Key Engineering Materials Vols. 493-494

Abstract: This paper reports on the response of hydroxyapatite (HA) coatings, fabricated using two deposition technologies, to immersion in simulated body fluid (SBF). The deposition methods used were: plasma spray, a commercial standard, and CoBlast, a novel low temperature microblast technique. In the case of the latter, HA coatings are deposited by simultaneous blasting HA and abrasive powders concentrically at a metallic substrate, resulting in a thin layer of HA (approx. 2.5 µm thick). Groups of the CoBlast and plasma spray HA coatings were immersed in 7 ml of SBF solution for 1, 2, 4, 7, 14 and 28 days, and were subsequently removed and examined for any alterations caused by the SBF solution. It was noted from this study that the CoBlast HA coatings appeared to undergo a two step calcium phosphate recrystallisation process; initial homogenous nucleation and subsequent heterogeneous nucleation. Conversely recrystallisation on the plasma spray coatings appeared to proceed largely through a heterogeneous nucleation process. Two factors that may influence the differences in HA recrystallisation is the presence of amorphous HA resulting in rapid dissolution, and/or the significantly lower surface area (roughness) offered to the SBF solution by the CoBlast coatings. The interpretation of recrystallisation mechanisms from this preliminary study is limited however by the differences in coating morphology and thickness (27 versus 2 µm) for the plasma spray and CoBlast HA coatings respectively.

Abstract: The use of metallic nanoparticles in the field of orthopaedics as antimicrobial components of coatings is receiving particular attention. An innovative approach has been developed whereby various metal/metal oxide nanoparticles are used to prevent infection occurring on the surface of prostheses. In this study nano metallic oxides (zinc oxide - ZnO and tungsten oxide - WO₃) were used. Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values of each nanoparticulate were determined against four species of bacteria (Staphylococcus aureus, Escherichia coli, Staphylococcus epidermidis and Pseudomonas aeruginosa). Subsequently the nanoparticles were prepared in a suspension of ethanol and sprayed onto the surface of glass using electrohydrodynamic deposition. Quantitative assessments as regards the antimicrobial properties of these coated samples were carried out. Comparisons of the antibacterial properties demonstrated that 2500 µg/ml or above of the oxides were required to kill the species of bacteria tested. WO₃ was the most effective oxide tested in suspension using growth inhibition tests. However, coated samples demonstrated that ZnO was more bactericidal than WO₃ under these conditions.

Abstract: A coating layer with hierarchical structure: Titanium-Zinc-Phosphate (Ti-Zn-PO₄) / Hydroxyapatite (HAp) coating layer was prepared on titanium (Ti). The Ti plates were treated using two step hydrothermal treatments: first step in acidic zinc phosphate solution to form Ti-Zn-PO₄ coating and second step in calcium chloride solution to form HAp. The Ti-Zn-PO₄ layer strongly attached to the Ti surface. The adhesive strength of the coating layer was measured higher than 48 MPa. The surface observation and element analysis indicated that the Ti plates were covered with Ti-Zn-PO₄ coating layer after hydrothermal treatment at 250°C. When Ti-Zn-PO₄ coating was treated hydrothermally with calcium chloride solution, crystalline HAp layer was formed on its surface.

Abstract: The purpose of the present study was to evaluate the role of bioactive surface coating and geometric design of orthopedic implants. In return, a 3-dimensional model with a interconnected macroscopic por system (IMPS) was designed. The model was created by using the place holder method with titanium powder and ammonium bicarbonate. After sintering one group of the IMPS-model was penetrated with plasma to create hydophilic surface. The second group was coated with the biomaterial NanoBone and the third was an untreated controll group. All three groups were used for an experimental pilot study in rabbit femora to determine the osseointegration process after 4 and 12 weeks. The biomaterial coated group points an approximately 10 % higher bone to implant contact compared with the two other groups.

Abstract: In this work myoglobin (Mb) adsorption was carried out in a batch system using hydroxyapatite (HA) powder during 24 hours at 37°C. The HA samples were analyzed after protein adsorption by Fourier Transformed Infrared (FTIR) and UV-Vis Spectroscopy in reflectance mode. UV-Vis analyses showed that Soret and Q bands shifted to lower wavelengths when Mb is associated with HA surface. This result suggests that Mb Heme group is sensitive to the protein adsorption onto HA surface. HA disks coated with myoglobin and cultured with human osteoblastic cells during 7 days showed that cell adhesion and proliferation were not inhibited by the protein coating after 7 days in cell culture.

Abstract: For the purpose of bioinert coating on electronic devices, we developed the non-hydrolytic sol-gel derived organic-inorganic hybrid materials by addition of epoxy groups which can adhere strongly to the surface of electronic silicon device. The adhesion and chemical properties of hybrids were investigated as a function of epoxy group contents. The hybrids were prepared from 3-metacrloxypropyltrimethoxysilane (MPTS) and 3-glycidoxypropyltrimethoxysilane (GPTS) and diphenylsilanediol. The transparent hybrids were obtained after curing by UV irradiation. The adhesion properties of the hybrids were estimated by the maximum load to resist in a scratch test. The adhesion property of the hybrids increased with addition of GPTS and the highest adhesion was obtained from the hybrid with 5-10 mol% of GPTS. From the element analysis, Si concentrations of all the solutions were less than 2 mM after soaking for 7 d. The Si concentrations were not changed with increasing soaking period. The addition of epoxy groups is effective on improvement of adhesion property of the silica-based hybrid without loosening its chemical stability.

Abstract: In this current study it was investigated the influence of positively and negatively charged surfaces on apatite nucleation process from a supersaturate solution containing calcium and phosphorus (SBF solution). Glass slides were coated with polyelectrolytes thin films using a standard method to produce self-assembled monolayers (SAMs). Slides without treatment were used as control. Positive and negative glass slides were soaking in simulated body fluid (1.5 SBF) for 2, 8, 24 and 96 hours. The surfaces were characterized by scanning electron microscopy (SEM). Accordingly, the apatite mineralization was observed on all surfaces, no matter the surface charge. No remarkable morphological changes were verified between the precipitate in both positive and negative surfaces. It suggests that the crystal growth is not influenced by the initial attraction between either a negative surface and Ca²⁺ ions or a positive one and PO₄^3- ions.

Abstract: A method to promote a bioactive surface on the cobalt base alloy ASTM F75 was tested. A set of cylindrical samples was obtained using the investment casting technique and one of the flat surfaces of each sample was polished. The samples were packed in wollastonite powder and then heat treated for 1 h at 1220°C. To characterize the in vitro bioactivity, a set of heat treated metallic specimens was immersed in a simulated body fluid with an ionic concentration nearly equal to that of human blood plasma (SBF) for 7, 10 and 21 days. To evaluate the effect of increasing the concentration of the simulated body fluid on the bioactivity of the material, a second set of heat treated samples was immersed in a more concentrated solution (1.5 SBF). In both cases the solution was renewed every 7 days. After heat treatment, fine agglomerates homogeneously distributed, containing O, Ca, Si and Al were observed on the metallic surface. After immersion of the samples in simulated body fluids, a ceramic layer containing Ca and P was formed on all the samples. A thicker layer, identified as apatite by XRD, was formed on the samples immersed for 21 days in SBF and as early as 7 days in 1.5 SBF. This may indicate that the heat treated material is useful for bone replacement and tissue regeneration under highly loaded conditions.

Abstract: Titanium has been used in the production of dental implants and orthopedic prostheses due to the low tendency to corrosion and good biocompatibility. Meanwhile, the surface of titanium is not bioactive. Several surface treatments have been developed to make the surface of such metals bioactive. The aim of this work was to evaluate two of these modification processes in commercially pure titanium grade 2, both of them using NaOH solutions: the anodic oxidation and the alkali treatment. The surface morphology was evaluated by SEM/EDS, the crystal structure by XRD, and the mechanical properties and scratch resistance by instrumented indentation. The anodic oxidation (AO) was carried out using NaOH electrolyte 0.1 mol/L and constant current density of 150 mA/cm² for one minute. The alkaline treatment (AT) was performed by soaking the Ti sample in NaOH 5 mol/L solution at 60 °C for 24 hours; after this, the sample was heat treated at 600 °C for one hour in atmospheric air. The AO produced a TiO₂ layer on Ti, whereas a thin sodium titanate layer was obtained by AT. Each surface modification resulted in a specific morphology, but both of them presented the increase in roughness as a common characteristic. The alkali treated Ti surfaces showed the lowest elastic modulus and hardness values. The largest increase in hardness between the treated surfaces was obtained for Ti after anodic oxidation. Scratch test indicates that the TiO₂ film from AO has higher strength to tangential loading than the Ti substrate. In addition, for the Ti submitted to AT, the scratch test indicates that the modified surface layer has a poor adhesion with the substrate. Based on these results it is possible to conclude that, using NaOH solutions, Ti surfaces treated by anodic oxidation present improved mechanical properties than the alkali-treated ones.

Abstract: Bioceramics used as coatings show different biocompatibility and bioactive behavior in relation to their chemical and morphological behavior. Bioactive ceramics such as β-tricalcium phosphate (β-TCP) promote and enhance biological fixation. Stable coatings require an optimum between resorption rate, flexural strength and adhesive strength of the coating. Therefore new bioceramic coating materials that ensure the balance between loss of substances and osteointegration need to be designed and investigated. By modifying the high velocity suspension flame spraying (HVSFS) process parameters, five coatings with different materials were obtained. The in vitro cytotoxicity was determined by the microculture tetrazolium (WST) assay after 24, 48 and 72 h. Cells were grown on the materials for 3, 7, 14, and 21 days and counted. Cell morphology, cell attachment, and cell spreading were investigated using fluorescence microscopy and raster scanning electron microscopy. All substrates supported sufficient cellular growth for 19 days and showed no cytotoxicity. On each material an identical cell colonisation of well communicating, polygonal, vital cells was verified.