Biomedical subjects

H Harasaki

Publications and source records attributed to H Harasaki.

149 records · Page 9Linked to original sources

PubMedDate not supplied

An N-substituted polyurea coating with high affinity for heparin.

A new N-substituted polyurea with tertiary amino groups in the polycarbamidic chain (NPUTA) has been synthesized. The polymer is soluble in C1-C4 alcohols, has high adhesion to polar molds, and has high H2O uptake (130-150%). The material can be coated on many biomaterials (polyurethanes, charcoal hemosorbents, cellulosic hemodialysis membranes), and high amounts of heparin can be adsorbed onto treated surfaces. NPUTA cast from 0.5-3.5% ethanol solutions can absorb large amounts of heparin from anti-coagulant solution (40-60 micrograms/cm2) and heparinized plasma. Heparin release into phosphate buffered saline (PBS) solution or plasma is minimal. The influence of NPUTA solution concentration and pre-absorbed heparin on the protein adsorption, platelet adhesion, surface induced hemolysis, and complement activation of these films has been investigated. Radiolabeled protein assays, radiolabeled platelet assays, and other methods were used. It was shown that modified surfaces for the listed materials, with heparinization, demonstrate improved in vitro blood compatibility without any changes in functional properties. For example, treatment with NPUTA/heparin does not reduce sorption of middle molecules by activated charcoal hemosorbent, while markedly and significantly decreasing platelet adhesion and complement activation. NPUTA/heparin modified, glutaraldehyde treated bovine pericardium exhibited significantly reduced calcification in a rat subcutaneous implant model. Other ex vivo circulation experiments also confirm the blood compatibility of different NPUTA treated surfaces.

Adsorption↗

PubMedDate not supplied

A new finger joint prosthesis.

A new finger joint prosthesis is being developed for the proximal and distal interphalangeal positions. Currently available "joint spacer" prostheses provide relief from pain and cosmetic improvement, but relatively poor long-term function. The new prosthesis employs a mechanical hinge at the joint. It is fabricated from titanium alloy (6A14V). The hinge mechanism avoids direct metal to metal contact by using high density polyethylene bearings. In vitro tests of the hinge mechanism have passed 75 million cycles of continuous flexure without failure (n = 12). The hinge also incorporates a mechanical limit stop to prevent hyperextension. The hinge mechanism is enclosed in a sealed elastomeric jacket that isolates the hinge from connective tissue ingrowth. The jacket, equivalent to an artificial synovial membrane, has an integrally textured exterior surface designed to promote tissue attachment to the implant to stabilize tissue capsule formation around the joint. To test the in vivo efficacy of the new design, a series of 12 devices were implanted in the knee joint position of adult rabbits. A jacketed prosthesis was implanted on one side, whereas 2 weeks later an unjacketed control was implanted contralaterally. The animals then were maintained for an 8 week period. At sacrifice, the implants were removed, and the response of the surrounding tissues was studied histologically. At the time of implantation, the range of motion of the joints was approximately 100-105 degrees. There was a progressive loss in range of motion observed in both groups. The fibrous tissue capsule around the jacketed implants, however, was significantly reduced in thickness compared with the controls (mean thickness, 1.5 mm vs. 4.5 mm).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMedDate not supplied

Progress in Cleveland Clinic-Nimbus total artificial heart development.

A totally implantable, Cleveland Clinic-Nimbus total artificial heart (TAH) uses electrohydraulic energy conversion and an automatic left master-alternate mode control scheme, with a filling sensitivity of 1.0 l/min/mmHg and a maximum output of 9.5 l/min. The TAHs were tested in 12 calves for 1-120 days with normal major organ and blood cell function. Post-operative suppression of platelet aggregation recovered by the second post-operative week. The gelatin-coated pump surface generally was clean without any anticoagulants and free from infection. Embolism, which occurred in two cases, was caused by complications attributable to fungal infection in a Dacron graft and by thrombus formed around a jugular vein catheter. A system with a hybridized microcircuit controller in the interventricular space has been tested successfully in the three most recent cases, with a peak device surface temperature elevation of 6.5 degrees C. Heat effects were confined to the tissues immediately adjacent to the hottest spots. The carbon fiber-reinforced epoxy housing and 60 ml butyl rubber compliance chamber showed good tissue compatibility with a thin, fibrous tissue capsule. The transcutaneous energy transmission system and the internal battery functioned well as designed in the most recent animal implant.

Animals↗

PubMedDate not supplied

Analysis of subcutaneous fluid in rats.

Subcutaneous implantation in rats is a commonly used model for biomaterial calcification studies. Although this model is frequently used, its components have not been characterized with respect to calcification. Exudate from the subcutaneous spaces of 18 young rats was collected using diffusion chambers. These chambers consisted of polymethylmethacrylate tubes with 0.22 micron pore filters covering each end allowing fluid, but not cells, to enter the chambers. Glutaraldehyde treated bovine pericardial strips were implanted subcutaneously, inside the chambers and outside the chambers, to test the calcification inducing abilities of the various environments. The animals were killed on postoperative day 10, and the exudate and materials were collected. The exudate was analyzed for ionic calcium, total calcium, inorganic phosphorus, and albumin, and for cells by a differentiated cell smear. The materials were analyzed for calcification by radiography, histology, and atomic absorption. Calcification was present in the materials inside the chambers where no cells were present and in the materials that were not in chambers. The distinct features of the exudate were elevated ionic calcium, a high Ca x P product, and elevated phosphorus.

Adult↗

PubMedDate not supplied

Heat from an implanted power source is mainly dissipated by blood perfusion.

Heat dissipation and its effects on tissue and blood interfaces are common problems associated with the development and increased use of artificial hearts, because all of the implantable actuators for artificial hearts generate waste heat due to inefficiencies of energy conversion. To determine the mechanisms of heat dissipation from artificial hearts, heated disks producing constant heat fluxes of 0.08 watts/cm2 were implanted adjacent to the left lung and the latissimus dorsi muscle in calves for 2 weeks, 4 weeks, and 7 weeks. At the end of each experiment, a series of acute studies was performed in which blood perfusion to the heated tissue was decreased or stopped to observe the contribution of blood perfusion to heat dissipation. The cooling effect of ventilation was also examined to determine its relative contribution to heat dissipation in lung tissue by decreasing the minute ventilation volume. The importance of blood perfusion for heat dissipation was demonstrated by the temperature rise after cessation of blood perfusion to the heated tissue. The contribution of ventilation to heat dissipation in the heated lung tissue was minimal. Contribution of total blood perfusion to heat dissipation was increased with time in the muscle tissue, which has relatively low resting blood perfusion, but not in the lung tissue, which has relatively high blood perfusion. In the heated muscle tissue, the in vivo adaptive response to chronic heat was functionally shown by the increased perfusion. In conclusion, blood perfusion was the main mechanism of heat dissipation from tissues that were adjacent to an implanted power source.

Adaptation, Physiological↗