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Femtosecond laser direct write (fs-LDW) is a promising technology for three-dimensional (3D) printing due to its high resolution, flexibility, and versatility. A protein solution can be used as a precursor to fabricate 3D proteinaceous microstructures that retain the protein's native function. The large diversity of protein molecules with different native functions allows diverse applications of this technology. However, our limited understanding of the mechanism of the printing process restricts the design and generation of 3D microstructures for biomedical applications. Therefore, we used eight commercially available homopeptides as precursors for fs-LDW of 3D structures. Our experimental results show that tyrosine, histidine, glutamic acid, and lysine contribute more to the fabrication process than do proline, threonine, phenylalanine, and alanine. In particular, we show that tyrosine is highly beneficial in the fabrication process. The beneficial effect of the charged amino acids glutamic acid and lysine suggests that the printing mechanism involves ions in addition to the previously proposed radical mechanism. Our results further suggest that the uneven electron density over larger amino acid molecules is key in aiding fs-LDW. The findings presented here will help generate more desired 3D proteinaceous microstructures by modifying protein precursors with beneficial amino acids. Femtosecond laser direct write (fs-LDW) offers a three-dimensional (3D) printing capability for creating well-defined micro-and nanostructures. Applying this technology to proteins enables the manufacture of complex biomimetic 3D micro-and nanoarchitectures with retention of their original protein functions. To our knowledge, homopeptides themselves have never been used as precursor for fs-LDW so far. Our study gains several new insights into the 3D printing mechanism of pure protein for the first time. We believe that the experimental evidence presented greatly benefits the community of 3D printing of protein in particular and the biomaterial science community in general. With the gained insight, we aspire to expand the possibilities of biomaterial and biomedical applications of this technique. [Display omitted] [ABSTRACT FROM AUTHOR]

Photonic chips have been recognized as a promising platform for information technology. On‐chip optical interferometers as fundamental building blocks of photonic chips are under extensive research with both conventional and novel fabrication techniques. Among them, recently, femtosecond laser has been attracting a great deal of attention as a powerful tool for directly writing micro‐optical devices in various materials due to its flexibility and three‐dimensional fabrication capability. This article gives a review on the working principles and recent achievements of on‐chip waveguides and interferometers fabricated by femtosecond laser, showing their potential applications in various scenarios. [ABSTRACT FROM AUTHOR]

The mechanical strength of hydrogel microstructures is crucial for obtaining the desired flexibility, robustness, and biocompatibility for various applications such as cell scaffolds and soft microrobots. In this study, we demonstrate the fabrication of microstructures composed of cellulose nanofibers (CNFs) and poly(ethylene glycol) diacrylate (PEGDA) hydrogels by multiphoton polymerization. The stress of the fabricated microstructure during tensile testing increased with an increase in the CNF concentration, indicating that the mechanical strength of the microstructure was enhanced by using CNFs as fillers. Moreover, the swelling ratio of the microstructure increased with increasing CNF concentration in the PEGDA hydrogel. Our results show the potential of the technique for the microfabrication of advanced cell scaffolds and soft microrobots with the desired mechanical strength. [ABSTRACT FROM AUTHOR]

Abstract: Development of tunable microlenses by taking advantage of the physical adaptability of fluids is one of the challenges of optofluidic techniques, since it offers many applications in biochips, consumer electronics, and medical engineering. Current optofluidic tuning methods using electrowetting or pneumatic pressure typically suffer from high complexity involving external electromechanical actuating devices and limited tuning performance. In this paper, a novel and simple tuning method is proposed that changes the liquid refractive index in an optofluidic channel while leaving the shape of the microlens unchanged. To create an optofluidic microlens with high robustness and optical performance, built‐in microlenses are fabricated inside 3D glass microfluidic channels by optimized single‐operation wet etching assisted by a femtosecond laser. Tuning of focusing properties is demonstrated by filling the channel with media having different indices. Continuous tuning over a wide range (more than threefold tunability for both focal length and focal spot size) is also achieved by pumping sucrose solutions with different concentrations into the microchip channels. Reversible tuning is experimentally verified, indicating intriguing properties of the all‐glass optofluidic microchip. Both the proposed tuning method and the all‐glass architecture with built‐in microlens offer great potential toward numerous applications, including microfluidic adaptive imaging and biomedical sensing. [ABSTRACT FROM AUTHOR]

True three-dimensionally (3D) integrated biochips are crucial for realizing high performance biochemical analysis and cell engineering, which remain ultimate challenges. In this paper, a new method termed hybrid femtosecond laser microfabrication which consists of successive subtractive (femtosecond laser-assisted wet etching of glass) and additive (two-photon polymerization of polymer) 3D microprocessing was proposed for realizing 3D 'ship-in-a-bottle' microchip. Such novel microchips were fabricated by integrating various 3D polymer micro/nanostructures into flexible 3D glass microfluidic channels. The high quality of microchips was ensured by quantitatively investigating the experimental processes containing 'line-to-line' scanning mode, improved annealing temperature (645°C), increased prebaking time (18 h for 1mm-length channel), optimal laser power (1.9 times larger than that on the surface) and longer developing time (6 times larger). The ship-in-a-bottle biochips show high capabilities to provide simultaneous filtering and mixing with 87% efficiency in a shorter distance and on-chip synthesis of ZnO microflower particles. [ABSTRACT FROM AUTHOR]

Abstract: A microchip made of UV transparent polymer (CYTOP) that can perform selective cell culture has been fabricated by F2 laser surface modification. The refractive index of CYTOP is almost the same as that of culture medium, which is essential for three-dimensional (3D) observation of cells. The F2 laser modification of CYTOP achieves hydrophilicity only on the laser irradiated area with little deterioration of the optical properties and surface smoothness. After the laser modification, HeLa cells were successfully cultured and strongly adhered only on the modified area of CYTOP. The cells patterned on CYTOP were applied for clear 3D observation using an optical microscope in phase contrast mode. [Copyright &y& Elsevier]

Abstract: We demonstrate fabrication of microchips with microfluidic structures for dynamic analysis of living cells using a femtosecond (fs) laser. Fs laser direct writing followed by annealing and successive wet etching in dilute hydrofluoric (HF) acid solution resulted in formation of three dimensional (3D) hollow microstructures embedded in photostructurable glass. The embedded microchannel structure enabled us to analyze unique phenomenon of Cryptomonas, which suddenly swims very fast under certain condition. Vector analysis of the driving force for the rapid motion was also carried out by introducing nano-beads into the microchannel, in which Cryptomonas was encapsulated. We also fabricated a microchip for observation of Phormidium moving toward a seedling root, which accelerates growth of the seedling. Using the embedded microchannel in the microchip, observation of Phormidium assemblage to the seedling root was easily carried out. Such microchips with microfluidic structures, referred to as a nano-aquarium, realize the efficient and highly functional observation of living cells. [Copyright &y& Elsevier]

Abstract: We investigated micro- and nano-fabrication of wide band-gap semiconductor gallium nitride (GaN) using a femtosecond (fs) laser. Nanoscale craters were successfully formed by wet-chemical-assisted fs-laser ablation, in which the laser beam is focused onto a single-crystal GaN substrate in a hydrochloric acid (HCl) solution. This allows efficient removal of ablation debris produced by chemical reactions during ablation, resulting in high-quality ablation. However, a two-step processing method involving irradiation by a fs-laser beam in air followed by wet etching, distorts the shape of the crater because of residual debris. The threshold fluence for wet-chemical-assisted fs-laser ablation is lower than that for fs-laser ablation in air, which is advantageous for improving fabrication resolution since it reduces thermal effects. We have fabricated craters as small as 510nm by using a high numerical aperture (NA) objective lens with an NA of 0.73. Furthermore, we have formed three-dimensional hollow microchannels in GaN by fs-laser direct-writing in HCl solution. [Copyright &y& Elsevier]

Abstract: Three-dimensional hollow microstructures acting as microfluidic and microoptical components were directly formed inside a photoetchable glass, Foturan, using femtosecond (fs) laser direct writing followed by post-annealing and successive chemical etching. Benefiting from a multiphoton process and a focus-shaping technique, a resolution as high as 10μm was achieved in both the transverse and longitudinal directions. Microreactors containing microchannels, microcells, and microvalves were fabricated by this technique, and functions like sample mixing and fluid switching were demonstrated. Also, microoptics, such as micromirrors and microbeam splitters, were fabricated by this technique. The microfluidic and microoptical components were also integrated into the same chip for creating microfluidic dye lasers. A dual-color microfluidic laser array which can simultaneously emit light with wavelengths centered at 568 and 618nm was also fabricated and its lasing properties examined. [Copyright &y& Elsevier]

Abstract: We show that uniform nanoripples can be produced on the sidewalls of the micro-cell vertically embedded in fused silica glass by femtosecond laser direct ablation. The nanoripples can be used for homogeneous liquid crystal (LC) alignment with different azimuthal angles. The azimuthal anchoring energy at the interface between the LC and nanoripples is obtained by measuring the twist angle of LC director in the fabricated twisted nematic LC micro-cell. This method allows for fabrication of LC micro-cells integrated in glass chip with three-dimensional (3D) configurations, opening a new venue to fabrication of 3D miniaturized LC devices. [ABSTRACT FROM AUTHOR]

Abstract: We demonstrate that a Raman sensor integrated with a micro-heater, a microfluidic chamber, and a surface-enhanced Raman scattering (SERS) substrate can be fabricated in a glass chip by femtosecond laser micromachining. The micro-heater and the SERS substrate are fabricated by selective metallization on the glass surface using a femtosecond laser oscillator, whereas the microfluidic chamber embedded in the glass sample is fabricated by femtosecond laser ablation using a femtosecond laser amplifier. We believed that this new strategy for fabricating multifunctional integrated microchips has great potential application for lab-on-a-chips. [Copyright &y& Elsevier]