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Using Cellulose Nanowhisker as a Cross-linker to Improve the Mechanical and Thermal Properties of
Gelatin Hydrogels
Rajalaxmi Dash and Arthur J. Ragauskas
School of Chemistry & Biochemistry Institute of Paper Science and Technology
Georgia Institute of Technology 10th April 2012
2
Outline
Background Experimental methods Results and discussions Conclusions
4
Hydrogels
Hydrogels are defined as a water insoluble polymer network which can absorb and retain large amount of water
Hydrogels
Physical Chemical
Glassy nodules, lamellar microcrystals, double triple helices (elastomers/block copolymers, Gelatin) Hydrogen bonds,
ionic and hydrophobic associations, agglomerations (xanthan, paint, polymer-polymer complexes, gum)
Strong Weak
Condensation
Polyester gel
Addition
Kinetic growth, grafting (polydivinyl benzene,
CMC-g-acrylic acid)
Cross-linking
End-linking, random cross-linking (polydimethyl siloxane,
cis-polyisoprene)
Natural
Synthetic
Gulrez, S. K.H and Al-Assaf, S and Phillips, G. O (2011) Hydrogels: Methods of Preparation, Characterization and Applications in Molecular and Environmental Bioengineering. Glyndŵr University Research Online
5
http://www.datlof.com/8Axamal/docs/Marketing/jhu/JE/index.htm www.nano.org.uk www.medline.com
Applications of hydrogels
Food packaging – absorbing or delivering moisture for freshness and appearance Personal hygiene products- diapers, skin care, hair care Pharmaceutical and Biomedical – contact lenses, wound dressings, plasma expander, hard or soft capsules, drug delivery, tissue engineering
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Heat(>35 OC)
cool
Random coil in solution Helix formation in gel
Gelatin is a single strain protein obtained by denaturation of collagen
Gelatin
Properties: High water content capacity Biocompatible Biodegradable Non-immunogenic
Major Drawback
To use cellulose nanowhiskers as cross-linkers in order to stabilize gelatin gels by establishing cross-links between the protein chains
7
Cellulose nanowhiskers (CNWs)
Cellulose nanowhiskers are defined as crystalline rod-like nanoparticles which are obtained by acid hydrolysis of cellulose fibers
G. Siqueira, J. Bras, A. Dufresne, Biomacromolecules 2009, 10, 425-432. M. A. S. Azizi Samir, F. Alloin, A. Dufresne, Biomacromolecules 2005, 6, 612-626. S. Beck-Candanedo, M. Roman, D. G. Gray, Biomacromolecules 2005, 6, 1048-1054. M. M. de Souza Lima, R. Borsali, Macromol. Rapid Commun. 2004, 25, 771-787.
Microfibril
Plant cell
Acid hydrolysis
Wood
8
Evolution of scientific papers on cellulose nanoparticles
* Source: SciFinder literature research system (March 2012). ** Research based on Cellulose Whiskers and Cellulose Nanocrystals terminologies
Motivation for using CNW
Nano-dimension Hydrophilicity High surface area High mechanical property (152 GPa) Renewability Biodegradability Non-toxicity 0
50
100
150
200
250
2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011
9
Effect of reaction parameters on cellulose nanowhiskers properties from pulp
J. Araki et. al. Colloids Surfaces A, 1998, 142, 75 – 82. J. Araki et. al. J. wood Sci. 1999, 45, 258 - 261
Sample
Amounts of acidic groups on surface (mmol kg-1)
Strong acid groups
Weak acid groups
H2SO4 84 26
HCl 0 <18 TEM images of (a) H2SO4 (b) HCl hydrolyzed whiskers
Reaction conditions
(reaction time (min), acid/pulp)
Length
(nm)
Aspect ratio
Sulfur
content(%)
Surface charge density (e/nm2)
25, 8.75 141±6 28.2 0.89±0.06 0.33±0.02
45, 8.75 120±5 24.5 1.06±0.02 0.38±0.01
45, 17.5 105±4 23.3 1.26±0.01
Effect of reaction conditions on whisker properties (H2SO4 hydrolysis, softwood pulp)
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Cellulose nanowhiskers potential areas of application
Nanocomposites Paper & Paperboard Biomedical
Packaging, Adhesive Electronic displays, Foams
Aerogels, Films Coatings / barriers
Bioimaging nanodevice, drug
delivery technology, skin care
Arboranano* is a new Canadian Forest NanoProducts
Network whose objective is to develop high value products from
nanocrystalline cellulose.
*Canada’s Business-led Networks of Centers of Excellence program, FPInnovations and NanoQuébec.
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Synthesis of cellulose nanowhiskers
64% H2SO4
Pre-heating
45°C
for 45 min Stir
Several Centrifugations 10,000 rpm, 10 min
Several days of dialysis
Sonication 6 min
Centrifugation 10,000 rpm, 7min
Yield 20-30%
Soft wood pulp
Cellulose
whiskers in de-
ionized water
Oxidation of cellulose nanowhiskers (CNWs)
45oC, 45 min
Cellulose fibers Cellulose nanowhiskers
Cellulose nanowhiskers DACX
X= 1, 2, 3, 4 =Weight ratio of NaIO4 to cellulose = 0.1, 0.3, 0.5, 0.7 DAC= Dialdehyde cellulose whiskers
r=0.80
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Gelatin in water 40 OC
Oxidized whisker suspension in H2O at
40 OC
casting
Gelatin Gelatin cross-linked with nanowhiskers
Dialdehyde cellulose nanowhiskers
40 OC
30min
Hydrogel formulation Gelatin (90 wt%) + Dialdehyde nanowhisker (10 wt %)
Preparation of hydrogels
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Samples NaIO4/CNWs (w/w)
Carbonyl content (mmols g-1)
CNWs 0.00 0.006
DAC1 0.10 0.060
DAC2 0.30 0.114
DAC3
DAC4
0.50
0.70
0.150
0.231
Characterization of dialdehyde cellulose nanowhiskers
FT-IR spectra of (a) nanowhisker (b)DAC1 (c) DAC2 (c) DAC3 (d) DAC4
Estimation of aldehyde content of dialdehyde cellulose nanowhiskers by copper number titration
17
FT-IR spectra of hydrogels
Evidence of chemical interaction between gelatin and cellulose nanowhisker!
Dialdehyde cellulose nanowhiskers
Gelatin
Gelatin-nanowhiskers
-
C=O
18
Cross-linking density of hydrogels
Cross-linking density was determined by UV spectrometer following a Ninhydrin assay measuring the free amine groups
Degree of cross-linking (%) = {1- (Absorbance of cross-linked gel/Absorbance of non cross-linked gel)} × 100
Degree of cross-linking increases with the level of oxidation!
19
Degree of chemical cross-linking (%) % Ridge % Mobile
0 35 65
7 44 56
21 42 58 25 50 50 33 50 50
Relative rigid and mobile components of the hydrogels
Determined by 1H spin-spin relaxation (T2) NMR experiments - T2 relaxation decay intensity is sensitive to the local chain dynamics
- The faster the T2 the more rigid components the sample has
Relatively higher chain rigidity of the cross-linked hydrogels!
20
Equilibrium swelling ratio of hydrogels
• Hydrogels were swelled in water for 2 days •Equilibrium fluid content (%) = {1- (weight of dry gel/weight of swollen gel)} × 100
Decrease in swelling ratio with increase in cross-linking!
21
Viscoelastic properties of the gelatin gels
G’: Elastic modulus G”: Loss modulus
G’>>G”
Hydrogels showing elastic network!
22
Effect of chemical cross-linking on the storage modulus of the gelatin gels
Cross-linking significantly increases storage modulus!
23
Effect of temperature on dynamic rheological behavior of the physical gelatin gels
Gelatin hydrogel becomes liquid like after 35 OC!
Temperature ramp of 27 to 50 °C Heating rate of 1.5 °C/min Frequency 1 Hz Shear rate of 0.05
24
Effect of temperature on storage modulus of chemically cross-linked gelatin gels
Cross-linked hydrogels become stable well above 35 OC (melting point)!
Temperature ramp 27 to 50 °C Heating rate of 1.5 °C/min Frequency 1 Hz Shear rate of 0.05
25
a
b c
d e
Cross-sectional morphologies of hydrogels
(a) gelatin and (b) 7%, (c) 21%, (d) 25%, (e) 33% cross-linked gels (scale bar 20 μm)
Swollen samples were quickly frozen in liquid nitrogen and then freeze dried.
Morphological changes: Increase in compactness Pores become more regular Decrease in pore size
26
Conclusions
First successful study on the synthesis of gelatin hydrogels chemically cross-linked by dialdehyde cellulose nanowhiskers.
The increase in aldehyde groups resulted in an increase in degree of cross-linking leading to the formation of a rigid dense network .
The rigid network reduced water uptake ability of the hydrogels.
Further, the increase in degree of cross-linking improved the mechanical properties of hydrogels by 150% and increased the thermal stability of the gels as the gels did not degrade until 50 oC.
These findings on this work would broaden the biomedical applications of the chemically cross-linked gelatin hydrogels in wound dressing, tissue engineering and sustained release applications.
27
Acknowledgements
Dr. Arthur J. Ragauskas Marcus Foston Shaobo Pan Department of Energy for providing support for this study
28 TEM image Birefringence
S=O
Characterization of cellulose nanowhiskers
C-H stretching
O-H stretching
O-H bending
L: 150-300 nm D: 4-8 nm
XPS
S (At %) 0.83
FTIR
200nm
30
Thermal properties of cross-linked hydrogels
0
3000
6000
9000
12000
15000
18000
25 30 35 40 45 50
Temp (°C)
Sh
ea
r m
od
ulu
s(G
')
KP
a
Gelatin
DAC1-gelatin
DAC2-gelatin
DAC3-gelatin
Hydrogels are stable until 50oC!
31
Cellulose nanowhiskers
The geometric dimensions depend on the source of the cellulosic material and hydrolysis conditions.
Dimensions: Length: 100 – 1000 nm; Diameter: 4 – 50 nm.
L/D=67.0
L/D=25.0
Habibi, Y.; Goffin, A.-L.; Schiltz, N.; Duquesne, E.; Dubois, P.; Dufresne, A. J. Mater. Chem. 2008, 18, 5002. Azizi Samir, M. A. S.; Alloin, F.; Paillet, M.; Dufresne, A. Macromolecules 2004, 37, 4313. Roohani, M.; Habibi, Y.; Belgacem, N. M.; Ebrahim, G.; Karimi, A. N.; Dufresne, A. Eur. Polym. J. 2008, 44, 2489.Favier, V.; Canova, G. R.; Cavaille, J. Y.; Chanzy, H.; Dufresne, A.; Gauthier, C. Polym. AdV. Technol. 1995, 6, 351.
L/D=11.8 L/D=28.6
Cotton Ramie Wood Tunicate