Low-intensity electric fields can induce changes in cell differentiation and cytoskeletal stresses that facilitate manipulation of osteoblasts and mesenchymal stem cells; however, the application times (tens of minutes) are of the order of physiological mechanisms, which can complicate treatment consistency. Intense nanosecond pulsed electric fields (nsPEFs) can overcome these challenges by inducing similar stresses on shorter timescales while additionally inducing plasma membrane nanoporation, ion transport and intracellular structure manipulation. This paper shows that treating myoblasts and osteoblasts with five 300 ns PEFs with intensities from 1.5 to 25 kV cm −1 increased proliferation and differentiation. While nsPEFs above 5 kV cm −1 decreased myoblast population growth, 10 and 20 kV cm −1 trains increased myoblast population by approximately fivefold 48 h after exposure when all cell densities were set to the same level after exposure. Three trials of the PEF-treated osteoblasts showed that PEF trains between 2.5 and 10 kV cm −1 induced the greatest population growth compared to the control 48 h after treatment. Trains of nsPEFs between 1.5 and 5 kV cm −1 induced the most nodule formation in osteoblasts, indicating bone formation. These results demonstrate the potential utility for nsPEFs to rapidly modulate stem cells for proliferation and differentiation and motivate future experiments to optimize PEF parameters for in vivo applications.

Antibiotic resistance mechanisms render current antibiotics ineffective, requiring higher concentrations of existing drugs or the development of more powerful drugs for infection treatment. This study demonstrates the synergistic inactivation of a gram-positive (Staphylococcus aureus) and a gram-negative (Escherichia coli) bacteria by combining either tobramycin or rifampicin with 300-ns electric pulses (EPs). For EPs depositing the same total energy density into the sample with no drug, higher electric fields induced greater inactivation, indicating a threshold for irreversible electroporation at these fields and membrane recovery in between lower intensity EPs. Synergistic inactivation generally increased with increasing drug concentration up to 20 μg/mL compared to strictly EP treatment. Combining even 1/20 of the clinical dose of tobramycin with a train of EPs induced between 2.5 and 3.5 log inactivation after only 10 min of exposure compared to hours to induce inactivation with a clinical dose with no EPs. Similarly, combining a train of EPs with a clinically relevant dose of rifampicin induced 7 to 9 log inactivation over the same time of exposure. These results indicate the promise of combining EPs with antibiotics to rapidly inactivate antibiotic-resistant bacteria in localized treatment areas.

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Gas breakdown is typically driven by Townsend avalanche and predicted mathematically by Paschen's law (PL). Gas breakdown deviates from PL at microscale due to field emission, which depends critically on electrode condition; however, understanding of the impact of initial electrode surface roughness and multiple breakdown events on breakdown voltage is incomplete. This paper assesses the variation of breakdown voltage for a pin-to-plate electrode setup in air at atmospheric pressure for gap distances of 1 ± 0.5 μm, 5 ± 0.5 μm, and 10 ± 0.5 μm with different surface roughnesses. Breakdown voltage generally increases with increasing gap distance and decreasing surface roughness for a single breakdown event; however, the breakdown voltage after ten breakdown events does not depend on initial gap distance. Atomic force microscopy and optical microscopy show that multiple discharges create circular craters on the flat cathode up to 40 μm deep, with more pronounced craters created at smaller gap sizes and greater cathode surface roughness. The resulting effective gap distances (d eff , the sum of cathode placement distance and crater depth) for subsequent breakdown events are similar to those of the initially larger gap distances. Moreover, d eff becomes sufficiently large to exceed the Meek criterion for streamer formation, indicating a potential for breakdown mechanisms to change from field emission to Townsend avalanche to streamer formation for a single electrode separation distance. The resulting impact of this change in the breakdown mechanism could have significant implications for ensuring consistent microdevice operation.Published under license by AIP Publishing. https://doi.

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