Project UpdateJune 22, 2006

ME342A

Project Goal

• Design a bioMEMs substrate to apply and

measure electromechanical forces in the

differentiation of human embryonic stem cell-

derived (hESC)-cardiac myocytes (CM)

Undifferentiated hESCs-Fluc-eGFP

(DAPI nuclear stain)

hESC-CMs organized in embryoid body

bioMEMS device

Contractility

Electrophysiology

Mechanical force

BioMEMS: Engineering Specs

Device Requirement Target Value

1. Apply mechanical strain Up to 10%

2. Apply electric field ~O(1) V/cm

3. Measure electric potential (ECG) 100μV—1mV

4. Area of mechanical deformation A < 1cm2

5. Size of electrodes diameter = 20μm

6. Inter-electrode spacing spacing = 250μm

7. Area of cell culture A > 1cm2

8. Thickness of substrate t < 1mm

BioMEMS: Device Design

Poly(dimethylsiloxane) (PDMS): A biocompatible elastomeric polymer with low water permeability

Quartz: Optically transparent substrate

Gold: Biocompatible thin film electrodes

Indium-Tin Oxide (ITO): Transparent thin film conducting electrodes traces

A. Unstrained state B. Strained state

BioMEMS: Loading Curves

• Young’s Modulus PDMS E = 500kPa

• Thickness = 50um

• Membrane length = 1cm

• Loading post length = 0.7cm

0

2

4

6

8

10

12

14

0 20 40 60 80 100 120

Pressure (-kPa)

Elo

ng

ati

on

(%

)

Equibiaxial Strain

Uniaxial Strain

1. Double polished quartz wafer ~ 500μm

BioMEMS: Fabrication

Quartz

2. Laser cut alignment marks & pressure channels

(frontside wafer)

BioMEMS: Fabrication

Quartz

Channels etched to apply suction pressure to PDMS substrate

3. Laser cut channels to connect to pressure lines

(backside wafer)

BioMEMS: Fabrication

Quartz

Channels backside to connect to vacuum source

3a. Laser cut channels to connect to pressure lines

(backside wafer)

Alternative Step—Replace 3 & 4

Quartz

Channels frontside etch to connect to vacuum source

*will require punch holes in PDMS layer, so need alignment marks on PDMS layer for this interface…same as uFluidic interconnect

4. Bond a second quartz wafer to the first quartz

wafer

BioMEMS: Fabrication

Quartz

Channels backside to connect to vacuum source

5. Fill with sacrificial layer—acrylate or

agaraose. Squeeqy off.

BioMEMS: Fabrication

Quartz

Sacrificial later

Channels backside to connect to vacuum source

6. Spin photoresist and expose area for second

sacrificial layer (loading posts and vacuum

channel are covered).

BioMEMS: Fabrication

Quartz

Sacrificial later

Photoresist

Channels backside to connect to vacuum source

7. Cast second sacrificial layer of acrylate

BioMEMS: Fabrication

Quartz

Sacrificial later

Photoresist

Channels backside to connect to vacuum source

8. Strip photoresist (should remove sacrificial

layer from alignment marks here) and plasma

surface area for PDMS

BioMEMS: Fabrication

Quartz

Sacrificial later

Photoresist

Channels backside to connect to vacuum source

9. Spin PDMS

BioMEMS: Fabrication

Quartz

Sacrificial later

Photoresist

PDMS

10. Spin photoresist

BioMEMS: Fabrication

Quartz

Sacrificial later

Photoresist

PDMS

10. Ebeam 20nm Ti (adhesion layer for gold and

traces for electrodes)

BioMEMS: Fabrication

Quartz

Sacrificial layer

Photoresist

PDMS

Titanium

11. Ebeam 150nm gold film (actual stretchable

traces—geometry)

BioMEMS: Fabrication

Quartz

Sacrificial layer

Photoresist

PDMS

Titanium

Gold

12. Strip and pattern photo resist for

BioMEMS: Fabrication

Quartz

Sacrificial layer

Photoresist

PDMS

Titanium

Gold

13. Strip and pattern photo resist for electrodes,

gauges, contact pads

BioMEMS: Fabrication

Quartz

Sacrificial layer

Photoresist

PDMS

Titanium

Gold

14. Ebeam gold electrodes

BioMEMS: Fabrication

Quartz

Sacrificial layer

Photoresist

PDMS

Titanium

Gold

Passivation layer

15. Strip photoresist and passivate

BioMEMS: Fabrication

Quartz

Sacrificial layer

Photoresist

PDMS

Titanium

Gold

Passivation layer

16. Dissolve sacrificial layer

BioMEMS: Fabrication

Quartz

Sacrificial layer

Photoresist

PDMS

Titanium

Gold

BioMEMS: Stretchable Electrodes

C. S. Park, M. Maghribi Characterizing the Material Properties of Polymer-Based Microelectrode Arrays for Retinal Prosthesis

Stimulation Electrodes

• Goal: To pattern gold electrodes within a flow

chamber for selectively stimulating hESCs– Electrodes 100μm x 5000μm (10 per well)– Interelectrode distance 1000μm– Contacts pads 2mm x 2mm (10 per well)

• Polished glass wafers 1 mm thick

BioMEMS: Strain gauge

• Need a strain gauge and a reference strain

gauge for every deformable area.

Strain gauge design

• Length (L = 1 mm)

• Trace width (w = 50 um)

• Distance between turns (p = 450 um)

• Number of turns (t = 3—38)

• Thickness of gold electrodes ~several hundred nm

Mechanical Strain

• Goal: To apply cyclic mechanical strain to hESC

precursor cells and observe differentiation

Next Steps

• QFD write-up for Beth

• Refine process cartoons

• Define geometry of membrane and electrodes

• ANSYS analysis of membrane and electrode deformation

• Define redundant layers—ie, cover up alignment marks w/ foil

• Creation of Ledit mask

• Selection of machines

• Training