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NaturalPolymersasBiomaterials
SourceInformationforthefollowingslides:
1)Okada,M.Prog.Polym.Sci.2002,27,87133.
2)Nair,L.etal.Prog.Polym.Sci.2007,32,762798.
3)B.
Ratner,
A.
Hoffman,
F.
Schoen,
and
J.
Lemons:
BiomaterialsScience, 2nd
edition(SanDiego:ElsevierAcademicPress.2004).
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EnzymaticallyDegradablePolymers
ProteinsandPoly(aminoacids)
Collagen Naturalpoly(aminoacids)
Syntheticpoly(aminoacids) Poly(Lglutamicacid)
Poly(aspartic
acid)
Elastin
Elastinlikepeptides
Albumin
Fibrin
Polysaccharides Chitinandchitosan
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NaturalPolymers:Background
Egypt: Animalsinewusedforsutures
100:
Disemboweledsoldiers
treated
with
natural
biomaterials
1667: Bloodtransfusionwithlambblood
(France) 1700:Caranium transplantationfromdog(Russia)
1936:ArthurBowen(England)usedporcinesmall
intestineas
asoft
tissue
alternative.
Abundant
material,lowimmunogenicity
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NaturalPolymers:Background
Relevance:naturaltissuesinbiomedicineisamultibillion
dollarindustry
Fabrication:mostlylivingtissuesfromhumans(autograft,
allograft)or
animals
(xenograft)
that
have
been
decellularized
usingsterilants.
Applications:Heartvalves,meniscusregeneration,drug
delivery,sutures
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NaturalMaterials
Naturalmaterialsareoftensimilar,ifnotidenticaltomacromolecular
materialsthebiologicalenvironmentcanrecognizeandprocessthrough
metabolicpathways
Naturalmaterialscanfunctionbiologicallyatthemolecularlevel,notjust
macroscopiclevel
Inflammatoryresponse
invoked
by
synthetic
material
is
suppressed
with
naturalmaterials
Naturalpolymerscanoftenbedegradedbynaturallyoccurringenzymes
leadingto
the
material
being
metabolized
by
physiological
mechanisms
Isthisadisadvantage? Perhapsincertainapplications,butinothersitcanbequite
advantageous. Forexample,implantsdesignedtodeliveraspecificfunctionfora
temporaryamountoftime.
Crosslinksmakeless degradable
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NaturalMaterials
Disadvantagesofnaturalmaterials:
Similarityto
biological
substances
often
invokes
aimmunogenic
response
(thisisparticularlyaproblemforproteins). Bodysimmunesystem
recognizesforeignmaterialandattemptstodestroy.
High
degree
of
variability
in
natural
materials
derived
from
animal
sources
Structurallymorecomplexthantraditionalmaterials;manipulationmore
elaborateandcomplicated
Limitedprocessing
routes
in
many
cases
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NaturalPolymers:StructureandFunction
Whatstheconnectionbetweenbodilytissuesandpolymers?
FourPrincipleTissueTypes Epithelial linessurfacesandcavities;protectsstructures,fluidtransport
Connective fibrous,loadbearing
Muscle contractilefilaments;externalandinternallocomotion
Nervous muscleandmentalactivity
Principletissuesarelargelycomposedbythreetypesof
biopolymers:
Proteins chainsofaminoacids(silk,collagen,elastin,fibrin)
Polysaccharides chainsofsugar(chitin,glycosaminoglycans)
Polynucleotides chainsofnucleotides(DNA,RNA)
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NaturalPolymers:StructureandFunction
Iftheconstituentmoleculesinnaturaltissuearesimilar,what
influences
the
material
properties?
Molecularconfiguration 29differenttypesofcollagenhavebeenidentifiedwithdifferentcrosslinksandstructuralhierarchies
Composition cartilagehas
30x
more
polysaccharides
than
ligament
Organization cartilageisisotropic,ligamenthasapreferreddirection
OverridingPrinciple: Natureadaptsstructuretoperformaspecificfunction
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NaturalPolymers:StructureandFunction
Thestructuralelementsofthehumanbodyarethecellsand
the
extracellular
matrix
(ECM) the
cells
secrete
Inbiomaterials,wegenerallyusenaturalpolymersfromthe
ECMofconnectivetissues(e.g.tendon,skin,ligament,blood
vessels,cartilage,
bone
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NaturalPolymers:StructureandFunction
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NaturalPolymers Proteins
Protein
Structure:
Polymer:chainsofaminoacid
Bonding:covalent
peptide
bonds
Hydrophoblic core,hydrophilicexteriorinteractswithaqueous
environment
Proteinfoldinaspecificmannerforaspecificfunction(most
complicatedmacromolecules
in
the
human
body)
Function
Actasenzymes(assemble/disassembleothermolecules)
Also
serve
to
provide
structural
stability
(connective
tissue)
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Collagen
Collagenisthemostabundantproteinpresentinthehumanbodybeing
themajorcomponentofskinandothermusculoskeletaltissues.
Collagenisarodtypepolymernearly300 nmlongwithamolecular
weightof
300,000.
Morethantwentytwodifferenttypesofcollagenidentifiedsofarinthe
humanbody,withthemostcommonbeingTypeIIV.
TypeIcollagenisthesinglemostabundantproteinpresentinmammals
and
is
the
most
thoroughly
studied
protein. TypeIcollageniscomposedofthreepolypeptidesubunitswithsimilar
aminoacidcompositions.Eachpolypeptideiscomposedofabout1050
aminoacids,containingapproximately33%glycine,25%proline and25%
hydroxyproline witharelativeabundanceoflysine.
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CollagenTypes
Type StructuralFeatures RepresentativeTissues
Fibrillar Collagens
I 300nm
long
fibrils Skin,
tendon,
bone,
ligaments,dentin,
interstitialtissues
II 300nmlongfibrils Cartilage,vitreoushumor
III 300nm
long
fibrils;
often
withtypeISkin,
muscle,
blood
vessels
V 390nmlongfibrilswith
globularNterminal
domain;oftenwithtypeI
SimilartotypeI;alsocell
cultures,fetaltissues
SOURCE:K.Kuhn,1987,inR.Mayne andR.Burgeson,eds.,Structureand
Functionof
Collagen
Types,
Academic
Press,
p.
2;
M.
van
der
Rest
and
R.
Garrone,1991,FASEBJ.5:2814.
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StructuralOrderinCollagen
Structuralorderincollagenoccursatseveraldiscretelevels
Primarystructure sequenceofaminoacids
Secondarystructure
local
configurationofpolypeptidechainsthatresultsfromsatisfactionofstereochemicalanglesandhydrogenbonding
betweenpeptide
residues
Tertiary globalconfiguarations ofpolypeptidechains.triplehelicalcollagenmolecule
Quaternarydenotes
repeating
supramolecular unitstructurecomprisingseveralmoleculespackedintoaspecificlattice.Basicunitofthemicrofibril
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NaturalPolymers Proteins
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NaturalPolymers Proteins
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B.Ratner,A.Hoffman,F.Schoen,andJ.Lemons:BiomaterialsScience, 2ndedition(SanDiego:ElsevierAcademicPress.2004).134.
Collagenundergoesenzymaticdegradationwithinthebodyviaenzymes,suchascollagenases
andmetalloproteinases,
to
yieldthecorrespondingaminoacids.
Duetotheirenzymaticdegradability,uniquephysicochemical,mechanicaland
biologicalproperties
collagen
hasbeenextensivelyinvestigatedforbiomedicalapplications.
Collagenismostlysolubleinacidicaqueoussolutionsand
canbe
processed
into
different
formssuchassheets,tubes,sponges,foams,nanofibrousmatrices,powders,fleeces,injectableviscoussolutionsanddispersions.
Studieshave
also
shown
that
thedegradationrateofcollagenusedforbiomedicalapplicationscanbesignificantlyalteredbyenzymaticpretreatmentorcrosslinkingusing
variouscross
linking
agents.
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NaturalPolymers Polysaccharides
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NaturalPolymers Polysaccharides
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NaturalPolymers Polysaccharides
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B.Ratner,A.Hoffman,F.Schoen,andJ.Lemons:BiomaterialsScience, 2ndedition(SanDiego:ElsevierAcademicPress.2004).135.
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NaturalPolymers Polysaccharides
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