Post on 14-Dec-2015
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
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
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
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