The aim of this work is to study the effects of the titanium plasma spray (TPS) coating process on the fatigue resistance of a titanium-6Al-4V substrate. The combination of TPS processes and Ti alloy substrate is widely applied on components intended for cementless total hip replacement (THR). In order to understand the coating process mechanism behind the implants’ fatigue resistance decrease, one air-developed coating (Ti-APS) and one controlled atmosphere developed coating (Ti-CAPS) were considered. The effects of the most representative parameters of the plasma spray process on the fatigue resistance were analysed: the sandblasting process, the plasma and the coating powder. Fatigue resistance studies were performed by means of rotating bending fatigue testing. After fatigue failure specimens underwent morphological analyses both on the primary crack surface and on the cross-sectional area complemented by of the metallographic analyses of the coating. The titanium substrate fatigue resistance decreased after being blasted with direct relationship with the grain size. Ti-CAPS process showed a relatively limited further influence on the fatigue resistance reduction with respect to only sandblasted samples. By contrary a remarkable fatigue limit decreased was seen for Ti-APS coated samples against Ti-CAPS and simply sandblasted samples. The experiment pointed out the critical importance of cracks oxidation as a fatigue failure driving factor.

Cold Gas Spray (CGS) technology has allowed the development of biofunctional composite coatings composed of 45S5 and Polyetheretherketone (PEEK). The combination of a bioactive glass material embedded in a biocompatible polymeric matrix becomes this new composite in an interesting material for orthopedic applications since meet the biomechanical and biological requirements of an artificial implant. In the present study, blends of bioactive glass 45S5 and PEEK powder with different granulometry and 45S5/PEEK ratio have been prepared. These mixtures of powders have been deposited onto PEEK substrates by CGS with the goal of incorporating a bioactive additive to the biocompatible polymer, which can improve the bone-implant interaction of PEEK. The deposition efficiency (DE) and thickness of the coatings have been evaluated and from the results obtained, it was possible to conclude that DE and coating thickness are significantly affected by the granulometry and by the 45S5/PEEK ratio of the blends. By Scanning Electron Microscopy (SEM) inspection, it was observed that the use of blends with high 45S5/PEEK ratio led to the deposition of coatings with high content of 45S5 particles embedded in the polymeric matrix. Finally, the friction behavior of the coatings was analyzed performing ball-on-disk tests and these experiments showed that the presence of glass particles has a beneficial role in the wear resistance of the coatings.

In this work, two agglomerated hydroxyapatite (HA) powders, with and without heat treatment, were cold sprayed using various spraying parameters on metallic (Ti-6Al-4V) and polymeric (PVA) substrates. The structure of the agglomerated powders and corresponding features of the coatings were examined. For both types of substrates, it was shown that submicron HA powders produce homogenous layers with submicron HA grains. In the case of non-heat treated particles, thick layers could be obtained due to the binding action of residual by-products. HA layers were also found to be adherent after immersion in water, which could potentially lead to the fabrication of ceramic coated hydrogels.

Previous studies have shown that nanostructured coatings produced by plasma spraying can stimulate cellular activity and promote bone healing. Since then, a number of studies have been conducted to better understand how coating nanotopography can be controlled and how it influences bioactivity and healing. This paper reviews some of the key findings in three areas: the effects of nanotopography on bone cell adhesion, the effects of nanotopography on bone-like apatite formation in simulated body fluid, and how to refine the nanotopography of plasma-sprayed coatings.

In this study, hydroxyapatite (HA) and HA-SiO 2 coatings are applied to unalloyed Ti by atmospheric plasma spraying and corrosion resistance is assessed by immersion in Ringer’s solution for 24 h. The results show that the HA coating improves corrosion resistance, which is further improved with the addition of SiO 2 . An analysis based on Scherrer’s equation confirms an observed increase in crystallite size in the coated samples.

This work serves as a proof-of-concept for the application of plasma sprayed hydroxyapatite (HA) coatings on biopolymer implants. In the absence of a conventional plasma sprayer, coating samples were produced by manually injecting HA powder into a plasma cutting torch fitted with a custom made nozzle. Using the improvised setup, hydroxyapatite was successfully deposited on PLA, PEEK, and PVA discs as well as Al and Ti substrates. The coatings were characterized by thermal imaging and scanning electron microscopy, and the results are presented and discussed.

This paper presents a summary of some of the research conducted on sponge-like titanium coatings developed for orthopedic use. It assesses the pore structure, adhesion properties, and in-vitro and in-vivo biological characteristics of porous titanium coatings deposited by vacuum plasma spraying on metals, PEEK polymer, and two bioceramics, Mg-toughened ZrO 2 and ZrO 2 -toughened Al 2 O 3 . The plasma sprayed coatings show good flexibility in terms of pore size (100-800 µm), overall porosity (40-70%), and coating thickness (600-1500 µm).

Effect of different thickness of bio-medical coatings on the bone stress distribution near the hip implant- bone interface is very important factors for the bio-coated implant design and clinical application. However, in the traditional finite element analysis, the muscle forces have not been considered, which results in a difference between the original analysis models from the actual condition. In this study, the hip contact forces, as well as the associated muscle forces are imposed. Wollastonite coatings and titanium alloy (Ti6Al4V) for implants are used in the model, which is constructed through using SolidWorks software. The bone and coating stress distributions near the hip implant coated with different thickness from 50 to 250 µm are calculated and analyzed by means of finite element analysis by ANSYS WORKBENCH Software. After hip replacement, the von Mises stress distribution is similar to that before the total hip arthroplasty, whereas the corresponding results decrease obviously. Effect of coating thickness has an indistinct influence on the bone stress near the hip implant.

This research aims at introducing new biodegradable/non-biodegradable materials (biopolymers) to the existing Hydroxyapatite (HA)-titanium combination or as a single coating in order to overcome some of the limitations of HA coatings. Biopolymers can act as drug carriers for a localised drug release following implantation; they can also have a structural role by improving the mechanical performance of implants at the bone –implant interface. The proposed materials consisted of biodegradable and non-biodegradable polymers widely used as drug delivery systems: polymethylmethacrylate and polyhydroxybutyrate 98%/ polyhydroxyvalerate 2%. The method used to apply the polymeric powders was oxygen/acetylene flame spraying, due to its superior mechanical advantages over other techniques. Screening tests were used to determine the suitable range of spraying parameters, followed by optimisation to understand of the effects of spraying parameters on coating characteristics (thickness, roughness, adhesion, wettability), in order to obtain an optimal coating design. The polymers were sprayed onto bare titanium substrates. FTIR results showed that the coatings underwent little chemical degradation. Biocompatibility tests showed that cells proliferated well on flame sprayed polymer coatings, which confirms that the coating technique used did not affect the biological performance of the material.

A primary goal in modern orthopaedics is increasing the rate and long-lasting anchoring of implants in the human body. Hydroxyapatite, having a chemical structure and chemistry that is identical to bone, significantly enhances the on growth and subsequent ingrowth of natural bone material. Nevertheless some aspects of the performance of hydroxyapatite coatings have not been investigated sufficiently; for example the in vivo, long-term behaviour of the material, including the time-dependent dissolution accompanied by changes of mechanical properties have been poorly documented. The current study creates an idealized, virtual microstructural coating model that examines the time-dependent behaviour and properties of hydroxyapatite coatings. The analyses examine time vs. dissolution dependencies that reflect in vivo behaviour.

In this study, titania and hydroxyapatite nanopowder mixtures are deposited on medical grade titanium substrates by HVOF spraying. To assess bioperformance, human mesenchymal stem cells (hMSCs) were cultured from 1 to 21 days on the surface of HVOF-sprayed TiO 2 and TiO 2 -HA samples. Plasma sprayed HA and uncoated Ti-6Al-4V substrates were used as controls. The active cultures were evaluated for cell proliferation, cytoskeleton organization, and cell-substrate interaction. The results for HVOF-sprayed TiO 2 -HA nanocomposite coatings show strong evidence of bone growth, proliferation, and attachment with cell-substrate interaction levels superior to those of air plasma sprayed HA coatings. Although there are no clear explanations for this favorable behavior, the topography and chemical composition of the surface of the coating appear to be playing important roles.

In this investigation, bioactive ceramic materials, including dicalcium silicate, titania, and zirconia, were deposited on titanium substrates by plasma spraying in order to determine their effect on the bioactivity of metal implants. Cell-seeding tests show that MG63 osteoblast-like cells grow and proliferate well on each of the coating materials. In the case of Ca 2 SiO 4 , the presence of silicon ions is thought to be the key to this behavior. In regard to TiO 2 and ZrO 2 , the bioactivity is thought to result from the nanostructured surfaces and special surface compositions.

HA-coatings have been widely used in human surgery to increase the biocompatibility of metal alloys used as arthroplasty material. Their characteristics are of fundamental importance for their behaviour in the organism and in particular their degradation rate. We had the opportunity to perform histological analysis of human femurs containing well functioning HA-coated hip prostheses implanted for various periods from a few days up to several years. It was showed that the coatings exhibit degradation signs very early after the implantation and the released debris have different fates depending their size and shape. These results can be compared with those obtained in animals or in vitro. It was shown that the bone tolerate the contaminant phases which can be formed during the plasma spraying.

Nanostructured titania (TiO 2 ) coatings were produced by high velocity oxy-fuel (HVOF) spraying. They were engineered as a possible candidate to replace hydroxyapatite (HA) coatings produced by air plasma spray (APS) on implants. They exhibited mechanical properties, such as hardness and bond strength, much superior to those of APS HA coatings. In addition to these characteristics, the surface of the nanostructured coatings exhibited regions with nanotextured features originating from the semi-molten nanostructured feedstock particles. This nanotexture is considered an asset, due to its better interaction with the adhesion proteins of the osteoblast cells, such as fibronectin, which exhibit dimensions in the order of nanometers. Osteoblast cell culture demonstrated that this type of coating supported osteoblast cell growth and did not negatively affect cell viability.

The crystallinity of hydroxyapatite (HA) coatings used in femoral implant applications is a crucial factor. A coating containing a large percentage of amorphous phases will dissolve quickly. This leaves the coating mechanical weak and thus reduces its functional life. The crystallinity of the final coating largely depends on the parameters selected during the spraying process. In this study the design of experiment technique was used to investigate the parameters that have the greatest effect on the crystallinity of the coating. The effect of furnace heat treatment in air at 600°C, 700°C and 800°C on the crystallinity of the coating was also investigated. The coatings were analysed using scanning electron microscopy (SEM) and X-ray diffraction (XRD).

One of the largest successes of modern medicine is the total hip replacement. Presently this procedure has one of the highest success rate among surgical interventions, only second to the appendix removal procedure. However the lifetime of the prosthesis itself is still limited to 10 to 20 years, which means that for numerous patients replacement of the procedure will become mandatory. This replacement finds its origin in aseptic loosening of the prosthesis mainly caused by the formation of wear particles at articular joints and by the difference in stiffness between the bone and the metallic prosthesis leading phenomena called stress shielding. To overcome this problem, new designs of more biomimetic prostheses, with stiffness similar to that of cortical bone, are being studied. Among the latter, a novel design based on polymer composite materials of total hip replacement prosthesis is under development. One of the key characteristics of this biomimetic prosthesis is its hydroxyapatite coating, which permits Osseo integration (integration into the bone). Thermally sprayed hydroxyapatite coatings are already used successfully for metallic implants, but plasma sprayed hydroxyapatite coatings have yet to be developed for polymer composites due to quite challenging heat management and adhesion concerns. This paper describes and discusses the optimization of the plasma sprayed technique and the formation of the adequate underlayer enabling the plasma spray on highly heat sensitive substrate. Adhesion, shear and fatigue results are presented. Abstract only; no full-text paper available.

Crystallized calcium carbonate, CaCO 3 , is a mineral phase that occurs in nature as aragonite. It is well known that CaCO 3 shows excellent chemical interaction and intensive binding in direct contact to bone structures. This paper discusses the development of a plasma spraying process that shows promise for producing dense calcium carbonate layers with good adhesion properties. Tests reveal that the resulting coatings are fully biocompatible and have faster resorption times than plasma sprayed hydroxyapatite. Paper includes a German-language abstract.

Ultra-fine hydroxyapatite powders were successfully synthesized using radio frequency (RF) suspension plasma spraying (SPS). This novel technique utilises the inherent characteristics of the RF plasma to axially feed and spheroidise a liquid suspension to produce spherical ultra-fine HA powders. This offers an alternative approach over conventional D.C. and flame spheroidising techniques which are better suited for solid feed stocks. Rietveld analysis was subsequently applied using Rietquan Quantitative Analysis software package to determine the amount of decomposed phases and amorphous content of the as-sprayed powder. This was also compared against quantitative XRD analysis employing internal and external standards. However, pure phases needed for calibration is scarce and amorphous calcium phosphate (ACP) is virtually impossible to isolate. In addition, the long and laborious task of obtaining calibration curves makes this technique unpopular. Nevertheless, conventional quantitative phase analysis (QPA) was carried out, using relative peak height ratios of HA and the phase involved, but the calculated decomposition only shows relative trends for a particular parameter variation. Determining the actual phase content is critical because of possible variations in biological responses when used as coatings and inserts in restorative orthopaedic implants. Varying tissue responses can arise from decomposed phases such as α and β-tricalcium phosphate (TCP) and tetra-calcium phosphate (TTCP) as well as ACP which generally have higher solubility as compared to crystalline. QPA via the Rietveld method provides a powerful tool that offers the user simultaneous quantitative phase determination of multiphase systems containing amorphous content. Unlike XRD QPA, the amorphous content could be indirectly calculated using crystalline alumina standard. XRD QPA results showed that decomposition generally rose with plate power without considering the amorphous content. With Rietveld QPA, the results showed an initial rise in decomposition before decreasing at higher plate powers. The amorphous phase content was calculated at different plate powers and concentration of suspension with the aid of alumina as an external standard. Results showed that the amorphous content increased substantially at higher powers. This study demonstrates the ability of Rietveld analysis to completely quantify all associated amorphous and crystalline phases within a multiphase system for any thermally treated material.

This paper compares two types of hydroxyapatite (HA) composite coatings, HA/Ti-6Al-4V and HA/Y-ZrO2. The powders used in the study were prepared using a slurry process then deposited by plasma spraying. The resulting coatings were characterized based on their microstructure, mechanical properties, and biocompatibility. Both composite coatings performed better than pure HA coatings in tensile adhesion and indentation tests. Testing also revealed that the HA/Y-ZrO2 coatings had favorable strength and fracture toughness and that the HA/Ti-6Al-4V coatings had good affinity to living tissue and sufficient mechanical strength.

Only one material is used for thermally sprayed layers in medical technology: hydroxyapatite. This is considered to be stable for long-term and is being used more and more in endoprosthetics. This paper presents and examines a previously unused material, calcium carbonate, for its suitability for injection-molding processing. The first in-vitro results round off the very positive results so far. Paper includes a German-language abstract.