GOALI/Collaborative Research: Thixotropic Metal Processing and 3D Printing of Zinc-Magnesium Bio-Alloys for Biomedical Implant Applications

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This Grant Opportunity for Academic Liaison with Industry (GOALI) award supports fundamental research to explore a novel manufacturing system that is capable of 3D printing zinc-magnesium bio-alloys. These alloys are highly desirable in implanted medical devices for their biodegradability and high strength. However, powder fusion 3D printing of these bio-alloys is very difficult to control because of vaporization and oxidization under high power laser. Not having a direct printing process for zinc-magnesium bio-alloys makes it nearly impossible to manufacture custom devices. To overcome this hurdle, a new thixotropic 3D printing methodology in which the viscosity is controlled, could allow zinc-magnesium bio-alloys to be directly printed via an extrusion process into accurate, customized 3D shapes. The new technology is expected to benefit skeletal and soft tissue fixation tools, vascular inflation stents, and bone tissue scaffolds. This would lead to improvements in orthopedic, spinal and vascular surgery by providing patient-tailored medical devices that are strong and biodegradable/absorbable in the body. The new process may also be adapted to the fabrication of aluminum-based alloys for other industrial applications. The project will be used in educational outreach activities, especially to middle/high school and underrepresented minority students, to showcase high-tech bio-fabrication, biomaterials, and their surgical engineering applications.Molten alloys have low viscosity but high surface tension, making stable 3D printing nearly impossible. It is hypothesized that a two-phase micro-slurry with a fine globular morphology can be created for zinc-magnesium bio-alloys by thixotropic processing, and this can effectively make the slurry suitable for 3D printing by extrusion. Three research tasks will be performed to test this hypothesis and establish the technical feasibility of the method: 1) Conduct basic research on alloy design, morphological formation, relation between thixotropy and printability, and relation of processing, structure and property in thixotropic extrusion and printing; 2) Study the process dynamics and develop modeling capability for thixotropic 3D printing; 3) Establish a laboratory setup for freeform fabrication of zinc-magnesium bio-alloys. Researchers will obtain fundamental understanding of the unique processing-structure-property relationships of the new thixotropic metal forming and 3D printing methods and the new zinc-magnesium bio-alloy. New scientific knowledge is particularly anticipated in the following areas: a) mechanisms of promoting thixotropy of alloys in semi-solid metal processing; b) fluid mechanics and rheology in high-stress mixing of alloys; c) fundamental relationships between thixotropy and printability in semi-solid-state deposition; and d) fundamental relationships of processing, structure and property regarding biodegradability and performance of a new zinc-magnesium bio-alloy.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.