Bone regeneration scaffolds represent a promising solution for bone grafting of large and severe bone defects. The ideal bone substitute material is considered to have excellent biocompatibility, osteoconductivity, osteoinductivity, and mechanical properties similar to bone. Different scaffold materials are currently available for clinical application, but despite the broad selection, no material has yet been described that has both excellent biological and mechanical properties. Bioceramics such as zirconia and alumina matrix composites could be promising alternative materials for bone grafting. Non-porous full density zirconia and alumina matrix composite implants require bioactive surface coating for osseointegration and bone formation, but porous scaffolds made of those materials may eliminate the need for bioactive porous coatings. The aim of the present study was to investigate the long-term biocompatibility and osseointegration of directly foamed porous yttria-stabilized tetragonal zirconia (Y-TZP) and zirconia-toughened alumina (ZTA) scaffolds in calvarial and femoral bone defects in an ovine model in vivo. Cytocompatibility of ceramic material and scaffolds was investigated in vitro. Porous Y-TZP and ZTA scaffolds with different porosities (60% and 70%) were implanted into calvarial and femoral bone defects in sheep in vivo. Osseointegration, bone formation, and host response were histopathologically analyzed 12 and 24 weeks post implantation. The in vitro studies showed no negative influence on the cytocompatibility. In vivo, all implants were fully integrated into defect sites at both time points without any material degradation. A thick fibrous layer was present at the calvarial implant sites, which was associated with the implant's geometric misfit. After 12 weeks, early osseointegration was observed with Y-TZP 70% and ZTA 70%, which seemed to be rather dependent on porosity than ceramic material. After 24 weeks, bone formation and osseointegration increased and were similar for all scaffolds. A slight to moderate host response was present at both time points for all scaffolds, which was manifested by rare to mild macrophage and lymphocyte tissue infiltration and was considered an essential part of the healing process. Porous Y-TZP and ZTA scaffolds demonstrated early osseointegration, good cytocompatibility, and long-term biocompatibility in vivo. The porous surface of the scaffolds enables direct contact between the ceramic material and the bone, eliminating the need for additional coatings. Also, higher scaffold porosity together with pore interconnectivity facilitates intraporous bone formation, thus representing a promising alternative for bone scaffold materials for various medical applications such as orthopedics, dentistry, and cranio-maxillofacial surgery.
Lackner et al. (Fri,) studied this question.