The outstanding mechanical response and bone regeneration capacity of robocast dilute magnesium-doped wollastonite scaffolds in critical size bone defects

The regeneration and repair of damaged load-bearing segmental bones require considerable mechanical strength for the artificial implants. The ideal biomaterials should also facilitate the production of porous implants with high bioactivity desirable for stimulating new bone growth. Here we developed a new mechanically strong, highly bioactive dilute magnesium-doped wollastonite (CaSiO3-Mg; CSi-Mg) porous scaffold by the robocasting technique. The sintered scaffolds had interconnected pores 350 mm in size and over 50% porosity with appreciable compressive strength (> 110 MPa), 5-10 times higher than those of pure CSi and beta-TCP porous ceramics. Extensive in vitro and in vivo investigations revealed that such Ca-silicate bioceramic scaffolds were particularly beneficial for osteogenic cell activity and osteogenic capacity in critical size femoral bone defects. The CSi-Mg porous constructs were accompanied by an accelerated new bone growth (6-18 weeks) and a mechanically outstanding elastoplastic response to finally match the strength (10-15 MPa) of the rabbit femur host bone after 18 weeks, and the material itself experienced mild resorption and apatite-like phase transformation. In contrast, the new bone regeneration in the b-TCP scaffolds was substantially retarded after 6-12 weeks of implantation, and exhibited a low level of mechanical strength (< 10 MPa) similar to the pure CSi scaffolds. These results suggest a promising application of robocast CSi-Mg scaffolds in the clinic, especially for the load-bearing bone defects.