Being watched by a humanoid robot and a human: Effects on affect-related psychophysiological responses.

Eye contact with a humanoid robot has been shown to evoke similar affect and affiliation related psychophysiological responses as eye contact with another human. In this pre-registered study, we investigated whether these effects are dependent on the experience of being "watched". Psychophysiological responses (SCR, zygomatic and corrugator facial EMG, frontal EEG asymmetry) to a humanoid robot's or a human model's direct vs. averted gaze were measured while manipulating the participants' belief of whether the robot/human model could see them or not. The results showed greater autonomic arousal responses and facial responses related to positive affect both to the robot's and the human model's direct vs. averted gaze, regardless of the belief condition. The belief condition influenced the overall magnitude of these responses to both stimulus models, however, to a lesser extent for the robot than for the human model. For the frontal EEG asymmetry, the effect of gaze direction was non-significant in both belief conditions. The results lend further support for the importance of eye contact in human-robot interaction and provide insights into people's implicit attributions of humanoid robots' mental capacities.

Programmable Droplet Microfluidics Based on Machine Learning and Acoustic Manipulation.

Typical microfluidic devices are application-specific and have to be carefully designed to implement the necessary functionalities for the targeted application. Programmable microfluidic chips try to overcome this by offering reconfigurable functionalities, allowing the same chip to be used in multiple different applications. In this work, we demonstrate a programmable microfluidic chip for the two-dimensional manipulation of droplets, based on ultrasonic bulk acoustic waves and a closed-loop machine-learning-based control algorithm. The algorithm has no prior knowledge of the acoustic fields but learns to control the droplets on the fly. The manipulation is based on switching the frequency of a single ultrasonic transducer. Using this method, we demonstrate 2D transportation and merging of water droplets in oil and oil droplets in water, and we performed the chemistry that underlies the basis of a colorimetric glucose assay. We show that we can manipulate drops with volumes ranging from ∼200 pL up to ∼30 nL with our setup. We also demonstrate that our method is robust, by changing the system parameters and showing that the machine learning algorithm can still complete the manipulation tasks. In short, our method uses ultrasonics to flexibly manipulate droplets, enabling programmable droplet microfluidic devices.

Controlled Manipulation and Active Sorting of Particles Inside Microfluidic Chips Using Bulk Acoustic Waves and Machine Learning.

Manipulation of cells, droplets, and particles via ultrasound within microfluidic chips is a rapidly growing field, with applications in cell and particle sorting, blood fractionation, droplet transport, and enrichment of rare or cancerous cells, among others. However, current methods with a single ultrasonic transducer offer limited control of the position of single particles. In this paper, we demonstrate closed-loop two-dimensional manipulation of particles inside closed-channel microfluidic chips, by controlling the frequency of a single ultrasound transducer, based on machine-vision-measured positions of the particles. For the control task, we propose using algorithms derived from the family of multi-armed bandit algorithms. We show that these algorithms can achieve controlled manipulation with no prior information on the acoustic field shapes. The method learns as it goes: there is no need to restart the experiment at any point. Starting with no knowledge of the field shapes, the algorithms can (eventually) move a particle from one position inside the chamber to another. This makes the method very robust to changes in chip and particle properties. We demonstrate that the method can be used to manipulate a single particle, three particles simultaneously, and also a single particle in the presence of a bubble in the chip. Finally, we demonstrate the practical applications of this method in active sorting of particles, by guiding each particle to exit the chip through one of three different outlets at will. Because the method requires no model or calibration, the work paves the way toward the acoustic manipulation of microparticles inside unstructured environments.

Magnetically switchable soft suction grippers.

Grasping is one of the key tasks for robots. Gripping fragile and complex three-dimensional (3D) objects without applying excessive contact forces has been a challenge for traditional rigid robot grippers. To solve this challenge, soft robotic grippers have been recently proposed for applying small forces and for conforming to complex 3D object shapes passively and easily. However, rigid grippers are still able to exert larger forces, necessary for picking heavy objects. Therefore, in this study, we propose a magnetically switchable soft suction gripper (diameter: 20 mm) to be able to apply both small and large forces. The suction gripper is in its soft state during approach and attachment while it is switched to its rigid state during picking. Such stiffness switching is enabled by filling the soft suction cup with a magnetorheological fluid (MR fluid), which is switched between low-viscosity (soft) and high-viscosity (rigid) states using a strong magnetic field. We characterized the gripper by measuring the force required to pull the gripper from a smooth glass surface. The force was up to 90% larger when the magnetic field was applied (7.1 N vs. 3.8 N). We also demonstrated picking of curved, rough, and wet 3D objects, and thin and delicate films. The proposed stiffness-switchable gripper can also carry heavy objects and still be delicate while handling fragile objects, which is very beneficial for future potential industrial part pick-and-place applications.

Copper Oxide Microtufts on Natural Fractals for Efficient Water Harvesting.

Hierarchical surfaces that aid in the droplet nucleation, growth, and removal is highly desirable for fog and moisture harvesting applications. Taking inspiration from the unique architecture of leaf skeletons, we present a multiscale surface capable of rapidly nucleating, growing, and directional transport of the water droplets. Copper oxide microtufts were fabricated onto the Ficus religiosa leaf skeletons via electroplating and chemical oxidation techniques. The fabricated surfaces with microtufts had high wettability and very good fog harvesting ability. CuO surfaces tend to become hydrophobic over time because of the adsorption of the airborne species. The surfaces were efficient in fog harvesting even when the hydrophobic coating is present. The overall water collection efficiencies were determined, and the role of the microtufts, fractal structures, and the orientation of leaf veins was investigated. Compared to the planar control surfaces, the noncoated and hydrophobic layer-coated copper oxide microtufts on the leaf skeletons displayed a significant increase in the fog harvesting efficiency. For superhydrophilic skeleton surfaces, the water collection rate was also observed to slightly vary with the vein orientation. The CuO microtufts along with high surface area fractals allowed an effective and sustainable way to capture and transport water. The study is expected to provide valuable insights into the design and fabrication of sustainable and efficient fog harvesting systems.

Making eye contact with a robot: Psychophysiological responses to eye contact with a human and with a humanoid robot.

Previous research has shown that eye contact, in human-human interaction, elicits increased affective and attention related psychophysiological responses. In the present study, we investigated whether eye contact with a humanoid robot would elicit these responses. Participants were facing a humanoid robot (NAO) or a human partner, both physically present and looking at or away from the participant. The results showed that both in human-robot and human-human condition, eye contact versus averted gaze elicited greater skin conductance responses indexing autonomic arousal, greater facial zygomatic muscle responses (and smaller corrugator responses) associated with positive affect, and greater heart deceleration responses indexing attention allocation. With regard to the skin conductance and zygomatic responses, the human model's gaze direction had a greater effect on the responses as compared to the robot's gaze direction. In conclusion, eye contact elicits automatic affective and attentional reactions both when shared with a humanoid robot and with another human.

Analytical Expressions for Spring Constants of Capillary Bridges and Snap-in Forces of Hydrophobic Surfaces.

When a force probe with a small liquid drop adhered to its tip makes contact with a substrate of interest, the normal force right after contact is called the snap-in force. This snap-in force is related to the advancing contact angle or the contact radius at the substrate. Measuring snap-in forces has been proposed as an alternative to measure the advancing contact angles of surfaces. The snap-in occurs when the distance between the probe surface and the substrate is hS, which is amenable to geometry, assuming the drop was a spherical cap before snap-in. Equilibrium is reached at a distance hE < hS. At equilibrium, the normal force F = 0, and the capillary bridge is a spherical segment, amenable again to geometry. For a small normal displacement Δ h = h - hE, the normal force can be approximated with F ≈ - k1Δ h or F ≈ - k1Δ h - k2Δ h2, where k1 = -∂ F/∂ h and k2 = -1/2·∂2 F/∂ h2 are the effective linear and quadratic spring constants of the bridge, respectively. Analytical expressions for k1,2 are found using Kenmotsu's parameterization. Fixed contact angle and fixed contact radius conditions give different forms of k1,2. The expressions for k1 found here are simpler, yet equivalent to the earlier derivation by Kusumaatmaja and Lipowsky (2010). Approximate snap-in forces are obtained by setting Δ h = hS - hE. These approximate analytical snap-in forces agree with the experimental data from Liimatainen et al. (2017) and a numerical method based on solving the shape of the interface. In particular, the approximations are most accurate for super liquid-repellent surfaces. For such surfaces, readers may find this new analytical method more convenient than solving the shape of the interface numerically.

Large-scale efficient water harvesting using bioinspired micro-patterned copper oxide nanoneedle surfaces and guided droplet transport.

As the Earth's atmosphere contains an abundant amount of water as vapors, a device which can capture a fraction of this water could be a cost-effective and practical way of solving the water crisis. There are many biological surfaces found in nature which display unique wettability due to the presence of hierarchical micro-nanostructures and play a major role in water deposition. Inspired by these biological microstructures, we present a large scale, facile and cost-effective method to fabricate water-harvesting functional surfaces consisting of high-density copper oxide nanoneedles. A controlled chemical oxidation approach on copper surfaces was employed to fabricate nanoneedles with controlled morphology, assisted by bisulfate ion adsorption on the surface. The fabricated surfaces with nanoneedles displayed high wettability and excellent fog harvesting capability. Furthermore, when the fabricated nanoneedles were subjected to hydrophobic coating, these were able to rapidly generate and shed coalesced droplets leading to further increase in fog harvesting efficiency. Overall, ∼99% and ∼150% increase in fog harvesting efficiency was achieved with non-coated and hydrophobic layer coated copper oxide nanoneedle surfaces respectively when compared to the control surfaces. As the transport of the harvested water is very important in any fog collection system, hydrophilic channels inspired by leaf veins were made on the surfaces via a milling technique which allowed an effective and sustainable way to transport the captured water and further enhanced the water collection efficiency by ∼9%. The system presented in this study can provide valuable insights towards the design and fabrication of fog harvesting systems, adaptable to arid or semi-arid environmental conditions.

Publisher Correction: Mapping microscale wetting variations on biological and synthetic water-repellent surfaces.

The original version of this Article contained an error in Fig. 2b. The y-axis label in Fig. 2b was incorrectly labelled 'Snap-in force (µN)'. In the correct version, the axis is labelled 'Snap-in force (nN)'. In the original version of this Article, the "Butterfly wings" section of the Methods incorrectly stated the name of the butterfly as 'Golden bird'. In the correct version, the name of the butterfly is 'Golden birdwing'. These have now been corrected in both the PDF and HTML versions of the article.

Mapping microscale wetting variations on biological and synthetic water-repellent surfaces.

Droplets slip and bounce on superhydrophobic surfaces, enabling remarkable functions in biology and technology. These surfaces often contain microscopic irregularities in surface texture and chemical composition, which may affect or even govern macroscopic wetting phenomena. However, effective ways to quantify and map microscopic variations of wettability are still missing, because existing contact angle and force-based methods lack sensitivity and spatial resolution. Here, we introduce wetting maps that visualize local variations in wetting through droplet adhesion forces, which correlate with wettability. We develop scanning droplet adhesion microscopy, a technique to obtain wetting maps with spatial resolution down to 10 µm and three orders of magnitude better force sensitivity than current tensiometers. The microscope allows characterization of challenging non-flat surfaces, like the butterfly wing, previously difficult to characterize by contact angle method due to obscured view. Furthermore, the technique reveals wetting heterogeneity of micropillared model surfaces previously assumed to be uniform.

Surface tension-driven self-alignment.

Surface tension-driven self-alignment is a passive and highly-accurate positioning mechanism that can significantly simplify and enhance the construction of advanced microsystems. After years of research, demonstrations and developments, the surface engineering and manufacturing technology enabling capillary self-alignment has achieved a degree of maturity conducive to a successful transfer to industrial practice. In view of this transition, a broad and accessible review of the physics, material science and applications of capillary self-alignment is presented. Statics and dynamics of the self-aligning action of deformed liquid bridges are explained through simple models and experiments, and all fundamental aspects of surface patterning and conditioning, of choice, deposition and confinement of liquids, and of component feeding and interconnection to substrates are illustrated through relevant applications in micro- and nanotechnology. A final outline addresses remaining challenges and additional extensions envisioned to further spread the use and fully exploit the potential of the technique.

Controlling the motion of multiple objects on a Chladni plate.

The origin of the idea of moving objects by acoustic vibration can be traced back to 1787, when Ernst Chladni reported the first detailed studies on the aggregation of sand onto nodal lines of a vibrating plate. Since then and to this date, the prevailing view has been that the particle motion out of nodal lines is random, implying uncontrollability. But how random really is the out-of-nodal-lines motion on a Chladni plate? Here we show that the motion is sufficiently regular to be statistically modelled, predicted and controlled. By playing carefully selected musical notes, we can control the position of multiple objects simultaneously and independently using a single acoustic actuator. Our method allows independent trajectory following, pattern transformation and sorting of multiple miniature objects in a wide range of materials, including electronic components, water droplets loaded on solid carriers, plant seeds, candy balls and metal parts.

Segmented molecular design of self-healing proteinaceous materials.

Hierarchical assembly of self-healing adhesive proteins creates strong and robust structural and interfacial materials, but understanding of the molecular design and structure-property relationships of structural proteins remains unclear. Elucidating this relationship would allow rational design of next generation genetically engineered self-healing structural proteins. Here we report a general self-healing and -assembly strategy based on a multiphase recombinant protein based material. Segmented structure of the protein shows soft glycine- and tyrosine-rich segments with self-healing capability and hard beta-sheet segments. The soft segments are strongly plasticized by water, lowering the self-healing temperature close to body temperature. The hard segments self-assemble into nanoconfined domains to reinforce the material. The healing strength scales sublinearly with contact time, which associates with diffusion and wetting of autohesion. The finding suggests that recombinant structural proteins from heterologous expression have potential as strong and repairable engineering materials.

The effect of pulsed electromagnetic fields and dehydroepiandrosterone on viability and osteo-induction of human mesenchymal stem cells.

The hypothesis of this work was that human bone marrow-derived mesenchymal stem cells (MSCs) are regulated by pulsed electromagnetic fields (PEMFs) and by intracrine conversion of an adrenal prohormone to dihydrotestosterone. The effect of PEMF and dehydroepiandrosterone (DHEA) on viability and osteogenic differentiation of human MSCs and on the viability of osteoblastic SaOS-2 cells was evaluated. It was found that PEMF promoted the viability rate of both cell types, whereas DHEA decreased the viability rate in a concentration-dependent manner. PEMF did not have major effects on osteo-induction at this low seeding density level (3000 cells/cm(2) ). Instead, DHEA, after MSC-mediated and 5α-reductase-dependent conversion to dihydrotestosterone, clearly promoted the osteo-induction of MSCs induced with ß-glyserophosphate, ascorbate and dexamethasone. Alkaline phosphatase (ALP), SMAD1, RUNX2, osteopontin (OP) and osteocalcin (OC) RNA levels were increased and alizarin red S- and hydroxyapatite-specific OsteoImage(TM) stainings disclosed a promoted mineralization process. In addition, DHEA increased OP and OC mRNA levels of non-induced MSCs. A sequential use of mitogenic PEMF early during the fracture healing, followed by later administration of DHEA with osteogenic differentiating effect, might be worth subjecting to a randomized clinical trial.