ABSTRACT
Biomimetic mineralization of apatite on bacterial cellulose (BC) was investigated by soaking different modified BC templates in a simulated body fluid (1.5 SBF) and/or alternate soaking in 0.05 M calcium chloride and 0.03 M sodium dihydrogen phosphate solutions prepared with a calcium:phosphorus molar ratio of 1.67 at a physiological temperature of 37°C. Modification of BC includes surface modification by 2182,2,6,6-tetramethylpyperidine-1-oxyl (TEMPO)-mediated oxidation and medium modification by addition of amino sugar N-acetylglucosamine (GlcNAc) during cellulose biosynthesis. The carboxylate content of TEMPO-oxidized BC (BC-TEMPO) measured by conductimetric titration was 0.25 mmol/g cellulose. The amount of GlcNAc incorporated in BC determined by the radiolabeling method was 0.03–0.36 mole%, depending on the amount of nonradioactive GlcNAc present in the culture medium and the type of starter culture used. Attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) and inductively coupled plasma atomic emission spectroscopy (ICP-AES) analysis indicated that the crystalline phase nucleated on the BC microfibrils surface was calcium-deficient carbonated apatite through the initial formation of octacalcium phosphate (OCP) or OCP-like calcium phosphate phase. From field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM) observations, the apatite mineral was in the form of globules or clusters of thin film plates, which varied in size from less than 1 µm to approximately 6 µm with respect to different BC templates and the soaking method. The BC-TEMPO having active carboxyl functional groups showed a faster nucleation rate than native BC and GlcNAc-incorporated BC. It was found that the ability of BC templates to induce mineral nucleation differed according to the surface structure of the BC, which strongly influenced the growth behavior of the apatite crystals.
