Poly(vinyl alcohol)-based hydrogels for joint prosthesis

Introduction: The best treatment currently available for severe joint disease is total joint replacement by a prosthesis, which involves biocompatible metal alloys articulating against a metal, ceramic or polyethylene part. These devices often fail due to wear of the polymer by the harder counterface, which may cause inflammation, osteolysis and consequent implant loosening. Hydrogels, namely polyvinyl alcohol-based hydrogels (PVA), have been studied and mentioned as a possible alternative for materials used in prostheses because of their biocompatibility, swelling ability and tribological behavior. The main objective of this work is to evaluate the effect of the molecular weight of PVA on properties of PVA based hydrogels, relevant for the referred application. Materials and methods: Gel preparation : Cast-dried gels were prepared from: PVA L (40500 g/mol, Sigma Aldrich); PVA M (145000 g/mol, Kuraray) and PVA H (166000 g/mol, Sigma Aldrich). Swelling behaviour : Dry gels were weighted, immersed in DD water and weighted again until weight stabilized. Wettability : The water contact angle was measured using the captive bubble method. Thermotropic behaviour : Hydrated samples are analyzed by Differential Scanning Calorimetry (DSC). Mechanical properties : tensile tests and unconfined compression tests were performed to ascertain the Young's modulus, ultimate tensile strength and toughness. Results: % Water content (swelling) % Water content (DSC) Contact angle (°) Tensile Young's Modulus (MPa) Compressive Young's Modulus (MPa) Ultimate Tensile Strength (MPa) Fracture Toughness (MPa/mm 1/2 ) Fracture Toughness at a stress level of 500 KPa (MPa/mm 1/2 ) Compressive Toughness at a stress level of 500 KPa (MPa/mm 1/2 ) PVA L 66 - 51 2.13 - 0.67 18 - - PVA M 62 75 48 2.42 3.60 ≥7.86 ≥493* 5.73 47.87 PVA H 58 65 45 2.55 4.46 ≥7.48 ≥543* 5.55 40.20 Cartilage 65-85 [ 1 ] - 4.3-25 [ 2 ] 0.24-12 0.8-25 [ 2 ] 305-391 [ 3 ] - - *measured at a strain rate of 3 Discussion and conclusions: The water content is progressively lower as molecular weight increases, but the values are similar to those of natural cartilage. The contact angles are low and thus gels are hydrophilic, just as cartilage. The values of tensile and compressive Young's modulus and toughness at 500 KPa show that PVA is stiffer under compressive loads, contradicting the behaviour of natural cartilage, which is stiffer under tensile loads. The ultimate tensile strength and fracture toughness show that PVA L