Polymer Characterization for Soft-Tissue Fixation Devices By Jonathan Schlotthauer University of Wyoming Mechanical Engineering Department Advisors: Dr. Frick, Amy DiRienzo

Overview Soft Tissue Fixation Devices Porous Biomaterials Mechanical Behavior of Porous Structures Objectives Procedure Experimental Results Conclusions and Future Work

Soft Tissue Fixation Devices Uses in the medical field: Knee ligament reconstruction Rotator cuff reinforcement Bicep tenodesis Anterior cruciate ligament (ACL) Concept: Reattachment of tissue or ligament to the bone after injury Must provide sufficient strength Must not interfere with soft tissue healing Must be biocompatible for long-term use Sources: (a-b)

Materials Used for Soft-Tissue Fixation Devices Metallic Devices (a, c) : Imaging Technique Incompatibilities Strength and Stiffness Relativity To Trabecular Bone (Stress Shielding) Biodegradable Polymers: Substantial Degrading of Mechanical Properties Source: (d)

Porous Biomaterials Osteointegration: Interface Between Implant and Bone Cells Penetrate Porous Structure Trabecular Bone (e-f) : Ideal Pore Size Range From μm Pores Allow Healthy Cellular Function

Mechanical Theory of Porous Structures Stress-Strain Behavior of Porous Materials Modulus of Elasticity (Tension): Primarily a Function of: Porosity Strength (Yield): Primarily a Function of: Pore Size Rule of Mixtures: Provides Theoretical Material Properties Source: (g)

Theoretical Porous Effects On Modulus of Elasticity

SRP Background Self-Reinforced Polyphenylene [SRP]: Reinforced molecular backbone Directly linked phenyl units Benefits of SRP: High Modulus of Elasticity High Strength Chemically Inert Biocompatible Source: (h)

SRP vs. Various Polymers

Theoretical Modulus of Elasticity

Research Goals and Expectations Create Manufacturing Process: Sample Production Sample Testing Examine Damage Progression Characterize Porous SRP: Porosity Ranges of 50-80% Varying Pore Sizes Small: μm Large: 500+ μm

Systematic Procedure Use of Various Salts Uncontrolled Pore Sizes Controlled Porosity Create Hot-Press Samples Create Tensile Samples Salt Leeching Process Testing Porous Tensile Samples

Systematic Procedure Attempted Various Parameters for Hot-Press Samples: Temperature:200 ˚C 230 ˚C 240 ˚C 250 ˚C Pressure:300 psia 450 psia 600 psia Time:10 mins. 30 mins. 60 mins. 90 mins. 120 mins.

Testing Procedure Specify Tensile Shape: ASTM D IMP Machine Setup: MTS 858 Mini Bionix II Load Frame MTS LX 500 Extensometer Testing Conditions: Ramp Rate: 0.01 mm/s Room Temperature

Porous Damage Progression 75% Porous Tensile SRP Sample SEM Images (a): Sample Strained to 1.3% (b ): Sample Strained to 4.2% (c): Sample Strained to fracture (b) (c)

Porous Sample Procedure Characterize Pore Size: Sifting salt for small and large porous sizes Create Varying Porous SRP Tensile Samples: Mixing salt and SRP: Volumetric Ratio based on density Flat Plate Samples: Temperature:250 ˚C Pressure:600 psia Time:60-90 min. Tensile Strip Samples: Dimensions Replicate ASTM Mold Leeching: Soak in distilled water Time:2 days

Results for Porous SRP Samples

Results for Porous SRP Testing

Conclusion Optimum Osteointegration Specific Range of Porosity Specific Pore Size Rule of Mixtures: Theoretical vs. Experimental Data

Future Work and Expectations Further Optical Imagery: SEM Images on Current Porous SRP Sample Obtain Micro-CT Images Further Porous SRP Compression Analysis Analysis on Foam Mold Casting Prototypes

Sources (a) Brand, J., Weiler, A., Caborn, D.N.M., Brown, C.H., and Johnson, D.L., Graft fixation in cruciate ligament reconstruction. American Journal of Sports Medicine, (5): p (b) Barber, F.A., Herbert, M.A., Beavis, R.C., and Oro, F.B., Suture anchor materials, eyelets, and designs: Update Arthroscopy-the Journal of Arthroscopic and Related Surgery, (8): p (c) Shellock, F.G., Mink, J.H., Curtin, S., and Friedman, M.J., Mr imaging and metallic implants for anterior cruciate ligament reconstruction - assessment of ferromagnetism and artifact. Jmri-Journal of Magnetic Resonance Imaging, (2): p (d) Pinned hip fracture, X-ray: C009/5258. Science Photo Library. Retrieved from

Sources (e) Karageorgiou, V. and Kaplan, D., Porosity of 3d biornaterial scaffolds and osteogenesis. Biomaterials, (27): p (f) Hulbert, S.F., Young, F.A., Mathews, R.S., Klawitter, J.J., Talbert, C.D., and Stelling, F.H., Potential of ceramic materials as permanently implantable skeletal prostheses. Journal of Biomedical Materials Research, (3): p (g) Liu, Q.L. and Subhash, G., A phenomenological constitutive model for foams under large deformations. Polymer Engineering and Science, (3): p (h) PrimoSpire self-reinforced polyphenlyne. Solvay Plastics, Retrieved from s/Spire_Ultra_Polymers/Pages/PrimoSpire.aspx