Assessment of focused ultrasound stimulation to induce peripheral nerve activity and potential damage in vivo.

Introduction: Peripheral neuroprostheses are aimed to restore loss of sensory and motor functions by interfacing axons in the peripheral nerves. Most common interfaces in neuroprostheses are electrodes that establish electrical connection with peripheral axons. However, some challenges arise related to long-term functionality, durability, and body response. Recently, focused ultrasound stimulation (FUS) has emerged as a non-invasive approach to modulate the nervous system. However, it is controversial whether FUS can induce axon depolarization. Methods: We have assessed FUS applied in vivo to the rat peripheral nerve, with two objectives: first, to test whether FUS activates peripheral nerves under different stimulation conditions, and second, to evaluate if FUS inflicts damage to the nerve. FUS was delivered with three ultrasound transducers (Sonic Concept H115, H107, and H102) covering the largest set of parameters examined for FUS of peripheral nerves so far. Results: We did not obtain reliable evoked action potentials in either nerves or muscles, under any FUS condition applied, neither over the skin nor directly to the nerve exposed. Additional experiments ex vivo and in vivo on mice, confirmed this conclusion. When FUS stimulation was applied directly to the exposed sciatic nerve, neuromuscular function decreased significantly, and recovered one week later, except for FUS at 0.25 MHz. Histologically, degenerating nerve fibers were observed, with a tendency to be higher with the lower FUS frequency. Discussion: Past reports on the ability of ultrasound to stimulate the peripheral nerve are controversial. After testing a wide range of FUS conditions, we conclude that it is not a reliable and safe method for stimulating the peripheral nerve. Special consideration should be taken, especially when low-frequency FUS is applied, as it may lead to nerve damage.

High Performance Wearable Ultrasound as a Human-Machine Interface for Wrist and Hand Kinematic Tracking.

OBJECTIVE: Non-invasive human machine interfaces (HMIs) have high potential in medical, entertainment, and industrial applications. Traditionally, surface electromyography (sEMG) has been used to track muscular activity and infer motor intention. Ultrasound (US) has received increasing attention as an alternative to sEMG-based HMIs. Here, we developed a portable US armband system with 24 channels and a multiple receiver approach, and compared it with existing sEMG- and US-based HMIs on movement intention decoding. METHODS: US and motion capture data was recorded while participants performed wrist and hand movements of four degrees of freedom (DoFs) and their combinations. A linear regression model was used to offline predict hand kinematics from the US (or sEMG, for comparison) features. The method was further validated in real-time for a 3-DoF target reaching task. RESULTS: In the offline analysis, the wearable US system achieved an average [Formula: see text] of 0.94 in the prediction of four DoFs of the wrist and hand while sEMG reached a performance of [Formula: see text]= 0.60. In online control, the participants achieved an average 93% completion rate of the targets. CONCLUSION: When tailored for HMIs, the proposed US A-mode system and processing pipeline can successfully regress hand kinematics both in offline and online settings with performances comparable or superior to previously published interfaces. SIGNIFICANCE: Wearable US technology may provide a new generation of HMIs that use muscular deformation to estimate limb movements. The wearable US system allowed for robust proportional and simultaneous control over multiple DoFs in both offline and online settings.

A Novel Quantitative 500-MHz Acoustic Microscopy System for Ophthalmologic Tissues.

OBJECTIVE: This paper describes development of a novel 500-MHz scanning acoustic microscope (SAM) for assessing the mechanical properties of ocular tissues at fine resolution. The mechanical properties of some ocular tissues, such as lamina cribrosa (LC) in the optic nerve head, are believed to play a pivotal role in eye pathogenesis. METHODS: A novel etching technology was used to fabricate silicon-based lens for a 500-MHz transducer. The transducer was tested in a custom-designed scanning system on human eyes. Two-dimensional (2-D) maps of bulk modulus (K) and mass density (ρ) were derived using improved versions of current state-of-the-art signal processing approaches. RESULTS: The transducer employed a lens radius of 125 µm and had a center frequency of 479 MHz with a -6-dB bandwidth of 264 MHz and a lateral resolution of 4 µm. The LC, Bruch's membrane (BM) at the interface of the retina and choroid, and Bowman's layer (BL) at the interface of the corneal epithelium and stroma, were successfully imaged and resolved. Analysis of the 2-D parameter maps revealed average values of LC, BM, and BL with KLC = 2.81 ±0.17; GPa, KBM = 2.89 ±0.18; GPa, KBL = 2.6 ±0.09 ; GPa, ρ LC = 0.96 ±0.03 g/cm3; ρ BM = 0.97 ±0.04 g/cm3; ρ BL = 0.98 ±0.04 g/cm3. SIGNIFICANCE: This novel SAM was shown to be capable of measuring mechanical properties of soft biological tissues at microscopic resolution; it is currently the only system that allows simultaneous measurement of K, ρ, and attenuation in large lateral scales (field area >9 mm2) and at fine resolutions.

Fluorescence response of human HER2+ cancer- and MCF-12F normal cells to 200MHz ultrasound microbeam stimulation: a preliminary study of membrane permeability variation.

Targeted mechanical cell stimulation has been extensively studied for a better understanding of its effect on cellular mechanotransduction signaling pathways and structures by utilizing a variety of mechanical sources. In this work, an ultrasound-driven single cell stimulation method is thus proposed, and a preliminary study is carried out by comparing the fluorescence intensities representing a change in cell membrane permeability between MDA-MB-435 human HER2+ cancer cells (∼40-50µm in diameter) and MCF-12F normal cells (∼50-60µm) in the presence of ultrasound. A 200MHz single element zinc oxide (ZnO) transducer is employed to generate ultrasound microbeam (UM) whose beamwidth and depth of focus are 9.5 and 60µm, comparable to typical cell size. The cells in tetramethyl rhodamine methyl ester (TMRM) are interrogated with 200MHz sinusoidal bursts. The number of cycles per burst is 5 and the pulse repetition frequency (PRF) is 1kHz. The temporal variation of fluorescence intensity in each cell is measured as a function of input voltage to the transducer (16, 32, and 47V), and its corresponding fluorescence images are obtained via a confocal microscope. A systematic method for visualizing UM's focus by adding Rhodamine B to the immersion medium is also proposed to enhance the precision in aiming the beam at an individual cell. Both types of cells exhibit a decrease in the intensity upon UM irradiation. In particular, normal cells show more fluorescence reduction (down to 0.7 in normalized intensity) than cancer cells (∼0.9) under the same excitation condition of the transducer. With UM being turned off, the normalized intensity level in normal cells is slowly increased to 1.1. The cell images taken before and after UM exposure indicate that the intensity reduction is more pronounced in those cells after exposure. Hence the results show the potential of UM as a non-invasive in vitro stimulation tool for facilitating targeted drug delivery and gene transfection as well as for studying cellular mechanotransduction.

Targeted cell immobilization by ultrasound microbeam.

Various techniques exerting mechanical stress on cells have been developed to investigate cellular responses to externally controlled stimuli. Fundamental mechanotransduction processes about how applied physical forces are converted into biochemical signals have often been examined by transmitting such forces through cells and probing its pathway at cellular levels. In fact, many cellular biomechanics studies have been performed by trapping (or immobilizing) individual cells, either attached to solid substrates or suspended in liquid media. In that context, we demonstrated two-dimensional acoustic trapping, where a lipid droplet of 125 µm in diameter was directed transversely toward the focus (or the trap center) similar to that of optical tweezers. Under the influence of restoring forces created by a 30 MHz focused ultrasound beam, the trapped droplet behaved as if tethered to the focus by a linear spring. In order to apply this method to cellular manipulation in the Mie regime (cell diameter > wavelength), the availability of sound beams with its beamwidth approaching cell size is crucial. This can only be achieved at a frequency higher than 100 MHz. We define ultrasound beams in the frequency range from 100 MHz to a few GHz as ultrasound microbeams because the lateral beamwidth at the focus would be in the micron range. Hence a zinc oxide (ZnO) transducer that was designed and fabricated to transmit a 200 MHz focused sound beam was employed to immobilize a 10 µm human leukemia cell (K-562) within the trap. The cell was laterally displaced with respect to the trap center by mechanically translating the transducer over the focal plane. Both lateral displacement and position trajectory of the trapped cell were probed in a two-dimensional space, indicating that the retracting motion of these cells was similar to that of the lipid droplets at 30 MHz. The potential of this tool for studying cellular adhesion between white blood cells and endothelial cells was discussed, suggesting its capability as a single cell manipulator.

Novel single-source precursors for the fabrication of PbTiO3, PbZrO3 and Pb(Zr(1-x)Ti(x))O3 thin-films by chemical vapor deposition.

Lead titanate, lead zirconate, and lead zirconate titanate (PZT) films in the sub-µm-range were produced at temperatures around 400 °C using novel single-source precursors in a classical thermal CVD process. The design of two bimetallic alkoxide compounds, a lead titanate and a lead zirconate source with almost identical physical properties and complement miscibility, resulted in a new quasi-single-source PZT precursor, an azeotropic mixture that evaporates at 30 °C and at a pressure of 4 × 10(-1) mbar. After thermal treatment at 650 °C, transparent (100)-oriented PZT films with remnant polarization of 20 µC cm(-2) and a coercive field strength of 20 V µm(-1) were achieved. An additional lead source is not required.

Nanocomposite cerium oxide polymer matching layers with adjustable acoustic impedance between 4 MRayl and 7 MRayl.

A new class of materials for ultrasonic matching layers is presented. The materials consist of nanoscale cerium oxide particles in an epoxy functionalized organic inorganic hybrid polymer matrix. The cerium oxide agglomerates to particles with 20 nm diameters. The content of particles in the polymer matrix could be increased to 75 wt.% which corresponds to 37 vol.%. The most technical important piezoelectrical ceramics have an acoustic impedance of about 30 MRayl, to improve coupling into water or biological tissue with an acoustic impedance of about 1.5 MRayl a matching layer should have an acoustic impedance of about 6.8 MRayl. With a filling degree of 75 wt.% the new composite material reaches an acoustic impedance of 7 MRayl. The materials are synthesized by a hydrolytic condensation combined with polymerization. This way of synthesis allows the use of organic solvents to adjust the viscosity of the sol and the application of different coating techniques. Ultrasound transducers (100 MHz) were built to test the new matching layers and an increase of the voltage signal amplitude of about 100% could be detected.