1
CTEA Symposium
Pulin Wang, Ph.D., M.S.Tech.Comm.
Stretch Med, Inc., A spin-off from the University of Texas at Austin
Applications of Skin-Mounted Sensors
Mobile Health
Human-Machine Interface
Bricks-On-Strips Chips-On-Tapes
When Bio Meets Electronics
Skin vs. Silicon
ESi = 130 x 109 Pa ESkin = 130 x 103 Pa
Credit: Intel Credit: ICTGraphicsLab @ USC
Flexible Electronics
Sony, 2007
PolyIC, 2006
Rogers, UIUC, 2008 Lumalive, Philips, 2010
Someya, U of Tokyo, 2005 PowerFilm, 2004
Stretchable Electronics
Science 333, 838 (2011). Nature Materials 10, 316 (2011).
Epidermal Electronics Balloon Catheter Heart “Sock”
Nature Comm. 5, 3329 (2014).
PNAS 108, 1788 (2010).
Tunable Electronic Eyeball
Nature Materials 9, 929 (2010).
Conformal LED Stretchable Transistors
Science 321, 1468 (2008).
e = 100%
3cm
1.04%
0.01%
0.61%
Experiment Numerical Simulation
Stretchable Structure - Serpentine
3cm e = 40%
0.28%
-0.02%
0.13%
e = 30%
3cm
0.36%
0.00%
0.18%
Microfabrication of Stretchable Electronics
Rigid wafer
PI precursor
Flexible
substrate
SOI
PDMS Stamp
Doped Si nanomembrane PI
Au
Si PI
Stretchability & Cycleability
0 50 100 150 2000
2
4
6AlAu RTDEPCoil
R/R
0
Applied Strain (%)
5 mm 0% 30% 90% 199%
0% 30% 90%
30% 90%
115%
68%
2
mm
a
b 0%
c
Coil
EP
RTD 1 10 100 1000 10000
-2
0
2
4
6
8e= 20%
e= 30%
R
/R0 (
%)
Number of Cycles
Apps
Amplifie
r
LED Solar Cell
T Sensor e
Gauge
L Coil
Multi-Functionality
antenna LED
wireless power coil RF coil
temp. sensor strain gauge
RF diode ECG/EMG sensor
0.5mm
Kim*, Lu*, Ma* (*equal contribution), Rogers, et al., Science 333, 838, (2011).
Mounting and Removal of Epidermal Electronics
Epidermal Electronics on A Skin Replica
Yeo, Rogers, et al, Advanced Materials 25, 2773–2778 (2013).
Why Is Conformability Important?
Fully-Conformal (FC)
Non-Conformal (NC)
Partially conformal (PC)
Jeong, et. al., Adv. Mater. 2013, 25, 6839
Conformable contact ensures
• Low interface impedance
higher signal to noise ratio
• Less relative motion less motion
artifacts
• Better heat or mass transfer
Skin
Conventional
Jeong, et. al., Adv. Healthcare Mater. 2014, 3, 642–
648
Epidermal
Skin
Skin
Recent Development in Epidermal Electronics
Kim*, Lu*, Ma* (*equal contribution), Rogers, et al., Science 333, 838, (2011).
Memory & drug delivery
Son et al, Nat. Nanotech. 9, 397 (2014).
Skin temp. mapping
Webb et al, Nat. Mater. 12, 938 (2013).
Jeong et al, Adv. Mater. 25, 6839 (2013).
HMI
Xu et al, Science 344, 70 (2014).
Wireless ECG sensor
Dagdeviren et al, Nat. Mater. 14, 728 (2015).
Skin stiffness
Yeo et al, Adv. Mater. 25, 2773 (2013).
Respiratory rate sensor
Microfabrication of Stretchable Electronics
Rigid wafer
PI precursor
Flexible
substrate
SOI
PDMS Stamp
Doped Si nanomembrane PI
Au
Si PI
Cleanroom, time consuming, low yield, high cost, wafer-based
Cost and Time Effective “Cut-and-Paste” Method
a. APT_Cutting Mat b. Cutting c. Peeling from
mat
d. Removal f. ESS
Au_PET Thermal Release Tape (TRT) Cutting Mat
Deactivated TRT Target Substrate
e. Printing
Yang, et al, Adv. Mater. DOI: 10.1002/adma.201502386 (2015).
Subtractive, dry, desktop, portable, green & roll-to-roll compatible
Multiparametric Epidermal Sensor System
Planar FS coil
RTD
EP sensor
Hydration sensor
20 mm Capacitor
Disposable Epidermal Sensor System (ESS)
Yang, et al, Adv. Mater. DOI: 10.1002/adma.201502386 (2015).
0
10
20
30
Resis
tan
ce
RTD (100)
Before
After
Al Coil ()
Different Types of Substrates
On KRST
On tattoo paper
On Tegaderm
a b c d
e f g h
i j k l
Yang, et al, Adv. Mater. DOI: 10.1002/adma.201502386 (2015).
Multifunctional Epidermal Sensor System (ESS)
ECG
Heart
Muscl
e
0 1 2 3 4-0.8
-0.4
0.0
0.4
0.8 ESS
Conventional
Vo
lta
ge
(m
V)
Time (s)
0 1 2 3 4 5 6-0.3
-0.2
-0.1
0.0
0.1
0.2
0.3
Time (s)
Vo
ltag
e (
mV
)
Force 44N
Force 14NEMG
Skin Hydration
0 1 2 3 428.5
29.0
29.5
30.0
30.5
Thermal couple
RTD on ESS
Tem
pe
ratu
re (
oC
)
Time(min)
Skin Temp.
Skin temperature
0 4 8 12 1660
70
80
90
100
110
Time (min)
Hyd
r. L
evel (a
.u.)
H Sensor on ESS
Corneometer
Calm Espresso
0 5 10 15 20-1.0
-0.5
0.0
0.5
1.0
R
/R (
%)
Time (s)Respiration
Respiratory rate
0123
Conventional
ESS
× 10- 4
0 20 40 60 80 1000369
× 10- 12
Frequency (Hz)
Eye open
Eye closed
EEG
a rhythm
FFT
(mV
/Hz)
Brain
Yang, et al, Adv. Mater. DOI: 10.1002/adma.201502386 (2015).
Synchronous Multimodal Measurements
Chen et al, to be submitted (2016).
Core T
Skin T
Skin T
Skin H Heart Rate
ECG by gel electrodes
ECG by EES
Exp. 1 - EMG Sensor on Muscles
Quantification of Muscle Fatigue
EMG for Quantification of Muscle Fatigue &
Recovery Epidermal electrodes Conventional gel electrodes
EM
G (
mV
)
EM
G (
mV
)
2 122 124 0 2 122 124 0 2 122 124
Time (Min)
2 122 124 0 2 122 124 0 2 122 124
Time (Min)
A
B
C
D
E
F
G
H
I
J
Fa
tig
ue
In
de
x
MF (
Hz)
EM
G (
mV
) R
aw
EM
G
(mV
) H
GF (
N)
MF (
Hz)
EM
G (
mV
) R
aw
EM
G
(mV
) H
GF (
N)
Fa
tig
ue
In
de
x
EMG Sensor
Hand
Dynamometer
Exp. 2 - Soft Strain Gauges Measuring Skin Deformation
0 5 10 15 20-1.0
-0.5
0.0
0.5
1.0
R
/R (
%)
Time (s)Respiration
Respiratory rate
Respiratory Rate Sensor
Wireless Tremor Detection and Auto-Warning
Exp. 3 - Skin Mounted Heater
Perioperative Warming
Expedited Transdermal Drug Delivery
Son et al, Nature Nanotechnology 9, 397–404 (2014).
Thermal joint therapy
Epidermal Programmable Heater
Epidermal heater integrated
with T sensor allowed
feedback control
Exp. 4 - Electrotactile Stimulator
10 mm
hand mold
Ying, Bonifas, Lu et al., Nanotech 23, 344004 (2012).
10 mm
finger-
tube
flattened finger-tube
PDMS stamp
gla
ss
device
10 mm
electrotactile stimulator
10 mm
So
urc
e V
olt
ag
e (V
)
Sensation
No
Sensation
28
36
32
0 40 80 120
40
Frequency (Hz)
Exp. 5 Multifunctional Epidermal Glucose
Sensor
B D
A C
Prof. Dae-Hyeong
Kim @ Seoul National
Univ.
pH Correction Is Important
Sensor Is Validated against Gold
Standard
On-Demand Metformin Release
• Multifunctional: sensing, stimulation, therapeutics
• Address challenges in wireless communication and
power supply
• Epidermal sensor is a platform technology
• Initial product offering – ECG patch
What’s Next?
Thank you