Towards laser-induced forward transfer of phase intact NiTi voxels for in-vivo actuated medical devices

Laser-induced forward transfer (LIFT) is a versatile direct-write technique that can be used to print a wide variety of materials with no contact and high accuracy. In recent years, LIFT printing of functional devices [1] is getting increasingly popular due to the relative simplicity of the process, which offers printing in ambient conditions without any post-processing. Shape memory alloys (SMAs) are a type of active material that can be deformed but return to their original shape when heated to a transition temperature. In addition to this shape memory effect, Nickel-Titanium (NiTi) SMAs are also biocompatible and can have a transition temperature close to body temperature. Hence, we plan to use LIFT to fabricate micron-scale NiTi actuators with SMA properties for in-vivo medical applications. LIFT uses a pulsed laser to sequentially print sub-voxels of material from a donor thin film onto a substrate. In the case of printing metal, this process is based on the phase transformation of the donor film. Due to the high cooling rates involved during LIFT, the transferred micro deposit is generally amorphous. One way to transfer metal without any phase and structural change is to use a sacrificial layer between the laser pulse and the material to be transferred. However, it is challenging to produce phase-intact solid deposits of high quality without the formation of any debris. Our approach is to ultrashort pulses to pre-machine donor layers that facilitates easier separation from the carrier using a spatially shaped laser pulse. In this talk, we present the preliminary results of this approach to obtain Nickel voxels using a pre-machined, multi-donor layer and phase-only spatial light modulator.

[1] Fogel, O., Winter, S., Benjamin, E., et al., 3D printing of functional metallic microstructures and its implementation in electrothermal actuators. Additive Manufacturing, 21, 307–311, (2018).