Live Imaging of 3D Hanging Drop Arrays through Manipulation of Light-Responsive Pyroelectric Slippery Surface and Chip Adhesion.

Three-dimensional (3D) hanging drop cell culture is widely used in organoid culture because of its lack of selection pressure and rapid cell aggregation. However, current hanging drop technology has limitations, such as a dependence on complex microfluidic transport channels or specific capillary force templates for drop formation, which leads to unchangeable drop features. These methods also hinder live imaging because of space and complexity constraints. Here, we have developed a hanging drop construction method and created a flexible 3D hanging drop construction platform composed of a manipulation module and an adhesion module. Their harmonious operation allows for the easy construction of hanging drops of varying sizes, types, and patterns. Our platform produces a cell hanging drop chip with small sizes and clear fields of view, thereby making it compatible with live imaging. This platform has great potential for personalized medicine, cancer and drug discovery, tissue engineering, and stem cell research.

Accelerating Neurite Growth and Directing Neuronal Connections Constrained by 3D Porous Microtubes.

Investigation of neural growth and connection is crucial in the field of neural tissue engineering. Here, using a femtosecond laser direct writing (fs-DLW) technique, we propose a directionally aligned porous microtube array as a culture system for accelerating the growth of neurons and directing the connection of neurites. These microtubes exhibited an unprecedented guidance effect toward the outgrowth of primary embryonic rat hippocampal neurons, with a wrap resembling the myelin sheaths of neurons. The speed of neurite growth inside these microtubes was significantly faster than that outside these microtubes. We also achieved selective/directing connection of neural networks inside the magnetic microtubes via precise microtube delivery to a gap between two neural clusters. This work not only proposes a powerful microtube platform for accelerated growth of neurons but also offers a new idea for constructing biological neural circuits by arranging the size, location, and pattern of microtubes.

Functional Shape-Morphing Microarchitectures Fabricated by Dynamic Holographically Shifted Femtosecond Multifoci.

Functional microdevices based on responsive hydrogel show great promise in targeted delivery and biomedical analysis. Among state-of-the-art techniques for manufacturing hydrogel-based microarchitectures, femtosecond laser two-photon polymerization distinguishes itself by high designability and precision, but the point-by-point writing scheme requires mechanical apparatuses to support focus scanning. In this work, by predesigning holograms combined with lens phase modulation, multiple femtosecond laser spots are holographically generated and shifted for prototyping of three-dimensional shape-morphing structures without any moving equipment in the construction process. The microcage array is rapidly fabricated for high-performance target capturing enabled by switching environmental pH. Moreover, the built scaffolds can serve as arrayed analytical platforms for observing cell behaviors in normal or changeable living spaces or revealing the anticancer effects of loaded drugs. The proposed approach opens a new path for facile and flexible manufacturing of hydrogel-based functional microstructures with great versatility in micro-object manipulation.

A Biocompatible Vibration-Actuated Omni-Droplets Rectifier with Large Volume Range Fabricated by Femtosecond Laser.

High-performance droplet transport is crucial for diverse applications including biomedical detection, chemical micro-reaction, and droplet microfluidics. Despite extensive progress, traditional passive and active strategies are restricted to limited liquid types, small droplet volume ranges, and poor biocompatibilities. Moreover, more challenges occur for biological fluids due to large viscosity and low surface tension. Here, a vibration-actuated omni-droplets rectifier (VAODR) consisting of slippery ratchet arrays fabricated by femtosecond laser and vibration platforms is reported. Through the relative competition between the asymmetric adhesive resistance originating from the lubricant meniscus on the VAODR and the periodic inertial driving force originating from isotropic vibration, the fast (up to ≈60 mm s-1 ), programmable, and robust transport of droplets is achieved for a large volume range (0.05-2000 µL, Vmax /Vmin  ≈ 40 000) and in various transport modes including transport of liquid slugs in tubes, programmable and sequential transport, and bidirectional transport. This VAODR is general to a high diversity of biological and medical fluids, and thus can be used for biomedical detection including ABO blood-group tests and anticancer drugs screening. These strategies provide a complementary and promising platform for maneuvering omni-droplets that are fundamental to biomedical applications and other high-throughput omni-droplet operation fields.

Guiding the Patterned Growth of Neuronal Axons and Dendrites Using Anisotropic Micropillar Scaffolds.

The patterning of axonal and dendritic growth is an important topic in neural tissue engineering and critical for generating directed neuronal networks in vitro. Evidence shows that artificial micro/nanotopography can better mimic the environment for neuronal growth in vivo. However, the potential mechanisms by which neurons interact with true three dimensional (3D) topographical cues and form directional networks are unclear. Herein, 3D micropillar scaffolds are designed to guide the growth of neural stem cells and hippocampal neurons in vitro. Discontinuous and anisotropic micropillars are fabricated by femtosecond direct laser writing to form patterned scaffolds with various spacings and heights, which are found to affect the branching and orientation of axons and dendrites. Interestingly, axons and dendrites tend to grow on an array of 3D micropillar scaffolds of the same height and form functionally connected neuronal networks, as reflected by synchronous neuronal activity visualized by calcium imaging. This method may represent a promising tool for studying neuron behavior and directed neuronal networks in a 3D environment.

Ancient genomes from northern China suggest links between subsistence changes and human migration.

Northern China harbored the world's earliest complex societies based on millet farming, in two major centers in the Yellow (YR) and West Liao (WLR) River basins. Until now, their genetic histories have remained largely unknown. Here we present 55 ancient genomes dating to 7500-1700 BP from the YR, WLR, and Amur River (AR) regions. Contrary to the genetic stability in the AR, the YR and WLR genetic profiles substantially changed over time. The YR populations show a monotonic increase over time in their genetic affinity with present-day southern Chinese and Southeast Asians. In the WLR, intensification of farming in the Late Neolithic is correlated with increased YR affinity while the inclusion of a pastoral economy in the Bronze Age was correlated with increased AR affinity. Our results suggest a link between changes in subsistence strategy and human migration, and fuel the debate about archaeolinguistic signatures of past human migration.

Stimuli-Responsive Actuator Fabricated by Dynamic Asymmetric Femtosecond Bessel Beam for In Situ Particle and Cell Manipulation.

Microscale intelligent actuators capable of sensitive and accurate manipulation under external stimuli hold great promise in various fields including precision sensors and biomedical devices. Current microactuators, however, are often limited to a multiple-step fabrication process and multimaterials. Here, a pH-triggered soft microactuator (<100 µm) with simple structure, one-step fabrication process, and single material is proposed, which is composed of deformable hydrogel microstructures fabricated by an asymmetric femtosecond Bessel beam. To further explore the swelling-shrinking mechanism, the hydrogel porosity difference between expansion and contraction states is investigated. In addition, by introducing the dynamic holographic processing and splicing processing method, more complex responsive microstructures (S-shaped, C-shaped, and tortile chiral structures) are rapidly fabricated, which exhibit tremendous expected deformation characteristics. Finally, as a proof of concept, a pH-responsive microgripper is fabricated for in situ capturing polystyrene (PS) particles and neural stem cells rapidly. This flexible, designable, and one-step approach manufacturing of intelligent actuator provides a versatile platform for micro-objects manipulation and drug delivery.

Efficient fabrication of a high-aspect-ratio AFM tip by one-step exposure of a long focal depth holographic femtosecond axilens beam.

In this Letter, we demonstrate a laser fabrication strategy that uses the long focal depth femtosecond axilens laser beam to manufacture the high-aspect-ratio (HAR) micropillars and atomic force microscopy (AFM) probes by one-step exposure. The long depth of focus is generated by modulating laser beam focused at different positions. By adjusting the exposure height, the morphology of HAR micropillars can be tuned flexibly, and the micropillar with an ultra-high aspect ratio (diameter of 1.5 µm, height of 102 µm, ${\rm AR}={70}$AR=70) can be fabricated within 10 ms which is a great challenge for other processing methods to obtain such a HAR microstructure in such a short time. In addition, the HAR micropillar is fabricated onto a cantilever to form the AFM probe. The homemade probe shows fine imaging quality. This method greatly improves the processing efficiency while ensuring the fabrication resolution which provides a powerful method for processing HAR microstructures.

Conical Hollow Microhelices with Superior Swimming Capabilities for Targeted Cargo Delivery.

Inspired by flagellate microorganisms in nature, the microhelix is considered as an ideal model for transportation in fluid environment with low Reynolds number. However, how to promote the swimming and loading capabilities of microhelices with controllable geometries remains challenging. In this study, a novel kind of conical hollow microhelices is proposed and a method is developed to rapidly fabricate these microhelices with controllable parameters by femtosecond vortex beams generated from spatial light modulation along helical scanning. Conical hollow microhelices with designable heights (H = 45-75 µm), diameters (D = 6-18 µm), pitch numbers (Pi = 2-4), taper angles (T = 0.1-0.6 rad), and pitch periods (ΔP = 10-30 µm) are efficiently fabricated. In addition, compared with straight microhelices, the forward swimming capability of conical microhelices increases by 50% and the lateral drift of the conical hollow microhelices is reduced by 70%. Finally, the capabilities of these conical hollow microhelices for nanocargo loading and release by the inner hollow core, as well as transportation of neural stem cells by the outer surface are demonstrated. This work provides new insights into faster and simultaneous transportation of multicargoes for hybrid drug delivery, targeted therapy, and noninvasive surgery in vivo.

Microtubes with Complex Cross Section Fabricated by C-Shaped Bessel Laser Beam for Mimicking Stomata That Opens and Closes Rapidly.

This article presents a new method for fabricating complex cross-sectional microtubes with a high aspect ratio at micro/nanoscale. The microtubes are directly written in a photoresist using a femtosecond pulsed laser combined with a spatial light modulator (SLM). A new method for generating a C-shaped Bessel beam by modifying the Bessel beams with a SLM is reported for the first time. Using this gap-ring-shaped light field, microtubes with special cross section (trefoil-shaped, clover-shaped, spiral, etc.) have been first achieved through two-photo polymerization rapidly. The microtube wall can reach about 800 nm and the diameter of the gap-ring structure is only a few micrometers. As a demonstration, artificial stomata were manufactured with the same size as actual plants stomata consisting of gap-ring microtubes. This artificial stomata can mimic the function of the real stomata with rapid opening and closing, demonstrating its ability to trap and release microparticles regulated by rinse solvent.