(J-363) Photonic Crystal Sensors for Continuous and Visible Monitoring of Wound Healing

Introduction:: The skin can be easily threatened by unexpected dangers such as chemical, physical, and biological terrorization to protect organs. The damaged skin has a series of reconstructive processes and the local pH can transform swiftly to basic and acidic depending on the condition of the wound due to macrophage metabolism and the accumulation of epidermal cells. Since the wound recovery process is linked, the wound returned to a local basic state due to the production of macrophage metabolism by re-inflammation, which slows recovery and makes it vulnerable to chronic inflammation, making the patient's life more threatening. Therefore, it is necessary to continuously monitor wound recovery and quickly inform patients of the infection. Applying a pH change in the wound healing process as an indicator for biosensors, we propose pH-sensitive photonic crystal sensors for continuous and visible wound monitoring. The silicon-based photonic crystal has a periodic linear pattern that is freely controlled through electrochemical etching by sinusoidal waveform and reflects the sharp wavelength. Reflected visible light can be blue-shift due to hydrolysis in the outer pore wall, which can visibly report the stage of the wound in real-time. And then the patients can immediately identify the condition of the wound with the naked eye. This photonic crystal patch serves as an alarm for patients to detect second inflammation, which can lead to the scar and the development of severe diseases. We suggest a continuous and visible PC patch that can help the patients conveniently and intuitively manage damaged tissue without scarring.


Materials and Methods:: The photonic crystal film (PC film) was freely produced by electrochemical etching through a sinusoidal waveform which empowers the specific reflectance wavelength with one color by the naked eye. The PC film was incubated in basic and acid solution to quantify the blue shift kinetics depending on the pH and the released Si ion was measured by ICP-OCS. To identify the abnormal wound recovery and pH rising, inflamed 20 mm wounds by LPS were monitored for 3 weeks. To prove the performance of quick alarming, the photonic crystal patch (PC patch) was fabricated by embedding PC film in PVA/PCL hydrogel. The PC patches were attached to a 5 mm wound of the SD rat’s dorsal on the 4th day and the 5 mm wounds were inflamed by LPS and infected by MRSA bacteria on the 5th day. All wound models were monitored by camera and the pH of wounds was measured by skin pH meter every 2 or 3 days.


Results, Conclusions, and Discussions:: The PC film was incubated at pH 5.5, 6.5, 7.5, and 8.5 to verify the kinetics of blue shift through hydrolysis by hydroxide for 36 hours. In the basic solution, the PC film degraded 4 times faster than the acidic solution, resulting in a tau value of 18.57 at pH 5.5 and 4.73 at pH 8.5. and the red-colored PC film turned green by a change of internal microstructure corresponding to the peak shift and degraded Si ion. In the inflamed wound model, the recovery process was delayed more than the control group on every occasion, and the local pH elevated to an alkali state, which shows that the re-inflamed wounds in the recovery prolong the wound healing period and lead to scaring and chronic wounds. In the histological data, the wound area occupied a smaller area than that of the re-inflamed group, and the dermal layer of the inflamed group was immature, unlike the difference seen on the surface of the skin. Also, in the collagen area, the group with secondary inflammation occupied a smaller area than the normal group. In the animal model applied with a PC patch, The 5 mm wound was healed for 10 days, while a PC patch was applied on the 4th day and it was inflamed with LPS or bacteria on the 5th day. Because the recovery progressed normally from the 4th to 5th day, the color of the PC patch slowly changed while maintaining the red color. However, on the 5th day, it was confirmed that the color of the PC patch quickly changed to green because the pH of the wound rose again due to inflammatory and infection reactions. And the tau value of 192 at the PC patch without LPS and 50 at the PC patch with LPS represents a coincidence with in vitro experiment. 5 mm wound histological data shows deprived dermal cell layers and collagen area. These results make the patient handily manage the wounds without scarring and The PC patch can be a breakthrough for monitoring wound recovery by visibly and continuously offering the condition of wounds.


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