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Biomedical subjects

D F Williams

Publications and source records attributed to D F Williams.

At least 73 records · Page 4Linked to original sources
PubMed1994

Plasma recalcification as a measure of contact phase activation and heparinization efficacy after contact with biomaterials.

The rate of plasma clotting was measured in order to investigate two different processes. In both cases normal, pooled platelet-poor plasma was used as a substrate for measurement of clotting. The intrinsic coagulation pathway was studied by bringing a variety of biomaterials into contact with a plasma aliquot and observing the rate of clotting diminish by virtue of factor XII activation. The efficacy of heparinization was investigated by measuring the increase in clotting time of a plasma aliquot during biomaterial contact. In both cases, clotting time was measured turbidometrically. Marked differences in intrinsic pathway activation were observed between a variety of materials. There were clear differences between the materials and the negative and positive controls. The assay showed that heparinized materials could be distinguished from non-heparinized materials and a non-activated plasma control.

Biocompatible Materials↗
PubMed1994

Biodegradation of hyaluronic acid derivatives by hyaluronidase.

Hyaluronic acid (salt) (HA) has been chemically modified as a biomaterial for medical applications such as controlled drug release matrices, nerve guides and wound dressings. A series of HA derivatives, which include different ester types and different degrees of esterification, have been used to investigate the stability of these materials in testicular hyaluronidase. Gel permeation chromatography and capillary viscometer have been employed to determine the size of the molecules, the former used for the water insoluble derivatives that dissolve in dimethyl sulphoxide, the latter for the water soluble samples. The preliminary experimental results indicated that the molecular weight of fully esterified hyaluronic acid (both ethyl and benzyl esters) did not decrease after treatment in the enzyme for 7 and 14 days while the water soluble partially esterified HA were degraded by the enzyme producing a sharp reduction of viscosity within minutes. These observations tend to suggest that the carboxylic groups in the beta-glucoronic acid unit are the activation centre of this enzyme and the total blockage of these groups can restrict the cleavage of beta (1-->4) glycoside bonds by this enzyme.

Biocompatible Materials↗
PubMed1994

Modelling the pattern of cell distribution around implanted materials.

The analysis of the cellular soft tissue response has traditionally focused on using highly skilled human assessment to determine the severity or presence of a particular type of response. This has taken the form of many different assessment criteria, some even attempting some form of 'quantitative' grading index. With the complexity of this response and the availability of high performance computer systems it is not sufficient and no longer necessary to describe a tissue response subjectively. The soft tissue response to a number of implanted materials has been analysed using a combination of immunohistochemistry and image analysis to reproducibly stain and count the cells involved in a soft tissue response to implanted materials, as well as measure their position relative to the implanted material. The combination of cell count and pattern of cell distribution revealed that although the magnitude of the cellular responses changes with respect to time the position of cells with respect to an implanted material does not change significantly over time. The position of cells is controlled more by the type of implant material and the change in subject the material is implanted in.

Animals↗
PubMed1993

Mechanisms of polymer degradation in implantable devices. 2. Poly(DL-lactic acid).

The hydrolytic degradation of poly(DL-lactic acid) in an aqueous environment in which hydroxyl radicals have been generated has been investigated. Different methods (gel permeation chromatography, differential scanning calorimetry, and scanning electron microscopy) were employed to study the mechanisms of degradation of this amorphous physiologically absorbable polymer. The data indicated that the hydroxyl radical is likely to be a significant factor in the degradation of this polymer.

Biodegradation, Environmental↗
PubMed1993

Schistosoma mansoni: membranes from adult worms reversibly perturb shape, volume, and membrane organization of intact human red blood cells.

Adult forms of Schistosoma mansoni ingest host (human) red blood cells (RBCs). To elucidate potential mechanisms by which contact with adult parasites perturbs RBC membranes, we studied the effects of the membrane fraction of isolated schistosomes on RBC shape, volume, potassium ion content, and phospholipid and transmembrane protein lateral mobility. S. mansoni-treated RBCs exhibited rapid but spontaneously reversible shape change from discocytes to spheroechinocytes, reversible decrease in cell volume, and rapid loss of intracellular potassium ions. Treated RBCs also showed rapid but spontaneously reversible immobilization of membrane phospholipids and of band 3, the major transmembrane protein. These data suggest that components of adult S. mansoni membranes can perturb host RBC volume and membrane organization. In the absence of RBC lysis, RBC metabolic and repair mechanisms can reverse these effects.

Animals↗
PubMed1993

Does the fibrin coat around a central venous catheter influence catheter-related sepsis?

The purpose of this study was to determine whether the fibrin sheath that develops around an intravenous silicone catheter influences catheter-related sepsis. A rat model with a central intravenous silicone catheter was used. Staphylococcus aureus, dose 1 x 10(7) colony forming units (cfu), were injected via the tail vein, either immediately after catheter insertion (group 1, n = 23) or after the catheter had been in situ for at least 7 days (group 2, n = 22). Blood cultures were done on at 24 hours and 7 days. Animals were killed on day 7 and the catheter was removed for culture (Maki and broth) and scanning electronmicroscopy (SEM). The was no significant difference (P > .05) between the number of positive blood cultures in groups 1 and 2 at 24 hours (16 v 9) and 7 days (12 v 6). In group 1 there were significantly more positive catheter cultures by both methods (23 v 16 in group 2; P < .05) and more cfu/per centimeter catheter (group 1 mean, 520, range, 197 to 600; group 2 mean 195, range 9 to 600; P < .001). In group 1, 12 animals had catheter sepsis compared with 5 in group 2 (P = NS). On SEM a fibrinous sheath was identified on all catheters removed on day 7 but not on 5 catheters inserted and removed after 10 minutes.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Image analysis in the evaluation of biomaterials.

An examination regime, based on a computer-aided image analysis system, has been developed for the quantitative evaluation of the local tissue response to biomaterials. This procedure involves the immunoenzymic staining of tissue sections using monoclonal antibodies specific for certain inflammatory cell types. An avidin-biotin-horseradish peroxidase staining method is used to identify antibody binding sites and the sections are assayed using a computer-aided image analysis system. This regime facilitates the rapid and accurate measurement of 30 cell related parameters in sections stained for macrophages, polymorphonuclear leucocytes, and other cells.

Animals↗
PubMed1993

Quantitative in vivo assessment of the tissue response to dermal sheep collagen in abdominal wall defects.

We quantified the tissue response, tissue organization and patency of biodegradable patches for the repair of abdominal wall defects. We used dermal sheep collagen, cross-linked with hexamethylenediisocyanate in a model. The collagen patches were implanted either untreated or plasma polymerized with tetrafluoroethylene (TFE), to improve the properties of the patch for bowel adhesion and rate of degradation. The implants with surrounding tissue were retrieved after 3 d, 1, 2, 4, 6 and 8 wk, then sectioned and stained specifically for macrophages, neutrophils, T-lymphocytes and endothelium. Only macrophages and neutrophils were observed in the implant and surrounding tissue, with different antigen expression in the macrophages. This was found to be dependent on whether the macrophages were found within the implant or in the surrounding tissue. The neutrophils and macrophages were assessed using image analysis techniques to quantify the tissue responses to treated and untreated collagen, enabling comparison of the respective tissue responses. No significant differences were found between the two forms of this collagen. Infection played a key role in the severity of the tissue response around both types of implants, resulting in large variations in cell counts at each time period. Treating the collagen with TFE did not significantly improve its performance in this application.

Abdominal Muscles↗
PubMed1993

Mechanisms of polymer degradation in implantable devices. I. Poly(caprolactone).

Poly(caprolactone) is a biodegradable aliphatic (poly(alpha-hydroxy acid), with important applications in the field of human therapy, due to its biocompatibility and bioresorbability. The degradation of poly(alpha-hydroxy acids) depends on chemical hydrolysis, but there is much interest in the precise mechanisms, including the role of free radicals, especially oxygen free radicals and their role in human disease. The hydrolytic degradation of poly(caprolactone) in aqueous environments was used as the control in a study of the effects of hydroxyl radicals in aqueous solutions. Different methods (GPC, DSC, SEM) were employed to investigate the mechanism of degradation of this semicrystalline physiologically absorbable polymer. The data indicate that hydroxyl radical is likely to be a major factor in the degradation of this polymer.

Biocompatible Materials↗
PubMed1993

Biocompatibility of glass ionomer cements.

Glass ionomer cements (GICs) are widely used in the dental field and are increasingly being considered as materials with potentially good osteogenic properties. This paper details a comprehensive biocompatibility evaluation of a number of GICs. These include conventional, commercially available materials, novel formulations and a new light cured material. The experimental programme entailed in vitro cell culture studies using direct contact and extraction tests and an in vitro rat model in which the GICs were in intimate contact with bone for periods up to 8 wk. The results demonstrate clear differences between the materials and in particular highlight the poor cellular response to the light cured material. Methylthiazolyldiphenyl tetrazolium assay demonstrates stimulation of cell growth by some GIC formulations and indicates that cytotoxic leachable agents can be removed from others. The results obtained following implantation into bone are comprehensively presented using photomicrographs. New bone formation with time is demonstrated with a number of formulations.

Animals↗
PubMed1993

Human neutrophil chemokinesis and polarization induced by hyaluronic acid derivatives.

Neutrophils and macrophages are known to undergo significant modifications in their morphology and basal metabolism in response to chemical factors, in particular changes in the shape, movement, phagocytic activity and degranulation. These phenomena often involve an increase in chemokinesis and cellular secretory activity, usually expressed in antimicrobial activity. Once activated, the cells can move quickly towards the source of the stimulus, where they produce and release great amounts of enzymes (e.g. proteases, hydrolases, lysozyme) and reactive oxygen metabolites (e.g. O2-., H2O2, OH.). This study has examined the ability of surfaces of selected biomaterials to influence neutrophil morphology and locomotion. The surface of two films derived from hyaluronic acid derivatives were compared with that of glass. The two hyaluronic acid derivatives, despite having a similar chemical structure, were shown to interact with human neutrophils in different ways. A hyaluronic acid ethyl ester stimulated the whole population of neutrophils to take up a non-spherical morphology (polarize) and to move with a velocity similar to that of N-formyl-methionine-leucine-phenylalanine-stimulated cells on a glass surface. In contrast, only 44% of the examined cells on the surface of hyaluronic acid benzyl ester were polarized and their mean speed was only slightly higher with respect to that found with non-stimulated cells on glass. Moreover, while on the benzyl ester and on glass a correlation between neutrophil circularity (i.e. the shape of the cell) and cell speed was found, the ethyl ester did not show any correlation.

Biocompatible Materials↗
PubMed1993

The characteristics and performance of dentine bonding agents.

Several attempts have been made to synthesise dentine bonding systems, but low bonding strength, increased variance, toxicity and poor hydrolytic stability were some of the disadvantages excluding them from being widely approved. However, many dentine bonding systems are considered to be biocompatible and have become commercially available. These adhesives are thought to have one or two bifunctional agents where one part of the molecule is intended to bond to the inorganic part of the dentine (calcium ions of the apatite), or to the organic part of the dentine (amino and hydroxy groups of the collagen), and the methacrylate part of the molecule is intended to copolymerise with the restorative resin. This review demonstrates that further work is needed to achieve the synthesis of novel dentine bonding agents which bond chemically to dentine by strong covalent bonds, and which are hydrolytically durable and non-toxic to the oral environment.

Dental Bonding↗
PubMed1993

Non-invasive magnetic resonance imaging of the soft tissue response to a biomaterial.

Magnetic resonance imaging (MRI) has been employed to visualize the tissue response to hydrogel implants in rats. High contrast MR images of the implant site were obtained. Distinct tissue variations in the MR images have been observed. These can be attributed to either the surgical procedure or the application of a tissue irritant to produce inflammation and have been verified histologically. This study demonstrates that MRI is potentially a useful tool for the non-invasive in-vivo evaluation of biomaterials.

Animals↗
PubMed1993

Synolite as a base resin for dental composites and related biomaterials.

Synolite resin was analysed using FTIR, NMR and HPLC to determine its components and purity. The resin was found to be predominantly BIS-GMA containing traces of its two isomers. The analysis indicated that there was no unreacted methacrylic acid or other impurities.

Bisphenol A-Glycidyl Methacrylate↗
PubMed1993

Fleas (Siphonaptera) infesting giant kangaroo rats (Dipodomys ingens) on the Elkhorn and Carrizo Plains, San Luis Obispo County, California.

The giant kangaroo rat, Dipodomys ingens (Merriam), has a limited distribution in the San Joaquin Valley, CA. Because of reductions in its geographic range, largely resulting from humans, the species was listed as an endangered species in 1980 by the California Fish and Game Commission. As part of a study of the community ecology of southern California endangered species, including D. ingens, we were able to make flea collections from the rats when they were trapped and marked for population studies. All but one of the fleas collected from the D. ingens in this study were Hoplopsyllus anomalus, a flea normally associated with ground squirrels (Sciuridae). It has been suggested that giant kangaroo rats fill the ground squirrel niche within their range. Our data indicate that this role includes a normal association with Hoplopsyllus anomalus.

Animals↗
PubMed1993

The economics of advanced biomaterials.

A patient who has previously lost an eye through trauma develops a cataract in his remaining eye. Two types of intraocular lens are available for his treatment, one of modest cost, which is effective in all but a few high-risk patients, the other much more expensive, which gives marginally better results on average, but better performance in those with diabetes or glaucoma. Should the higher-cost lens be used even if there is no direct evidence that it will do better in this patient who does not have these conditions, or is it ethically justified to use the lower-cost lens even though failure would result in the total loss of sight? This case is used as the basis of a discussion on the use of high-cost materials and medical devices.

Biocompatible Materials↗