Hydroxyapatite nanoparticles in situ grown on carbon nanotube as a reinforcement for poly (ε-caprolactone) bone scaffold

The incorporation of carbon nanotubes (CNT) and hydroxyapatite (HA) into biopolymer as bone scaffold is expected to combine the excellent mechanical properties of CNT and bioactivity of HA. However, the dispersion of CNT and HA in biopolymer is a challenge. In this paper, under the condition of hydrothermal reaction, HA nanoparticles were in situ synthesized on the surface of carboxyl multi-walled CNT to prevent their aggregation in poly (ε-caprolactone) (PCL) scaffold prepared by selective laser sintering (SLS). The mechanism of in situ synthesis of HA nanoparticles was that the carboxyl functional groups of cCNT acted as anchor sites for Ca2+ deposition, and then Ca2+ attracted HPO42− via electrovalent bonding to in situ nucleation and synthesis of HA nanocrystals. The results demonstrated that HA nanoparticles ranged from about 10 to 30 nm in diameter and 40–80 nm in length were homogeneously generated on the surface of cCNT. Compared with the pure PCL scaffold, the scaffold with contenting of 12% cCNT-HA was increased by 86.6% and 31.9% in tensile and compressive strength, respectively. The strengthening mechanisms could be explained from the bridging and pulling out of the cCNT-HA. Meanwhile, the mineralization experiment results demonstrated that the Ca/P ratio of apatite layer formed on the surface of the PCL/12% cCNT-HA scaffold was 1.66, which was close to that of human bone tissue, indicating the scaffold possessed good bioactivity for inducing the formation of apatite mineralization. Besides, the scaffolds displayed good cytocompatibility for cell attachment, growth and proliferation.