Enhancement of bone to polylactic acid plate bonding by carbonate apatite coating

Abstract

Polylactic acid (PLA) has no osteoconductivity, causing the early failure of PLA implants. For obviating this problem, coating, rather than incorporation, of PLA with calcium phosphate is considered to be effective. In this study, PLA plates were coated with granular carbonate apatite (CAp), the inorganic component of bone, using the thermal fusion bonding method. The water contact angles of the CAp-coated PLA (CAp/PLA) plates and PLA were 0.7° ± 0.1° and 90.3° ± 3.9°, respectively. Thus, CAp coating significantly improved the wettability of the PLA surface. Furthermore, the roughness (Ra) of CAp/PLA and PLA was 11.7 ± 2.2 μm and 1.8 ± 0.2 μm, respectively. CAp coating involved two types of micropores (~30–80 μm and ~2 μm). Thus, CAp coating provided a rough surface and micropores to the PLA plate. The CAp/PLA and uncoated PLA plates were fixed onto a rabbit tibial surface to evaluate their bone formation and adhesion abilities. Four weeks after implantation, new bone formed on the surface of the CAp/PLA plates. In contrast, no tissue was present in most of the regions between the uncoated PLA plate and the tibia. The tensile bond strengths of the CAp/PLA and PLA plates to the tibia were 4.0 ± 2.5 and 0 N, respectively. Thus, CAp coating of PLA promoted new bone formation on the plate surface and increased the ability to bond to the bone surface at an early stage. CAp coating of PLA is an effective strategy for achieving rapid and robust bone fixation.