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Architected materials are considered the state of the art of engineering ingenuity. Specifically, mechanical metamaterials have been accentuated due to their unconventional and augmented responses. They have been gingerly investigated under the context of ultralight-ultrastiff structures for aerospace applications, tailored buckling mechanisms for energy storage, soft robotics and controlled wave propagation and designed anisotropy for tissue engineering.Albeit the plethora of remarkable results promulgating this subject, the analysis of architected materials has many questions that need to be addressed. There is no rigorous explanation for the selection of specific 3D designs that have been thoroughly utilized in the literature (regarding the selection of specific design variables and cost functions). Consequently, in practice specific structures are repeatedly used, without any explanation whether further search of the design space could not provide a substantially improved result. Therefore, the lack of understanding of the design space and the inherent physical phenomena has not elucidated the tools to obtain a globally optimal design. Thus, tailoring mechanical metamaterials is extremely arduous and has led to an obstacle in the progress of this field.This thesis aims to provide an analysis for the design of architected materials by illuminating the physical mechanisms and how to model and optimize such problems. The structure of this thesis is comprised of two main themes. The first method aims to control the mechanical performance through interconnected beam members that enhance the densification of the structure and impede catastrophic failure. The second method is related to geometrical defects that dictate the localized failure and anisotropic behavior. Furthermore, the optimization of specific design examples will be presented, employing low computational power for large design spaces and demonstrate how such design problems can be addressed, setting the framework for the systematic design and characterization of architected materials.

Since the middle of the 20th century inorganic and polymer nanomaterials have been increasingly appearing in everyday life. Starting from the phenomenal discoveries of the Toyota Central Research team in the 1990s until today, nanomaterials are used as a reinforcement agent for polymer matrices improving their mechanical, thermal or chemical properties. Consequently, nanofillers led to the significant expansion of polymers applicability. However, it is of great importance to better understand the nature and mechanisms behind these phenomena. The aim of current thesis is focused on boehmite and boehmite-based materials with regard to its unique nature of intermolecular interactions. Unlike many other nanomaterials, boehmite particles are characterized by repelling each other. On the other hand, it shows high attraction with diverse materials including polymers. This provides good ground for the development of outstanding boehmite-based nanocomposites. In this work, the nature of interactions for boehmite-boehmite and boehmite-polymer was studied. A hypothesis in the thesis states that the size of the nanocrystallites, the distances between the γ-AlOOH layers in the boehmite, or/and its surface modification affect intermolecular interactions. To confirm this theory, a range of comprehensive techniques and methods has been applied. The first part of the research was focused on growth of boehmite nanocrystals large enough for targeted investigation. It is worth mentioning, that even though this material is nanocrystalline by structure, the synthesis of boehmite with the crystals larger than 50 nm is a tremendous challenge. Nevertheless, boehmite particles of about 200 nm in crystalline size (abbreviated ACNO) has been achieved in this work. To further characterize materials of focus Small- and Wide-angle X-ray Scattering (SAXS and WAXS) analysis, X-ray Photoelectron Spectroscopy (XPS), Electron Energy Loss Spectroscopy (EELS), Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM) and Raman Spectroscopy have been used. The particular attention was given to the studies of intermolecular interactions. For this purpose, an advanced Atomic Force Microscopy (AFM) method has been applied, for which custom-made AFM probe was developed. Geological boehmite, ACNO and commercial boehmite (HP14) with various surface modifications of the last were compared. The Hamaker constant for these materials was successfully determined and the plasmonic behavior of the boehmite was studied. Further studies were focused on boehmite-polymer interactions. State-of-the-art 3D microfabrication technique, such as Multiphoton Lithography (MPL), was used to prepare polymer and nanocomposites, based on ACNO boehmite and SZ2080 photoresist. Meanwhile investigating pristine photoresist, an interesting phenomenon of strong but fading adhesion of the polymer microstructures to the AFM tip was discovered. For this purpose, ageing experiments of 3D microstructure sample was performed by means of AFM, XPS and SEM. As a result, time-dependent behavior of SZ2080 was described. This study provides important information for the material science community using MPL printing technique. Nanocomposites based on SZ2080 photoresist and 2 wt% of different types of boehmite as nanofiller prepared by MPL technique, were designed with regard to abovementioned results on long-time behavior. SEM, Intermodulation AFM (ImAFM) and Nanoscale Thermal Analysis (NanoTA) were performed to study the effect of the nanomaterial on the change of topography, Young’s modulus, glass transition temperature, stiffness and energy dissipation. The nanocomposite exhibited different mechanical properties compared to the pure polymer and the nanofiller. Moreover, the inhibition phenomenon of boehmite nanoparticles embedment on photoresist side polymerization, during storage was observed. However, this aspect needs further investigation. This thesis is devoted to a comprehensive thorough study of the interactions between nanoparticles that repel each other, meanwhile attract to other materials. The findings of this thesis bring many answers to currently unexplored questions like estimating Hamaker constant of repulsive materials and the complexity of its nature. Based on the outcome of this work many engineering guidelines for the use of nanocomposites and their design can be gathered., Seit Mitte des 20. Jahrhunderts tauchen anorganische und polymere Nanomaterialien immer häufiger im täglichen Leben auf. Seit den phänomenalen Entdeckungen des Toyota Central Research Teams in den 1990er Jahren bis heute werden Nanomaterialien als Verstärkungsmittel für Polymermatrices verwendet, um deren mechanische, thermische oder chemische Eigenschaften zu verbessern. Folglich haben Nanofüllstoffe zu einer erheblichen Erweiterung der Anwendungsmöglichkeiten von Polymeren geführt. Es ist jedoch von großer Bedeutung, die Natur und die Mechanismen hinter diesen Phänomenen besser zu verstehen. Die vorliegende Arbeit befasst sich mit Böhmit und auf Böhmit basierenden Materialien im Hinblick auf die einzigartige Natur der intermolekularen Wechselwirkungen. Im Gegensatz zu vielen anderen Nanomaterialien zeichnen sich Böhmitpartikel dadurch aus, dass sie sich gegenseitig abstoßen. Auf der anderen Seite zeigt es eine hohe Anziehungskraft auf verschiedene Materialien, einschließlich Polymere. Dies bietet eine gute Grundlage für die Entwicklung hervorragender Nanokomposite auf Böhmitbasis. In dieser Arbeit wurde die Art der Wechselwirkungen von Böhmit-Böhmit und Böhmit-Polymer untersucht. Eine Hypothese in dieser Arbeit besagt, dass die Größe der Nanokristallite, die Abstände zwischen den γ-AlOOH-Schichten im Böhmit oder/und seine Oberflächenmodifikation die intermolekularen Wechselwirkungen beeinflussen. Um diese Theorie zu bestätigen, wurde eine Reihe umfassender Techniken und Methoden angewandt. Der erste Teil der Forschung konzentrierte sich auf das Wachstum von Böhmit-Nanokristallen, die groß genug für eine gezielte Untersuchung waren. Obwohl dieses Material von seiner Struktur her nanokristallin ist, stellt die Synthese von Böhmit mit Kristallen von mehr als 50 nm eine enorme Herausforderung dar. Dennoch wurden in dieser Arbeit Böhmitpartikel mit einer Kristallgröße von etwa 200 nm (abgekürzt ACNO) hergestellt. Zur weiteren Charakterisierung der Materialien wurden Klein- und Weitwinkel-Röntgenstreuungsanalysen (SAXS und WAXS), Röntgenphotoelektronenspektroskopie (XPS), Elektronenenergieverlustspektroskopie (EELS), Transmissionselektronenmikroskopie (TEM), Rasterelektronenmikroskopie (SEM) und Raman-Spektroskopie eingesetzt. Besonderes Augenmerk wurde auf die Untersuchung der intermolekularen Wechselwirkungen gelegt. Zu diesem Zweck wurde eine fortschrittliche Methode der Rasterkraftmikroskopie (AFM) angewandt, wobei eine maßgeschneiderte AFM-Sonde entwickelt wurde. Verglichen wurden geologischer Böhmit, ACNO und kommerzieller Böhmit (HP14) mit verschiedenen Oberflächenmodifikationen des letzteren. Die Hamaker-Konstante für diese Materialien wurde erfolgreich bestimmt und das plasmonische Verhalten des Böhmits wurde untersucht. Weitere Studien konzentrierten sich auf die Wechselwirkungen zwischen Böhmit und Polymer. Modernste 3D-Mikrofabrikationstechniken wie die Multiphotonenlithografie (MPL) wurden zur Herstellung von Polymer- und Nanokompositen auf der Grundlage von ACNO-Böhmit und SZ2080-Photoresist eingesetzt. Bei der Untersuchung von unbehandeltem Fotolack wurde das interessante Phänomen einer starken, aber nachlassenden Haftung der Polymermikrostrukturen an der AFM-Spitze entdeckt. Zu diesem Zweck wurden Alterungsexperimente an 3D-Mikrostrukturproben mit Hilfe von AFM, XPS und SEM durchgeführt. Als Ergebnis wurde das zeitabhängige Verhalten von SZ2080 beschrieben. Diese Studie liefert wichtige Informationen für die Materialwissenschaft, die die MPL-Drucktechnik einsetzt. Nanokomposite auf der Basis von SZ2080-Photoresist und 2 Gew.-% verschiedener Böhmit-Typen als Nano-Füllstoff, die mit der MPL-Technik hergestellt wurden, wurden im Hinblick auf die oben genannten Ergebnisse zum Langzeitverhalten entwickelt. SEM, Intermodulations-AFM (ImAFM) und thermische Analyse im Nanomaßstab (NanoTA) wurden durchgeführt, um die Auswirkungen des Nanomaterials auf die Veränderung der Topografie, des Elastizitätsmoduls, der Glasübergangstemperatur, der Steifigkeit und der Energiedissipation zu untersuchen. Das Nanokomposit wies im Vergleich zum reinen Polymer und zum Nanofüllstoff unterschiedliche mechanische Eigenschaften auf. Außerdem wurde das Phänomen der Einbettung von Böhmit-Nanopartikeln in die Polymerisation auf der Fotolackseite während der Lagerung beobachtet. Dieser Aspekt muss jedoch weiter untersucht werden. Diese Arbeit widmet sich einer umfassenden Untersuchung der Wechselwirkungen zwischen Nanopartikeln, die sich gegenseitig abstoßen, während sie sich zu anderen Materialien anziehen. Die Ergebnisse dieser Arbeit liefern viele Antworten auf bisher unerforschte Fragen wie die Abschätzung der Hamaker-Konstante von abstoßenden Materialien und die Komplexität ihrer Natur. Auf der Grundlage der Ergebnisse dieser Arbeit können viele technische Richtlinien für die Verwendung von Nanokompositen und deren Design erstellt werden.

Fully metallic micrometer-scale 3D architectures can be fabricated via a hybrid additive methodology combining multi-photon lithography with electrochemical deposition of metals. The methodology – referred to as two-photon templated electrodeposition (2PTE) – has significant design freedom that enables the creation of complicated, traditionally difficult-to-make, high aspect ratio metallic structures such as microneedles. These complicated geometries, combined with their fully metallic nature, can enable precision surgical applications such as inner ear drug delivery or fluid sampling. However, the process involves electrochemical deposition of metals into complicated 3D lithography patterns thicker than 500 μm. This causes potential and chemical gradients to develop within the 3D template, creating limitations to what can be designed. These limitations can be explored, understood, and overcome via numerical modeling. Herein we introduce a numerical model as a design tool that can predict growth for manufacturing complicated 3D metallic geometries. The model is successful in predicting the geometric result of 2PTE, and enables extraction of insights about geometric constraints through exploration of its mechanics.

High-resolution imaging is essential for analysis of the steps and way stations of cargo transport in in vitro models of the endothelium. In this study, we demonstrate a microfluidic system consisting of two channels horizontally separated by a cell-growth-promoting membrane. Its design allows for high-resolution (down to single-molecule level) imaging using a high numerical aperture objective with a short working distance. To reduce optical aberrations and enable single-molecule-sensitive imaging, an observation window was constructed in the membrane via laser cutting with subsequent structuring using 3D multiphoton lithography for improved cell growth. The upper channel was loaded with endothelial cells under flow conditions, which showed polarization and junction formation. A coculture of human vascular endothelial cells with pericytes was developed that mimics the blood–brain barrier. Finally, this dual channel microfluidics system enabled 3D localization microscopy of the cytoskeleton and 3D single-molecule-sensitive tracing of lipoprotein particles.

We design and fabricate ultra-broadband achromatic metalenses operating from the visible into the short-wave infrared, 450–1700 nm, with diffraction-limited performance. A hybrid 3D architecture, which combines nanoholes with a phase plate, allows realization in low refractive index materials. As a result, two-photon lithography can be used for prototyping while molding can be used for mass production. Experimentally, a 0.27 numerical aperture (NA) metalens exhibits 60% average focusing efficiency and 6% maximum focal length error over the entire bandwidth. In addition, a 200 μm diameter, 0.04 NA metalens was used to demonstrate achromatic imaging over the same broad spectral range. These results show that 3D metalens architectures yield excellent performance even using low-refractive index materials, and that two-photon lithography can produce metalenses operating at visible wavelengths.

Nanofabrication techniques that can generate large and complex 3D structures with nanoscale features are becoming increasingly important in the fields of biomedicine, micro-optics, and microfluidics. Direct laser writing via two-photon polymerization (DLW-TPP) is one such technique that relies on nonlinear absorption of light to form nanoscale 3D features. Although DLW-TPP provides the required nanoscale resolution, its built height is often limited to less than a millimetre. This height limitation is driven by the need to tightly focus the laser beam at arbitrary depths within the photopolymer. This requirement necessitates matching the photopolymer's refractive index to specific values but the required techniques have not been disseminated widely in the open scientific literature. To address this knowledge gap, we test two universal, different approaches to generate refractive index-matched polymeric and preceramic resins and demonstrate their performance by printing of fine submicron features in 3D structures as tall as 2.5 mm. Specifically, we achieve index-matching by mixing commercially-available resins or covalent modification of functional monomers. This work investigates the relationship of voxel shape to RI mismatch, and presents tuning of RI through mixing and covalent modification to a nonconventional material system of preceramic resin which has never been demonstrated before. We demonstrate the material flexibility by generating 3D silicon oxycarbide structures from preceramic resists while simultaneously eliminating the part-height limitation of conventional DLW-TPP.

In recent years, flow photolithography (FL) has emerged as a powerful synthetic tool for the creation of barcoded microparticles with complex morphologies and chemical compositions which have been shown to be useful in a range of multiplexed bioassay applications. More specifically, FL has been highly successful in producing micron-sized, encoded particles of bespoke shape, size, and color. That said, to date, FL has been restricted to generating barcoded microparticles and has lacked the ability to produce hybrid fibers which are structurally and spectrally encoded. To this end, we herein present a method that combines a continuous flow microfluidic system with two-photon polymerization (2PP) to fabricate microscale-encoded fibers and Janus strips in a high-throughput manner. Specifically, two co-flow liquid streams containing a monomer and initiator are introduced through a Y-shape channel to form a stable interface in the center of a microfluidic channel. The flow containing the (fluorescently labeled) monomer is then patterned by scanning the voxel of the 2PP laser across the interface to selectively polymerize different regions of the forming fiber/particle. Such a process allows for rapid spectral encoding at the single fiber level, with the resulting structurally coded fibers having obvious application in the fields of security identification and anticounterfeiting.

Many surfaces in nature have interesting topographies that lead to properties that may be desirable for engineering applications, such as superhydrophobicity (lotus leaf), high adhesion (frog toes), and drag reduction (shark skin). Although simple replication processes via polydimethylsiloxane molding have been used to replicate these topographies, they cannot be used to modify or combine these topographies for added functionality. This paper presents a novel method to digitize an arbitrary surface, either from nature or manmade, replicate it, modify it, and print it. A banana skin, an eastern wahoo leaf, and a coin were digitized using a 3D laser scanning confocal microscope and modified with arbitrary additional textures. The digitized surfaces were then printed using a UV-sensitive polymer based on two-photon polymerization. The printed surfaces replicate the original surfaces with submicron accuracy; and additional textures were added to illustrate the ability to modify the surface topography. This method enables novel surface topographies to be created that cannot be found in nature.

Additive manufacturing at small scales enables advances in micro- and nanoelectromechanical systems, micro-optics, and medical devices. Materials that lend themselves to AM at the nanoscale, especially for optical applications, are limited. State-of-the-art AM processes for high-refractive-index materials typically suffer from high porosity and poor repeatability and require complex experimental procedures. We developed an AM process to fabricate complex 3D architectures out of fully dense titanium dioxide (TiO₂) with a refractive index of 2.3 and nanosized critical dimensions. Transmission electron microscopy (TEM) analysis proves this material to be rutile phase of nanocrystalline TiO₂, with an average grain size of 110 nm and

Two-photon lithography (TPL) is a photopolymerization-based additive manufacturing technique that enables fabrication of millimeter scale complex three-dimensional (3D) structures with submicron features. Despite this unique capability, TPL has experienced limited industrial adoption due to its low throughput. The recently developed parallel projection technique, called femtosecond projection TPL (FP-TPL), is a promising approach to scale up this process as it increases the throughput up to three orders of magnitude. However, it requires tuning of process parameters, including photopolymer material properties, to minimize over-polymerization-based defects. Here, we show how a modification of the optical projection strategy can be used to control these over-polymerization defects without tuning the photopolymer composition. Through optical modeling of the projection technique, we show that these defects can be minimized by altering the density of the projected mask. In addition, the aspect ratio of the submicron features can by reduced from more than 2 to 1.2. Thus, this optimal projection strategy transforms FP-TPL into a more robust process suitable for high-throughput high-quality 3D printing of micro and nanoscale structures.

Understanding the mechanisms underlying cell-surface interaction is of fundamental importance for the rational design of scaffolds aiming at tissue engineering, tissue repair and neural regeneration applications. Here, we examined patterns of neuroblastoma cells cultured in three-dimensional polymeric scaffolds obtained by two-photon lithography. Because of the intrinsic resolution of the technique, the micrometric cylinders composing the scaffold have a lateral step size of ~200 nm, a surface roughness of around 20 nm, and large values of fractal dimension approaching 2.7. We found that cells in the scaffold assemble into separate groups with many elements per group. After cell wiring, we found that resulting networks exhibit high clustering, small path lengths, and small-world characteristics. These values of the topological characteristics of the network can potentially enhance the quality, quantity and density of information transported in the network compared to equivalent random graphs of the same size. This is one of the first direct observations of cells developing into 3D small-world networks in an artificial matrix.

Two-photon direct laser writing (TP-DLW) is widely used in stereolithographic processes for realizing sophisticated micro- and nanoscale structures with application in fluidics, photonics, and biomedical devices. In this chapter, it is detailed how leveraging on metal-dielectric metastructures with peculiar optical functionalities is possible to enhance the performance of a generic TP-DLW device, thus enabling the fabrication of all-dielectric nanostructures with hyper-resolution in height ($15\:nm$) and width as small as $150\:nm$. The results open new frontiers toward the realization of all-dielectric ultraflat optical elements in a noticeably shorter time than standard time-consuming electron and deep-UV lithography processes.

Combining an advanced additive manufacturing technique, the Two-Photon Direct Laser Writing (TP-DLW), with the peculiar electro-optical properties of Quantum Dots (QDs) allows the creation of hybrid metastructures consisting in 3D photo-luminescent objects featuring sub-millimetric details. The study of the the interaction between the QDs and the UV-sensitive photo-resist during the TP-DLW allows the fine tuning of the emitted photo-luminescence. During the polymerization, the cross-linking of the monomers expels the majority of QDs from the irradiated volume, but they get excited and trigger a surrounding thermal polymerization, which changes the structure resolution. Here, the various steps of the TP-DLW procedures of such hybrid systems are illustrated in detail. The study defines the best conditions to modulate the QDs density in the created nanostructures to be integrated in optical devices, almost down to the single QDs. Moreover, the combined use of TP-DLW and single photon lithography introduces a further degree of freedom in the local QDs density control, allowing for the fabrication of even more complex object, such as the already mentioned hybrid metastructures. As a possible application of this technique, anti-counterfeiting is discussed with the fabrication of a 3D fluorescent design hidden in a polymeric microstructure. The rapidity of the process makes it suitable for industrial applications.

Additive manufacturing – specifically 3D laser lithography – has become a powerful technology for the fabrication of 3D objects with sub-micrometric resolution. This technique has already been applied in a broad range of fields, including metamaterials, biomedicine, and optics. However, there is a growing interest in the incorporation of new features or functionalities in the printed structures that can open up new opportunities in the field.1,2 The lecture will present our latest advances in the design of functional polymer based photoresists for 3D laser lithography. In particular, a new class of on-demand cleavable materials will be introduced that can be removed after being printed (subtractive manufacturing).3 Futhermore, new photoresists based on stimuli-responsive materials for the preparation of dynamic and programable microstructures will be presented. We believe that these new materials will have significant impact on future applications, where the advantages of high resolution additive and response on-demand can be combined. [1] C. A. Spiegel, M. Hippler, A. Munschinger, M. Bastmeyer, C. Barner-Kowollik, M. Wegener, E. Blasco. Adv Funct Mater, 2020, 30, 1907615. [2] C. Barner-Kowollik, M. Bastmeyer, E. Blasco, G. Delaittre, P. Mueller, B. Richter, M. Wegener. Angew Chem Int Ed, 56, 15828 (2017). [3] R. Batchelor, T. Messer, M. Hippler, M. Wegener, C. Barner-Kowollik, E. Blasco. Adv Mater, 31, 1904085 (2019).

The major bottleneck in fabrication of engineered 3D nanostructures is the choice of materials. Adding functionality to these nanostructures is a daunting task. In order to mitigate these issues, we report a two-photon patternable all carbon material system which can be used to fabricate fluorescent 3D micro/nanostructures using two-photon lithography, with subwavelength resolution. The synthesized material system eliminates the need to use conventional two-photon absorbing materials such as two-photon dyes or two-photon initiators. We have used two different trifunctional acrylate monomers and carbon dots, synthesized hydrothermally from a polyphenolic precursor, to formulate a two-photon processable resin. Upon two-photon excitation, photogenerated electrons in the excited states of the carbon dots facilitate the free radical formation at the surface of the carbon dots. These radicals, upon interaction with vinyl moieties, enable cross-linking of acrylate monomers. Free-radical induced two-photon polymerization of acrylate monomers without any conventional proprietary two-photon absorbing materials was accomplished at an ultrafine subwavelength resolution of 250 nm using 800 nm laser excitation. The effect of critical parameters such as average laser power, carbon dot concentration, and radiation exposure were determined for the fabrication of one-, two-, and three-dimensional functional nanostructures, applicable in a range of domains where fluorescence and toxicity are of the utmost importance. A fabrication speed as high as 100 mm/s was achieved. The ability to fabricate functional 3D micro-/nanostructures is anticipated to instigate a paradigm shift in various areas such as metamaterials, energy storage, drug delivery, and optoelectronics to name a few.

Multi-material 3D printing has attracted much attention due to its ability to produce functional 3D structures. We have developed several types of multi-material micro stereolithography systems including multi-tank type and single cylinder type. Recently, a multi-material micro stereolithography system based on single-photon polymerization using multiple droplets was also developed. In the multi-material micro stereolithography system, several types of photocurable resins are stored on a palette that is moved by a translation stage. Heterogeneous 3D microstructures are formed by accumulating each layer while exchanging the resins. In this system, two cleaning tanks are installed to prevent contamination of resin. Additionally, to prevent inclusion of air bubbles into the 3D-printed parts, the platform supporting the 3D-printed part was moved in horizontal plane. As a result, air bubbles were successfully pushed out of the fabrication area. Using several types of photocurable resins with different colors, multicolor 3D microstructures such as cubes and lattices were fabricated. By adjusting the number of accumulated layers, the color of the 3D-printed structure can be controlled. These multi-material micro stereolithography systems will be useful for producing functional microdevices including microfluidic elements, micromachines and scaffolds.

Interference lithography is a promising method for fabricating large-area, defect-free three-dimensional photonic crystal structures which can be used for facilitating the realization of photonic devices with a fast processing time. Although they can be used in waveguides, resonators, and detectors, their repeated regular array patterns can only be used for limited applications. In this study, we demonstrate a method for fabricating large-area photonic crystal structures with controlled defects by combining interference lithography and two-photon lithography using a light-curable resin. By combining regular array structures and controlled patterns, monotonous but large-area regular structures can be obtained. Furthermore, the patterned structures have considerable potential for use in various applications, such as solar cells, sensors, photodetectors, micro-/nano-electronics, and cell growth.

The paper describes the possibilities of additive manufacturing with multiphoton lithography. The basis of this technology is that a laser beam (with a certain wavelength) is fired into the mixture of a monomer and a photo-initiator. When the energy of the laser is high enough, the latter acts as a catalyser for the polymerization of the monomer compound. This study focuses on the influences of certain parameters of the multiphoton lithography process. One of the important aspects is the choice of the solvent for the post processing. In sequence to the solvent problem, the influence of the layer height is examined. Furthermore the limits and possibilities of the setup in use are investigated. As an example the differences in fabrication with the laser firing with "constant frequency" and "constant density" were subject of this investigation. The second goal of the study was to compare three different structures consisting of periodically repeating elements, scaled in size and number of elements per side.

Multiphoton lithography, based on multiphoton polymerization, is a powerful technique for the fabrication of complex three-dimensional (3D) structures. Herein, we report on the photostructuring of novel biopolymer-based hybrid hydrogels, comprising gelatin methacrylamide and a water-soluble chitosan derivative, via multiphoton polymerization. The nontoxic, Food and Drug Administration-approved, biocompatible photosensitizer eosin Y was exploited as the sole photoinitiator, without the coinitiators and/or comonomer that are commonly used, allowing for further expansion of the available wavelengths up to 800 nm. Importantly, the obtained hybrid material exhibits excellent biocompatibility, evidenced by the increased proliferation of dental pulp stem cells, compared with the individual components and the polystyrene control, after 7 days in culture. Additionally, the 3D hybrid scaffolds promote the matrix mineralization, following their functionalization with bone morphogenetic protein 2. These tailor-made synthetic, biocompatible materials pave the way for further opportunities in 3D scaffold fabrication, including in situ and in vivo biofabrication.

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.

Two-photon lithography allows writing of arbitrary nanoarchitectures in photopolymers. This design flexibility opens almost limitless possibilities for biological studies, but the acrylate-based polymers frequently used do not allow for adhesion and growth of some types of cells. Indeed, we found that lithographically defined structures made from OrmoComp do not support E18 murine cortical neurons. We reacted OrmoComp structures with several diamines, thereby rendering the surfaces directly permissive for neuron attachment and growth by presenting a surface coating similar to the traditional cell biology coating achieved with poly-d-lysine (PDL) and laminin. However, in contrast to PDL-laminin coatings that cover the entire surface, the amine-terminated OrmoComp structures are orthogonally modified in deference to the surrounding glass or plastic substrate, adding yet another design element for advanced biological studies.

Cells sense and respond to the physical nature of their microenvironment by mechanically probing their surroundings via cytoskeletal contractions. The material response to these stresses can be measured via traction force microscopy (TFM). Traditional TFM platforms present several limitations including variable spatial resolution, difficulty in attaining the full three-dimensional (3D) deformation/stress profile, and the requirement to remove or relax the cells being measured to determine the zero-stress state. To overcome these limitations, we developed a two-photon, photochemical coupling approach to fabricate a new TFM platform that provides high-resolution control over the 3D placement of fluorescent fiducial markers for facile measurement of cell-generated shear and normal components of traction forces. The highly controlled placement of the 3D marker array provides a built-in, zero stress state eliminating the need to perturb the cells being measured while also providing increased throughput. Using this platform, we discovered that the magnitude of cell-generated shear and normal force components are linked both spatially and temporally. The facile nature and increased throughput of measuring cell-generated forces afforded by this new platform will be useful to the mechanotransduction community and others.

In this study, we demonstrated a novel strategy for fabricating deformation-resistant nano-textured surfaces. Ordered arrays of IP-DIP photoresist nanodots of various diameters were first fabricated using two-photon lithography. IP-DIP/Al2O3 core-shell nanostructures (CSNs) were then formed by conformally coating the nanodots with Al2O3 of different thicknesses via atomic layer deposition (ALD). The CSNs showed 85% lower coefficients of friction than the bare IP-DIP nanodots and exhibited minimal nanostructure deformation at contact pressures greater than 20 GPa. The IP-DIP/Al2O3 CSNs also have lower adhesion forces than the bare IP-DIP nanodots. The excellent deformation resistance and superior tribological properties of these CSNs demonstrate that the combination of two-photon lithography and ALD is a very promising solution to tribological issues in miniaturized systems.

This paper addresses a nanoengineering approach to create a fully three-dimensional (3D) network of living cells, providing an advanced solution to in vitro studies on either neuronal networks or artificial organs. The concept of our work relies on stackable scaffolds composed of microcontainers designed and dimensioned to favor the geometrically constrained growth of cells. The container geometry allows cells to communicate in the culture medium and freely grow their projections to form a 3D arrangement of living cells. Scaffolds are fabricated using two-photon polymerization of IP-L 780 photoresist and are coated with collagen. They are stacked by mechanical micromanipulation. Technical details of the proposed nanofabrication scheme and assembly of the modular culture environment are explained. Preliminary in vitro results using PC12 cells have shown that this structure provides a good basis for healthy cell growth for at least 16 days. Our approach is envisioned to provide tailor-made solutions of future 3D cell assemblies for potential applications in drug screening or creating artificial organs.