In vitro biocompatibility evaluation of functional electrically stimulating microelectrodes on primary glia.

Neural interfacing devices interact with the central nervous system to alleviate functional deficits arising from disease or injury. This often entails the use of invasive microelectrode implants that elicit inflammatory responses from glial cells and leads to loss of device function. Previous work focused on improving implant biocompatibility by modifying electrode composition; here, we investigated the direct effects of electrical stimulation on glial cells at the electrode interface. A high-throughput in vitro system that assesses primary glial cell response to biphasic stimulation waveforms at 0 mA, 0.15 mA, and 1.5 mA was developed and optimized. Primary mixed glial cell cultures were generated from heterozygous CX3CR-1+/EGFP mice, electrically stimulated for 4 h/day over 3 days using 75 µm platinum-iridium microelectrodes, and biomarker immunofluorescence was measured. Electrodes were then imaged on a scanning electron microscope to assess sustained electrode damage. Fluorescence and electron microscopy analyses suggest varying degrees of localized responses for each biomarker assayed (Hoescht, EGFP, GFAP, and IL-1ß), a result that expands on comparable in vivo models. This system allows for the comparison of a breadth of electrical stimulation parameters, and opens another avenue through which neural interfacing device developers can improve biocompatibility and longevity of electrodes in tissue.

The effects of electrical stimulation on glial cell behaviour.

Neural interface devices interact with the central nervous system (CNS) to substitute for some sort of functional deficit and improve quality of life for persons with disabilities. Design of safe, biocompatible neural interface devices is a fast-emerging field of neuroscience research. Development of invasive implant materials designed to directly interface with brain or spinal cord tissue has focussed on mitigation of glial scar reactivity toward the implant itself, but little exists in the literature that directly documents the effects of electrical stimulation on glial cells. In this review, a survey of studies documenting such effects has been compiled and categorized based on the various types of stimulation paradigms used and their observed effects on glia. A hybrid neuroscience cell biology-engineering perspective is offered to highlight considerations that must be made in both disciplines in the development of a safe implant. To advance knowledge on how electrical stimulation affects glia, we also suggest experiments elucidating electrochemical reactions that may occur as a result of electrical stimulation and how such reactions may affect glia. Designing a biocompatible stimulation paradigm should be a forefront consideration in the development of a device with improved safety and longevity.

Applying a novel 3D hydrogel cell culture to investigate activation of microglia due to rotational kinematics associated with mild traumatic brain injury.

Many investigations on mild traumatic brain injury (mTBI) aim to further understand how cells in the brain react to the mechanical forces associated with the injury. While it is known that rapid head rotation is a mechanism contributing to mTBI, establishing definitive thresholds for head rotation has proved challenging. One way to advance determining mechanisms and thresholds for injury is through in vitro models. Here, an apparatus has been designed that is capable of delivering rotational forces to three-dimensional (3D) hydrogel cell cultures. Using an in vitro model, we test the hypothesis that rotational kinematics can activate microglia suspended in a 3-dimensional mixed glia environment (absent neurons). The impact apparatus was able to deliver peak angular velocities of approximately 45 rad/s, a magnitude for angular velocity that in select literature is associated with diffuse brain injury. However, no measurable glial cell reactivity was observed in response to the rotational kinematics through any of the chosen metrics (nitric oxide, pro-inflammatory cytokine release and proportion of amoeboid activated microglia). The results generated from this study suggest that rotation of the glia alone did not cause activation - in future work we will investigate the effect of neuronal contributions in activating glia.