Single-Phase, Antibacterial Trimagnesium Phosphate Hydrate Coatings on Polyetheretherketone (PEEK) Implants by Rapid Microwave Irradiation Technique

This Article reports the fabrication and evaluation of single-phase, silver-doped trimagnesium phosphate hydrate (Ag-TMPH) nanosheet coatings on polyetheretherketone (PEEK), a well-known material used to fabricate orthopedic and spinal implants. While PEEK has better biomechanical compatibility with bone compared to metallic implants, it is also quite inert. Therefore, it is a common practice to coat PEEK implants with conventional calcium phosphates (CaPs) to enhance cell attachment, proliferation and differentiation. As opposed to well-studied CaP compounds, relatively less-explored magnesium phosphates (MgPs) are also becoming interesting orthopedic biomaterials and is the prime focus in this research. The novel aspects of this paper are as follows. First, we report developing TMPH coatings within minutes with the help of microwave irradiation technology. Microwave irradiation plays an important role in the coating formation with accelerated kinetics. Scanning electron microscopy (SEM) confirmed the fabrication of approximately 650 nm thick TMPH coatings. The coatings resulted in submicron level surface roughness and in vitro cell studies confirmed enhanced MC3T3 cell adhesion within 4 h on such surfaces. The coatings also resulted in significant apatite formation after immersing in simulated body fluid for 7 days. Second, multifunctionality was achieved by doping TMPH coatings with Ag, thus rendering the coatings antibacterial. The antibacterial properties were evaluated against two most common infection-causing bacterial strains—Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus. The results indicated good bacterial resistance and bactericidal properties of the Ag-TMPH coatings. Third, in spite of Ag doping, the single-phase nature of the coatings were retained (without forming composite systems) with the help of the low-processing temperature of the microwave irradiation. The inductive coupled plasma technique confirmed that the doped single-phase TMPH coatings supported a uniform and controlled release of Ag+ ions over a period of 3 weeks. MTT assay evaluations and SEM micrographs confirmed no signs of cytotoxicity and healthy proliferation of cells in all cases. Quantitative real time PCR (qRT-PCR) indicated a significant rise in collagen (Col1) and osteocalcin (OCN) gene expression levels in the case of TMPH coated PEEK. Thus, microwave irradiation was successfully employed in forming multifunctional, that is, bioactive, cytocompatible, and antibacterial MgP coatings on PEEK.