Shengyun Ji

High efficiency fabrication of complex microtube arrays by scanning focused femtosecond laser Bessel beam for trapping/releasing biological cells

In this paper, we present a focused femtosecond laser Bessel beam scanning technique for the rapid fabrication of large-area 3D complex microtube arrays. The femtosecond laser beam is converted into several Bessel beams by two-dimensional phase modulation using a spatial light modulator. By scanning the focused Bessel beam along a designed route, microtubes with variable size and flexible geometry are rapidly fabricated by two-photon polymerization. The fabrication time is reduced by two orders of magnitude in comparison with conventional point-to-point scanning. Moreover, we construct an effective microoperating system for single cell manipulation using microtube arrays, and demonstrate its use in the capture, transfer, and release of embryonic fibroblast mouse cells as well as human breast cancer cells. The new fabrication strategy provides a novel method for the rapid fabrication of functional devices using a flexibly tailored laser beam.

Two-photon polymerization of microstructures by a non-diffraction multifoci pattern generated from a superposed Bessel beam

In this Letter, superposed Bessel beams (SBBs) are realized by alternatively imprinting holograms of opposite-order Bessel beams along the radial direction on a spatial light modulator. The propagation invariance and non-rotation properties of SBBs are theoretically predicted and experimentally demonstrated. The focusing property of SBBs with a high numerical aperture (NA) objective is investigated with the Debye vectorial diffraction theory. Near the focal plane, a circularly distributed multiple foci pattern is achieved. The multiple foci generated from SBBs are adopted in a two-photon fabrication system, and micropattern fabrication by a single exposure is demonstrated. Facile fabrication of three-dimensional microstructures with SBBs is realized by dynamically controlling the number of focal spots, and the diameter and rotation of the focal pattern.

Direct laser writing of complex microtubes using femtosecond vortex beams

Microfabrication by using structured laser beams provides a rapid and facile way for creating some specific microstructures. As an important member in the structured beam category, optical vortices can be easily generated by a helical phase and focused into a geometry-tunable pattern by an objective. In this work, optical vortices with diverse intensity distributions, e.g., different sizes, geometries, and deflection angles, are generated by controlling the phase factors imprinted on optical vortices, including topological charge, fold number, and modulation depth, respectively. The focusing properties of the measured optical vortices in a high numerical aperture laser microfabrication system agree with the theoretical calculation by the Debye vectorial diffraction theory. Three dimensional complex microtubes are rapidly realized by simply scanning the optical vortices along a designed route in a photoresist. With this method, microtubes with controlled diameters, polygonal geometry, winding edges, and ev...

Mechanical-Tunable Capillary-Force-Driven Self-Assembled Hierarchical Structures on Soft Substrate

Capillary-force-driven self-assembly (CFSA) has been combined with many top-down fabrication methods to be alternatives to conventional single micro/nano manufacturing techniques for constructing complicated micro/nanostructures. However, most CFSA structures are fabricated on a rigid substrate, and little attention is paid to the tuning of CFSA, which means that the pattern of structures cannot be regulated once they are manufactured. Here, by combining femtosecond laser direct writing with CFSA, a flexible method is proposed to fabricate self-assembled hierarchical structures on a soft substrate. Then, the tuning of the self-assembly process is realized with a mechanical-stretching strategy. With this method, different patterns of tunable self-assembled structures are obtained before tuning and after release, which is difficult to achieve with other techniques. In addition, as a proof-of-concept application, this mechanical tunable self-assembly of microstructures on a soft substrate is used for smart displays and versatile micro-object trapping.

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.

Dimension‐Controllable Microtube Arrays by Dynamic Holographic Processing as 3D Yeast Culture Scaffolds for Asymmetrical Growth Regulation

Transparent microtubes can function as unique cell culture scaffolds, because the tubular 3D microenvironment they provide is very similar to the narrow space of capillaries in vivo. However, how to realize the fabrication of microtube-arrays with variable cross-section dynamically remains challenging. Here, a dynamic holographic processing method for producing high aspect ratio (≈20) microtubes with tunable outside diameter (6-16 µm) and inside diameter (1-10 µm) as yeast culture scaffolds is reported. A ring-structure Bessel beam is modulated from a typical Gaussian-distributed femtosecond laser beam by a spatial light modulator. By combining the axial scanning of the focused beam and the dynamic display of holograms, dimension-controllable microtube arrays (straight, conical, and drum-shape) are rapidly produced by two-photon polymerization. The outside and inside diameters, tube heights, and spatial arrangements are readily tuned by loading different computer-generated holograms and changing the processing parameters. The transparent microtube array as a nontrivial tool for capturing and culturing the budding yeasts reveals the significant effect of tube diameter on budding characteristics. In particular, the conical tube with the inside diameter varying from 5 to 10 µm has remarkable asymmetrical regulation on the growth trend of captured yeasts.