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Biomedical subjects

M Szycher

Publications and source records attributed to M Szycher.

At least 19 recordsLinked to original sources
PubMed1992

Modern wound dressings: a systematic approach to wound healing.

The advent of modern wound care management constitutes one of the most innovative applications of medical device technology. The foundation for wound care recent advances has been built upon the developments achieved in polymer technology over the last three decades. New and unique materials have been engineered to provide properties with significant technical and clinical benefits. These new wound care products were made possible by the convergence of three interrelated disciplines: (1) more complete understanding of the underlying principles of dermal wound healing processes, (2) new elastomeric polymers capable of being fabricated into protective dressings, and (3) advances in breathable adhesive technology. The following discussion provides a critical review of the current status of technology and the worldwide opportunities for improved wound management products. Particular attention is focused on the clinical applications of the newer, breathable dressing products, which approximate a temporary synthetic artificial skin.

Bandages↗
PubMed1991

Polyurethane-covered mammary prosthesis: a nine year follow-up assessment.

We have examined ten tissue capsules from patients ranging from five months to nine years of mammary implantation. Contrary to published reports of polyurethane foam "fragmentation" or "disappearance" in the capsules evaluated, the polyurethane foam was still present and embedded in the surrounding tissue capsule. The foam was nearly always invisible by gross observation, or manual palpation. Only after enzymatic digestion of the tissue capsule did the foam become clearly visible as continuous sheets. ESCA analyses show that explanted foams are devoid of nitrogen peaks. Only carbon, oxygen and silicone signals are observed. The same foams do show nitrogen peaks (due to urethane linkages) when probed by FTIR. Since ESCA only analyzes the first 40-50 Angstroms of a surface, we believe that a "protective coating" composed of soft segments has formed. Beneath this "coating" the original polyurethane composition is still present as evidenced by FTIR analysis. Three possible explanations are advanced: (1) The surface hydrolysis, which takes place within the soft segment of the polyurethane polymer, results in the formation of oligomer(s). These oligomers, devoid of urethane linkages, appear to protect the polymer from further bioresorption, by significantly retarding the rate of additional surface hydrolysis. (2) Chain cleavage occurs in the soft segment producing a hydrophilic polyester chain end which orients into the interfacial area. These chain ends then produce a skin effect which increases the distance from the surface to the hard segments, or urethane-containing linkages. (3) Macromolecular motion in the soft segment phases of the polymer could be reorienting under the influence of the in vivo environment, thus producing a surface layer or "coating" which is predominantly soft segment in composition. Regardless of which of the three hypotheses proves to be most plausible, we interpret the data as showing that the polyurethane foam cover undergoes very slow bioresorption, even after 9 years of human implantation. The data further suggests that the in vivo surface of the polyurethane foam cover is biocompatible and interfacial interactions with inflammatory cells are downregulated or reduced because of the apparent biocompatibility of the material.

Biocompatible Materials↗
PubMed1991

An assessment of 2,4 TDA formation from Surgitek polyurethane foam under simulated physiological conditions.

Samples of polyurethane foam used in the manufacture of mammary prostheses were enzymatically treated for a total of thirty days. Papain (a plant thiol endopeptidase which has similar activity to the human lysosomal enzyme cathepsin B) was our enzyme of choice since it has both amidase as well as esterase activity. The experiment was conducted under physiological conditions closely simulating the microenvironment likely to be found around an implanted mammary prosthesis. In our tests, 2,4 TDA was formed during enzymatic attack of this TDI-based polyurethane foam for the first four (4) days, reaching a maximum of 8.3 parts per million. After the initial burst, no further TDA was observed within the limits of detection of the experiment (10 parts per billion). Based on standard risk assessment, this amount of TDA translates into a risk of developing cancer of one in four hundred million.

Animals↗
PubMed1991

In vivo testing of a biostable polyurethane.

At present all the commercially available "medical grade" urethane elastomers exhibit a phenomenon known as environmental stress cracking (ESC). This phenomenon is characterized by surface microcracking when the elastomer is elongated while in vivo. The degree of strain that is required to initiate microcracking varies from composition to composition. It has been found that harder compounds generally tend to have a higher strain threshold than corresponding softer ones. We theorized that this degradation occurs when certain enzymes (present only in vivo) attack and break down the ether linkages that link the polymer molecules together. Those elastomers that contain more ether linkages (such as the softer compositions) appear to microcrack more easily than elastomers with fewer ether linkages (such as the harder ones). The molecular composition of ChronoFlex urethane has been chosen so that the finished elastomer will be free of ether linkages; thus, it is expected to be immune from environmental stress cracking.

Animals↗
PubMed1987

Blood compatible polyurethane elastomers.

Medical applications of blood compatible polyurethane elastomers contribute significantly to the quality and effectiveness of the nation's health system. These projects range from artificial hearts to diagnostic/therapeutic cardiac catheters which are saving the lives of many critically ill patients.

Animals↗
PubMed1986

The human heart: vault of the soul or pump?

Medical causes that led to the development of artificial hearts are reviewed. Ventricular assist systems are compared with other designs. A discussion of the functioning and surgical implantation of Thermedics Corporation's ventricular assist pump provides a context for an analysis of technical challenges still to be solved.

Assisted Circulation↗
PubMed1986

Thermedics' approach to ventricular support systems.

Temporary and permanent ventricular assist systems, developed by Thermedics, Inc., are described, including rationale, design, operation and surgical applications. Clinical data are presented for pneumatically driven temporary left ventricular assist devices (LVAD). Usefulness of this device rests on the assumption that tissue of a weakened heart can recover if relieved for a time by an LVAD. The surgical implantation of an LVAD is reported in a case where the patient later received a heart transplant. The concept and technology of the subsystems of a permanent ventricular assist system (VAS), now ready for preclinical trials, are discussed. Design of a low-speed, torque-motor driven blood pump is described. Details are presented on transcutaneous energy transmission by means of a transformer, one of whose coils is embedded under the skin. Though less efficient than percutaneous transmission, the method eliminates infection risk. Special types of polyurethanes are analyzed in respect to their biocompatibility. It is concluded that flocking of the polyurethane surface allows the growth of a biological lining which is highly antithrombogenic. Sintered metal powders are found to be most efficient for fabrication of rigid pump components. A lenticular pump design is proposed to solve the problem of pressure differentials in the sealed device. Cardiac endocrine functions are cited in support of using assist devices that leave the heart in place.

Assisted Circulation↗