Search PubMed⌕ Search

Biomedical subjects

S D Bruck

Publications and source records attributed to S D Bruck.

At least 19 recordsLinked to original sources
PubMed1997

Current and future directions of biomedical materials research.

Biomedical materials and implants are not synonymous. Materials per se are not implanted--after configuring, processing, and finishing operations, they constitute parts of implants and other devices. The U.S. Food and Drug Administration currently does not "approve" biomaterials; rather, it approves medical devices, biologicals, and drugs. There have been important advances during the past 40 years in the clinical uses of medical implants and other devices, especially in ophthalmology, cardiology, orthopaedics, surgery and dialysis. In the 21st Century, there will be increased emphasis on curing and preventing major genetic diseases. There will be many nontraditional clinical applications of biomaterials, such as viral- and nonviral-mediated delivery agents in gene therapy, synthetic biomaterials with pharmacologic effects, and biomaterials that can integrate with the biological system to form a long-term, living, renewable interface with prosthetic implants. Therefore, those working in the field of biomaterials must become familiar with new molecular biological techniques and be able to collaborate effectively with molecular biologists.

Biocompatible Materials↗
PubMed1993

Long-term stability of intraocular lenses: literature review, assessment, and testing protocol.

A critical review of the literature confirms the generally excellent, very long-term clinical stability and performance of polymethylmethacrylate (PMMA) in intraocular lenses. In contrast, only short-term, largely nonsystematic data are available on the performance of other, newer materials, such as soft silicones based on polydimethylsiloxane and copolymers of dimethyl- and diphenylsiloxane, hydrogels based on poly(2-hydroxyethylmethacrylate), and various "temporary" and "permanent" hydrophilic coatings. Some conflicting reports have been published on the long-term stability of isotactic polypropylene loop materials. However, the medical consensus seems to be that these are essentially stable to ultraviolet light energy reaching intraocular lenses during the expected service life in excess of 20 years. Uncertainty still surrounds the use of various ultraviolet-absorbing chromophores in the optics and/or haptics of intraocular lenses. Published reports indicate varying transmittance and effectiveness of ultraviolet-absorbing intraocular lenses. Furthermore, there is concern about the fate of the ultraviolet-absorbing chromophores during clinical conditions, especially with regard to degradation and leaching. Although a number of papers has been published on the effect of ultraviolet light energy on intraocular lenses, the experimental approaches differed substantively, so that intercomparative deductions must be made guardedly. A few papers have been published on the long-term biostability (hydrolytic, oxidative, and enzymatic) of intraocular lens materials. However, much of what has appeared in the literature is often illustrative of simplistic assumptions that largely ignore the environment of the eye. Clearly, the eventual success of newer materials must be based on performance characteristics that exceed those of the time-tested polymethylmethacrylate and the refined manufacturing technology designed to transform this polymer into intraocular lenses. The unquestioned clinical success of intraocular lenses rests on long historical data with PMMA that are unavailable with proposed newer materials. Thus, the entry of such new materials into the commercial market, meriting the acceptance of clinicians (and patients), must follow rather than precede thorough in vitro accelerated testing procedures under conditions that permit intercomparative conclusions and recommendations.

Biodegradation, Environmental↗
PubMed1992

Implant retrieval, analysis, and database: a challenge for the medical devices industry.

Despite the widespread use of various medical implant devices since the 1960s, there has not been any systematic effort developed for implant retrieval, analysis, and data banking. Most medical implants fail prematurely because of selection of wrong materials and/or processing conditions, selection of wrong in vitro testing methods, inappropriate extrapolation to in vivo conditions, and/or ignorance of the state of the art. Inasmuch as another federal effort is unlikely to deal effectively with these problems, it is proposed that the medical devices industry establish an independent Institute for Medical Implant Retrieval and Analysis using a small percentage of the profits gained from the sale of implants. In addition to carrying out in-house work, this Institute would support appropriate projects in selected academic institutions, with appropriate feedback to regulatory agencies internationally.

Academies and Institutes↗
PubMed1991

Biostability of materials and implants.

The purpose of this paper is to discuss some important parameters that are involved in the biostability of materials and implants aimed at the eventual development of improved in vitro testing and evaluation procedures. In view of the fact that certain terms have been the subject of misunderstandings, definitions are offered for the terms "biomaterials", "bioerosion", "biostability", and "bioresorption". Following brief descriptions of various classes of materials used in biomedical applications, the in vitro and in vivo degradations of selected materials are discussed. The main conclusions are as follows: (1) most synthetic polymers degrade in vivo by nonenzymatic hydrolysis. Hence, it is recommended that initial, in vitro testing schemes of most synthetic polymers and implants omit the use of enzyme solutions. The use of enzyme solutions is appropriate in the case of natural biopolymers as well as synthetic biodegradable polymers that contain peptidic-, glycosidic-, or phosphatidic bonds. (2) The biostability of materials and implants may be greatly affected by the simultaneous presence of stresses and active components in the physiologic environment that may lead to environmental stress cracking. (3) The biostability of polymeric materials is influenced not only by adsorption but also by the absorption of components in the physiologic environment.

Biocompatible Materials↗
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↗