PubMed · 10554929
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A Atala. 1999. Tissue engineering applications for erectile dysfunction.. https://doi.org/10.1038/sj.ijir.3900483
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In western industrial countries, coronary heart disease is the most common cause of death. The reason is a coronary sclerosis, which by the generation of plaques narrows the inner lumen of an artery and, thus, deteriorates the blood supply. This leads to symptoms like burning pain or increased pressure in the chest, and finally to an under supply and damage of the heart muscle. In order to keep those portions of arteries that are covered by a plaque open, the stent technique was developed in the 1980s and is increasingly used since about 13 years. These stents are usually made of wires or of a slotted tube and are of two kinds: self-expanding and balloon expanding. Both types are implanted after being mounted on a catheter and expanded in the desired position. Self-expanding stents make use of the elastic deformation, while the other group of stents are expanded by a balloon, which brings about a plastic deformation of certain regions of the stent structure. Thus, after implantation, parts of these stents undergo two steps of distinct plastic deformation. First during compression, which is necessary for the mounting procedure on the catheter (crimping), and second during expansion for implantation. In this article, the residual stresses generated during crimping and expansion are presented and discussed. These stresses are stored in the structure of a portion of a stent after implantation and are superimposed on those stresses generated by the more than 700 million cyclic heart beats during the patient's life. This work is a part of several interdisciplinary research projects by the authors in order to gain reliable fail-safe criteria for the static and cyclic mechanical properties of coronary stents.
A frequent long-term complication of total joint arthroplasty is aseptic loosening, the end result of wear debris accumulation, synovitis, and osteolysis about the implant-bone or cement-bone interface. Complement, an effector system in plasma, synovial fluid, and tissue, has powerful chemotactic, inflammatory, and osteoclast-activating potentials. This study explored the complement-activating ability of polyethylene, a material used in joint implants. In vitro hemolytic assays using sheep red blood cells (E(sh)), human serum, and particulate polyethylene suggested alternative pathway complement activation, as well as polyethylene adsorption of activated complement components. These results were confirmed by enzyme-linked immunosorbent assay (ELISA) quantification of activated complement factors Bb and C3b. In situ double antibody immunoperoxidase staining for factors Bb, C3a, iC3b, and SC5-9 in synovial tissue from revision hip specimens showed localized alternative pathway activation and component adsorption. These results introduce a likely role for complement activation in particle-mediated recruitment, proliferation, and activation of macrophages during early events in osteolysis and implant loosening.
The objective of this paper was to study the release of bovine serum albumin (BSA) from a series of biodegradable hydrogels having a wide range of hydrophilicity to hydrophobicity, swelling, and biodegradation properties. BSA was incorporated into a series of biodegradable hydrogels made from a dextran derivative of allyl isocyanate (dex-AI, as the hydrophilic constituent) and poly(DL-lactic acid) diacrylate macromer (PDLLAM, as the hydrophobic constituent). The release kinetics of BSA from these dex-AI/PDLLAM hydrogels was studied. Laser confocal scanning microscopy was used to investigate the morphological change of the hydrogels, as well as BSA distribution in the hydrogels, as a function of dex-AI to PDLLAM composition ratio and incubation time. We found that the incorporation of PDLLAM into dex-AI reduced the initial burst release of BSA due to its more homogeneous distribution in the hydrogels. As the PDLLAM component increased, the rate of formation of a loose three-dimensional (3D) network structure increased; consequently, the sustained rate and extent of BSA release increased. Both release index and diffusion coefficient (from release kinetics data) increased as the PDLLAM component increased in the hydrogels. The data suggest that the release of BSA was controlled by both diffusion of BSA through swelling of the hydrophilic phase during an early stage, and degradation of the hydrophobic phase during a late stage, and also that the magnitude of diffusion versus degradation controlled release is dependent on composition ratio and immersion time.