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Lasers are instrumental in enabling precise processing and fostering the development of new technologies. Particularly, ultrafast lasers, due to their unique interaction with matter, can achieve not only exceptional spatial precision but also meticulously determine the degree of modification. A prime example of this is laser‐based 3D printing through multi‐photon lithography (MPL). This approach remarkably enables the printing of true 3D structures at the micro‐ and nanoscale, without the need for masks or cumbersome tools, simply by using computer‐aided designs. Owing to these unique capabilities, MPL has emerged as a powerful manufacturing technique across various multidisciplinary fields. The ongoing growth in MPL's utilization has led to notable advancements in printing highly complex structures on different substrates, as well as improvements in resolution and throughput, and the development of novel photosensitive materials, which impressively facilitated MPL's expansion into broader fields over the last few years. In this perspective article, the aim is to highlight these advancements and recent trends in MPL. The current challenges of MPL will be explored, which need to be addressed to ensure its further integration into advanced Additive Manufacturing at the micro‐ and nanoscale. The future perspectives and opportunities of MPL as a laser‐based 3D printing approach will also be discussed. [ABSTRACT FROM AUTHOR]

This document is an editorial discussing a special issue of the European Physical Journal: Special Topics focused on the study of the sleeping brain and brain pathology. The editorial emphasizes the importance of sleep for restoring energy and brain health, and highlights the potential for developing new technologies and therapies for brain diseases through the study of sleep patterns. The special issue includes research papers on various topics such as hemispheric asymmetry during sleep, mechanisms controlling sleep-wake stages, and innovative methods for analyzing the sleeping brain. The authors express gratitude to the contributors and reviewers of the studies, and provide information on data availability. [Extracted from the article]

This perspective is an overview of a recent direction in optical 3D printing, where polymerization of crosslinkable materials and nanomaterial fillers can be guided to the final structures and new composites via high temperature annealing (HTA). Defining 3D nano/micro‐structures by ultrafast laser direct writing and tailoring their precursor composition with subsequent tunability of the final properties during 750–1500 °C HTA step takes place at the large surface‐to‐volume ratio conditions favoring efficient pyrolysis and calcination, which are required for exchange of chemical materials/gases between glass/ceramic phase and surrounding. Previously, unexplored inorganic material formation conditions in terms of fast thermal quenching, composition mixing and surface tension guided formation can be harnessed by glass making for creation of new materials endowed with preferable technical properties. An immediate application perspective for a high durability, integrated, and active 3D micro‐optics is foreseen. [ABSTRACT FROM AUTHOR]

The increasing demand for functional nanodevices in sustainable energy applications necessitates the development of innovative approaches. In this study, we present the fabrication and characterization of three-dimensional (3D) structures coated with titanium dioxide (TiO 2) nanorods (NRs). These novel devices are created through the integration of four distinct techniques, multi-photon lithography, post-thermal treatment, pulsed laser deposition, and an aqueous chemical growth, enabling their unique properties and functionalities in photocatalysis. The photocatalytic performance of the 3D devices is evaluated through the degradation of organic pollutants, such as methylene blue and stearic acid, showcasing their efficiency in reducing pollutant concentrations. The devices demonstrate a remarkable decomposition coefficient (k = 0.059 min − 1 ), highlighting their enhanced photocatalytic efficiency. Additionally, we propose a rapid fabrication technique using 3D holographic printing to create large-area TiO 2 -coated micro-structured photocatalytic devices at the mesoscale regime. This approach increases the active surface area, further enhancing the devices' photocatalytic capabilities. By combining additive micro-manufacturing, TiO 2 NR coating, and holographic printing, our work introduces a promising avenue for the development of advanced nanodevices with superior photocatalytic performance in sustainable energy applications. [ABSTRACT FROM AUTHOR]

Abstract: Research into the three-dimensional nanostructuring of photopolymers by ultrashort laser pulses has seen immense growth over the last decade. In this paper, we review the basic principles and the most important developments and applications of this technology. We discuss the mechanisms the linear and nonlinear light absorption at tight focusing conditions, and we present some typical laser writing conditions with numerical examples. The photochemistry of traditional and novel photopolymers together with strategies for their photosensitization for laser structuring by ultra-short pulses are discussed. We also discuss current and potential future applications in diverse fields such as metamaterials, plasmonics, micro-optics, and biomedical devices and implants. [Copyright &y& Elsevier]

Abstract: A new method is demonstrated, where three-dimensional protein structures are made by employing multi-photon polymerization and photobiotin photolysis. The technique enables the construction of arbitrary two- and three-dimensional shapes with submicron resolution. The integrity of the immobilized biotin is confirmed by derivatization with fluorescently labeled streptavidin. Fluorescence microscopy is used in order to visualize the distribution of fluorescent streptavidin on the 3D structure. [Copyright &y& Elsevier]

Abstract: We report two-photon polymerization of an acrylate composite using a femtosecond laser at 1028nm. The composite consists of an acrylate monomer, a free-radical co-initiator and a photo-sensitizer. The material is transparent to infrared laser radiation and absorbs strongly in the visible. By scanning the tightly focused laser beam, we employ two-photon absorption to polymerize and selectively solidify the material. Two photo-polymerization of organic composites permits the construction of complex-shaped three-dimensional structures of sub-micron resolution. Due to their versatile optical and chemical properties and the ability to mix them with active molecules, the materials described in this work are particularly useful for a variety of applications such as photonic devices, actuators and micro-fluidic devices. In addition, as both the single photon and the two-photon wavelengths are not in the ultraviolet part of the spectrum, this technique is particularly promising for incorporation into the photo-polymer of active molecules that are sensitive to UV radiation. [Copyright &y& Elsevier]

The article focuses on the functionality of two-photon polymerization (2PP) technology in laser applications and in the fabrication of fully three-dimensional (3D) structures. It notes the potential of the 3D nature of the 2PP together with the high transparency of sol-gel materials in the fabrication of nanophotonic devices. The quality of the 2PP in biological applications such as in implantable microelectromechanical systems (MEMS) and scaffolds for tissue in engineering is discussed.

Abstract: We have studied laser ablation of silicon carbide with emphasis on the influence of pulse duration and laser wavelength. Experiments with 193 and 248nm excimer nanosecond lasers have been carried out as well as fs-UV experiments with a distributed feedback dye laser system amplified by an excimer laser, delivering 500fs pulses at 248nm. Additional experiments were performed with solid state lasers providing radiation at 1040 and 1026nm at a pulse duration of 300 and 400fs, respectively. Experiments in the UV show a significant difference in the ablation quality between 193nm and 248nm radiation. The ablated cavity indicates a higher thermal impact in the case of 248nm radiation. The application of 500fs pulses at this particular wavelength results in an improved edge definition and surface quality of the ablated area. Experiments carried out with the femtosecond solid state lasers show high ablation rates and good edge quality. The sample used in our work was a polished 3C–SiC wafer. [Copyright &y& Elsevier]

Mechanical metamaterials demonstrate augmented properties derived from their engineered structure. Advances in three-dimensional (3D) printing technologies have enabled the fabrication of complex metamaterial structures even at the microscale, contributing to the development of light-weight materials with superior mechanical properties. However, understanding of metamaterial strain hardening that is intrinsic to both the structure and arrangement of novel unit cells is sparse and fairly empirical. The main objective of this study was to introduce a new design approach for 3D mechanical metamaterials with enhanced strain hardening and energy absorption, fabricated at the microscale by multiphoton lithography, which is the only fabrication technique that can produce micrometer length scales and high structural complexity. This was accomplished by intertwining simple polyhedra to create more complex geometries in 3D space, using penetration twins as a point of reference, a mechanism of crystal in-growth wherein distinct crystals appear to penetrate each other. This structural principle was used to intertwine the lattice members of the structure and tailor their buckling behavior. The present design is inspired by the first stellation of the rhombic dodecahedron. With this concept, plastic deformation can be controlled through localized buckling of select lattice members. Finite element simulations and nanoindentation experiments demonstrate remarkably improved performance with respect to both strain hardening and energy dissipation of the structure compared to both the bulk material and one of the most thoroughly studied ultralight, ultrastiff mechanical metamaterials, the octet truss. [ABSTRACT FROM AUTHOR]

The rapid development of additive manufacturing has fueled a revolution in various research fields and industrial applications. Among the myriad of advanced 3D printing techniques, two‐photon polymerization lithography (TPL) uniquely offers a significant advantage in nanoscale print resolution, and has been widely employed in diverse fields, for example, life sciences, materials sciences, mechanics, and microfluidics. More recently, by virtue of the optical transparency of most of the resins used, TPL is finding new applications in optics and photonics, with nanometer to millimeter feature dimensions. It enables the minimization of optical elements and systems, and exploration of light‐matter interactions with new degrees of freedom, never possible before. To review the recent progress in the TPL related optical research, it starts with the fundamentals of TPL and material formulation, then discusses novel fabrication methods, and a wide range of optical applications. These applications notably include diffractive, topological, quantum, and color optics. With a panoramic view of the development, it is concluded with insights and perspectives of the future development of TPL and related potential optical applications. [ABSTRACT FROM AUTHOR]

Optical activity (polarization rotation of light) is one of the most desired features of chiral media, as it is important for many polarization‐related applications. However, in the THz region, chiral media with strong optical activity are not available in nature. Here, a chiral metamaterial (CMM) structure composed of pairs of vertical U‐shape resonators of "twisted" arms is studied, and it is revealed that it demonstrates large pure optical activity (i.e., optical activity associated with negligible transmitted wave ellipticity) in the low THz regime. The experimental data show polarization rotation up to 25° for an unmatched bandwidth of 1 THz (relative bandwidth 80%), from a 130 µm‐thickness structure, while theoretical optimizations show that the rotation can reach 45°. The enhanced chiral response of the structure is analyzed through an equivalent RLC circuit model, which also provides simple optimization rules for the enhancement of its chiral response. The proposed chiral design allows for easy fabrication via direct laser writing (DLW) and electroless metal plating, making the associated structures suitable candidates for polarization control applications. [ABSTRACT FROM AUTHOR]

Damage in the Peripheral Nervous System (PNS) is related to numerous neurodegenerative diseases and has consequently drawn the attention of Tissue Engineering (TE), which is considered a promising alternative to already established methods such as surgery and autografts. TE focuses on the design, optimization, and use of scaffolds in vitro and in vivo. In this work, the authors used a novel scaffold geometry fabricated via Multiphoton Lithography (MPL), a commonly used fabrication method, for the mono- and co-cultures of glial Schwann (SW10) and neuronal Neuro-2a (N2a) cells. Both cell types have already been used for the study of various neurodegenerative diseases. However, their focus has been on only one of the cell types at a time, with studies regarding their co-culture only recently documented. Here, the suitability of the fabricated scaffolds has been explored and the effects of topography on SW10 and N2a behavior have been investigated. Our findings demonstrate that scaffold co-culture systems favor the presence of neurites compared to mono-cultures at 21 days (31.4 ± 5.5% and 15.4 ± 5.4%, respectively), while there is also a significant decrease in long neurites in the mono-culture over time (45.3 ± 15.9% at 7 days versus 15.4 ± 5.4% at 21 days). It has been shown that the scaffolds can successfully manipulate cell growth, elongation, and morphology, and these results can form a basis for the development of an experimental model for the study of PNS-related diseases and understanding of key cell functions such as myelination. [ABSTRACT FROM AUTHOR]

For a great variety of research fields extending from photonics to tissue engineering applications, the requests for the construction of three-dimensional structures with high resolution grow more and more imperative. Towards this aim, the direct laser writing technique by multi-photon polymerization, due to its unique properties and characteristics, has proven to be an indispensable tool to high accuracy structuring and has been put on the map as an emerging technology for scaffold 3D printing. In the present review, the basic principles of multi-photon polymerization are presented, the experimental set-up requirements are described and the employed materials demands are thoroughly mentioned as well as the most representative examples of the recent developments in the field. [ABSTRACT FROM AUTHOR]

[Display omitted] • Uniform deposition of Ni nanoparticles on NF by PLD technique. • An optimum deposition thickness was revealed. • A 15-fold increase in ECSA of Ni-decorated NF electrodes. • Improved electrochemical values over Ni/NF electrodes. In this work, we investigated Nickel Foam (NF) electrodes decorated with Ni nanoparticles at various deposited thicknesses through the Pulsed Laser Deposition technique for the hydrogen evolution reaction (HER). Field Emission Scanning Electron Microscopy (FE-SEM), X-ray diffraction spectroscopy (XRD), and X-ray photoelectron spectroscopy (XPS) were employed to gain insight into the structural and morphological characteristics of the prepared electrodes. The optimum deposition thickness was found to be 300 nm. The NF electrode decorated with 300 nm Ni nanoparticles (Ni/NF 300) exhibited improved electrochemical characteristics, i.e., reduced overpotential value s |η 10 | = 0.11 V and lower Tafel slope 99 mV dec-1, as compared to the values of 0.24 V and 134 mV dec-1, respectively, for bare NF electrode. In addition, the Ni/NF 300 electrode presents a 15-fold increase in its electrochemically active surface area (ECSA) in comparison to an NF electrode. [ABSTRACT FROM AUTHOR]

This study describes the fabrication of ultrafast laser-induced periodic nanostructures on Nickel sheets and their use as cathodes in alkaline electrolysis. For the first time, to the best of our knowledge, laser-nanostructured Ni sheets were used as cathode electrodes in a custom-made electrolysis cell at actual, Hydrogen producing conditions, and their efficiency has been compared to the untreated Nickel sheets. The electrochemical evaluation showed higher J peaks , lower overpotential, and enhanced double-layer capacitance for the nanostructured electrode. A decrease in the Tafel slope was also found for the nanostructured electrode. The hydrogen production efficiency was found to be 3.7 times larger for the laser-nanostructured Nickel electrode, which was also confirmed by current-time measurements during electrolysis. Also, a novel approach is proposed to improve the stability of the current density during electrolysis and, therefore, the hydrogen production process by about 10%. [Display omitted] • Laser nanostructured Ni electrodes produce higher values of hydrogen gas. • An Electrochemical evaluation of laser nanostructured Ni electrodes. • A Correlation between electrical measurements and hydrogen production during electrolysis. [ABSTRACT FROM AUTHOR]

The article focuses on use a previously unexplored Bayesian optimization framework, "evolutionary Monte Carlo sampling," tosystematically design the arrangement of defects in an architected microlattice to maximize its strain energy density before undergoing catastrophic failure. Topics include the algorithm searches a design space with billions of 4 × 4 × 5 3D lattices, yet it finds the global optimum with only 250 cost function evaluations.

Single ultra-short pulses from Gaussian and vortex beams have been used for the fabrication of complex micro-structures via multi-photon polymerization. The complexity of the resultant micro-structures stems from the modification of both transverse intensity and phase profiles of these single pulses to create modulated scaffolds and hollow cylinders. Experimental results are compared to theoretical models, and good agreement is shown. [ABSTRACT FROM AUTHOR]

A split-cube-resonator-based metamaterial structure that can act as a polarization- and direction-selective perfect absorber for the infrared region is theoretically and experimentally demonstrated. The structure, fabricated by direct laser writing and electroless silver plating, is comprised of four layers of conductively-coupled split-cube magnetic resonators, appropriately rotated to each other to bestow the desired electromagnetic properties. We show narrowband polarization-selective perfect absorption when the structure is illuminated from one side; the situation is reversed when illuminating from the other side, with the orthogonal linear polarization being absorbed. The absorption peak can be tuned in a wide frequency range by a sparser or denser arrangement of the split cube resonators, allowing to cover the entire atmospheric transparency window. The proposed metamaterial structure can find applications in polarization-selective thermal emission at the IR atmospheric transparency window for radiative cooling, in cost-effective infrared sensing devices, and in narrowband filters and linear polarizers in reflection mode. [ABSTRACT FROM AUTHOR]

Exploiting the unique properties of three‐dimensional (3D) auxetic scaffolds in tissue engineering and regenerative medicine applications provides new impetus to these fields. Herein, the results on the fabrication and characterization of 3D auxetic scaffolds for tissue engineering applications are presented. The scaffolds are based on the well‐known re‐entrant hexagonal geometry (bowtie) and they are fabricated by multiphoton lithography using the organic−inorganic photopolymer SZ2080. In situ scanning electron microscopy–microindentations and nanoindention experiments are employed to characterize the photocurable resin SZ2080 and the scaffolds fabricated with it. Despite SZ2080 being a stiff material with a positive Poisson's ratio, the scaffolds exhibit a negative Poisson's ratio and high elasticity due to their architecture. Next, mouse fibroblasts are used to seed the scaffolds, showing that they can readily penetrate them and proliferate in them, adapting the scaffold shape to suit the cells' requirements. Moreover, the scaffold architecture provides the cells with a predilection to specific directions, an imperative parameter for regenerative medicine in many cell‐based applications. This research paves the way for the utility of 3D auxetic metamaterials as the next‐generation adaptable scaffolds for tissue engineering. [ABSTRACT FROM AUTHOR]

[Display omitted] • Laser-nanostructuring of Nickel and iron electrodes. • Increased double layer capacitance values of Ni-Fe laser-nanostructured electrodes. • Enhanced OER and HER values of Ni-Fe laser-nanostructured electrodes. There is an increasing interest in developing an Ni-Fe supercapacitor-electrolyser system (SCES) for electricity storage and efficient hydrogen production. In this study, periodic nanostructures on nickel [(λ Ni = 570 ± 30) nm] and on iron sheets [(λ Fe = 553 ± 6) nm] have been fabricated and were used as electrodes in an alkaline SCES. Their efficiency was compared to untreated nickel and iron sheets. The electrochemical evaluation of the nanostructured electrodes showed lower overpotential (η 10 and η 100) and lower Tafel slope for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). The hydrogen production efficiency of the laser-nanostructured electrodes was significantly enhanced. Moreover, the laser-nanostructured electrodes' double-layer capacitance (C DL) values were increased 1.5 times for laser-nanostructured Fe electrodes and 5.3 times for laser-nanostructured Ni electrodes. These results show the potential of the fabricated electrodes in applications serving a dual purpose, i.e., enhanced hydrogen production and increased charge storage. [ABSTRACT FROM AUTHOR]

The combination of materials with targeted optical properties and of complex, 3D architectures, which can be nowadays obtained by additive manufacturing, opens unprecedented opportunities for developing new integrated systems in photonics and optoelectronics. The recent progress in additive technologies for processing optical materials is here presented, with emphasis on accessible geometries, achievable spatial resolution, and requirements for printable optical materials. Relevant examples of photonic and optoelectronic devices fabricated by 3D printing are shown, which include light‐emitting diodes, lasers, waveguides, optical sensors, photonic crystals and metamaterials, and micro‐optical components. The potential of additive manufacturing applied to photonics and optoelectronics is enormous, and the field is still in its infancy. Future directions for research include the development of fully printable optical and architected materials, of effective and versatile platforms for multimaterial processing, and of high‐throughput 3D printing technologies that can concomitantly reach high resolution and large working volumes. 3D printing technologies are opening new routes for photonics and optoelectronics, enabling devices with 3D architecture and with unprecedented level of integration. Here, the authors review the recent advances in additive manufacturing of optical materials, highlighting achievable spatial resolution, requirements for printable systems, and relevant examples of photonic and optoelectronic devices fabricated by 3D printing. [ABSTRACT FROM AUTHOR]

In this paper, we reveal that the mathematical discrete model of Hencky type, introduced in [1] , is appropriate for describing the mechanical behavior of micro-metric pantographic elementary modules. This behavior does not differ remarkably from what has been observed for milli-metric modules, as we prove with suitably designed experiments. Therefore, we conclude that the concept of pantographic microstructure seems feasible for micro-metrically architected microstructured (meta)materials as well. These results are particularly indicative of the possibility of fabricating materials that can have an underlying pantographic microstructure at micrometric scale, so that its unique behavior can be exploited in a larger range of technological applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • HER efficiency depended on electrodeposition time. • Facile and time-effective one-step electrode fabrication. • 50% enhanced hydrogen production compared to untreated electrodes. • 6.5 times higher ECSA of electrodeposited Ni foam. Nickel foam electrodes were treated with a facile and cost-effective electrodeposition method to increase the hydrogen production efficiency in alkaline electrolysis setups. The treated electrodes (Electrodeposited Nickel Foam – ENF) exhibit enhanced electrochemical values compared to a bare nickel foam electrode (NF). A comprehensive analysis is presented on how the electrodeposition time determines the kinetics of hydrogen evolution reaction (HER) and the electrochemical values of the ENF electrodes. It was revealed that deposition time plays a decisive role in the total hydrogen production efficiency. In particular, the ENF electrode with 10 min of electrodeposition, presents a lower Tafel slope, lower overpotentials (|η 10 |=135 mV, |η 100 | = 230 mV), and enhanced hydrogen production (1.5 times higher) compared to an NF electrode. The improved characteristics are mainly attributed to the increased electrochemically active area (6.5 times higher than the NF electrode). Field emission scanning electron microscopy (SEM), Energy dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD) were used for the structural and morphological analysis of the electrodeposited nickel foam electrodes. [ABSTRACT FROM AUTHOR]

The regeneration of bone via a tissue engineering approach involves components from the macroscopic to the nanoscopic level, including appropriate 3D scaffolds, cells and growth factors. In this study, hexagonal scaffolds of different diagonals were fabricated by Direct Laser Writing using a photopolymerizable hybrid material. The proliferation of bone marrow (BM) mesenchymal stem cells (MSCs) cultured on structures with various diagonals, 50, 100, 150 and 200 μm increased significantly after 10 days in culture, however without significant differences among them. Next, recombinant human bone morphogenetic protein 2 (rhBMP-2) was immobilized onto the hybrid material both via covalent binding and physical adsorption. Both immobilization types exhibited similar high releaseate bioactivity profiles and a sustained delivery of rhBMP-2. The collagen and calcium levels produced in the extracellular matrix (ECM) were significantly elevated for the samples functionalized with BMP-2 compared to those in the osteogenic medium. Furthermore, significant upregulation of gene expression in both types of BMP-2 immobilized scaffolds was observed for alkaline phosphatase (ALPL ) and osteocalcin ( BGLAP ) at days 7, 14, and 21, for RUNX2 at day 21, and for osteonectin (SPARC) at days 7 and 14. The results suggest that the release of bioactive rhBMP-2 from the hybrid scaffolds enhance the control over the osteogenic differentiation during cell culture. [ABSTRACT FROM AUTHOR]

The aim of this study is to demonstrate the accuracy required for the investigation of the role of solid scaffolds’ porosity in cell proliferation. We therefore present a qualitative investigation into the effect of porosity on MC3T3-E1 pre-osteoblastic cell ingrowth of three-dimensional (3D) scaffolds fabricated by direct femtosecond laser writing. The material we used is a purpose made photosensitive pre-polymer based on polylactide. We designed and fabricated complex, geometry-controlled 3D scaffolds with pore sizes ranging from 25 to 110 μm, representing porosities 70%, 82%, 86%, and 90%. The 70% porosity scaffolds did not support cell growth initially and in the long term. For the other porosities, we found a strong adhesion of the pre-osteoblastic cells from the first hours after seeding and a remarkable proliferation increase after 3 weeks and up to 8 weeks. The 86% porosity scaffolds exhibited a higher efficiency compared to 82% and 90%. In addition, bulk material degradation studies showed that the employed, highly-acrylated polylactide is degradable. These findings support the potential use of the proposed material and the scaffold fabrication technique in bone tissue engineering. [ABSTRACT FROM AUTHOR]

A set of thioxanthone derivatives bearing strongly electron-donating dialkylamino groups have been synthesized efficiently via the Buchwald-Hartwig, Sonogashira, and Heck reactions. Compounds possessing both one and two donors have been prepared. Their optical properties proved to be intriguing. The presence of the amino group alone increased the fluorescence quantum yield 100 times. Dyes possessing arylethylene and arylethynyl linkages absorbed UV radiation and violet light while emitting (weakly) red light, as a consequence of different geometries at ground and excited states. Our design led to an increase in two-photon absorption cross sections at the wavelength of interest (800 nm) to the highest values ever recorded for thioxanthones, while maintaining excellent solubility due to the fact that all new photoinitiators are highly viscous oils at room temperature. Some of the prepared D-η-A-η-D systems also proved to be initiators in two-photon polymerization. [ABSTRACT FROM AUTHOR]

Engineering biomaterial scaffolds that promote attachment and growth of mesenchymal stem cells in three dimensions is a crucial parameter for successful bone tissue engineering. Towards this direction, a lot of research effort has focused recently into the development of three-dimensional porous scaffolds, aiming to elicit positive cellular behavior. However, the fabrication of three-dimensional tissue scaffolds with a precise geometry and complex micro- and nano-features, supporting cell in-growth remains a challenge. In this study we report on a positive cellular response of human bone marrow-derived (BM) mesenchymal stem cells (MSCs) onto hybrid material scaffolds consisting of methacryloxypropyl trimethoxysilane, zirconium propoxide, and 2-(dimethylamino)ethyl methacrylate (DMAEMA). First, we use Direct fs Laser Writing, a 3D scaffolding technology to fabricate the complex structures. Subsequently, we investigate the morphology, viability and proliferation of BM-MSCs onto the hybrid scaffolds and examine the cellular response from different donors. Finally, we explore the effect of the materials' chemical composition on cell proliferation, employing three different material surfaces: (i) a hybrid consisting of methacryloxypropyl trimethoxysilane, zirconium propoxide and 50 mol% DMAEMA, (ii) a hybrid material comprising methacryloxypropyl trimethoxysilane and zirconium propoxide, and (iii) a purely organic polyDMAEMA. Our results show a strong adhesion of BM-MSCs onto the hybrid material containing 50% DMAEMA from the first 2 h after seeding, and up to several days, and a proliferation increase after 14 and 21 days, similar to the polystyrene control, independent of cell donor. These findings support the potential use of our proposed cell–material combination in bone tissue engineering. [ABSTRACT FROM AUTHOR]

Thetwo-step method for the synthesis of acyl–phosphineoxides from aromatic aldehydes was optimized giving the products in52–97% overall yield. Linear and nonlinear optical propertiesof series of acyl–phosphine oxides possessing substituentswith different electron-donating ability were investigated. Two-photonabsorption cross sections (σ2) of push–pullacyl–phosphine oxide was determined as 9GM via z-scan measurements with femtosecond laser pulses. Using acyl–phosphineoxides possessing dipolar structure as initiators, 3D nanopatternswere successfully fabricated by two-photon initiated polymerization.These compounds also initiate classical photopolymerization when excitedwith UV radiation. [ABSTRACT FROM AUTHOR]

We report for the first time on theredox multiphoton polymerizationof an organic–inorganic composite material, in which one ofthe components, a vanadium metallo-organic complex, initiates thepolymerization. The composite employs multiphoton absorption to self-generateradicals by photoinduced reduction of the metal species from vanadium(V) to vanadium (IV). We exploit this material for the fabricationof fully 3D structures by multiphoton polymerization with 200 nm resolution,employing a femtosecond laser operating at 800 nm, in the absenceof a photoinitiator. Nonlinear absorption measurements indicate thatthe use of an 800 nm laser initiates the photopolymerization due tothree-photon absorption of the vanadium alkoxide. The laser powerrequired to induce this three-photon polymerization is comparableto what is required for inducing two-photon polymerization in materialsusing standard two-photon absorbers, most likely due to the high contentof vanadium in the final composite (up to 50% mole). [ABSTRACT FROM AUTHOR]

This paper reports on the conceptual design and fabrication of a complex shape, readily assembled micro check valve using the two-photon polymerization technique. The material used for the fabrication of the valve is a zirconium containing organic–inorganic hybrid photosensitive sol-gel known to exhibit negligible distortion during photopolymerization. A preliminary computational fluid dynamics study has been carried out in order to evaluate the flow performance of the valve under blood pressures exhibited in healthy human veins. The fabricated micro-valves exhibit good dimensional accuracy when compared to the CAD-created valve design and the capability of an internal moving component to perform its intended function. [ABSTRACT FROM AUTHOR]

Photochromic spiropyran molecules are utilized as additives for the development of polymer surfaces whose wetting characteristics can reversibly respond to irradiation with laser beams of properly chosen photon energy. The hydrophilicity is enhanced upon UV laser irradiation due to the photo-induced isomerization of the non-polar spiropyran molecules to the polar merocyanine. The situation is reversed upon green laser irradiation. Micropatterning of the photochromic-polymer films using soft lithography or photo-polymerization techniques affects their wettability towards a more hydrophobic or more hydrophilic behavior depending on the dimensions of the patterned features and on the hydrophilicity/hydrophobicity of the flat surface. The light-induced wettability variations of the structured surfaces are enhanced by up to a factor of three as compared to those on the flat surfaces. This enhancement is attributed to the photo-induced reversible volume changes to the imprinted gratings, which additionally contribute to the wettability changes due to the light-induced photochromic interconversions. [ABSTRACT FROM AUTHOR]

The need for control of the elastic properties of architected materials has been accentuated due to the advances in modelling and characterization. Among the plethora of unconventional mechanical responses, controlled anisotropy and auxeticity have been promulgated as a new avenue in bioengineering applications. This paper aims to delineate the mechanical performance of characteristic auxetic and anisotropic designs fabricated by multiphoton lithography. Through finite element analysis the distinct responses of representative topologies are conveyed. In addition, nanoindentation experiments observed in-situ through scanning electron microscopy enable the validation of the modeling and the observation of the anisotropic or auxetic phenomena. Our results herald how these categories of architected materials can be investigated at the microscale. [ABSTRACT FROM AUTHOR]

Laser-made 3D Auxetic Metamaterial Scaffolds for Tissue Engineering Applications B Front Cover b : In article number 2000238 by Anthi Ranella, Maria Farsari, and co-workers, multiphoton lithography is employed for the fabrication of 3D cell scaffolds with negative Poisson's ratio. It is shown that even though the photoresist SZ2080, is stiff, the scaffolds are elastic and cells penetrate them and proliferate in them, adapting the scaffold shape to suit their requirements. [Extracted from the article]

The authors demonstrate here a method for three-dimensional patterning of proteins and other biological molecules. The method employs femtosecond-laser-induced three-photon polymerization, a technique which enables the construction of arbitrary two- and three-dimensional structures of submicron resolution. Biotin is subsequently attached to the three-dimensional (3D) structures via UV-activated cross-linking. The integrity of the photolytically immobilized biotin is confirmed by detecting the binding of fluorescently labeled avidin via fluorescence microscopy and via a surface acoustic sensor technique. In all, the technique opens the way for the fabrication of structures with a wide range of biomaterials as well as studying their dynamics within complex 3D structures. [ABSTRACT FROM AUTHOR]

We demonstrate the enhancement of the wetting properties of smart photochromic surfaces by a specifically developed, gentle interferometric patterning employing green light. We realized photochromic gratings with 2.5–10.0 μm period by a blend consisting of a green-curable matrix and spiropyran molecules. The structured surfaces exhibit photocontrolled and reversible wettability, and enhanced hydrophilicity with respect to the native substrates. The dynamics of liquid spreading onto the gratings was also investigated, and the wetting behavior analyzed according to Wenzel’s [Ind. Eng. Chem. 28, 988 (1936)] model for rough surfaces. These results indicate switchable gratings as promising functional components for microfluidics and modulation, and green-light interferometry as a reliable lithographic method for patterning organics without degradation or photochemical reactions. [ABSTRACT FROM AUTHOR]

Multiphoton lithography (MPL), based on multiphoton polymerization (MPP), is a powerful technique for the fabrication of 3D structures used in tissue engineering and other biomedical applications, microoptics, nanophotonics, micro‐/nanomechanics, and micro‐/nanofluidics. MPL is based on the localized polymerization/cross‐linking of photosensitive materials induced by femtosecond laser pulses. The use of an appropriate photoinitiator (PI) is required to initiate the polymerization/cross‐linking process. However, several studies have demonstrated the cytotoxicity of the PIs and their derived free radicals. The photo‐cross‐linking of a pre‐synthesized photosensitive gelatin methacrylamide (GelMA) biopolymer using an initiator‐free MPP process is reported for the first time. This is achieved by employing a femtosecond laser operating in the visible range of the spectrum (520 nm). It is demonstrated that multiphoton absorption can cause the cleavage of the polymer double bonds and induce the cross‐linking process. GelMA‐based 3D structures accurately replicating the original computer‐aided design are fabricated, and their excellent biocompatibility is demonstrated in vitro using 3D cell culture experiments with NIH‐3T3 fibroblast cells. Three‐dimensional structures based on gelatin methacrylamide are fabricated by initiator‐free multiphoton polymerization using a femtosecond laser operating in the visible range. The elimination of the toxic photoinitiator and its derived free radicals renders the approach very attractive in 3D scaffold fabrication. [ABSTRACT FROM AUTHOR]

Multimode high-power laser diodes suffer from inefficient beam focusing, leading to a focal spot 10-100 times greater than the diffraction limit. This inevitably restricts their wider use in ‘direct-diode’ applications in materials processing and biomedical photonics. We report here a ‘super-focusing’ characteristic for laser diodes, where the exploitation of self-interference of modes enables a significant reduction of the focal spot size. This is achieved by employing a conical microlens fabricated on the tip of a multimode optical fibre using 3D laser nano-printing (also known as multi-photon lithography). When refracted by the conical surface, the modes of the fibre-coupled laser beam self-interfere and form an elongated narrow focus, usually referred to as a ‘needle’ beam. The multiphoton lithography technique allows the realisation of almost any optical element on a fibre tip, thus providing the most suitable interface for free-space applications of multimode fibre-delivered laser beams. In addition, we demonstrate the optical trapping of microscopic objects with a super-focused multimode laser diode beam thus rising new opportunities within the applications sector where lab-on-chip configurations can be exploited. Most importantly, the demonstrated super-focusing approach opens up new avenues for the ‘direct-diode’ applications in material processing and 3D printing, where both high power and tight focusing is required. [ABSTRACT FROM AUTHOR]