Biomaterials

OutlineOutline
 DefinitionDefinition
 Characteristics of BiomaterialsCharacteristics of Biomaterials
 HistoryHistory
 Biomaterials ScienceBiomaterials Science
 Generations of BiomaterialsGenerations of Biomaterials
 Examples of BiomaterialsExamples of Biomaterials
 Detail on Vascular GraftsDetail on Vascular Grafts
 Detail on Hip ReplacementsDetail on Hip Replacements
 BiocompatibilityBiocompatibility
 ChallengesChallenges
 Biomaterials As An Emerging IndustryBiomaterials As An Emerging Industry
 CompaniesCompanies

DefinitionDefinition
 A biomaterial is a nonviable material usedA biomaterial is a nonviable material used
in a medical device, intended to interactin a medical device, intended to interact
with biological systems.with biological systems.
 Defined by their applicationDefined by their application NOTNOT chemicalchemical
make-up.make-up.

Characteristics of BiomaterialsCharacteristics of Biomaterials
 Physical RequirementsPhysical Requirements
 Hard Materials.Hard Materials.
 Flexible Material.Flexible Material.
 Chemical RequirementsChemical Requirements
 Must not react with any tissue in theMust not react with any tissue in the
body.body.
 Must be non-toxic to the body.Must be non-toxic to the body.
 Long-term replacement must not beLong-term replacement must not be
biodegradable.biodegradable.

HistoryHistory
 More than 2000 years ago, Romans,More than 2000 years ago, Romans,
Chinese, and Aztec’s used gold inChinese, and Aztec’s used gold in
dentistry.dentistry.
 Turn of century, synthetic implants becomeTurn of century, synthetic implants become
available.available.
 1937 Poly(methyl methacrylate) (PMMA)1937 Poly(methyl methacrylate) (PMMA)
introduced in dentistry.introduced in dentistry.
 1958, Rob suggests Dacron Fabrics can be1958, Rob suggests Dacron Fabrics can be
used to fabricate an arterial prosthetic.used to fabricate an arterial prosthetic.

History (Continued)History (Continued)
 1960 Charnley uses PMMA, ultrahigh-1960 Charnley uses PMMA, ultrahigh-
molecular-weight polyethylend, andmolecular-weight polyethylend, and
stainless steal for total hip replacement.stainless steal for total hip replacement.
 Late 1960 – early 1970’s biomaterial fieldLate 1960 – early 1970’s biomaterial field
solidified.solidified.
 1975 Society for Biomaterials formed.1975 Society for Biomaterials formed.

Biomaterials ScienceBiomaterials Science
 Grow cells in culture.Grow cells in culture.
 Apparatus for handling proteins in theApparatus for handling proteins in the
laboratory.laboratory.
 Devices to regulate fertility in cattle.Devices to regulate fertility in cattle.
 Aquaculture of oysters.Aquaculture of oysters.
 Cell-silicon “Biochip”.Cell-silicon “Biochip”.

Metals
Semiconductor
Materials
Ceramics
Polymers
Synthetic
BIOMATERIALS
Orthopedic
screws/fixation
Dental Implants Dental Implants
Heart
valves
Bone
replacements
Biosensors
Implantable
Microelectrodes
Skin/cartilage
Drug Delivery
Devices
Ocular implants

Biomaterial ScienceBiomaterial Science

First Generation BiomaterialsFirst Generation Biomaterials
 Specified by physicians using commonSpecified by physicians using common
and borrowed materials.and borrowed materials.
 Most successes were accidental ratherMost successes were accidental rather
than by design.than by design.

Second Generation of BiomaterialsSecond Generation of Biomaterials
 Developed through collaborations ofDeveloped through collaborations of
physicians and engineers.physicians and engineers.
 Engineered implants using common andEngineered implants using common and
borrowed materials.borrowed materials.
 Built on first generation experiences.Built on first generation experiences.
 Used advances in materials scienceUsed advances in materials science
(from other fields).(from other fields).

Third generation implantsThird generation implants
 Bioengineered implants using bioengineeredBioengineered implants using bioengineered
materials.materials.
 Few examples on the market.Few examples on the market.
 Some modified and new polymeric devices.Some modified and new polymeric devices.
 Many under development.Many under development.

Examples of BiomaterialExamples of Biomaterial
ApplicationsApplications
 Heart ValveHeart Valve
 Artificial TissueArtificial Tissue
 Dental ImplantsDental Implants
 Intraocular LensesIntraocular Lenses
 Vascular GraftsVascular Grafts
 Hip ReplacementsHip Replacements

Heart ValveHeart Valve
 Fabricated from carbons, metals,Fabricated from carbons, metals,
elastomers, fabrics, and natural valves.elastomers, fabrics, and natural valves.
 MustMust NOTNOT React With Chemicals inReact With Chemicals in
Body.Body.
 Attached By Polyester Mesh.Attached By Polyester Mesh.
 Tissue Growth Facilitated By PolarTissue Growth Facilitated By Polar
Oxygen-Containing Groups.Oxygen-Containing Groups.

Heart ValveHeart Valve
 Almost as soon as valve implantedAlmost as soon as valve implanted
cardiac function is restored to nearcardiac function is restored to near
normal.normal.
 Bileaflet tilting disk heart valve usedBileaflet tilting disk heart valve used
most widely.most widely.
 More than 45,000 replacement valvesMore than 45,000 replacement valves
implanted every year in the Unitedimplanted every year in the United
States.States.

Bileaflet Heart ValvesBileaflet Heart Valves

Problems with Heart Valve’sProblems with Heart Valve’s
 Degeneration of Tissue.Degeneration of Tissue.
 Mechanical Failure.Mechanical Failure.
 Postoperative infection.Postoperative infection.
 Induction of blood clots.Induction of blood clots.

Artificial TissueArtificial Tissue
 BiodegradableBiodegradable
 Polymer Result ofPolymer Result of
Condensation ofCondensation of
Lactic Acid andLactic Acid and
Glycolyic AcidGlycolyic Acid

 Small titanium fixture that serves as the
replacement for the root portion of a missing
natural tooth.
 Implant is placed in the bone of the upper or
lower jaw and allowed to bond with the bone.
 Most dental implants are: pure titanium
screw-shaped cylinders that act as roots for
crowns and bridges, or as supports for
dentures.
Dental ImplantsDental Implants

 Capable of bonding to bone, a
phenomenon known as "osseointegration”.
 Bio-inert, there is no reaction in tissue and
no rejection or allergic reactions.

Intraocular LensesIntraocular Lenses
 Made of PMM, silicone elastomer, andMade of PMM, silicone elastomer, and
other materials.other materials.
 By age 75 more than 50% of populationBy age 75 more than 50% of population
suffers from cataracts.suffers from cataracts.
 1.4 million implantations in the United1.4 million implantations in the United
States yearly.States yearly.
 Good vision is generally restored almostGood vision is generally restored almost
immediately after lens is inserted.immediately after lens is inserted.

Intraocular LensesIntraocular Lenses
 Implantation often performed onImplantation often performed on
outpatient basis.outpatient basis.

Vascular GraftsVascular Grafts
 Must Be Flexible.Must Be Flexible.
 Designed With OpenDesigned With Open
Porous Structure.Porous Structure.
 Often RecognizedOften Recognized
By Body As Foreign.By Body As Foreign.

Hip-ReplacementsHip-Replacements
 Most Common Medical Practice UsingMost Common Medical Practice Using
Biomaterials.Biomaterials.
 Corrosion Resistant high-strength MetalCorrosion Resistant high-strength Metal
Alloys.Alloys.
 Very High Molecular Weight Polymers.Very High Molecular Weight Polymers.
 Thermoset Plastics.Thermoset Plastics.

 Some hip replacements ambulatory functionSome hip replacements ambulatory function
restored within days after surgery.restored within days after surgery.
 Others require an extensive healing periodOthers require an extensive healing period
for attachment between bone and thefor attachment between bone and the
implant.implant.
 Most cases good function restored.Most cases good function restored.
 After 10-15 years, implant loosens requiringAfter 10-15 years, implant loosens requiring
another operation.another operation.

 Achieve and maintain homeostasis.Achieve and maintain homeostasis.
 Porous.Porous.
 Permeable.Permeable.
 Good structure retention.Good structure retention.
 Adequate burst strength.Adequate burst strength.
 High fatigue resistance.High fatigue resistance.
 Low thrombogenecity.Low thrombogenecity.
 Good handling properties.Good handling properties.
 Biostable.Biostable.

 Braids, weaves, and knits.Braids, weaves, and knits.
 PorosityPorosity
 PermeabilityPermeability
 ThicknessThickness
 Burst strengthBurst strength
 Kink resistanceKink resistance
 Suture retentionSuture retention
 Wall thicknessWall thickness
 Tensile propertiesTensile properties
 Ravel resistanceRavel resistance

Vascular Grafts PermeabilityVascular Grafts Permeability
 BraidsBraids
 350 to 2500 ml cm350 to 2500 ml cm22
/min/min
 KnitsKnits
 Loosely Woven KnitsLoosely Woven Knits
 1200 to 2000 ml cm1200 to 2000 ml cm22
/min/min
 Tightly Woven KnitsTightly Woven Knits
 2000 to 5000 ml cm2000 to 5000 ml cm22
/min/min
 WeavesWeaves
 Below 800 ml cmBelow 800 ml cm22
/min/min

Filtration and FlowFiltration and Flow
 µ viscosity of fluidµ viscosity of fluid
 t thickness oft thickness of
membranemembrane
 V velocity of fluidV velocity of fluid
 Δp pressure dropΔp pressure drop
across membraneacross membrane
p
tv
B
∆
=
µ

Void Content Kozeny-CarmenVoid Content Kozeny-Carmen
EquationEquation
 KKoo is the Kozeny constant.is the Kozeny constant.
 SSoo is the shape factor.is the shape factor.
 Φ is the porosity.Φ is the porosity.
( )2
3
2
1
1
φ
φ
−
∗=
oo SK
B
( )2
3
2
1
1
φ
φ
−
∗=
oo SK
B

Shape FactorShape Factor
Volume
aSurfaceAre
So =

Biomaterials: An ExampleBiomaterials: An Example
Biomechanics of Artificial JointsBiomechanics of Artificial Joints

Normal versus Arthritic HipNormal versus Arthritic Hip
Sir John Charnely: 1960's, fundamental principles of the artificial hip
Frank Gunston: 1969, developed one of the first artificial knee joints.
Hip replacements done in the world per year: between 500,000 and 1
million.
Number of knee replacements done in the world per year: between
250,000 and 500,000.
Of all the factors leading to total hip replacement, osteoarthritis is the most
common, accounting for 65% of all total hips.

Normal versus Arthritic HipNormal versus Arthritic Hip
Normal Hip: note the space
between the femur and
acetabulum, due to cartilage
Arthritic Hip: No space
visible in joint, as
cartilage is missing

Two design issues in attachingTwo design issues in attaching
materials to bonematerials to bone
1)1) the geometric and material design ofthe geometric and material design of
the articulating surfacesthe articulating surfaces
2)2) design of the interface between thedesign of the interface between the
artificial joint and the surroundingartificial joint and the surrounding
bone. bone.

using a Polymethylmethacrylate
(PMMA) cement to adhere the
metal to the bone
using a porous metal
surface to create a bone
ingrowth interface
Two attachment methodsTwo attachment methods

the acetabulum and the proximal
femur have been replaced. The
femoral side is completely metal.
The acetabular side is composed
of the polyethylene bearing
surface
Overview of femoralOverview of femoral
replacementreplacement

The two materials are
bonded and equal force is
applied to both
Load transfer in CompositeLoad transfer in Composite
materialsmaterials

Comparison: Modului ofComparison: Modului of
ElasticityElasticity
Modulus of elasticity of different implant materials and bone (in GPa)

Implant bondingImplant bonding
A bonded interface is
characteristic of a
cemented prosthesis
(left)
non-bonded interface is
characteristic of a non-
cemented press fit
prosthesis (right)

Degradation ProblemsDegradation Problems
Example of fractured
artificial cartilage from
a failed hip
replacement

BiocompatibilityBiocompatibility
 The ability of a material to elicit anThe ability of a material to elicit an
appropriate biological response in aappropriate biological response in a
specific application byspecific application by NOTNOT
producing a toxic, injurious, orproducing a toxic, injurious, or
immunological response in livingimmunological response in living
tissue.tissue.
 Strongly determined by primary chemicalStrongly determined by primary chemical
structure.structure.

Host Reactions to BiomaterialsHost Reactions to Biomaterials
 ThrombosisThrombosis
 HemolysisHemolysis
 InflammationInflammation
 Infection and SterilizationInfection and Sterilization
 CarcinogenesisCarcinogenesis
 HypersensitivityHypersensitivity
 Systemic EffectsSystemic Effects

What are some of theWhat are some of the
Challenges?Challenges?
 To more closely replicate complex tissueTo more closely replicate complex tissue
architecture and arrangementarchitecture and arrangement in vitro.in vitro.
 To better understand extracellular andTo better understand extracellular and
intracellular modulators of cell function.intracellular modulators of cell function.
 To develop novel materials and processingTo develop novel materials and processing
techniques that are compatible with biologicaltechniques that are compatible with biological
interfaces.interfaces.
 To find better strategies for immuneTo find better strategies for immune
acceptance.acceptance.

Biomaterials - An EmergingBiomaterials - An Emerging
IndustryIndustry
 Next generation of medical implants andNext generation of medical implants and
therapeutic modalities.therapeutic modalities.
 Interface of biotechnology and traditionalInterface of biotechnology and traditional
engineering.engineering.
 Significant industrial growth in the next 15Significant industrial growth in the next 15
years -- potential of a multi-billion dollaryears -- potential of a multi-billion dollar
industry.industry.

Biomaterials Companies
•Baxter International develops technologies related to the blood and circulatory system.
• Biocompatibles Ltd. develops commercial applications for technology in the field of biocompatibility.
• Carmeda makes a biologically active surface that interacts with and supports the bodys own control mechanisms
• Collagen Aesthetics Inc. bovine and human placental sourced collagens, recombinant collagens, and PEG-polymers
• Endura-Tec Systems Corp. bio-mechanical endurance testing ofstents, grafts, and cardiovascular materials
• Howmedica develops and manufactures products in orthopaedics.
• MATECH Biomedical Technologies, development of biomaterials by chemical polymerization methods.
• Medtronic, Inc. is a medical technology company specializing in implantable and invasive therapies.
• Molecular Geodesics Inc., biomimetic materials for biomedical, industrial, and military applications
• Polymer Technology Group is involved in the synthesis, characterization, and manufacture of new polymer products.
• SurModics, offers PhotoLink(R) surface modification technology that can be used to immobilize biomolecules
• W.L. Gore Medical Products Division, PTFE microstructures configured to exclude or accept tissue ingrowth.
• Zimmer, design, manufacture and distribution of orthopaedic implants and related equipment and supplies

Biomaterials

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