Processing of cardiac valve allografts: 2. Effects of antimicrobial treatment on sterility, structure and mechanical properties.
This is the second in a series of papers that report experiments to investigate the properties required for effective tissue valve implants. This paper is concerned with investigations into alternative antimicrobial treatments and the effect these treatments produce on the structural and biomechanical properties of ovine aortic valves. Six treatments were studied: heat, peracetic acid (at two concentrations), chlorine dioxide, a surfactant cleaning agent and a solvent/detergent treatment. Samples of myocardial tissue were exposed to a mixed bacterial culture or one of three virus cultures and then decontaminated. Two of the six treatments (0.35% peracetic acid and heat) were effective in removing both bacterial and viral contamination, reducing levels of contamination by 2.5 to 3 logs, whilst a third (chlorine dioxide) was effective against viruses ( approximately 3 log reduction). Valves subjected to these treatments were examined by microscopy and measurements of mechanical properties were made. All three treatments seriously damaged endothelial cells and leaflet fibroblasts. Heat treatment also damaged connective tissue components (collagen and elastin) but these changes were not seen after chemical treatment. Mechanical testing confirmed severe damage following heat treatment but chemical treatment showed only minor effects on the elasticity of the leaflets and none on extensibility. These minor effects could be mitigated by exposure to a lower dose of peracetic acid and this treatment could be safely combined with cryopreservation or storage in 85% glycerol. Peracetic acid was the preferred disinfection method for use in the subsequent in vivo studies in sheep.