One-step preparation of functionally hierarchical and structurally hierarchical biomimetic bioceramics composed of porous hydroxyapatite and carbon fiber reinforced hydroxyapatite composites

Abstract

Based on human bone structure characteristics and from the perspective of bionics, we designed and constructed hierarchical bioceramics which included porous hydroxyapatite (PHA) providing better bioactive functionality and carbon fiber (CF) reinforced hydroxyapatite (CF/HA) biocomposites with strengthened mechanical properties from the center to the outer part via one-step preparation. The effects of pore forming agent (NH4HCO3) and temperatures on the morphology, mechanical performance, biological properties were studied. The pore sizes of PHA were basically distributed from 20 μm to 200 μm. With the increase of NH4HCO3 contents, both the total number of the pores and interconnected pores increased, and internally connected small micropores were produced among the large pores. The compressive strength of PHA with 30 wt% NH4HCO3 (30%PHA) sintered at 1130 °C was 27.74 ± 0.52 MPa, which lay in the range of cancellous bone. In the hierarchical bioceramics, the interface between the PHA and CF/HA composites was so well bonded that it can be hardly distinguish the different regions in cross-section. The compressive strength of hierarchical bioceramics was 35.43 MPa, which increased by 27.7% compared with 30%PHA. Fracture toughness from the center to the outer part of the ceramics was 0.70 ± 0.15 MPa m1/2 and 1.37 ± 0.29 MPa m1/2, respectively. The high porosity favored the formation of apatite layer and improved the bioactivity compared with the dense hydroxyapatite (HA). The results of the expression of osteogenic genes (BMP2, Runx2, Opn and Ocn) detected by real-time PCR showed that the 30%PHA was positive to bone development. In vivo study indicated that the implanted PHA contributed to the ingrowth of more new bone tissue. This hierarchical bioceramics possess not only the enhanced mechanical properties but also excellent bioactivity and osteogenic properties. The study provides a promising biomimetic hierarchical bone repair materials which can tailor mechanical properties and bioactive functionality via simply adjusting constitution of CF reinforced and porous bioceramics.