PubMed · 15326795
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Coatings and surface modifications.. https://pubmed.ncbi.nlm.nih.gov/15326795/
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This article investigates the thermal-mechanical performance of hydroxyapatite/titanium (HA/Ti) functionally graded (FG) dental implants with the three-dimensional finite element method. The stresses induced by occlusal force for the present HA/Ti FG implant are calculated to compare with the corresponding stresses for the titanium dental implant. Thermal-mechanical effect of temperature variation due to daily oral activity is also studied. The HA/Ti FG dental implant performance is evaluated against the maximum von Mises stress, which is the general performance indicator, the first principal/tensile stress for mechanical failure of implant-bone-bond and the third principal/compressive stress for bone absorption. Simulation results indicate that under the influence of occlusal force only, the FG implants with different HA fraction along the implant length perform almost equally well, while the titanium implant sustains much higher von Mises stress. However, when thermal stress is also considered, the FG implant having HA fraction exponential index of m = 2 with temperature decrease of 20 degrees C yields the highest first principal and von Mises stresses among all the FG and titanium implants.
In this study, a glow discharge plasma deposition system previously used for treating flat substrates was successfully modified and optimized to produce a PEO-like coating on the inner surface of 1-3 mm ID polyethylene tubing by deposition of tetra ethylene glycol dimethyl ether (tetraglyme). The plasma treatment conditions were varied in order to find operating values that would produce coatings with the ultralow (< 5 ng/cm(2)) fibrinogen adsorption (Gamma(Fg)) previously shown necessary to significantly reduce platelet adhesion. The flow rate of gaseous tetraglyme monomer, pressure, and plasma generating power were found to be the most important parameters affecting the uniformity and chemical structure of the coating. The coating uniformity and quality were assessed by measuring Gamma(Fg) at positions 1 cm apart along the entire tube and the fraction of C1s carbon that was in an ether bond (ether-carbon ratio) by electron spectroscopy of chemical analysis. Under optimized conditions, tetraglyme plasma-coated tubes of up to 20 cm in length had ultralow Gamma(Fg). The region of the tube that had ultralow Gamma(Fg) also had C1s ether-carbon ratios that are greater than 50%.
The compatibility and biological efficacy of biomedical implants can be enhanced by coating their surface with appropriate agents. For predictable functioning of implants in situ, it is often desirable to obtain an extremely uniform coating thickness without effects on component dimensions or functions. Conventional coating techniques require rigorous processing conditions and often have limited adhesion and composition properties. In the present study, the authors report a novel precision electrospraying technique that allows both degradable and nondegradable coatings to be placed. Thin metallic slabs, springs, and biodegradable sintered microsphere scaffolds were coated with poly(lactide-co-glycolide) (PLAGA) using this technique. The effects of process parameters such as coating material concentration and applied voltage were studied using PLAGA and poly(ethylene glycol) coatings. Morphologies of coated surfaces were qualitatively characterized by scanning electron microscopy. Qualitative observations suggested that the coatings were composed of particles of various size/shape and agglomerates with different porous architectures. PLAGA coatings of uniform thickness were observed on all surfaces. Spherical nanoparticle poly(ethylene glycol) coatings (462-930 nm) were observed at all concentrations studied. This study found that the precision electrospraying technique is elegant, rapid, and reproducible with precise control over coating thickness (mum to mm) and is a useful alternative method for surface modification of biomedical implants.