Materials and Technologies for Implantable Focal Brain Cooling Systems

Focal cooling is a promising treatment strategy for some neurological conditions, such as medically intractable epilepsy. Cooling is achieved by invasive implants placed in direct contact with neural tissue at the afflicted sites. Direct cooling of brain tissue has been demonstrated with both solid-state and liquid circulatory systems. Current cooling systems seen in pre-clinical proof-of-concept studies are mechanically stiff and too bulky to integrate with delicate neural tissues without the risk of causing compression injury over time. Here we will describe our efforts to assemble a miniaturised implantable system capable of simultaneous focal cooling and Electrocorticography (ECoG) recordings. The system comprises of a solid-state thermoelectric element, a microfluidic heat management system, integrated thermocouples, recording electrodes and a microcontroller circuit. The implantable portion of the system consists of discrete electronic elements embedded in a mechanically soft probe. The soft probe has overall dimensions of 8 x 8 x 4 mm³ and is realised using direct ink writing (3D printing) of biocompatible silicones. The integration of thermally conductive and printable silicones in our design is further aimed to assist heat dissipation from the implant. The system was tested in vitro using hydrogel models of brain tissue. In the model tissue, we were able to achieve rapid cooling rates of 2°C/s, which is required for efficient seizure suppression.<br/>Our long-term aim is to develop a closed-loop and personalised epilepsy implant that detects epileptic seizures and responds with targeted thermal neuromodulation.