Cavity-agnostic acoustofluidic manipulations enabled by guided flexural waves on a membrane acoustic waveguide actuator

This article presents an in-depth exploration of the acoustofluidic capabilities of guided flexural waves(GFWs)generated by a membrane acoustic waveguide actuator(MAWA).By harnessing the potential of GFWs,cavity-agnostic advanced particle manipulation functions are achieved,unlocking new avenues for microfluidic systems and lab-on-a-chip development.The localized acoustofluidic effects of GFWs arising from the evanescent nature of the acoustic fields they induce inside a liquid medium are numerically investigated to highlight their unique and promising characteristics.Unlike traditional acoustofluidic technologies,the GFWs propagating on the MAWA’s membrane waveguide allow for cavity-agnostic particle manipulation,irrespective of the resonant properties of the fluidic chamber.Moreover,the acoustofluidic functions enabled by the device depend on the flexural mode populating the active region of the membrane waveguide.Experimental demonstrations using two types of particles include in-sessile-droplet particle transport,mixing,and spatial separation based on particle diameter,along with streaming-induced counter-flow virtual channel generation in microfluidic PDMS channels.These experiments emphasize the versatility and potential applications of the MAWA as a microfluidic platform targeted at lab-on-a-chip development and showcase the MAWA’s compatibility with existing microfluidic systems.

Nanomechanical thermometry for probing sub-nW thermal transport

Accurate local temperature measurement at micro and nanoscales requires thermometry with high resolution because of ultra-low thermal transport.Among the various methods for measuring temperature,optical techniques have shown the most precise temperature detection,with resolutions reaching(-10^(-9) K).In this work,we present a nanomechanical device with nano-Kelvin resolution(-10^(-9) K)at room temperature and 1 atm.The device uses a 20 nm thick silicon nitride(SiN)membrane,forming an air chamber as the sensing area.The presented device has a temperature sensing area>1 mm^(2)for micro/nanoscale objects with reduced target placement constraints as the target can be placed anywhere on the>1 mm^(2)sensing area.The temperature resolution of the SiN membrane device is determined by deflection at the center of the membrane.The temperature resolution is inversely proportional to the membrane's stiffness,as detailed through analysis and measurements of stiffness and noise equivalent temperature(NET)in the pre-stressed SiN membrane.The achievable heat flow resolution of the membrane device is 100 pW,making it suitable for examining thermal transport on micro and nanoscales.

Ultrasonically actuated neural probes for reduced trauma and inflammation in mouse brain

Electrical neural recordings measured using direct electrical interfaces with neural tissue suffer from a short lifespan because the signal strength decreases over time.The inflammatory response to the inserted microprobe can create insulating tissue over the electrical interfaces,reducing the recorded signal below noise levels.One of the factors contributing to this inflammatory response is the tissue damage caused during probe insertion.Here,we explore the use of ultrasonic actuation of the neural probe during insertion to minimize tissue damage in mice.Silicon neural microprobes were designed and fabricated with integrated electrical recording sites and piezoelectric transducers.The microprobes were actuated at ultrasonic frequencies using integrated piezoelectric transducers.The microprobes were inserted into mouse brains under a glass window over the brain surface to image the tissue surrounding the probe using two-photon microscopy.The mechanical force required to penetrate the tissue was reduced by a factor of 2–3 when the microprobe was driven at ultrasonic frequencies.Tissue histology at the probe insertion site showed a reduced area of damage and decreased microglia counts with increasing ultrasonic actuation of the probes.Twophoton imaging of the microprobe over weeks demonstrated stabilization of the inflammatory response.Recording of electrical signals from neurons over time suggests that microprobes inserted using ultrasound have a higher signal-tonoise ratio over an extended time period.

Polymer interdigitated pillar electrostatic(PIPE)actuators

This work reports a three-dimensional polymer interdigitated pillar electrostatic actuator that can produce force densities 5-10×higher than those of biological muscles.The theory of operation,scaling,and stability is investigated using analytical and FEM models.The actuator consists of two high-density arrays of interdigitated pillars that work against a restoring force generated by an integrated flexure spring.The actuator architecture enables linear actuation with higher displacements and pull-in free actuation to prevent the in-use stiction associated with other electrostatic actuators.The pillars and springs are 3D printed together in the same structure.The pillars are coated with a gold-palladium alloy layer to form conductive electrodes.The space between the pillars is filled with liquid dielectrics for higher breakdown voltages and larger electrostatic forces due to the increase in the dielectric constant.We demonstrated a prototype actuator that produced a maximum work density of 54.6μJ/cc and an electrical-tomechanical energy coupling factor of 32%when actuated at 4000 V.The device was operated for more than 100,000 cycles with no degradation in displacements.The flexible polymer body was robust,allowing the actuator to operate even after high mechanical force impact,which was demonstrated by operation after drop tests.As it is scaled further,the reported actuator will enable soft and flexible muscle-like actuators that can be stacked in series and parallel to scale the resulting forces.This work paves the way for high-energy density actuators for microrobotic applications.