Adsorption behavior and osteoblastic cellular activity of metronidazole molecule with octacalcium phosphate and hydroxyapatite materials

Octacalcium phosphate (OCP) has received recognition as a highly osteoconductive bone substitute. Metronidazole is an antimicrobial agent that could improve bone regeneration with artificial materials. This study aims to investigate the adsorption and release behavior of metronidazole on OCP and hydroxyapatite (HA) along with examining the effects of metronidazole on mesenchymal stem cell (MSC) proliferation and osteoblastic differentiation. OCP and HA were incubated in a Tris(hydroxymethyl)aminomethane-HCl buffer solution (pH 7.4 at 37 °C) containing metronidazole. After incubation, the adsorbed metronidazole amount was measured. Fourier transform infrared spectroscopy (FTIR) was also used to characterize the incubated OCP and HA granules. After adsorption, the amount of metronidazole released from each material was determined from supernatant analysis following incubation. For the adsorption in OCP, the isotherms were better described by Hill (r2 = 0.956) adsorption model compared to Langmuir (r2 = 0.858) and Freundlich adsorption (r2 = 0.776) models. However, for the adsorption in HA, both Hill (r2 = 0.949) and Langmuir (r2 = 0.947) adsorption models were the best-fitted models. The adsorption affinity estimated by Hill's equation was higher for the OCP (KH = 4.63 mL/mg) than the HA (KH = 1.11 mL/mg), although the saturated amount of adsorption was larger for the HA (q0 = 0.59 mg/m2) than the OCP (q0 = 0.23 mg/m2). The FTIR spectra detected metronidazole molecules on both the OCP and HA granules after adsorption. The release of metronidazole from both OCP and HA occurred in bursts and sustained over a certain period of time. Additionally, the osteoblastic differentiation of MSCs was investigated by examining the alkaline phosphatase (ALP) activity by incubating OCP with metronidazole for 7 and 14 days. Metronidazole does not inhibit the proliferation (p > 0.05) or osteoblastic differentiation (p > 0.05) of MSCs. Overall, these results suggest that metronidazole may potentially be used as an antibacterial agent together with OCP bone substitutes.