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The in vitro calcification and enzymatic degradation of bovine pericardia (BP) after a series of surface treatments were studied as a function of exposure time. The degradation of these treated surfaces was monitored by scanning electron micrography and tensile strength measurements. Polyethylene glycol-(PEG) grafted BP and glutaraldehyde-(GA) treated BPs retained maximum stability in collagenase digestion compared with SDS-treated BP. The ability of alpha chymotrypsin, bromelain, esterase, trypsin, and collagenase to modulate the degradation of SDS-, GA-, PEG-, Carbodiimide-, and glycidylether-treated BPs also was investigated. Incubation of various enzymes to these crosslinked pericardia variably reduced the tensile strength of these tissues. It is conceivable that chemical treatments of pericardial tissues might have altered their physical and chemical configuration and the subsequent degradation properties. In vitro calcification studies showed a substantial reduction in the calcification profile of PEG-grafted bovine pericardia compared to other treated tissues. Furthermore, the biocompatibility aspects of pericardial tissues were established by platelet adhesion and octane contact angle. In conclusion, it seems that the surface modification of bovine pericardia via GA-PEG grafting may provide new ways of controlling biodegradation and calcification.

To develop artificial materials for prolonged use in the vascular system, the complicated process of surface-induced calcification must be better understood. Calcification was examined on porous polyurethane incubated in metastable solutions of calcium phosphate, and the role of certain antibiotics in the medium was evaluated. It seems that certain aminoglycoside antibiotics can modify polyurethane surfaces and, subsequently, their mineralization process. In addition, these antibiotics may alter the calcium transport through polyurethanes. Therefore, it is conceivable that certain antibiotics can, in addition to producing their antibacterial effect, modulate surface calcium binding by changing the calcium mobilization and crystallization. Additional studies are needed to develop applications.

Cardiovascular calcification, the formation of calcium phosphate deposits in cardiovascular tissue, is a common end stage phenomenon affecting a wide variety of bioprosthesis. This study proposes a novel approach of reducing pericardial calcification and thrombosis via coupling polyethylene glycols (PEG) to glutaraldehyde treated bovine pericardium via acetal linkages. The calcification of the PEG modified tissue and the control pericardium (extracted and glutaraldehyde treated) was investigated by in vivo rat subcutaneous implantation models and by in vitro meta stable calcium phosphate solutions. Scanning electron microscopy showed that calcification primarily involved the surface of collagen fibrils and the intrafibrillar spaces. However, the grafting of pericardium with PEG-20,000 had dramatically modified the surface and subsequently inhibited the deposits of calcium. Further, the modified tissue had also reduced the platelet surface attachment. Such a reduced calcification of PEG modified tissues can be explained by decrease of free aldehyde groups, a space filling effect and therefore improved biostability and synergistic blood compatible effects of PEG after coupling to the tissues. This simple method can be a useful anticalcification treatment for implantable tissue valves.

Calcification is a frequent cause of the clinical failure of bio-prosthetic heart valves fabricated from glutaraldehyde pretreated bovine pericardium (GATBP). This article reports on various chemical techniques for grafting polyethylene glycol (PEG) on bovine pericardium, their biostability, and calcification. The process of calcification profile was studied by in vitro experiments via the incubation of pericardial samples in a metastable solution of calcium phosphate. The calcification profile of PEG-modified bovine pericardium through glutaraldehyde linkages was significantly reduced compared to other methods of grafting. The mechanical property of these PEG-modified tissues after enzyme (collagenase) digestion and calcification were also investigated. PEG grafting of BP via glutaraldehyde or hexamethylene diisocyanate had shown better mechanical stability compared to other grafting methods used. In conclusion, it seems that the surface modification of bovine pericardium through high molecular weight PEGs via glutaraldehyde linkages may provide new ways of controlling tissue biodegradation and calcification.