Gold-doped wollastonite nanohybrids enhance bone regeneration <i>via</i> the bone morphogenetic protein-2, SMAD1, and Runt-related transcription factor-2 signalling pathway

This study examines the prospect of bone regeneration using pure wollastonite and gold-doped wollastonite nanohybrids prepared using a wet chemical method. After four weeks of soaking in simulated body fluid, the bio-mineralization of wollastonite was accelerated, with excellent apatite layer deposition accomplished at varying ratios (<i>i.e.</i> 0, 1.25, 2.5, 5, and 7.5 wt/v%). The <i>in vitro</i> biodegradation and swellability of the prepared composites revealed controlled and stable bone defect behavior, with enhanced adequate swellability. W/Au 5 wt/v% demonstrated the highest potential for water absorption, amounting to approximately 80-85%. X-ray photoelectron spectroscopy analysis confirmed the composition of the CaSiO₃ sample for pure wollastonite while showing that gold nanoparticles or a thin layer of gold was deposited on the surface of CaSiO₃ in the case of the gold-doped wollastonite nanohybrid (7.5 wt/v%). The mechanical strength increased considerably with gold nanoparticle doping. <i>In vivo</i> bone osteogenesis was assessed in a rat femur bone defect model to demonstrate the bone regeneration ability of the fabricated nanocomposites. Results showed up-regulation of the osteogenic markers, including bone morphogenetic protein 2 (Bmp2), Smad1, and Runx2 signalling, which is involved in osteoblast differentiation. Enhanced alkaline phosphatase (ALP) activity, which affects the mineralization ability of cells, was also evaluated. Furthermore, gold nanoparticle doping reduced glycogen synthase kinase-3β (GSK 3β) levels compared to the positive control, which stimulated bone formation and increased bone mineral density (BMD) after 2 months of implantation. These results aligned with histopathological studies that showed increased osteoblast proliferation and blood vessel regeneration. The findings demonstrate that wollastonite nanohybrids, both pure and gold-doped, show promise as materials for bone replacement and regeneration applications.