

Hi minus Hp (7)













5 Summary




Acknowledgments


References




Polymer chain


65degC

90degC

37degC

37degC

hυheat

hυheat

Shape memory effect


Step 1programming

Step 2application























































































































Advances in



Journal of

Chemistry















Journal of





Volume 2018









Journal of


Na

nom

ate

ria

ls




Tabl

e1

Materialsystemswith

theirsw

itching


metho

dsaswella

sstructural

featuresg

eometriesand

aspect

ratio

sof

repo

rted

SMP-micro-nano

structured

substrates

Materialsystem

T sw

Curingmetho

dsStructural

dimensio

nsandfeatures

Geometries

AR

Ref

Polymers

Polyno

rbornenep

ristinefullerenes

NA

3Dnano

lens

arrays

H250nm

1[55]

D250nm

S250nm



copo

lymer

51NA

25D

pillararrays

H100μm

5[57]

D20

μmS

20μm

Prepolym

ers

PCLtrim

ethacrylatedietho

xyacetop

heno

ne40

Photo

3D3μm

times1μm

[50]

Hexnu

ts10

μmtimes1μm

Boom

erangs

NOA-63a

polyurethane

which

isend-lin

kedby

athiol-b

asecrosslink

erusingph

otoinitia

tedthiol-e

necrosslink

ing

Altered

Photo

2DHsim92μm

006

[58]

Groovepatte

rns

Wsim140μm

Ssim140μm

Tetra-branched

PCLwith

acrylate

end-grou

ps33

ermo

2Dgroo

vepatte

rns

H150nm

015

[32]

Linear

PCLtelechelic

diacrylates

W1μm

S2μm


acetate)d

icum

ylperoxide

63Ph

oto

3DFo

rmicroprism

05

[53]

Microprism

array

microlens

arraysw

hite-ligh

tho

logram

transmiss

iongrating

H72

μmW

150μm

Linear

PCL

37ndash4

6

ermo

25D

H15

μm3

[56]

Allyla

lcoh

olPillararrays

D5μm

Benzoylp

eroxide

S5μm

Precursors

Bispheno

ladiglycidyl

ether(BADGE)

poly(propylene

glycol)bis(2-am

inop

ropyle

ther)

decylamine

60

ermo

25D

pillararrays

H4μm

4[30]

D1μm

S1or

2μm

Bispheno

ladiglycidyl

ether(BADGE)

poly(propylene

glycol)bis(2-am

inop

ropyle

ther)

decylamine

60

ermo

25D

pillararrays

D10

μm2ndash

3[31]

S5ndash

30μm

Diglycidyletherof

bispheno

lan

epoxymon

omerm

-xylylenediam

inen-octylamine

78

ermo

25D

pillayarrays

H10

μm1

[40]

W10

μmS

5102

030

μmDiglycidyle

ther

ofbispheno

lan

epoxymon

omer

poly(propylene

glycol)bis(2-am

inop

ropyle

ther)

neop

entylg

lycold

iglycidyle

ther

35ndash6

5

ermo

3Dpyramids-term

edmicrotip

sH

12ndash21μm

07

[52]

W17ndash3

0μm

S100μm

Methylm

ethacrylatepo

ly(ethyleneglycol

dimethacrylate)p

hotoinitiator

95Ph

oto

Groovepatte

rns

H194nm

02

[51]

W834nm

S834nm

Hheigh

tW

widthD

diameterS

spacing








Polymer

Mold

Thigh

Tlow

(a)

Prepolymer

Mold

Tlow

Thigh

Curing

(b)

MoldCuring

Precursors

Tlow Tlow Tlow

(c)






(a) (b)


Heat to T gt Ttrans


Hot plate

(a)


Glass slide

(b)



(c)



(d)



Test shear

adhesion

Test normaladhesion


Cool down below Tg

(a) (b)

(c) (d)


0 300 6000

25

50

75

Ver

tical

dim

ensio

n (n

m)


00 05 10 15 20 25

ndash100

ndash50

0

50

100

150


Ver

tical

dim

ensio

n (n

m)

00 05 10 15 20 25

ndash100

ndash50

0

50

100

150


Ver

tical

dim

ensio

n (n

m)

0

00 05 10 15 20 25

ndash100

ndash50

50

100

150


Ver

tical

dim

ensio

n (n

m) S1 S2

S1 S2

S3

S1 S2

S3

00 05 10 15 20 25

ndash100

ndash50

0

50

100

150


Ver

tical

dim

ensio

n (n

m)

00 05 10 15 20 25

ndash100

ndash50

0

50

100

150


Ver

tical

dim

ensio

n (n

m)

S1 S2

S3

S4

(a)

(c)

(d) (e)

(b)







Rr Hrecovered

Hpermanent (4)



(5)






















0

20

40

60

80

100Tr

ansm

ittan

ce (

)

(a)

0

20

40

60

80

100


Tran

smitt

ance

()



(b)


(c)


PVA filmwith SMP

micromatrices

Thighstretching

Tlowshape

fixation


matrices









Rr Hr minus Hp

Hi minus Hp (7)













5 Summary




Acknowledgments


References




Polymer chain


65degC

90degC

37degC

37degC

hυheat

hυheat

Shape memory effect


Step 1programming

Step 2application























































































































Advances in



Journal of

Chemistry















Journal of





Volume 2018









Journal of


Na

nom

ate

ria

ls










Polymer

Mold

Thigh

Tlow

(a)

Prepolymer

Mold

Tlow

Thigh

Curing

(b)

MoldCuring

Precursors

Tlow Tlow Tlow

(c)






(a) (b)


Heat to T gt Ttrans


Hot plate

(a)


Glass slide

(b)



(c)



(d)



Test shear

adhesion

Test normaladhesion


Cool down below Tg

(a) (b)

(c) (d)


0 300 6000

25

50

75

Ver

tical

dim

ensio

n (n

m)


00 05 10 15 20 25

ndash100

ndash50

0

50

100

150


Ver

tical

dim

ensio

n (n

m)

00 05 10 15 20 25

ndash100

ndash50

0

50

100

150


Ver

tical

dim

ensio

n (n

m)

0

00 05 10 15 20 25

ndash100

ndash50

50

100

150


Ver

tical

dim

ensio

n (n

m) S1 S2

S1 S2

S3

S1 S2

S3

00 05 10 15 20 25

ndash100

ndash50

0

50

100

150


Ver

tical

dim

ensio

n (n

m)

00 05 10 15 20 25

ndash100

ndash50

0

50

100

150


Ver

tical

dim

ensio

n (n

m)

S1 S2

S3

S4

(a)

(c)

(d) (e)

(b)







Rr Hrecovered

Hpermanent (4)



(5)






















0

20

40

60

80

100Tr

ansm

ittan

ce (

)

(a)

0

20

40

60

80

100


Tran

smitt

ance

()



(b)


(c)


PVA filmwith SMP

micromatrices

Thighstretching

Tlowshape

fixation


matrices









Rr Hr minus Hp

Hi minus Hp (7)













5 Summary




Acknowledgments


References




Polymer chain


65degC

90degC

37degC

37degC

hυheat

hυheat

Shape memory effect


Step 1programming

Step 2application























































































































Advances in



Journal of

Chemistry















Journal of





Volume 2018









Journal of


Na

nom

ate

ria

ls







(a) (b)


Heat to T gt Ttrans


Hot plate

(a)


Glass slide

(b)



(c)



(d)



Test shear

adhesion

Test normaladhesion


Cool down below Tg

(a) (b)

(c) (d)


0 300 6000

25

50

75

Ver

tical

dim

ensio

n (n

m)


00 05 10 15 20 25

ndash100

ndash50

0

50

100

150


Ver

tical

dim

ensio

n (n

m)

00 05 10 15 20 25

ndash100

ndash50

0

50

100

150


Ver

tical

dim

ensio

n (n

m)

0

00 05 10 15 20 25

ndash100

ndash50

50

100

150


Ver

tical

dim

ensio

n (n

m) S1 S2

S1 S2

S3

S1 S2

S3

00 05 10 15 20 25

ndash100

ndash50

0

50

100

150


Ver

tical

dim

ensio

n (n

m)

00 05 10 15 20 25

ndash100

ndash50

0

50

100

150


Ver

tical

dim

ensio

n (n

m)

S1 S2

S3

S4

(a)

(c)

(d) (e)

(b)







Rr Hrecovered

Hpermanent (4)



(5)






















0

20

40

60

80

100Tr

ansm

ittan

ce (

)

(a)

0

20

40

60

80

100


Tran

smitt

ance

()



(b)


(c)


PVA filmwith SMP

micromatrices

Thighstretching

Tlowshape

fixation


matrices









Rr Hr minus Hp

Hi minus Hp (7)













5 Summary




Acknowledgments


References




Polymer chain


65degC

90degC

37degC

37degC

hυheat

hυheat

Shape memory effect


Step 1programming

Step 2application























































































































Advances in



Journal of

Chemistry















Journal of





Volume 2018









Journal of


Na

nom

ate

ria

ls




Test shear

adhesion

Test normaladhesion


Cool down below Tg

(a) (b)

(c) (d)


0 300 6000

25

50

75

Ver

tical

dim

ensio

n (n

m)


00 05 10 15 20 25

ndash100

ndash50

0

50

100

150


Ver

tical

dim

ensio

n (n

m)

00 05 10 15 20 25

ndash100

ndash50

0

50

100

150


Ver

tical

dim

ensio

n (n

m)

0

00 05 10 15 20 25

ndash100

ndash50

50

100

150


Ver

tical

dim

ensio

n (n

m) S1 S2

S1 S2

S3

S1 S2

S3

00 05 10 15 20 25

ndash100

ndash50

0

50

100

150


Ver

tical

dim

ensio

n (n

m)

00 05 10 15 20 25

ndash100

ndash50

0

50

100

150


Ver

tical

dim

ensio

n (n

m)

S1 S2

S3

S4

(a)

(c)

(d) (e)

(b)







Rr Hrecovered

Hpermanent (4)



(5)






















0

20

40

60

80

100Tr

ansm

ittan

ce (

)

(a)

0

20

40

60

80

100


Tran

smitt

ance

()



(b)


(c)


PVA filmwith SMP

micromatrices

Thighstretching

Tlowshape

fixation


matrices









Rr Hr minus Hp

Hi minus Hp (7)













5 Summary




Acknowledgments


References




Polymer chain


65degC

90degC

37degC

37degC

hυheat

hυheat

Shape memory effect


Step 1programming

Step 2application























































































































Advances in



Journal of

Chemistry















Journal of





Volume 2018









Journal of


Na

nom

ate

ria

ls








Rr Hrecovered

Hpermanent (4)



(5)






















0

20

40

60

80

100Tr

ansm

ittan

ce (

)

(a)

0

20

40

60

80

100


Tran

smitt

ance

()



(b)


(c)


PVA filmwith SMP

micromatrices

Thighstretching

Tlowshape

fixation


matrices









Rr Hr minus Hp

Hi minus Hp (7)













5 Summary




Acknowledgments


References




Polymer chain


65degC

90degC

37degC

37degC

hυheat

hυheat

Shape memory effect


Step 1programming

Step 2application























































































































Advances in



Journal of

Chemistry















Journal of





Volume 2018









Journal of


Na

nom

ate

ria

ls



















0

20

40

60

80

100Tr

ansm

ittan

ce (

)

(a)

0

20

40

60

80

100


Tran

smitt

ance

()



(b)


(c)


PVA filmwith SMP

micromatrices

Thighstretching

Tlowshape

fixation


matrices









Rr Hr minus Hp

Hi minus Hp (7)













5 Summary




Acknowledgments


References




Polymer chain


65degC

90degC

37degC

37degC

hυheat

hυheat

Shape memory effect


Step 1programming

Step 2application























































































































Advances in



Journal of

Chemistry















Journal of





Volume 2018









Journal of


Na

nom

ate

ria

ls








0

20

40

60

80

100Tr

ansm

ittan

ce (

)

(a)

0

20

40

60

80

100


Tran

smitt

ance

()



(b)


(c)


PVA filmwith SMP

micromatrices

Thighstretching

Tlowshape

fixation


matrices









Rr Hr minus Hp

Hi minus Hp (7)













5 Summary




Acknowledgments


References




Polymer chain


65degC

90degC

37degC

37degC

hυheat

hυheat

Shape memory effect


Step 1programming

Step 2application























































































































Advances in



Journal of

Chemistry















Journal of





Volume 2018









Journal of


Na

nom

ate

ria

ls









Rr Hr minus Hp

Hi minus Hp (7)













5 Summary




Acknowledgments


References




Polymer chain


65degC

90degC

37degC

37degC

hυheat

hυheat

Shape memory effect


Step 1programming

Step 2application























































































































Advances in



Journal of

Chemistry















Journal of





Volume 2018









Journal of


Na

nom

ate

ria

ls







5 Summary




Acknowledgments


References




Polymer chain


65degC

90degC

37degC

37degC

hυheat

hυheat

Shape memory effect


Step 1programming

Step 2application























































































































Advances in



Journal of

Chemistry















Journal of





Volume 2018









Journal of


Na

nom

ate

ria

ls























































































































Advances in



Journal of

Chemistry















Journal of





Volume 2018









Journal of


Na

nom

ate

ria

ls


















































































Advances in



Journal of

Chemistry















Journal of





Volume 2018









Journal of


Na

nom

ate

ria

ls
















































Advances in



Journal of

Chemistry















Journal of





Volume 2018









Journal of


Na

nom

ate

ria

ls













Advances in



Journal of

Chemistry















Journal of





Volume 2018









Journal of


Na

nom

ate

ria

ls






Advances in



Journal of

Chemistry















Journal of





Volume 2018









Journal of


Na

nom

ate

ria

ls




Documents

Surface Structures, Particles, and Fibers of Shape-Memory ...downloads.hindawi.com/journals/apt/2020/7639724.pdf · 7/1/2019 · Review Article Surface Structures, Particles, and