Cheng Sun

Accurate constitutive characterization of miniaturized tensile specimens is challenging because grip‐to‐grip displacement measurement includes deformation from both the gauge and shoulder sections, leading to systematic errors in the measured stress–strain response. Existing compliance‐correction methods are limited to linear elastic characterization and require multiple specimen geometries, whereas inverse finite element methods (iFEM) reconstruct nonlinear constitutive behavior at substantial computational cost. Here, an explicit constitutive reconstruction framework that accurately recovers the intrinsic nonlinear stress–strain response from a single tensile test using only grip‐to‐grip displacement measurements was presented. The proposed method sequentially reconstructs the constitutive response through incremental tangent modulus updating, transforming constitutive reconstruction from an inverse optimization problem into an explicit sequential solution. A progressive three‐stage validation was conducted comprising self‐consistency across different gauge lengths, analytical comparison with the regression‐based compliance correction method, and numerical benchmarking against the published iFEM. The proposed method reduced the intergroup constitutive variation from 18.8% to 2.1%, reconstructed Young's modulus within 4.4% error against the regression method, and achieved a maximum error below 4.8% relative to iFEM while reducing computation time from approximately 40 min to 0.75 s per specimen. The proposed framework provides an accurate and computationally efficient approach for constitutive characterization of miniaturized specimens.

Visual neuroscience requires precise spatiotemporal projection of optical stimulation onto the retina, especially in experimental mouse models. However, in vivo patterned stimulation in mice is profoundly hindered by the extreme optical power and severe anatomical aberrations of the eye. Consequently, visual stimulation relies mainly on unverifiable, open-loop approximations that often lack spatial precision. Here, we introduce a closed-loop, spatially modulated stimulation platform that overcomes these barriers. By integrating a digital micromirror device (DMD) with electronically tunable lenses (ETLs) and a real-time, fundus camera-guided focus optimization module, we directly verify the location of patterned stimuli on the retina while dynamically correcting for chromatic and geometric defocus. This platform delivers quantitatively verified static and dynamic patterned stimuli to the living retina with lateral resolutions as fine as 6.7 µm. Guided by ray-tracing optical analysis, our work establishes a technological foundation that enables highly reproducible, cellular-scale interrogations of the visual pathway.

Spectroscopic single-molecule localization microscopy (sSMLM) enables multiplexed super-resolution imaging by simultaneously acquiring the spatial position and spectral information of individual fluorophores. Dual-wedge prism (DWP)–based implementations provide a compact, alignment-stable approach to spectral dispersion, but trade-offs between localization precision, spectral precision, and experimental complexity remain. We systematically compare five DWP-based sSMLM configurations, including two-dimensional (2D) and three-dimensional (3D) implementations using single DWP (DWP-sSMLM) and symmetrically-dispersed DWP (SDDWP-sSMLM). We evaluate lateral precision, spectral precision, and ease of use. SDDWP configurations acquire spectral images in both channels and utilize both for spatial localization, yielding the highest lateral and spectral precision. However, for applications that do not require axial information, 2D-DWP provides a simple, plug-and-play solution with robust performance. This work offers a guideline for selecting DWP configurations based on experimental needs.

Achromatic structured focusing in flat optics is important for compact depth-resolved imaging and three-dimensional localization, yet simultaneously achieving broadband operation and a depth-encoding focal field remains challenging. Here, we demonstrate an achromatic double-helix metalens operating across the visible range of 600-650 nm. The target phase profile combines an exact hyperbolic lens phase with a double-helix phase synthesized from Laguerre-Gaussian mode bases, whose coefficients are optimized by particle swarm optimization. Broadband implementation is achieved through a meta-atom library designed by jointly considering phase delay, group delay, and group delay dispersion. The fabricated device exhibits strong structural fidelity and experimentally reproduces the rotating two-lobe focal field at 625 nm as well as across the target wavelength range. This work extends achromatic metalenses beyond conventional focusing to broadband structured focusing and provides a compact platform for depth-resolved imaging.

Understanding how neuronal activity couples with local energy metabolism is fundamental to brain function. Oxygen exchange between individual neurons and red blood cells (RBCs) is central to this process, yet no existing method can simultaneously capture their dynamics at single-cell resolution in vivo. Here, we introduce integrated two-photon and photoacoustic microscopy (TPM-PAM), which enables real-time imaging of single-neuron calcium activity alongside oxygen release from individual RBCs in awake mice. In TPM-PAM, a transparent micro-ring resonator-based ultrasound sensor breaks the long-standing tradeoff between optical access and acoustic sensitivity, while dual-wavelength kymography simultaneously quantifies single-RBC oxygenation and flow to derive the oxygen release rate. Incorporating nonlinear optical manipulation of the neurovascular unit with cellular precision, TPM-PAM reveals distinct neurometabolic responses to whisker stimulation, single-capillary occlusion, and single-neuron stimulation. This work establishes a powerful platform for dissecting neurometabolic coupling at the cellular scale and understanding oxygen-metabolic regulation in brain health and disease.

Autonomous robotic-assisted surgery (RAS) has emerged as a promising objective in biomedical technology, further enhanced by miniaturization toward microrobotic-assisted surgery (μ-RAS). This reduction in scale promises minimally invasive, partially or fully automated surgical procedures, with the potential to reduce patient recovery times, lower medical costs, and enable previously unavailable procedural options. This perspective highlights the specific advances in RAS that potentially map to the microscale (μ-RAS), organized across five surgical domains: endovascular, endoluminal, laparoscopic, ophthalmic, and orthopedic. We examine both clinical demands and technological advances in surgical robotics and identify the key innovations required for progress across these surgical fields. Our contribution is distinct in combining the perspectives of both surgical experts and bioengineering innovators, outlining a roadmap for the advancement and eventual integration of autonomous RAS and μ-RAS into mainstream surgical practice.

Traumatic cranial defects often involve concurrent loss of soft and hard tissues and can progress to chronic defects due to delayed healing associated with infection or other co-morbidities. Despite autologous reconstruction remaining the clinical standard, it requires staged procedures using heterogeneous tissues, increasing operative time, costs, and surgical risks. Moreover, current tissue engineering approaches focus on single tissues or acute tissue defect models, limiting their clinical applications. Herein, we describe an acellular, material-driven 3D-printed composite scaffold designed to regenerate both bone and skin within composite cranial defects. The scaffold integrates controlled copper ion release from both organic and inorganic components with 3D-printed citrate polymer and citrate polymer–ceramic composites. Integrated thermoresponsive citrate-based hydrogels further enable spatially defined dermoconductive and osteoconductive properties, supporting a one-step surgical approach. At 12 weeks post-implantation, our scaffold enhanced keratinocyte organization, collagen deposition, and defect coverage with mature bone, achieving histological outcomes comparable to autografts. Furthermore, the system suppressed bacterial burden. Thus, this acellular platform represents a clinically promising synchronized strategy to address the complex demands of traumatic craniofacial composite defects.

This article presents an approach to extend the capabilities of vat photopolymerization (VPP) 3D printing using a robotic arm, with a focus on robust path planning. The robotic cell consists of a Mecademic Meca500 six-axis robot mounted on a Zaber X-LRQ300AP linear guide. The kinematic chain is inverted to reflect the logic of VPP: the world reference frame is fixed to the robot’s tool (the build plate), while the tool frame is attached to the polymerization zone. A virtual degree of freedom for screen image rotation is introduced, bringing the system to eight degrees of freedom. Inverse kinematics are solved under constraints (pose tolerance, joint limits, collision avoidance, and continuity) and evaluated using multi-criteria metrics: manipulability, normalized joint-limit margin, and positional/angular sensitivity. The algorithm follows a deterministic coarse-to-fine search procedure: discrete sweeping of global part orientations, initial sampling with Halton sequences, abd feasibility filtering on a sparsified trajectory, followed by refinement and multi-criteria ranking. The pipeline successfully discarded infeasible orientations and identified feasible printing trajectories for six of the seven benchmark parts, while the remaining case highlights a limitation that may be addressed in future improvements.

Microvascular function and oxygen metabolism are central to tissue and organ health. However, label-free methods for imaging oxygen dynamics in three-dimensional (3D) microvascular networks at the level of single red blood cells (RBCs)—the fundamental units of oxygen transport in vivo—remain lacking. Here, we introduce super-resolution functional photoacoustic microscopy (SR-fPAM), which spatiotemporally tracks RBC movements under dual-wavelength excitation. SR-fPAM reconstructs super-resolved 3D microvascular architecture comparable to two-photon microscopy while providing quantitative measurements of RBC flow and oxygenation. In live mice, SR-fPAM revealed redistribution of oxygen and hemodynamics across 3D microvascular networks following a single-vessel stroke. These findings establish SR-fPAM as an enabling tool that bridges a critical gap in oxygen-metabolism imaging and opens new avenues for studying microvascular health and disease with unprecedented functional insights.

Optical coherence tomography (OCT) has transformed clinical eye care by providing high-resolution volumetric imaging of the retina. Recently, ultrawide-field-of-view (FOV) OCT played an increasingly significant clinical role; however, most clinical OCT systems offer only a rather limited FOV. We increased the FOV of clinical OCT by volumetrically montaging multiple OCT datasets in three dimensions (3D). We performed volumetric montaging by representing the internal limiting membrane (ILM) and retinal pigment epithelium (RPE) in each volume as point clouds and using these point clouds to compute transformations that map each volume to a common reference frame. We validated our methodology using datasets from three institutions with different OCT hardware and data-acquisition procedures. Using the mean surface distance between point clouds, we found the error in montaging was less than the lateral pixel size. Our method enabled existing clinical OCT to achieve ultrawide FOV imaging without any hardware modification.