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The current protocols for biocompatibility assessment of biomaterials, based on histopathology, require the sacrifice of a huge number of laboratory animals with an unsustainable ethical burden and remarkable cost. Intravital microscopy techniques can be used to study implantation outcomes in real time though with limited capabilities of quantification in longitudinal studies, mainly restricted by the light penetration and the spatial resolution in deep tissues. We present the outline and first tests of a novel chip which aims to enable longitudinal studies of the reaction to the biomaterial implant. The chip is composed of a regular reference microstructure fabricated via two-photon polymerization in the SZ2080 resist. The geometrical design and the planar raster spacing largely determine the mechanical and spectroscopic features of the microstructures. The development, in-vitro characterization and in vivo validation of the Microatlas is performed in living chicken embryos by fluorescence microscopy 3 and 4 days after the implant; the quantification of cell infiltration inside the Microatlas demonstrates its potential as novel scaffold for tissue regeneration.

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.

Since the global energy demand increases annually, a great need is arising in energy-related technologies. Photocatalysis plays a major role in these technologies, as it exploits one of the renewable types of energy, solar energy. For this reason, there is a plethora of scientific investigations in the research field of photocatalysis. In particular, the variety of materials that could be employed to efficiently enhance the procedure, is extensively studied. One of the most widely used materials is titania (TiO 2 ) due to its efficiency in photocatalysis [1] , while maintaining and other notable properties such as non-toxicity, chemo-stability, enhanced electronic and optical characteristics.

Ultrafast laser 3D lithography based on non-linear light–matter interactions, widely known as multi-photon lithography (MPL), offers unrivaled precision rapid prototyping and flexible additive manufacturing options. 3D printing equipment based on MPL is already commercially available, yet there is still no comprehensive understanding of factors determining spatial resolution, accuracy, fabrication throughput, repeatability, and standardized metrology methods for the accurate characterization of the produced 3D objects and their functionalities. The photoexcitation mechanisms, spatial-control or photo-modified volumes, and the variety of processable materials are topics actively investigated. The complexity of the research field is underlined by a limited understanding and fragmented knowledge of light-excitation and material response. Research to date has only provided case-specific findings on photoexcitation, chemical modification, and material characterization of the experimental data. In this review, we aim to provide a consistent and comprehensive summary of the existing literature on photopolymerization mechanisms under highly confined spatial and temporal conditions, where, besides the excitation and cross-linking, parameters such as diffusion, temperature accumulation, and the finite amount of monomer molecules start to become of critical importance. Key parameters such as photoexcitation, polymerization kinetics, and the properties of the additively manufactured materials at the nanoscale in 3D are examined, whereas, the perspectives for future research and as well as emerging applications are outlined.

Ultrafast laser 3D lithography based on non-linear light-matter interactions, widely known as multi-photon lithography (MPL), offers unrivaled precision rapid prototyping and flexible additive manufacturing options. 3D printing equipment based on MPL are already commercially available, yet there is still no comprehensive understanding of factors determining spatial resolution, accuracy, fabrication throughput, repeatability, and standardized metrology methods for the accurate characterization of the produced 3D objects and their functionalities. The photoexcitation mechanisms, spatial-control or photo-modified volumes, and the variety of processable materials are topics actively investigated. The complexity of the research field is underlined by limited understanding and fragmented knowledge of light-excitation and material response. Research to date has only provided case-specific findings on photoexcitation, chemical modification, and material characterization of the experimental data. In this review, we aim to provide a consistent and comprehensive summary of the existing literature on photopolymerization mechanisms under highly confined spatial and temporal conditions, where, besides the excitation and cross-linking, parameters such as diffusion, temperature accumulation, and the finite amount of monomer molecules start to become of critical importance. Key parameters such as, photoexcitation, polymerization kinetics, and the properties of the additively manufactured materials at the nanoscale in 3D are examined, whereas, the perspectives for future research and as well as emerging applications are outlined.

The development of dynamically responsive 3D photonic elements, which is crucial for the design of active integrated photonic circuits, requires the incorporation of material systems with fast and tunable response. To this end, semiconductor quantum dots have been widely used to perform as the active material system to be integrated; nonetheless, multiple-step processing is usually required for the active functions to be preserved, thereby restricting functionality of integrated 3D quantum photonic elements mostly to the infrared. Here, we report a simple scheme for the realization of visible light active 3D photonic devices by combining direct laser writing with two-photon absorption and in situ synthesis of cadmium sulfide (CdS) nanoparticles. The novel active 3D printable hybrid material is synthesized by crosslinking precursors of CdS quantum dots into a photo-structurable organic–inorganic zirconium–silicon hybrid composite integrating functional properties of both high spatial resolution and high third-order nonlinearity into the photonic matrix. As a proof-of-demonstration for 3D printed active photonic devices, woodpile photonic crystals with an inlayer periodicity down to 500 nm are successfully fabricated showing clear photonic stop bands in the visible spectral region, while for the first time, evidence of an ultrafast dynamic response in the visible is also demonstrated.

We report for the first time on the redox multiphoton polymerization of an organic-inorganic composite material, in which one of the components, a vanadium metallo-organic complex, initiates the polymerization. The composite employs multiphoton absorption to self-generate radicals by photoinduced reduction of the metal species from vanadium (V) to vanadium (IV). We exploit this material for the fabrication of fully 3D structures by multiphoton polymerization with 200 nm resolution, employing a femtosecond laser operating at 800 nm, in the absence of a photoinitiator. Nonlinear absorption measurements indicate that the use of an 800 nm laser initiates the photopolymerization due to three-photon absorption of the vanadium alkoxide. The laser power required to induce this three-photon polymerization is comparable to what is required for inducing two-photon polymerization in materials using standard two-photon absorbers, most likely due to the high content of vanadium in the final composite (up to 50% mole).

In this work, we present our most recent results on the fabrication of 3D high-resolution woodpile photonic crystals containing an organic-inorganic silicon-zirconium (Si-Zr) composite and cadmium sulfide (CdS) quantum dots (QDs). The structures are fabricated by combining 3D Direct Laser Writing by two-photon absorption and in-situ synthesis of CdS nanoparticles inside the 3D photonic matrix. The CdS-Zr-Si composite material exhibits a high nonlinear refractive index value measured by means of Z-scan method. 3D woodpile photonic structures with varying inlayer periodicity from 600nm to 500nm show clear photonic stop bands in the wavelength region between 1000nm to 450nm.

We present our investigations into the direct laser writing of a novel germanium-containing hybrid sol–gel photosensitive material for optical applications at micro scale. We employ this material in the fabrication of photonic micro-structures, such as aspheric lenses and prisms; these are well-shaped and provided good optical performance. The material exhibits good transparency and structurability, and three-dimensional structures with sub-100 nm resolution are achieved. We demonstrate the suitability of the direct laser writing method for the rapid production of custom shaped microoptical components. Since germanium glasses are widely used in fiber optics, the combination of direct laser writing with this specially designed, functional material opens an interesting way in fabricating structures for controlling light flow.

Recent work in three-dimensional microstructuring of photosensitive materials by femtosecond lasers is reviewed. The applications of nonlinear and quenching phenomena allow one to overcome both surface absorption and the diffraction limit to produce 3D microstructures with sub-diffraction limit resolution. Potential applications in the emerging fields of photonics and microfluidics are discussed.

A novel organic-inorganic hybrid material is presented containing a quenching moiety for improving the resolution of Direct femtosecond Laser Writing by multi-photon polymerization. By exploiting the diffusion of the quencher molecule for confining radical diffusion in the scanned area, sub-100nm resolution is achieved. 3D woodpile structures with rod spacing of 400nm are successfully fabricated. We optically characterize these woodpiles structures and we show that they exhibit well-ordered diffraction patterns and stopgaps down to near-infrared wavelengths.

We present a new method for increasing the resolution of direct femtosecond laser writing by multiphoton polymerization, based on quencher diffusion. This method relies on the combination of a mobile quenching molecule with a slow laser scanning speed, allowing the diffusion of the quencher in the scanned area and the depletion of the multiphoton-generated radicals. The material we use is an organic-inorganic hybrid, while the quencher is a photopolymerizable amine-based monomer which is bound on the polymer backbone upon fabrication of the structures. We use this method to fabricate woodpile structures with a 400 nm intralayer period. This is comparable to the results produced by direct laser writing based on stimulated-emission-depletion microscopy, the method considered today as state-of-the-art in 3D structure fabrication. We optically characterize these woodpiles to show that they exhibit well-ordered diffraction patterns and stopgaps down to near-infrared wavelengths. Finally, we model the quencher diffusion, and we show that radical inhibition is responsible for the increased resolution.

We present our most recent work on Direct fs Laser Writing and its applications in Photonics, Metamaterials and Biomedicine.

We present our investigations on the fabrication of three-dimensional nanostructures by direct laser writing using organic-inorganic hybrid materials that (i) can be structured accurately to sub-100nm, (ii) contain quantum dots, and (iii) can be selectively covered with metal.

We present our most recent results on the fabrication of 3D high-resolution nanostructures containing Cadmium Sulfide (CdS) quantum dots (QDs) and exhibiting higher order diffraction patterns and stop-gaps at visible wavelengths. These are fabricated using direct laser writing (DLW) and novel, organic-inorganic hybrid materials.

This paper demonstrates the fabrication of 3D nanostructures by multiphoton polymerization using a material that does not contain a photoinitiator. The material used is a novel organic-inorganic hybrid material containing Vanadium and Silicon alkoxides and methacrylate polymerizable moieties. This hybrid material employs two-photon absorption to self-generate radicals, by a redox reaction of the metal species, which initiate the polymerization. This material is used to make high resolution 3D photonic crystals and other photonic nanostructures.