Wound healing with nonthermal microplasma jets generated in arrays of hourglass microcavity devices

Clinical studies are reported in which artificial wounds in rat epidermal and dermal tissue have been treated by arrays of sub-500 μm diameter, low temperature plasma microjets. Fabricated in Al/nanoporous alumina (Al₂O₃) by wet chemical and microablation processes, each plasma jet device has a double parabolic (hourglass) structure, and arrays as large as 6 x 6 devices with 500 μm diameter apertures have been tested to date. Treatment of 1 cm²acute epidermal wounds for 20-40 s daily with an array of microplasma jets generated in He feedstock gas promoted wound recovery significantly, as evidenced by tissue histology and measured wound area. Seven days after wound formation, the wound area of the untreated control was 40 ± 2% of its initial value, whereas that for an identical wound treated twice daily for 20 s was 9 ± 2% of its original surface area. No histological distinctions were observed between wounds treated twice each day for 10 or 20 s - only the full recovery time differed. Spectra produced in the visible and ultraviolet by He jets in room air are dominated by atomic oxygen (3p ⁵P → 3s ⁵S) at 777 nm and violet fluorescence (391.4 nm) from N₂⁺, a species produced when the He (2s ³S₁) metastable is deactivated by Penning ionization of N₂. Although the combined cross-sectional area of the jets in the array is only 7% of the wound area, the microplasma treatment results in spatially uniform, and accelerated, wound healing. Both effects are attributed to the increased surface area of the jet array (relative to a single jet having an equivalent diameter) and the concomitant enhancement in the generation of molecular radicals, and metastable atoms and molecules (such as N₂(A³Σ_u⁺).