Paper Based Partially Disposable MEMS Smart Bandage

Presented to the MEMS Fab to App class Spring 2013By:

Lisa Anders (Electrical Engineering) Vivek Jayabalan (Mechanical Engineering)Sai Ma (Biomedical Engineering)

Healthcare-Associated Infection Rates

4.5 HAI’s for

every 100 hospital admissions annually

1,737,125

cases of Infection

290,485Surgical site infection

COST OF $35.7-45.0 billion

70%

$25.0-31.5 billion

The goal is to create a "smart" bandage that would

incorporate an inexpensive modular sensing platform for

monitoring healing including temperature, pressure,

attachment, and bandage viability using an active

electronics design.

Objective

Amplifier A/D Converter

MicrocontrollerMSP430 Launchpad

TX

RX at hospital

Encoding

Sampling

Signals from sensors

ANT

Temperature

Pressure

Attachment

Moisture

Disposable Reusable

Temperature Pressure

AttachmentMoisture

Sensors intended to be incorporatedinfection symptom

monitor bandage attachment

Bandage viability, want dry environment to prevent infection

monitor person movement, self-care

TEMPERATURE

Skin Temperature & Infection

Temperature difference between periwound skin and an equivalent contralateral control site was found to be less than 2°C.If infection is present, the difference is greater than 2°C

On average, the day one skin temperature at the hottest spot on the affected limb was 34.4 degrees C, compared with 30.9 on the unaffected limb.

http://http://ovidsp.tx.ovid.com

increase2 °C

Temperature sensing theoryThermocouple:

Two dissimilar conductors in contactwhich produce a voltage when heatedConvert a temperature into electricity

Type T (copper – constantan) thermocoupleRange: -250-300°C)Sensitivity: 43 µV/°CSkin temp: 32-37°C

Unsheathed fine gage T type thermocouple(0.025mm to 0.81mm)

Choose 0.125 mm for prototype

http://hypertextbook.com/facts/2001/AbantyFarzana.shtml

Temperature calibration

15 20 25 30 35 40 45 50 55

-0.40

-0.20

0.00

0.20

0.40

0.60

0.80

1.00

1.20

f(x) = 0.0409785714285714 x − 1.01910714285714R² = 0.999851540443336

Chart Title

Temperature (C)Vo

ltag

e (m

V)

34 35 36 37 38 39 40 410.35

0.40

0.45

0.50

0.55

0.60

0.65

f(x) = 0.0390857142857 x − 0.9527142857143R² = 0.999724350139427

Chart Title

PRESSURE

Diaphragm Based Pressure Sensor

Bend due to differential pressure can be measured as a change in capacitance

Trivial Fabrication

PDMS

Modelling Pressure Sensors

𝑤 (𝑟 )= 𝑃 𝑎4

64 𝐷 [1−( 𝑟𝑎 )2]2

𝐷= 𝐸h3

12 (1−𝜈2 )

is the deflection at a particular radius is the pressure is the Radius of the plate and is its thickness is the Young’s modulus and is the Poisson's ratio

[1]

[2]

[2]

[1] Eaton, William P., and James H. Smith. "Micromachined pressure sensors: review and recent developments." Smart Materials and Structures 6.5 (1997): 530.[2] Young, Warren C., and Richard G. Budynas. Roark's formulas for stress and strain. Vol. 6. New York: McGraw-Hill, 2002.

Applied Pressure

Reference Pressure

Change in capacitance

𝐶=𝜖 𝐴

𝑑−𝑤 ′

is the Average Displacement

𝑤′=1𝑎∫0

𝑎𝑃 𝑎4

64𝐷 [1−( 𝑟𝑎 )2]2

𝑑𝑟

¿ 815

𝑃 𝑎4

64𝐷

Pressure v/s Δ Capacitance

𝑐 (𝑃 )=𝜖 𝐴

𝑑− 815

𝑃 𝑎4

64𝐷

-

Δ𝑐 (𝑃 )=𝜖 𝐴 8

15𝑃 𝑎4

64𝐷

𝑑− 815

𝑃 𝑎4

64𝐷

Δ𝑐 (𝑃 )≅𝜖 𝐴 8

15𝑃 𝑎4

64 𝐷𝑑

=ℂ1𝑃

Assuming that:

𝑃

Δ𝑐 (𝑃 )

Slope =

TESTING THE SENSORS

Testing

CAPACITIVE SENSOR

(TENMA 72-1025)

Results

No of BoltsWeight (in gm)

Average Change(in pF)

5 26.09 1.58677 33.23 1.6967

10 43.85 2.2717 68.73 3.3733

Conclusion

• Established that we can build simple paper based pressure sensors, that responds to pressure changes

CHALLENGES• Non-Linear• Sensitive Equipment• Elaborate Calibration

POTENTIAL• Inexpensive• Sensitive • Easy Fabrication• Other than Electronics,

requires no instruments

ATTACHMENT/MOISTURE

Skin resistance

• Nonhomogenous: connective tissue, blood vessels, nerve cells. • Resistance varies based on skin layer, thickness, skin hydration,

electrode size and geometry• At low frequencies current goes around cells

From Bioimpedance and Bioelectricity, 2008Skin image from http://klimadeodorant.com/skin1/images/custom/pages/skin.jpg

Switch approach for measuring attachment

0.5 1 1.5 2 2.5 3 3.50

5

10

15

20

25

30

35

40

45

50

Position versus Resistance

Across pinkie finger Mohm Across pointer finger MohmAcross arm Mohm

Distance between electrodes (cm)

Resis

tanc

e (M

ohm

s)

At 10 kHz

From Bioimpedance and Bioelectricity, 2008

Decouple with a hydrophobic layer

Attachment Moisture/Bandage Viability

Paper/ Bandage

Wax

Electrodes

Gauze

Electrodes

Theoretical fluid values:

Resistance of paper doped with fluid

Blood 0.7 S/m-> 0.49 ohmsConductivity of DI and tap water from: http://www.mbhes.com/conductivity_measurement.htm

DI Tap PBS0

0.5

1

1.5

2

2.5

3

3.5

2.86 2.45 0.074

Liquid type

Resis

tanc

e (M

ohm

s)

From Bioimpedance and Bioelectricity, 2008

70 kohms 1.4 ohms 0.05 ohms

INCORPORATION TEMP AND ATTACHMENT

Testing temperature of 3 people

Lower arm Middle arm Upper arm2526272829303132333435

Temperature vs. Position

Tem

pera

ture

/ °C

Lower arm Middle arm Upper arm25

26

27

28

29

30

31

32

33

34

Lisa Sai Vivek

Tem

pera

ture

/ °C

Temperature measurementDirectly on skin

Temperature measurementThin gauze barrier

Thin gauze barrier seems decreases the measured temperature a bit

Individual variation supports “switch” approach

inside w

rist

forearm

inside elbow

elbowbice

ptri

cep

0.01

0.1

1

10

100

Day 2

Lisa Sai Vivek

inside w

rist

forearm

inside elbow

elbowbice

ptri

cep

0.01

0.1

1

10

100

Day 1

Resi

stan

ce (M

ohm

s)

90 Mohms

.7 Mohms

Price can be reduced through a bulk fabrication process

• Thermocouple: $ 3.600• 1 piece of filter paper: $.0649• 9 cm conductive tape: $1.032• Gauze: $0.442• Wax: $0.19

• Total: $5.3289

Screen Printing

Screen Printing

Screen Printing

Screen Printing

Future Work

• Microcontroller and ANT incorporation– MSP430- ultra low power– ANT- ultra low power, +95dB,

• Unobtrusive and discreet• Screen printed electrodes• Further safety studies• More sensors!– Pressure sensor– pH Sensor

Ti.com

Conclusion

• Successfully designed, built, and tested a Smart Bandage prototype

• Interdisciplinary project between ECE, ME, and BMES• Shows promise to improve healthcare conditions and

patient recovery

Images from: http://coachmunro.com/wp-content/uploads/2011/05/band_aid-2830.jpg,http://rashaba.com/net/file/pic/photo/03afdbd66e7929b125f8597834fa83a4_500.png

DEMONSTRATION

Thanks for listening!

• Special thanks to:

• Dr. Agah• Diana Nakkide• ICTAS building• Kris Dixon• Elizabeth Elvington

Attachment/Bandage Viability Measurements

From Agilent 34401A manual

Testing temperature of 3 people over 2 days

Lower arm Middle arm Upper arm2526272829303132333435

Temperature vs. Position

Tem

pera

ture

/ °C

Lower arm Middle arm Upper arm25

26

27

28

29

30

31

32

33

34

Lisa Sai Vivek

Tem

pera

ture

/ °C

Temperature measurementDirectly on skin

Temperature measurementThin gauze barrier

Thin gauze barrier seems decreases the measured temperature a bit

Individual variation supports “switch” approach

inside w

rist

forearm

inside elbow

elbowbice

ptri

cep

0.01

0.1

1

10

100

Day 2

Lisa Sai Vivek

inside w

rist

forearm

inside elbow

elbowbice

ptri

cep

0.01

0.1

1

10

100

Day 1

Resi

stan

ce (M

ohm

s)

90 Mohms

.7 Mohms