GOALI: Modeling, analysis and numerical simulations of gels in the biomedical industry

该GOALI项目支持明尼苏达大学和美敦力公司的研究人员之间的合作。为了改进植入式医疗设备的设计，研究者和她的同事们开发了聚合物和溶剂相互作用导致聚合物膨胀的基本理解和建模工具。许多植入式装置由塑料和金属部件组成，它们通过粘合剂相互粘附。当这种装置被放置在人体内时，由聚合物制成的塑料部件与周围的流体相互作用并膨胀，而金属部件则不受流体的影响。随之而来的膨胀错配导致界面处的高应力，这可能导致组件变形，如果界面剪切应力超过粘合剂制造商保证的临界值，则会导致界面分层。变形和分层会导致设备失效。对组件行为建模的能力在植入式医疗设备（如除颤器、起搏器和神经设备）的设计中至关重要。该项目解决了以下问题：(1)聚合物如何在没有聚合物链松弛的情况下膨胀？（这里只考虑了弹性，而忽略了粘滞效应。）(2)当聚合物链在同一时间内松弛时，膨胀是如何进行的？(3)如果对试样施加机械应变，膨胀是如何进行的？(4)如果两个由相同聚合物制成但初始溶胀不同的样品粘合在一起，溶胀是如何进行的？许多聚合物可以吸收相当于其自身重量1%的水；水凝胶可以吸收数倍于自身体积的水分。聚合物的膨胀发生在许多应用中，特别是在由金属和塑料聚合物组件制成的植入式生物医学设备中，这些设备通常埋在湿组织中。由于粘弹性的特性，聚合物可以随着时间的推移而放松机械载荷和变形。肿胀引起的压力或尺寸变化也可以放松。聚合物的实际应力和几何变化是由松弛和膨胀过程共同决定的。这些过程中的每一个都与水扩散、聚合物链运动和水-聚合物相互作用有关。评估这些过程和相互作用对于理解膨胀引起的变形、分层和稳定性至关重要，这些都是医疗器械设计和质量控制中的关键因素。在美敦力公司和明尼苏达大学现有合作的基础上，研究者和她的同事开发了数学模型、分析、计算和可视化工具，以提高对聚合物和溶剂相互作用的基本理解；这些工具可以用来识别不合适的聚合物，从而将美敦力聚合物科学家进行的实验室实验数量减少一半以上。学生和博士后是该项目的一部分，该项目还包括与美敦力联合主办的研讨会、讲习班和外展活动。

CaldererDMS-1009181 This GOALI project supports a collaboration betweeninvestigators at the University of Minnesota and at Medtronic,Inc. To improve the design of implantable medical devices, theinvestigator and her colleagues develop fundamental understandingof, and modeling tools for, polymer and solvent interactions thatresult in swelling of the polymer. Many implantable devicesconsist of plastic and metal components that are affixed to eachother by adhesives. When such a device is placed in the humanbody, the plastic parts, made from polymer, interact with thesurrounding fluid and swell, while the metal parts are notaffected by the fluid. The consequent swelling mismatch causes ahigh stress at the interface, which can lead to deformation ofthe components and, if interfacial shear stresses exceed criticalvalues guaranteed by the adhesive manufacturer, to interfacedelamination. Deformation and delamination can cause devices tofail. The ability to model the behavior of the components iscritical in the design of implantable medical devices, such asdefibrillators, pacemakers, and neurological devices. Thisproject addresses the questions: (1) How does polymer swelling proceed without polymer chainrelaxation? (Only elasticity is accounted for, and viscouseffects are neglected.) (2) How does swelling proceed when polymer chains relax withinthe same time frame? (3) How does swelling proceed if there is mechanical strainapplied to the sample? (4) How does swelling proceed if two samples made of the samepolymer but with different initial swelling are bonded together? Many polymers can absorb an amount of water equivalent toabout 1 percent of their own weights; hydrogel can absorb watermany times its own volume. Swelling of polymers occurs in manyapplications, particularly in implantable biomedical devices,made of metal and plastic polymer components, that typically areburied in wet tissue. Polymers can relax mechanical loading anddeformation over time due to viscoelastic properties. Swelling-induced stress or size changes can relax as well. Theactual stress and geometric changes in polymers are determined bythe combined relaxation and swelling process. Each of theseprocesses is related to water diffusion, polymer chain motion,and water-polymer interactions. Estimation of these processesand interactions is critical for understanding swelling-induceddeformation, delamination, and stability, key factors in thedesign and quality control of medical devices. Building on anexisting collaboration between Medtronic Inc and the Universityof Minnesota, the investigator and her colleagues developmathematical models, analysis, and computational andvisualization tools to improve fundamental understanding ofpolymer and solvent interactions; the tools can be used toidentify unsuitable polymers and so reduce the number oflaboratory experiments performed by polymer scientists atMedtronic by more than half. Students and postdocs are part ofthe project, which also includes seminars, workshops, andoutreach activities sponsored jointly with Medtronic.