Compounding of hydroxyapatite crystals to molecularly aligned crab tendon chitosan: the effect of heat treatment

The aim of this study was to demonstrate the effect of heat treatment on the formation of hydroxyapatite crystals in molecularly aligned chitosan. Molecularly aligned chitosan was prepared from crab (Macrocheira Kaempferi) tendons by treatment with ethanol and a 4 wt.% NaOH solution to remove proteins and calcium phosphate, subsequently performed was deacetyl treatment using a 50 wt.% NaOH solution at 100 °C. The tendon chitosan (t-chitosan) obtained was compounded with hydroxyapatite (HAp) before and after heat treatment by applying an alternate soaking method. The amount of compounded HAp to t-chitosan before heat treatment was larger than that after heat treatment as shown by thermogravimetric and differential thermal analysis (TG-DTA) analysis. The HAp compounded to t-chitosan before heat treatment was distributed on the whole area as shown by energy dispersive X-ray spectroscopy (EDS) analysis. On the other hand, the compound after heat treatment was distributed only on the surface of t-chitosan. The compounded HAp crystals to t-chitosan before heat treatment were aligned in the horizontal direction to t-chitosan molecules as shown by transmission electron microscopy (TEM) and electron diffraction technique. These results suggest the control of crystallographic orientation in HAp by aligned amino groups.