Key Engineering Materials Vols. 493-494

Abstract: In this work, the resistance to scratch and wear (pin-on-flat) tests of five different porous TiO₂ films were compared. Such tribological tests were carried out under dry conditions. The coatings were electrodeposited on commercially pure-Ti by anodic oxidation method in different electrolyte solutions at constant voltages. The scratch tests were conducted by applying increasing normal loads up to 400 mN. The coefficient of friction (COF) varied from 0.2 up to 0.5, and increased at larger penetrations depths. When the electrolyte concentration was changed from 0.5 into 1.0M H₂SO₄, the COF slightly decreased. Scanning electron microscopy indicated that the coatings produced in H₂SO₄/150V and Na₂SO₄/100V did not have their substrates revealed. In addition, the samples anodized in H₂SO₄/150V had the highest elastic recoveries. Therefore, such coatings seem to be more resistant to scratch tests than the others. The wear tests were carried out with Berkovich tip as counter-face under constant normal loads of 10 mN in 10 forward-backward cycles. The coatings deposited in H₂SO₄/150V had the lowest wear volume rates. The findings suggest that the porous Ti oxide coatings electrodeposited above their rupture voltages are more suitable to both scratch- and wear-resistance compared to those prepared at the lowest voltage (H₂SO₄/100V).

Abstract: The present work is aimed at the optimisation of an electrolyte system for the development of an oxide layer on Ti-6Al-4V implant material by plasma electrolytic oxidation (PEO) process, to improve its corrosion resistance under 4.5 pH osteoclast bioresorption and 7.4 pH simulated body fluid physiological conditions. All the PEO experiments were conducted for 12 min in constant current mode by a DC power supply unit with 7 different electrolyte systems consisting of methodically varied concentrations of tri-sodium ortho phosphate (Na₃PO₄.12H₂O), sodium meta silicate (Na₂SiO₃.9H₂O) and potassium hydroxide (KOH). The phase composition of the fabricated oxide coatings was analyzed by X-ray diffraction (XRD) technique. The morphology and thickness of the coatings were determined by scanning electron microscopy (SEM) and the corrosion characteristics were assessed by potentiodynamic polarization and electrochemical impedance spectroscopic techniques. The XRD results demonstrated that the oxide coatings mainly consisted of anatase and rutile phases with different proportions. While the average surface pore size was in the range of 3 to 6 µm, the thickness of the coating varied from 5 to 20 µm. A significant improvement in the corrosion resistance and an added capacitive nature was observed for the PEO treated Ti-6Al-4V implant material compared to that of the untreated. The variation in the proportions of anatase and rutile phases, the surface pore size distribution, the thickness of the coating and the corrosion characteristics of the developed coatings were correlated with the composition and concentration of the electrolyte system. Of the seven different electrolyte systems employed in the present study, the one consisting of 10 g Na₃PO₄.12H₂O, 2 g Na₂SiO₃.9H₂O and 2 g of KOH was established to be an optimized electrolyte system for developing oxide coatings on Ti-6Al-4V to minimise corrosion and thereby reduce the metal ion release under physiological conditions.

Abstract: Calcium-incorporated titanium (Ti) recently reported a large degree of effectiveness in many in vitro and in vivo studies. The implants with the deeper thread provide the higher surface area and will have an advantage in soft bone. We used the Ti implants with deep threads and investigated osseintegration of the implants with resorbable blast media (RBM) surfaces produced by grit-blasting or XPEED surfaces by coating of the nanostrucutred calcium.The Ti implants with deep threads had a thread diameter of 4.0 mm, a length of 5.0 mm and a thread depth of 1.0 mm. The Ti implants with calcium-incorporated surfaces (XPEED surfaces) were hydrothermally prepared from the Ti implants with RBM surfaces in alkaline calcium containing solution. The surface characteristics were evaluated by using scanning electron microscope (SEM) and surface roughness measuring system. Thirty-implants with RBM surfaces and thirty-implants with XPEED surfaces were randomly placed in the proximal tibiae and in the femoral condyles of ten New Zealand White rabbits. The osseointegration was evaluated by removal torque test in the proximal tibiae and histomorphometric analysis in the femoral condyles. The Ti implants with XPEED surfaces showed a similar surface morphology and surface roughness to those of the Ti implants with RBM surfaces. The mean removal torque of the Ti implants with XPEED surfaces was higher than the Ti implants with RBM surfaces (p < 0.05). The percentage of bone-to-implant contact (BIC %) were increased for the Ti implants with XPEED surfaces compared with the Ti implants with RBM surfaces (p < 0.05).The Ti implants with XPEED surfaces significantly enhanced the removal torque and the BIC %. The Ti implants with XPEED surfaces may be shorten healing time of bone by improving osseointegration of Ti implants with deep threads.

Abstract: The clinical use of plasma-sprayed hydroxyapatite (HA) coatings on metal implants has been widely investigated as the HA coating can achieve the firm and direct biological fixation with the surrounding bone tissue. It is shown in previous studies that the mechanical properties of HA coatings are improved by the addition of ZrO2 particles during the deposition of the coating on the substrate. Subsequently, the cohesive and adhesive strengths of plasma-sprayed hydroxyapatite (HA) coatings were strengthened by the ZrO2 particles addition as a reinforcing agent in the HA coating (HA+ZrO2 composite coating). The aim of the present work is to investigate and evaluate the in vitro bioactivity assessment of HA and HA/ZrO2 coatings, on stainless steel substrate, soaked in c-SBF, in order to study and compare their biological responses. The coatings were produced using vapor plasma spraying (VPS). The characterization of the surface of the coatings before and after soaking in SBF solution was performed using Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM) and X-ray Diffraction analysis (XRD). All samples were smoothed before insertion in the medium and the in vitro bioactivity of all coating samples was tested in conventional Simulated Body Fluid (c-SBF) solution for various immersion times.

Abstract: The bioactivity of materials was evaluated based on the ability to induce a bond-like apatite layer on the surface in simulated body fluid (SBF). The aim of this study was to investigate the coatings containing strontium on bioactivity after heat treatment. After the materials were soaked in SBF for 1 day, precipitates did not form on the surface of heat-treated MAO coating without strontium. The precipitates were observed on surface of heat-treated MAO coatings containing strontium. After 7 days, the surface of heat-treated MAO coatings containing strontium was completely covered with precipitates. The precipitates were found to be composed of fiber structures using scanning electron microscope (SEM). The phase was identified as the apatite phase using thin film X-ray diffraction (TF-XRD). The results show that heat-treated MAO coatings containing strontium can induce the formation of an apatite layer on their surface. All finding in this study indicated that heat-treated MAO coatings containing strontium have good bioactivity for clinical applications.

Abstract: This paper reports the results of a study aimed to deposit a biomimetic apatitic coating on the porous surface of Ti alloy acetabular cups, produced with AM techniques. To this purpose, we utilized a slight supersaturated Ca/P solution at physiological values of pH and temperature. The results of the XRD, SEM and EDS investigation indicate the 6 h immersion in the calcifying solution are sufficient to provoke the deposition of a uniform coating of poor crystalline apatite on the surface and inside the porous structure of the substrates.

Abstract: A two-step, biomimetic approach was applied for the rapid deposition of octacalcium phosphate (OCP) coatings on zirconia ceramics (Y-TZP). In the first step, sintered zirconia discs were immersed into a supersaturated Ca-P solution with pH=7.4 (CPS1). In the second step, the substrates were transferred from the CPS1 to another Ca-P solution with a lower pH (CPS2). After 6 hours of immersion in the CPS2, a thick coating consisting of large OCP crystals was obtained. Afterwards, the coated substrates were subjected to a thermal treatment in order to improve the attachment of the coating to the substrate.

Abstract: The apposition of bone at early stages is critical for rapid loading and therefore there is much effort in improving the implant surfaces for a rapid osseointegration. The aim of this study is to investigate the effect of roughness, hydrophilicity and coating on osseointegration. Machined (smooth), sand-blasted (rough), hydrophilic and coated implants were tested in vivo for 2, 4 and 6 weeks. The hydrophilic surfaces were obtained by atmospheric oxygen plasma treatment of machined and sand-blasted implants. The coating is obtained by a spin-spray-process using sol-gel-technique. SEM and TEM investigations revealed that the coating consists of a nanoporous silica matrix with embedded synthetic, nanocrystalline hydroxyapatite. Histological polished sections were manufactured and the bone-to-implant-contact was calculated. The difference between smooth and rough implants was marginal and not significant. There were no statistical differences between hydrophilic and control implants, whereas the BIC of the hydrophilic surfaces was lower by trend. All coated implants offered an increased bone to implant-contact. However, the BIC was decreasing at 6 weeks due to the missing of mechanical stress and a faster bone metabolism in rabbits. The coating offers a new opportunity to enhance the osseointegration and therefore an earlier implant loading.

Abstract: In this present work, we characterize HAp thin films deposited by dual magnetron sputtering device DMS on silicon (Si/HAp). The sputtering RF power was varied from 90 watts to 120 watts and deposition times from 60 to 180 minutes. The argon and oxygen pressure were fixed at 5.0 mTorr and 1.0 mTorr, respectively. Grazing incidence X-ray diffraction (GIXRD) from synchrotron radiation, infrared spectroscopy (FTIR) and atomic force microscopy (AFM) were used for the structural characterization. At lower deposition times, a crystalline phase with preferential orientation along apatite (002) and a disordered nanocrystalline phase were identified. The coating crystallinity was improved with the increase of the deposition time besides the sputtering power.

Abstract: This study proposes a hydrothermal process to produce monetite and zinc-doped calcium phosphate coatings with different (Ca+Zn)/P molar ratios, in an attempt to incorporate zinc benefits on bone formation to hydroxyapatite precursors. The method consists of coating niobium and titanium substrates in an aqueous solution rich in (PO4)^3- and calcium (Ca)²⁺ ions under specific conditions (pH ≡ 3.7, 80°C). Scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses were performed to characterize the coatings. From XRD analysis, we concluded that substitution of Ca by Zn was feasible up to 15% mol Zn, and the new phase obtained was parascholzite (JCPDS-01-086-2372).