Department of Mechanical and Aerospace Engineering, University of Miami, Coral Gables, FL, USA.
Department of Mechanical and Aerospace Engineering, North Carolina State University, Raleigh, NC, USA.
J Mech Behav Biomed Mater. 2018 Apr;80:97-103. doi: 10.1016/j.jmbbm.2018.01.030. Epub 2018 Jan 31.
Lipid uptake and subsequent degradation was characterized as a function of molecular weight and styrene content in four different formulations of poly(styrene-block-Isobutylene-block-styrene) (SIBS). Mechanical testing in uniaxial tension at varying lipid concentrations showed a consistent decrease in tensile strength for all specimens due to lipid contamination. Higher styrene content was associated with an improved resistance to lipid intrusion. A decrease in elongation at break was observed for low molecular weight formulations only; an expected result of the stiffer network and local chain motion restriction due to increased entanglements in high molecular weight SIBS. A new, coupled diffusion/finite element method was used to recover the swelling coefficient of the four different SIBS formulations. The Ogden strain-density energy function recovered from unidirectional tensile testing and diffusion properties from gravimetric analysis were used to construct the finite element model. The predicted swelling behavior matched experimental data and the swelling coefficients were recovered for all formulations tested. Results indicate that the higher lipid affinity of the isobutylene phase contributed to increased swelling, as expected. This novel method to calculate swelling coefficient effectively circumvents the inability of commonly-used thermal deswelling methods to characterize lipid and oil-induced swelling behavior; enabling better prediction of long-term in vivo performance of polymer-based biomedical devices and more accurate evaluation of lipid-induced degradation and swelling.
四种不同配方的聚（苯乙烯-异丁烯-苯乙烯）（SIBS）的分子量和苯乙烯含量对其脂质摄取和随后的降解进行了研究。在不同脂质浓度下进行的单轴拉伸力学测试表明，由于脂质污染，所有样品的拉伸强度都一致降低。较高的苯乙烯含量与对脂质侵入的抵抗力提高有关。只有低分子量配方观察到断裂伸长率降低；这是由于高分子量 SIBS 中缠结增加导致网络变硬和局部链运动受限的预期结果。使用一种新的耦合扩散/有限元方法来恢复四种不同 SIBS 配方的溶胀系数。从单向拉伸测试中恢复的 Ogden 应变-密度能量函数和从重量分析中获得的扩散特性用于构建有限元模型。预测的溶胀行为与实验数据吻合，并且恢复了所有测试配方的溶胀系数。结果表明，正如预期的那样，异丁烯相的更高脂质亲和力导致了溶胀的增加。这种计算溶胀系数的新方法有效地避免了常用的热解吸方法无法表征脂质和油诱导的溶胀行为的问题；从而能够更好地预测基于聚合物的生物医学设备的长期体内性能，并更准确地评估脂质诱导的降解和溶胀。
