“soft” fabrication and polymers...steven s. saliterman advantages of polymers 1. improved and...

Introduction to BioMEMS & Medical Microdevices

“Soft” Fabrication and Polymers Companion lecture to the textbook: Fundamentals of BioMEMS and Medical Microdevices, by Prof. Steven S. Saliterman, http://saliterman.umn.edu/

R012408

Steven S. Saliterman

Biomaterials

What is a biomaterial? Natural, synthetic and biological materials.

Classes of biomaterials: Implanted or have other direct contact with

living tissue (in vivo), Transport or containment function (in vitro), Process function (functionalized materials).


Advantages of Polymers

1. Improved and easier machinability. 2. Optical transparency for certain detection

strategies 3. Biocompatibility. 4. Acceptable thermal and electrical properties. 5. Ability to enclose high-aspect-ratio

microstructures. 6. Ability for surface modification and

functionalization.


“Soft” Fabrication

1. “Soft” lithography. 2. Micromolding. 3. 3-D Photopolymerization. 4. “Smart” polymers and hydrogels. 5. Nanomedicine techniques. 6. Thick-film technologies. 7. Array patterning.


Micro-Contact Printing (µCP)

Nguyen, N.T. and S.T. Wereley, Fundamentals and Applications of Microfluidics, Artech House, Boston, MA (2002).


PDMS (Silicone) Stamp

PDMS (Silicone) Stamp

PDMS (Silicone) Monomer Nguyen, N.T. and S.T. Wereley, Fundamentals and Applications of Microfluidics, Artech House, Boston, MA (2002).


Example: PDMS Microfluidic Device

Jaehoon Chung & Euisik Yoon


PDMS Molding Station


PDMS Castings


UV-Ozone Surface Treatment


Inspecting the PDMS casting


Alignment on Substrate


Video Inspection of Alignment


Inspecting the Final Device


Test Apparatus

Steven S. Saliterman Jaehoon Chung & Euisik Yoon


Micromolding

Injection Molding Reaction Injection Molding Hot Embossing Injection Compression Molding Thermoforming Atmospheric Molding AMANDA


Injection Molding

Left: Heckele, M. and W.K. Schomburg, Review on micro molding of thermoplastic polymers. Journal of Micromechanics and Microengineering 14(3), pp. 1-14 (2004). Right: Image courtesy of Thermotech

Steven S. Saliterman Heckele, M. and W.K. Schomburg, Review on micro molding of thermoplastic polymers. Journal of Micromechanics and Microengineering 14(3), pp. 1-14 (2004).

Variotherm Process


Hot Embossing

Heckele, M. and W.K. Schomburg, Review on micro molding of thermoplastic polymers. Journal of Micromechanics and Microengineering 14(3), pp. 1-14 (2004).


Thermoforming

Heckele, M. and W.K. Schomburg, Review on micro molding of thermoplastic polymers. Journal of Micromechanics and Microengineering 14(3), pp. 1-14 (2004).


3-D Photopolymerization

Three-dimensional photopolymerization is based on layer-by-layer assembly, and is used for rapid production of devices for modeling and prototyping: Stereolithography (SL) Microstereolithography (MSL) Dynamic Projection MSL


Photopolymerization

UV curing occurs between 225 and 550 nm. Free radical curing:

When the photoinitiator is exposed to UV, they break down leaving components with an unpaired electron, or free radicals.

Propagation occurs with addition of monomers, and transfer of the free radical down the propagating chain to continue the process of addition of monomers.

Termination occurs when the growing chain stops. Acrylates are associated with free radical

polymerization.


Ionic polymerization: Involves an attack on the π electron pair of a

monomer. Cationic curing :

Cationic polymerization occurs when the active site has a positive charge (in contrast to anionic polymerization in which the active site has a negative charge).

Addition of monomers moves the charge down the chain until termination occurs.

Epoxies are associated with cationic curing .


Microstereolithography (MSL)

Suzumori, K. and et al., Microfabrication of integrated FMAs using stereolithography. Proceedings of IEEE MEMS, pp. 136-141 (1994)


Dynamic Mask Projection MSL

Bertsch, A. et al., Microsterolithography using a liquid crystal display as dynamic generator. Microsystem Technology 3(2), pp. 42-47 (1997).


Clips Car

Gear Bone Bertsch A., 1998, 1999, 2001, Personal Correspondence.

MSL Fabricated Parts


Pipe Cup

Gear Screw Bertsch A., 1997, 1999, Personal Correspondence.


Smart Polymers and Hydrogels

“Smart” polymeric materials exhibit significant changes in their characteristics with small changes in their environment.

These external stimuli include pH, calcium, magnesium, organic solvents, temperature, magnetic field, electrical potential, and IR and UV radiation.

Some materials respond to dual stimuli such as calcium and PEG, calcium and temperature, calcium and acetonitrile, pH and temperature, and light and temperature.

Electroactive polymers (EAPs) respond to electrical stimulation.


Smart polymers are either reversible soluble-insoluble (SIS) in aqueous media or cross-linked in the form of hydrogels.

SIS polymers include synthetic polymers such as poly (N-isopropylacrylamide) (PNIPAAm) and methyl-methacrylate polymers; and natural polymers such as alginate and chitosan (polysaccharides).

CH

H2C

C

CH CH3O

NH

*

*

H3C

n

Poly(N-isopropylacrylamide) (PNIPAAm)


O

OO

OO OOH OH

O

OH

OH

O

HOHO

*

*

HO

COO-

-OOC

-OOC

COO-

H2N

n

Alginate

O

O

OH

O

OHO

**

NH2

NH

COH3C

HOH2C

CH2OHn

Chitosan

Natural Polymers


Hydrogels

Oosterbroek, R.E. and A. van den Berg, Lab-on-a-Chip: Miniaturized Systems for (Bio)Chemical Analysis and Synthesis, 1st ed. Amsterdam, Elsevier (2003).


When a stimulus is applied at a critical level, both SIS and hydrogels increase or decrease their overall hydrophilicity and either swell or shrink respectively.

Physical hydrogels are held together with noncovalent forces and have hydrophilic and hydrophobic domains.

Chemical hydrogels are held together by crosslinking, and have regions of high and low crosslinking. Areas of low crosslinking allow higher swelling.


Synthesis

OH

O

Acrylic Acid (AA)

OOH

O

2-hydroxyethyl methacrylate (HEMA)

OO

O

H2O

Ethyleneglyco dimethacrylate (EGDMA)

O

OCH3

Ph

OCH3

2,2'-dimethoxy-2-phenyl acetophenone (DMPA)


Synthetic Hydrogels


Hydrogel Applications

Controlled drug delivery. Thermo-responsive microfluidic actuator. Ultrasensitive microcantilever sensor. Combined with optically active nanoparticles,

light frequency-dependent optical switching can be accomplished.

Optical control by fiberoptics at a distance. Tissue scaffolding devices with selective

diffusion.


Summary

Biomaterials for medical diagnostics and therapeutics include natural, synthetic and biological materials that have contact with humans or human products such as blood, urine, cerebral spinal fluid, organs and other tissue.

“Soft Fabrication” includes: “Soft” lithography. Micromolding. 3-D Photopolymerization. “Smart” polymers and hydrogels. Nanomedicine techniques. (see textbook) Thick-film technologies. (see textbook) Array patterning (to be covered later).

“soft” fabrication and polymers...steven s. saliterman advantages of polymers 1. improved and...

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