Objective. Evaluate electrochemical properties, biological response, and surface characterization of a conductive hydrogel (CH) coating following chronic in vivo stimulation. Approach. Coated CH or uncoated smooth platinum (Pt) electrode arrays were implanted into the cochlea of rats and stimulated over a 5 week period with more than 57 million biphasic current pulses. Electrochemical impedance spectroscopy (EIS), charge storage capacity (CSC), charge injection limit (CIL), and voltage transient (VT) impedance were measured on the bench before and after stimulation, and in vivo during the stimulation program. Electrically-evoked auditory brainstem responses were recorded to monitor neural function. Following explant, the cochleae were examined histologically and electrodes were examined using scanning electron microscopy. Main results. CH coated electrodes demonstrated a bench-top electrochemical advantage over Pt electrodes before and after the electrical stimulation program. In vivo, CH coated electrodes also had a significant advantage over Pt electrodes throughout the stimulation program, exhibiting higher CSC (p= 0.002), larger CIL (p = 0.002), and lower VT impedance (p < 0.001). The CH cohort exhibited a greater tissue response (p= 0.003) with small deposits of particulate material within the tissue capsule. There was no loss in auditory neuron density or change in neural response thresholds in any cochleae. Examination of the electrode surface revealed that most CH electrodes exhibited some coating loss; however, there was no evidence of corrosion in the underlying Pt. Significance. CH coated electrodes demonstrated significant electrochemical advantages on the bench-top and in vivo and maintained neural function despite an increased tissue response and coating loss. While further research is required to understand the cause of the coating loss, CH electrodes provide promise for use in neural prostheses.

A living electrode construct that enables integration of cells within bionic devices has been developed. The layered construct uses a combination of non-degradable conductive hydrogel and degradable biosynthetic hydrogel to support cell encapsulation at device surfaces. In this study, the material system is designed and analyzed to understand the impact of the cell carrying component on electrode characteristics. The cell carrying layer is shown to provide a soft interface that supports extracellular matrix development within the electrode while not significantly reducing the charge transfer characteristics. The living layer was shown to degrade over 21 days with minimal swelling upon implantation.

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Advances in electrode design are key to enabling wide-ranging applications in bioelectronics and neural interfaces. The use of bioelectronics in the treatment of brain diseases and neural prosthetics to improve quality of life for chronic conditions is an exciting area of research, with wide-ranging impact for global health. The use of inorganic biomaterials as electrode materials in these applications will be discussed, both in the context of electrical performance and biocompatibility. A detailed discussion will then be delivered on the development and fabrication of state-of-the-art and emerging designs of bioelectronic devices, as well as emerging hybrid and next-generation materials in this field.

Fabrication of three-dimensional (3D) constructs to model body tissues and organs can contribute to research into tissue development and models for studying disease, as well as supporting preclinical drug screening in vitro. Furthermore, 3D constructs can also be used for diagnosis and therapy of disease conditions via lab on a chip and microarrays for diagnosis and engineered products for tissue repair, replacement, and regeneration. While cell culture approaches for studying tissue development and disease in two dimensions are long-established, the translation of this knowledge into 3D environments remains a fertile field of research. In this Tutorial, we specifically focus on the application of biosynthetic hydrogels for neural cell encapsulation. The Tutorial briefly covers background on using biosynthetic hydrogels for cell encapsulation, as well as common fabrication techniques. The Methods section focuses on the hydrogel design and characterization, highlighting key elements and tips for more effective approaches. Coencapsulation of different cell types, and the challenges associated with different growth and maintenance requirements, is the main focus of this Tutorial. Much care is needed to blend different cell types, and this Tutorial provides tips and insights that have proven successful for 3D coculture in biosynthetic hydrogels.