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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 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 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]

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]

Optics manufacturing technology is predicted to play a major role in the future production of integrated photonic circuits. One of the major drawbacks in the realization of photonic circuits is the damage of optical materials by intense laser pulses. Here, we report on the preparation of a series of organic–inorganic hybrid photoresists that exhibit enhanced laser-induced damage threshold. These photoresists showed to be candidates for the fabrication of micro-optical elements (MOEs) using three-dimensional multiphoton lithography. Moreover, they demonstrate pattern ability by nanoimprint lithography, making them suitable for future mass production of MOEs. [ABSTRACT FROM AUTHOR]

A micro-optical Fabry-Perot cavity fabricated by non-linear laser lithography on the endface of a standard telecom fiber is tested here as a microsensor for identifying oily liquids. The device operates within the 1550 nm spectral region, while the spectra recorded in reflection mode correlate to the refractive index of the oily liquids used, as well as, to the diffusion dynamics in the time domain of the oily samples inside the porous photo-polymerized sensing head. The operation of the microresonator sensing probe is explained by using a three-layer Fabry-Perot model and basic diffusion physics to estimate diffusivities for three series of refractive index matching oils with different chemical compositions that had been used in those experiments. The distinct spectro-temporal response of this sensing probe to the different oil samples is demonstrated and discussed. [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]

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]