Biomechanics Design Lab Presentation FINAL (2)

Click here to load reader

  • date post

  • Category


  • view

  • download


Embed Size (px)



Transcript of Biomechanics Design Lab Presentation FINAL (2)

Biomechanics Design Lab: Viscoelasticity of Chicken Cartilage

Biomechanics Design Lab: Viscoelasticity of Chicken Femoral CartilageGroup 7

Priyanka Parajuli, Hemali Patel, Catherine Porter, Shri Rajan, Linh Phan

Introduction: Viscoelasticity ViscosityFluid PropertiesGradual Deformation:Time-dependentEquation: = ()ElasticitySolid Properties Instantaneous Deformation:Time-independentEquation: =(, ) Articular CartilageFunction:Reduces friction between bones at jointCovers the diarthrodial jointsAlleviates compressive loads at jointComposition:60-85% water by weight15-22% type II collagen by weightVarious electrolytes (Na+, Cl-, Ca++)Proteoglycans and chondrocytes

Conclusion: Articular cartilage is a viscoelastic material3

introduction: Articular Cartilage PropertiesInhomogeneousMultiphasic MaterialAnisotropicResistant to Compression and Physical PropertiesInhomogeneousAnisotropicMultiphasic MaterialResistant to compression

4Introduction: Maxwell Model

Spring and dashpot connected in series Fluid viscoelastic model Equation:

Introduction: Kelvin-Voigt Model

Spring and dashpot connected in parallel Solid viscoelastic model Equation:

Under solid viscoelastic behavior talk about how this is due to the deformation being restricted by the response of the spring to the applied force6Introduction: Standard Solid Model

Combine Kelvin-Voigt solid model and Maxwell fluid model to derive complex viscoelastic model Equation:

Only accounts for a single relaxation time7

introduction: Indentation Tests Characterize mechanical properties of cartilage outside the body Stress-Relaxation Test Indent material and maintain constant strain Observe stress response of material Viscoelastic material responds with initial high stress and then decreases over time Load-to-Failure Test Constantly increasing stress Last point on curve is rupture, failure strength Viscoelastic materials typically have same ultimate and failure strength

Ozkaya et al., Fundamentals of biomechanics: Equilibrium, motion, and deformation (3rd ed.)8Motivation:Osteoarthritis, sports injuries, etc. Current replacement grafts and surgical reconstructions often result in complications and instability that worsen current conditions. Dynamic environment of the human body requires physical characterization of articular cartilage in addition to biological characterization.Mathematical modeling provides unique insight for further treatment of cartilaginous injuries. Help understand diseases and injuries

If you understand the mechanical properties of cartilage then will be able to create more compatible synthetic materials9Objective:To assess the mechanical and viscoelastic properties of chicken femoral cartilage and model its viscoelastic behavior as a mathematical equation. 10Materials Methods:

1 chicken femur (from Publix)Large-grit sandpaperForcepsIris Scissors GlovesPaper towelsCement mixing bowlAluminum cylinderBone cement (Surgical Simplex, Stryker)COE Tray Plastic Self-Curing Liquid (Patterson Dental)Plumbers puttySaline solutionGauze pads

2.15mm Indenter TipNeedle to record cartilage depthMTS 858 MiniBionix (15,000 N load cell)

11Methods: Preparation of the SampleClean chicken femur cartilage (removing excess tissue)Remove periosteal tissue around bone shaft with sandpaperPosition distal side of chicken femur vertically in the aluminum cylinder using plumber puttyMix methyl methacrylate bone cement with the Tray Plastic Self-Curing Liquid at a 1:1 ratioPour cement in cylinder and allow it to solidify for approximately 10 minutesBe sure to keep cartilage moist with saline solution and gauze during this process

12Methods: Stress-Relaxation Test

*Before load-to-failureClamp cartilage perpendicular to indenterMeasure initial thickness (needle and caliper)Attach 15kN load cell and scale back to 1.5kN total loadIndent to 1mmHold for 1 minuteMeasure indented thickness (needle and caliper)Remove loadLet relax for 10 minMeasure final thickness (to ensure back to normal for load-to-failure test)*Sample rate: 100Hz

13Methods: Load-To-Failure Test

Data Analysis: Stress-Relaxation Test

15Results: Stress-Relaxation Test

Data Analysis: Wiechert Model

Wiechert Model:Relaxation Modulus: being received from the experiment will be in stress vs timeThe wiechert model will be rearranged to also be stress vs time17Data Analysis: Wiechert ModelUse Matrix to Solve E coefficients:System of Equations:

Explain advantages of this model18

Results: Stress-relaxation test Modeled

Results: Wiechert Model applied to all Groups

R = 0R = 0.939R = 0R = 0

Data Analysis: load-to-failure test

MATLAB was used to calculate the stresses and strain Plot vs.

Results: load-to-failure test

Group NumberUltimate Stress (Pa)Group 61.55E+07Group 72.24E+07Group 81.96E+07Group 91.40E+07

Results: group Elastic ModuliGroup NumberElastic Moduli (Pa)Group 62.42E+04Group 78.37E+04Group 82.05E+04Group 93.92E+04DiscussionDifference between Load-to-Failure GraphsOur sample exhibited higher mechanical properties:High ultimate strength (strong)High elastic modulus (stiff)Other samples exhibited lower mechanical properties:Lower ultimate strengthsLow elastic moduli (ductile)Possible Sources of Variance:Chicken ageCartilage moistureChicken genderChicken physical activity and healthDiscussion (Cont.)Wiechert Model Best Fit Line

9th Degree Polynomial Best Fit Line (MATLAB Curve Fitting Tool)

Correlation Coefficient = 0.987Correlation Coefficient = 0.939Discussion (Cont.)Statistical Analysis Mechanical PropertiesAverage (Pa)Standard Deviation (Pa)Failure Stress1.79E+07 3.85E+06Elastic Modulus4.19E+04 2.90E+04Possible Sources of Error: Thickness measurement Machine error Bone alignment Overlap of stress- relaxation and load-to-failure test locations

References:Ahearne, M., Siamantouras, E., Yang, Y., & Liu, K.-K. (2009). Mechanical characterization of biomimetic membranes by micro-shaft poking. Journal of the Royal Society Interface, 6(34), 471478., C., Lakez, S. P., Small, M. S. and Weiss, J. A. (2005), Viscoelastic properties of the human medial collateral ligament under longitudinal, transverse and shear loading. J. Orthop. Res., 23: 6776. doi: 10.1016/j.orthres.2004.06.002Kaufman, J. D., Miller, G. J., Morgan, E. F., & Klapperich, C. M. (2008). Time-dependent mechanical characterization of poly(2-hydroxyethyl methacrylate) hydrogels using nanoindentation and unconfined compression. Journal of Materials Research, 23(5), 14721481., C., Phan, A. -V., Pearsall, A. W., & Madanagopal, S. (2006). Viscoelastic studies of human subscapularis tendon: Relaxation test and a Wiechert model. Computer Methods and Programs in Biomedicine, 83(1), 29-33.Ozkaya, N., Nordin, M., Goldsheyder, D., & Leger, D. (2012). Fundamentals of biomechanics: Equilibrium, motion, and deformation (3rd ed.). New York: Springer.