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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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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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Polymerization

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Addition polymerization:

Initiation, Free radicals,

Propagation,

Termination.

Step-growth polymerization:

Condensation polymers

Photopolymerization

Photoinitiators.

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Physical Properties

Mechanical

Electrical

Optical

Thermodynamic Kinetic

Heat Transport

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Mechanical Properties

Thermoplastics

Liquid Crystal Polymers

Rubbers or elastomers

Lightly Crosslinked Thermosets

Heavily crosslinked

Cure

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Viscoelasticity

Bower 2002

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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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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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Dielectric Constant

The dielectric constant or relative

permittivity of a polymer is defined as

follows:

=0V

V

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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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Semiconductor Doping

Jastrzebski 1976

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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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Polarons, Biopolarons & Solitons

Mitchell 2004]

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Copolymers

+

*

*x

y

n

Cyclic olefin monomer Ethylene

Cyclic olefin copolymer

Catalyst

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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.