Shape Manipulation Research Articles

SAXS measurements of azobenzene lipid vesicles reveal buffer-dependent photoswitching and quantitative Z→E isomerisation by X-rays

Abstract Photoresponsive materials feature properties that can be adjusted by light near-instantaneously, reversibly, and with high spatiotemporal precision. There is considerable interest in maximising the degree of photoswitching, and in measuring this degree during illumination in complex environments. We study the switching of photoresponsive lipid membranes that allow for precise and reversible manipulation of membrane shape, permeability, and fluidity. Though these macroscopic responses are clear, it is unclear how large the changes of trans/cis ratio are, and whether they can be improved. Here, we used small-angle X-ray scattering to measure the thickness of photoswitchable lipid membranes, and we correlate lipid bilayer thickness to trans/cis ratios. This reveals an unexpected dependency of photoswitching ratio upon aqueous phase composition. In buffer with ionic strength, we observe thickness variations twice as large as previously observed. Furthermore, soft X-rays can quantitatively isomerise photolipid membranes to the all-trans state; enabling X-ray-based membrane control. High energy X-rays do not influence the state of the photoswitches, presumably because they deposit less dose in the sample.

Keypoint-Based Planar Bimanual Shaping of Deformable Linear Objects Under Environmental Constraints With Hierarchical Action Framework

This letter addresses the problem of contact-based manipulation of deformable linear objects (DLOs) towards desired shapes with a dual-arm robotic system. To alleviate the burden of high-dimensional continuous state-action spaces, we model DLOs as kinematic multibody systems via our proposed keypoint encoding network. This novel encoding is trained on a synthetic labeled image dataset without requiring any manual annotations and can be directly transferred to real manipulation scenarios.Our goal-conditioned policy efficiently rearranges the configuration of the DLO based on the keypoints. The proposed hierarchical action framework tackles the manipulation problem in a coarse-to-fine manner (with high-level task planning and low-level motion control) by leveraging two action primitives. The identification of deformation properties is bypassed since the algorithm replans its motion after each bimanual execution. The conducted experimental results reveal that our method achieves high performance in state representation and shaping manipulation of the DLO under environmental constraints.

Multifunctional Optical Vortex Beam Generator via Cross-Phase Based on Metasurface

We propose a multifunctional optical vortex beam (OVB) generator via cross-phase based on a metasurface. Accordingly, we separately investigate the two different propagation characteristics of OVB modulated by the low-order cross-phase (LOCP) and the high-order cross-phase (HOCP) in a self-selected area. When LOCP modulation is added to OVB, topological charges can be measured for any order of OVB. Moreover, we achieve the rotation tunable performance successfully by adding the rotation component. Then, we realize the function of polygonal beam generation and singularities regulation with the HOCP. The order of the HOCP is exactly equal to the number of a polygon OVB’s sides. The waist radius and usable width of the beam lengthens as the distance of the self-selected area increases. When the conversion rate is doubled, the distance between singularities widens by about 0.5 μm. The proposed OVB generator provides a simple strategy for detecting the value of topological charges and achieving OVB shaping and singularity manipulation simultaneously. We hope this can open new horizons for promoting the development of photon manipulation, optical communication, and vortex beam modulation.

HyBoDT: Hybrid Bounded Distance Transforms of Trimmed NURBS Models

Abstract Distance field representation of objects in 3D space has several applications such as shape manipulation, graphics rendering, path planning, etc. Distance transforms (DTs) are discrete representations of distance fields in a regular voxel grid. The two main limitations of using distance transforms are that they are compute-intensive, and there are errors introduced while representing the object using DTs. In this work, we develop a hybrid graphics processing unit (GPU)-accelerated marching wavefront method for computing DTs of models composed of trimmed non-uniform rational B-splines (NURBS) surfaces with theoretical bounds. Our hybrid marching approach eliminates the error due to calculating approximate distances by marching. We also calculate the bounds on the error introduced due to the tessellation of the trimmed NURBS surfaces and calculate the propagation of these bounds in computing the DT. Finally, we present computation times for both 2D and 3D GPU DTs of test objects. We show that our GPU-accelerated approach is significantly faster than existing CPU-based methods.

Reactive Jetting of High Viscosity Nanocomposites for Dielectric Elastomer Actuation

AbstractThe layer‐by‐layer nature of additive manufacturing is well matched to the layer construction of stacked dielectric actuators, with inkjet printing offering a unique opportunity due to its droplet‐on‐demand capability, suitable for multi‐material processing at high resolution. This paper demonstrates the use of high viscosity, multi‐material jetting to deposit two‐part reactive inks with functionalized nanofillers to digitally manufacture dielectric elastomers for soft robots with high precision, and shape manipulation. Graphene‐based fillers, including graphene oxide (GO) and thermally reduced graphene oxides (TRGOs), have been incorporated into a polydimethylsiloxane (PDMS) matrix at low loading (below the percolation threshold). Consequently, the dielectric constant of the elastomer dramatically increases (by 97%) compared to neat PDMS, yielding a more than 20‐fold increase in the electric‐field induced electromechanical contraction (from 0.3 to 6.7%). This study shows that the oxygen‐functionalities present in GO and TRGOs, which possess a moderate conductivity, improve the dispersion of those fillers in polymer matrices, thus significantly improving the dielectric constant of the polymer composites. Inkjet printing of high‐performance, soft electroactive composites enables high‐speed, reliable fabrication of monolithic artificial muscles (leading to stronger, cheaper, and more capable soft robotic devices) and provides a vital stepping stone towards fully additively manufactured soft robots.

Mesoporous, anisotropic nanostructures from bioinspired polymeric catecholamine neurotransmitters and their potential application as photoacoustic imaging agents.

Mesoporous polydopamine (PDA) nanobowls, which can be prepared using Pluronic® F-127, ammonia, and 1,3,5-trimethylbenzene (TMB), are one of the most studied anisotropic nanoparticle systems. However, only limited reports on polymerised analogues polynorepinephrine (PNE) and polyepinephrine (PEP) exist. Herein, we present modifications to a one-pot, soft template method, originally applied to make PDA nanobowls, to fabricate new shape-anisotropic nanoparticles (mesoporous nanospheres or "nano-golf balls" and nanobowls) using PNE and PEP for the first time. These modifications include the use of different oil phases (TMB, toluene and o-xylene) and ammonia concentrations to induce anisotropic growth of PDA, PNE, and PEP particles. Moreover, this work features the application of oddly shaped PDA, PNE, and PEP nanoparticles as intravascular photoacoustic imaging enhancers in Intralipid®-India ink-based tissue-mimicking phantoms. Photoacoustic imaging experiments showed that mesoporous nanobowls exhibit stronger enhancement, in comparison to their mesoporous nano-golf ball and nanoaggregate counterparts. The photoacoustic enhancement also followed the general trend PDA > PNE > PEP due to the differences in the rates of polymerisation of the monomers and the optical absorption of the resulting polymers. Lastly, about two- to four-fold enhancement in photoacoustic signals was observed for the mesoporous nanostructures, when compared to smooth nanospheres and their nano-aggregates. These results suggest that shape manipulation can aid in overcoming the inherently lower performance of PNE and PEP as photoacoustic imaging agents, compared to PDA. Since nanomaterials with mesoporous and anisotropic morphologies have significant, unexplored potential with emerging applications, these results set the groundwork for future studies on photoacoustically active oddly shaped PNE- and PEP-based nanosystems.

Two-dimensional coherent VCSEL arrays with configurable beam emissions

An accurate far-field intensity distribution model of coherent VCSEL array is established based on Fraunhofer diffraction theory, of which the calculated far-field pattern can be configured by tuning the phase distribution of the array. In experiment, configurable beam emissions are achieved in two-dimensional coherent square 2 × 2 VCSEL arrays and triangular 3-element VCSEL arrays by engineering the phase distribution of the array through simply constructing the array structure. Single-lobe beam, double-lobe beam, and four-lobe beam are obtained in these arrays. Besides, beam shape manipulation is also realized by adjusting the ratio of horizontal dimension to vertical dimension of the array. The experimental results are in good agreement with the calculated results from the established theoretical model.

Magnetic skyrmion shape manipulation by perpendicular magnetic anisotropy excitation within geometrically confined nanostructures

Magnetic skyrmions are promising features of spintronic devices including race-track memory and nano-oscillators. Skyrmion shape can act as an additional degree of freedom along with other properties including topological charge, polarity and helicity etc. Skyrmion excitation associated with shape deformation is significant for microwave devices. By means of micromagnetic simulation study, we report skyrmion excitation within nanodiscs by dynamically modulated perpendicular magnetic anisotropy (PMA). At higher resonance frequencies, skyrmion shows shape deformation into regular polygons including elliptic, trigon, tetragon, up to decagon, characterized as n = 2, 3, 4 …, 10, respectively. We build a phase diagram showing that regular polygon shape deformation occurs within a PMA amplitude window with minimum and maximum limits depending on resonance frequency and disc radius. Further analysis reveals that with increase in disc radius, modes with higher n appear, however, skyrmion is distorted into irregular shape, with no specific polygon-like pattern, even for smaller PMA. With a semi-quantitative analysis, we relate n for different modes to resonance frequency, disc size and PMA magnitude. These findings can assist in getting fundamental physics underlying skyrmion deformation and can help in designing energy-efficient microwave generator/detector and nano-oscillator where skyrmion dynamics are very important.

Humans Use a Temporally Local Code for Vibrotactile Perception.

Sensory environments are commonly characterized by specific physical features, which sensory systems might exploit using dedicated processing mechanisms. In the tactile sense, one such characteristic feature is frictional movement, which gives rise to short-lasting (<10 ms), information-carrying integument vibrations. Rather than generic integrative encoding (i.e., averaging or spectral analysis capturing the “intensity” and “best frequency”), the tactile system might benefit from, what we call a “temporally local” coding scheme that instantaneously detects and analyzes shapes of these short-lasting features. Here, by employing analytic psychophysical measurements, we tested whether the prerequisite of temporally local coding exists in the human tactile system. We employed pulsatile skin indentations at the fingertip that allowed us to trade manipulation of local pulse shape against changes in global intensity and frequency, achieved by adding pulses of the same shape. We found that manipulation of local pulse shape has strong effects on psychophysical performance, arguing for the notion that humans implement a temporally local coding scheme for perceptual decisions. As we found distinct differences in performance using different kinematic layouts of pulses, we inquired whether temporally local coding is tuned to a unique kinematic variable. This was not the case, since we observed different preferred kinematic variables in different ranges of pulse shapes. Using an established encoding model for primary afferences and indentation stimuli, we were able to demonstrate that the found kinematic preferences in human performance, may well be explained by the response characteristics of Pacinian corpuscles (PCs), a class of human tactile primary afferents.

Exercising With a Six Pack in Virtual Reality: Examining the Proteus Effect of Avatar Body Shape and Sex on Self-Efficacy for Core-Muscle Exercise, Self-Concept of Body Shape, and Actual Physical Activity.

This study investigates the Proteus effect from the first-person perspective and during avatar embodiment in actual exercise. In addition to the immediate measurements of the Proteus effect, prolonged effects such as next-day perception and exercise-related outcomes are also explored. We theorized the Proteus effect as altered perceived self-concept and explored the association between virtual reality (VR) avatar manipulation and self-concept in the exercise context. While existing studies have mainly investigated the Proteus effect in a non-VR environment or after VR embodiment, we aim to contribute to the literature by addressing this concern to explore how the Proteus effect works in actual VR exercise. Through a 2 (avatar body shape: with a six pack vs. normal) × 2 (sex: male vs. female) between-subject experiment, the results partially support the Proteus effect. Regarding actual physical activity, embodying an avatar with a six pack during exercise creates fewer body movements. No significant effect was found for perceived exertion. We also explored the role of sex as a potential moderator in the association of the Proteus effect on exercise outcomes. The Proteus effect was supported by immediate and next-day self-efficacy for core-muscle exercise only among female participants. The between-subject design allowed us to probe how avatar manipulation of muscular body shape with a six pack as opposed to normal body shape influences participants’ self-concept and exercise outcomes, as limited VR studies have employed within-subject comparisons. This also contributes to the literature by providing an upward comparison (e.g., muscular with a six pack vs. normal) as opposed to the previous downward comparison regarding body fitness (e.g., normal vs. obese). The overall results supported the Proteus effect in the context of core-muscle exercise when comparing normal and ideal body shape avatars. However, the Proteus effect as an altered self-concept and its effects on self-efficacy for exercise were supported among females but not males. Whereas the female participants who embodied avatars with a six pack associated themselves more with the muscular concept than other people, the male participants who embodied avatars with a six pack perceived themselves as more normal than others. Theoretical and practical implications are discussed.

SP-GAN

We present SP-GAN, a new unsupervised sphere-guided generative model for direct synthesis of 3D shapes in the form of point clouds. Compared with existing models, SP-GAN is able to synthesize diverse and high-quality shapes with fine details and promote controllability for part-aware shape generation and manipulation, yet trainable without any parts annotations. In SP-GAN, we incorporate a global prior (uniform points on a sphere) to spatially guide the generative process and attach a local prior (a random latent code) to each sphere point to provide local details. The key insight in our design is to disentangle the complex 3D shape generation task into a global shape modeling and a local structure adjustment, to ease the learning process and enhance the shape generation quality. Also, our model forms an implicit dense correspondence between the sphere points and points in every generated shape, enabling various forms of structure-aware shape manipulations such as part editing, part-wise shape interpolation, and multi-shape part composition, etc., beyond the existing generative models. Experimental results, which include both visual and quantitative evaluations, demonstrate that our model is able to synthesize diverse point clouds with fine details and less noise, as compared with the state-of-the-art models.

StyleCariGAN

We present a caricature generation framework based on shape and style manipulation using StyleGAN. Our framework, dubbed StyleCariGAN , automatically creates a realistic and detailed caricature from an input photo with optional controls on shape exaggeration degree and color stylization type. The key component of our method is shape exaggeration blocks that are used for modulating coarse layer feature maps of StyleGAN to produce desirable caricature shape exaggerations. We first build a layer-mixed StyleGAN for photo-to-caricature style conversion by swapping fine layers of the StyleGAN for photos to the corresponding layers of the StyleGAN trained to generate caricatures. Given an input photo, the layer-mixed model produces detailed color stylization for a caricature but without shape exaggerations. We then append shape exaggeration blocks to the coarse layers of the layer-mixed model and train the blocks to create shape exaggerations while preserving the characteristic appearances of the input. Experimental results show that our StyleCariGAN generates realistic and detailed caricatures compared to the current state-of-the-art methods. We demonstrate StyleCariGAN also supports other StyleGAN-based image manipulations, such as facial expression control.

3D Printing Magnetic Actuators for Biomimetic Applications.

Biomimetic actuators with stimuli-responsiveness, adaptivity, and designability have attracted extensive attention. Recently, soft intelligent actuators based on stimuli-responsive materials have been gradually developed, but it is still challenging to achieve various shape manipulations of actuators through a simple 3D printing technology. In this paper, a 3D printing strategy based on magneto-active materials is developed to manufacture various biomimetic magnetic actuators, in which the new printable magnetic filament is composed of a thermoplastic rubber material and magnetic particles. The continuous shape transformation of magnetic actuators is further demonstrated to imitate the motion characteristic of creatures, including the predation behavior of octopus tentacles, the flying behavior of the butterfly, and the flower blooming behavior of the plant. Furthermore, the magnetic field-induced deformation of the biomimetic structure can be simulated by the finite element method, which can further guide the structural design of the actuators. This work proves that the biomimetic actuator based on soft magneto-active materials has the advantages of programmable integrated structure, rapid prototyping, remote noncontact actuation, and rapid magnetic response. As a result, this 3D printing method possesses broad application prospects in soft robotics and other fields.

Regulating Asynchronous Deformations of Biopolyester Elastomers via Photoprogramming and Strain-Induced Crystallization

For shape-memory polymers (SMPs), introducing material heterogeneity is vital to tailor shape-shifting pathways. However, it is hard to reprogram the heterogeneity for both covalent networks and dynamic covalent networks after these networks are encoded. Here, photoactive coumarin derivative end-capped dangling chains were used to participate in building photoreversible polycaprolactone/poly(malic acid) networks, endowing the networks with reprogrammable heterogeneity and a capability of room-temperature storage of entropic energy. The alternations of network topology with 365/254 nm UV irradiation and strain-induced crystallization behavior of as-prepared bio-based elastomers were studied, aiming at quantitatively guiding the spatiotemporal release of entropic energy to regulate asynchronous deformations. This work provides applicable methods for simplifying shaping manipulation or for diversifying shape-shifting pathways of SMPs.

Differential effects of minified and magnified mirror visual feedback on the underlying misperception of hand size

Perception of the size of body parts, for instance the hand, has been shown to be distorted in healthy participants, with over- and underestimations of width and length, respectively. Illusory manipulations of body shape and size have highlighted the flexibility of the body representation and have also been found to update immediate perceptions of body size and surrounding objects. Here, we examined whether underlying misperceptions of hand width and length can be modified through exposure to illusory changes in hand size using a mirror visual feedback (MVF) paradigm. While questionnaire responses indicated subjective susceptibility to both magnified and minified manipulations, objective hand size estimates only showed significant differences following exposure to minifying mirrors. These variations might reflect differences in the way that stored representations are accessed or updated in response to size manipulations. Secondly, the findings further reinforce differences between subjective and objective outcomes of illusions on subsequent body perception.

Magnetism-Responsive Anisotropic Film with Self-Sensing and Multifunctional Shape Manipulation.

At small scales, shape-programmable magnetic materials and self-sensing conductive materials have an enticing potential for realizing the functionalities that are unattainable by traditional machines. This work reports a facile preparation method of aself-sensing magnetism-responsive anisotropic films (SMAF) in which magnetic materials and conductive materials can be predesigned, oriented, and patterned without requiring an external magnetic field generator or other expensive devices. A variety of shaped magnetoactive films with complex chain-orientation structures that can achieve advanced actuation functions have been developed, such as magnetically driven flowers, windmills, and leaves. It is also verified that the as-prepared samples coated with the sensing layer can distinguish different actuation modes, such as inward bending, outward bending, twisting, and combined deformation, which would be conducive to further exploration and development of directionally responsive applications in the smart actuating system and soft robotics.

Influence Function Measurement Technique Using the Direct and Indirect Piezoelectric Effect for Surface Shape Control in Adaptive Systems

Since the introduction of adaptive systems for corrective measures, static and dynamic disturbances have been reduced through the manipulation of surface shape in a well-controlled manner. One important application where adaptive systems are highly needed is in the future photo-lithography machines, particularly the wafer table where disturbances affect overlay and focus performance. To reduce overlay and focus errors, a dense array of actuators must be integrated into the wafer table to apply both in- and out-of-plane corrective deformations to the wafer surface. To realize a certain wafer shape, influence functions are linearly superimposed. Accurate models of the influence functions result in an accurate prediction of the final wafer shape. To reduce calibration errors, the influence function of every actuator needs to be determined. Here, we propose a technique to rapidly measure the influence function: the influence function measurement (IFM) technique. Using the actuate-sense property of piezoelectric materials, the influence function is determined by activating one piezo-actuator and measuring the charge induced on the neighboring piezo-actuators. The measured charges are compared to the results of finite element simulations and the absolute difference of 0.3 &#x0025; is reported for the inter-actuator charge coupling parameters. This clearly indicates the potential of the proposed technique. <i>Note to Practitioners</i>&#x2014;A critical step during the integrated-circuit lithographic fabrication process is the exposure. A particular practical challenge in this step is to correct for the mismatch between the optical image plane and the wafer surface, caused by wafer deformations. The mismatch negatively impacts the overlay and focus performance. To reduce the mismatch, actuators can be embedded into the wafer table to counteract wafer deformations, where the overall wafer surface shape is a superposition of each actuator&#x2019;s influence function. As part of the calibration for the embedded actuators, their influence functions are measured and stored. However, errors arise when influence functions are not measured for every actuator. Additionally, for different wafers, the influence functions vary hence the calibration should be done per wafer. This calibration process takes time and should not influence throughput. Our paper presents a viable approach that reduces the calibration time of active wafer tables, which is also relevant for other adaptive systems such as deformable mirrors. Since the technique requires the actuators to be mechanically coupled, it is limited to continuous surfaces. The proposed technique is numerically tested and experimentally verified to demonstrate performance.

Using reactive dissipative particle dynamics to understand local shape manipulation of polymer vesicles.

Biological cells have long been of interest to researchers due to their capacity to actively control their shape. Accordingly, there is significant interest in generating simplified synthetic protocells that can alter their shape based on an externally or internally generated stimulus. To date, most progress has been made towards controlling the global shape of a protocell, whereas less is known about generating a local shape change. Here, we seek to better understand the possible mechanisms for producing local morphological changes in a popular protocell system, the block copolymer vesicle. Accordingly, we have combined Dissipative Particle Dynamics (DPD) and the Split Reactive Brownian Dynamics algorithm (SRBD) to produce a simulation tool that is capable of modeling the dynamics of self-assembled polymer structures as they undergo chemical reactions. Using this Reactive DPD or RDPD method, we investigate local morphological change driven by either the microinjection of a stimulus or an enzymatically-produced stimulus. We find that sub-vesicle-scale morphological change can be induced by either a solvent stimulus that swells the vesicle membrane, or by a reactant stimulus that alters the chemistry of the block polymer in the membrane corona. Notably, the latter method results in a more persistent local deformation than the former, which we attribute to the slower diffusion of polymer chains relative to the solvent. We quantify this deformation and show that it can be modulated by altering the interaction parameter of the parts of the polymer chain that are affected by the stimulus.

Programmable Transformation and Controllable Locomotion of Magnetoactive Soft Materials with 3D-Patterned Magnetization.

Magnetoactive soft material (MASM) is distinguished for multifunctional shape manipulations under magnetic actuation, thereby holding a great promise in soft robotics, actuators, electronics, and metamaterials. However, the current research of MASM with continuum hard-magnetic profiles focuses little on the transformation mechanism, high dimensional shape transformation, and multistable locomotion. Herein, we developed a systematic methodology for programmable transformation and controllable locomotion of MASM with 3D-patterned continuum magnetization. An iterative computational model based on the equilibrium between magnetic torque and deformation-induced elastic torque was developed for precise prediction of MASM transformation. Multidimensional and complex shape manipulation ability of MASM was demonstrated by magnetically actuated transformations, including 1D to 2D, 2D to 3D, and 3D to 4D transformations of solid MASM, 2D to 3D pattern transformation of MASM-based elastin-like mesh, and 3D to 4D transformation of MASM-based cuboidal lattice. Multistable and controllable locomotion of MASM was verified by multimodal locomotion behaviors of a scallop-inspired robot for wall climbing in a dry frame and drug delivery in wet stomach, including roll, open, and close under self-locked and unlocked states.

In vivo manipulation of muscle shape and tendinous stiffness affects the human ability to generate torque rapidly.

What is the central question of this study? What are the determinants of muscle belly gearing, and how does it affect the torque rise? What is the main finding and its importance? Change in muscle thickness of the gastrocnemius medialis is related to variations in belly gearing. Belly gearing has a key role in the rise of muscle torque and rate of torque development (RTD). Besides, the increase of tendinous tissue stiffness could increase the torque rise as well, and in turn, the RTD. However, changes in the tendinous tissue stiffness showed no effects on muscle fascicle behaviour, suggesting a possible uncoupling between muscle and tendon mechanical properties. During fixed-end contractions, muscles bulge in thickness and/or width to maintain a constant volume, whereas tendons lengthen over the entire contraction period. These dynamic changes play a key functional role in modulating the generated torque. However, the literature has revealed a limited understanding of in vivo dynamic muscle-tendon changes during rapid contractions. Therefore, this study aimed to investigate the determinants of belly gearing (belly velocity/fascicle velocity) and its effects on rapid torque production during in vivo fixed-end contractions. Twenty healthy males were recruited for the study. Muscle shape and tendon stiffness were manipulated by applying a transverse load (2-10kg) and an ankle rotation manoeuvre, respectively. Ultrafast-ultrasound was employed to quantify medial gastrocnemius architecture during evoked contraction and a dynamometer was used to measure the muscle torque and quantify the rate of torque development (RTD). Torque and RTD diminished by transverse load application, whereas they increased during the ankle rotation manoeuvre. Belly gearing declined with increasing transverse load but was unaffected by tendinous stiffness variations. Alterations in belly gearing were strongly related to variations in muscle thickness throughout any load applied and affected the torque rise rapidly. In contrast, changes in tendinous tissue stiffness affected the torque rise only but did not modify the muscle shape. These data may suggest that concurrent manipulation of the tendinous tissue stiffness and muscle shape does not affect the explosive rise in torque capacity, suggesting a possible uncoupling between mechanical properties of muscle and tendon.