Streamer dynamics under repetitive nanosecond pulse (RNP) is of great importance to understand the streamer essence and breakdown phenomenon in non-equilibrium-plasma-based applications. However, the evolution of streamer dynamics, discharge mode transition, and influential mechanisms in high-pressure gas under long-term RNP were not sufficiently clear and required further investigations. We presented the pulse-sequence resolved analysis on streamer dynamics, discharge mode transition, and polarity effect in high-pressure nitrogen under longterm RNP of pulse width from 15 to 800 ns and RNP superimposed by DC sweep voltage. Under positive RNP, the corona discharge probability in a pulse train was affected by the pulse repetition frequency (PRF) and a transformation from the intermittent mode to continuous mode appeared under high PRF. The envelope curve of the number of applied pulses before breakdown followed the shape transformation from capital 'L' to 'U' with pressure from 0.1 to 0.4 MPa. The streamer channel contraction and the spatial shift of streamer initiation position under high PRF were observed. Under negative RNP, the corona discharge would be in the continuous mode from a low PRF. The average inception voltage and phase of following corona discharges were lower and earlier than those of the first one, respectively. The auxiliary sweep voltage illustrated dramatic and nonlinear effects on discharge characteristics under RNP, which was determined by the sweep voltage amplitude, pulse polarity, and PRF. The inception oscillation stage and steady-state stage were distinct under short-width RNP. An influential mechanism in high-pressure nitrogen was proposed with emphasis on the spatial electric field distortion caused by remaining space charges, which was affected by the pressure-dependent nonlinear diffusion and time-dependent space charge drift under a sweep voltage. The evolution of streamer dynamics and discharge mode transition would help in better understanding of the streamer essence and insulation capability criteria under long-term RNP.

No abstract

Various injury defense and repair functions are performed by the skin. Free radicals secreted after injury cause oxidative stress and inflammatory responses, which make wound healing difficult. However, the current metal nanomaterials for wound repair do not have sufficient catalytic activity or complex material design and cannot properly fit wounds. Therefore, it is imperative to develop more effective therapeutic approaches. This study investigated the effect of Ni 4 Cu 2 hollow nanospheres composited with F127 hydrogel on promoting wound healing by applying them to wounds. Ni 4 Cu 2 hollow nanospheres exhibited a superior spatial structure, contained many catalytic sites, and could be synthesized in a simple manner. In vitro experiments showed that Ni 4 Cu 2 hollow nanospheres had superoxide dismutase-like activity and promoted fibroblast migration, angiogenesis, and macrophage polarization. F127, which is a thermosensitive, nontoxic, phase-change and porous hydrogel material, has proven to be an effective choice for injectable and sprayable medical dressings. Ni 4 Cu 2 hollow nanospheres were mixed with F127 hydrogel without significantly affecting its performance. In addition to adapting to the complex, irregular gaps of acute wounds, the mixture lengthened the nanozyme release time, which enhanced healing. Based on the animal experiments, the Ni 4 Cu 2 /F127 composite hydrogel effectively promoted wound healing, epithelial regeneration, and the formation of skin appendages such as hair follicles in mice. Furthermore, the Ni 4 Cu 2 /F127 composite hydrogel was nontoxic to animals and had high biological safety. The Ni 4 Cu 2 /F127 composite hydrogel has provided an innovative strategy to develop composite hydrogels for the treatment of acute skin wounds.

No abstract

No abstract