Fabrication of three-dimensional helical microchannels with arbitrary length and uniform diameter inside fused silica

Wireless, Smart Hemostasis Device with All-Soft Sensing System for Quantitative and Real-Time Pressure Evaluation

The properly applied pressure between the skin and hemostasis devices is an essential parameter for preventing bleeding and postoperative complications after a transradial procedure. However, this parameter is usually controlled based on the subjective judgment of doctors, which might cause insufficient hemostatic effect or thrombosis. Here this study develops a compact and wireless sensing system for continuously monitoring the pressure applied on the radial artery and wrist skin in clinical practice. A liquid metal (LM)-based all-soft pressure sensor is fabricated to enable conformal attachment between the device and skin even under large deformation conditions. The linear sensitivity of 0.007 kPa-1 among the wide pressure range of 0-100 kPa is achieved and the real-time detection data can be wirelessly transmitted to mobile clients as a reference pressure value. With these devices, detailed pressure data can be collected, analyzed, and stored for medical assistance as well as to improve surgery quality.

Rapid Fabrication of Wavelength-Scale Micropores on Metal by Femtosecond MHz Burst Bessel Beam Ablation

The preparation of the wavelength-scale micropores on metallic surfaces is limited by the high opacity of metal. At present, most micropores reported in the literature are more than 20 µm in diameter, which is not only large in size, but renders them inefficient for processing so that it is difficult to meet the needs of some special fields, such as aerospace, biotechnology, and so on. In this paper, the rapid laser fabrications of the wavelength-scale micropores on various metallic surfaces are achieved through femtosecond MHz burst Bessel beam ablation. Taking advantage of the long-depth focal field of the Bessel beam, high-density micropores with a diameter of 1.3 µm and a depth of 10.5 µm are prepared on metal by MHz burst accumulation; in addition, the rapid fabrication of 2000 micropores can be achieved in 1 s. The guidelines and experimental results illustrate that the formations of the wavelength-scale porous structures are the result of the co-action of the laser-induced periodic surface structure (LIPSS) effect and Bessel beam interference. Porous metal can be used to store lubricant and form a lubricating layer on the metallic surface, thus endowing the metal resistance to various liquids' adhesion. The microporous formation process on metal provides a new physical insight for the rapid preparation of wavelength-scale metallic micropores, and promotes the application of porous metal in the fields of catalysis, gas adsorption, structural templates, and bio-transportation fields.

Insight on the regulation mechanism of the nanochannels in hard and brittle materials induced by sparially shaped femtosecond laser

The efficient fabrication of nanochannels on hard and brittle materials is a difficult task in the field of micro and nano processing. We have realized nanochannel arrays on silica with characteristic scales varying from 50–230 nm using a single femtosecond Bessel beam pulse of 515 nm. By characterizing the surface openings, we found that the characteristic scales of the nanopore openings are inextricably linked to the surface energy deposition effect. We achieved not only three asymmetric channel profiles by adjusting the laser-sample interaction region, but also high aspect ratio nanochannels with characteristic scales about 50 nm and aspect ratios over 100. These results on hard and brittle materials provide a broader platform and application scenarios for smart particle rectifiers, DNA molecular sequencing, biosensors, and nanofluidic devices, which are also more suitable for future practical applications due to their low cost, good durability, and high productivity.

Design of Metal-Based Slippery Liquid-Infused Porous Surfaces (SLIPSs) with Effective Liquid Repellency Achieved with a Femtosecond Laser

Slippery liquid-infused porous surfaces (SLIPSs) have become an effective method to provide materials with sliding performance and, thus, achieve liquid repellency, through the process of infusing lubricants into the microstructure of the surface. However, the construction of microstructures on high-strength metals is still a significant challenge. Herein, we used a femtosecond laser with a temporally shaped Bessel beam to process NiTi alloy, and created uniform porous structures with a microhole diameter of around 4 µm, in order to store and lock lubricant. In addition, as the lubricant is an important factor that can influence the sliding properties, five different lubricants were selected to prepare the SLIPSs, and were further compared in terms of their sliding behavior. The temperature cycle test and the hydraulic pressure test were implemented to characterize the durability of the samples, and different liquids were used to investigate the possible failure under complex fluid conditions. In general, the prepared SLIPSs exhibited superior liquid repellency. We believe that, in combination with a femtosecond laser, slippery liquid-infused porous surfaces are promising for applications in a wide range of areas.

Three-Dimensional Large-Scale Fused Silica Microfluidic Chips Enabled by Hybrid Laser Microfabrication for Continuous-Flow UV Photochemical Synthesis

We demonstrate a hybrid laser microfabrication approach, which combines the technical merits of ultrafast laser-assisted chemical etching and carbon dioxide laser-induced in situ melting for centimeter-scale and bonding-free fabrication of 3D complex hollow microstructures in fused silica glass. With the developed approach, large-scale fused silica microfluidic chips with integrated 3D cascaded micromixing units can be reliably manufactured. High-performance on-chip mixing and continuous-flow photochemical synthesis under UV irradiation at ~280 nm were demonstrated using the manufactured chip, indicating a powerful capability for versatile fabrication of highly transparent all-glass microfluidic reactors for on-chip photochemical synthesis.

Monolithic 3D micromixer with an impeller for glass microfluidic systems

The performance of micromixers, namely their mixing efficiency and throughput, is a critical component in increasing the overall efficiency of microfluidic systems (e.g., lab-on-a-chip and μ-TAS). Most previously reported high-performance micromixers use active elements with some external power to induce turbulence, or contain long and complex fluidic channels with obstacles to increase diffusion. In this paper, we introduce a new type of 3D impeller micromixer built within a single fused silica substrate. The proposed device is composed of microchannels with three inlets and a tank, with a mixing impeller passively rotated by axial flow. The passive micromixer is directly fabricated inside a glass plate using a selective laser-induced etching technique. The mixing tank, with its rotating shaft and 3D pitched blade impeller, exists within a micro-cavity with a volume of only 0.28 mm3. A mixing efficiency of 99% is achieved in mixing experiments involving three dye colours over flow rates ranging from 1.5-30 mL min-1, with the same flow rates also applied to a sodium hydroxide-based bromothymol blue indicator and a hydrochloric acid chemical solution. To verify the reliable performance of the proposed device, we compare the mixing index with a general self-circulation-type chamber mixer to demonstrate the improved mixing efficiency achieved by rotating the impeller. No cracking or breakage of the device is observed under high inner pressures or when the maximum flow rate is applied to the mixer. The proposed microfluidic system based on a compact built-in 3D micromixer with an impeller opens the door to robust, highly efficient, and high-throughput glass-based platforms for micro-centrifuges, cell sorters, micro-turbines, and micro-pumps.

Femtosecond laser hybrid fabrication of a 3D microfluidic chip for PCR application

Microfluidic chips have gradually become a focus of scientific research. However, the fabrication of key functional components in microfluidic chips is always limited by the existing processing methods. The microfluidic chip is difficult to be three-dimensional (3D) and integrated. In response to the key problems of 3D integrated microfluidic chip fabrication, this paper presents a hybrid method for fabricating a microfluidic chip integrated 3D microchannels and metal microstructures by femtosecond laser wet etch technology and liquid metal injection. The integrated microfluidic chip fabricated by this method is expected to be applied to the core reaction unit of integrated PCR devices.

Fabrication of arbitrary three-dimensional suspended hollow microstructures in transparent fused silica glass

Fused silica glass is the preferred material for applications which require long-term chemical and mechanical stability as well as excellent optical properties. The manufacturing of complex hollow microstructures within transparent fused silica glass is of particular interest for, among others, the miniaturization of chemical synthesis towards more versatile, configurable and environmentally friendly flow-through chemistry as well as high-quality optical waveguides or capillaries. However, microstructuring of such complex three-dimensional structures in glass has proven evasive due to its high thermal and chemical stability as well as mechanical hardness. Here we present an approach for the generation of hollow microstructures in fused silica glass with high precision and freedom of three-dimensional designs. The process combines the concept of sacrificial template replication with a room-temperature molding process for fused silica glass. The fabricated glass chips are versatile tools for, among other, the advance of miniaturization in chemical synthesis on chip.

Fused silica glass has excellent optical properties, chemical and thermal stability and hardness, but its microstructuring for miniaturized applications has proven difficult. Here the authors demonstrate obtainment of precise arbitrary three dimensional hollow microstructures in fused silica glass by sacrificial template replication.

3D Multi-Microchannel Helical Mixer Fabricated by Femtosecond Laser inside Fused Silica

Three-dimensional (3D) multi-microchannel mixers can meet the requirements of different combinations according to actual needs. Rapid and simple creation of 3D multi-microchannel mixers in a "lab-on-a-chip" platform is a significant challenge in micromachining. In order to realize the complex mixing functions of microfluidic chips, we fabricated two kinds of complex structure micromixers for multiple substance mixes simultaneously, separately, and in proper order. The 3D multi-microchannel mixers are fabricated by femtosecond laser wet etch technology inside fused silica. The 3D multi-microchannel helical mixers have desirable uniformity and consistency, which will greatly expand their utility and scope of application.

Guided Formation of 3D Helical Mesostructures by Mechanical Buckling: Analytical Modeling and Experimental Validation

Three-dimensional (3D) helical mesostructures are attractive for applications in a broad range of microsystem technologies, due to their mechanical and electromagnetic properties as stretchable interconnects, radio frequency antennas and others. Controlled compressive buckling of 2D serpentine-shaped ribbons provides a strategy to formation of such structures in wide ranging classes of materials (from soft polymers to brittle inorganic semiconductors) and length scales (from nanometer to centimeter), with an ability for automated, parallel assembly over large areas. The underlying relations between the helical configurations and fabrication parameters require a relevant theory as the basis of design for practical applications. Here, we present an analytic model of compressive buckling in serpentine microstructures, based on the minimization of total strain energy that results from various forms of spatially dependent deformations. Experiments at micro- and millimeter-scales, together with finite element analyses (FEA), were exploited to examine the validity of developed model. The theoretical analyses shed light on general scaling laws in terms of three groups of fabrication parameters (related to loading, material and 2D geometry), including a negligible effect of material parameters and a square root dependence of primary displacements on the compressive strain. Furthermore, analytic solutions were obtained for the key physical quantities (e.g., displacement, curvature and maximum strain). A demonstrative example illustrates how to leverage the analytic solutions in choosing the various design parameters, such that brittle fracture or plastic yield can be avoided in the assembly process.

Lens-on-lens microstructures

Microlenses with multiple focal lengths play an important role in three-dimensional imaging and the real-time detection of unconfined or fluctuating targets. In this Letter, we present a novel method of fabricating lens-on-lens microstructures (LLMs) using a two-step femtosecond laser wet etching process. A 3×3 LLM array was made with a diameter of 129.0 μm. The fabricated LLM has two focal lengths, 80.4 and 188.7 μm, showing excellent two-level focusing and imaging abilities. Its size and focal length can be controlled by adjusting laser power and etching time. Its surface roughness remains about 61 nm. This simple and efficient method for large-scale production of LLMs has potential applications in diverse optical systems.

Fabrication of large-area concave microlens array on silicon by femtosecond laser micromachining

In this Letter, a novel fabrication of large-area concave microlens array (MLA) on silicon is demonstrated by combination of high-speed laser scanning, which would result in single femtosecond laser pulse ablation on surface of silicon, and subsequent wet etching. Microscale concave microlenses with tunable dimensions and accessional aspherical profile are readily obtained on the 1  cm × 1  cm silicon film, which are useful as optical elements for infrared (IR) applications. The aperture diameter and height of the microlens were characterized and the results reveal that they are both proportional to the laser scanning speed. Moreover, the optical property of high-performance silicon MLAs as a reflective homogenizer was investigated for the visible wavelength, and it can be easily extended to IR light.

Large-scale high quality glass microlens arrays fabricated by laser enhanced wet etching

Large-scale high quality microlens arrays (MLAs) play an important role in enhancing the imaging quality of CCD and CMOS as well as the light extraction efficiency of LEDs and OLEDs. To meet the requirement in MLAs' wide application areas, a rapid fabrication method to fabricate large-scale MLAs with high quality, high fill factor and high uniformity is needed, especially on the glass substrate. In this paper, we present a simple and cost-efficient approach to the development of both concave and convex large-scale microlens arrays (MLAs) by using femtosecond laser wet etching method and replication technique. A large-scale high quality square-shaped microlens array with 512 × 512 units was fabricated.The unit size is 20 × 20 μm² on the whole scale of 1 × 1 cm². Its perfect uniformity and optical performance are demonstrated.

Three-dimensional printing of freeform helical microstructures: a review

Three-dimensional (3D) printing is a fabrication method that enables creation of structures from digital models. Among the different structures fabricated by 3D printing methods, helical microstructures attracted the attention of the researchers due to their potential in different fields such as MEMS, lab-on-a-chip systems, microelectronics and telecommunications. Here we review different types of 3D printing methods capable of fabricating 3D freeform helical microstructures. The techniques including two more common microfabrication methods (i.e., focused ion beam chemical vapour deposition and microstereolithography) and also five methods based on computer-controlled robotic direct deposition of ink filament (i.e., fused deposition modeling, meniscus-confined electrodeposition, conformal printing on a rotating mandrel, UV-assisted and solvent-cast 3D printings) and their advantages and disadvantages regarding their utilization for the fabrication of helical microstructures are discussed. Focused ion beam chemical vapour deposition and microstereolithography techniques enable the fabrication of very precise shapes with a resolution down to ∼100 nm. However, these techniques may have material constraints (e.g., low viscosity) and/or may need special process conditions (e.g., vacuum chamber) and expensive equipment. The five other techniques based on robotic extrusion of materials through a nozzle are relatively cost-effective, however show lower resolution and less precise features. The popular fused deposition modeling method offers a wide variety of printable materials but the helical microstructures manufactured featured a less precise geometry compared to the other printing methods discussed in this review. The UV-assisted and the solvent-cast 3D printing methods both demonstrated high performance for the printing of 3D freeform structures such as the helix shape. However, the compatible materials used in these methods were limited to UV-curable polymers and polylactic acid (PLA), respectively. Meniscus-confined electrodeposition is a flexible, low cost technique that is capable of fabricating 3D structures both in nano- and microscales including freeform helical microstructures (down to few microns) under room conditions using metals. However, the metals suitable for this technique are limited to those that can be electrochemically deposited with the use of an electrolyte solution. The highest precision on the helix geometry was achieved using the conformal printing on a rotating mandrel. This method offers the lowest shape deformation after printing but requires more tools (e.g., mandrel, motor) and the printed structure must be separated from the mandrel. Helical microstructures made of multifunctional materials (e.g., carbon nanotube nanocomposites, metallic coated polymer template) were used in different technological applications such as strain/load sensors, cell separators and micro-antennas. These innovative 3D microsystems exploiting the unique helix shape demonstrated their potential for better performance and more compact microsystems.

Polarization-independent etching of fused silica based on electrons dynamics control by shaped femtosecond pulse trains for microchannel fabrication

We propose an approach to realize polarization-independent etching of fused silica by using temporally shaped femtosecond pulse trains to control the localized transient electrons dynamics. Instead of nanograting formation using traditional unshaped pulses, for the pulse delay of pulse trains larger than 1 ps, coherent field-vector-related coupling is not possible and field orientation is lost. The exponential growth of the periodic structures is interrupted. In this case, disordered and interconnected nanostructures are formed, which is probably the main reason of etching independence on the laser polarization. As an application example, square-wave-shaped and arc-shaped microchannels are fabricated by using pulse trains to demonstrate the advantage of the proposed method in fabricating high-aspect-ratio and three-dimensional microchannels.

Etching rate enhancement by shaped femtosecond pulse train electron dynamics control for microchannels fabrication in fused silica glass

The dependence of the etching rate on the ultrafast pulse shaping is observed when microchannels are fabricated in fused silica glass using the method of femtosecond laser irradiation followed by chemical etching. In comparison with the conventional femtosecond pulses, the temporally shaped pulse trains can greatly enhance the etching rate under the same processing conditions. The enhancement is mainly attributed to the localized transient electron dynamics control by shaping the ultrafast pulse, resulting in higher photon absorption efficiency and uniform photomodification zone. Furthermore, processing parameters, including pulse delay and pulse energy distribution ratio, have also been investigated to optimize microchannels fabrication.

Enhancing depth of focus in tilted microfluidics channels by digital holography

In this Letter we propose a method to enhance the limited depth of field (DOF) in optical imaging systems, through digital holography. The proposed approach is based on the introduction of a cubic phase plate into the diffraction integral, analogous to what occurs in white-light imaging systems. By this approach we show that it is possible to improve the DOF and to recover the extended focus image of a tilted object in a single reconstruction step. Moreover, we demonstrate the possibility of obtaining well-focused biological cells flowing into a tilted microfluidic channel.

Controllable adhesive superhydrophobic surfaces based on PDMS microwell arrays

This paper presents a one-step method to fabricate superhydrophobic surfaces with extremely controllable adhesion based on PDMS microwell arrays. The microwell array structures are rapidly produced on PDMS films by a point-by-point femtosecond laser scanning process. The as-prepared superhydrophobic surfaces show water controllable adhesion that ranges from ultrahigh to ultralow by adjusting the extent of overlap of the adjacent microwells, on which the sliding angle can be controlled from 180° (a water droplet can not slide down even when the as-prepared surface is turned upside down) to 3°. A "micro-airbag effect" is introduced to explain the adhesion transition phenomenon of the microwell array structures. This work provides a facile and promising strategy to fabricate superhydrophobic surfaces with controllable adhesion.