Many animals employ a second frequency filter beyond the initial filtering of the eardrum (or tympanal membrane). In the field cricket ear, both the filtering mechanism and the transmission path from the posterior tympanal membrane (PTM) have remained unclear. A mismatch between PTM vibrations and sensilla tuning has prompted speculations of a second filter. PTM coupling to the tracheal branches is suggested to support a transmission pathway. Here, we present three independent lines of evidence converging on the same conclusion: the existence of a series of linked membranes with distinct resonant frequencies serving both filtering and transmission functions. Micro-computed tomography (µ-CT) highlighted the ‘dividing membrane (DivM)’, separating the tracheal branches and connected to the PTM via the dorsal membrane of the posterior tracheal branch (DM-PTB). Thickness analysis showed the DivM to share significant thinness similarity with the PTM. Laser Doppler vibrometry indicated the first of two PTM vibrational peaks, at 6 and 14 kHz, originates not from the PTM but from the coupled DM-PTB. This result was corroborated by µ-CT-based finite element analysis. These findings clarify further the biophysical source of neuroethological pathways in what is an important model of behavioural neuroscience. Tuned microscale coupled membranes may also hold biomimetic relevance.

Controlling the absorption and diffusion of sound in the audible range is an exciting field of research. Achieving miniaturized acoustic systems able to operate at audio frequencies is one of the main challenges of acoustic engineering for many practical applications. One viable approach to tackle this challenge is by using meta materials such that deep subwavelength control can be achieved. This work investigates the fabrication and experimental characterization of membrane-coupled Helmholtz resonators as directional attenuators via 3D-printing, and introduces a 3D-printed piezoelectric component to transform acoustic attenuation to electrical outputs.

The ability to create cell-laden fluidic models that mimic the geometries and physical properties of vascularized tissue would be extremely beneficial to the study of disease etiologies and future therapies, including in the case of cancer where there is increasing interest in studying alterations to the microvasculature. Engineered systems can present significant advantages over animal studies, alleviating challenges associated with variable complexity and control. Three-dimensional (3D)-printable tissue-mimicking hydrogels can offer an alternative, where control of the biophysical properties of the materials can be achieved. Hydrogel-based systems that can recreate complex 3D structures and channels with diameters <500 mu m are challenging to produce. We present a noncytotoxic photo-responsive hydrogel that supports 3D printing of complex 3D structures with microchannels down to 150 mu m in diameter. Fine tuning of the 3D-printing process has allowed the production of complex structures, where for demonstration purposes we present a helical channel with diameters between 250 and 370 mu m around a central channel of 150 mu m in diameter in materials with mechanical and acoustic properties that closely replicate those of tissue. The ability to control and accurately reproduce the complex features of the microvasculature has value across a wide range of biomedical applications, especially when the materials involved accurately mimic the physical properties of tissue. An approach that is additionally cell compatible provides a unique setup that can be exploited to study aspects of biomedical research with an unprecedented level of accuracy.

Controlling the absorption and diffusion of sound in the audible range constitutes an exciting field of research. Acoustic absorbers and diffusers perform extraordinarily well at high frequencies with sizes comparable to the wavelength of the working frequency. On the other hand, efficient low-frequency attenuators demand large volumes leading to unpractical sizes and high manufacturing costs. However, can the size of the resonator be reduced while also decreasing the working frequency? The answer is, counterintuitively, yes. This work investigates this phenomenon by studying a series of 3-D-printed monoatomic metamaterials based on membrane-coupled Helmholtz resonators. The results reveal that these systems, apart from significantly decreasing the bandgap frequency by around 36%, produce a cardioid directional response that contrasts with the omnidirectional response from traditional Helmholtz resonators. The obtained results suggest that by following this approach, low-frequency attenuation can be achieved via miniaturised devices while additionally providing them with a sense of directionality. This combination of features makes these sensors the perfect candidates for the next generation of acoustic hearing devices and acoustic attenuators, since the freedom that 3-D-printing provides allows for fine control of wave manipulation.

Many solid tumours (e.g. sarcoma, carcinoma and lymphoma) form a disorganized neo-vasculature that initiates uncontrolled vessel formation to support tumour growth. The complexity of these environments poses a significant challenge for tumour medicine research. While animal models are commonly used to address some of these challenges, they are time-consuming and raise ethical concerns. In vitro microphysiological systems have been explored as an alternative, but their production typically requires multi-step lithographic processes that limit their production. In this work, a novel approach to rapidly develop multi-material tissue-mimicking, cell-compatible platforms able to represent the complexity of a solid tumour's neo-vasculature is investigated via stereolithography three-dimensional printing. To do so, a series of acrylate resins that yield covalently photo-cross-linked hydrogels with healthy and diseased mechano-acoustic tissue-mimicking properties are designed and characterized. The potential viability of these materials to displace animal testing in preclinical research is assessed by studying the morphology, actin expression, focal adhesions and nitric oxide release of human umbilical vein endothelial cells. These materials are exploited to produce a simplified multi-material three-dimensional printed model of the neo-vasculature of a solid tumour, demonstrating the potential of our approach to replicate the complexity of solid tumours in vitro without the need for animal testing.

Kylie is a solitary common dolphin who inhabits a restricted area within the Firth of Clyde (Scotland). She spends most of her time around navigational buoys in the Hunterston/Fairlie channel, where she has been seen interacting with harbour porpoises. Recordings from 2016 and 2017 were used to study her acoustic behaviour when seen alone and with a porpoise. Clicks were classified as potential porpoise or dolphin clicks based on the waveform, power spectrum, and spectrogram, as well as direction of arrival, inter-click interval, amplitude, and centroid frequency variations. Kylie emitted clicks exclusively, which were of variable nature, including low, mid, and high-frequency (HF, centroid frequency > 100 kHz) as well as broad or narrowband. Some of Kylie’s HF clicks were similar to porpoise clicks both in the time (e.g. polycyclic) and frequency (e.g. narrowband with most energy between 100 and 150 kHz) domains, which cannot fully be explained by recording geometry and directionality effects.

Resistance Seam Welding (RSW) is frequently used in many industries where low-cost mass manufacturing of gas/fluid-tight seals are required. One particular use case is in the fabrication of canisters to store nuclear material. Given the expected long lifetime and high replacement cost associated with nuclear infrastructure, it is common for an increase in the design life to be sought during operation. This leads to a need to integrate NonDestructive Testing (NDT) techniques in a complex environment which frequently has accessibility issues. For the inspection of RSW nuclear canisters, one promising solution is to use Feature Guided Waves (FGWs) to rapidly screen the whole circumferential RSW joint from only partial circumferential access to ensure safe storage and targeted repackaging. FGWs can travel long distances while locally confining their energy to a topological feature such as a weld or stiffener. This paper explores such use of FGWs through both theoretical and practical experimental methods. To understand which FGW modes exist in the RSW joint, the Semi-Analytical Finite Element (SAFE) method was used, revealing four suitable wave modes. An anti-symmetric flexural RSW guided mode was down-selected due to its ease of excitation, intense energy concentration around the RSW, low dispersion and attenuation. Three-dimensional Finite Element (FE) simulations were conducted to explore the sensitivity of the flexural FGW to transverse cracks of differing dimensions. Experimental results on simplified and realistic geometries to transverse crack defects of >= 1 mm deep show the efficacy of using this method to efficiently screen nuclear canister RSW joints for such defects in-situ.

Bio-inspiration looks to nature to overcome challenges innovatively. Insects show many examples of efficient approaches to hearing considering the small sizes of their bodies. The nocturnal moth Achroia grisella is capable of directional hearing of wavelengths several times larger than the separation between its tympana. Directionality in this moth seems to be monoaural and dependent exclusively on morphology, so a model is developed to replicate the structure. We start from a simple circular model, progressively incorporating more complex elements to improve the resemblance to the natural system. The goal is to develop a model inspired by Achroia’s ear, that behaves similarly to it, and to 3D print devices that agree with the model. Equations, simulations, and 3D printed devices measured through Laser Doppler Vibrometry are compared.

Achroia grisella is a pyraloid moth capable of directional hearing. It is generally accepted that hearing arose in moths to avoid bats, their main predators, and, in this particular case, was later repurposed into a rudimentary mating tool. The male emits ultrasonic signals of a wavelength several times larger than the distance between their tympana during its mating process. Notwithstanding, the female moths are capable of somewhat efficiently reaching the males after some zigzagging. Another remarkable feature is the simple structure of the ear, consisting of a cluster of just four receptor cells attached directly to the tympanic membrane. Moths with only one functioning ear have been seen to reach the males still, which implies the tympanum structure itself must confer the moth with monoaural directionality. A model is developed in COMSOL to explain the behavior of the moth ear. The complexity of the model is increased by improving the resemblance to the natural one, starting from a circular plate and progressing to, eventually, a damped elliptical plate with two different thicknesses and an attached point mass.

The impedance matching layer has a critical effect on ultrasonic transducer performance, but it is difficult to source materials that have the appropriate acoustical properties. A method that utilises effective property relations of composites and finite element analysis is used to design a hydrogel-steel based phononic crystal, quarter wavelength impedance matching layer that can match bespoke configurations. Phononic crystal band structures are calculated to determine an appropriate lattice scale length, and frequency domain studies are carried out to compare this novel type of matching layer with an ideal bulk layer. Transmitted pressure curves are as expected and suggest that this design type will be suited for fabrication and testing.

Systemically circulating microbubbles are used as contrast agents to aid both drug targeting and delivery using ultrasound. Exploiting their acoustic behaviour in small diameter vessels is critical for both applications, but the highly controlled experiments required to support this are not possible in vivo and challenging in vitro. Experimental platforms with small diameter channels (below 200 microns) are not readily available nor able to represent vascular geometries, leaving the existence and extent of microbubble-microvessel interactions incompletely defined. In this work we present a 3D-printed microchannel platform using tissue-mimicking hydrogels featuring radii down to 75 microns. We demonstrate application to study microbubble behaviour via acoustic backscatter under controlled environments in physiologically-relevant conditions.

Acoustic bandgaps are ranges of frequencies in a medium at which sound cannot propagate. The classical model often used in solid-state physics is that of a 1D chain of masses and springs, the analysis of which can predict the speed of sound in a material, its dispersive nature, and any forbidden sound frequencies. We use a lumped parameter model for the acoustic inertance and compliance of pipes and cavities to create 1D monatomic, diatomic, and triatomic chains that demonstrate these acoustic bandgaps experimentally. The ease of 3D-printing these devices means that this method can be used to explore bandgap engineering in acoustic systems for low-frequency applications and used as a simple platform for creating acoustic analogs of the solid-state physical problem. Furthermore, it allows us to explore novel polyatomic behavior (e.g., tetratomic and pentatomic) and could ultimately find use as filters for experiments requiring miniaturized acoustic isolation.

Bio-inspiration, gathering insight from looking at nature, can be useful when trying to solve challenges innovatively. Insects are forced by their body size and the energy cost of a hearing organ to make many clever adaptations for hearing. Achroia grisella is a nocturnal moth with a hearing sense. It uses it both for avoiding predators and mating, the latter being an unconventional role among moths. The moth is capable of directionality that seems to be monoaural and dependent exclusively on morphology. We develop a model with the goal of 3D printing a structure whose behavior is similar to that of the moth ear, i.e., directionality at a low design cost. Starting from a simple circular plate model, we progressively incorporate more complex elements to improve the resemblance to the natural system. Equations, simulations, and 3D printed devices' frequency responses (measured through Laser Doppler Vibrometry) are compared. The directionality of the printed devices is analyzed.

Acoustic metamaterials are large-scale materials with small-scale structures. These structures allow for unusual interaction with propagating sound and endow the large-scale material with exceptional acoustic properties not found in normal materials. However, their multi-scale nature means that the manufacture of these materials is not trivial, often requiring micron-scale resolution over centimetre length scales. In this review, we bring together a variety of acoustic metamaterial designs and separately discuss ways to create them using the latest trends in additive manufacturing. We highlight the advantages and disadvantages of different techniques that act as barriers towards the development of realisable acoustic metamaterials for practical audio and ultrasonic applications and speculate on potential future developments.

A method for predicting the solidification and stress of a digital light processing 3D print process is presented, using a voxel-based, multi-layer model to predict the degree of polymerization of the material at every stage during the print. Additive manufacturing offers extremely short development cycles, making predictive modelling of the complex chemical and mechanical interactions of photo-polymerization during part construction unappealing compared to iterative work-flows. Accurate predictions of stress, and the impact of the print parameters and post-print process upon stress, become increasingly important for 3D printing micro-scale electrical and mechanical systems as we design resonators and conductive layers. The process uses a simple method of printed cantilevers to calibrate the stress from various print processes such as propagation of the polymerization front and polymerization gradient. The model is found to have good predictive value and is capable of stress and solidification prediction from a computer aided design file.

The reliance of many cancers on aerobic glycolysis has stimulated efforts to develop lactate dehydrogenase (LDH) inhibitors. However, despite significant efforts, LDH inhibitors (LDHi) with sufficient specificity and in vivo activity to determine whether LDH is a feasible drug target are lacking. We describe an LDHi with potent, on-target, in vivo activity. Using hyperpolarized magnetic resonance spectroscopic imaging (HP-MRSI), we demonstrate in vivo LDH inhibition in two glycolytic cancer models, MIA PaCa-2 and HT29, and we correlate depth and duration of LDH inhibition with direct anti-tumor activity. HP-MRSI also reveals a metabolic rewiring that occurs in vivo within 30 min of LDH inhibition, wherein pyruvate in a tumor is redirected toward mitochondrial metabolism. Using HP-MRSI, we show that inhibition of mitochondrial complex 1 rapidly redirects tumor pyruvate toward lactate. Inhibition of both mitochondrial complex 1 and LDH suppresses metabolic plasticity, causing metabolic quiescence in vitro and tumor growth inhibition in vivo.

Small-scale bioacoustic sensors, such as antennae in insects, are often considered, biomechanically, to be not much more than the sum of their basic geometric features. Therefore, little is known about the fine structure and material properties of these sensors—even less so about the degree to which the well-known sexual dimorphism of the insect antenna structure affects those properties. By using confocal laser scanning microscopy (CLSM), we determined material composition patterns and estimated distribution of stiffer and softer materials in the antennae of males and females of the non-biting midge Chironomus riparius. Using finite element modelling (FEM), we also have evidence that the differences in composition of these antennae can influence their mechanical responses. This study points to the possibility that modulating the elastic and viscoelastic properties along the length of the antennae can affect resonant characteristics beyond those expected of simple mass-on-a-spring systems—in this case, a simple banded structure can change the antennal frequency sensitivity. This constitutes a simple principle that, now demonstrated in another Dipteran group, could be widespread in insects to improve various passive and active sensory performances.

Harbour porpoises are well-suited for passive acoustic monitoring (PAM) as they produce highly stereotyped narrow-band high-frequency (NBHF) echolocation clicks. PAM systems must be coupled with a classification algorithm to identify the signals of interest. Here, the authors present a harbour porpoise click classifier (PorCC) developed in matlab, which uses the coefficients of two logistic regression models in a decision-making pathway to assign candidate signals to one of three categories: high-quality clicks (HQ), low-quality clicks (LQ), or high-frequency noise. The receiver operating characteristics of PorCC was compared to that of PAMGuard's Porpoise Click Detector/Classifier Module. PorCC outperformed PAMGuard's classifier achieving higher hit rates (correctly classified clicks) and lower false alarm levels (noise classified as HQ or LQ clicks). Additionally, the detectability index (d′) for HQ clicks for PAMGuard was 2.2 (overall d′ = 2.0) versus 4.1 for PorCC (overall d′ = 3.4). PorCC classification algorithm is a rapid and highly accurate method to classify NBHF clicks, which could be applied for real time monitoring, as well as to study harbour porpoises, and potentially other NBHF species, throughout their distribution range from data collected using towed hydrophones or static recorders. Moreover, PorCC is suitable for studies of acoustic communication of porpoises.

The behaviour of harbour porpoises can be deduced from the variation pattern of their vocalisations. They produce only narrow-band high-frequency (NBHF) clicks, emitted in so-called click trains. Therefore, available acoustic recordings can be used to increase our understanding of their behaviour. Behavioural studies, however, are time consuming and require an accurate, automated classifier and a click train identifier. Here, we present D-PorCCA, a graphical user interface to study recordings from harbour porpoises in the wild. D-PorCCA is an independent tool developed in Matlab and includes an impulsive-sound detector and a new high-accuracy porpoise click classifier (PorCC). PorCC classifies each signal as either: noise (N), low-quality (LQ), or high-quality (HQ) porpoise click. The user can decide on the echolocation events they want to visualise, specifying the length of the click train (including both HQ and LQ clicks) and the minimum separation time between echolocation events. These events are plotted as time vs amplitude, vs inter-click interval, and vs centroid frequency (or direction of arrival, if available). Additionally, the waveform, power spectrum, and spectrogram of each click within the echolocation event is available. Click trains of interest can be easily selected by the user and extracted for further analysis. These events are then automatically cleaned of echoes and other noise sources, after which the pattern of the click train is automatically investigated to determine whether there is one or more animals vocalising simultaneously (i.e., overlapping click trains), as well as which behaviour the animal was potentially engaged in (e.g., feeding). D-PorCCA is a user-friendly tool with potential for behavioural studies of wild harbour porpoises as well as other NBHF species, as it focuses on clicks trains, and can be used to fill knowledge gaps of these elusive species. Moreover, it has potential for application in large monitoring project, such as SAMBAH.