Life history of symbiont-bearing giant clams from stable isotope profiles.

Stable isotopic and shell-growth banding studies of the symbiont-bearing giant clam Tridacna maxima reveal the existence of two growth phases related to sexual maturity that can be discerned in the shells of extinct and extant mollusks. The changeover from the first to second growth phase at an age of approximately 10 years is accompanied by a decrease in rate of calcification and suggests a reordering of energy priorities between biomineralization and reproduction. The carbon-13 to carbon-12 ratio of Tridacna maxima is systematically depleted relative to symbiont-barren mollusks, making it possible to determine the importance of algal-molluscan symbiosis to the functional morphology and paleoecology of mollusks in the geologic record.

Seasonal Oxygen Isotopic Variations in Living Planktonic Foraminifera off Bermuda.

Seasonal variations in the oxygen-18/oxygen-16 ratio of calcite shells of living planktonic foraminifera in the Sargasso Sea off Bermuda are a direct function of surface water temperature. Seasonal occurrence as well as depth habitat are determining factors in the oxygen isotopic composition of planktonic foraminifera. These relationships may be used to determine the seasonal temperature contrast of oceans in the past.

Periodic freshwater flooding and stagnation of the eastern mediterranean sea during the late quaternary.

Major negative oxygen isotopic anomalies in planktonic foraminifera are associated with deep-sea anoxic mud layers (sapropels) deposited 9000 and 80,000 years ago in the eastern Mediterranean. The isotopic depletion in surface-dwelling foraminifera is significantly greater than in mesopelagic foraminifera. This difference in isotopic response suggests that surface-water salinities were drastically reduced during times of sapropel formation, possibly as the result of meltwater runoff from the Fennoscandian ice sheet into the eastern Mediterranean by way of the Black and Aegean seas.

Multicenter study to assess potential hazards from exposure to lipid peroxidation products in soya bean oil from Trilucent breast implants.

In response to a Hazard Notice by the Medical Devices Agency of the UK in 2000 regarding the Trilucent breast implant (TBI), an expert panel was convened to implement a research program to determine whether genotoxic compounds were formed in the soybean oil filler (SOF) of TBIs and whether these could be released to produce local or systemic genotoxicity. The panel established a research program involving six laboratories. The program recruited 47 patients who had received TBIs (9 patients had received silicone implants previously). A reference group (REBI) of 34 patients who had exchanged either silicone (17 patients) implants (REBI-E) or patients (17) who were to receive primary implantation augmentation with silicone (REBI-PIA), and who were included as needed to increase either the pre- or post-explantation sample number. Of the 17 REBI-E patients, 5 had silicone implants and 12 had saline implants previously (prior to the last exchange). Investigation was undertaken before and after replacement surgery in the TBI patients and before and after replacement or augmentation surgery in the REBI patients. The pre- to post-operative sample interval was 8-12 weeks. Pre-operative samples were collected within 7 days prior to the operation. Information on a variety of demographic and behavioral features was collected. Biochemical and biological endpoints relating to genotoxic lipid peroxidation (LPO) products potentially formed in the SOF, and released locally or distributed systemically, were measured. The SOF of explanted TBIs was found to have substantial levels of LPO products, particularly malondialdehyde (MDA), and low levels of trans-4-hydroxy-2-nonenal (HNE) not found in unused implants. Mutagenicity of the SOF was related to the levels of MDA. Capsules that formed around TBIs were microscopically similar to those of reference implants, but MDA-DNA adducts were observed in capsular macrophages and fibroblasts of only TBI capsules. These cell types are not progenitors of breast carcinoma (BCa) and the location of the implants precludes LPO products reaching the mammary epithelial cells which are progenitors of BCa. Blood levels of LPO products were not increased in TBI patients compared to REBI patients and did not change with explantation. In TBI patients, white blood cells did not show evidence of increased levels of LPO-related aldehyde DNA adducts. In conclusion, based on a number of measured parameters, there was no evident effect that would contribute to breast or systemic cancer risk in the TBI patients, and the recommended treatment of TBI patients involving explantation was judged appropriate.

Modulation of growth in retina-derived cells by extracellular matrices.

Intravitreal membranes from patients with proliferative vitreoretinopathy (PVR) consist partly of retinal glial (RG) and retinal pigment epithelial (RPE) cells surrounded by varying amounts of extracellular matrix (ECM). The contribution of the ECM to the growth of PVR membranes is unknown. This study was undertaken to determine if proliferation in cultured RPE and RG cells is affected by different substrates, including some ECM materials which have been identified in PVR membranes. Substrates tested included type I collagen, basement membrane Matrigel, and poly-D-lysine, as well as uncharacterized cell type-specific matrices deposited by cultured RPE and RG cells. Proliferation was quantified by 3H-thymidine incorporation and radioautography 24 hours after plating and by cell counts after 14 days in the presence of serum. Relative to uncoated culture plastic, growth of RPE cells was inhibited by Matrigel, enhanced by poly-D-lysine, and unaffected by type I collagen. In contrast, growth in RG cells was inhibited by type I collagen and unaffected by the other substrates. Analysis of the timing of DNA synthesis after plating suggested that the substrates which affected RPE growth did so by altering the fraction of cycling cells rather than the cell cycle time. For the cell-derived matrices, heterotypic matrix (matrix produced by the other retinal cell type) enhanced the growth of both RPE and RG. The results suggest that the ECM may modify the growth of cells contributing to PVR membranes. Of note is that the cell-derived matrices reciprocally stimulated growth of RG and RPE cells, cell types which may interact in PVR membranes.

Quantifying the soft tissue response to implanted materials.

As the diversity of biomaterials increases, new developments are aimed at these materials becoming interactive rather than passive with respect to the environment they are placed in. The need accurately and reproducibly to assess the response of the body to these materials increases. Historically, quantification of tissue responses has taken many forms but with the continuing development of powerful computers, our ability to quantify the tissue response to implanted materials has become a reality. Computer systems can now analyse sections automatically and then go on to sort the huge quantities of data created, into in depth patterns and cross comparisons so that subtle changes in tissue responses can be detected and understood.

Neutrophil polarization and immunoelectrophoresis assays in the study of complement activation by biomaterials.

The neutrophil polarization assay, a technique used to measure chemotaxis, was adapted to examine complement activation. Complement activation in serum which had been incubated with metallic and polymeric biomaterials was examined using the neutrophil polarization assay and immunoelectrophoresis assay. In agreement with previous publications, nylon activated the complement cascade, but PTFE did not. The neutrophil polarization assay was found to be the most sensitive technique for examining complement activation by endotoxin but the immunoelectrophoresis assay is the technique most sensitive for detecting complement activation by cobalt powder. In both assays, complement activation was not detected in serum incubated with chromium powder. However, serum incubated with silver and nickel powder stimulated neutrophils to polarize indicating that these powders may activate complement.

On the biodegradation of poly-beta-hydroxybutyrate (PHB) homopolymer and poly-beta-hydroxybutyrate-hydroxyvalerate copolymers.

The known biodegradability of PHB in certain biological environments has led to its proposed use as a 'biodegradable' implant material. Monofilaments of PHB homopolymer and two PHV-PHB copolymers have been studied in vivo and in vitro and assessed for changes in mechanical properties and topography. In vivo biodegradation was only observed with PHB when pre-degraded by 10.0 Mrad of gamma-irradiation before implantation. High temperature in vitro hydrolysis suggested that PHV copolymer additions retarded the rate of degradation of PHB. Hydration reactions had most effect on the ultimate tensile properties of the materials. In contrast, the elastic properties appeared to be relatively unaffected.

Albumin adsorption on metal surfaces.

Studies of adsorption kinetics, desorption and adsorption isotherms concerning the interaction between albumin and a range of metal and metal oxides were undertaken in vitro. Three distinct types of behaviour concerning the adsorption of albumin on to metal surfaces were identified. Some metals adsorb considerably greater amounts of protein than might be expected from surface energy alone and it is suggested that electrostatic forces could be responsible for this phenomenon.

Immune response in biocompatibility.

Biocompatibility is concerned with the interactions that occur between biomaterials and host tissues. As foreign objects in that host tissue these materials may initiate several types of response. It has often been postulated that the immune response, by which the host normally defends itself against invasion by foreign organisms, can be involved in the response to biomaterials. This review discusses the mechanisms by which this could occur and the evidence that suggests the immune response is indeed of significance in biocompatibility.

Preparation of non-thrombogenic materials using 2-methacryloyloxyethyl phosphorylcholine.

This review addresses the non-thrombogenic characteristics of copolymers based on 2-methacryloyloxyethyl phosphorylcholine (MPC), originally developed by Nakabayashi and colleagues. The hypothesis underlying these developments was that such materials would adsorb phospholipids from blood, yielding surfaces with good natural blood compatibility. Methacrylates were found to have excellent properties for this copolymerisation. The characteristics of the MPC copolymers relevant to the improved blood compatibility were minimisation of protein adsorption through an increase in the amount of free water in the MPC hydrogels, which prevents protein conformational change and increased protein stability in solution. Non-thrombogenicity has been evaluated by in vitro, ex vivo and in vivo procedures. Non-thrombogenic dialysis membranes and a durable glucose biosensor have been developed using this MPC copolymer.

Visualization of the spatial distribution of silver in histological sections.

The distribution of silver surrounding silver-containing implant devices can be clearly demonstrated using an autometallographic technique originally described by Danscher.

The in vivo and in vitro degradation of poly(glycolic acid) suture material as a function of applied strain.

The in vivo and in vitro stability of a degradable suture material, poly(glycolic acid) has been shown to be dependent on the magnitude of a pre-imposed strain. The degradation, monitored by changes in the tensile load at break, was considerably enhanced by pre-straining the material to one half of the normal extension at break, using a novel implantable device.

The response of bone to carbon--carbon composites.

A cloth-sandwich construction of a carbon-carbon composite material has been implanted in the femora of a series of rats and the response of the bone to this material compared to the response to titanium. It is shown that the carbon provides for excellent hard tissue biocompatibility. When the composite has a surface texture associated with fibre run out there is a degree of bony attachment, the interfacial shear strength for the composite-bone system being significantly greater than that for the titanium-bone system during the period 4-40 weeks post implantation.

Scanning electron microscopy of the metal-tissue interface. I. Fixation methods and interpretation of results.

Scanning electron microscopy has been used to study the interface between implants of pure metals and the muscular tissue of rats. Several problems arise in the interpretation of the observations made, due to the potential for disruption to the tissue and the exacerbation of any corrosion that may have occurred in vivo during the fixation periods. Details are given of the control experiments performed in order to ascertain the nature of potential artefacts and of the techniques eventually determined to be optimal for these purposes.

Scanning electron microscopy of the metal-tissue interface. II. Observations with lead, copper, nickel, aluminium, and cobalt.

The nature of the metal-tissue interface following the implantation of five pure metals, lead, copper, nickel, aluminium and cobalt, in rats has been observed by scanning electron microscopy. The general conclusion, derived from light microscopy that the tissue response to pure metals is characteristic of and specific to individual pure metals has been confirmed in this study. However, far more detailed observations of factors such as the extent of metallic corrosion, the distribution of red blood cells, platelets and other cells in the capsule and adherent to the metal surface, have been possible with SEM.

The response to the intramuscular implantation of pure metals.

Discs of five high-purity metals, cobalt, nickel, copper, aluminium and lead have been implanted intramuscularly in rats and the response observed histologically for period up to 52 weeks. A reproducible but different response was observed with each metal. Whenever corrosion occurred, as with copper, nickel and some cobalt specimens, the implants became loose. In the absence of corrosion, the implants were firmly held within a more confined capsule. A minimal response was seen with lead, implying normally toxic metals do elicit an immune response whilst some, especially copper and nickel appear to render the host more susceptible to disease. The implants appear to have a profound effect on the immediate vasculature, are able to cause a prolonged polymorphonuclear response in the same way as bacteria, are associated with varying amounts of haemosiderin laden macrophages but not with giant cells. The animals appear to be able to deal with bacteria introduced at surgery without hindrance from the metal.

Relationship between chemotaxis and complement activation by ceramic biomaterials.

This paper examines the relationship between complement activation by ceramic biomaterials and chemotaxis. Complement activation was examined by both neutrophil polarization (a technique which has previously been used to examine chemotaxis) and immunoelectrophoresis assays. The results suggest that at increasing serum concentrations of both calcium hydrogen phosphate and coral (calcium carbonate) powder, the quantity of C3 activation increased, as did the quantity of serum-derived chemotactic factors. In the case of tricalcium phosphate powder, the quantity of C3 activation and the neutrophil polarization response to serum were similar for serum levels between 20 and 80 mg/ml. Complement C3 was not activated in serum incubated with calcium hydrogen phosphate powder and serum incubated with this material was not chemotactic for neutrophils.

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.

Molecular biointeractions of biomedical polymers with extracellular exudate and inflammatory cells and their effects on the biocompatibility, in vivo.

The stability of biomedical polymers in physiological environments is crucial for the normal operation of devices, as well as determining their effect on the tissue response. Degradation is an important factor in polymer biocompatibility, since the environment of the human body can be aggressive to polymers. Most implanted polymers suffer degradation to some extent, and the kinetics and mechanisms of the processes can be affected significantly by various biologically active species, especially enzymes, lipids, peroxides, free radicals and phagocytic cells. The degradation of poly(caprolactone) and poly(DL-lactic acid) under controlled in vivo conditions was studied using a poly(methyl methacrylate) chamber designed to control the exposure of polymers to physiological environments. In particular they may be designed to allow access of extracellular exudate only or access to cells as well as the fluid. The chambers, sealed with filters of pore size either 0.45 micron (impervious to cells) or 3.0 microns (allowing cells to enter the chamber), were implanted subcutaneously into experimental animals for 10, 20 and 30 wk periods. Degradation and molecular interactions of the polymers were characterized by gel permeation chromatography and scanning electron microscopy. The extracellular exudate formed within the implanted chamber is active in promoting the degradation of some biomedical polymers. Inflammatory cells are involved in the biodegradation of implanted polymers by releasing biologically active species such as free radicals into the area surrounding the implant. The data have demonstrated that the hydroxyl radical is likely to be one of the main causes of polymer degradation.