Dissolution-precipitation synthesis and cold sintering of mussel shells-derived hydroxyapatite and hydroxyapatite/chitosan composites for bone tissue engineering

In the present work, seafood by-products and derivates were exploited as raw materials to produce nano- crystalline calcium phosphates-based composites in light of the rising demand for waste recovery and valor- isation. Mussel shells were transformed into hydroxyapatite by dissolution-precipitation synthesis at 45 ◦C, whereas chitosan from shrimp shells was introduced as a reinforcing biopolymer to produce hydroxyapatite/ chitosan composites. The synthesised hydroxyapatite and hydroxyapatite/chitosan composite powders were cold sintered at room temperature under 1 GPa pressure for 10 min. The materials were consolidated up to ~90% relative density and characterized mechanically. By increasing the polymer content up to 10 wt%, the flexural strength of the sintered pellets increases from ~45 MPa to ~57 MPa while the hardness decreases from ~1.1 GPa to ~0.8 GPa, thus better addressing the mechanical properties of cortical bone. Furthermore, hydroxyapatite/ chitosan composites were proven to be bioactive, this demonstrating their potential use in bone tissue engi- neering applications