Poster BB15 - A Novel Hydrogel Ionic Circuit Electrode for Safe and Effective Electrotaxis for Persistent Corneal Epithelial Defect Healing

Friday, October 25, 2024

3:30 PM - 4:30 PM EST

Location: Exhibit Hall E, F & G

Presenting Author(s)

Amir Salati, PhD

Postdoctoral Research Associate
University of Nebraska Medical Center, Nebraska, United States

Last Author(s)

Siwei Zhao, PhD (he/him/his)

Assistant Professor and Research Scientist
University of Nebraska Medical Center, Nebraska, United States

Introduction: Persistent corneal epithelial defects (PEDs) are wounds in the corneal epithelium that do not heal within two weeks. PED can occur in many settings, such as diabetes and chronic loss of corneal innervation. Current standard clinical treatments for PED, including lubricants, patching, bandage contact lenses, and tarsorrhaphy, do not directly address the underlying physiological impairment and consequently exhibit limited efficacy. Advanced treatments face challenges such as high costs (e.g., amniotic membrane, autologous serum, growth factor eye drops, and stem cells), complex preparation procedures (e.g., amniotic membrane and autologous serum), and the need for frequent administration (e.g., autologous serum and growth factor eye drops). There is a critical need for novel treatments that 1) effectively enhance corneal epithelial wound healing, 2) are easily accessible and convenient, and 3) do not impose a high financial burden. Direct current (DC) electric field (EF) can guide the directional migration of corneal epithelial cells (CECs) in vitro, a phenomenon called electrotaxis. Electrotaxis has been successful in healing in vitro cell exclusion zones with corneal epithelial cells and organ-cultured ex vivo corneal wounds. Despite its in vitro and ex vivo success, electrotaxis has not translated to in vivo corneal wound healing. The effective DC EF strength (150 mV/mm) for in vitro studies cannot be applied in vivo using conventional electrical stimulation (EStim) electrodes without causing tissue damage. Conventional carbon and metal electrodes conduct electron current, requiring conversion to ion current by electrochemical (EC) reactions at the electrode-tissue interface, inducing significant temperature increase and pH changes.

Materials and

Methods: To address the tissue-damaging issue of conventional electrodes, we developed novel hydrogel ionic circuit (HIC)-based EStim electrodes (Fig. 1A). The HIC anode and cathode each has a chamber filled with a phosphate salt solution at near-saturation concentration. This chamber is separated from the biological tissue by a polyethylene glycol (PEG) hydrogel membrane. During EStim, our HIC electrodes convert the electron current from a DC power supply to ion current and apply the ion current to the biological tissue. The pH changes at the carbon electrode-HIC interface are very effectively neutralized by the phosphate salt solution in HIC electrodes. This is because it has more than 50 times higher hydrogen/dihydrogen phosphate ion concentration than typical pH buffers. The heat generated at carbon-HIC interface is also absorbed by the phosphate salt solution in HIC electrodes. We used our HIC electrodes to apply high-strength DC EF at 150 and 500 mV/mm to the cornea of excised porcine eyes for 1 hour (Fig. 1B). We further tested the in vitro electrotaxis of primary human CECs in response to DC EF applied by our HIC electrodes. DC EF at 0, 50, 100, 150 and 200 mV/mm was applied to the cells for 1 hour (Fig. 2). Based on cell trajectories, we quantified the directedness and projected migration speed along the EF direction for the cells that are exposed to DC EF. Directedness is a measure of cell migration direction, which is the cosine of the angle between the migration and the EF vectors (Fig. 3).

Results, Conclusions, and Discussions: As shown in Fig. 4, the corneal surface temperature remained below 36°C (for 150 mV/mm) or 38°C (for 500 mV/mm) and the corneal surface pH remained between 6.4 and 6.9 (for 150 mV/mm) or 6.3 and 7.0 (for 500 mV/mm). These temperature and pH are considered safe for corneal tissues. Using conventional carbon electrodes to apply the same DC EF strengths, however, resulted in significantly higher temperature increase up to 46.1 ± 0.5°C (for 150 mV/mm) or 48.8 ± 0.8°C (for 500 mV/mm) on corneal surface (Fig. 4). The corneal surface pH also had a larger change to 1.4 ± 0.3 at anode and 12.6 ± 0.3 at cathode (for 150 mV/mm) or 0.8 ± 0.2 at anode and 13.3 ± 0.2 at cathode (for 500 mV/mm) (Fig. 4). These temperature and pH values are outside of the safe ranges for corneal tissues. We also found that 500 mV/mm DC EF applied by our HIC electrodes for 1 hour had a minimal impact on the viability of in vitro cultured primary human CECs (92.4 ± 2.1% of untreated control). As shown in Fig. 5, compared to the random migration of unstimulated cells, all DC EF-stimulated cells exhibited directional migration toward the cathode. As we increased the DC EF from 0 to 200 mV/mm, HIC-stimulated cells exhibited increasing projected migration speed and directedness. The highest speed and directedness were achieved at 200 mV/mm, which were 41.6 ± 21.4 μm/hour and 0.87 ± 0.25, respectively.
In summary, our results demonstrated that: 1) HIC electrodes could apply up to 500 mV/mm DC EF without causing tissue-damaging temperature or pH changes or significant CEC death; 2) HIC electrodes could effectively induce electrotaxis response in in vitro cultured primary human CECs; and 3) Increasing DC EF strength applied by HIC electrodes could increase the projected migration speed and directedness of primary human CECs.

Acknowledgements (Optional):