3D Printing of Micro-Scale Graded Shape Memory Components for In-Vivo Actuated Medical Devices

Academic Institution: Heriot-Watt University

Academic Supervisor: Professor Duncan Hand

Industry Partner: Renishaw plc

PhD Student:  Logaheswari (Loki) Muniraj

Start Date: 1 February 2020

Abstract

The overarching challenge is to create a manufacturing process for sub-mm and mm-scale Shape Memory Alloy (SMA) components with functional grading at a scale of 10’s of microns. This highly challenging concept requires 3D control – at the micro-scale – of both material composition and thermal treatment. This will be transformative as a highly flexible micro-additive 3D printing process for micro-actuators. Our driver is micro-scale actuation requirements in medical devices, including micro-robotics, which have great potential for evaluation and treatment of medical conditions.

Our solution is to exploit the high degree of control (both spatial and temporal) that is possible with laser-driven processes. Specifically, our approach will be based on an enhancement of the high precision laser LIFT (Laser Induced Forward Transfer) process – that can build components from sub-micron layers of different materials – in combination with highly localised thermal tailoring of SMA material parameters. Our Functionally Graded LIFT (FG-LIFT) concept is to use laser pulses to sequentially “print” thin “sub-voxels” of metal films onto a substrate, in order to construct voxels each consisting of a number of sub-voxel layers of different metals. As with LIFT, the process is driven by heating and phase change at the interface between the support substrate and the thin film of donor material.

Key to our concept is the use of a multi-track substrate reel-to-reel donor tape, with each ‘track’ consisting of a coating of a thin film of a different component material for an SMA alloy. By altering the laser parameters, subsequent thermal treatment will be used to provide control of interdiffusion within and between voxels providing very tight localised control of composition. 3D microstructures will hence be constructed by continuing to add additional voxels.