Comparisons among Mg, Zn, Sr, and Si doped nano-hydroxyapatite/chitosan composites for load-bearing bone tissue engineering applications

In load-bearing bone tissue engineering (BTE), ionic doping is a promising strategy to make up for the inherent defects of hydroxyapatite (HAp). However, the influence of doped elements on the structures and properties of in vitro mineralized HAp has not been investigated in detail so far. In addition, no systematic investigations have been found comparing the properties of different kinds of element doped HAp-based organic/inorganic composites. In this work, the hydroxyapatite/chitosan composite (CS/HAp) and Mg, Zn, Sr, and Si doped hydroxyapatite/chitosan composites (Mg-CS/HAp, Zn-CS/HAp, Sr-CS/HAp, and Si-CS/HAp) were synthesized by using a facile in situ precipitation method. The impacts of different kinds of doped elements on the crystallinity, crystal morphology, and crystal structure of the mineralized HAp were carefully studied. In addition, we also investigated and compared the surface morphology, surface roughness, thermal stability, mechanical strength, and in vitro cytocompatibility of the five samples in detail. We anticipate that our work could shed new light on the influence of ionic doping on the mineralization of HAp and inspire researchers to prepare an HAp-based organic/inorganic composite load-bearing bone substitute in the future. The Si-doped hydroxyapatite/chitosan composite has advantages over Mg, Zn, and Sr doped hydroxyapatite/chitosan composites in terms of bone tissue engineering.