(3bl) Development and Characterization of UHMWPE Fiber-Reinforced Hydrogels for Soft Tissue Replacement Applications

Meniscal tears are the most common orthopedic injuries to the human body. However, poor treatment options exist due to the complex anisotropic property distribution within the meniscus. A fiber-reinforced hydrogel-based synthetic meniscus allows tailoring of the mechanical properties and molding of the implant to the size and shape of the native cartilage. Physically cross-linked poly(vinyl alcohol) (PVA)-ultra high molecular weight polyethylene (UHMWPE) fiber composites were characterized in compression (0.1 MPa - 0.8 MPa) and tension (0.1 MPa - 250 MPa) showing fine control over mechanical properties based on PVA concentration, UHMWPE fiber volume fraction, and hydrogel freeze-thaw cycles.  Morphology and crystallinity analysis of PVA hydrogels showed both increases in crystallinity and structural ripening, phase separation, with freeze-thaw cycles.  Indicating that both factors increase hydrogel mechanical properties with cycling. Swelling studies were performed in an osmotic solution to replicate the swelling pressure present in the knee. Minimal swelling was observed for hydrogels with a PVA concentration of 30-35wt%, independently of hydrogel freeze-thaw cycles. This allows for independent tailoring of hydrogel modulus and pore structure using freeze-thaw cycles and swelling behavior using polymer concentration to match a wide range of properties needed for various soft tissue applications. Chemical grafting and oxygen plasma treatments were performed on UHMWPE fibers to improve fiber-hydrogel interfacial properties. Interfacial shear strength (IFSS) was characterized using a single fiber pull-out test. Improvements to IFSS occurred from 11 kPa without any treatment to above 200 kPa following treatment. Lastly, ex vivo gait simulations were performed on PVA-UHMWPE fiber implants using a human cadaver knee model. Preliminary results show improvement in contact pressures compared to a meniscectomy. In conclusion, PVA-UHMWPE fiber composites can be tailored over a wide range of mechanical properties, porosity, swelling behavior, and fiber-hydrogel adhesion. Indicating the potential to produce an implant that can reproduce the anisotropic nature of the meniscus. This research can also be applied to other soft tissue applications, including the ACL and the annulus fibrosus.