Hydroxyapatite formation on oxidized cellulose nanofibers in a solution mimicking body fluid

Abstract

Biomimetic processing using a solution mimicking the inorganic composition of the body fluid of humans (simulated body fluid (SBF)) may be one of the more promising routes for the construction of polymer/hydroxyapatite composites by an environmental-friendly method. In this process, hydroxyapatite nucleation on an organic polymer is an important event, yet the optimal surface characteristics of the organic polymer have not been determined. In the present study, a series of oxidized cellulose nanofibers with different contents of the carboxy groups (0-27% per glucose units of cellulose) were prepared. Their capability of forming hydroxyapatite in 1.5SBF (a solution in which the concentration of the inorganic ions was 1.5 times higher than that in SBF) was systematically investigated. It was found that hydroxyapatite formation on the nanofibers was the most enhanced with a nanofiber containing a carboxy group content of 9.9%, indicating that there was an optimum amount of carboxy groups that was required for the effective induction of hydroxyapatite nucleation. Carboxy groups are considered to be involved in the electrostatic interactions between the fibers and the calcium ions in solution and they induce heterogeneous nucleation of hydroxyapatite. Higher contents of carboxy groups, however, reduced the activity of the calcium ions for the nucleation of hydroxyapatite by forming complexes with the calcium ions.