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Introduction to BioMEMS & Medical Microdevices
Polymer Materials
Companion lecture to the textbook: Fundamentals of BioMEMS and Medical Microdevices, by
Dr. Steven S. Saliterman
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Steven S. Saliterman, MD, FACP
Polymer Composite Biomaterials
Ramakrishna and et al. 2001
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Steven S. Saliterman, MD, FACP
Advantages of Polymers
1. Improved and easier machinability.
2. Optical transparency for certain detectionstrategies
3. Biocompatibility.
4. Acceptable thermal and electrical properties.
5. Ability to enclose high-aspect-ratio
microstructures.
6. Ability for surface modification and
functionalization.
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Steven S. Saliterman, MD, FACP
Polymerization
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Steven S. Saliterman, MD, FACP
Addition polymerization:
Initiation, Free radicals,
Propagation,
Termination.
Step-growth polymerization:
Condensation polymers
Photopolymerization
Photoinitiators.
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Steven S. Saliterman, MD, FACP
Physical Properties
Mechanical
Electrical
Optical
Thermodynamic Kinetic
Heat Transport
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Steven S. Saliterman, MD, FACP
Mechanical Properties
Thermoplastics
Liquid Crystal Polymers
Rubbers or elastomers
Lightly Crosslinked Thermosets
Heavily crosslinked
Cure
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Steven S. Saliterman, MD, FACP
Viscoelasticity
Bower 2002
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Steven S. Saliterman, MD, FACP
Hookes Law
=
is the tensile stress (force/unit cross section),
is Young's modulus of the material, and
is the linear strain ( length/initial length).
Where
E
e
e
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Steven S. Saliterman, MD, FACP
Deviation from Ideal Elasticity Time and Temperature dependency of
response: Boltzmann superposition principle.
Yield or non-recovery of strain.
Non-linearity of response.
Large strains without fracture: Ductile fracture,
Brittle fracture,
Crack initiation and propagation, Crazing.
Anisotropy of response.
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Steven S. Saliterman, MD, FACP
Dielectric Constant
The dielectric constant or relative
permittivity of a polymer is defined as
follows:
=0V
V
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Steven S. Saliterman, MD, FACP
Electrical Conductivity
Intrinsically conductive based on -
electron conjugation.
Incorporated particles.
Ion-impregnated (e.g. LiClO4-impregnated poly(ethylene oxide).
-electron conjugation (e.g.poly(silanes).
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Steven S. Saliterman, MD, FACP
Semiconductor Doping
Jastrzebski 1976
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Steven S. Saliterman, MD, FACP
Polymer Conduction
HC
CH
HC
trans-Polyacetylene
CH
HC
CH
CH2
H2
C
CH2
H2
C
CH2
H2
C
CH2
H2
C
CH2
H2
C
Polyethyelene
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Steven S. Saliterman, MD, FACP
Polarons, Biopolarons & Solitons
Mitchell 2004]
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Steven S. Saliterman, MD, FACP
Copolymers
+
*
*x
y
n
Cyclic olefin monomer Ethylene
Cyclic olefin copolymer
Catalyst
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Steven S. Saliterman, MD, FACP
Summary Polymers are attractive for bioMEMS:
Improved and easier machinability. Optical transparency for certain detection strategies
Biocompatibility.
Acceptable thermal and electrical properties.
Ability to enclose high-aspect-ratio microstructures. Ability for surface modification and functionalization.
Soft fabrication techniques often utilizepolymer materials, both synthetic and natural.
Biopolymers, including DNA and proteins arenatural polymers.
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