Thiol‐ene/acrylate substrates for softening intracortical electrodes

Abstract

Neural interfaces have traditionally been fabricated on rigid and planar substrates, including silicon and engineering thermoplastics. However, the neural tissue with which these devices interact is both 3D and highly compliant. The mechanical mismatch at the biotic-abiotic interface is expected to contribute to the tissue response that limits chronic signal recording and stimulation. In this work, novel ternary thiol-ene/acrylate polymer networks are used to create softening substrates for neural recording electrodes. Thermomechanical properties of the substrates are studied through differential scanning calorimetry and dynamic mechanical analysis both before and after exposure physiological conditions. This substrate system softens from more than 1 GPa to 18 MPa on exposure to physiological conditions: reaching body temperature and taking up less than 3% fluid. The impedance of 177 µm(2) gold electrodes electroplated with platinum black fabricated on these substrates is measured to be 206 kΩ at 1 kHz. Specifically, intracortical electrodes are fabricated, implanted, and used to record driven neural activity. This work describes the first substrate system that can use the full capabilities of photolithography, respond to physiological conditions by softening markedly after insertion, and record driven neural activity for 4 weeks.

Thinking Small: Progress on Microscale Neurostimulation Technology

“…While SU-8 has a relatively positive literature supporting its in vitro and in vivo biocompatibility (65), it is not typically found in implantable biomedical devices and providers (e.g., MicroChem) may be hesitant to grant use for medical applications. Nevertheless, we remain optimistic that polymers, including those with shape memory thermomechanical characteristics (66,67), offer a solution for implantable microscale devices. We note that polymeric materials including silicone, parylene, and polyamide, are all components of the Medtronic DBS Lead Model 3387.…”

Organic light-emitting diodes on shape memory polymer substrates for wearable electronics

“…the chamber reached an ultra-high vacuum of <1.0 Â 10 À7 Torr, ene reactions (click reactions). Low cure-stresses are present 204 in the final polymer due to the nature of the step-growth 205 mechanism in this polymerization, which results in highly 206 uniform/dimensionally stable polymer networks with low shrink-207age and surface roughness, as well as strong adhesion to metal lay-208 ers[18]. More significantly, this allows for various material 209 properties (such as T g , rubbery modulus and hydrophobicity)…”

“…T g by DMA is 222 denoted by the peak of the tangent delta curve, which is shown 223 to be 43°C for this network. It has been shown that the T g of the 224 substrate will increase with increasing diacrylates mol%, but the 225 shear modulus below these transition temperatures will remain 226 relatively unchanged [18]. 227 The device structure for the OLED used in these experiments is …”

“…Reheating the 91 SMP causes strain relaxation within the polymer network and 92 induces recovery of its original shape. These substrates have made 93 a sizeable impact in solving neural interface issues for neural 94recording and stimulation applications[16][17][18] since the 'softened' state of the SMP has an elastic modulus that approaches that of 96 human tissue. These unique mechanical properties can also be 97 extended to a new branch of electronic device applications.…”

Bioelectric Medicine and Devices for the Treatment of Spinal Cord Injury

“…Over a few days, activated glia migrate to the implant site and begin to phagocytose cellular debris and damaged extracellular matrix. The accumulation of neurotoxic factors including cytokines, chemokines, and reactive oxygen species around the implant leads to a localized decrease in neuron density [Abidian et al, 2010] [Ware et al, 2014] may provide a solution to allow targeted implant insertion while reducing acute inflammation and local neuron death caused by larger and stiffer interfaces.…”