Deposition of bone‐like apatite on silk fiber in a solution that mimics extracellular fluid

Abstract

The fabrication of apatite-organic polymer hybrids is one of several attractive methods for the development of biomaterials as a substitute for bone. Such materials have both bone-bonding ability and mechanical properties analogous to natural bone. The biomimetic process has focused attention on fabricating such hybrids, where bone-like apatite is deposited on an organic polymer surface in solutions that mimic physiological conditions. In this process, a bone-like apatite layer can be coated onto organic substrates either by using a simulated body fluid (SBF) with ion concentrations nearly equal to those of human extracellular fluid, or by using fluids that are supersaturated with respect to apatite at ambient conditions. In this study, we investigated the ability of natural silk and its related materials to facilitate apatite deposition under biomimetic conditions. Cloths made of raw silk or normal silk fibers were soaked in 1.5SBF, which has 1.5 times the ion concentration of SBF. Sericin film, which is made from an extract of degummed raw silk, was soaked in 1.5SBF. The cloth and the film soaked in 1.5SBF then were characterized by scanning electron microscopic (SEM) observation, energy dispersive X-ray microanalysis (EDX), and thin-film X-ray diffraction (TF-XRD). Apatite deposition was observed on the surface of cloth made from raw silk fiber after it was soaked in 1.5SBF, but it was not observed on cloth made from normal silk fibers. The apatite deposition on the raw silk fiber cloth was accelerated when the fibers were subjected to treatment with CaCl(2) solution at a concentration of at least 1 kmol/m(3) before immersion in 1.5SBF. Apatite deposition also was observed on the sericin film after the film was soaked in 1.5SBF for 7 days. These results indicate that apatite deposition on raw silk cloth is attributable to the catalytic effect of sericin because the surface of raw silk consists of sericin whereas that of normal silk contains fibroin. The deposition of the apatite and its crystal growth are accelerated by the presence of calcium ions on the sericin after treatment with CaCl(2) solution. Thus, sericin on natural silk fiber has the potential to facilitate apatite deposition and can be useful as a polymer material in the fabrication of hybrid materials analogous to bone through biomimetic processes.

Effect of fetal bovine serum on mineralization in silk fibroin scaffolds

“…So far, active inhibition of mineralization by hMSCs could not be shown and further investigation would be needed to test this hypothesis. Spontaneous mineralization of acellular SF has been described before in SBF or CaCl 2 [21][22][23] but, to our knowledge, it was never shown in control or osteogenic medium or on other scaffold materials.…”

“…The amount of spontaneous mineralization is dependent on the ion concentration of the solution surrounding the substrate [21]. Differences in spontaneous mineralization between the four FBS types used can be explained by differences in elemental composition.…”

“…Ions are small enough to diffuse throughout the whole scaffold volume easily. Because spontaneous mineralization is dependent on local ion concentration [21], the spatial distribution of spontaneous mineralization on acellular scaffolds was expected to be more homogeneous compared to cell-seeded scaffolds. Quantitative evaluation of spatial distribution of mineralization volume confirmed this hypothesis and showed a significantly increased percentage of total BV in the center of acellular scaffolds (Fig.…”

“…SF is an interesting scaffold material for bone TE consid- ering its ability to regulate the formation of HA nanocrystals when exposed to simulated body fluid (SBF). SBF mimics ion concentrations of human blood serum [20,21]. It was shown that SF has the potential to mineralize spontaneously in SBF by inducing apatite deposition on its surface and provoking continuous growth and enrichment of HA crystals [21,22].…”

“…SBF mimics ion concentrations of human blood serum [20,21]. It was shown that SF has the potential to mineralize spontaneously in SBF by inducing apatite deposition on its surface and provoking continuous growth and enrichment of HA crystals [21,22]. Marelli et al [11] have shown that the amorphous connections between the b-sheets of SF act as nucleation sites for HA crystals similar to Col I in bone.…”