Development of porous chitosan/tripolyphosphate scaffolds with tunable uncross-linking primary amine content for bone tissue engineering

Highlights: • Porous chitosan/TPP scaffolds were fabricated with controlled amine content. • The ionic-dependent solubility of chitosan was applied. • The amine content was important in pH-responsive protein loading and release. - Abstract: The primary amine along the chitosan backbone plays a key role in biomedical applications. Although chitosan-based porous scaffolds have been widely used in tissue engineering, it remains very challenging to regulate uncross-linking primary amine content (C_N) in scaffolds in order to realize particular mechanical and biological properties. In the present study, chitosan/tripolyphosphate (TPP) scaffolds with controlled C_N (i.e., degree of cross-linking) were prepared based on the ionic-dependent solubility of chitosan together with the freezing process. The effects of the concentration of TPP (C_TPP) and NaCl (C_NaCl) in the cross-linking solution on C_N were studied by infrared spectroscopy, ninhydrin assays and elemental analysis. The results showed that C_N decreased with increasing C_TPP and decreasing C_NaCl. C_N affected physicomechanical properties such as swelling behavior and the mechanical strength of the chitosan/TPP scaffolds. The uncross-linking primary amine in scaffolds can be used for chemical and biological modifications. The protein loading of the scaffolds demonstrated that the pH-responsive adsorption and release behavior was influenced by C_N. Cell experiments also illustrated that C_N affected the proliferation of bone marrow mesenchymal stem cells (BM-MSCs). All of these results indicate that these porous chitosan/TPP scaffolds containing uncross-linking primary amines are potentially useful for applications in regenerative bone medicine.