IN VITRO ACCELERATED CALCIFICATION TESTER FOR BIOMATERI-ALS USING REAL BLOOD

Abstract

Purpose: Our previous studies of a polymer heart valve through animal experiments and numerical simulation indicated that mechanical tensile strain is one of the keys to induce calcification. Therefore, we have developed an in vitro accelerated fatigue tester for further analysis of calcification mechanism using real blood. Methods: A segmented-poly-urethane was selected as a test subject. Firstly, some polymer specimens were pre-fatigued under a cyclic sinusoidal tensile strain of 525% at a frequency of 20Hz for 20 days, which is equivalent to 400-days fatigue in a physiologic environment. This pre-fatigued specimen and a virgin specimen with the identical dimension and material were installed into each blood chamber. It was made by a flexible polyurethane with a blood volume of 50ml. Prior to blood compatibility tests, all components were sterilized. Accelerated cyclic strain of 5±5% was acted to both the specimens for 6 hours in a fresh heparinized porcine blood. Results: The comparative tests were conducted 3 times. Then, influence of the pre-fatigue on blood compatibility including calcification was investigated. In all three cases, deposit was only found on the surfaces of pre-fatigued specimens. On the contrary, no deposit was found on the surfaces of virgin specimens. Scanning electron microscopic views showed crystal-like formation of the pre-fatigued surfaces. Moreover, energy dispersive X-ray analysis revealed that the components of deposit included Calcium and Phosphorus. As these in vitro results are quite similar to a typical calcification observed in vivo, effectiveness of our new tester was demonstrated.