Phase variations in waste-derived CaSiO3 for efficient drug loading, releasing, and antimicrobial applications

Abstract

Calcium silicate is a bioactive material that enhances bone regeneration in compromised osteogenesis. Calcium silicate biomaterials were synthesized through a solid-state method (1000 °C) using SiO₂ and eggshell-derived CaCO₃ in varying ratios (2 : 1, 2 : 1.5, 2 : 2, and 2 : 3) as a source of Si and Ca, respectively. The samples were characterized using X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), X-ray photoelectron spectroscopy (XPS), and UV–visible spectrophotometry. Five phases (wollastonite, di-calcium silicate, larnite, rankinite, and calcium silicate hydroxide) of calcium silicate were confirmed by Rietveld refinement analysis. The powdered sample was shaped into a round pellet. It was sintered at 900 °C (four-stage temperature) to evaluate the antibiotic (ciprofloxacin, amoxicillin, and levofloxacin) loading and release profiles in simulated body fluid at different chosen time intervals for 21 days. The maximum drug loading (ciprofloxacin-loaded) and release were observed for the calcium silicate (2_SiO₂ : 1_CaCO₃) sample (crystallite size, 100.7130 nm) compared to the other three compositions (2 : 1.5, 2 : 2, and 2 : 3) due to the presence of the wollastonite and di-calcium silicate phases. The samples (drug-loaded, drug-released, and SBF-soaked) were examined using a field emission scanning electron microscope (FESEM), and their antimicrobial activity against Gram-positive (S. aureus) and Gram-negative (E. coli) bacteria was assessed; they presented larger inhibition zones than the standard against the two types of microbes.