An Investigation on Silicone and Silicone Rubber Stents in Comparison with Stainless Steel Stents: Introducing a Double Layer Stent Model
Mona A. El-Naggar *
Department of Engineering, Physics and Mathematics, Faculty of Engineering, Cairo University, Egypt
*Author to whom correspondence should be addressed.
Abstract
A single layer of different materials; silicone, silicone rubber and steel, is investigated for stent deployment. The response of the proposed stents to the mathematical simulation of radial blood pressure waveform is studied considering their mechanical properties. The stress-strain response and the stored strain energy are computed likewise. Furthermore, a model of a double layer stent made of silicone-silicone rubber is suggested. The behavior of the introduced double layer stent model is investigated under the effect of radial pulsating pressure. The model is tested for strain response, stored energy, inertial energy and power loss. This model employs the actual available physical constants. The results indicate that silicone and silicone rubber are not only biocompatible but also eliminate possible thrombosis as well. Moreover, they are electrically compatible, since they do not contribute to heating complications induced by electromagnetic field (EMF) exposure.
Aim: Study the viscoelastic behavior of an arterial transversally deployed stent, of suggested materials namely silicone and silicone rubber to be compared to the commonly used stainless steel. A proposed double layer stent model stress-strain response is mathematically tested for pulsatile radial pressure.
Study Design: Mechanical viscoelastic double layer model
Place and Duration of Study: Faculty of Engineering, Cairo Univ. April to Dec. 2013.
Methodology: Computer simulation of the presented mathematical model by MapleV release 4 is carried out.
Results: Table 1 shows the results obtained employing the single layer stent model to compare mechanical response of steel, silicone and silicone rubber. They are compared to the inner two layers of the human arterial wall. Silicone and intima media layers show highest strain responses, 3.98% and 0.54% respectively and consequently largest values of stored energy. Silicone rubber and adventitia show strain responses of 0.015% and 0.000603% respectively. These results recommended the proposed design of the double layer stent. Stress-strain complex functions are represented for the each layer besides the stored energy, inertia, and power loss.
Conclusion: Results largely elect the silicone materials to replace steel regarding the strain energy that provides backward pressure. Since stored strain energy contributes to the pulsatile motion of arterial wall then the higher strain lessens susceptibility to possible thrombosis or stagnation. In other words, the pulsating stent wall enhances a vibrating motion that compensates loss of elasticity of a stiff artery. The proposed design for the double layer silicone-silicone rubber stent shows highly fluctuating time response. The fluctuations provide adequate wall strain energy to push back and hence maintain the blood flow rate. This type of stent can be implanted in vessels suffering stiffness to overcome restenosis.
Keywords: Arterial wall, viscoelasticity, blood pressure, strain response, storage modulus, loss modulus, linear power density