Morphology, mechanical properties, and mineralization of rigid thermoplastic polyurethane/hydroxyapatite scaffolds for bone tissue applications: effects of fabrication approaches and hydroxyapatite size

Rigid thermoplastic polyurethane (TPU)/hydroxyapatite (HA) scaffolds were prepared with micro HA (mHA) and nano HA (nHA) particles, respectively, via the thermally induced phase separation method. The effects of solvent and co-solvent, addition of sodium chloride (NaCl) porogen, and HA particle size were studied together with the morphology, compressive properties, and mineralization behavior of the scaffolds. Depending on the solvent, co-solvent, or porogen used, different porous structures were produced. In particular, a ladder-like morphology was obtained when dioxane (Di) was used as the solvent, whereas an interconnected porous structure was obtained by using dioxane and deionized water (DiW) as co-solvents. Rectangular pores with interconnected channels on the pore walls were achieved by using NaCl crystals as porogens. The TPU/nHA scaffolds showed stronger compressive properties than the TPU/mHA scaffolds and the pure TPU scaffolds. The scaffolds prepared using dioxane and water as co-solvents exhibit the greatest compressive modulus. Furthermore, TPU scaffolds with nHA particles had the ability to form bone apatite when soaked in simulated body fluid (SBF). After being soaked in SBF for 3 weeks, the weight percentage of formed apatite in the TPU/nHA-DiW scaffold was 9.2 %wt of the initial TPU content. Preliminary cytotoxicity tests were conducted using NIH 3T3 fibroblast cells. The high survival rate of these cells and the mineralization behavior suggest biocompatibility and high potential of these composites being used in bone tissue engineering applications.