In vitro and in vivo evaluation of the osseointegration capacity of a polycarbonate‐urethane zirconium‐oxide composite material for application in a focal knee resurfacing implant
Pieter P. W. van Hugten, Ralph M. Jeuken, Erkan E. Asik, Henk Oevering, Tim J. M. Welting, Corrinus C. van Donkelaar, Jens Thies, Pieter J. Emans, Alex K. Roth
Abstract
Abstract Currently available focal knee resurfacing implants (FKRIs) are fully or partially composed of metals, which show a large disparity in elastic modulus relative to bone and cartilage tissue. Although titanium is known for its excellent osseointegration, the application in FKRIs can lead to potential stress‐shielding and metal implants can cause degeneration of the opposing articulating cartilage due to the high resulting contact stresses. Furthermore, metal implants do not allow for follow‐up using magnetic resonance imaging (MRI).To overcome the drawbacks of using metal based FKRIs, a biomimetic and MRI compatible bi‐layered non‐resorbable thermoplastic polycarbonate‐urethane (PCU)‐based FKRI was developed. The objective of this preclinical study was to evaluate the mechanical properties, biocompatibility and osteoconduction of a novel Bionate® 75D ‐ zirconium oxide (B75D‐ZrO 2 ) composite material in vitro and the osseointegration of a B75D‐ZrO 2 composite stem PCU implant in a caprine animal model. The tensile strength and elastic modulus of the B75D‐ZrO 2 composite were characterized through in vitro mechanical tests under ambient and physiological conditions. In vitro biocompatibility and osteoconductivity were evaluated by exposing human mesenchymal stem cells to the B75D‐ZrO 2 composite and culturing the cells under osteogenic conditions. Cell activity and mineralization were assessed and compared to Bionate® 75D (B75D) and titanium disks. The in vivo osseointegration of implants containing a B75D‐ZrO 2 stem was compared to implants with a B75D stem and titanium stem in a caprine large animal model. After a follow‐up of 6 months, bone histomorphometry was performed to assess the bone‐to‐implant contact area (BIC). Mechanical testing showed that the B75D‐ZrO 2 composite material possesses an elastic modulus in the range of the elastic modulus reported for trabecular bone. The B75D‐ZrO 2 composite material facilitated cell mediated mineralization to a comparable extent as titanium. A significantly higher bone‐to‐implant contact (BIC) score was observed in the B75D‐ZrO 2 implants compared to the B75D implants. The BIC of B75D‐ZrO 2 implants was not significantly different compared to titanium implants. A biocompatible B75D‐ZrO 2 composite approximating the elastic modulus of trabecular bone was developed by compounding B75D with zirconium oxide. In vivo evaluation showed an significant increase of osseointegration for B75D‐ZrO 2 composite stem implants compared to B75D polymer stem PCU implants. The osseointegration of B75D‐ZrO 2 composite stem PCU implants was not significantly different in comparison to analogous titanium stem metal implants.