A new microfluidic tool for simultaneous immobilization, force delivery and high resolution imaging of neuronal activity in living Caenorhabditis elegans .

It has long been known that thunderstorms produce strong electric field fluctuations in their immediate vicinity, but it has been little recognized that these storms can also be a source of strong ULF magnetic field fluctuations (ULF; frequencies less than 5 Hz). Some characteristics of these magnetic field fluctuations were documented for a thunderstorm occurring in 1990. We now describe further measurements of these magnetic field changes for a well-defined and comparatively intense thunderstorm that passed over the San Francisco Bay area on 8–9 September 1999. The thunderstorm is further characterized by measurements of its associated lightning by the National Lightning Detection Network. As compared with the results reported for the 1990 thunderstorm, the new measurements were made by two independent systems and more components of the magnetic field changes are measured. Given the possibility that the thunderstorm-related ULF magnetic field changes can stimulate ULF hydromagnetic waves in the ionosphere, these measurements suggest, once again, that thunderstorms may be a source of ULF energy in the magnetosphere that can, in turn, lead to the generation of some of the ULF geomagnetic pulsations commonly observed on the ground. In addition, it may also be significant that the frequencies associated with these hydromagnetic waves in the magnetosphere are ideally suited for them to interact with some populations of the protons and ions in the radiation belts, potentially inducing them to precipitate into the atmosphere.

We report a biolistic technology platform for physical delivery of particle formulations of drugs or vaccines using parallel arrays of microchannels, which generate highly collimated jets of particles with high spatial resolution. Our approach allows for effective delivery of therapeutics sequentially or concurrently (in mixture) at a specified target location or treatment area. We show this new platform enables the delivery of a broad range of particles with various densities and sizes into both in vitro and ex vivo skin models. Penetration depths of ∼1 mm have been achieved following a single ejection of 200 µg high-density gold particles, as well as 13.6 µg low-density polystyrene-based particles into gelatin-based skin simulants at 70 psi inlet gas pressure. Ejection of multiple shots at one treatment site enabled deeper penetration of ∼3 mm in vitro, and delivery of a higher dose of 1 mg gold particles at similar inlet gas pressure. We demonstrate that particle penetration depths can be optimized in vitro by adjusting the inlet pressure of the carrier gas, and dosing is controlled by drug reservoirs that hold precise quantities of the payload, which can be ejected continuously or in pulses. Future investigations include comparison between continuous versus pulsatile payload deliveries. We have successfully delivered plasmid DNA (pDNA)-coated gold particles (1.15 µm diameter) into ex vivo murine and porcine skin at low inlet pressures of ∼30 psi. Integrity analysis of these pDNA-coated gold particles confirmed the preservation of full-length pDNA after each particle preparation and jetting procedures. This technology platform provides distinct capabilities to effectively deliver a broad range of particle formulations into skin with specially designed high-speed microarray ejector nozzles.

Micro-actuators driven on resonance maximize reach and speed; however, due to their sensitivity to environmental factors (e.g., temperature and air pressure), the amplitude and phase response must be monitored to achieve an accurate actuator position. We introduce an MEMS (microelectromechanical system) amplitude and phase monitor (MAPM) with a signal-to-noise ratio of 51 dB and 11.0 kHz bandwidth, capable of simultaneously driving and sensing the movement of 1D and 2D electrostatically driven micro-actuators without modifying the chip or its packaging. The operational principle is to electromechanically modulate the amplitude of a high-frequency signal with the changing capacitance of the micro-actuator. MAPM operation is characterized and verified by simultaneously measuring the amplitude and phase frequency response of commercial micromirrors. We demonstrate that the MAPM circuitry is insensitive to complex relationships between capacitance and position of the MEMS actuators, and it is capable of giving real-time read-out of the micromirror motion. Our measurements also reveal and quantify observations of phase drift and crosstalk in 2D resonant operation. Measurements of phase changes over time under normal operation also verify the need for phase monitoring. The open-loop, high-sensitivity position sensor enables detailed characterization of dynamic micro-actuator behavior, leading to new insights and new types of operation, including improved control of nonlinear motion.