Intrafibrillar Growth of Hydroxyapatite Nanocrystals in Multiscale Collagen

Abstract

Collagen fibrils hierarchically assemble from microscale to macroscale, which endows the natural composite bone with good mechanical properties and remodeling functions. Revealing the intrafibrillar growth process of hydroxyapatite nanocrystals of collagen will guide the research of bone repair or collagen-based composites. Herein, we investigated the mineralization of multiscale collagen matrices and strongly proved the intrafibrillar hydroxyapatite nanocrystals in the collagen fibrils. The hydroxyapatite nanocrystals were deposited within collagen fibrils with co-orientation along the (002) crystal plane, which is the longitude of the fibril. The whole growth process was captured by TEM to demonstrated the five stages of the intrafibrillar growth process of hydroxyapatite nanocrystals. The infiltration and transformation of amorphous calcium phosphate in isolated collagen fibrils are both demonstrated. The intrafibrillar growth process of hydroxyapatite nanocrystals in collagen film was also investigated, showing that the growth area of collagen films increased linearly with time and the growth process. By studying the in situ mineralization under different reaction conditions, the kinetic equation of the mineralized area of collagen film under each condition was obtained, and the optimal hydroxyapatite mineralized solution was proved to be a solution with polyacrylic acid of 50 μG/mL and a pH of 7.5. Our work provides more detailed information of the growth process of HAP nanocrystals during the mineralization of collagen at different scales and would contribute to future research on the formation process of more minerals in collagen.

The “Forgotten” Hydroxyapatite Crystals in Regenerative Bone Tissue Engineering: A Critical Review

“…SAED can be used to describe crystal orientation and composition, measure lattice constants, and determine any defects (Figure 4). Xue et al used both HRTEM and SAED for the characterization of intrafibrillar HA nanocrystals of MCFs in vitro [137]. The usefulness of XRD In the identification of HA crystals is undeniable.…”

Assembled collagen films modified using polyacrylic acid with improved mechanical properties via mineralization

“…The result indicated that the c-axis of the crystal was all parallel to the long axis of collagen fibers, which is similar to the collagen-mineral arrangement in nature. 5,24,57 In addition, the ultrathin section of PAA-COL + CPAM-SBF was prepared to expose its internal structure. The TEM image (Fig.…”