Contact Lens

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BMEN 482/682 Polymeric Biomaterials Dr. Melissa
Grunlan
Contact Lens
bone plates
knee hip replacement
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What are MATERIALS?
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What are BIOMATERIALS?
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CLASSES OF BIOMATERIALS
Metals Ceramics Polymers
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What is a Metal?
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What is an alloy?

• Examples in biomaterials
• - Titanium alloy (Ti-6Al-4V)
• 90 Ti, 6 Al, 4 V low amounts of H, Fe, N,
  C
• femoral stem
• - Stainless steel 316L
• 63 Fe, 18 Cr, 13 Ni low amounts of N, Mn,
  Mo, P, Si, S, and C
• femoral head (occasionally)

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What is a Ceramic?

• Example in biomaterials
• Aluminum Oxide/ Alumina (Al2O3)
• Acetabular cup liner (occasionally)

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What is a Polymer?

• Example in biomaterials
• UHMWPE
• -CH2-CH2-
• MW 2-3 million g/mols (n 107,143)
• acetabular cup liner (most common)

n
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BIOMATERIALS CAN BE USED TO FORM
Exoprotheses Endoprotheses
Artificial Liver
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Useful Definitions

• Biocompatible
• the ability of a material to perform with an
  appropriate host response in a specific
  application
• Biomaterials must be biocompatible, but the
  level of biocompatibility varies.
• Extent of host response determines
  biocompatibility.

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Useful Definitions
Bioinert Causing no biological effect/ host
response Bioactive Produces an effect on living
tissue - For example, bioactive glasses stimulate
bone tissue growth Biodegradable Undergoes
degradation in the body - Degradation involves
bond breaking - Degradation products are
harmless and can be secreted naturally
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How do biomaterials fit into biomedical
engineering?
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FACILITATOR
ACTION

• Identify a need
• Treat disease
• Replace organ
• Cosmetic

Physician Engineer/Scientist
implementation
Engineer Physician
Device Design
Biomaterials Selection Biomaterials
Development Biomaterials Testing
Engineer Scientist
patient
Fabrication, sterilization, device testing,
regulatory, clinical use
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1. Identify a Need Replacement of Deteriorated
Hip Joint
Osteoarthritis loss of cartilage
The hip joint is the largest load-bearing joint.
A hip joint is lined with articular cartilage a
layer of tissue that provides low-friction and
shock-absorbing properties. Arthritis and injury
can damage this protective layer of cartilage,
causing extreme pain for a patient performing
even simple activities.
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2. Design Device Total Hip Replacement
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3. Biomaterial Selection
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KNEE REPLACEMENT
The healthy human knee joint is aslo lined with
articular cartilage. Arthritis and injury can
similarly damage this protective layer of
cartilage causing extreme pain.
wear
http//tc.engr.wisc.edu/UER/uer01/author1/content.
html
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POLYMERS IN OPHTHALMICS

• Intraocular Lens replace opaque crystalline
  lens (cataract) of the eye

Inflexible IOL Tg 105 ?C Rigid Larger
incision needed
Foldable IOL Tg (PDMS) -125 ?C
Flexible Smaller incision
PDMS PMMA
Silicone Acrylates
PMMA
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POLYMERS IN OPHTHALMICS
2. Soft Contact Lenses placed on cornea to
correct vision
Hydrogels lightly crosslinked polymers which
absorb large quantities of water
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BIODEGRADABLE STENTS
Stent inserted into a blocked artery to improve
blood flow

• Permanent Stainless Steel Stents
• Stainless Steel 316L E 193 GPa
• Restenosis re-blocking of artery due to the
  formation of (a) neointima thick
• smooth muscle tissue inside lumen or (b)
  late-stage thrombosis clot

Biodegradable Stent

• Biodegradable Polymer Stents
• Present long enough for vessel to
• re-model and then it dissolves
• Can be drug-loaded
• Minimize restenosis
• Disadvantage recoil (weaker than SS)

LASER LACE This biodegradable polymer stent
was cut by an ultrafast laser.
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BIODEGRADABLE ORTHOPEDIC DEVICES
Degradation Time (months)
Tg
cryst.
modulus
Poly(L-lactic acid) PLLA
40
2.7 GPa
60 ?C
gt 24
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Mechanical Properties of Biomaterials

• The mechanical properties of a biomaterial is
  determined by its structure.
• A biomaterial must meet mechanical property
  requirements to be successful in for a particular
  device
• For instance, the mechanical properties of the
  tissues which are being replaced or repaired must
  be matched or met.

• The higher modulus of the femoral stem vs. the
  surrounding bone tissue leads to stress shielding
  ? bone loss ? implant loosening ? revision surgery

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Mechanical Properties of Biomaterials

• Replacing permanent metallic devices with
  biodegradable polymeric devices is desirable but
  limited by polymers lower mechanical properties.