Biomaterials, medical devices, and artificial organs最新文献

The tissue response and bone remodeling associated with a flexible femoral intramedullary implant was evaluated. The implant consisted of wafers of porous Co-Cr-Mo alloy and microporous LTI pyrolytic carbon. Six wafers of each material were assembled in a stack and held together using a central acrylic rod. Radiography and histology demonstrated that these implants were associated with gross bone remodeling changes in the femoral shaft. The bone remodeling consisted of endosteal surface bone resorption and periosteal surface bone deposition, most likely due to a loss of structural support from the reamed medullary canal. The periosteal surface bone deposition resulted in an increase in femoral shaft diameter of 5% - 140%. The bone-implant interface consisted of a fibrous connective tissue with limited areas of bone ingrowth or bone apposition.

Previous studies have shown that the application of a porous coating to a solid substrate offers several advantages over current methods of implant fixation. However, the heat treatments required to sinter porous metal coatings have also been shown to cause significant decreases in the mechanical properties of the substrate. With Ti-6A1-4V alloy, sintering above the material beta transus results in a transformation from the as-received, equiaxed microstructure, recommended for surgical implants, to a lamellar alpha-beta microstructure. This lamellar structure has been shown to have inferior mechanical properties. In the present study, microstructural analysis and mechanical testing were performed on Ti-6A1-4V alloy subjected to various post-sintering heat treatments in an attempt to improve the mechanical properties. The microstructures examined were a fine and a coarse acicular alpha in a retained beta matrix. Tensile tests were performed on specimens containing these structures and results were compared with the lamellar and equiaxed microstructures. The fine acicular alpha structure was shown to exhibit the best tensile properties for the post-sintering Ti-6A1-4V alloy microstructures examined, displaying a 9.8% elongation value, as compared to the as-received, equiaxed microstructure value of 13.5%. This represents a significant improvement over the 5.1% value obtained with the lamellar microstructure.

C5a, released during activation of the complement cascade, was measured by radioimmunoassay in human plasma incubated with Dacron, preclotted Dacron, glutaraldehyde treated human umbilical vein (HUV), polytetrafluoroethylene (PTFE), and Dacron-collagen composite vascular grafts. Expressed as percent of C5a in control plasma incubated without graft, C5a generation by preclotted Dacron, and by the HUV was similar to that by Dacron (941 +/- 206% S.E.M.), while that due to PTFE was markedly less (p = 0.005). The Dacron-collagen composite vascular graft also generated significantly less C5a than Dacron and was similar to PTFE in this respect. These results expand on previous work suggesting that lower C5a generation by PTFE explained the negligible polymorphonuclear infiltrate seen on its surface in vivo, allowing it to endothelialise as rapidly as Dacron despite poorer attachment of seeded endothelial cells. The role of complement as a factor limiting endothelialisation of synthetic vascular prostheses needs further investigation.

This study was designed to examine the effect of inflammatory reaction elicited by percutaneous tube on bone induction. Inflammation was provoked by different types of biomaterials. In order to evaluate incorporation of percutaneous tubes, bone matrix and subcutaneous tissue, demineralizing bone matrix was implanted in the subcutaneous tissue of rats and was exposed to interaction with inflammatory conditions. Inhibition to the induction of cartilage and bone by the inflammatory process could be clearly demonstrated. It is suggested that the low pH levels, typical to enzymes operative in inflammation are a direct cause for inhibition of chondro and osteogenesis. The process of calcification is characterized by the activation of enzymes in high pH levels.

A technique for making individualized silicone rubber intravaginal balloons is described. The method entails investing alginate vaginal impressions in silicone rubber and casting a resin model which is then dipped repeatedly in a Silastic Dispersion (Dow Corning, Q7-2213). The range of forces developed by circumvaginal muscles during maximum contractions was determined to be 0.5-4 lbs. Pressure-volume relationships of the balloons showed that the pressure of filling fluid was an accurate replica of the mean pressure in the vagina.

Dielectric permittivity and conductivity of bone in different physiological conditions and collagen, a major component of bone are measured in the frequency range 400-1300 MHz using a Network analyzer. The dielectric dispersion observed in each cases are explained in terms of the relaxation of 'bound water' in this frequency range. The relaxation frequency as well as distribution parameter are computed in each case, under certain simplifying conditions, hydration as well as static dielectric permittivity of bound water attached with bone in different physiological conditions and collagen are also calculated. The effect of ultraviolet light irradiation on the dielectric properties of bone in this frequency range is also examined. The change in dielectric properties due to radiation is attributed to the breakage of hydrogen bonds in the ring structure. A consistent physical model in line with other data is presented.

The purpose of this study is to determine if the volume conduction of electrical current by blood can extend or possibly prevent clotting, and if so to determine where in the clotting sequence the effects occur. The important aspects of these based as follows: All cells and surfaces of the body carry an electrical charge. The magnitude of this surface charge is determined not only by the characteristics of the cells and particles themselves, but also by the liquid or solid in which they are immersed. The majority of the particles within the blood are negatively charged. Although the intima of the vascular system is negatively charged with respect to the adventitia of the vessel, trauma to the vessel will cause the negative charge to become zero or positive with a concomitant thrombosis at that point. An incision into a vessel will result in a positive voltage at the injury site. If the incision is kept negatively charged through application of an electrical current, coagulation at the site will be inhibited and the wound will ooze for many hours. If the current is reversed and made positive, clotting will accelerate. In the laboratory when two oppositely charged electrodes were cemmersed in a beaker of blood, a clot formed at the positive electrode only. If the procedure is carried out correctly, the blood surrounding the negative electrode will have highly effective anticoagulant properties. Furthermore, under similar conditions, leucocytes will migrate toward the negative electrode, thus indicating a change in cell polarity from negative to positive, possibly as a means to combat inflammation. A special bridge circuit and several original test cell designs were developed. Some of the results of this research are as follows: a means to electronically detect coagulation was devised; clotting was extended in excess of 400% by the application of electrical currents; currents below one milliamp per cm2 would not cause any noticeable trauma to the blood as determined by routine clinical laboratory methods. Analysis of the saline compartments resulted in the conclusion that there had not been any migration of the blood components into the saline. However, since the pore size would prohibit the migration of the blood components into the saline.(ABSTRACT TRUNCATED AT 400 WORDS)

Lactic acid was polymerized using tetraphenyl tin as a catalyst. The molecular weight of the resultant poly(lactic acid) varied between 0.89 X 10(6) and 2.94 X 10(6) depending upon the concentration of the catalyst used. In-vivo degradation of the poly(lactic acid) samples having 4 different molecular weights were studies by implanting these in Wistar rats. It was found that at the end of a 48-week implantation period lower molecular weight poly(lactic acid) samples were degraded at a faster rate than the higher molecular weight samples.