Hydroxyapatite [HAP] and tricalcium phosphate [ß-TCP] are a class of calcium phosphate related ceramic materials that are widely used in tissue regeneration and biomedical applications owing to their excellent bioactivity and biocompatibility. In this investigation, nanocrystalline pure HAP was prepared via sol–gel method by incorporating snail shell as calcium precursor with different phosphorus sources such as triethyl phosphate/phosphite (without using any additives like pH maintaining solutions or gelling agents). Nanocrystalline HAP and biphasic calcium phosphate (HAP + ß TCP) were prepared from triethyl phosphate and triethyl phosphite precursors, respectively. The prepared material was further characterized by powder XRD, IR, Raman spectroscopy, and thermo-gravimetrical analysis to confirm the phase purity, functional groups, and thermal stability. SEM coupled with EDAX was also used to examine the size, shape of particles, and elemental composition of Ca to P ratio in the material. Different phosphorus based HAP has shown rod and spherical shaped surface morphology which was further confirmed by TEM analysis. MTT assay was performed using NIH-3T3 fibroblast cell lines which indicated that the viability was not affected in various concentrations of pure nanocrystalline HAP (12.5–100 µg/ml). This study confirms the improved biocompatibility of biowaste converted HAP which would have implications in biomedical applications.

The purpose of this study is to synthesize and characterize nanosized titania (TiO₂), zinc oxide (ZnO), and its composite coating on Ti–6Al–4V to enhance its corrosion protection behavior in Ringer's solution. Nanosized powders of TiO₂ and ZnO was characterized by Fourier transform infrared spectroscopy (FTIR), powder X-ray diffraction (XRD), and scanning electron microscopy - energy dispersive atomic spectroscopy (SEM-EDAX) analysis. As a result of antibacterial activity, both ZnO and TiO₂/ZnO have produce remarkable inhibition zone on Escherichia coli. The antibacterial activity of composites are due to the combined effect of ZnO on TiO₂. The adherence and surface uniformity of TiO₂/ZnO composite film on titanium implant was examined by optical microscopy and Vickers microhardness test. Corrosion resistant behavior of the coating on titanium implant was investigated by tafel polarization and impedance analysis. The composite coatings on Ti–6Al–4V have produced improved corrosion resistance with a pronounced shift in the anodic corrosion potential (E_corr) with a corresponding less corrosion current density (I_corr) compared to monophase coating. Similar results have been obtained for impedance analysis which indicated a reduction in double layer capacitance (C_dl) and with enhancement in charge transfer resistance (R_ct). These observations suggest improved corrosion resistance property of TiO₂/ZnO composite coating on Ti–6Al–4V.

The sol–gel combustion method was employed to synthesize the nanocrystalline wollastonite by taking the raw eggshell powder as a calcium source and TEOS as a source of silicate. Glycine was used as a reductant or fuel and nitrate ions present in metal nitrate acts as an oxidizer. The phase purity of the wollastonite was analysed by powder XRD and the product is found to contain single-phasic wollastonite. FT–IR spectrum shows the characteristic peaks of the functional groups present in the wollastonite. SEM images show that particles are agglomerated and the particle size is found to be in the nanoregime. The calcination temperature was optimized based on the thermal analysis of the precursor. The bioactivity of wollastonite was investigated by immersing the scaffold in a simulated body fluid for 15 days at 37 °C and intermediate analysis of the surface by XRD shows the deposition of hydroxyapatite layer after 5 days.

Graphical abstract of novel 5%@Ag:HAP–Fe₃O₄–CS hybrid composites and biological investigations.