A simple and effective approach was developed to synthesize chitosan–silk sericin/hydroxyapatite nanocomposites by in situ precipitation and two methods of alkali diffusion were carried out in this study. The objective of this paper was to investigate the different properties of the nanocomposites. SEM showed that the rod-like hydroxyapatite particles with a diameter of 20–50 nm were distributed homogeneously within the chitosan–silk sericin matrix, and the formation mechanism was also investigated. The results of FTIR and XRD indicated that the inorganic phase in the nanocomposite was carbonate-substituted hydroxyapatite with low crystallinity. In terms of mechanical properties, chitosan–silk sericin/hydroxyapatite nanocomposites exhibited a higher elastic modulus and compressive strength than that of the chitosan/hydroxyapatite nanocomposites. In vitro cytocompatibility of the nanocomposite was evaluated by CCK-8 assay and SEM through MG63 osteoblast cells cultured on the samples, which demonstrated that they are non-toxic and support cell growth. These results suggest that the chitosan–silk sericin/hydroxyapatite nanocomposites are promising biomaterials for bone tissue engineering.

Chitosan–multiwalled carbon nanotubes/hydroxyapatite nanocomposites were synthesized by a novel in situ precipitation method. The electrostatic adsorption between multiwalled carbon nanotubes and chitosan was investigated and explained by Fourier transform infrared spectroscopy analysis. Morphology studies showed that uniform distribution of hydroxyapatite particles and multiwalled carbon nanotubes in the polymer matrix was observed. In chitosan–multiwalled carbon nanotubes/hydroxyapatite nanocomposites, the diameters of multiwalled carbon nanotubes were about 10 nm. The mechanical properties of the composites were evaluated by measuring their compressive strength and elastic modulus. The elastic modulus and compressive strength increased sharply from 509.9 to 1089.1 MPa and from 33.2 to 105.5 MPa with an increase of multiwalled carbon/chitosan weight ratios from 0 to 5 %, respectively. Finally, the cell biocompatibility of the composites was tested in vitro, which showed that they have good biocompatibility. These results suggest that the chitosan–multiwalled carbon nanotubes/hydroxyapatite nanocomposites are promising biomaterials for bone tissue engineering.

Homogeneous nanocomposites composed of hydroxyapatite (HAp) and collagen were synthesized using a novel in situ precipitation method through dual template-driven. The morphological and componential properties of nanocomposites were investigated. The HAp particulates, in sizes of about 50–100 nm, were distributed homogeneously in the organic collagen hydrogel. Highly magnified TEM observation showed that HAp inorganic particles were composed of fine sub-particles (2–5 nm) without regular crystallographic orientation. Based on these homogeneous nanocomposites, a novel HAp/collagen nanocomposite scaffold with hierarchical porosity was prepared by multilevel freeze-drying technique. Compared to other conventional scaffolds for tissue engineering, this novel in situ method endows synthesized composite scaffolds with unique morphology—ultrafine HAp particles dispersed homogenously in collagen at nano level and the foam scaffold with hierarchical pore structures. The mechanical performance increased obviously compared with neat collagen. These results provided an efficient approach toward new biomimetic tissue scaffold for the biomedical applications with enhanced intensity/bioactivity and controlled resorption rates. This novel method, we expect, will lead to a wide application in many other hydrogel systems and may be useful for fabrication of various homogeneous inorganic/organic nanocomposites.

Homogeneous nanocomposites composed of carbonate apatite and chitosan in the presence of citric acid were synthesized by a novel in situ precipitation method. The morphological and componential properties of composites were investigated. The carbonate apatite particulates, in sizes of about 50–100 nm, were distributed within the network chitosan hydrogel homogeneously, moreover, inorganic particles could be controlled by the size of networks of organic matrix which was mediated with crosslink degree of chitosan. Through highly magnified TEM observation, it can be shown that inorganic particles were composed of more fine sub-particles whose diameters were between 2 and 5 nm in size without regular crystallographic orientation. The concept of multiple-order template mediation was brought forward for the first time. A novel hierarchical porous nanocomposite scaffold was also prepared by multilevel freeze-drying technique and its mechanical performance had obvious increase compared with neat chitosan. These results provided an efficient approach toward new biomimetic tissue scaffold for the biomedical applications with enhanced intensity/bioactivity and controlled resorption rates.

Through microcalorimetric analysis of the precipitation process of CaCO3 in solutions, it is revealed that amorphous calcium carbonate (ACC) forms at the initial stage as a transient phase and finally transforms into crystalline phase. Due to the lowest dissolvability of calcite compares with other polymorphs, the transformation from the metastable phase to calcite is an endothermic process in this research. L-Asp can induce and stabilize the existence of vaterite, meanwhile, it can accelerate the initial stage of precipitation as an accelerator.

Acidic amino acids, such as aspartic acid (l-Asp) and glutamic acid, are the primary bioactive molecules of the glycoprotein on the organic/inorganic interface of biomineralized tissues. In this study, the induction of chitosan film modified with l-Asp on the crystal growth of hydroxyapatite (HAP) was investigated by a novel in situ analysis approach, quartz crystal microbalance (QCM), associated with the dynamically structural and morphological characterization of precipitation products on various phases by X-ray diffraction (XRD), Fourier-transformed infrared (FT-IR) spectroscopy and scanning electron microscopy (SEM). The natural chitosan exhibited no inducing ability on the crystal growth of HAP. However, the growth rate of induced HAP was dramatically accelerated by the l-Asp modification of chitosan film and increased with the increase of the concentration of l-Asp in the chitosan substrate. It was shown that the chelation of calcium ion with l-Asp provided a nucleation centre and the cluster nuclei was formed by adsorbing further PO43−, Ca2+, and then HAP deposited on the original HAP coating in the supersaturated calcification solution (SCS). The developed method allows a kinetic evaluation of the induction of organic film on crystal nucleation and the growth of HAP in vitro.