3D printing of micro-scale graded shape memory components for in-vivo actuated medical devices

点击翻译按钮获取中文摘要

Micro-robots have great potential for evaluation and treatment of medical conditions. Such devices require highly controlled actuation at a micro-scale to provide controlled motion, testing of tissue compliance, biopsy, etc, and this is a prospect offered by functionally-graded shape memory alloys (SMAs). An SMA has the ability to "remember" its original shape and that when deformed returns to its pre-deformed shape when heated. Such alloys have sparked great interest ever since their first development. Functional grading of SMAs (i.e. locally modifying the properties of the material to tailor the SMA effect in different parts of the device) allow the design of more complex and hence much more controllable actuation mechanisms. Devices and components manufactured from functionally graded SMAs can provide actuation in response to external stimulation (stress or temperature variation, e.g. via induction heating), outperforming conventional actuation mechanisms such as electromagnets or electrical motors in terms of work output density. Such performance is ideal for micro-devices for minimally invasive medical applications such as precise incision, tissue identification, tactile sensing for disease and tweezing, as well as more ambitious shape transformations for "unpacking" structures in situ and "intelligent" stents and patches.The manufacturing challenge here is to achieve that functional grading at a micro-scale, by a combination of locally tailoring the material composition and thermal history. This will be achieved via development of a novel process, functionally graded Laser Induced Forward Transfer (FG-LIFT). This process will use a multi-track 'donor ribbon' (rather like a multicoloured typewriter ribbon) to deposit "sub-voxels" (of typical dimensions a few microns across and hundreds of nm high) of different metals, e.g. Ti, Ni and Cu onto a target substrate, in order to construct voxels each consisting of a number of subvoxel layers of different metals. 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. This FG-LIFT process will be used to manufacture sub-mm and mm-scale 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. By depositing the functionally graded SMA material onto substrates with appropriate material properties (e.g. carbon fibre mats or trace heaters), additional tailoring of the overall performance of the device will be achieved.