Paper MN-TuM12
A Low-Temperature Packaging Process for Mechanically-Adaptive Neural Interfaces for Microfluidic-Aided Drug Delivery

Tuesday, October 22, 2019, 11:40 am, Room A210

Advances in polymer-based materials development have led to an array of environmentally-responsive materials that are uniquely suited for biomedical implant applications. Compatible microfabrication processes continue to be developed to integrate these responsive materials into biomedical microdevices. Progressing beyond proof-of-concept devices into functional implants for long-term use requires additional development of compatible and reliable packaging strategies to facilitate interfacing the microdevices with peripheral components. Our group has previously developed a mechanically-adaptive, polymer nanocomposite-based (NC) intracortical implant with a microfluidic channel for diffusion-based drug delivery. Interfacing the device with fluid pumps requires a means for secure attachment of polyethylene tubing to the inlet and outlet ports of the neural microdevice that will remain stable under physiological conditions. Packaging process considerations include incompatibilities of NC with organic solvents and temperatures exceeding 80°C. Additionally, out-of-plane forces on the devices must be minimized in order to maintain the integrity of the microfluidic channels.

We designed connectors to interface polyethylene tubing with the NC-based neural microdevices, to be built using a multi-jet 3D printer. Components produced using multi-jet printers typically have a plastic structural material and a wax-based support material that is removed during post-processing operations. However, our approach involves using a controlled, thin layer of the wax support material as a functional adhesive between the plastic connector and the NC device. With a melting point of 60°C, the wax is stable at body temperature (37°C) and can be melted and reformed at temperatures below the processing limit for the device. Because the wax is printed as part of the connector, the tubing ports can be aligned to the microfluidic inlet and outlet in a single step. Through this approach, we established a leak-free connector design and packaging process to facilitate a fluidic connection between syringe or osmotic pumps and NC-based microdevices. The adhesive bonding strength provided by the wax to the NC exceeded 37 MPa, much higher than the 0.75 MPa required to pump fluid through the connector and microfluidic channel. Packaged devices remained functional in phosphate buffered saline heated to 37°C, even after soaking for 24 hours. The potential for scaling the packaging process and for applying to other materials will also be discussed.