Biomaterials

1. BiomaterialsBiomaterials

2. 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
Challenges Challenges
Biomaterials As An Emerging IndustryBiomaterials As An Emerging Industry
Companies Companies

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

4. 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 the Must 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 be Long-term replacement must not be
biodegradable.biodegradable.

5. HistoryHistory
More than 2000 years ago, Romans, More than 2000 years ago, Romans,
Chinese, and Aztec’s used gold in Chinese, and Aztec’s used gold in
dentistry.dentistry.
Turn of century, synthetic implants become Turn 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 be 1958, Rob suggests Dacron Fabrics can be
used to fabricate an arterial prosthetic.used to fabricate an arterial prosthetic.

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

7. Biomaterials ScienceBiomaterials Science
Grow cells in culture.Grow cells in culture.
Apparatus for handling proteins in the Apparatus 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”.

8. 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

9. Biomaterial ScienceBiomaterial Science

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

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

12. Third generation implantsThird generation implants
Bioengineered implants using bioengineered Bioengineered 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.

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

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

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

16. Bileaflet Heart ValvesBileaflet Heart Valves

17. 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.

18. Artificial TissueArtificial Tissue
BiodegradableBiodegradable
Polymer Result of Polymer Result of
Condensation of Condensation of
Lactic Acid and Lactic Acid and
Glycolyic AcidGlycolyic Acid

19. 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

20. 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.

21. Dental ImplantsDental Implants

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

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

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

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

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

27. Hip-ReplacementsHip-Replacements

28. Vascular GraftsVascular Grafts
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.

29. Vascular GraftsVascular Grafts
Braids, weaves, and knits.Braids, weaves, and knits.
PorosityPorosity
PermeabilityPermeability
Thickness Thickness
Burst strengthBurst strength
Kink resistanceKink resistance
Suture retentionSuture retention
Wall thicknessWall thickness
Tensile propertiesTensile properties
Ravel resistance Ravel resistance

30. Vascular Grafts PermeabilityVascular Grafts Permeability
BraidsBraids
350 to 2500 ml cm350 to 2500 ml cm
22
/min /min
KnitsKnits
Loosely Woven KnitsLoosely Woven Knits
1200 to 2000 ml cm1200 to 2000 ml cm
22
/min /min
Tightly Woven Knits Tightly Woven Knits
2000 to 5000 ml cm2000 to 5000 ml cm
22
/min /min
WeavesWeaves
Below 800 ml cmBelow 800 ml cm
22
/min /min

31. Knit GraftsKnit Grafts

32. Filtration and FlowFiltration and Flow
µ viscosity of fluidµ viscosity of fluid
t thickness of t thickness of
membranemembrane
V velocity of fluidV velocity of fluid
Δp pressure drop Δp pressure drop
across membraneacross membrane
p
tv
B
D
=
m

33. Void Content Kozeny-Carmen Void Content Kozeny-Carmen
EquationEquation
KK
o o is the Kozeny constant.is the Kozeny constant.
SS
o o is the shape factor.is the shape factor.
Φ is the porosity.Φ is the porosity.
( )
2
3
2
1
1
f
f
-
*=
oo
SK
B
( )
2
3
2
1
1
f
f
-
*=
oo
SK
B

34. Shape FactorShape Factor
Volume
aSurfaceAre
S
o=

35. Biomaterials: An ExampleBiomaterials: An Example
Biomechanics of Artificial Joints Biomechanics of Artificial Joints

36. 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.

37. 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

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

39. 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

40. 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 femoral Overview of femoral
replacementreplacement

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

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

43. 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)

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

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

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

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

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

49. 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