Abstract
In this paper, a well-crystallized hydroxyapatite (HA) and nanocrystalline apatites (NCA) were used to interpret the adsorption process of two bisphosphonates (BPs), namely Tiludronate (Tilu) and Risedronate (Rise). These BPs are among the most prescribed classes of drugs for the treatment of bone disorders disease, particularly Osteoporosis. The equilibrium data used to express the variation of uptake capacity as a function of concentration were determined by varying some experimental physicochemical conditions (e.g. temperature and pH). A preliminary analysis of all the adsorption isotherms obviously indicates that the adsorption quantity tends towards a saturation level. This suggests a finite number of adsorbed layers involved in the adsorption mechanisms. To give a reasonable analysis of the drug adsorption process, three advanced models are proposed and developed in the light of a statistical physics treatment which is tested and discussed. The modeling analysis reveals that the adsorption of the two drugs occurs by the formation of two different adsorbed layers on the apatite surface. Based on the analysis of the selected model parameters, it was deduced that both drugs molecules were anchored alternately with parallel and non-parallel positions on the apatite substrate. The study of the uptake capacities at saturation showed that these parameters followed the sequence: Qasat (Rise-NCA) ˃ Qasat (Rise-HA) ˃ Qasat (Tilu-HA), indicating that the NCA adsorbent was more effective for the Rise drug adsorption than the HA adsorbent. The estimated adsorption energies globally varied from 9.20 to 19.52 kJ/mol, confirming the physical nature of the adsorption process for the investigated systems. Conventionally, to characterize the adsorption process, the entropy (Sa), the enthalpy of Gibbs (G) and the internal energy (Eint) were treated and interpreted.
•Modeling of tiludronate and risedronate isotherms by the double layer model with two energies•Steric and energetic interpretation of adsorption process•The adsorption energy, thermodynamic functions were calculated.