Highly-compliant, microcable neuroelectrodes fabricated from thin-film gold and PDMS

Abstract

Bio-electrodes have traditionally been made of materials such as metal and silicon that are much stiffer than the tissue from which they record or stimulate. This difference in mechanical compliance can cause incomplete or ineffective contact with the tissue. The electrode stiffness has also been hypothesized to cause chronic low-grade injury and scar-tissue encapsulation, reducing stimulation and recording efficiency. As an initial step to resolve these issues with electrode performance, we have developed and characterized electrically-functional, low-Young's modulus, microcable-shaped neuroelectrodes and demonstrated electrophysiological recording functionality. The microcable geometry gives the electrodes a similar footprint to traditional wire and microwire neuroelectrodes, while reducing the difference in Young's modulus from nervous tissue by orders of magnitude. The electrodes are composed of PDMS and thin-film gold, affording them a high-level of compliance that is well suited for in vivo applications. The composite Young's modulus of the electrode was experimentally determined to be 1.81 ± 0.01 MPa. By incorporating a high-tear-strength silicone, Sylgard 186, the load at failure was increased by 92%, relative to that of the commonly used Sylgard 184. The microcable electrodes were also electromechanically tested, with measurable conductivity (220 kΩ) at an average 8% strain (n = 2) after the application of 200% strain. Electrophysiological recording is demonstrated by wrapping the electrode around a peripheral nerve, utilizing the compliance and string-like profile of the electrode for effective recording in nerve tissue.

The Development of a ɛ-Polycaprolactone Scaffold for Central Nervous System Repair

“…Conversely, myelinating cultures plated on glass coverslips and conditioned with astrocytes plated on PCL (B) displayed significantly lower levels of myelination compared to control cultures plated on glass coverslips (All n = 3, t-test, Bonferroni corrected, *p < 0.05). Color images available online at www.liebertpub.com/tea [36][37][38][39][40] this difference in supporting myelination highlights the importance of examining interactions of candidate substrates with CNS cells beyond just neurite outgrowth. PDMS, on the other hand, is not a biodegradable material, even though it is extensively used in biomedical engineering, incorporated into microscale devices and permanent implants.…”

“…PDMS, on the other hand, is not a biodegradable material, even though it is extensively used in biomedical engineering, incorporated into microscale devices and permanent implants. 40,41 The molecular weight of the macromer units can have a significant effect on the final polymer interactions with CNS cells, with a lower molecular weight PCL being more supportive of myelination compared to the other polymers, including a higher molecular weight PCL. The influence of macromer weights on cells has been recognized in hydrogels, 41 although the lower molecular weight PCL was unsuitable for fabrication, as the PCL membrane degraded during the embossing procedure.…”

Highly Stretchable Patterned Gold Electrodes Made of Au Nanosheets

“…The Au nanosheet film transferred onto a polydimethylsiloxane (PDMS) substrate also showed similar electromechanical behavior (Figures S9,S10, Supporting Information), but a thick substrate (2 mm in thickness) suffered mechanical fracture at ϵ ≈ 60%. We used the thick PDMS substrate for convenience of handling although thin PDMS (<200 nm) can be stretched over 200% 24…”

Implantable Neural Interfaces and Wearable Tactile Systems for Bidirectional Neuroprosthetics Systems

“…However the signal quality tends to degrade over time, due mainly for two reasons: i) in the short term after implantation, a fibrotic response is triggered by the mechanical trauma and by the presence of a foreign body, thus reducing neuron density around the implant; ii) in longer term after implantation, electrode failure may occur (e.g., delamination, fracture, breakage of leads or connector) and micromotions due to head movements or brain pulsatile activity may drift the active sites from the optimal recording location . Mitigations actions to these risk may be optimization of insertion speed to minimize initial trauma, the delivery of antiinflammatory agents, the use of bioactive molecules to enhance cell adhesion and the use of softer material to reduce the mechanical impedance gap with the tissue …”