| Background and aims of the studyThe two main types of prosthetic heart valves (PHV) are mechanical heart valve (MHV) and bioprosthetic heart valve (BHV) which have their own advantages and defects respectively. At present, there are still not ideal PHV in terms of durability and anticoagulant effect. Expanded Polytetrafluoroethylene (ePTFE) is a kind of inert polymer material. It has been used to make artificial blood vessels and patches for many years and has gained satisfactory effect. We planed to design a kind of PHV which was made of ePTFE. In this article we tested calcification and biomechanical properties of ePTFE to demonstrate the feasibility.Part I the experimental studies of calcification and biomechanicalproperties of Ultramicroporous ePTFE in vivo in rabbits 1. Materials and Methods1.1 Materials: Ultramicroporous ePTFE (UePTFE) sheets were taken as experimental group controlled with bovine pericardium (BP) sheets which had been treated with glutaral (GA). The materials were tailored in suitable shape before be embedded beneath skin of the rabbits.1.2 Methods: Using a randomized factorial design, six 1-month-age New Zealand white rabbits were processed calcification and biomechanical measurement of the materials. Each rabbit was made 6 incisions in the back. All UePTFE (experimental group) and BP (control group) sheets were pairwise embedded beneath skin of each incision, then two pairs of materials in each rabbits were randomly taken out to be tested on 1,3,6 months, compared with unembedded materials.1.2.1 Measurement of calcium increase: The to-be-tested materials were washed with phosphate buffer solution (PBS) three times; dehydrated; weighed; digested respectively, then were determined concentration of calcium with a flame absorption spectrophotometer and calculated the calcium increase.1.2.2 Measurement of biomechanical properties: The to-be-tested materials were taken shape of "I", then were tested and recorded data by MTS 858 MiniBionix. The data were transformed into stress-strain curves. According to the curves, modulus of elasticity, yield stress, yield strain, rupture stress and rupture strain of each sheet could be figured out.1.3 Statistical analysis: The data of calcium increase and biomechanical properties were analyzed by Dept. of Medical Statistics of First Military Medical University with SPSS 10.0.2. Results2.1 Comparison of calcium increase (Tab. 1): Calcium content of UePTFE (78.71±51.09mg/g) increased less and slower than BP (201.82±77.07mg/g) significantly (P=0.000), although these two kinds of materials were both calcified.2.2 Comparison of biomechanical properties: Modulus of elasticity of UePTFE (544.01±100.99kPa) was significantly higher than BP (369.41±220.42kPa) (F=30.441, P=0.000) and went up with time elapsed against BP (Tab. 2). The difference of yield strain between UePTFE (34.50±15.65%) and BP (33.97±12.07%) was statistically insignificant (P=0.980). Yield strains of both UePTFE and BP declined with time elapsed (Tab. 3). Yield stress of UePTFE (26.42±2.12MPa) which got no statistical changes with time elapsed (P>0.05) was significantly higher than BP (9.39±4.48MPa) (F=639.471, P=0.000) which lowered with time elapsed (P<0.05) (Tab. 4). Rupture strain of UePTFE (57.97±18.29%) was significantly higher than BP (39.20±13.37%) (F=22.684, P=0.000), but both decreased with time elapsed (F=10.244, P=0.000) (Tab. 5). Rupturestress of UePTFE (34.22±4.05MPa) which got no statistical changes with time elapsed (P=0.169) was significantly higher than BP (10.62±5.12MPa) (F=570.026, P=0.000) which lowered with time elapsed (P=0.000) (Tab. 6).Part II the experimental studies of pathological changes of UePTFE in vivo in rabbits1. Materials and Methods1.1 Materials: UePTFE sheets were taken as experimental group controlled with BP sheets which had been treated with GA. The materials were tailored in suitable shape before be embedded beneath skin... |
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