Effect of temperature, microstructure and intramolecular dynamics of fibrillary collagen on apatitogenesis in scaffolds

The structure and physicochemical properties of scaffolds obtained from collagen gel using connective tissue sheaths of paravertebral tendons of Wistar rats were studied. The scaffolds were obtained at 37 °C (filmy) and 6 °C (volumetric). During hardening, the scaffolds form globular and extraglomerular fractions, which is typical for collagen gels obtained from tendon membranes. The ratio of the fraction volumes is determined by the pore structure and kinking of collagen fibrils. In the filmy scaffold, closed-type pores with weakened kinking are formed, which leads to the dominance of the extraglomerular scaffold. In the volumetric scaffold, kinking is intensified, open-type pores are formed, which determines the dominance of the globular scaffold. The morphogenetic factors of dominant fraction formation are ordering and increased rigidity, while the subdominant fractions are chaotization and elasticization of collagen frameworks. Fibrillar collagen undergoes extra- and intrafibrillar mineralization in situ with structuring of calcium phosphates along the apatite direction. The micromechanical properties of scaffolds induce extrafibrillar synthesis and determine the direction of apatitogenesis: stoichiometric hydroxyapatite is synthesized on rigid matrices, while carbonate-hydroxyapatites are synthesized on loose ones. Intrafibrillar synthesis in combination with temperature determines the degree of crystallinity and the composition of cationic and anionic sublattices of hydroxyapatites. On matrices of fibrillar collagen with strengthened bonds of peptide and carbonate groups, stoichiometric hydroxyapatite is formed, the degree of crystallinity of which is moderated by temperature − the higher the synthesis temperature, the higher the degree of crystallinity and saturation with calcium would be. On matrices with weakened peptide and C−O bonds, carbonate-hydroxyapatites are formed, in which substitutions in the anionic sublattice are regulated by temperature: at elevated temperatures, CO₃^2– groups predominantly replace OH^–, and at lower temperatures, PO₄^3– groups.

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