Facile
Preparation of Poly(lactic acid)/Brushite Bilayer
Coating on Biodegradable Magnesium Alloys with Multiple Functionalities
for Orthopedic Application
Recently
magnesium
and its alloys have been proposed as a promising
next generation orthopedic implant material, whereas the poor corrosion
behavior, potential cytotoxicity, and the lack of efficient drug delivery
system have limited its further clinical application, especially for
the local treatment of infections or musculoskeletal disorders and
diseases. In this study, we designed and developed a multifunctional
bilayer composite coating of poly(lactic acid)/brushite with high
interfacial bonding strength on a Mg–Nd–Zn–Zr
alloy, aiming to improve the biocorrosion resistance and biocompatibility
of the magnesium-based substrate, as well as to further incorporate
the biofunctionality of localized drug delivery. The composite coating
consisted of an inner layer of poly(lactic acid) serving as a drug
carrier and an outer layer composed of brushite generated through
chemical solution deposition, where a facile pretreatment of UV irradiation
was applied to the poly(lactic acid) coating to facilitate the heterogeneous
nucleation of brushite. The in vitro degradation results of electrochemical
measurements and immersion tests indicated a considerable reduction
of magnesium degradation provided the composite coating. A systematic
investigation of cellular response with cell viability, adhesion,
and ALP assays confirmed the coated Mg alloy induced no toxicity to
MC3T3-E1 osteoblastic cells but rather fostered cell attachment and
proliferation and promoted osteogenic differentiation, revealing excellent
biosafety and biocompatibility and enhanced osteoinductive potential.
An in vitro drug release profile of paclitaxel from the composite
coating was monitored with UV–vis spectroscopy, showing an
alleviated initial burst release and a sustained and controlled release
feature of the drug-loaded composite coating. These findings suggested
that the bilayer poly(lactic acid)/brushite coating provided effective
protection for Mg alloy, greatly enhanced cytocompatibility and bioactivity,
and, moreover, possessed local drug delivery capability; hence magnesium
alloy with poly(lactic acid)/brushite coating presents great potential
in orthopedic clinical applications, especially for localized bone
therapy.