Biomedical subjects
Publications and source records attributed to M Szycher.
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Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Mechanical circulatory support was accomplished in 20 calves (mean, 140 days) and in 5 patients following operation for acquired heart disease (range, 1 hour to 8 days) employing a pneumatically actuated xenograft-valved assist pump interposed between the left ventricular apex and aorta. Following pump implantation in calves, hematocrit and platelets decreased transiently and returned to normal within 14 days. Plasma hemoglobin and erythrocyte mechanical fragility values were elevated for 48 hours. Platelet survival was slightly reduced, but erythrocyte survival values were similar to controls. In patients who received assist pumps, plasma hemoglobin and erythrocyte mechanical fragility were transiently elevated, but rapidly decreased to normal. Thrombocytopenia occurred only in the presence of bleeding and renal failure requiring hemodialysis. Pump flow of the left ventricular assist device was maintained above 2.0 L/min/m2 despite serious arrhythmias. Postmortem examination revealed no evidence of thromboemboli in the clinical patients although anticoagulant agents were not administered.
Marked improvements were realized in the development of electrically driven left ventricular assist systems. A volume reduction of 46%, a system weight reduction of 63%, and a factor of 2 improvement in overall efficiency (29%) were realized. The system, operating at a pressure of 120 mm Hg with a flow rate of approximately 7 L, requires only 7.5 W of input power. In addition, a unique brushless commutator was designed to replace standard brushes, thus increasing system life. A new polyurethane was synthesized for utilization in the TMS. This material has demonstrated high flex life in addition to being biocompatible. Further improvements in system weight and size, as well as efficiency, will be realized when flat plate pumps are mated to electric drivers.
A study was undertaken to select 2 of the most promising bladder materials from a list of 8 carefully chosen polymers. The polymers chosen for testing included a wide spectrum of urethanes, as well as a polyester resin and a millable polyolefin rubber. The following materials were studied: Adiprene LW-500, Avcothane 51, Biomer, Hexsyn, Hytrel 4055, Mobay 240313, Pellethane 2103-80 AE, and Tecoflex HR. The selection process was based on a test matrix which was divided into segmented steps, each a logical sequel from its predecessor, and each of increasing technical complexity. Hydrolytic stability, flexure endurance, fabricability, tissue compatibility, hemocompatibility and chronic tissue compatibility were evaluated, forming the basis for the acceptance/rejection criteria. As a result of this search, 2 biomaterials were identified as most suitable for use in conventionally flocked bladders; Biomer and Tecoflex HR. Both Biomer and Tecoflex HR bladders have demonstrated impressive results in circulatory analog loop endurance tests, with Tecoflex bladders surpassing 50 million flexes to date, and Biomer bladders (the longest running bladders) exceeding 150 million flexes. Tests are continuing.
Development of a small diameter (4 mm inner diameter [ID]) prosthetic vascular graft with functional groups accessible for covalent binding of recombinant hirudin (a potent anticoagulant) should create a more hemocompatible surface. The purpose of this study was to develop a technique for generating carboxylic acid groups on the surface of precast 4 mm ID poly-(carbonate urea)-urethane vascular grafts and to evaluate the accessibility of these groups. A polycarbonate based urethane with the chain extender 2,2-bis(hydroxymethyl)propionic acid was synthesized. A precast 4 mm ID poly(carbonate urea)-urethane vascular graft (Chronoflex [CF]; CardioTech International, Woburn, MA) was then placed into a 4% carboxylated polyurethane (cPU) solution (in 1% dimethyl acetamide) and incubated for 30 minutes (cPU graft). To determine the accessibility of the carboxylic acid groups, a standard textile technique using methylene blue dye was used. Macroscopic cross-sections, which were cut and evaluated for dye penetration, showed greatest concentration of carboxylic acid groups at the luminal and capsule surfaces, with minimal penetration into the mid-portion of the graft. Analysis of dye baths for absorbance reduction resulted in the cPU grafts having 3.7-fold and 5.4-fold more accessible carboxylic acid groups compared with untreated and dimethyl acetamide dipped CF grafts. Thus, a novel small diameter vascular graft has been developed that contains reactive carboxylic acid groups accessible for protein binding.
Development of a small diameter prosthetic vascular graft with surface based antithrombin properties should aid in maintaining early graft patency in small vessel reconstruction. The purpose of this study was to bind covalently a basecoat protein (canine serum albumin [CSAJ) and a potent antithrombin agent (recombinant hirudin [rHir]) to 4 mm inner diameter poly(carbonate urea) urethane grafts with reactive carboxylic acid groups (cPU). 125I-CSA was covalently bound to 1 cm length segments of cPU grafts using the carbodimide cross-linker, 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC). To bind 125I-rHir covalently, CSA was modified with the heterobifunctional cross-linker sulfosuccinimidyl 4-(N-maleimidomethyl) cyclohexane-1-carboxylate (sulfo-SMCC) before linkage to the cPU surface with EDC (cPU-CSA-SMCC). 125I-rHir was modified with Traut's reagent and reacted with the cPU-CSA-SMCC surface, covalently linking 125I-rHir to surface bound CSA. 125I-CSA binding to the cPU graft surface (34,235 ng/segment) was ninefold, sevenfold, and 10-fold greater than controls with nonspecifically bound 125I-CSA. Covalent linkage of 125I-rHir to the cPU-CSA-SMCC surface (9,974 ng/segment) was 172, 192, and 142-fold greater than controls with nonspecifically bound 125I-rHir. Surface antithrombin properties were characterized using a chromogenic assay to measure residual thrombin activity. Evaluation of surface antithrombin activity showed significantly greater 131I-thrombin inhibition and binding by the cPU surface with covalently bound 125I-rHir, as compared with controls. Release of 125I-rHir from the cPU surface was minimal as compared with controls. Therefore, rHir can be covalently linked to a novel small diameter polyurethane vascular graft surface while maintaining its potent antithrombin properties.
Infection is a major complication when using biomaterials such as polyurethane in the clinical setting. The purpose of this study was to develop a novel infection resistant polyurethane biomaterial using textile dyeing technology. This procedure results in incorporation of the antibiotic into the polymer, resulting in a slow, sustained release of antibiotic from the material over time, without the use of exogenous binder agents. Polycarbonate based urethanes were synthesized that contained either a non-ionic (bdPU) or anionic (cPU) chain extender within the polymer backbone and cast into films. The fluoroquinolone antibiotic ciprofloxacin (Cipro) was applied to bdPU and cPU using textile dyeing technology, with Cipro uptake determined by absorbance reduction of the "dyebath." These dyed bdPU/cPU samples were then evaluated for prolonged Cipro release and antimicrobial activity by means of spectrophotometric and zone of inhibition assays, respectively. Cipro release and antimicrobial activity by dyed cPU segments that were aggressively washed persisted over 9 days, compared with dyed bdPU and dipped cPU control segments that lasted < 24 hours. Dyed cPU segments, which remained in a static wash solution, maintained antimicrobial activity for 11 days (length of study), whereas controls again lost antimicrobial activity within 24 hours. Thus, application of Cipro to the cPU polymer by means of dyeing technology results in a slow sustained release of antibiotic with persistent bacteriocidal properties over extended periods of time.