Thin Film Multi-Electrode Softening Cuffs for Selective Neuromodulation

Abstract

Silicone nerve cuff electrodes are commonly implanted on relatively large and accessible somatic nerves as peripheral neural interfaces. While these cuff electrodes are soft (1–50 MPa), their self-closing mechanism requires of thick walls (200–600 µm), which in turn contribute to fibrotic tissue growth around and inside the device, compromising the neural interface. We report the use of thiol-ene/acrylate shape memory polymer (SMP) for the fabrication of thin film multi-electrode softening cuffs (MSC). We fabricated multi-size MSC with eight titanium nitride (TiN) electrodes ranging from 1.35 to 13.95 × 10−4 cm2 (1–3 kΩ) and eight smaller gold (Au) electrodes (3.3 × 10−5 cm2; 750 kΩ), that soften at physiological conditions to a modulus of 550 MPa. While the SMP material is not as soft as silicone, the flexural forces of the SMP cuff are about 70–700 times lower in the MSC devices due to the 30 μm thick film compared to the 600 μm thick walls of the silicone cuffs. We demonstrated the efficacy of the MSC to record neural signals from rat sciatic and pelvic nerves (1000 µm and 200 µm diameter, respectively), and the selective fascicular stimulation by current steering. When implanted side-by-side and histologically compared 30 days thereafter, the MSC devices showed significantly less inflammation, indicated by a 70–80% reduction in ED1 positive macrophages, and 54–56% less fibrotic vimentin immunoreactivity. Together, the data supports the use of MSC as compliant and adaptable technology for the interfacing of somatic and autonomic peripheral nerves.

An Injectable Neural Stimulation Electrode Made from an In‐Body Curing Polymer/Metal Composite

“…Similarly, the Charles Lieber group has demonstrated that a ultraflexible open mesh electrode array can be injected into the rodent brain via syringe and minimize the chronic immune response, enabling high‐quality chronic recordings for periods of at least 12 weeks . More recently, the Romero‐Ortega group has demonstrated that SMP cuffs can be surgically implanted directly on the rat sciatic and pelvic nerves and both record and intermittently stimulate for periods of at least 30 d, while minimizing the immune response compared to stiffer control devices . In comparison to the Injectrode, these promising technologies have the clear advantage of higher channel counts, as well as predictable electrode geometries and spacing.…”

Multi-channel intraneural vagus nerve recordings with a novel high-density carbon fiber microelectrode array

“…Although electrical stimulation-evoked responses can be useful in determining the type of activated fibers, these responses do not represent physiological neural signaling. A few research groups have obtained physiological neural recordings from autonomic nerves using extraneural cuff electrodes [31][32][33][34][35] . However, extraneural electrodes lack spatial selectivity, as these electrodes record the compound activity of hundreds to thousands of axons from outside the nerve.…”

Flexible Hybrid Electronics for Digital Healthcare

“…Traditional extraneural electrodes such as the 3D cuff electrode ( Figure a), helical electrode (Figure b), and the 2D PI‐based electrode (Figure c) have been widely used in clinical practice. In addition, more recently developed electrodes based on shape memory polymers (Figure d,e) have moved forward on the flexible neural interface. However, the drawbacks are still obvious: large mechanical and geometrical mismatches and complicated surgical implantation and fixation procedures often induce irreversible neural damage, such as inflammation and axonal degradation.…”

“…e) SMP cuff electrode implanted onto sciatic nerve, where the arrowheads point to the sutures for the fixation. Reproduced with permission . Copyright 2018, Nature Research.…”