Search Results for surgical

One cause of aseptic loosening of total hip replacement (THR) results from the hard polymetylmethacrylate (PMMA) bone cement debris embedded within some of acetabular cups [1]. To prevent this failure, PMMA can be replaced by a titanium coating with a specific roughness to promote the bone bonding. In this work, inert and atmospheric plasma spraying was used to coat Ti.6A1.4V implants with titanium.] In order to evaluate the effect of the deposition process on the coating corrosion resistance, different electrochemical techniques were implemented in physiological (i. e., Ringer) and in acidic solutions. Results show that the spraying parameters and the coating morphology affect the corrosion behaviour. Thus, if the reactivity is not affected by the pH evolution, the pitting sensitivity depends on the process. It was found that coatings deposited under inert gas are free of oxides and dense, even when the atmosphere contains some hydrogen. In that case a significant improvement of the intrinsic localized corrosion resistance is observed versus deposits obtained using atmospheric plasma spraying.

Fatigue properties of the Al 2 O3 plasma-sprayed SUS316L stainless steel rod specimens coated on different spraying conditions have been studied in a physiological saline solution (0.9 % NaCl solution) to evaluate the potential of surgical implant application. Fatigue tests were conducted in push-pull loading at the stress ratio of R = -1, and frequency of 2 Hz. Microstructure related with fatigue damage was examined by SEM and TEM. The fatigue strength of Al 2 O 3 plasma-sprayed metals significantly depended on spraying conditions: the effects of spraying on fatigue strength decreased with increasing the applied stress amplitude. As-blasted specimens were higher in fatigue strength than Al2O3 plasma-sprayed specimens. It was found that the plasma spraying had significant effects on fatigue crack growth behavior in the early stage of crack propagation. Fatigue cracks preferentially originated from dents that had been caused on the substrata metal surface subjected to grit-blasting. These results are discussed with both the compressive residual stresses due to the grit blasting which was carried out prior to plasma spraying and the corrosion-resistance of the alumina deposit.

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.

The SUS316L stainless steel rod specimen coated with plasma-sprayed Al 2 O 3 deposits has been fatigued in a physiological saline solution (0.9 % NaCl solution) to evaluate the potential of its application to prosthetic implant materials. Push-pull loading fatigue tests were conducted at the stress ratio of R = -1, and at the frequency of 2 Hz. Pure titanium powder was selected for undercoat. Fatigue damage was examined on longitudinal section of the specimen and fracture surface by optical and electron microscopy from the microstructural viewpoints. The plasma spraying of Al 2 O 3 powder has significantly improved fatigue properties of the substrate metal in the longer range of fatigue lives, compared with the results of the non-coated steel specimen. It was found from electrochemical experiments that titanium for undercoat metal has acted as sacrificial anode to protect the substrate metal from corrosive attack and under lower stress amplitudes the plasma sprayed Al 2 O 3 coating kept the solution out at an early stage of fatigue lives. Fatigue cracks preferentially originated from flaws, which had been caused on the substrate metal surface through grit blasting, and extended into the bulk of substrate metal. Fatigue cracks appear not to develop into plasma-sprayed deposits while the deposits could accommodate themselves to the crack opening displacement at the surface of substrate metal. It was understood that the plasma sprayed coating has enhanced fatigue properties in the solution both by keeping the solution out during the early stage of fatigue lives and by electrochemical effects of the undercoat metal when the topcoat was cracked in macroscopic scale.

HVOF has the potential to produce Hydroxyapatite HA (Bio-ceramic) coatings based on its experience with other sprayed ceramic materials. This technique should offer mechanical and biological results comparable to other thermal spraying processes such as plasma spray currently FDA approved for HA deposition. Deposition of HA via HVOF is a new venture especially using the Sulzer Metco Diamond Jet (DJ) process, hence the aim of this paper. In this research, a Design of Experiment (DOE) model as developed to optimize the HVOF process for the deposition of HA. Five parameters (factors) were researched over two levels namely: oxygen flow rate, propylene flow rate, air flow rate, spray distance and powder flow rate. Coating crystallinity and purity were measured as the responses to the factors used. The research showed that: propylene, air flow rate, spray distance and powder feed rate had the largest effect on the responses and the study aimed to find the desired optimised settings. This research found crystallinity and purity values of 93.8% and 99.8% respectively for a set of HVOF parameters which were improved findings compared to the crystallinity and purity of 87.6 % and 99.4 % respectively found using the FDA approved Plasma thermal spray process. Hence a new technique for HA deposition now exists using the DJ HVOF facility. Future research aims to evaluate the biological response to these coatings through in vitro tests.

In this paper, three goals are attacked, namely synthesis of nanostructured hydroxyapatite (HA) powder, obtaining HA phase constitution close to that of the bone hydroxyapatite, and preserving the initial HA composition and crystal structure in the sprayed coating. HA-aluminum composite coatings are produced using the cold gas dynamic spray method (CGDS). It is observed that the CGDS process enables the application of coatings without changing the phase composition of the HA, whereby the HA biocompatibility is retained. Paper includes a German-language abstract.

Titanium has an excellent corrosion property in chloride containing environments such as seawater. A modified HVOF spray process was developed by introducing a mixing chamber between the combustion chamber and the powder feed port. Nitrogen gas was fed into the mixing chamber to control the temperature of the combustion gas generated in the combustion chamber. By controlling the flow rate of nitrogen, various Ti coatings with different degree of oxidation and porosity could be fabricated. The densest coating produced by this process with surface polishing treatment maintained excellent corrosion protection over a steel substrate in artificial seawater in a laboratory test over 1 month.

New advanced polymeric biomaterials such as implantable poly(etheretherketone) (PEEK) are changing the face of the implantable medical device industry. Due to its bioactive behavior in vivo, hydroxyapatite (HA) coatings are used to improve the bone growth and to repair around metallic implant. The objective of this work is to study the feasibility of plasma sprayed hydroxyapatite coating on PEEK material. Different PEEK (unfilled and composite) specimens were successfully coated with a 150 µm thick coating. Chemical and crystallographic compositions, adhesions and microstructures of HA coatings on PEEK and on Ti-6Al-4V were compared. The results showed that the structure of HA coatings were appreciably equivalent. Mechanical tests showed that the plasma spraying process did not severely degrade the initial properties of the PEEK substrate.

Aerosol cold spraying (ACS) is modification of low-pressure cold spray technology which allows to deposit ceramic and metal-based coatings. ACS technology in vacuum possesses the formation of films from sub-micro and nanoparticles directly at room temperature. The ACS technology is still under development to cover more application and discover solutions of spraying different kind of powders on different types of material substrate and optimizing spraying conditions to obtain the best results. The main objective of the present work is to develop a new ACS cold spray technology of Hydroxyapatite (HA) and Copper powder deposition onto both the implants and ceramic substrates. The new AD spraying system with radial injection of particles to be deposited is constructed and tried. An influence of technology parameters on the coating structure and properties are presented. In addition, the combined cold spray and sintering technology technique is further investigated for additive manufacturing applications.

This work shows that hydroxyapatite (HA) can be cold sprayed simultaneously with titanium to form thick biocompatible coatings without compromising the phase constituents of the bioceramic material. XRD analysis indicates that the phase composition of the HA in the deposit is identical to that of the powder. The work also shows that very dense Ti and Ti-HA composite coatings can be produced using sponge Ti powders and nitrogen process gas. The adhesion strength of the cold-sprayed Ti-HA exceeded the reported values of comparable 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.

Plasma sprayed hydroxyapatite coating can bond to living bony tissue, and it is being widely used in clinical application. The problem of hydroxyapatite coating on metal substrate may mainly come from the instability of coating-substrate interface and the unstable duration of coating in the presence of body fluid. Therefore, it is desirable to develop newly bioactive coatings with good bioactivity and mechanical properties. In this paper, new progress in plasma sprayed bioactive coatings at Shanghai Institute of Ceramics are reviewed. The novel coatings including wollastonite, dicalcium silicate, diopside and titania were deposited. All the bioactive coatings mentioned above form a bone-like apatite layer on their surface immersed in simulated body fluid, indicating their good bioactivity. The formation of bone-like apatite is induced by Si-OH and Ti-OH on the surface of coatings. The results of cell culture test indicated that novel coatings can enhance osteoblast adhesion, proliferation and differentiation, indicating their good biocompatibility.

This work investigates the effects of cerium oxide (CeO 2 ) coatings on the response of osteoblasts to H 2 O 2 -induced oxidative stress. The results show that the coatings have a protective effect, promoting both osteoblast growth and differentiation. This indicates that the CeO 2 coating reduces the production of reactive oxygen species in H 2 O 2 -treated osteoblasts. These coatings, with their antioxidant properties, appear quite promising for bone regeneration.

In the current investigation plasma spray technique was used for depositing hydroxyapatite (HA) and hydroxyapatite – silicon oxide (SiO 2 ) coatings on 316L SS substrate. In HA-SiO 2 coating, 20 wt% SiO 2 was mixed with HA. The feedstock and coatings were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) / energy-dispersive X-ray spectroscopy (EDX) analyses. The corrosion resistance of the uncoated, HA coated and HA + 20 wt% SiO 2 coated 316L SS was investigated by electrochemical corrosion testing in simulated human body fluid (Ringer’s solution). After the corrosion testing, the samples were analyzed by XRD and SEM / EDX analyses. The addition of SiO 2 reduces the crystallinity of the coating. The corrosion resistance of the 316L SS was found to increase after the deposition of the HA + 20 wt% SiO 2 and HA coatings.

Instabilities in plasma spray jets can result in coatings with inconsistent properties. The arc root fluctuation and shear layer instability due to strong gradients are of foremost concern. The shear layer instabilities result from shear between the high velocity, low density hot core gas, the intermediate density and velocity boundary layer, and the high density quiescent environment. A cold-flow facility with density gradients similar to a plasma torch has been used for implementation of traditional fluid dynamics measurements such as hot-wire anemometry. Methods to control these instabilities are developed and tested using both the plasma torch and the cold flow facility. Through nozzle design modifications the instabilities resulting from arc root fluctuations and high density gradients have been reduced. The effectiveness of the control on the plasma jet is determined using in-flight particle characterization along with high speed imaging and photodiode measurements of the jet.

Spheroidization of powder particles is one of the successful commercial applications of induction plasma technology. A review is presented of case studies in which powder densification and spheroidization using induction plasma technology has played a key role in substantial improvement of powder quality and fluidity. Results are given for both metallic and ceramic powders at the pilot plant and industrial scale production. The presentation will cover both technical and economic features of the process. A detailed economic analysis of the process is presented for a production capacity of 15 and 30 kg per hour of tungsten carbide powder.

This study investigates the effect of composition on the antibacterial and antiviral properties of hydroxyapatite/titania composite coatings deposited by suspension plasma spraying. Hydroxyapatite is a bioceramic material used as a plasma-sprayed coating to promote osseointegration of femoral stems. TiO2 has promising photocatalytic activity and good efficiency in destroying bacteria, viral species, and parasites. Prior to coating, substrates were grit blasted, ultrasonically cleaned, and heated to enhance adhesion strength. The microstructure of the resulting coatings was then characterized using XRD and Raman spectroscopy. Test results indicated that SPS transformed Ti2O3 into TiO2 with mixed phases. Ti4O7 and Ti3O5 phases were also identified, which show photocatalytic activity due to oxygen vacancies. Antibacterial and antiviral tests were conducted as well.

Quasicrystalline phases improve many alloy properties such as thermomechanical stability, thermal and electrical conductivity, and tribological performance. High hardness, however, is accompanied by brittleness, an undesired property in many applications. Reduced brittleness can be achieved by embedding quasicrystalline phases in a more ductile material, forming a metal-matrix composite that retains some quasicrystalline properties. This study evaluates thermally sprayed coatings made from different compositions of such composites. The coatings assessed were produced by arc-wire, HVOF, and atmospheric plasma spraying using various forms of feed material, including blended, agglomerated, chemical encased, and attrition-milled powders and filled wires. The investigation involved metallurgical analysis, proving the existence of quasicrystal content and assessing the matrix phase, and tests showing how sliding wear is influenced by the composition of quasicrystalline phases.

Hydroxyapatite (HA) coatings are used to improve the adhesion of bone onto implanted devices. This approach increases the integrity and hence the lifetime of the implant. Several orthopaedic appliances (HA coated and macrotextured) were recovered from patients after revision surgery. The implants were cleaned and sterilised in ethanol or formaldehyde before being photographed and sectioned for analysis. X-ray diffraction indicated that the remaining coating was of high crystallinity. Micro textured areas such as ribbings and fenestrations subjected the coating to different modes of stress which has affected the coating. Adhesive failure was evident on implants attributed to dissolution of the amorphous phase at the interface. Observation of the microstructure with scanning electron microscopy showed that coating degradation begins at the surface where the coating is resorbed and continues along the substrate-coating interface thereby compromising interface strength. The microstructure and the dissolution of retrieved implants are discussed in relation to the general coating features in plasma sprayed HA coatings.

Quasicrystalline materials offer outstanding properties: High thermal stability in mechanical behaviour combined with special thermal and electrical conductivity as well as excellent tribological performance. High hardness is accompanied by heavy brittleness - an undesired property when looking for possible applications. A reduction of brittleness can be achieved by embedding quasicrystalline phases into a more ductile material to form a metal-matrix-composite material keeping some quasicrystalline properties. For thermal spraying blended, agglomerated, chemical encased or attrition milled powders as well as filled wires are processable to form such a metal-matrix-composite coating. The research work included spray trials using material-input prepared by the methods described. These different inputs have been processed in different compositions each. Spray trials have been processed by following techniques: Arc-wire-spraying, APS-spraying, wire-flame-spraying and HVOF-spraying. This paper gives an overview about HVOF-sprayed coatings with blended powders. On the one hand investigation were focused on metallurgical analysis for proving the existence of quasicrystal contents as well as determining adherence and embedding behaviour of the matrix-phase. On the other hand tests were centred onto the evaluation of the sliding-wear-behaviour in respect of interdependencies to the coatings composition and microstructure.