Three-dimensional femtosecond laser processing for lab-on-a-chip applications

AbstractThe extremely high peak intensity associated with ultrashort pulse width of femtosecond laser allows us to induce nonlinear interaction such as multiphoton absorption and tunneling ionization with materials that are transparent to the laser wavelength. More importantly, focusing the femtosecond laser beam inside the transparent materials confines the nonlinear interaction only within the focal volume, enabling three-dimensional (3D) micro- and nanofabrication. This 3D capability offers three different schemes, which involve undeformative, subtractive, and additive processing. The undeformative processing preforms internal refractive index modification to construct optical microcomponents including optical waveguides. Subtractive processing can realize the direct fabrication of 3D microfluidics, micromechanics, microelectronics, and photonic microcomponents in glass. Additive processing represented by two-photon polymerization enables the fabrication of 3D polymer micro- and nanostructures for photonic and microfluidic devices. These different schemes can be integrated to realize more functional microdevices including lab-on-a-chip devices, which are miniaturized laboratories that can perform reaction, detection, analysis, separation, and synthesis of biochemical materials with high efficiency, high speed, high sensitivity, low reagent consumption, and low waste production. This review paper describes the principles and applications of femtosecond laser 3D micro- and nanofabrication for lab-on-a-chip applications. A hybrid technique that promises to enhance functionality of lab-on-a-chip devices is also introduced

Integrated polymer photonics : fabrication, design, characterization and applications

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4D Microprinting Based on Liquid Crystalline Elastomers

Two-photon laser printing (2PLP) is a disruptive three-dimensional (3D) printing technique that can afford structural fabrication at the submicrometer scale. Apart from constructing static 3D structures, research in fabricating dynamic ones, known as "4D printing”, is becoming a burgeoning field. 4D printed structures exhibit adaptability or tunability towards their environment through the control of an external stimulus. In contrast to the rapid growth in macroscale fabrication, progress in microprinted actuators has only been scarcely reported. Liquid crystal elastomer (LCE) stands out among the promising classes of smart materials for fabricating microrobotics or microactuators due to its distinct anisotropic property, which enables the printed structures to exhibit automated reversible movements upon exposure to stimuli without environmental limitations. Nevertheless, the use of 2PLP for the manufacture of 4D printed LCE microstructures with high versatility and complexity have presented some challenges, limiting their implementation in final applications. This thesis aims to overcome two main obstacles faced in this regard: first, the limitation of two-photon printable stimuli-responsive materials; and second, the lack of a facile approach for aligning liquid crystal (LC) within three dimensions. The first part of this thesis aims on expanding the library of materials used for implementing light responsiveness into LC microstructures, as light provides a higher degree of temporal and spatial control compared to other stimuli. The initial approach has involved incorporation of acrylate-functionalized photoresponsive molecules, such as azobenzene and the donor-acceptor Stenhouse adduct (DASA), into a LC ink using a conventional synthetic method. However, several challenges, such as compatibility with the LC ink, have prevented the achievement of 4D printing via 2PLP. The second approach is based on post-modifying printed LC structures and successfully fabricated microactuators with five different photoresponsive features by individually incorporating each light-absorbing molecule. Furthermore, LC microactuators that exhibit distinct actuation patterns under different colors of light were fabricated by simultaneously implementing orthogonal photoresponsive molecules. The second project presented in this thesis focuses on developing a new strategy to induce alignment domains in a more flexible manner, with the aim of spatially tailoring the LC topology of the 3D printed microstructures. This is achieved by microprinting 3D scaffolds based on polydimethylsiloxane (PDMS) to manipulate the alignment directions of LC molecules. Taking advantage of 2PLP to fabricate arbitrary scaffolds, LC alignments, including planar and radial patterns, could be introduced freely and simultaneously in three-dimensional space with varying degrees of complexity. The applicability of this alignment approach was demonstrated by fabricating responsive LC microstructures within different PDMS environments, and distinct actuation patterns were observed. Overall, these two breakthroughs have unveiled a wide array of new potentials for the utilization of responsive LC microsystems with tunable functionalities and customizable actuation responses, that can be applied across various domains and applications

Processes and materials used for direct writing technologies:A review

Direct Writing (DW), also known as Robocasting, is an extrusion-based layer-by-layer manufacturing technique suitable for manufacturing complex geometries. Different types of materials such as metals, composites, ceramics, biomaterials, and shape memory alloys can be used for DW. The simplicity and cost-efficiency of DW makes it convenient for different applications, from biomedical to optics. Recent studies on DW show a tendency towards the development of new materials and applications. This represents the necessity of a deep understanding of the principles and parameters of each technique, material, and process challenge. This review highlights the principles of many DW techniques, the recent advancements in material development, applications, process parameters, and challenges in each DW process. Since the quality of the printed parts by DW highly depend on the material extrusion, the focus of this review is mainly on the ceramic extrusion process and its challenges from rheological and material development point of view. This review delivers an insight into DW processes and the challenges to overcome for development of new materials and applications. The main objective of the review is to deliver necessary information for non-specialist and interdisciplinary researchers

Glassy Materials Based Microdevices

Microtechnology has changed our world since the last century, when silicon microelectronics revolutionized sensor, control and communication areas, with applications extending from domotics to automotive, and from security to biomedicine. The present century, however, is also seeing an accelerating pace of innovation in glassy materials; as an example, glass-ceramics, which successfully combine the properties of an amorphous matrix with those of micro- or nano-crystals, offer a very high flexibility of design to chemists, physicists and engineers, who can conceive and implement advanced microdevices. In a very similar way, the synthesis of glassy polymers in a very wide range of chemical structures offers unprecedented potential of applications. The contemporary availability of microfabrication technologies, such as direct laser writing or 3D printing, which add to the most common processes (deposition, lithography and etching), facilitates the development of novel or advanced microdevices based on glassy materials. Biochemical and biomedical sensors, especially with the lab-on-a-chip target, are one of the most evident proofs of the success of this material platform. Other applications have also emerged in environment, food, and chemical industries. The present Special Issue of Micromachines aims at reviewing the current state-of-the-art and presenting perspectives of further development. Contributions related to the technologies, glassy materials, design and fabrication processes, characterization, and, eventually, applications are welcome

Manipulation of Cell and Particle Trajectory in Microfluidic Devices

Microfluidics, the manipulation of fluid samples on the order of nanoliters and picoliters, is rapidly emerging as an important field of research. The ability to miniaturize existing scientific and medical tools, while also enabling entirely new ones, positions microfluidic technology at the forefront of a revolution in chemical and biological analysis. There remain, however, many hurdles to overcome before mainstream adoption of these devices is realized. One area of intense study is the control of cell motion within microfluidic channels. To perform sorting, purification, and analysis of single cells or rare populations, precise and consistent ways of directing cells through the microfluidic maze must be perfected. The aims of this study focused on developing novel and improved methods of controlling the motion of cells within microfluidic devices, while simultaneously probing their physical and chemical properties. To this end we developed protein-patterned smart surfaces capable of inducing changes in cell motion through interaction with membrane-bound ligands. By linking chemical properties to physical behavior, protein expression could then be visually identified without the need for traditional fluorescent staining. Tracking and understanding motion on cytotactic surfaces guided our development of new software tools for analyzing this motion. To enhance these cell-surface interactions, we then explored methods to adjust and measure the proximity of cells to the channel walls using electrokinetic forces and 3D printed microstructures. Combining our work with patterned substrates and 3-dimensional microfabrication, we created micro-robots capable of rapid and precise movements via magnetic actuation. The micro-robots were shown to be effective tools for mixing laminar flows, capturing or transporting individual cells, and selectively isolating cells on the basis of size. In the course of development of these microfluidic tools we gained valuable new insights into the differences and limitations of planar vs. 3D lithography, especially for fabrication of magnetic micro-machines. This work as a whole enables new mechanisms of control within microfluidics, improving our ability to detect, sort, and analyze cells in both a high throughput and high resolution manner

Advances in Nanofibers

Book Advances in Nanofibers is a research publication that covers original research on developments within the Nanofibers field of study. The book is a collection of reviewed scholarly contributions written by different authors. Each scholarly contribution represents a chapter and each chapter is complete in itself but related to the major topics and objectives. The target audience comprises scholars and specialists in the field

Factories of the Future

Engineering; Industrial engineering; Production engineerin

Lithography-based additive manufacturing of ceramics from siloxane preceramic polymers

Additive manufacturing is a fabrication approach which offers the possibility to build complex 3D structures from a virtual model without requiring moulds or costly post-processing steps to accom-plish the final structures. Digital Light Processing (DLP) and 2-Photon-Lithography (2PL), two lithog-raphy-based techniques, represent additive manufacturing processes, which offer the highest de-gree of achievable complexity and resolution in their printed structures. Both techniques print their 3D structures by using light to polymerise photosensitive materials. Photocurable preceramic poly-mer resins offer the possibility to be shaped by both DLP and 2PL printing and are subsequently transformed into ceramic material through pyrolysis, while maintaining their predetermined printed structure. This work is divided into four parts and presents complementary approaches at the material and production level to build highly complex 3D ceramic macro- and micro-structures, all based on the printing of a photosensitive siloxane preceramic polymer. In the first part the photosensitive polysiloxane is blended with other preceramic siloxane resins, of-fering no photosensitivity but a high ceramic yield upon pyrolysis. Complicated structures with cm-sized dimensions and resolution as low as 30 µm are shaped via DLP printing and turned into SiOC macro-structures with complete shape maintenance. The blending of two siloxanes offers the pos-sibility to control and alter the ceramic yield, shrinkage, resolution and free-carbon content of the structures, while at the same time exhibiting no diminished printing capability. Detailed sinter- and mechanical properties of one of the blends was investigated in detail and at all scales and demon-strated that, while the overall shape of ceramic structures are preserved during pyrolysis, different shrinkages as well as a change in aspect ratio depending on the structural configuration can occur and has to be taken into consideration. The photosensitive polysiloxane, already used for macro-fabrication to gain SiOC structures, was al-so used in 2PL printing to fabricate structures of the same complexity at the microscale. SiOC ce-ramics with homogenous shrinkage and feature sizes as low as 800 nm were built with the help of a new printing configuration and printed support structures. The third part of this work describes a complementary approach at the processing level, when SiOC ceramic structures are fabricated with a new hybrid additive manufacturing approach, combining DLP and 2PL printing. The advantages of DLP, the free standing and easy handling of macro-dimensional structures, are joined with the resolution capability of 2PL printing. Precisely positioned 3D structures with sub-µm sized features on top of cm-sized structured components were printed. In the final part the polymer processing capability of preceramic polymers and their transformation into a reactive ceramic phase upon pyrolysis is exploited. Instead of producing pure SiOC ceramics, the photocurable siloxane preceramic polymer is combined with alumina powders to develop a new ceramic phase, mullite, upon sintering. The phase transformation at low sintering temperatures de-veloped the new mullite phase within the 3D structure, fabricated due to the photosensitive capabil-ities of the siloxane via DLP printing. Due to the complementary approach in this work, 3D ceramic structures have been fabricated at the macroscale (DLP), microscale (2PL) and multi-scale (Hybrid additive manufacturing; DLP + 2PL) on basis of a photosensitive preceramic polymer. Different ceramic materials, SiOC and mullite, have been produced from the polysiloxane thanks to its transformation capability into SiOC ceramic and reactive SiO2 phase at high temperatures. Through the addition of passive and active fillers complex, dense, pore- and crack-free ceramic structures with no sign of delamination and complete mainte-nance of shape have been developed with varying properties