International Journal of Emerging Technology and Advanced
Engineering Website: www.ijetae.com (ISSN 2250-2459, Volume 2,
Issue 4, April 2012) 91 A Review on Biomaterials: Scope,
Applications &Human Anatomy Significance Nitesh R. Patel1,
Piyush P. Gohil2 1,2Department of Mechanical Engineering,Faculty of
Technology & Engineering Charotar University of Science &
Technology, Changa (Gujarat) [email protected]
[email protected]
AbstractBiomaterialsintheformofimplants(sutures,
boneplates,jointreplacements,etc.)andmedicaldevices
(pacemakers,artificialhearts,bloodtubes,etc.)arewidely
usedtoreplaceand/orrestorethefunctionoftraumatizedor degenerated
tissues or organs, and thus improve the quality of life of the
patients. The first and foremost requirement for the
choiceofthebiomaterialisitsacceptabilitybythehuman
body.Abiomaterialusedforimplantshouldpossesssome
importantpropertiesinordertolong-termusageinthebody without
rejection. The most common classes of materials used
asbiomedicalmaterialsareMetals,Polymers,Ceramics,and
Composite.Thesefourclassesareusedsinglyandin
combinationtoformmostoftheimplantationdevices available today. This
review should be of value to researchers
whoareinterestedinthestateoftheartofbiomaterial evaluation and
selection of biomaterials. KeywordsApplication, Biomaterials, Human
Anatomy I.INTRODUCTION TheNationalInstitutesofHealthConsensus
DevelopmentConferencedefinedabiomaterialasAny substance (other than
a drug) or combination of substances,
syntheticornaturalinorigin,whichcanbeusedforany
periodoftime,asawholeorasapartofasystemwhich
treats,augments,orreplacesanytissue,organ,orfunction
ofthebody(BoretosandEden,1984).Useof
biomaterialsdatesfarbackintoancientcivilizations.
Artificialeyes,ears,teeth,andnoseswerefoundon
Egyptianmummies[1].ChineseandIndiansusedwaxes,
glues,andtissuesinreconstructingmissingordefective
partsofthebody.Overthecenturies,advancementsin
syntheticmaterials,surgicaltechniques,andsterilization
methodshavepermittedtheuseofbiomaterialsinmany ways [2]. Medical
practice today utilizes a large number of devices and implants.
Biomaterials in theform of implants (ligaments, vascular grafts,
heart valves, intraocular lenses,
dentalimplants,etc.)andmedicaldevices(pacemakers, biosensors,
artificial hearts, etc.) are widely used to replace
and/orrestorethefunctionoftraumatizedordegenerated tissues or
organs, and thus improve the quality of life of the
patients.Intheearlydaysallkindsofnaturalmaterialssuchas
wood,glueandrubber,andtissuesfromlivingforms,and
manufacturedmaterialssuchasiron,gold,zincandglass
wereusedasbiomaterials.Thehostresponsestothese
materialswereextremelyvaried.Undercertainconditions
(characteristicsofthehosttissuesandsurgicalprocedure)
somematerialsweretoleratedbythebody,whereasthe samematerials were
rejected in another situation. Over the
last30yearsconsiderableprogresshasbeenmadein
understandingtheinteractionsbetweenthetissuesandthe materials. It
has been acknowledged that there are profound
differencesbetweennon-living(avital)andliving(vital) materials. A
wide range of materials encompassing all the classical
materialssuchasMetals(gold,tantalum,Ti6Al4V,316L
stainlesssteel,Co-CrAlloys,titaniumalloys),Ceramics
(alumina,zirconia,carbon,titania,bioglass,
hydroxyapatite(HA)),Composite(Silica/SR,
CF/UHMWPE,CF/PTFE,HA/PE,CF/epoxy,CF/PEEK,
CF/C,Al2O3/PTFE),Polymers(Ultrahighmolecular
weightpolyethylene(UHMWPE),Polyurethane(PE),
Polyurethane(PU),Polytetrafuoroethylene(PTFE),
Polyacetal(PA),Polymethylmethacrylate(PMMA),
PolyethyleneTerepthalate(PET),SiliconeRubber(SR),
Polyetheretherketone(PEEK),Poly(lacticacid)(PLA),
Polysulfone(PS))havebeeninvestigatedasbiomaterials. Researchers
also classified materials into several types such as bioinert and
bioactive, biostableand biodegradable, etc.
[4].Inbroadterms,inert(morestrictly,nearlyinert)
materialsprohibitedorminimaltissueresponse.Active
materialsencouragebondingtosurroundingtissuewith.
Degradableorresorbablematerialsareincorporatedinto
thesurroundingtissue,ormayevendissolvecompletely
overaperiodoftime.Metalsaretypicallyinert,ceramics
maybeinert,activeorresorbableandpolymersmaybe inert or resorbable
[5]. Biomaterials must be nontoxic,
non-carcinogenic,chemicallyinert,stable,andmechanically
strongenoughtowithstandtherepeatedforcesofa lifetime. International
Journal of Emerging Technology and Advanced Engineering Website:
www.ijetae.com (ISSN 2250-2459, Volume 2, Issue 4, April 2012) 92
Newer biomaterials even incorporate living cells in order to
provide a true biological and mechanical match for the living
tissue. II.SELECTION PARAMETERS FOR BIOMATERIALS
ABiomaterialusedforimplantshouldpossesssome
importantpropertiesinordertolong-termusageinthe
bodywithoutrejection.Thedesignandselectionof
biomaterialsdependondifferentpropertieswhichare characterized in
this section. A.Host Response:
Hostresponseisdefinedastheresponseofthehost organism (local and
systemic) to theimplantedmaterial or device [6].
B.Biocompatibility: Researchershavecoinedthewords`biomaterial'and
`biocompatibility'[7]toindicatethebiological performance
ofmaterials. Materials thatarebiocompatible
arecalledbiomaterials,andthebiocompatibilityisa descriptive term
which indicates the ability of a material to
performwithanappropriatehostresponse,inaspecific
application[8].Insimpletermsitimpliescompatibilityor
harmonyofthebiomaterialwiththelivingsystems.
Biocompatibilityistheabilitytoexistincontactwith tissues of the
human body without causing an unacceptable
degreeofharmtothebody.Itisnotonlyassociatedto
toxicity,buttoalltheadverseeffectsofamaterialina
biologicalsystem[9,10].Itmustnotadverselyaffectthe
localandsystemichostenvironmentofinteraction(bone,
softtissues,ioniccompositionofplasma,aswellasintra and
extracellular fluids) [11]. It refers to a set of properties
thatamaterialmusthavetobeusedsafelyinabiological
organism.Itshouldbenon-carinogenic,non-pyrogenic,
non-toxic,non-allergenic,bloodcompatible,non-inflammatory.Theoperationaldefinitionofbiocompatible
is "The patient is alive so it must be biocompatible".
C.Biofunctionality[11]:
Biofunctionalityisplayingaspecificfunctionin
physicalandmechanicalterms.Thematerialmustsatisfy its design
requirements in service:
Loadtransmissionandstressdistribution(e.g.bone replacement)
Articulationtoallowmovement(e.g.artificialknee joint) Control of
blood and fluid flow (e.g. artificial heart) Space filling (e.g.
cosmetic surgery) Electrical stimuli (e.g. pacemaker) Light
transmission (e.g. implanted lenses) Sound transmission (e.g.
cochlear implant) D.Functional Tissue Structure and Pathobiology:
Biomaterialsincorporatedintomedicaldevicesare
implantedintotissuesandorgans.Therefore,thekey
principlesgoverningthestructureofnormalandabnormal
cells,tissuesororgans,thetechniquebywhichthe
structureandfunctionofnormalandabnormaltissuesare
studied,andthefundamentalmechanismsofdisease processes are critical
considerations to workers in thefield [12]. E.Toxicology:
Abiomaterialshouldnotbetoxic,unlessitis specifically engineered for
such requirements (for example
a"smart"bomb"drugdeliverysystemthattargetscancer
cellsanddestroythem).Toxicologyforbiomaterialsdeals
withthesubstancesthatmigrateoutofthebiomaterials.It
isreasonabletosaythatabiomaterialshouldnotgiveoff anything from
itsmassunless it isspecifically designed to do so [12].
F.Appropriate Design and Manufacturability:
Biomaterialsshouldbemachinable,moldable, extrudable. Finite element
analysis is a powerful analytical
toolusedinthedesignofanyimplants.Currentlymodern
manufacturingprocessesarenecessarytoguaranteethe quality needed in
orthopaedic devices. G.Mechanical Properties of Biomaterials:
Someofthemostimportantpropertiesofbiomaterials
thatshouldbecarefullystudiedandanalysedintheir
applicationsaretensilestrength,yieldstrength,elastic
modulus,corrosionandfatigueresistance,surfacefinish,
creep,andhardness.Physicalpropertiesarealsotakingin
toaccountwhileselectingmaterials.Thedialysis
membranehasaspecifiedpermeability.Thearticularcup of thehip joint
hashigh lubricity. Theintraocular lenshas clarity and refraction
requirements. H.High corrosion resistance:
Singh&Dahotre[13]didresearchoncorrosion
resistanceasisanimportantissueinselectionofmetallic biomaterials
because the corrosion of metallic implants due
tothecorrosivebodyfluidisunavoidable.Theimplants
releaseundesirablemetalionswhicharenon-biocompatible.Corrosioncanreducethelifeofimplant
deviceandconsequentlymayimposerevisionsurgery.In addition thehuman
lifemay be decreased by the corrosion phenomenon. Okazaki &
Gotoh [14] expressed the fact that
dissolvedmetalions(corrosionproduct)eithercan
accumulateintissues,neartheimplantortheymaybe transported to other
parts of the body. International Journal of Emerging Technology and
Advanced Engineering Website: www.ijetae.com (ISSN 2250-2459,
Volume 2, Issue 4, April 2012) 93 I.High wear resistance:
Thelowwearresistanceorhighcoefficientoffriction results in implant
loosening [15, 16]. Wear debris are found
tobebiologicallyactiveandmakeasevereinflammatory
responsethatleadtothedestructionofthehealthybone
whichsupportstheactualimplant.Corrosioncausedby
frictionisabigconcernsinceitreleasesnoncompatible
metallicions.Itshouldbepointedoutthatmechanical loading also can
result in corrosion fatigue and accelerated wear processes [15].
J.Long fatigue life: Thefatiguestrengthisrelatedtotheresponseofthe
material to the repeated cyclic loads. Fatigue fracture leads some
of major problems associated with implant loosening,
stress-shieldingandultimateimplantfailureanditis
frequentlyreportedforhipprostheses[17].Fatigue characteristics are
strongly depends on the microstructures.
Themicrostructuresofmetallicbiomaterialsalter
accordingtotheprocessingandheattreatmentemployed [6]. K.Adequate
Strength: Strengthofmaterialsfromwhichtheimplantsare
fabricatedhasinfluencethefractureofartificialorgan.In
adequatestrengthcancausetofracturetheimplant.When
theboneimplantinterfacestartstofail,developingasoft
fibroustissueattheinterfacecanmakemorerelative
motionbetweentheimplantandtheboneunderloading
[9].Thisfactcausespaintothepatientandafteracertain
period,thepainbecomesunbearableandtheimplantmust be replaced, by a
revision procedure [15]. L.Modulus equivalent to that of bone:
Formajorapplicationssuchastotaljointreplacement,
higheryieldstrengthisbasicallycoupledwiththe
requirementofalowermodulusclosetothatofhuman
bones[19,20].Themagnitudeofbonemodulusvaries from 4 to 30 GPa
depending on the type of the bone and the
measurementdirection[21].Largedifferenceinthe
Youngsmodulusbetweenimplantmaterialandthe
surroundingbonecancontributetogenerationofsevere
stressconcentration,namelyloadshieldingfromnatural
bonethatmayweakentheboneanddeterioratethe
implant/boneinterface,looseningandconsequentlyfailure
ofimplant[9,22].Themodulusisconsideredasamain factor for selection
of any biomaterials. III.HUMAN ANATOMY The first and foremost
requirement for the choice of the biomaterial is its acceptability
by the human body (Fig. 1).
Thesuccessofabiomaterialoranimplantishighly
dependentonthreemajorfactors(i)Theproperties
(mechanical,chemicalandtribological)ofthebiomaterial
(ii)biocompatibilityoftheimplantand(iii)thehealth
conditionoftherecipientandthecompetencyofthe surgeon
[23].Generally, tissues are grouped into hard and soft tissues.
Boneandtoothareexamplesofhardtissues,andskin,
bloodvessels,cartilageandligamentsareafewexamples
ofsofttissues.Asthenamessuggest,ingeneralthehard
tissuesstiffer(elasticmodulus)andstronger(tensile strength) than
the soft tissues (Tables 1 and 2). Considering
thestructuralormechanicalcompatibilitywithtissues,
metalsorceramicsarechosenforhardtissueapplications,
andpolymersforthesofttissueapplications.Oneofthe
primaryreasonsthatbiomaterialsareusedistophysically
replacehardorsofttissuesthathavebecomedamagedor
destroyedthroughsomepathologicalprocess[24].Under
thesecircumstances,itmaybepossibletoremovethe
diseasedtissueandreplaceitwithsomesuitablesynthetic material. TABLE
1 MECHANICAL PROPERTIES OF HARD TISSUE [25] Hard tissue Modulus
(GPa) Tensile Strength (MPa) Cortical bone (longitudinal direction)
17.7133 Cortical bone(transverse direction) 12.852 Cancellous
bone0.47.4 Enamel84.310 Dentine11.039.3 TABLE 2 MECHANICAL
PROPERTIES OF SOFT TISSUE [25] Soft tissue Modulus (MPa) Tensile
Strength (MPa) Articular cartilage 10.527.5 Fibrocartilage159.110.4
Ligament303.029.5 Tendon401.546.5 Skin0.1-0.27.6 Intraocular
lens5.62.3 International Journal of Emerging Technology and
Advanced Engineering Website: www.ijetae.com (ISSN 2250-2459,
Volume 2, Issue 4, April 2012) 94 FIGURE 1: IMPLANTS FOR HUMAN
ANATOMY SIGNIFICANCE IV.IMPLANTABLE MATERIALS Thescience of
biomedicalmaterials involves astudy of the composition and
properties of materials and theway in which they interact with the
environment in which they are
placed.Themostcommonclassesofmaterialsusedas
biomedicalmaterialsaremetals,polymers,ceramics,and
composite.Thesefourclassesareusedsinglyandin
combinationtoformmostoftheimplantationdevices available today.
A.Metals and Alloys:
Metalshavebeenusedalmostexclusivelyforload-bearingimplants,suchashipandkneeprosthesesand
fracturefixationwires,pins,screws,andplates.Although
puremetalsaresometimesused,alloysfrequentlyprovide
improvementinmaterialproperties,suchasstrengthand
corrosionresistance.Threematerialgroupsdominate
biomedicalmetals:Stainlesssteel,cobalt-chromium-molybdenum alloy,
and titanium and titanium alloys.
Themainconsiderationsinselectingmetalsandalloys for biomedical
applications are their excellent electrical and
thermalconductivity,biocompatibility,appropriate mechanical
properties, corrosion resistance, and reasonable cost. It is very
important to know the physical and chemical
propertiesofthedifferentmetallicmaterialsusedinany
surgeryaswellastheirinteractionwiththehosttissueof the human body.
Stainless Steel: Stainlesssteelwasfirstusedsuccessfullyasan
important material in the surgical field. Stainless steel is the
genericnameforanumberofdifferentsteelsused
primarilybecauseoftheirresistancetoawiderangeof corrosiveagents[10,
15]. Stainless steelhas been used for
widerangeofapplicationduetoeasyavailability,lower
cost,excellentfabricationproperties,accepted biocompatibility and
great strength. Cohlear Implants Intacts Cardiovascular Implants
(Vascular Grafts) Prosthetic Arthroplasty Bone Fixation, Bone
Plates & Screws Knee joint Replacement, Tendon / Ligament,
Cartilage ReplacementLumbar Disc Replacement, Spine Cage, Plate,
Rods and Screws Total Hip Replacement, Acetabular Pacemaker
Shoulder ProsthesisDental Implants, Dental Post, Arch Wire &
Brackets, Dental Bridges, Dental Restorative Material Abdominal
Wall Prosthesis Intramedullary Nails Bone Cement International
Journal of Emerging Technology and Advanced Engineering Website:
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Cobalt-Chrome: Cobaltchromiumalloyscanbebasicallycategorized
intotwotypes;oneisTheCoCrMoalloy[Cr(27-30%), Mo (5-7%), Ni (2.5%)]
has been used for many decades in dentistry, and in making
artificial joints and the second one The CoNiCrMo alloy [Cr
(19-21%), Ni (33-37%), and Mo (9-11%)] has been used for making the
stems of prostheses for heavily loaded joints, such as knee and hip
[15]. Cobalt-basedalloysarehighlyresistanttocorrosionevenin
chlorideenvironmentduetospontaneousformationof
passiveoxidelayerwithinthehumanbodyenvironment [10, 15, 16, 26,
27]. The thermal treatments used to Co-Cr-Mo alloys modify the
microstructure of the alloy and alters
theelectrochemicalandmechanicalpropertiesofthe
biomaterial[26].ThecorrosionproductsofCo-Cr-Moare more toxic than
those of stainless steel 316L. Titanium and its Alloys: There are
three structural types of titanium alloys: Alpha
(),Alpha-Beta(-)ormetastableandBeta().The
phaseinTialloystendstoexhibitamuchlowermodulus
thanphase,andalsoitsatisfiesmostoftheother
necessitiesorrequirementsfororthopedicapplication[28,
29].Tialloysduetothecombinationofitsexcellent
characteristicssuchashighstrength,lowdensity,high
specificstrength,goodresistancetocorrosion,complete
inertnesstobodyenvironment,enhancedbiocompatibility,
moderateelasticmodulusofapproximately110GPaarea suitable choice for
implantation. Long-term performance of
titaniumanditsalloysmainlyTi64hasraisedsome concerns because of
releasing aluminumandvanadium [9,
10].BothAlandVionsareassociatedwithlongterm
healthproblems,likeAlzheimerdiseaseandneuropathy.
Furthermorewhentitaniumisrubbedbetweenitselfor between other
metals, it suffers from severe wear
[30].Themechanicalpropertiesofmaterialsareofgreat
importancewhendesigningload-bearingorthopedicand
dentalimplants.Somemechanicalpropertiesofmetallic
biomaterialsarelistedinTable3.Themechanical properties of a
specific implant depend not only on the type
ofmetalbutalsoontheprocessesusedtofabricatethe material and device.
The elastic moduli of the metals listed
inTable3areatleastseventimesgreaterthanthatof natural bone. TABLE 3
MECHANICAL PROPERTIES OF METALLIC BIOMATERIALS [31] Material Youngs
Modulus, E (GPa) Yield Strength, sy (MPa) Tensile Strength, sUTS
(MPa) Fatigue Limit, send (MPa) Stainless
steel1902211,2135861,351241820 Co-Cr
alloys2102534481,6066551,896207950 Titanium (Ti)110485760300
Ti-6Al-4V1168961,0349651,103620 Cortical bone1530307070150 TABLE 4
APPLICATION OF METALS AS IMPLANTS USED IN HUMAN BODY Types of
MaterialsApplications Stainless steel Joint replacements (hip,
knee), Bone plate for fracture fixation, Dental implant for tooth
fixation, Heart valve, Spinal Instruments, Surgical Instruments,
Screws, dental root Implant, pacer, fracture plates, hip nails,
Shoulder prosthesis Cobalt-chromium alloy Bone plate for fracture
fixation, Screws, dental root implant, pacer, and Suture,
dentistry, orthopedic prosthesis, Mini plates, Surgical tools, Bone
and Joint replacements (hip, knee), dental implants Titanium and
its Alloys Cochlear replacement, Bone and Joint Replacements(hip,
knee),Dental Implants for tooth fixation, Screws, Suture, parts for
orthodontic surgery, bone fixation devices like nails, screws and
plates, artificial heart valves and surgical instruments, heart
pacemakers, artificial heart valves B.Ceramics
Ceramicsarepolycrystallinematerials.Themain
characteristicsofceramicmaterialsarehardnessand
brittleness,greatstrengthandstiffness,resistanceto corrosion and
wear, and low density. They work mainly on
compressionforces;ontensionforces,theirbehavioris
poor.Ceramicsaretypicallyelectricalandthermal
insulators.Ceramicsareusedinseveraldifferentfields such as
dentistry, orthopedics, and as medical sensors. [32].
Overall,however,thesebiomaterialshavebeenusedless
extensivelythaneithermetalsorpolymers.Ceramics
typicallyfailwithlittle,ifany,plasticdeformation,and they are
sensitive to the presence of cracks or other defects. International
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Ceramicshavebecomeadiverseclassofbiomaterials
presentlyincludingthreebasictypes:bioinert,bioactive,
bioresorbableceramics[33].Alumina(Al2O3),Zirconia
(ZrO2)andPyrolyticcarbonaretermedbioinert.Bioglass
andglassceramicsarebioactive.Calciumphosphate ceramics are
categorized as bioresorbable.
Bioinertreferstoamaterialthatretainsitsstructureinthe
bodyafterimplantationanddoesnotinduceany immunologic host
reactions. Alumina (Al2O3): High density high purity (>99.5%)
alumina (Al2O3) was
thefirstceramicwidelyusedclinically.Itisusedinload-bearinghipprosthesesanddentalimplants,becauseofits
combinationofexcellentcorrosionresistance,good
biocompatibility,andhighwearresistance,andhigh
strength.Thereasonsfortheexcellentwearandfriction
behaviorof(Al2O3)areassociatedwiththesurfaceenergy
andsurfacesmoothnessofthisceramic.The
biocompatibilityofaluminaceramichasbeentestedby
manyresearchers.Noirietal.[34]evaluatedthe
biocompatibilityofalumina-ceramicmaterial
histopathalogicallyforeightweeksbyimplantinginthe
eyesocketsofalbinorabbits.Theresultsshowednosigns
ofimplantrejectionorprolapseoftheimplantedpiece.
Afteraperiodoffourweeksofimplantation,fibroblast
proliferationandvascularinvasionwerenotedandby
eighthweek,tissuegrowthwasnotedintheporesofthe
implant[34].Singlecrystalaluminascrewsandpinswere
implantedinthefemoralboneofmaturerabbits.Changes in
theimplant-boneinterfacewereobserved.Aluminawas never in direct
contact with the bone and hemidesmosomes were not observed in the
interface [35]. The cytotoxicity of
singlecrystalaluminaceramicswasstudiedinLcellline
culture.Theydisplayedthesamecolonyformationand
survivalratesasthecontrolsshowedthattheyhaveno
cytotoxicityandifimplantedinbonemarrowtheywould not be toxic to
circumferential tissue [36]. Zirconia (ZrO2): Zirconia is a
biomaterial that has a bright future because
ofitshighmechanicalstrengthandfracturetoughness.
Zirconiaceramicshaveseveraladvantagesoverother
ceramicmaterialsduetothetransformationtoughening
mechanismsoperatingintheirmicrostructurethatcanbe manifested in
componentsmadeout of them. Theresearch on the use of zirconia
ceramics as biomaterials commenced
abouttwentyyearsagoandnowzirconiaisinclinicaluse
intotalhipreplacement(THR)butdevelopmentsarein
progressforapplicationinothermedicaldevices.Today's main
application of zirconia ceramics is in THR ball heads
[37].Theosteointegrationofzirconiawasinvestigatedin normal and
osteopenic rats by means of histomorphometry. The data showed that
the tested material was biocompatible in vitro and confirmed that
bone mineral density is a strong
predictoroftheosteointegrationofanorthopedicimplant and that the
use of pathological animal models is necessary
tocompletelycharacterizebiomaterials[38].Itissaidthat
verysmalltracesofradioelements,whichcanbefound
eveninfullyrefinedceramics,haveanegativeeffecton
organsandtissues.Zirconiacontainsverysmalltracesof
radioelements[39].Thecytotoxicityofpolycrystalline
zirconiawasspeculatedinLcelllineculture.Thestudy revealed its
noncytotoxicity [36]. Pyrolytic Carbon:
Carbonisaversatileelementandexistsinavarietyof
forms.Goodcompatibilityofcarbonaceousmaterialswith
boneandothertissueandthesimilarityofthemechanical properties of
carbon to those of bone indicate that carbon is
anexcitingcandidatefororthopedicimplants[40].Unlike
metals,polymersandotherceramics,thesecarbonaceous
materialsdonotsufferfromfatigue.However,their intrinsic brittleness
and low tensile strength limits their use
inmajorloadbearingapplications.Themechanical
bondingbetweenthecarbonfiberreinforcedcarbonand
hosttissuewasinvestigated.Thebondingdevelopedthree months after
intrabone implantation and is accompanied by a decrease of the
implant strength [41].
Bioactivereferstomaterialsthatformdirectchemical
bondswithboneorevenwithsofttissueofaliving organism. Bioglass &
Glass Ceramic: A common characteristic of such bioactive materials
is a modificationofthesurfacethatoccursuponimplantation.
Bondingtobonewasfirstdemonstratedforarangeof
bioactiveglasses,whichcontainedspecificamountsof
SiO2,CaO,andP2O5[42].Thismaterialhasbeenwidely
usedforfillingbonedefects.Theporosityofbioglassis beneficial for
resorption and bioactivity [43]. The interface
reactionwasinterpretedasachemicalprocess,which includes a slight
solubility of the glass ceramic and a solid-state reaction between
the stable apatite crystals in the glass ceramic and the bone [44].
Bioresorbablereferstomaterialsthatdegrade(by
hydrolyticbreakdown)inthebodywhiletheyarebeing
replacedbyregeneratingnaturaltissue;thechemicalby-productsofthedegradingmaterialsareabsorbedand
released via metabolic processes of the body. Calcium phosphate
ceramics: Different phases of calcium phosphate ceramics are used
depending uponwhether a resorbable or bioactivematerial is desired.
International Journal of Emerging Technology and Advanced
Engineering Website: www.ijetae.com (ISSN 2250-2459, Volume 2,
Issue 4, April 2012) 97
Calciumphosphate(CaP)biomaterialsareavailablein various physical
forms. One of their main characteristics is their porosity. The
ideal pore size for bioceramic is similar
tothatofspongybone[45].Theprimerequirementfor
calciumphosphatematerialstobebioactiveandbondto living bone is the
formation of a bone like apatite layer on their surface [46]. The
major drawbacks to the use of ceramics and glasses
asimplantsaretheirbrittlenessandpoortensileproperties
(Table5).Althoughtheycanhaveoutstandingstrength
whenloadedincompression,ceramicsandglassesfailat
lowstresswhenloadedintensionorbending.Among
biomedicalceramics,aluminahasthehighestmechanical properties, but
its tensile properties are still below those of metallic
biomaterials. TABLE 5 MECHANICAL PROPERTIES OF CERAMIC BIOMATERIALS
[47] Youngs Modulus, E (GPa) Compressive Strength, sUCS (MPa)
Tensile Strength, sUTS (MPa) Alumina3804500350
Zirconia150-2002000200-500 Pyrolytic carbon 18-28517280-560
Bioglass-ceramics 2250056-83 Calcium phosphates 40-117510-89669-193
TABLE 6 APPLICATION OF CERAMICS AS IMPLANTS USED IN HUMAN BODY
Types of MaterialsApplications Alumina Artificial total joint
replacement, acetabular and femoral components, vertebrae spacers
and extensors, orthodontic anchors, dental implant for tooth
fixation Zirconia Replacement for hips, knees, teeth, tendons and
ligaments, repair for periodontal disease, bone fillers after tumor
surgery Pyrolytic carbon Prosthetic heart valves, End osseous tooth
replacement implants, permanently implanted artificial limbs
Bioglass-ceramics Dental implants, middle ear implants, heart
valves, artificial total joint replacement, bone plates, screws,
wires, intramedullary nails, spinal fusion, tooth replacement
implants Calcium phosphates Skin treatments, dental implants,
jawbone reconstruction, orthopedics, facial surgery, ear, nose and
throat repair, dental implant C.POLYMERIC BIOMATERIALS
Thedevelopmentofpolymericbiomaterialscanbe
consideredasanevolutionaryprocess.Reportsonthe
applicationsofnaturalpolymersasbiomaterialsdateback thousands of
years [48]. Polymers are the most widely used
materialsinbiomedicalapplications.Polymersareorganic materials that
form large chains made up of many repeating
units.Theusesforpolymericmaterialsaremorediverse
thanformetallicimplants,buttheirinterchangeabilityis not as great.
In most of applications, polymers have little or no competition
from other types of materials. Their unique
propertiesare:Flexibility,Resistancetobiochemical
attack,Goodbiocompatibility,Lightweight,Availableina
widevarietyofcompositionswithadequatephysicaland
mechanicalproperties,Canbeeasilymanufacturedinto products with the
desired shape. A few of the major classes of polymer are listed
below: Poly (methyl methacrylate), PMMA: It is ahard brittlepolymer
thatappears to beunsuitable
formostclinicalapplications,butitdoeshaveseveral important
characteristics. It can be prepared under ambient
conditionssothatitcanbemanipulatedintheoperating
theaterordentalclinic,explainingitsuseindenturesand bone cement.
The relative success of many joint prostheses
isdependentontheperformanceofthePMMAcement,
whichispreparedintraoperativelybymixingpowdered polymer with
monomeric methylmethacrylate, which forms dough that can be placed
in the bone, where it then sets. Silicone Rubbers: Both
heat-vulcanizing and room temperature vulcanizing
siliconesareinusetodayandbothexhibitadvantagesand disadvantages.
Room temperature vulcanizing silicones are supplied as single-
paste systems. Heat-vulcanizing silicone
issuppliedasasemi-solidmaterialthatrequiresmilling, packing under
pressure. Ultra High Molecular Weight Polyethylene (UHMWPE):
Muchresearchisprogressinginexaminingthewear
propertiesofUHMWPE.Thecoefficientoffriction between polyethyleneand
cobalt-chromium alloy has been
reportedtobebetween0.03and0.16,withexcellentwear rates. UHMWPE is
used as the bearing surface in total joint arthroplasty, it has 90%
success rates at 15 years with metal
onpolyethylene.Submicronparticlesfoundin periprosthetic tissues
when polyethylene wear present. (But no better material has been
developed to date) Themechanicalpropertiesofpolymersdependon
severalfactors,includingthecompositionandstructureof
themacromolecularchainsandtheirmolecularweight.
Table7listssomemechanicalpropertiesofselected polymeric
biomaterials. International Journal of Emerging Technology and
Advanced Engineering Website: www.ijetae.com (ISSN 2250-2459,
Volume 2, Issue 4, April 2012) 98 Examples of current applications
include vascular grafts,
heartvalves,artificialhearts,breastimplants,contact
lenses,intraocularlenses,componentsofextracorporeal
oxygenators,dialyzersandplasmapheresisunits,coatings for
pharmaceutical tablets and capsules, sutures, adhesives, and blood
substitutes, kidney, liver, pancreas, bladder, bone
cement,catheters, externaland internalear repairs, cardiac
assistdevices,implantablepumps,jointreplacements,
pacemaker,encapsulations,soft-tissuereplacement,
artificialbloodvessels,artificialskin,Dentistry,Drug delivery and
targeting into sites of inflammation or tumors, Bags for the
transport of blood plasma. TABLE 7 MECHANICAL PROPERTIES OF
POLYMERS [49] Polymer Tensile Strength SUTS(MPa) Youngs Modulus,
E(GPa) % Elongation Poly(methyl methacrylate) (PMMA) 302.21.4 Nylon
6/6762.890 Poly(ethylene terephthalate) 532.14300 Poly(lactic
acid)28-501.2-32-6 Polypropylene28-361.1-1.55400-900
Polytetrafluoroethylene17-280.5120-350 Silicone rubber2.8Up to
10160 Ultra-high-molecular-weight polyethylene (UHMWPE)
>354-12>300 D.BIOCOMPOSITE MATERIALS
Biocompositesarecompositematerialscomposedof
biodegradablematrixandbiodegradablenaturalfibresas
reinforcement.Thedevelopmentofbiocompositeshas
attractedgreatinterestduetotheirenvironmentalbenefit
andimprovedperformance[50].Plant-basedfiberslike flax, jute, sisal
and kenaf have been frequently used (Table 8). Most of studies
concern biodegradable matrix based on
aliphaticpolyestersreinforcedwithvariousvegetable
fillers.Withwide-rangingusesfromenvironment-friendly
biodegradablecompositestobiomedicalcompositesfor
drug/genedelivery,tissueengineeringapplicationsand
cosmeticorthodontics.Theyoftenmimicthestructuresof
thelivingmaterialsinvolvedintheprocessinadditionto the
strengthening properties of the matrix that was used but
stillprovidingbiocompatibility.Thosemarketsare
significantlyrising,mainlybecauseoftheincreaseinoil price, and
recycling and environment necessities [51]. Bone itself achieves
most of its mechanical properties as
anaturalcompositematerialcomposedofcalcium
phosphateceramicsinahighlyorganizedcollagenmatrix.
Compositebiomaterialsaremadewithafiller
(reinforcement)additiontoamatrixmaterialinorderto
obtainpropertiesthatimproveeveryoneofthe
components.Thismeansthatthecompositematerialsmay
haveseveralphases.Somematrixmaterialsmaybe
combinedwithdifferenttypesoffillers.Polymers
containingparticulatefillersareknownasparticulate
composites.Thefirstcompositetocomeintogeneraluse, initially made by
an orthopedic surgeon, was the plaster of
Parisbandage.Thishasbeenrefinedtofiberglasswitha polymeric matrix
in the current synthetic casting materials. A composite for
internal prosthetic applications is based on
theadditionofchoppedcarbonfibertoimprovethe
mechanicalpropertiesofpolyethylenecomponents[52].
Onlycarbonfiberisbeingstudiedfororthopedic
applications[53].Compositestructuresaretypically
producedfromlaminates.Alaminateisathinsheetof
compositematerialinwhichallthefibersruninone
directionandareheldtogetherbyathincoatingofthe
polymermatrixmaterial.Thislaminateiscombinedwith other laminates to
form a bulk composite; the properties of
thiscompositevarydependingontheorientationofeach
layerofthelaminate[54].Noneofthesematerialsare
currentlyinclinicalusebecauseoftheinabilitytomodify
theshapesoftheimplantsintraoperativelytofitthebone;
becauseofliberationofcarbonfibersintotheadjacent
tissues;andbecausethedifficultiesofpredictingthe
resorptionofpolymersinlargerloadbearingimplants,as opposed to
screws and pins, has thus far precluded their use
fortheselargerimplants.Nodoubt,implantsinthis
categorywillbeavailableinthefuture,perhapseven containing bone
inductive proteins. TABLE 8 CONSTITUENTS OF BIOMEDICAL COMPOSITES
ParticlesFibersMatrix Inorganic Glass Alumina Polymers Aromatic
Polyamides (aramids) UHMWPE Polyesters Polyolefins PTFE Thermosets
Epoxy Polyacrylates Polymethacrylates Polyesters Silicones Organic
Polyacrylate Polymethacrylate Resorbable polymers Polylactide, and
its copolymers with polyglyocolide Thermoplastics Polyolefins (PP,
PE) UHMWPE Polysulfones International Journal of Emerging
Technology and Advanced Engineering Website: www.ijetae.com (ISSN
2250-2459, Volume 2, Issue 4, April 2012) 99 Silk Collagen
Poly(ether ketones) Polyesters Inorganic Carbon Glass
Hydroxyapatite Tricalcium phosphate Inorganic Hydroxyapatite Glass
ceramics Calcium carbonate ceramics Calcium phosphate ceramics
Carbon Steel Titanium Resorbable polymers Polylactide,
polyglycolide and their copolymers Polydioxanone TABLE 9
APPLICATION OF COMPOSITE AS IMPLANTS USED IN HUMAN BODY
ApplicationsTypes of materials Dentistry CF/C, SiC/C,CF/Epoxy,
GF/Polyester, GF/PC, GF/PP, GF/Nylon, GF/PMMA,UHMWPE/PMMA, CF/PMMA,
GF/PMMA, KF/PMMA, Silica/BIS-GMA Vascular Grafts Cells/PTFE,
Cells/PET, PET/Collagen, PET/Gelation, PU/PU-PELA Joint
replacements PET/PHEMA, KF/PMA, KF/PE, CF/PTFE,CF/PLLA, GF/PU,
PET/PU, PTFE/PU, CF/PTFE, CF/C, CF/UHMWPE,UHMWPE/UHMWPE, CF/Epoxy,
CF/PS, CF/PEEK, CF/UHMWPE, CF/PE, Bone cement Bone particles/PMMA,
Titanium/PMMA, UHMWPE/PMMA, GF/PMMA, CF/PMMA, Bio-Glass/Bis-GMA
Bone Replacement Materials HA/PHB, HA/PEG-PHB, CF/PTFE, PET/PU,
HA/HDPE, HA/PE, Bio-Glass/PE, Bio-Glass/PHB, Bio-Glass/PS, HA/PLA
Spine Cage, Plate, Rods, Screws, Disc, Finger Joint, Intramedullary
Nails, Abdominal wall Prosthesis, PET/PU, PET/Collagen, CF/LCP,
CF/PEEK, GF/PEEK, CF/Epoxy, CF/PS, Bio-glass/PU, Bio-glass/PS,
PET/SR, PET/Hydrogel, CF/UHMWPE V.CONCLUDING REMARKS
Abiomaterialisanysubstance(otherthandrugs),
naturalorsynthetic,thattreats,augments,orreplacesany
tissue,organ,andbodyfunction.Biomaterialselectionis
oneofthemostchallengingissuesduetocrucial requirements and
biocompatibility,so ithas been ofmajor interest to material
designers in recent years. This review of
biomaterialshasattemptedtodemonstratethevery
significantprogressthathasbeenmadewiththeuseof
advancedmaterialswithinthehumanbody.Thepresent
studyreviewedthecurrentlyusedbiomaterials;metals, ceramics,
polymers, and composite.
Metalsaresusceptibletodegradationbycorrosion,a process that can
release by-products that may cause adverse
biologicalresponses.Ceramicsareattractiveasbiological
implantsfortheirbiocompatibility.Thestudiesshowthat alumina with
high mechanical strength show minimal or no tissuereaction,
nontoxicto tissues and blood compatibility
testswerealsosatisfactory.Carbonwithsimilar mechanicalproperties of
boneis an exciting candidate, for
itelicitsbloodcompatibility,notissuereactionand
nontoxicitytocells.Theavailabilityofawiderangeof
polymerssignificantlyinfluencedthegrowthoftissue
engineeringandcontrolleddrugdeliverytechnologies.
Innovationsinthecompositematerialdesignand fabrication processes
are raising the possibility of realizing
implantswithimprovedperformance.However,for
successfulapplication,surgeonsmustbeconvincedwith
thelongtermdurabilityandreliabilityofcomposite biomaterials.
Inthepast,successofmaterialsinbiomedical
applicationswasnotsomuchtheoutcomeofmeticulous
selectionbasedonbiocompatibilitycriteriabutratherthe
resultofserendipity,continuousrefinementinfabrication
technology,andadvancesinmaterialsurfacetreatment.In
thepresentandfuture,electionofabiomaterialfora
specificapplicationmustbebasedonseveralcriteria.
Biocompatibilityistheparamountcriterionthatmustbe
metbyeverybiomaterial.Medicalresearchcontinuesto
explorenewscientificfrontiersfordiagnosing,treating,
curing,andpreventingdiseasesatthemolecular/genetic
level.Thisreviewshouldbeofvaluetoresearcherswho
areinterestedinthestateoftheartofbiomaterial evaluation and
selection of biomaterials. International Journal of Emerging
Technology and Advanced Engineering Website: www.ijetae.com (ISSN
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