Volume 12, Issue 1
March 1989, pages 1-93
pp 1-1 March 1989
pp 3-15 March 1989
This paper is concerned with the activation of platelets by polymers, a key-process in the behaviour of prosthetic devices in contact with blood.
Platelets are activated by contact with many different types of polymer surfaces, which must therefore be regarded as thrombogenic. Two procedures for reducing thrombogenicity are discussed: (i) the chemical attachment of inhibitors of platelet aggregation and (ii) gross modification of the nature of the surface, e.g. by making it more hydrophilic. For purposes of (i) the potent prostaglandin analogue BW 245C has been used, while for (ii) grafting of poly(ethylene glycol) (PEG) has been explored. Both methods give greatly reduced platelet adhesion inin vitro tests.
The second part of the paper deals with the properties of adducts of inhibitors of platelet aggregation (BW 245C, dipyridamole) with water-soluble macromolecules [poly(N-vinyl pyrrolidone), PEG, dextran]. Adducts have been synthesized with terminal and side-chain coupling. On adduction the two inhibitors mentioned show opposite types of behaviour: the molar activity of BW 245C is dramatically reduced, but that of dipyridamole is significantly increased. Remarkable synergistic effects have been recorded for BW 245C adducts. These observations are interpreted in terms of differences in stereochemistry in the drug-receptor interactions.
Appropriate chemical techniques for coupling are outlined, attention being drawn to the special uses of haloalkyl- and haloacyl-isocyanates and 2-isocyanatoethyl methacrylate as reagents.
pp 17-25 March 1989
Smooth, perfectly spherical, highly hydrophilic microspheres have been prepared from crosslinked poly(methyl methacrylate) microspheres by alkaline hydrolysis in ethylene glycol at elevated temperatures. These microspheres absorb varying quantities of water depending upon the extent of hydrolysis. Subcutaneous implantation studies on rabbits demonstrated that the microspheres are biocompatible. Implantation studies in the renal arteries of dogs demonstrated the occlusion effect produced by the microspheres. Microspheres could be made radiopaque by the incorporation of barium sulphate. Potential uses envisaged for these microspheres in the biomedical area are that of artificial emboli for endovascular embolization and as microcarriers for the growth and propagation of anchorage dependent mammalian cells.
pp 27-32 March 1989
Hydrolysed poly(methyl methacrylate) microspheres with carboxyl residues distributed throughout the matrix were tested for their ability to support cell adhesion and growth. Cell growth as determined by protein content, phase contrast and scanning electron microscopy showed that these microspheres are growth-supportive. Further, preliminary experiments pointed to their usefulness in microcarrier culture.
pp 33-40 March 1989
A novel small diameter (3·8 mm ID) arterial prosthesis has been designed, manufactured and tested as a replacement for the carotid artery in the dog.
The graft is compliant in the longitudinal, circumferential and radial directions. It is anisotropic with compliances similar to those of the natural canine carotid artery. It is flexible, the inner blood contacting surface being smooth to the naked eye. It is composed of micro-fibres of 1·0 µm diameter, electrostatically drawn from a solution of polyetherurethane urea and deposited onto a rotating steel mandrel. Of 22 grafts confirmed by ultra-sound Doppler waveform analysis to be patent at 2 weeks after implantation, 17 were patent when removed at 2 years.
The histological features of the excised grafts are described.
pp 41-47 March 1989
The various requirements placed on materials that might serve as suitable components in drug delivery systems are discussed. Special attention is paid to the interactions between the drug delivery constructs and the biological environment, using the interactions in the vascular compartment of the body as an example.
Two alternative general approaches are compared: (a) “controlled drug release”, which aims to reduce or eliminate side effects by producing a steady therapeutic concentration of drug in the body; (b) “site-selective drug delivery”, which aims to ensure that the drug is delivered to the site of its biochemical and disease-related site of action, at the same time maintaining the drug inactive elsewhere in the body.
It is concluded that materials for delivering drugs to selected sites of disease within the body must be designed to utilise the unique features (structure, function, rhythm) of the main elements involved in the disease. Equally important is to design drug carriers that do not interact non-specifically within the body so that their specific action would be prevented. It is difficult to see how this could be achieved using materials entirely “foreign” to the body. Utilising the primary structures used by the biological systems (proteins, glycoproteins, carbohydrates) and creating novel higher structures (secondary, tertiary, quartenary) that mimic the native material is the logical way forward in the search for new drug delivery systems, and we need to turn more and more to the molecular basis of biology for guidance and inspiration.
pp 49-52 March 1989
Ionising radiation provides a clean and controllable method of producing and modifying polymers for use as biomaterials. The present work surveys some of the recent advances in this field, with emphasis on recent achievements in this field as a result of the work done at the Bhabha Atomic Research Centre, such as a strip for the quick detection of jaundice, which involves a detecting agent encapsulated in a radiation crosslinked polymeric gel and the trapping of bacteria in radiation crosslinked polymers for biological control of mosquito larvae.
pp 53-56 March 1989
The spin-state equilibria of cobalt ions in the system La1−xNaxCo1−xNbxO3 (x⩽0·40) has been studied by measuring its magnetic susceptibility as a function of temperature in the range 300–600 K. It is found that the behaviour of the samples withx⩽0·10 is similar to that of LaCoO3, while compositions withx⩾0·20 behave quite differently, exhibiting simple paramagnetic behaviour.
pp 57-62 March 1989
Pyroelectric properties of Gd-doped and undoped potassium vanadate and lithium vanadate investigated in the temperature range covering their transition points show sharp increase at Curie temperature for undoped and for 0·025, 0·05, 0·1 mol% Gd2O3-doped, but no remarkable peak at Curie temperature for 0·5, 1, 3 mol% Gd2O3-doped KVO3 and LiVO3. The Curie temperature of all the samples remains the same for various concentrations of Gd.
pp 63-80 March 1989
The oxygen-deficient phase of the highTc superconductor, YBa2Cu3O7, was oxygen-enriched using the fluidization technique to give good superconducting properties. The normal method of oxygen treatment at 900°C for 24 h and at 600°C for 24 h has been reduced to just one treatment at 600°C for 12 h by the fluidization technique to achieve almost the same strength of superconducting signal for the YBa2Cu3O7 powder, which establishes the attractiveness of the latter route for the large-scale preparation of superconducting material. The particle sizes were in the range 0–90, 90–180 and 180–420 µm. The fluidized particles were crystalline with orthorhombic distortion.Tconset, estimated using the a.c. magnetic susceptibility method, was 91·3 K. The volume fraction of superconducting material in the product was 83·7–85·3%, one of the highest values reported so far for YBa2Cu3O7.
pp 81-93 March 1989
The effect of oxide additives-CuO, SiO2, Y2O3, Bi2O3 and ZnO in 1–10 mol% on the sintering and superconducting properties of YBa2Cu3O7 was studied. SEM studies indicated improvement of grain size and interconnectivity due to the additives, the best results being obtained with Bi2O3, SiO2 and Y2O3. The superconducting transition temperature is unaffected (92±2 K) even with 10 mol % of the additives. ZnO, however, decreases theTc as expected.
Volume 42 | Issue 6
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