PubMed Health⌕ Search

Biomedical subjects

S D Bruck

Publications and source records attributed to S D Bruck.

At least 19 recordsLinked to original sources
PubMed1990

Leachable components in polymeric medical implants and disposables: a brief critical review.

This paper presents a brief, critical analysis of the role of potential leachable ingredients in polymeric implants in relation to performance characteristics when in contact with the physiologic environment. Leaching is the reverse phenomenon of sorption, in which diffusing small molecules, such as additives, are removed by constant or non-constant rates from the bulk to the surface of polymeric materials from which they enter the physiologic milieu. Improved extraction procedures must be accompanied by thorough physico-chemical, mechanical, and biological testings aimed at the better simulation of the in vivo performance. There is a need to develop potentially non-leaching additives for polymers intended for biomedical uses.

Biocompatible Materials↗
PubMed1989

Reference standards for implantable materials: problems and needs.

Medical implant materials that come in contact with tissues, body fluids (including blood) constitute an area in medical devices where reliability and clinical performance limitations are vital. Polymeric implant materials differ in important aspects from metals and alloys, and ceramics (including glasses and carbons) with respect to their atomic and molecular structures and morphology. It is suggested that four categories of 'standards' be developed: (1) certified primary reference materials to be used for calibration purposes, (2) reference materials to be used for the comparative evaluation of physico-chemical and biological properties, (3) 'fabrication-grade' reference materials for intercomparative evaluation of processing conditions, and (4) reference implants aimed at the intercomparative evaluation of possible synergistic effects of additives, processing aids, and fabrication processes on in vivo service life, including biological and mechanical performance.

Biocompatible Materials↗
PubMed1988

Radiation sterilization of polymeric implant materials.

High-energy irradiation sterilization of medical devices and implants composed of polymeric biomaterials that are in contact with tissue and/or blood, may adversely affect their long-term mechanical and/or biological performance (tissue and/or blood compatibility). Since many polymeric implants may contain trace quantities of catalysts and/or other additives, the effect of high-energy radiation on these additives, and possible synergistic effects with the polymer chains under the influence of high-energy radiation, must be considered. It is essential to indicate whether polymeric implants are used in short-term (acute) or long-term (chronic) applications. Relatively small changes in their physicochemical, mechanical, and biological properties may be tolerable in the short term, whereas similar changes may lead to catastrophic failures in long-term applications. Therefore, polymeric implants which are to be sterilized by high-energy irradiation should be carefully evaluated for long-term property changes which may be induced by the radiation.

Biocompatible Materials↗
PubMed1988

Materials and biological aspects of synthetic polymers in controlled drug release systems: problems and challenges.

The physico-chemical and biological aspects of polymeric materials represent vital areas in the reliable, safe, and efficacious functioning of controlled drug-delivery devices. In the case of implantable systems, potential biological problems include incompatibility of the polymers and their degradation products with the physiological environment, adverse metabolic consequences of the degradation products, and occlusion of the drug conduits (catheters) with thrombi and/or drugs, (i.e., insulin aggregates). In the case of transcutaneous drug delivery systems, proper consideration must be given to avoid skin irritation and allergic responses as well as other toxic effects. With biodegradable systems that may follow simple hydrolysis and/or enzyme-catalyzed degradation of labile chemical side-chains that hold the drug molecule and/or the main polymer chain, increased attention must be given not only to the short-term but also the long-term metabolic consequences of the degradation products. Although the term "biodegradation" is often used for in vitro situations it should be reserved only for in vivo circumstances as, at the present time, no in vitro experiments can completely simulate the in vivo environment. The misuse of this term may lead to premature predictions as to the performance of a device in vivo, a situation that ought to be avoided. Appropriate attention must also be given to the effect of drugs on polymers as drug/polymer interactions may influence the stability of both the polymers and drugs and may result in altered therapeutic performance. Standards are needed to clearly differentiate between controlled drug delivery systems and older "sustained" and "time-release" preparations.

Biodegradation, Environmental↗
PubMed1988

Materials aspects of implantable cardiac pacemaker leads.

The reliability of the leads of the entire pacemaker system is vital as the risks of failure include: (1) loss of pacing due to the deterioration of the polymeric insulator in the physiological environment; (2) thromboembolism due to inadequate blood compatibility of the insulator; (3) tissue reactions at the electrode/tissue interface; (4) general foreign body rejection phenomena; (5) perforation of the leads; and (6) excessive stress applied by sutures causing abrasion and stress cracking. Although silicone has been used widely, some years ago Pellethane (a segmented polyetherurethane-urea) has been introduced as an alternate lead insulator, chiefly because it can be extruded using additives into smooth and thin tubes. The additives (antioxidants), extrusion aids, and low molecular weight polymer chains (oligomers) together represent up to approximately 8% by weight of leachables, depending on the extraction medium. The in vivo degradation of Pellethane is biologic in nature and is most likely associated with the absorption and premeation of body fluids from the surrounding physiologic environment leading to stress cracking via the formation of microvoids. Thermally and biologically unstable biuret and allophonate groups in this polyurethane, exposure of the polymer to high extrusion temperatures, and stresses created within the polymer also play key roles in the degradation process. In the case of electrodes, some corrosion can occur even with noble metals and ions formed with the involvement of penetrating body fluids which may combine with the urethane and/or urea groups of the polyurethane, leading to its further degradation in vivo. The totality of the situation indicates a need for the development of a standard guideline for the uniform and consistent pre-clinical testing and evaluation of new materials and fabrication processes of implantable pacemaker leads. Such guidelines should take into consideration, among others, the physiological environment, species-differences between test animals and humans, and observe reliable statistical interpretations based on sufficient data.

Electrocardiography↗
PubMed1982

Medical applications of polymeric materials.

This review presents a critical analysis of the use of polymeric materials in medicine, other than orthopedic and dental applications. Primary focus is on problem areas with various polymers and plastics in disposable products, implants, and devices, including artificial heart valves, cardiovascular prostheses, cardiopulmonary bypass, and hemodialysis. Several problems are presented especially in the biological evaluation of polymeric materials and devices, including species-related hematological differences and the role of the complement system in blood compatibility. Finally, examples of newer medical applications of polymeric materials are discussed, such as controlled drug delivery, polymeric drugs, and artificial skin.

Biocompatible Materials↗
PubMed1981

Possible causes for the calcification of glutaraldehyde-treated tissue heart valves and blood contacting elastomers during prolonged use in medical devices: a physico-chemical view.

Calcification of glutaraldehyde-treated porcine tissue heart valves (xenografts) is not a unique phenomenon but characteristic of a variety of synthetic elastomers and to a lesser extent of non-elastomeric polymers. The main commonality between them is their relative flexibility, permeability, and porosity, and differing capability to adsorb and to absorb various blood components. Although the possibility of biochemical factors involving calcium homeostasis and vitamin K-dependent protein carboxylation as recently proposed by others should not be ignored, it should be noted that calcification of synthetic elastomers has been reported with or without continuous anticoagulation with coumarin derivatives. This paper presents a physico-chemical view showing that despite the observed calcifications with a small number of xenograft valves, their otherwise impressive performance in the physiological environment is due to a significant extent to thermodynamic, molecular and supramolecular factors. The longevity of glutaraldehyde-treated tissue valves can be further improved by special methods. Calcification is especially characteristic for flexing and otherwise moving and pulsating surfaces, typical of many experimental circulatory assist devices and artificial hearts intended for long-term uses.

Aldehydes↗
PubMed1980

Problems and artefacts in the evaluation of polymeric materials for medical uses.

The terms 'biocompatibility', 'blood compatibility', and 'thrombogenicity' are often used interchangeably which leads to confusion in the scientific and medical literatures. No single test can reliably predict the 'blood compatibility' of materials, and tests for thrombogenicity are not necessarily indicators of blood compatibility. Although the toxicological screening of biomaterials is important, the absence of adverse effects does not assure biocompatibility. Acute toxicological screenings should be carried in the biological evaluation phases of biomaterials but the results should be interpreted with caution because polymers degrade in the physiological environment by time-dependent mechanisms leading to the formation of potentially toxic products, including carcinogens. Increased efforts are needed to screen potential biomaterials for carcinogenesis and mutagenesis. Biological tests should be conducted with animals whose haematological profile closely resembles that of humans rather than rely on results obtained wity species such as dogs and calves. Accelerated fatigue testing of elastomers must be conducted under condition that closely approximate the properties of the biological environment to avoid catastrophic failures.

Animals↗
PubMed1980

The role of biomaterials in insulin delivery systems.

The control of blood glucose levels in diabetes involving devices are critically reviewed, and the role of blood-contacting biomaterial components analyzed. These include mechanical insulin-delivery systems of the closed-loop type that require an electronic glucose sensor and feedback, and open-loop systems that deliver insulin without a sensor and feedback. Whole pancreatic and islet transplantations, islet encapsulation, and the potential role of polymeric sustained drug delivery systems are discussed. The medical and social impacts of diabetes mellitus are of prime public health concern and of even greater magnitude than those of heart disease in the United States. While future advances in device design, miniaturization, and biomaterials technology will significantly add to the arsenal of therapeutic alternatives, devices capable of controlling blood glucose levels ought to be viewed as mere interim phases rather than as final goals of the problem.

Animals↗
PubMed1979

Some factors affecting the long-term performance of glutaraldehyde-crosslinked heteroprostheses.

Crosslinked proteins undergo degradation in the physiological environment. Recent cumulative evidence with glutaraldehyde-crosslinked xenograft heart valves emphasizes the fact that caution is in order, despite the generally good performance of these valves in comparison to early formaldehyde-crosslinked prostheses. Glutaraldehyde involves complex chemistry yielding heterogeneous crosslinks with respect to the nature and number of crosslinks with proteins and mucopolysaccharides, all of which contribute significantly to physical and biological performance.

Aldehydes↗