ABSTRACT
Total disc replacement (TDR) is a modern technique employed to treat degenerative disc disease that has the benefit of preserving motion compared with the clinically established spinal fusion. The wear performance of implants based on articulating designs is a key factor that determines their longevity and it is hypothesized that this will be the case for TDR devices. A detailed analysis of the surface of Charité lumbar disc replacements during simulated wear for five million cycles (MC), with inputs defined by the ISO18192-1 standard, is presented. After each million cycles the disc asperity heights, asperity curvature radii and their distributions on the surface of the core of the implant were determined at different locations. Two distinct areas on the surface of Charité polyethylene disc were identified based on the surface topography change during the wear simulation process. Within the area corresponding to the dome the initial roughness decreased, but after 2 MC the surface appeared to roughen with material build-up. More peripherally on the dome the surface roughness decreased after the first MC and remained constant. No effect was noticed on the rim. Furthermore, no statistical difference was noticed between the inferior and superior sides of the core of the disc. The study demonstrated that the wear on the two surfaces of the disc was uneven. This spatial variation is important in modelling the wear processes and providing strategies for reducing wear through enhanced design and modifications to the biotribological properties of the device.
Subject(s)
Intervertebral Disc , Lumbar Vertebrae , Materials Testing , Models, Biological , Prosthesis Design , Humans , Stress, Mechanical , Surface PropertiesABSTRACT
Photodynamic therapy (PDT) has been proposed as a new technique to inactivate microorganisms as it does not lead to the selection of mutant resistant strains; a clear benefit compared to antibiotic treatment. PDT has also attracted the interest of nanotechnology as the effectiveness of the treatment can be greatly enhanced by the use of nanoparticles. In the last decade, different approaches to the combination of nanoparticles and PDT have been investigated in relation to the antimicrobial applications of the technique. One use of the nanoparticles is to improve the delivery of photosensitiser to the bacteria; others use the nanoparticles to improve the inactivation kinetics. A different approach utilises nanoparticles as a photosensitiser. In this review these diverse types of interactions will be described.
Subject(s)
Bacterial Infections/drug therapy , Nanoparticles/chemistry , Photochemotherapy , Photosensitizing Agents/administration & dosage , Anti-Bacterial Agents/chemistry , Anti-Bacterial Agents/therapeutic use , Humans , Photosensitizing Agents/chemistry , Photosensitizing Agents/therapeutic useABSTRACT
A range of experiments were performed on the dead-end ultrafiltration (UF) of poly(ethylene glycol) (PEG) of different molecular weights. Deviations from a linear dependence of the filtration rate with the applied membrane pressure difference were found. It is shown that these deviations are not caused by an osmotic pressure influence but determined by the reversible adsorption of PEG molecules inside the pores of the ultrafiltration membranes used. A theoretical model of the process is suggested, which describes the reversible adsorption inside the membrane pores and the corresponding reduction of the filtration velocity. Comparison of the theory predictions with experimental data on the ultrafiltration of PEG shows a good agreement between the theoretical predictions and experimental data. A theory is presented for calculation of the PEG rejection coefficient in the case of ultrafiltration.
