The effect of different treatment modalities on the calcification potential and cross-linking stability of bovine pericardium

[摘要] English: In the quest for suitable substitution materials to be used in surgical procedures, alarge variety of different kinds of materials have been investigated. Incardiothoracic surgery, biological tissues such as porcine heart valves and bovinepericardium exhibited the most suitable properties for use as substitute material,while a variety of synthetic materials are also being used.Biological materials must meet a lengthy list of requirements, before it can besuccessfully and safely employed as substitution material. Amongst others, itneeds to be stable against biological breakdown, easily sterilizable, expressminimal immunogenicity, maintain mechanical strength and tissue stability, resistcalcification, be non-carcinogenic and non-toxic and permit easy handling.Numerous chemicals and methodologies have been investigated in order toproduce the most suitable materials attaining these properties. Glutaraldehyde hasemerged as the chemical agent rendering most of these requirements to tissuesfollowing fixation and cross-linking with it.Despite the continued use of GA-fixed bovine pericardium worldwide, calcificationand tissue degradation after 10-12 years post-implant remains a big problem. Themain objective of this study was to try and identify additional biochemicaltreatment/s which can be employed in the fixation and storage of bovinepericardium, that will minimize the calcification potential of the tissue significantlywithout compromising the physical properties or the quality of the tissue.GA-fixed pericardial tissue was used as the control, and the outcomes of all theparameters for the other tissue treatments were compared against it. Numericaland categorical data were collected.In the first phase of study, four different methods of tissue treatment werecompared for extractable calcium and water contents following 8 weeksimplantation of treated samples in the subcutaneous rat model. Aluminium astreatment model was discarded due to the severe calcification of the implants.Results of tissue treated with GAGs were promising and compared favorably withcommercial Glycar-treated tissue, and this prompted more detailed investigation.In the next phase of the study, mechanical properties (tensile strength) and crosslinkingstability (thermal denaturation temperatures) of tissues treated with differentconcentrations of GAGs were compared with GA and Glycar-treated tissue.Treatment with a GAG concentration of 0.01M yielded tissue with comparabletensile strength and thermal denaturation temperatures above the minimumbenchmark. This concentration was identified as the optimal GAG concentration tobe investigated in subcutaneous rat implant studies.In the final phase, treated pericardial samples were implanted into weanling rats for8 weeks and evaluated on the calcification potential, water content, antigenicityand extent of cross-linking of the collagen in the tissues. Tissue treated with 0.01MGAG compared favorably with the commercial Glycar patches regarding all ofthese parameters, outperforming GA-fixed control tissue significantly.Significant evidence was however found that added GAGs were still not effectivelystabilized despite adding metaperiodate as fixative. GAGs leached out of tissuefollowing an extended storage period. Only a limited amount of GAGs was visibleon the outer surface of the explants compared to the layer of GAGs superficiallybound to the tissue before implantation. Despite decreasing the tissue calcificationsubstantially while maintaining good mechanical strength and low antigenicity,stabilization of the GAGs in treated tissues will have to be adequately addressedbefore clinical application of such tissues can be approved.

[发布机构] University of the Free State