Early Growth of Nano-Sized Calcium Phosphate on Phosphorylated Bacterial Cellulose Nanofibers

Abstract

It is believed that studies on the early hydroxyapatite (HAp) deposition on nano-sized substrates may possibly allow us to understand the formation mechanisms of biominerals at the molecular level. In this study, bacterial cellulose (BC) nanofibers were phosphorylated and used as nano-sized templates for early mineralization of calcium phosphate (Ca-P). To initiate mineralization the BC nanofibers were immersed in 1.5 times simulated body fluids (1.5 SBF) at 37 degreees C for varying periods of time. The deposited minerals on the nanofiber surfaces were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transformed infrared spectroscopy (FTIR). SEM observations confirmed that early growth (at 4 h) of the Ca-P minerals was heterogeneous, which was followed by extensive spread of the minerals on the entire surfaces of the nanofibers. XRD and FTIR analyses indicated that octacalcium phosphate (OCP) was the precursor of HAp formed on BC nanofibers. Furthermore, HAp deposited on BC nanofibers elongated along the c axis. Nucleation and growth of the Ca-P minerals were analyzed in this paper.

Surface controlled calcium phosphate formation on three-dimensional bacterial cellulose-based nanofibers

“…Similarly, Nge et al declared that the initial precursor of HAP on BC was OCP [24]. However, to the best knowledge of the authors, none of the previous studies regarding Ca-P formation on BC nanofibers [21,22,24,26,38,39] has observed the formation of ACP and TCP probably due to the fact that such techniques as XRD and SEM are unable to capture the information of nascent Ca-P deposits. It is believed that studies on the early Ca-P formation on nano-sized substrates may possibly allow us to understand the formation mechanisms of biominerals at the molecular level [26] and thus enable us to develop synthetic biomaterials which would resemble natural ones more closely.…”

“…To this end, Ca-P formation on pristine and surface-modified BC nanofibers has been reported by using conventional techniques such as XRD, TEM, and FTIR [19][20][21][22][23][24][25]. For many years, it has been believed that octacalcium phosphate (OCP) is the precursor of hydroxyapatite (HAP) on BC nanofibers regardless of surface nature [24,26]. However, that finding is inconsistent with the common notion that amorphous calcium phosphate (ACP) is the first-formed solid Ca-P phase which evolves into crystalline phases [13,27,28] and that the surface nature of templates can significantly alter the nucleation and transformation of the mineralizing crystals [29][30][31].…”

“…Accordingly, more investigation is needed for the understanding of the biomineralization mechanisms and the construction of organic-inorganic hybrids and bone scaffolds. Unlike previous studies regarding Ca-P formation on BC [19][20][21][22][23][24][25][26], for the first time we systemically investigate the structure and chemical states of newly formed Ca-P deposits on BC-based nanofibers by XANES spectroscopy in an attempt to understand the early (as short as 2 min) formation of nascent precursors and thereafter the evolution of Ca-P minerals and determine the influence of surface coating on Ca-P formation and evolution of Ca-P minerals. To this end, phosphorylated BC (P-BC), gelatin-immobilized BC (Gel-BC), and ε-polylysine-immobilized BC (PLL-BC) were used as the nanofibrous templates (either negative or positive surface) for the deposition of Ca-P minerals.…”

“…Therefore, XANES results suggest that the nascent phase of Ca-P was ACP, which experienced subsequent transitions to TCP and then to OCP and/or HAP. In our previous work, SEM, XRD, and FTIR were applied to explore the early growth (starting from 4 h) of Ca-P minerals on the surface of BC nanofibers and it was found that OCP was the precursor of HAP [26]. Similarly, Nge et al declared that the initial precursor of HAP on BC was OCP [24].…”

Biocompatibility of Bacterial Cellulose Based Biomaterials

“…Other biomaterials used to improve the biocompatibility of BC include starch [22,47], hydroxyapatite [12,16,48,49,50,51,52], poly(vinyl alcohol) [53,54,55], poly(methyl methacrylate) [56] and polyacrylamide [57]. …”