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

University Of Minnesota-Twin Cities, Minneapolis MN

Investigators

Abstract

Calderer DMS-1009181 This GOALI project supports a collaboration between investigators at the University of Minnesota and at Medtronic, Inc. To improve the design of implantable medical devices, the investigator and her colleagues develop fundamental understanding of, and modeling tools for, polymer and solvent interactions that result in swelling of the polymer. Many implantable devices consist of plastic and metal components that are affixed to each other by adhesives. When such a device is placed in the human body, the plastic parts, made from polymer, interact with the surrounding fluid and swell, while the metal parts are not affected by the fluid. The consequent swelling mismatch causes a high stress at the interface, which can lead to deformation of the components and, if interfacial shear stresses exceed critical values guaranteed by the adhesive manufacturer, to interface delamination. Deformation and delamination can cause devices to fail. The ability to model the behavior of the components is critical in the design of implantable medical devices, such as defibrillators, pacemakers, and neurological devices. This project addresses the questions: (1) How does polymer swelling proceed without polymer chain relaxation? (Only elasticity is accounted for, and viscous effects are neglected.) (2) How does swelling proceed when polymer chains relax within the same time frame? (3) How does swelling proceed if there is mechanical strain applied to the sample? (4) How does swelling proceed if two samples made of the same polymer but with different initial swelling are bonded together? Many polymers can absorb an amount of water equivalent to about 1 percent of their own weights; hydrogel can absorb water many times its own volume. Swelling of polymers occurs in many applications, particularly in implantable biomedical devices, made of metal and plastic polymer components, that typically are buried in wet tissue. Polymers can relax mechanical loading and deformation over time due to viscoelastic properties. Swelling-induced stress or size changes can relax as well. The actual stress and geometric changes in polymers are determined by the combined relaxation and swelling process. Each of these processes is related to water diffusion, polymer chain motion, and water-polymer interactions. Estimation of these processes and interactions is critical for understanding swelling-induced deformation, delamination, and stability, key factors in the design and quality control of medical devices. Building on an existing collaboration between Medtronic Inc and the University of Minnesota, the investigator and her colleagues develop mathematical models, analysis, and computational and visualization tools to improve fundamental understanding of polymer and solvent interactions; the tools can be used to identify unsuitable polymers and so reduce the number of laboratory experiments performed by polymer scientists at Medtronic by more than half. Students and postdocs are part of the project, which also includes seminars, workshops, and outreach activities sponsored jointly with Medtronic.