Team 3

Brandon Bachert1, Joseph Erthal1, Tony John1& Kristen Smith1

 Advisor: Dr. Wan Y. Shih1, Dr. Wei-Heng Shih2,

 

1 Biomedical Engineering, Drexel University

2 Materials Science and Engineering, Drexel University

Simultaneous Determination of Elastic Modulus and Thickness of Skin with

Piezoelectric Fingers

Problem Statement

Effects of Aging:

$5.8 billion spent annually on anti-aging products as of 2008 Quantitative measurements

– Provide customers with a fair and unbiased assessment of their effectiveness (Global Industry Analysts, 2009)

Young’s Modulus(kPa)

Thickness(mm)

Under 30 years 420 0.5-1.1Over 30 years 850 Decreases by 0.2 - 0.3

% Change 15% 34%

Introduction to Skin & its Properties

(http://www.clarian.org/ADAM/doc/graphics/images/en/8912.jpg)

Skin

Fat

Young's Modulus of skin 420 kPa-850 kPaThickness of skin 0.5 mm–1.1 mmYoung's Modulus of fat ~10 kPa

Current Methods

• DermCup 2020® only measures skin thickness• Echorheometer only measures elastic modulus• Tensometer only measures elastic modulus• J&J Photography technique qualitative test

Criteria Device must measure:

Device must see changes produced by supplements such as Dermavite ™ (Thom 2005)

Young's Modulus accuracy 7.5%Thickness accuracy 17%

SkinYoung's Modulus 420 kPa-850 kPaThickness of skin 0.5 mm–1.1 mmFat Young's Modulus ~10 kPa

Constraints

Area of Advisor expertise – Self Exciting, Self Sesning, Piezoelectric Cantilevers

Available equipment – Voltage source – Oscilloscope– Laser Displacement Meter

Must be designed for eventual use on humans

PZTSteel

Testing Criteria - Phantom

Top “Skin” LayerEskin = 420-850 kPa

Bottom “Fat” LayerEfat = 3-10 kPa

0.5-1.1 mm

>1.0 mm (Hendriks)

Wire Probe

Cantilever

OUR SOLUTION

Cantilever Design (Side-view)

Driving PZT

Sensing PZTStainless Steel

Wire ProbeClamp

Clamp

20 mm

12 mm

127 microns

127 microns

50 microns

Sample

Probe Size(Yegingil 2007)

Probe Diameter

Depth Sensitivity

2 x Diameter(mm)

Cantilever A 0.60 1.12Cantilever B 0.71 1.42Cantilever C 0.91 1.83

Skin

Fat

Probing

Depth

= 2*D

Diameter = D

2.1 mm

1 mm

THEORY

Theory (Springs in Series)

DepthModulusElastick

21

111kkkeff

Layer 1

Layer 2

(Yegingil et al. 2007)

Known and Unknown Values

EA

Eskin

Efat

Tskin

DA-Tskin

DA

EB

Eskin

Efat

Tskin

DB-Tskin

DB

EC

Eskin

Efat

Tskin

DC-Tskin

DC

Calculations to determine Elastic Modulus of Sample

)T-(DE

1

TE

1

DE

1 :A CantileverFor skinA

fatskin

skinA

A

)T-(DE

1

TE

1

DE

1 :B CantileverFor skinB

fatskin

skinB

B

)T-(DE

1

TE

1

DE

1 :C CantileverFor skinC

fatskin

skinC

C

Max Cantilever Spring ConstantTo achieve 10% strain for patient comfort and meet our constraint to design for use on humans.

Estimating Cantilever Dimensions

Length (mm)

Estimated Driving PZT

Sensing PZT

Desired Width (mm)

Desired Spring Constant (N/m)

E from Yegingil Cantilevers (Pa)

20 12 2 100 5.7 x 107

Used published cantilever dimensions and k values (Yegingil 2007) to estimate E of cantilevers.

Prototype (1 of 3 cantilevers pictured)

Measuring Spring Constant (k)

Mass (g)Force = mg (N x 10-04)

Weight 1 0.0323 3.17

Weight 2 0.0828 8.12

Weight 3 0.1395 13.7

Weight 4 0.1931 18.9

Weight 5 0.2703 26.5

Spring Constant Results

Measured Cantilever Spring ConstantsSpring Constant (k)

3 TrialsStd Dev of 3 Trials

(+/-)

Cantilever A 107 N/m 0.8%

Cantilever B 115 N/m 2.9%

Cantilever C 101 N/m 0.4%

Testing Criteria - Phantom Design

Top “Skin” LayerMaterial: Versaflex Rubber

Eskin = about 500 kPa

Bottom “Fat” LayerMaterial: Lab Gelatin

Efat = 3-10 kPa

1.0 mm

>1.0 mm (Hendriks)

Wire Probe

Cantilever

Cutting Versaflex1mm Thickness with Diamond Saw

Results1.03 ± 0.08mm

Versaflex Sample

Diamond Saw Blade

Glass Slide

Versaflex Rubber

GelatinPetri Dish

Phantom

Versaflex 1(mm)

Petri Dish

Gelatin (1mm)

Experimental Setup

DC Power SupplyO-scope

Applied Voltage

Induced Voltage

Laser Displacement

Meter

0.0000 mm

Experimental Setup

Laser Displacement Meter

Sample

Induced Voltage

Ground Applied Voltage

Cantilever

Indentation Test

Sample Data One Cantilever- Versaflex

Determining Effective Modulus

V(induced w/sample) (Volts)

E eff

)()1()( 0,2

21 2

1

ininA

ineff

VVKvX

whereVXE

A= circular contact areaK= Cantilever spring constantv= Poisson’s Ratio=0.5(Yegingil et al. 2007)

Monitoring Displacement to Validate Induced Voltage Readings

Conclusion: Induced voltage does not reflect displacement. Displacement will be used to make measurements.

Calculation of Young’s Modulus Using Displacement

Results: E of Gelatin = 5.6 kPaMeets Criteria Measuring E in range of Fat

Gelatin (5mm)

Petri Dish

Results: E of Versaflex = 354 kPaDoes Not Meet Criteria for Measuring E in Range of Skin

Versaflex (5mm)

Petri Dish

Results: E of Gelatin on Versaflex = 9.6 kPaInverse Configuration of Skin) - 20% Error

Versaflex (5mm)

Petri Dish

Gelatin (1mm)

Versaflex Rubber

GelatinPetri Dish

Testing the Phantom

Phantom Trial 1

Phantom Trial 2

Expected/ Theoretical

Cantilever A EA (kPa) 61 190 81

Cantilever B EB (kPa) 160 410 32

Cantilever C EC (kPa) 210 330 21

Results: E of Skin Phantom

Testing Effect of Petri Dish

Versaflex on Plastic (>500kPa Expected)

Versaflex on 5mm Gelatin

Expected/ Theoretical

Cantilever A EA (kPa)

87 130 81Cantilever B EB

(kPa)25 64 32

Cantilever C EC (kPa)

40 120 21

Versaflex (1mm)

Petri Dish

Gelatin (5mm)

Versaflex (1mm)

Petri Dish

Testing effect of Cantilever Placement

“0” Position

“-100 microns

”

“-200 microns

”

“-300 microns

”

“-400 microns

”

“-500 microns

”

“-300 microns” trial 2

“-400 microns” trial 2

Cantilever A EA (kPa)

19 23 13 1200 1200 --- 1200 ---

Cantilever B EB (kPa)

230 470 650 770 1000 1000 --- 1000

Cantilever C EC (kPa)

290 400 560 610 800 800 --- 800

Conclusions

Wire cutter did not cut flat surface on wire probes.– Assumed area is not correct. Probe does not have good

contact with sample. As the probe moves into the sample, full elastic

resistance from sample is realized.

Conclusions

Little/No Resistance From SampleSmall Difference between Slope with

and without Sample

Large Resistance From SampleBig Difference between Slope with

and without Sample

Conclusions

Meeting Criteria– Cantilevers are capable of measuring

E in the range of skin and fat– Accuracy must be improved by

making flat probes

Suggestions

Use wire saw to cut the probes to ensure flat, even surface

Alternative: Use probes as is and…– Formulate testing procedure to ensure consistent

probe contact area is achieved during testing– Determine fitting constant experimentally to

determine actual contact area– Use fitting constant when calculating E– Use E equation for cone geometry

Budget

Competitive MatrixPiezoelectric Cantilever DermCup

2020®

Echo-rheometer

J&J Photo-technique

Tensometer

Low Price Yes No No No NoSkin Layer differentiation

Yes No No No No

Quantitatively measures skin thickness

Yes Yes No No No

Quantitatively Measures Elastic Modulus

Yes No Yes No Yes

Small Portable Size

Yes No No Yes No

Year 1 Year 2 Year 3 Year 4 Year 5 Year 6

Development Stage Cantilever Design

Cantilever Prototyping/T

esting

Animal Studies

Clinical Protyping

Clinical Testing

FDA Approval

Laboratory Prototype Created-IP X XClinical Prototype Created-IP XPatent(s) Applied For X XPatents Awarded X XInstit. Tech. Transfer License X XReceive FDA Approval XNew Health Care Business Created X

Estimated R & D CostsPatent Fees 10,000$ 10,000$ 10,000$ 10,000$ 10,000$ 10,000$ Animal Research -$ -$ 150,000$ 50,000$ 50,000$ 25,000$ Clinical Testing -$ -$ -$ 500,000$ 500,000$ 50,000$ FDA Compliance Fees -$ -$ -$ -$ -$ 30,000$

Opearting CostsOffice / Research Workspace 42,000$ 42,000$ 42,000$ 42,000$ 42,000$ 42,000$ Research Operating Costs 20,000$ 20,000$ 20,000$ 20,000$ 20,000$ 20,000$ Research Supplies 200$ 200$ 200$ 200$ 200$ 200$ Employee Wages 325,000$ 375,000$ 375,000$ 400,000$ 400,000$ 400,000$ Office Expenses 40,000$ 40,000$ 40,000$ 40,000$ 40,000$ 40,000$ Website Maintainance -$ -$ 1,000$ 1,000$ 2,000$ 3,000$ Advertising -$ -$ 25,000$ 25,000$ 40,000$ 40,000$ Legal Services 200,000$ 200,000$ 200,000$ 200,000$ 200,000$ 200,000$ Total Operating Costs 637,200$ 687,200$ 863,200$ 1,288,200$ 1,304,200$ 860,200$ Miscellaneous (10% of O.C) 63,720$ 68,720$ 86,320$ 128,820$ 130,420$ 86,020$ Total Expenditures 700,920$ 755,920$ 949,520$ 1,417,020$ 1,434,620$ 946,220$ Profit / Loss -$700,920 -$755,920 -$949,520 -$1,417,020 -$1,434,620 -$946,220

Cumulative Cash Flow -$700,920 -$1,456,840 -$2,406,360 -$3,823,380 -$5,258,000 -$6,204,220

Research and Development

Product Launch

Economic Analysis

Intellectual Property

•Utility Patent of the three layer design:

Driving PZT

Sensing PZTStainless Steel

•No current Technologies similar to our device

•Has a novel, functional, and unique design

Regulatory & Environmental

Approval by FDA’s Center for Devices and

Radiologic Health

Effect on the cosmetic and pharmaceutical

industry

Disposal of device - contains lead

Future Applications

Monitoring– UV Damage

Known to effect skin E and thicknessQuantitative effects are currently unclear

– Progression of a variety skin diseasesPsoriasis, Cancer

ScheduleKey

Completed

In Progress

To be completed

Fall 2008Task Wk1 Wk2 Wk3 Wk4 Wk5 Wk6 Wk7 Wk8 Wk9 Wk10 Wk11 BREAKWork on proposed biorhythm device

Research (ongoing) - PZT properties, applications, cantilever properties, skin thickness & elasticity, etc.

Brainstorm, develop and revise Problem Statement, Constraints, and Criteria

Discuss feasibility and alternative solutions with advisor

Online lab safety - Acquire key from Dr. Knight

Calculate theoretical values of PZT and Stainless steel to achieve theoretical K value in the range we have specified

Practice work with cantilevers and materials (cutting, gluing, and sanding materials as they are fragile and crack easily)

Build several cantilever (cut materials to proper dimensions, glue layers together, sand cantilever)

Order clamps and probes from Machine Shop

Check impedance of cantilevers to be within a certain range

ScheduleWinter 2009

Task Wk1 Wk2 Wk3 Wk4 Wk5 Wk6 Wk7 Wk8 Wk9 Wk10

Meet with advisor                    

Clarify calculations                    

Discuss limitations discovered this far                    

Develop Probes (Probes from machine shop were wrong size)                    

Continue building cantilevers                    

Check impedance of cantilevers                    

Attach probes to cantilevers                    

Insert cantilever into clamp                    

Solder wires to cantilever                    

Test K value using method involving resistance to force from stainless steel cantilever                    

Test K value using weights method                    

Build/Develop skin model                    

Initial testing of prototype using skin model                    

Make adjustments on final cantilever prototype                    

Spring 2009

Task Wk1 Wk2 Wk3 Wk4 Wk5 Wk6 Wk7 Wk8 Wk9 Wk10

Final cantilever prototype testing on gelatin and skin model                    

Analyze results from LabView Testing                   `

Thank You Dr. Wan Shih, Dr. Wei-Heng Shih, Josa Hanzlik, Xiatong

Gao, Dr. Karen Moxon, Dr. Elisabeth Papazaglou and Dr. Ken

Barbee for all of your help.

Acknowledgements

QUESTIONS???

•Thom, E. "A Randomized, Double-Blind, Placebo-Controlled Study on the Clinical Efficacy of Oral Treatment with DermaVite on Ageing Symptoms of the Skin." J Int Med Res 33.3 (2005): 267-72.•Escoffier, C., de Rigal, J., Rochefort, A., Vasselet, R., Leveque, J. L., & Agache, P. G. (1989). Age-related mechanical properties of human skin: An in vivo study. The Journal of Investigative Dermatology, 93(3), 353-357. •Agache, P. G., Monneur, C., Leveque, J. L., & De Rigal, J. (1980). Mechanical properties and young's modulus of human skin in vivo. Archives of Dermatological Research, 269(3), 221-232. •Anti-Aging Products. Rep. Jan. & feb. 2009. Global Indistry Analysts, Inc. <http://www.worldhealth.net/news/global_anti-aging_products_market_to_rea>.•Merola, Kenneth, Nikiforos Kollias, Jeffrey Pote, and Gregory Payonk. Method of promoting skin care products. Johnson & Johnson Consumer Companies, Inc., assignee. Patent 6922523. July 26, 2005.•Hendriks, F.M, Brokken, D., Oomens, C.W.J., Baaijens, F.P.T., and Horsten, J.B.A.M. “Mechanical Properties of Different Layers of Human Skin.” Dept.of Materials Technology, Eindhoben Univ.of Technology, PO Box 513: 5600.

References