Hydroxyapatite needle-shaped particles/poly(l -lactic acid) electrospun scaffolds with perfect particle-along-nanofiber orientation and significantly enhanced mechanical properties

Electrospun hydroxyapatite (HA)/biopolymer fibrous composites have attracted much interest in the field of hard-tissue engineering. Unfortunately, poor mechanical property is a continuing problem and limits their usefulness in many applications. In this study, we attempted to improve the mechanical strength, modulus, and toughness of the HA/poly(l-lactic acid) (PLLA) electrospun scaffold by aligning the needle-shaped HA particles within the PLLA nanofibers. Three types of HA particles with different aspect ratios and sizes were incorporated into PLLA nanofibrous scaffolds with a random or aligned fibrous assembly. It was the first time that the needle-shaped HA particles with high aspect ratios were perfectly oriented along the long axes of the nanofibers. All HA particles significantly enhanced the tensile modulus, strength, and toughness of the corresponding scaffold, but to different extents. The dramatic reinforcement effects for different morphologies were rationalized using the Halpin-Tsai and shear-lag models for composites.