Biomedical subjects

T G Mackay

Publications and source records attributed to T G Mackay.

21 records · Page 2Linked to original sources

PubMed1992

Chemical modification of bovine pericardium and its effect on calcification in the rat subdermal model.

Specific modification of functional groups in collagen has been used to investigate their influence on calcification and thermal stability of bovine pericardium. Pretreatment of pericardium with iron (III) citrate reduced calcification in the rat subcutaneous implant model, as did acyl azide activation of carboxyl and amide groups. Chondroitin sulphate had no significant effect, while cyanamide treatment was mainly effective in combination with iron (III) citrate. Glutaraldehyde pretreatment restricted reaction with other modifying agents, but, as a post-fixation treatment, improved the thermal stability of other agents. Glutaraldehyde post-fixation had no significant relationship to the calcification rate.

Animals↗

PubMed1992

In vitro calcification of bioprosthetic heart valves: report of a novel method and review of the biochemical factors involved.

The lifetime of bioprosthetic heart valves is limited by primary tissue failure and calcification of the valve leaflets. There are indications that synthetic elastomeric materials may also be subject to this problem. The mechanism of calcification is not known, but it is of interest that calcification can be induced in tissue even in the absence of cellular mechanisms, outside the body. Many hypotheses relate to inhibitory or promotory factors rather than primary instigators of calcification and none has led to a satisfactory solution of the problem. The study of calcification in replacement valves generally utilises in vivo test methods i.e. complex biologic systems. This creates difficulty in defining the primary factors involved. The use of in vitro test methods, including a novel fatigue tester method, has been reviewed. Various test media have been used, including simple salt solutions (allowing definition and controlled modification of the calcification medium) and bovine plasma. Comparison of static and dynamic in vitro methods with the rat subcutaneous implant model indicated a lower degree of calcification in vitro: the calcification achieved was, however, significantly greater than similar material not subject to calcification processes. Dynamic in vitro tests produced greater calcification than static in vitro tests. Porcine aortic valve material, in static tests, behaved similarly to bovine pericardium. In vitro calcification testing has a useful role to play in the economic screening of new materials or modifications of existing materials prior to in vivo testing. It may also aid the definition of the mechanism of calcification and hence the development of solutions to the problem.

Animals↗

PubMed1992

Calcification modelling in artificial heart valves.

This study has examined a range of methods of studying the calcification process in bovine pericardial and polyurethane biomaterials. The calcification methods include static and dynamic, in vitro and in vivo tests. The analytical methods include measurement of depletion rates of calcium and phosphate from in vitro calcifying solutions, analysis of tissue contents of calcium, histological staining of tissue sections for calcium, X-ray elemental analysis, by scanning electron microscopy, of calcium and phosphorus distributions over valve leaflets calcified in vitro under dynamic conditions. Bovine pericardium, in all test settings, calcified to a much greater degree than polyurethane biomaterials. Polyurethane extracts calcified to a greater degree than bulk polyurethanes. The test protocol used allows progress through increasingly demanding calcification tests, with the possibility of eliminating unsuitable materials with tests of limited complexity and expense.

Animals↗