Biomimetic Synthesis of Self-Assembled Mineralized Collagen-Based Composites for Bone Tissue Engineering - Biomimetics: Advancing Nanobiomaterials and Tissue Engineering - page 38

engineering because of its innovative characteristics of non-virus dan-
gers and mini-immunogenicity. Furthermore, the amino acid sequence of
RHLC can be designed [65]. In 2005, RHLC were used to mediate mineral-
ization in vitro for the fi rst time [66, 67]. The assembly and morphology of
the mineralized recombinant collagen fi brils, especially the crystal struc-
tures and chemical interactions between RHLC and calcium phosphate
crystals were examined by SEM, TEM, Selected Area Electron Diffraction
(SAED) and FTIR. TEM images and SAED exhibited that the RHLC fi bers
in the mineralized samples were surrounded by HA nanocrystals, which
was similar with the mineralized native collagen fi brils. The FTIR spectra
showed that the peak for amide I also shifted to a lower wavenumber
because carbonyl groups of RHLC chelated with calcium ions. It revealed
that the RHLC preferred to chelate calcium ions in solution and so can
subsequently regulate the mineralization process forming self-assembled
RHLC/HA composites. All these results indicate that the RHLC have
the same function in the initial mineralization stage as natural collagen,
although the content of various amino acids of them is not uniform.
2.3.3 In Vitro Self-Assembly of Mineralized Silk Fibroin
Fibrils
Silks are generally defi ned as protein polymers that are spun into fi bers by
some Lepidoptera larvae such as silkworms, spiders, scorpions, mites and
fl ies. Degummed silk fi bers (i.e., fi broin) have been used as many kinds
of biomaterials like drug delivery systems, artifi cial skin, and so on, for a
long time [68]. Recently, fi broin was applied as a template for mimicking
biomineralization.
Takeuchi et al. [69] had used silk sericin to induce the apatite deposition
on its surface because sericin has more carboxyl groups to induce miner-
alization. However, it has been demonstrated that sericin protein, when
used in biomaterials, would cause adverse problems for biocompatibility
and hypersensitivity [70]. On the other hand, silk fi broin has been proven
to be good biocompatible material and has been successfully used for
various medical applications. Kong et al. [71] used soluble fi broin, which
was obtained from Bombyx mori silk fi bers after deguming sericin, as the
organic template to regulate the mineralization of calcium phosphate. The
calcium phosphate crystals precipitated in the aqueous solution of silk
fi broin at pH 8 and room temperature. Fibroin protein could signifi cantly
promote the crystal growth forming carbonate-substituted HA crystals
that were compounded with fi broin. The mineralized nanofi brils in the
composites are rod like in shape with a diameter of about 2-3 nm. In addi-
tion, the concentration of fi broin solute affected the biomineralization of
calcium phosphate [72]. Fibroin with a higher concentration had a more
positive effect on the biomineralization process.