Development of a rapidly made, easily personalized drug-eluting polymer film on the electrode array of a cochlear implant during surgery

Enhancing biocompatibility of the brain-machine interface: A review

In vivo implantation of microelectrodes opens the door to studying neural circuits and restoring damaged neural pathways through direct electrical stimulation and recording. Although some neuroprostheses have achieved clinical success, electrode material properties, inflammatory response, and glial scar formation at the electrode-tissue interfaces affect performance and sustainability. Those challenges can be addressed by improving some of the materials' mechanical, physical, chemical, and electrical properties. This paper reviews materials and designs of current microelectrodes and discusses perspectives to advance neuroprosthetics performance.

Zwitterionic Polymer/Polydopamine Coating of Electrode Arrays Reduces Fibrosis and Residual Hearing Loss after Cochlear Implantation

Since the first surgery 50 years ago, cochlear implantation (CI) is the major treatment for patients with severe sensorineural hearing loss. However, unexpected foreign body reactions (FBRs) after surgery are reported in 90% of CI recipients, resulting in the formation of fibrosis in the cochlea and progressive residual hearing loss. Zwitterion modification is universally used to reduce bio-fouling and suppress FBRs but never for CI. In the present study, a zwitterionic coating is developed, which is composed of poly sulfobetaine methacrylate (PSB) and polydopamine (PDA) for cochlear implants. The PSB-PDA coating shows a series of characters for an ideal anti-FBRs material, including super-hydrophilicity, low protein and cell adsorption, long-term stability, and high biocompatibility. Compared to the uncoated controls, PSB-PDA coating inhibits the activation of macrophages and reduces the release of inflammatory factors (TNF-α, IL-1β, NO) and fibrosis-related factors (TGF-β1, α-SMA, collagen I). PSB-PDA coated electrode arrays suppress fibrosis completely and preserve residual hearing significantly in rat CI models. These results suggest that PSB-PDA coating is a novel strategy for anti-fibrosis to improve the outcomes of CI.

PLLA Coating of Active Implants for Dual Drug Release

Cochlear implants, like other active implants, rely on precise and effective electrical stimulation of the target tissue but become encapsulated by different amounts of fibrous tissue. The current study aimed at the development of a dual drug release from a PLLA coating and from the bulk material to address short-term and long-lasting release of anti-inflammatory drugs. Inner-ear cytocompatibility of drugs was studied in vitro. A PLLA coating (containing diclofenac) of medical-grade silicone (containing 5% dexamethasone) was developed and release profiles were determined. The influence of different coating thicknesses (2.5, 5 and 10 µm) and loadings (10% and 20% diclofenac) on impedances of electrical contacts were measured with and without pulsatile electrical stimulation. Diclofenac can be applied to the inner ear at concentrations of or below 4 × 10⁻⁵ mol/L. Release of dexamethasone from the silicone is diminished by surface coating but not blocked. Addition of 20% diclofenac enhances the dexamethasone release again. All PLLA coatings serve as insulator. This can be overcome by using removable masking on the contacts during the coating process. Dual drug release with different kinetics can be realized by adding drug-loaded coatings to drug-loaded silicone arrays without compromising electrical stimulation.

Hearing Protection Outcomes of Analog Electrode Arrays Coated with Different Drug-Eluting Polymer Films Implanted into Guinea Pig Cochleae

Objective

To investigate the hearing protection outcomes of different drug-eluting analog electrode arrays implanted into guinea pig cochleae.

Methods

Sixty guinea pigs were randomly divided into a negative control group and five experimental groups implanted separately with blank (drug carrier), dexamethasone (DXM), aracytine (Ara-C), Ara-C+DXM, and nicotinamide adenine dinucleotide (NAD+) eluting analog electrode arrays. Micro CT was used to supervise the surgical procedure. Auditory brainstem response (ABR) thresholds of the guinea pigs were measured and analyzed.

Results and Conclusions

Compared with the negative control, all other groups showed a significant increase in ABR threshold (p<0.001) after surgery. Among them, there was no obvious difference between the blank (0 vs 90 days: 59.70±10.57 vs 64.60±9.47 dB SPL) and the NAD+ group (0 vs 90 days: 59.90±9.87 vs 64.70±8.65 dB SPL). On the other hand, the ABR thresholds in the DXM (0 days: 58.10±10.73 dB SPL; 90 days: 51.70±9.07 dB SPL) and the Ara-C group (0 days: 59.00±10.05 dB SPL; 90 days: 51.60±8.48 dB SPL) decreased significantly compared with the former two groups (p<0.001). However, the Ara-C+DXM group showed no further benefit (p>0.05). In addition, a significantly higher survival rate of spiral ganglion neurons in cochleae was observed in the Ara-C and/or DXM groups.