Glutamic acid concentration dependent collagen mineralization in aqueous solution.

The aim of this research is to evaluate the effects of glutamic acid (Glu) on the process of collagen mineralization, the structure and property of mineralized composites. Collagen mineralization was initiated by introducing PBS to blended solutions containing 1 mg/mL collagen, 6 mmol/L calcium and Glu ranged from 0 to 550 mmol/L. The kinetic curves and quantitation analyses showed that Glu could delay the collagen mineralization, and reduce the crystalline size and the amount of hydroxyapatite. With the Glu concentration increased from 50 to 200 mmol/L, the collagen self-assembly was promoted, resulting in the improvement of hardness and thermal stability of mineralized composites. However, further increase in the Glu concentration to 400 mmol/L or above would significantly inhibit the self-assembly of collagen and reduce the hardness and thermal stability of mineralized composites. Scanning electron microscopy revealed that the diameter of collagen became thicker as the Glu concentration increased. Moreover, hydroxyapatite with spherical morphology was uniformly dispersed and well combined with collagen fibril at Glu concentration of 200 mmol/L. These results may provide a broader understanding of the potential mechanism of biomineralization and be critical in the design of biomimetic scaffolds for bone tissue engineering.

Stable and biocompatible hydrogel composites based on collagen and dialdehyde carboxymethyl cellulose in a biphasic solvent system.

Stable hydrogels with a mechanically strong matrix microenvironment are favorable biomaterials for three-dimensional cell culture. Acidic collagen solution is commonly combined with chemical crosslinkers for rapid network formation. Herein, dialdehyde carboxymethyl cellulose (DCMC) was selected as an optimal crosslinking reagent for its excellent biocompatibility and suitable chemical reactivity. Both shielding of electrostatic attractions between these two oppositely charged biomaterials and obtaining concentrated collagen solution were achieved using a novel biphasic acetic acid /1-ethyl-3-methylimidazolim acetate (AA/[EMIM][Ac]) solvent system. Hydrogel composites containing more crosslinks were obtained by increasing collagen concentrations (5-25 mg/mL), as confirmed by the improved mechanical properties, thermal denaturation temperature, anti-enzymatic ability and compact microstructure. Moreover, cell proliferation assay demonstrated that all the obtained DCMC-crosslinked collagen hydrogel composites ensures commendable biocompatibility. This study provides a promising strategy for manipulating stable and biocompatible hydrogel composites by blending concentrated collagen solution with DCMC in a biphasic solvent system.

Investigation on the behavior of collagen self-assembly in vitro via adding sodium silicate.

Silicon, a trace element found in human body, plays a critical role in the process of collagen self-assembly. In this study, the intermolecular interaction and fibrillogenesis process were investigated to understand the effects of various concentrations of sodium silicate (SS) on collagen self-assembly in vitro. Fourier transform infrared spectroscopy analysis indicated that the triple helical structure of collagen was not significantly affected by SS. Hydrophobic interactions and particle sizes of collagen aggregates, which were measured using pyrene fluorescence and dynamic light scanning, enhanced via adding 2 mM SS whereas decreased with further increasing concentrations (4-8 mM). Kinetic analysis revealed that an increase in hydrophobic interactions boosted collagen self-assembly in the presence of 2 mM SS. The inhibition of self-assembly with the addition of 4-8 mM SS, as illustrated by a reduction in the fibrillogenesis rate and turbidity, was potentially attributed to weak hydrophobic interactions and strong electrostatic repulsion. The observation of microscopy demonstrated that the fibrils exhibited the characteristic D-periodicity at 2 mM SS. The inhibitory effect of 4 mM SS was slight and the fibrils still formed, while the microstructure was consisted of clustered collagen aggregates as SS ≥ 6 mM owing to serious inhibition on collagen self-assembly.