Biomaterials, medical devices, and artificial organs最新文献

When large numbers of battle casualties arrive at a field hospital, the requisite skills, facilities, and time may not be available to perform all necessary, but non-life-threatening, end-to-end vascular anastomoses with sutures. A sutureless concept was proposed in which the proximal and distal ends of a severed vessel are everted over ferrules, and then the everted ends are held together with a low-temperature, biocompatible, heat-shrinkable sleeve. Two essential elements in the sutureless concept, a surgical vascular everting instrument and the heat-shrinkable sleeve, have been developed, and the sutureless technique has been demonstrated on one laboratory animal.

Previous studies have shown that the application of a porous Ti-6A1-4V alloy coating results in a substantial decrease in the substrate material fatigue properties. This phenomenon is due to both a microstructural change from the equiaxed alpha-beta microstructure to a lamellar structure and a notch effect created by the porous coating. The lamellar microstructure has been shown to exhibit the worst fatigue properties of the most common structures obtained in Ti-6A1-4V alloy. This study examined various post-sintering heat treatments which would alter the material microstructure and possibly result in improved fatigue performance. The heat treatments examined produced alternate microstructures to the lamellar structure and some approached the totally transformed acicular alpha structure. The acicular alpha structure has been shown to exhibit the best fatigue properties for Ti-6A1-4V alloy in the notched condition.

The characterisation of a polyester material for cardiovascular applications can be carried out to various levels of sophistication. This paper focuses on certain methods which could give information about important aspects of material characterisation such as chemical identity, molecular parameters, surface studies, extraction studies, removal of oligomers, mechanical properties and thermal properties. Significance of the results obtained from such analyses are also discussed.

In our previous work, pyridoxylated polyhemoglobin (PP-PolyHB) was shown to have a P50 = 16-18 torr, and a half-life (T 1/2) of 20 hrs in the circulation of rats given a 75% isovolemic exchange transfusion. For the present study, a rapid and lethal hemorrhagic shock model has been specifically designed to assess the ability of PP-PolyHB to function as an emergency resuscitation fluid. Using 48 fully conscious rats with special chronic arterial and venous cannulations, shock was induced by bleeding 67% of total blood volume in less than 40 min; producing 100% mortality in nonresuscitated controls. Resuscitation was carried out using one of the following infusion fluids equivalent in volume to the bled volume: Ringer's solution, albumin solution, stroma-free Hb (SFHb), pyridoxylated SFHb (PP-SFHb), PP-PolyHb, and whole blood. Long-term (greater than 8 day) survival rate of rats (n = 12) resuscitated with PP-PolyHb was 75% compared to 83% for autologous whole blood. Survival following resuscitation with the other fluids was substantially lower. These results indicate that PP-PolyHb could effectively resuscitate lethal hemorrhagic shock in conscious rats, and provide long-term survival afterwards, even in the absence of any additional fluid maintenance.

Insulin has been encapsulated in biodegradable polylactic acid microcapsules and non-biodegradable ethylcellulose microcapsules by using an emulsification-solvent evaporation process. Gelatin and polyvinylalcohol were used as protective colloids. The concentrations and types of protective colloids affecting the micromeritic properties and release behavior of insulin microcapsules were studied. The higher the concentration of protective colloids the smaller the particle size of microcapsules. The median diameter of microcapsules decreased with the increase of the viscosity of protective colloids. Scanning electron microscopic observations suggested that microcapsules prepared from higher concentrations of polyvinylalcohol solution resulted in a nonporous and compact surface on the microcapsules, compared to the porous microcapsules prepared from gelatin solution. The residual crystals and porous structure of microcapsules affected the release rate of microcapsules. After the initial burst effect the release rate of insulin from microcapsules was found to be constant, so that prolonged release was obtainable. Three percent of polyvinylalcohol was the best choice for the preparation of polylactic acid microcapsules.

An irrigatable bandage has been developed to hold fluid over a wound. Starting with superficial skin wounds on the back of guinea pigs, the bandage has been used to hold saline or phosphate-buffered saline containing antibiotics over the wound for up to 48 hours. Animals tolerated the bandage well for this period and bacterial contamination and wound maceration were not complications. The extent of reepithelialization with time was measured histologically under three separate conditions: wound exposed to air, wound covered and kept moist, and wound covered with liquid. By 24 hours 2 +/- 1%, 16 +/- 4% and 60 +/- 8% of the wound surface interfollicular areas showed some reepithelialization, respectively. On the average, at the same time these areas showed 15 +/- 2%, 19 +/- 2% and 37 +/- 1% coverage by epithelium. By these measurements, the liquid cover enhanced the rate of wound closure significantly.

Polyvinyl alcohol-silica (PVA-SiO2) composite and heparinized PVA-SiO2 were examined in vitro and in vivo as materials to coat artificial vessels to be used for the replacement of small arteries. PVA-SiO2 was observed to prolong coagulation time and on heparinized PVA-SiO2 surfaces no blood coagulation was noticed after a period of two days using the Lee-White and plasma recalcification methods. After placing non-coated and coated surfaces in contact with blood components in vitro and in vivo, the degree of blood component adhesion was greater in non-coated woven Dacron than in PVA-SiO2 coated Dacron. The degree of adhesion was even less in heparinized PVA-SiO2 coated Dacron. Furthermore, artificial vessels made of these 3 types of materials were used to replace parts of the canine abdominal aorta and were removed one and a half years later. Patency rates were as follows: non-coated 2/7, PVA-SiO2-coated 4/7, heparinized PVA-SiO2-coated 8/12. The inner surfaces of these prostheses were observed with light microscopy and scanning electron microscopy. Intima formation was thinner on the PVA-SiO2 composite surfaces than on the control surfaces. Heparin acted as a local anticoagulant and PVA-SiO2 limited intima formation. This report showed that PVA-SiO2 composite coated surfaces can be effective for small artery replacement due to good tissue affinity and anticoagulability.

The potential of the finite element method as a computational aid for making objective clinical decisions has not yet been exploited due to the unreliability of the results obtained. The main reasons for this may be attributed to the poor quality of the finite elements available in the conventional softwares, improper modeling of the three dimensional problem, and errors introduced by incorrect representation of geometry and material properties. Herein, we report an attempt to derive a three-dimensional finite element model for the adult human femur which permits reliable representation of the local stress patterns. The geometry was obtained by serial computed tomography scans. The mechanical properties were based on laboratory tests and information available in the literature. The analysis is performed with a new generation software. Preliminary results suggest that the scheme could be automated and used for in vivo analysis.

Liposome-type artificial red blood cells (ARBC) stabilized with carboxymethyl chitin (CM chitin) containing human hemolysate were prepared by a two-step emulsification technique, Oxygen binding abilities of the ARBC and human hemolysate were measured by the use of a Clark-type oxygen electrode. Both of theARBC and human hemolysate exhibited a striking similarity in oxygenation behavior, indicating that the oxygen binding ability of the former is almost identical with that of the latter. Disintegration tests on the ARBC using the enzymes (lysozyme, chitinase and phospholipase C), that can digest the components of the ARBC membrane, suggested that the membrane has a structure in which the phospholipid layer is covered by a mesh of CM chitin molecules. The acute toxicity of the ARBC to male mice (BALB/c) was examined and the LD 50 value of the ARBC for 2 ml of intravenous injection was evaluated to be 13.8 ml/kg by means of the Litchfield-Wilcoxon method.