The significance of controlled single-cell rotation extends well beyond a clever laboratory demonstration. When a cell can be turned at will, researchers can perform true three-dimensional imaging with conventional microscopes, capturing morphology and internal architecture from multiple viewing angles. Rotation also matters for mechanobiology, the study of how cells sense and respond to mechanical forces, because orientation relative to a substrate or a neighboring cell influences how forces are transmitted and interpreted. Controlled rotation can further support investigations of cell-cell interactions, intracellular dynamics, and developmental processes in which the spatial arrangement of cellular components is central to function.

Yet programmable rotation has long been an elusive goal. Optical tweezers, magnetic manipulation, electric fields, and acoustic techniques have each made substantial contributions to single-cell control, but most existing approaches depend on specially engineered beam structures, microfabricated mechanical components, or intrinsic asymmetries in the objects being manipulated. Spherical particles and many living cells present a particular difficulty: because they are geometrically symmetric, there is no natural feature that defines a rotation axis. Dynamically switching between different rotation modes within a single platform has remained largely unexplored, which has limited the flexibility of previous systems and confined many of them to narrow, pre-set operating regimes.

The new platform is built on a plasmonic substrate composed of gold nano-islands functionalized with bovine serum albumin, or BSA. When laser light illuminates these nanostructures, they generate localized temperature gradients that drive strong thermo-osmotic flows along the solid-liquid interface. Thermo-osmotic flow is a well-characterized phenomenon in which a temperature gradient at a boundary produces directed fluid motion, and plasmonic substrates are especially effective at creating steep, highly localized gradients because the nanostructures concentrate optical energy into nanoscale volumes. The BSA functionalization plays a complementary role in stabilizing cells at the interface, while polyethylene glycol molecules in the surrounding solution generate depletion forces that gently confine cells near the substrate surface, precisely where the thermo-osmotic flow is strongest.

Control over the flow field comes from a spatial light modulator, a device that can dynamically project programmable laser patterns onto the substrate. By reshaping these patterns in real time, the researchers tailor both the temperature distribution and the resulting flow field, and with them the forces and torques acting on individual cells. This is the conceptual heart of the platform: the rotation axis is not dictated by the geometry of the object but is instead written into the engineered flow field itself. The same cell, sitting in the same spot, can be made to spin in entirely different ways depending only on how the laser light is patterned.

The team first validated the concept using spherical polydimethylsiloxane particles, an ideal test case precisely because a sphere possesses complete geometric symmetry and its rotation axes cannot be defined by shape. Numerical simulations revealed that a single Gaussian laser spot positioned asymmetrically relative to a particle creates a highly non-uniform thermo-osmotic flow field around it. That asymmetry in the flow produces a hydrodynamic torque of sufficient magnitude to drive stable rotation. Crucially, by simply moving the position of the laser spot, the direction of the torque can be tuned continuously, allowing the particle to rotate about different axes. Experimental observations confirmed the theoretical predictions and demonstrated arbitrary-axis rotation of spherical particles, establishing that the axis of rotation is defined entirely by the engineered flow field rather than by particle geometry.

With the principle demonstrated on synthetic spheres, the researchers extended the approach to biological cells, using yeast as a model system. They showed that two distinct rotational modes can be selectively activated through optical pattern engineering. Under a single Gaussian laser spot, the induced thermo-osmotic torque drives the cell to rotate around its major axis, the long axis of the cell body. When the laser pattern is reconfigured into a half-ring shape, an optical torque joins the thermo-osmotic torque, and the combined action reorients the cell and drives continuous rotation around its minor axis. The two modes are therefore not separate operating regimes requiring different hardware; they are two settings of the same optical interface.

Perhaps the most striking capability of the platform is the speed and cleanliness of the switching between these modes. In the reported experiments, the team maintained stable major-axis rotation with a Gaussian beam, then changed the illumination pattern to a half-ring configuration. The cell transitioned into minor-axis rotation in less than one second. The entire process occurred without mechanical movement, sample repositioning, or physical contact, relying solely on optical reconfiguration. For live-cell imaging, this matters enormously: cells are fragile, and any approach that avoids contact, labeling, or chemical modification preserves the native state of the specimen while it is being manipulated.

To understand why the system works so well, the researchers combined multiphysics simulations with electromagnetic calculations. Their analysis showed that major-axis rotation is predominantly driven by thermo-osmotic torque, whereas minor-axis rotation arises from the synergistic coupling of thermo-osmotic and optical torques. Together, these torques create a continuous torque landscape that sustains rotation throughout the entire cycle without trapping the cell in stable equilibrium states. In other words, the optical patterns are designed so that at no point in the rotational cycle does the cell find a configuration where the torques vanish and motion stops; the driving torque persists around the full revolution, which is what enables continuous, stable spinning.

The practical advantages of the platform are considerable. It operates at relatively low optical power, which reduces the risk of photothermal damage to living specimens. It requires no labeling or modification of cells, making it a genuinely label-free technique. It offers exceptional programmability through dynamic optical pattern generation, and unlike many conventional rotational manipulation techniques, it does not depend on complex beam shaping or specialized particle geometries. The researchers believe the technique could become a powerful tool across a broad range of biological and biomedical applications. By integrating with confocal microscopy and other advanced imaging modalities, the platform may enable label-free three-dimensional cellular imaging and reconstruction. It could also facilitate studies of cell mechanics, cellular interactions, developmental biology, and drug screening, where observing a cell from multiple orientations under controlled conditions would add a valuable new dimension to existing assays.

Looking forward, the team envisions combining opto-thermo-osmotic manipulation with emerging metasurface and integrated photonic technologies. Metasurfaces, which are engineered planar optical structures capable of shaping light with subwavelength precision, could replace bulky spatial light modulators with compact, chip-scale pattern generators. Such integration could lead to miniature platforms capable of high-throughput cellular manipulation and analysis, opening new opportunities for next-generation bioanalytical systems in which individual cells are imaged, rotated, and characterized automatically. If that vision is realized, the ability to spin a single cell along any axis with nothing more than a reconfigured beam of light may become as routine a capability in the biology laboratory as focusing the objective lens is today.

Subject of Research: Programmable opto-thermo-osmotic rotation of single cells along arbitrary axes

Article Title: Programmable rotation of single cells along arbitrary axes via opto-thermo-osmotic torque

Article References: Programmable rotation of single cells along arbitrary axes via opto-thermo-osmotic torque. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: cell rotation, opto-thermo-osmotic torque, plasmonic substrate, gold nano-islands, thermo-osmotic flow, spatial light modulator, yeast cells, three-dimensional imaging, mechanobiology, optical manipulation, label-free imaging, Light Science & Applications

The work, published in Nature Photonics by Jiaan Gan, Yong Yang, Siwei Zhu, Shengjiang Chang and Xiaocong Yuan, with Gan and Yang contributing equally, introduces a cascaded light-field propagation mechanism for volumetrically continuous 3D dynamic holography. Rather than treating each depth plane of a 3D scene as an independent reconstruction target, the new design paradigm reuses the light that exits one plane as constructive input for the next. In doing so, the very light that conventional approaches treat as noise becomes a useful signal, allowing projections that are continuous both along the depth axis and across the lateral dimensions of the scene.

To appreciate why this matters, it helps to understand how most 3D holographic displays work today. A spatial light modulator, a device that can sculpt the phase of a laser beam pixel by pixel, is programmed with a computer-generated hologram. When illuminated, the modulated beam propagates through free space and reconstructs the target scene. Because a single hologram cannot easily encode an entire volume, most systems approximate a 3D object as a stack of discrete planes, separated by some axial distance. The trouble is that the light field designed to form an image on one plane does not simply vanish beyond it; it continues propagating and contaminates the neighboring planes. The closer the planes are spaced, the worse this crosstalk becomes.

State-of-the-art techniques have therefore faced an uncomfortable trade-off. Widely spaced planes yield clean reconstructions but produce a display that flickers or jumps between depths as a viewer moves, destroying the sense of a solid, continuous object. Tightly packed planes promise continuity but drown the image in crosstalk. Optimization methods, including non-convex numerical approaches and deep-learning-based hologram design, have pushed the balance point, but the fundamental tension between plane spacing and crosstalk has remained. The new work sidesteps this balance entirely by changing the underlying design logic: instead of asking each plane to form its image independently, the cascaded approach asks the light leaving one plane to serve as the imaging light for the next.

The conceptual shift is subtle but profound. In a conventional layer-wise design, the outgoing light from a plane that misses its target is scattered into random speckle, wasted energy that degrades neighboring reconstructions. In the cascaded paradigm, that outgoing light is deliberately shaped so that, as it propagates toward the next plane, it contributes constructively to the image forming there. The crosstalk is transformed from a parasitic effect into a resource. The result, demonstrated experimentally with a spatial light modulator, is free-space 3D light-field projection that is continuous along both the axial and lateral directions, something the authors describe as volumetrically continuous projection.

Designing such a system is computationally formidable. The optical field must be propagated through a cascade of planes, with each plane’s contribution entangled with every other, and the hologram must be optimized so that the entire chain produces the desired 3D light field. Brute-force optimization over such a high-dimensional space would be prohibitively expensive, particularly for dynamic holography, where new holograms must be generated rapidly as the displayed scene changes. The team’s answer is a computational framework they call Holo-Prior-Net, a physics-embedded, untrained holographic diffractive prior neural network.

The phrase untrained is key. Unlike conventional deep-learning approaches to holography, which require massive datasets of hologram-and-image pairs and lengthy pretraining on GPU clusters, Holo-Prior-Net embeds the physics of light propagation directly into its architecture. The network’s structure itself encodes a prior, an expectation of how diffractive optical fields behave, so that it can efficiently design 3D holograms without any pretraining at all. This architectural prior dramatically reduces the computational burden, making it feasible to design holograms for continuous volumetric scenes on demand. The approach draws on ideas from physics-informed neural networks and untrained network priors, fields that have recently shown that carefully constructed network architectures can solve inverse imaging problems without learning from data.

The experimental demonstrations are striking. Using a spatial light modulator, the team projected a continuous DNA double helix spanning an 80-millimeter axial range, with a lateral dimension of just 0.6 millimeters and a linewidth of approximately 50 micrometers. They also reconstructed a continuous hollow cylinder, 5 millimeters in diameter with a wall thickness of 100 micrometers, across a 40-millimeter axial range, and a hollow light sphere with a 1-millimeter lateral extent and a 40-millimeter axial range. Crucially, the continuity was not merely inferred from volume-rendered reconstructions on a screen. The researchers scanned a camera through the projected volume in fine steps, including depths that were never explicitly sampled during the design process, and confirmed that the light field remained sharp and continuous throughout.

Perhaps most compellingly, the 3D continuity is directly observable with the naked eye across a wide range of viewing angles, without postprocessing or screen rendering. In one demonstration, the team projected a dynamically rotating 3D double-helix light field into scattering smoke, loading twenty holograms corresponding to different spatial orientations of the structure in sequence onto the modulator. In another, a sequence of fourteen target light-field distributions was designed rapidly and displayed dynamically, with a camera capturing the results at less than half a second per frame. These experiments confirm that the method is not a numerical curiosity but a physically realized display technology capable of dynamic operation.

The implications reach well beyond the laboratory. True-to-life 3D video display is a highly sought-after goal for virtual and augmented reality, where current systems rely on stereoscopic tricks that can cause eye strain and fail to produce correct focus cues. A holographic display that projects a genuinely continuous volumetric light field would, in principle, present the eyes with exactly the wavefronts that a real object would, solving the accommodation-convergence conflict at its root. The untrained, physics-embedded design framework also points toward practical deployment, since it avoids the enormous datasets and training costs that have limited learned holography approaches. By reconstructing the underlying design logic of 3D holographic projection rather than incrementally improving image metrics, the researchers have opened an alternative route toward projecting volumetrically continuous 3D objects, one in which the oldest enemy of holography, crosstalk, has been turned into its most unexpected ally.

Subject of Research: Volumetrically continuous 3D dynamic holography using cascaded light-field propagation and an untrained neural network framework

Article Title: Volumetrically continuous 3D dynamic holography via cascaded light-field propagation

Article References: Gan, J., Yang, Y., Zhu, S., Chang, S., & Yuan, X. (2026). Volumetrically continuous 3D dynamic holography via cascaded light-field propagation. Nature Photonics. https://doi.org/10.1038/s41566-026-02016-9

Image Credits: AI Generated

DOI: 10.1038/s41566-026-02016-9

Keywords: holography, 3D display, light-field propagation, crosstalk, spatial light modulator, untrained neural network, physics-informed computing, computer-generated holograms, virtual reality, augmented reality, Nature Photonics, volumetric display

The central challenge in cardiac electrophysiology is that heart cells communicate through rapidly propagating electrical waves. In a healthy heart, a precisely timed wave of depolarization sweeps across the muscle, triggering coordinated contraction. In diseased tissue, these waves can fragment, circle back on themselves, or originate from ectopic sites, producing arrhythmias that range from benign to lethal. Conventional interventions, from antiarrhythmic drugs to implanted pacemakers and ablation catheters, act on slow timescales or with coarse spatial resolution. What has been missing is a tool that can both observe and modulate cardiac electrical activity at the scale of individual cells, on millisecond timescales, within a continuous feedback loop.

The new work addresses this gap by exploiting optogenetics, a technique in which light-sensitive proteins borrowed from microbes are expressed in target cells. When blue light strikes channelrhodopsin, a light-gated ion channel embedded in the cell membrane, the channel opens and positive ions flow inward, depolarizing the cell and triggering an action potential. By genetically engineering human induced pluripotent stem cell-derived cardiomyocytes to express such opsins, researchers gain a remote, genetically specified actuator: any region of the cellular network can be electrically stimulated simply by illuminating it, with no physical contact required.

Stimulation alone, however, is only half of the control problem. The other half is sensing. The system pairs optogenetic actuation with optical voltage imaging, using fluorescent indicators whose emission changes with membrane potential. High-speed cameras capture the fluorescence of the cardiomyocyte network frame by frame, allowing the researchers to reconstruct the electrical state of the tissue in real time: which cells are resting, which are firing, and how excitation waves are propagating across the culture. This optical readout replaces the electrode arrays traditionally used to map cardiac activity, eliminating the invasiveness, wiring complexity, and spatial limitations of contact-based sensing.

The truly novel element is the holographic light engine that ties sensing and actuation together. Rather than illuminating the culture with a uniform beam or scanning a single laser spot, the researchers use a spatial light modulator to shape light into arbitrary two-dimensional patterns, projected onto the cell layer through holographic principles. A computer-generated hologram determines, pixel by pixel, where light intensity is delivered. This means the system can stimulate a single cell, a stripe of tissue, a curved wavefront mimicking the sinus node, or multiple disconnected regions simultaneously, all with subcellular spatial resolution and microsecond-scale temporal precision. The hologram can be updated faster than the dynamics of a cardiac action potential, which is essential for genuine real-time control.

Closing the loop requires software that can translate what the cameras see into what the light projector should do next. The control algorithm continuously monitors the optical voltage signals, compares the observed electrical behavior against a desired target state, and computes the illumination pattern needed to drive the network toward that state. If an excitation wave propagates too slowly, the system can deliver light pulses ahead of the wavefront to accelerate it. If an unwanted wave appears in the wrong location, the system can suppress it or redirect it. If the goal is a specific pacing frequency, the controller adjusts the timing and geometry of optical stimuli on every beat, compensating for the natural variability of biological tissue. This is the defining feature of closed-loop control: the intervention is not preprogrammed but continuously recalculated from live measurements.

The researchers demonstrated that this architecture can reliably entrain human cardiomyocyte networks to desired pacing patterns, guiding the rhythm of electrically active tissue that would otherwise beat at its own intrinsic rate. Beyond simple pacing, the holographic system’s spatial freedom enables more sophisticated interventions, such as shaping the direction and curvature of propagating waves or confining activity to defined regions of the network. Such capabilities are directly relevant to the study of arrhythmia mechanisms, where reentrant waves, spiral waves, and conduction blocks are the underlying culprits. A tool that can create, steer, and terminate such waves on demand in human-derived tissue provides an unprecedented experimental platform for arrhythmia research.

The significance for drug development and precision medicine is considerable. Human induced pluripotent stem cell-derived cardiomyocytes already allow pharmaceutical researchers to test compounds on human heart cells rather than animal tissue, but standard assays capture only bulk behavior, such as average beat rate or field potential duration. A closed-loop optical system adds an active dimension: it can probe how a tissue responds to perturbation, measure its vulnerability to arrhythmia induction, and quantify the effects of drugs on conduction velocity, refractory periods, and wave dynamics under precisely controlled stimulation conditions. In principle, patient-specific cell lines could be engineered with opsins and screened not just for passive responses but for behavior under stress, revealing proarrhythmic risks that conventional tests miss.

Looking further ahead, the all-optical nature of the approach suggests possibilities beyond the laboratory dish. Because neither sensing nor actuation requires physical contact, the conceptual framework is compatible with future cardiac therapies in which light delivered through optical fibers or implanted micro-LEDs could pace or resynchronize heart tissue in a feedback-controlled manner, guided by optical or electrical sensors. Such light-based pacemakers could adapt their stimulation pattern beat by beat, something conventional devices, which deliver fixed electrical pulses on fixed schedules, cannot do. Significant hurdles remain before any clinical translation, including delivering opsins safely to adult human myocardium, achieving sufficient light penetration in thick tissue, and ensuring long-term stability of both the genetic and optical components. The current study is confined to engineered cell networks in vitro, and the authors’ achievement should be understood as a foundational demonstration of control methodology rather than a therapy.

Even within that scope, the work marks a conceptual milestone. It shows that a living, electrically excitable human tissue can be observed, modeled, and steered in real time by a machine that touches nothing, intervening only through shaped light. The convergence of optogenetics, holographic projection, fast fluorescence imaging, and feedback control points toward a broader paradigm in synthetic biology and bioelectronic medicine: organs and organoids treated not as passive specimens but as dynamic systems that can be regulated the way engineers regulate any other process. For cardiac science, where rhythm is everything, the ability to write rhythm into human heart tissue with light, and to correct it when it goes wrong, may reshape how arrhythmias are studied, how drugs are validated, and, eventually, how failing electrical systems in the heart are repaired.

Subject of Research: All-optical closed-loop control of human cardiomyocyte networks using holographic optogenetics

Article Title: All-optical closed-loop control of human cardiomyocyte networks exploiting holographic optogenetics

Article References: Wendland, R., Schmieder, F., Sikandar, M. A., Knüppel, F. P., Zimmermann, W.-H., Bergmann, O., Büttner, L., & Czarske, J. W. (2026). All-optical closed-loop control of human cardiomyocyte networks exploiting holographic optogenetics. Communications Engineering, 5(1), Article 159. https://doi.org/10.1038/s44172-026-00779-1

Image Credits: AI Generated

DOI: 10.1038/s44172-026-00779-1

Keywords: holographic optogenetics, cardiomyocytes, closed-loop control, cardiac electrophysiology, optical voltage imaging, arrhythmia, induced pluripotent stem cells, channelrhodopsin, spatial light modulator, cardiac tissue engineering, bioelectronic medicine, optogenetic pacing