(C-102) Shape-changing Deployable Intracortical Microelectrode Arrays

Thursday, October 12, 2023

9:30 AM – 10:30 AM PDT

Location: Exhibit Hall - Row C - Poster # 102

Presenting Author(s)

YT

Yeh-Chia Tseng

Graduate Research Assistant
Texas A&M University
College Station, Texas, United States

Co-Author(s)

MJ

Mahjabeen Javed

PhD
Texas A&M University, United States
YL

Yoo Jin Lee

Graduate Research Assistant
Texas A&M University, United States

Primary Investigator(s)

TW

Taylor Ware

Associate Professor
Texas A&M University, United States

Introduction:: The utilization of chronically-stable intracortical microelectrode arrays offers new possibilities for neural activity recording and stimulation. However, current arrays typically place electrodes along a line or along a plane thus targeting only small groups of neurons. To overcome these challenges, we propose developing deployable intracortical microelectrode arrays based on liquid crystal elastomers (LCEs). In this work, we focus on creating a substrate that deploys electrodes. The material must be designed with a sufficient elastic modulus to ensure it can be inserted into the brain without experiencing buckling. Furthermore, a new deployment mechanism is needed such that an implanted device can change shape in the brain after insertion in the flat state.

Materials and Methods:: Our prior work has demonstrated that LCEs are suitable substrates for intracortical electrode arrays. Nematic diacrylate monomers are combined with a primary amine chain extender to create a monomer mixture with a nematic to isotropic transition temperature (T_NI) well above 37 ˚C. One of these monomers contains a photoresponsive dye, azobenzene. This mixture is then filled into a mold with programmed surfaces, which aligns the monomers in a way that dictates the future mechanical deployment of the final device. The reaction proceeds through a two-step aza-Michael addition, with the diacrylates reacting with the amine. The resulting oligomers undergo crosslinking via free-radical crosslinking at an elevated temperature within the nematic phase. The elastic modulus and photoresponse of the candidate materials are characterized using dynamic mechanical analysis and deployment in agar phantoms, respectively.

Results, Conclusions, and Discussions:: Our prior work demonstrated that LCEs are cytocompatible and not functionally neurotoxic. Microelectrode arrays fabricated on LCEs remain stable and excellent electrophysiological recordings for 30 days in phosphate-buffered saline and support viable cortical neuronal cultures for 27 days in vitro [1]. The designed monomer mixture exhibited a T_NI of around 135 ˚C before undergoing oligomerization and increased to approximately 145 ˚C after oligomerization. The high T_NI allows the programmed LCE substrates to show shape change when cooling down to the body temperature, thereby obviating the necessity for an external stimulus. By maximizing the temperature difference between crosslinking temperature and body temperature, it results in an increased strain for the LCE substrates [2]. After crosslinking, the film was released from the glass substrate. The film morphs into an actuated shape as anisotropic shrinking and expansion occur as dictated by the alignment on the surfaces of the mold. Here, we programmed the molecular alignment to make LCE film adopt a 3D cone shape at room temperature. The height of the cone could reach 50 µm. The film was exposed to UV light at 365 nm. This process converts azobenzene molecules in films from a stable trans state into a cis state, which triggers disorder and brings additional shape change. This light exposure changes the shape of LCE film from a 3D cone to a flat shape. Over time, the film reverts spontaneously to the trans state, changing its shape from a flat state to a 3D cone shape state after approximately 1 hour at 37 °C.

We design a monomer mixture with a high T_NI, enabling increased strain for the LCE film. In addition, by converting azobenzene from trans to cis state, we bring the 3D cone to a flat shape for implantation. The azobenzene then reverts to trans state, restoring the cone shape within an hour under physiological conditions. Further mechanical tests will be evaluated to provide sufficient strength for insertion.

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[1] Rihani, Rashed T., Hyun Kim, Bryan J. Black, Rahul Atmaramani, Mohand O. Saed, Joseph J. Pancrazio, and Taylor H. Ware. "Liquid crystal elastomer-based microelectrode array for in vitro neuronal recordings." Micromachines 9, no. 8 (2018): 416.

[2] Kim, Hyun, John Gibson, Jimin Maeng, Mohand O. Saed, Krystine Pimentel, Rashed T. Rihani, Joseph J. Pancrazio, Stavros V. Georgakopoulos, and Taylor H. Ware. "Responsive, 3D electronics enabled by liquid crystal elastomer substrates." ACS applied materials & interfaces 11, no. 21 (2019): 19506-19513.