Summary: The objective of this study was to evaluate a non-resorbable implant for the focal repair of osteochondral defects. Enhanced adherence of repair cartilage overgrowing the implants was the secondary goal and was tested by introducing porosities on the articular surface of the implant. This study evaluated four versions of the construct composed of a polycarbonate-urethane-urea biomaterial (elastomer) and a bone anchor. In order to induce porosities on the surface of the implant, either vertical holes were punched into it, or the chondral component was 3D-printed onto the implant. Fabrication, biomechanical characterization and cell infiltration of the implant were evaluated in-vitro. Subsequently the implants were tested in an in-vivo study in four Shetland ponies for 5 weeks. Enhanced porosity was successfully obtained for all implants. The 3D-printing of the elastomeric material produced pore diameters of 775μm and 690μm whilst the micro-punched pores had a diameter of 319μm. The elastic modulus of the elastomer decreased with the introduction of porosity but stayed above values of native cartilage in all versions of the implant. Clinically the implant was well tolerated. The over-growing repair tissue was mostly flush with surrounding cartilage and attached to the elastomer through ingrowth of the tissue into the pores. Overall the tested implants all showed good mechanical performance in vitro and subjectively also in vivo. The repair cartilage was solidly attached to the porous surface of the implant. The printing approach potentially enables fine-tuning of the biomechanical properties of the implant depending on the specific requirements for a given location.

Osteoarthritis of the hip is a painful and debilitating condition commonly occurring in humans and dogs. One of the main causes that leads to hip osteoarthritis is hip dysplasia. Although the current surgical methods to correct dysplasia work satisfactorily in many circumstances, these are associated with serious complications, tissue resorption, and degeneration. In this study, a one-step fabrication of a regenerative hip implant with a patient-specific design and load-bearing properties is reported. The regenerative hip implant is fabricated based on patient imaging files and by an extrusion assisted 3D printing process using a flexible, bone-inducing biomaterial. The novel implant can be fixed with metallic screws to host bone and can be loaded up to physiological loads without signs of critical permanent deformation or failure. Moreover, after exposing the hip implant to accelerated in vitro degradation, it is confirmed that it is still able to support physiological loads even after losing ≈40% of its initial mass. In addition, the osteopromotive properties of the novel hip implant is demonstrated as shown by an increased expression of osteonectin and osteocalcin by cultured human mesenchymal stem cells after 21 days. Overall, the proposed hip implant provides an innovative regenerative and mechanically stable solution for hip dysplasia treatment.