Body mechanics in the nematode Caenorhabditis elegans are central to both mechanosensation and locomotion. Previous work revealed that the mechanics of the outer shell, rather than internal hydrostatic pressure, dominates stiffness. This shell is comprised of the cuticle and the body wall muscles, either of which could contribute to the body mechanics. Here, we tested the hypothesis that the muscles are an important contributor by modulating muscle tone using optogenetic and pharmacological tools, and measuring animal stiffness using piezoresistive microcantilevers. As a proxy for muscle tone, we measured changes in animal length under the same treatments. We found that treatments that induce muscle contraction generally resulted in body shortening and stiffening. Conversely, methods to relax the muscles more modestly increased length and decreased stiffness. The results support the idea that body wall muscle activation contributes significantly to and can modulate C. elegans body mechanics. Modulation of body stiffness would enable nematodes to tune locomotion or swimming gaits and may have implications in touch sensation.

We present an on-chip microfluidic sample concentrator and detection triggering system for microparticles based on a combination of insulator-based dielectrophoresis (iDEP) and electrical impedance measurement. This platform operates by first using iDEP to selectively concentrate microparticles of interest based on their electrical and physiological characteristics in a primary fluidic channel; the concentrated microparticles are then directed into a side channel configured for particle detection using electrical impedance measurements with embedded electrodes. This is the first study showing iDEP concentration with subsequent sample diversion down an analysis channel and is the first to demonstrate iDEP in the presence of pressure driven flow. Experimental results demonstrating the capabilities of this platform were obtained using polystyrene microspheres and Bacillus subtilis spores. The feasibility of selective iDEP trapping and impedance detection of these particles was demonstrated. The system is intended for use as a front-end unit that can be easily paired with multiple biodetection/bioidentification systems. This platform is envisioned to act as a decision-making component to determine if confirmatory downstream identification assays are required. Without a front end component that triggers downstream analysis only when necessary, bio-identification systems (based on current analytical technologies such as PCR and immunoassays) may incur prohibitively high costs to operate due to continuous consumption of expensive reagents.

Operation of electrostatic actuators in liquid media has various proposed applications, especially in biological environments. The devices are operated by modulating at a frequency higher than the relaxation rate of the ions in solution. We present circuit models based on electric double layer theories to obtain analytical expression for the frequency-dependent force response of electrostatic actuators in ionic media. The model has been compared with experimental measurements of actuation in media of conductivity spanning five orders of magnitude. Further, impedance spectroscopy is used to measure the values of the circuit models, which are compared with the experiments. These measurements also quantify the parasitic impedances in the devices. A conformal layer of Parylene-C is demonstrated as a passivation scheme for the electrodes in corrosive media. The heating effects due to parasitic impedances are also quantified by temperature measurements of devices in fluids.

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Neurosensory mechanotransduction, the conversion of a force stimulus to an electrical signal, is the fundamental process governing touch sensation. Understanding how the touch receptor neurons (TRNs) of Caenorhabditis elegans mediate this conversion can unravel how touch works. The classical method is to score its response to mechanical stimuli applied with an eyebrow hair or a micro-von Frey hair. However, both methods lack repeatability, precision and resolution. In particular, the sensitivity and resolution possible with micro-von Frey hairs is at least an order of magnitude larger than the threshold for activation of force-gated currents in TRNs in vivo. To overcome these issues, we developed a force clamp system capable of applying fixed loads with high force resolution (sub-nN), a fast response (1 kHz), and a large dynamic range (50 dB) to enable the quantitative evaluation of C. elegans touch. We developed a piezoresistive micro-cantilever force probe and integrated it with a piezoelectric actuator and a programmable real-time controller. We implemented a computer vision-based x-y tracking system in parallel with the force-clamp system, which allows the desired force to be applied precisely at a selected location on a moving C. elegans. We first measured the threshold for behavioral responses to touch is between 0.1 and 1 mN. We have confirmed that mutations affecting MEC-4, a subunit of the forcegated ion channel expressed in TRNs disrupt responses to stimuli applied to the animal's body, but not its nose. The effect of additional mutations that selectively disrupt distinct classes of mechanosensory neurons and body mechanics will be presented. This system is a powerful tool for determining force sensitivity in wild-type and mutant nematodes and provides a new method to understand how factors like body mechanics affect touch sensitivity in this tiny nematode.