Roman A. Surmenev

Significance of calcium phosphate coatings for the enhancement of new bone osteogenesis – A review ☆

A systematic analysis of results available from in vitro, in vivo and clinical trials on the effects of biocompatible calcium phosphate (CaP) coatings is presented. An overview of the most frequently used methods to prepare CaP-based coatings was conducted. Dense, homogeneous, highly adherent and biocompatible CaP or hybrid organic/inorganic CaP coatings with tailored properties can be deposited. It has been demonstrated that CaP coatings have a significant effect on the bone regeneration process. In vitro experiments using different cells (e.g. SaOS-2, human mesenchymal stem cells and osteoblast-like cells) have revealed that CaP coatings enhance cellular adhesion, proliferation and differentiation to promote bone regeneration. However, in vivo, the exact mechanism of osteogenesis in response to CaP coatings is unclear; indeed, there are conflicting reports of the effectiveness of CaP coatings, with results ranging from highly effective to no significant or even negative effects. This review therefore highlights progress in CaP coatings for orthopaedic implants and discusses the future research and use of these devices. Currently, an exciting area of research is in bioactive hybrid composite CaP-based coatings containing both inorganic (CaP coating) and organic (collagen, bone morphogenetic proteins, arginylglycylaspartic acid etc.) components with the aim of promoting tissue ingrowth and vascularization. Further investigations are necessary to reveal the relative influences of implant design, surgical procedure, and coating characteristics (thickness, structure, topography, porosity, wettability etc.) on the long-term clinical effects of hybrid CaP coatings. In addition to commercially available plasma spraying, other effective routes for the fabrication of hybrid CaP coatings for clinical use still need to be determined and current progress is discussed.

Preparation of a silicate-containing hydroxyapatite-based coating by magnetron sputtering: structure and osteoblast-like MG63 cells in vitro study

Silicate-containing hydroxyapatite-based coatings with different structure and calcium/phosphate ratios were prepared by radio-frequency magnetron sputtering on silicon and titanium substrates, respectively. Scanning electron microscopy, X-ray diffraction and IR spectroscopy were used to investigate the effect of the substrate bias on the properties of the silicate-containing hydroxyapatite-based coatings. The deposition rate, composition, and microstructure of the deposited coatings were all controlled by changing the bias voltage from grounded (0 V) to −50 and −100 V. The biocompatibility was assessed by cell culture with human osteoblast-like cells (MG-63 cell line), showing a good biocompatibility and cell growth on the substrates.

In-vitro investigation of magnetron-sputtered coatings based on silicon-substituted hydroxyapatite

Silicon-containing calcium phosphate (Si-CaP) coatings on titanium and austenite steel substrates have been prepared by method of high-frequency magnetron sputtering. The powder of silicon-containing hydroxyapatite Ca10(PO4)6 − x(SiO4)x(HO)2 − x (Si-HA), where x = 0.5 obtained using a mechanochemical technique, was used as a target material. The obtained coatings were X-ray amorphous; the elemental composition of the coatings depended on the composition of the target to be sputtered. The coatings were heated in air for 3 hours to the temperature 700°C with the aim of changing their structure. The bioactivity of the coatings was studied using in-vitro tests. The solution of the simulated body fluid (SBF) oversaturated with respect to HA was used as a model medium. The phase elemental composition and morphology of the deposited and annealed Si-CaP coatings before and after submersion into the solution were controlled using the methods of X-ray diffraction (XRD), energy-dispersive X-ray analysis (EDAX), and scanning electron microscopy (SEM). According to the XFA and IR-spectroscopy data, heat treatment in the air yields the formation of an apatite-like phase in the coating. Thermostating of “metal + coating” specimens in the solution of simulated body fluid revealed that all obtained coatings were biologically active, and a calcium phosphate layer was formed on the coating surface during mineralization. The annealed coatings show a higher chemical stability under physiological conditions as compared to amorphous coatings.

Nano-hydroxyapatite-coated metal-ceramic composite of iron-tricalcium phosphate: Improving the surface wettability, adhesion and proliferation of mesenchymal stem cells in vitro

Thin radio-frequency magnetron sputter deposited nano-hydroxyapatite (HA) films were prepared on the surface of a Fe-tricalcium phosphate (Fe-TCP) bioceramic composite, which was obtained using a conventional powder injection moulding technique. The obtained nano-hydroxyapatite coated Fe-TCP biocomposites (nano-HA-Fe-TCP) were studied with respect to their chemical and phase composition, surface morphology, water contact angle, surface free energy and hysteresis. The deposition process resulted in a homogeneous, single-phase HA coating. The ability of the surface to support adhesion and the proliferation of human mesenchymal stem cells (hMSCs) was studied using biological short-term tests in vitro. The surface of the uncoated Fe-TCP bioceramic composite showed an initial cell attachment after 24h of seeding, but adhesion, proliferation and growth did not persist during 14 days of culture. However, the HA-Fe-TCP surfaces allowed cell adhesion, and proliferation during 14 days. The deposition of the nano-HA films on the Fe-TCP surface resulted in higher surface energy, improved hydrophilicity and biocompatibility compared with the surface of the uncoated Fe-TCP. Furthermore, it is suggested that an increase in the polar component of the surface energy was responsible for the enhanced cell adhesion and proliferation in the case of the nano-HA-Fe-TCP biocomposites.

Surface wettability and energy effects on the biological performance of poly-3-hydroxybutyrate films treated with RF plasma.

The surface properties of poly-3-hydroxybutyrate (P3HB) membranes were modified using oxygen and an ammonia radio-frequency (RF, 13.56 MHz) plasma. The plasma treatment procedures used in the study only affected the surface properties, including surface topography, without inducing any significant changes in the crystalline structure of the polymer, with the exception being a power level of 250 W. The wettability of the modified P3HB surfaces was significantly increased after the plasma treatment, irrespective of the treatment procedure used. It was revealed that both surface chemistry and surface roughness changes caused by the plasma treatment affected surface wettability. A treatment-induced surface aging effect was observed and resulted in an increase in the water contact angle and a decrease in the surface free energy. However, the difference in the water contact angle between the polymers that had been treated for 4 weeks and the untreated polymer surfaces was still significant. A dependence between cell adhesion and proliferation and the polar component of the surface energy was revealed. The increase in the polar component after the ammonia plasma modification significantly increased cell adhesion and proliferation on biodegradable polymer surfaces compared to the untreated P3HB and the P3HB modified using an oxygen plasma.

Enhancement of the mechanical properties of AZ31 magnesium alloy via nanostructured hydroxyapatite thin films fabricated via radio-frequency magnetron sputtering

The structure, composition and morphology of a radio-frequency (RF) magnetron sputter-deposited dense nano-hydroxyapatite (HA) coating that was deposited on the surface of an AZ31 magnesium alloy were characterized using AFM, SEM, EDX and XRD. The results obtained from SEM and XRD experiments revealed that the bias applied during the deposition of the HA coating resulted in a decrease in the grain and crystallite size of the film having a crucial role in enhancing the mechanical properties of the fabricated biocomposites. A maximum hardness of 9.04 GPa was found for the HA coating, which was prepared using a bias of -50 V. The hardness of the HA film deposited on the grounded substrate (GS) was found to be 4.9 GPa. The elastic strain to failure (H/E) and the plastic deformation resistance (H(3)/E(2)) for an indentation depth of 50 nm for the HA coating fabricated at a bias of -50 V was found to increase by ~30% and ~74%, respectively, compared with the coating deposited at the GS holder. The nanoindentation tests demonstrated that all of the HA coatings increased the surface hardness on both the microscale and the nanoscale. Therefore, the results revealed that the films deposited on the surface of the AZ31 magnesium alloy at a negative substrate bias can significantly enhance the wear resistance of this resorbable alloy.

A biodegradable AZ91 magnesium alloy coated with a thin nanostructured hydroxyapatite for improving the corrosion resistance

The main aim of this study was to investigate the properties of an AZ91 alloy coated with nanostructured hydroxyapatite (HA) prepared by radio frequency (RF) magnetron sputtering. The bioactivity and biomineralization of the AZ91 magnesium alloy coated with HA were investigated in simulated body fluid (SBF) via an in vitro test. Scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, and X-ray diffraction (XRD) analyses were performed. The samples were immersed in SBF to study the ability of the surface to promote the formation of an apatite layer as well as corrosion resistance and mass change of the HA-coated AZ91 alloy. Electrochemical tests were performed to estimate the corrosion behaviour of HA-coated and uncoated samples. The results revealed the capability of the HA coating to significantly improve the corrosion resistance of the uncoated AZ91 alloy.

Application of High-Frequency Magnetron Sputtering to Deposit Thin Calcium-Phosphate Biocompatible Coatings on a Titanium Surface

Thin calcium-phosphate coatings were deposited on titanium substrates by high-frequency magnetron sputtering. The elemental composition of coatings and types of chemical bonds were studied by Rutherford backscattering (RBS) and Fourier transform infrared spectroscopy (FTIR), respectively. An analysis of the IR spectra detected absorption bands caused by vibrations of phosphate PO43− groups and pyrophosphate H2PO4− anions, which are typical of apatites. The RBS results showed that the coating contains elements typical of calcium phosphates, i.e., Ca, P, and O; 45.4 ± 1.1, 3.6 ± 0.5, and 41.1 ± 0.7 at %, respectively. The Ca/P atomic ratio depends on sputtering conditions and varies in the range 1.7–4.0. The physicomechanical characteristics of the coatings and their solubility in a biological liquid were studied. The grown coatings can significantly reduce dissolution of substrates and extraction of dopants into the surrounding solution.

Incorporation of silver nanoparticles into magnetron-sputtered calcium phosphate layers on titanium as an antibacterial coating

A three-layer system of nanocrystalline hydroxyapatite (first layer; 1000nm thick), silver nanoparticles (second layer; 1.5μg Ag cm-2) and calcium phosphate (third layer, either 150 or 1000nm thick) on titanium was prepared by a combination of electrophoretic deposition of silver nanoparticles and the deposition of calcium phosphate by radio frequency magnetron sputtering. Scanning electron microscopy showed that the silver nanoparticles were evenly distributed over the surface. The adhesion of multilayered coating on the substrate was evaluated using the scratch test method. The resistance to cracking and delamination indicated that the multilayered coating has good resistance to contact damage. The release of silver ions from the hydroxyapatite/silver nanoparticle/calcium phosphate system into the phosphate-buffered saline (PBS) solution was measured by atomic absorption spectroscopy (AAS). Approximately one-third of the incorporated silver was released after 3days immersion into PBS, indicating a total release time of the order of weeks. There were no signs of cracks on the surface of the coating after immersion after various periods, indicating the excellent mechanical stability of the multilayered coating in the physiological environment. An antimicrobial effect against Escherichia coli was found for a 150nm thick outer layer of the calcium phosphate using a semi-quantitative turbidity test.

Adhesion properties of a silicon-containing calcium phosphate coating deposited by RF magnetron sputtering on a heated substrate

Silicon-containing hydroxyapatite coatings 400–700 nm in thickness are prepared by means of radio-frequency (RF) magnetron sputtering on a heated (to 200°C) titanium substrate chemically etched and treated with a pulsed electron beam. The morphology and phase composition of the coating are studied. The morphology and roughness of the composite “calcium-phosphate coating-titanium substrate” differ depending on the treatment procedure of the substrate before deposition. The scratch test method is used to assess the adhesion strength of the coatings formed at different values of bias potential applied to the substrate. It is observed that the adhesion strength of the coating changes with decreasing crystallite size.