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
strainsGram-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.
Biomimetic coating process is one of the most versatile techniques developed for coating various orthopedic implant surfaces. The surface of an orthopedic implant, whether it is biodegradable or non-biodegradable, needs to be bioactive for osseointegration (direct bonding with bone). The above mentioned coating technique is employed to deposit a bone-like apatite (calcium phosphate) on the implant surfaces, so that the implants become more bioactive, resulting in osseointegration. Simulated body fluids (SBFs) play a critical role in this method. This short review describes and critiques the progresses made in this field by focusing on: 1) the compositional aspects of various SBFs; 2) the strategies to enhance the coating kinetics; and 3) examples of coating various types of surfaces of implants fabricated from polymers and metals, both biodegradable and non-biodegradable in nature.
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