Effects of alkali pretreatment of silk fibroin on microstructure and properties of hydroxyapatite–silk fibroin nanocomposite

Nanocomposites comprising hydroxyapatite (HAp) and silk fibroin (SF) were synthesized from Ca(OH)2 suspension co-dispersed with SF fine particles and H3PO4 solution via a wet-mechanochemical route. The SF particles were modified with an alkali solution to increase contact points between HAp phase and SF matrix. HAp crystallites grow more preferentially along c-axis on alkali pretreated SF substrates. The composites exhibit porous microstructure with 70% of open porosity and about 70% of the interpores ranging from 40 to 115 μm in diameter. The peak shifts in amide II band of SF indicate that the chemical interactions between HAp crystals and SF matrix are intensified by the alkali pretreatment of SF. The stronger inorganic-organic interactions promote the formation of three-dimensional network extending throughout the composites, bringing about an increase of 63% in the Vickers hardness to the composite.