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Spider silk has fascinated mankind for millennia, but it is only in recent decades that scientific research has begun to unravel all its characteristics and applications. The uniqueness of spider silk resides in its versatility, in which a combination of high strength and extensibility results in extraordinary toughness, superior to almost all natural and man-made fibers. Dragline silk consists of proteins with highly repetitive amino acid sequences, which have been correlated with specific secondary structures responsible for its physical properties. The native fiber also shows high cytocompatibility coupled with low immunogenicity, making it a promising natural biomaterial for numerous biomedical applications. Recently, novel technologies have enabled new insights into the material and biomedical properties of silk. Due to the increasing interest in spider silk, as well as the desire to produce synthetic alternatives, we present an update on the current knowledge of silk fibers produced by the spider genus Trichonephila.

The search for a suitable material to promote regeneration after long‐distance peripheral nerve defects turned the spotlight on spider silk. Nerve conduits enriched with native spider silk fibers as internal guiding structures previously demonstrated a regenerative outcome similar to autologous nerve grafts in animal studies. Nevertheless, spider silk is a natural material with associated limitations for clinical use. A promising alternative is the production of recombinant silk fibers that should mimic the outstanding properties of their native counterpart. However, in vitro data on the regenerative features that native silk fibers provide for cells involved in nerve regeneration are scarce. Thus, there is a lack of reference parameters to evaluate whether recombinant silk fiber candidates will be eligible for nerve repair in vivo. To gain insight into the regenerative effect of native spider silk, our study aims to define the behavioral response of primary Schwann cells (SCs), nerve‐associated fibroblasts (FBs), and dorsal root ganglion (DRG) neurons cultured on native dragline silk from the genus Nephila and on laminin coated dishes. The established multi‐color immunostaining panels together with confocal microscopy and live cell imaging enabled the analysis of cell identity, morphology, proliferation, and migration on both substrates in detail. Our findings demonstrated that native spider silk rivals laminin coating as it allowed attachment and proliferation and supported the characteristic behavior of all tested cell types. Axonal out‐growth of DRG neurons occurred along longitudinally aligned SCs that formed sustained bundled structures resembling Bungner bands present in regenerating nerves. The migration of SCs along the silk fibers achieved the reported distance of regenerating axons of about 1 mm per day, but lacked directionality. Furthermore, rFBs significantly reduced the velocity of rSCs in co‐cultures on silk fibers. In summary, this study (a) reveals features recombinant silk must possess and what modifications or combinations could be useful for enhanced nerve repair and (b) provides assays to evaluate the regenerative performance of silk fibers in vitro before being applied as internal guiding structure in nerve conduits in vivo.

Graphene oxide (GO) is a potential precursor for graphene. The electrochemical reduction of graphene oxide on electrode interfaces is a low-cost and green approach. The mechanism of the reduction, as well as the final structure of the reduced form have been the focus of the present study. In this work, the reduction of graphene oxide was investigated by in-situ spectroelectrochemistry. FTIR spectroscopy showed the generation and degeneration of oxygen containing functional groups and C=C bonds. The evaluation of these results was done via Multivariate Curve Resolution - Alternating Least Squares (MCR-ALS) to assign spectral features to various reactants. The possibility of controlling the composition and structure of reduced graphene oxide (rGO) is discussed.

Pulse laser ablation experiments at semiconductor-grade silicon 〈111〉 and SAE 304 stainless steel were performed with femto- and nanosecond pulse durations. Threshold fluences in dependence of beam radius (1.6–100 μm) and density of low-density defects (LDDs) have been determined for both materials and pulse durations. The experimental findings are supported by a recent quantitative model describing the strong dependence of the modification/ablation/damage threshold fluence on beam radius and pulse number. The importance of LDDs in the ablation mechanism has been confirmed.

Laser spot size and pulse number are two major parameters influencing the ablation of solids. The extended defect model describes the dependence of the threshold fluence on the basis of high and low density defects. This model was successfully applied to silicon and stainless steel. It is demonstrated that heat accumulation cannot describe the experimental results.

The formation mechanisms of microbumps and nanojets on films composed of single and double Cu/Ag layers deposited on a glass substrate and irradiated by a single 60 fs laser pulse are investigated experimentally and in atomistic simulations. The composition of the laser-modified bilayers is probed with the energy dispersive X-ray spectroscopy and used as a marker for processes responsible for the modification of the film morphology. For the bilayer with the top Ag layer facing the laser, the increase in fluence is found to result in a sequential appearance of a Ag microbump, the exposure of the Cu underlayer by removal of the Ag layer, a Cu microbump, and a frozen nanojet. The Cu on Ag bilayer exhibits a partial spallation of the top Cu film, followed by the generation of surface structures that mainly consist of Ag at higher fluences. The experimental observations are explained with atomistic simulations, which reveal that the stronger electron-phonon coupling of Cu results in the confinement of the deposited laser energy in the top Cu layer in the Cu on Ag case and channelling of the energy from the top Ag layer to the underlying Cu layer in the Ag on Cu case. This difference in the energy (re)distribution directly translates into differences in the morphology of the laser-modified bilayers. In all systems, the generation of microbumps and nanojets occurs in the molten state. It is driven by the dynamic relaxation of the laser-induced stresses and, at higher fluences, the release of vapor at the interface with the substrate. The resistance of the colder periphery of the laser spot to the ejection of spalled layers as well as the rapid solidification of the transient molten structures are largely defining the final shapes of the surface structures.

Short pulse laser irradiation has the ability to bring a material into a state of strong electronic, thermal, phase, and mechanical nonequilibrium and trigger a sequence of structural transformations leading to the generation of complex multiscale surface morphologies, unusual metastable phases, and microstructures that cannot be produced by any other means. In this article, we provide an overview of recent advancements and existing challenges in the understanding of the fundamental mechanisms of short pulse laser interaction with materials, including the material response to strong electronic excitation, ultrafast redistribution and partitioning of the deposited laser energy, the peculiarities of phase transformations occurring under conditions of strong superheating/undercooling, as well as laser-induced generation of crystal defects and modification of surface microstructure.

The successful reconstruction of supercritical peripheral nerve injuries remains a major challenge in modern medicine. Progress in tissue engineering has enabled the development of nerve guidance conduits as an alternative to autologous nerve transplantation and the enrichment of conduits with fibrous materials or hydrogels has shown great potential in bridging nerve defects. The application of the dragline silk of spider genus Nephila as a filament for nerve guidance conduits has led to promising results. However, the use of spider silk has been phenomenological so far and the reasons for its success are still not identified. This renders a targeted tuning of synthetic fibrous luminal fillings such as recombinant silk out of reach.In this work the existing research was extended and in addition to dragline, the cocoon silk of Nephila edulis, as well as the connecting and attaching silk of Avicularia avicularia were investigated. Scanning electron microscopy revealed a difference in size and morphology of the spider silks. However, in vitro experiments indicated that Schwann cells adhere to the four fibers, independent of these two attributes. Raman spectroscopy in native state and aqueous environment demonstrated similar secondary protein structures for dragline, cocoon, and connecting silk. In contrast, the attaching silk showed a significant lower conformation of β-sheets, crucial for the stiffness of the silk. This was in line with the in vitro experiments, where the flexible attaching silk fibers adhered to each other when placed in liquid. This resulted in their inability to guide Schwann cells, leading to the generation of cell agglomerations. This direct comparison demonstrated the crucial role of β-sheets conformation for the guidance properties of natural spider silk, providing essential insights into the necessary material properties for the integration of fibrous luminal fillings in nerve guidance conduits.

This work presents a systematic study of the significant role of the surface physicochemical alterations produced during the laser ablation of massive iron disks submerged in different solvents on the generation of colloidal iron nanoparticles. For that purpose, the laser ablation thresholds and the incubation coefficients for various pulse numbers per site and pulse energies have been measured under distilled water (DW) and ethanol (EtOH). After that, a complete physicochemical characterization of these targets indicated higher threshold fluence values for the ablation experiments conducted in EtOH than those performed in DW. The threshold fluence values decreased also with the decrease of the pulse overlap for both solvents, being it much more pronounced in EtOH. In addition, the related incubation coefficient showed that the incubation effect is lower for experiments conducted in DW. The characteristics of the synthesized nZVI particles were also a function of the solvent nature and the pulse overlap: laser ablation in DW leaded to iron oxide nanoparticles, whereas core-shell iron nanoparticles were obtained in EtOH. Moreover, high pulse overlap values lead to chemical alterations, resulting in a decrease of the composition homogeneity and a strong increase of the nanoparticle polydispersity.

The spot size dependence of pulse laser-induced ablation thresholds of solid materials cannot be satisfactory described by the two existing quantitative models based on defect densities and on heat accumulation. In the present study, the heat accumulation model was amended but still yielded results in contradiction to experimental observations. The existing defect model was extended to account for incubation where optically active high-density defects with a separation below the radiation wavelength are generated. The reduction of the threshold for large beam radii could be ascribed to the laser spot covering a finite number of optically active low-density defects (LDD) embedded in the matrix material. This new generic model combining the spot size and pulse number dependence of femtosecond pulse laser-induced ablation thresholds was demonstrated with high-impact polystyrene. The average distance of the optically active LDD obtained from the generic model could be confirmed by scanning electron microscopy.

Laser nano- and micromachining exhibits multiple technological applications particularly in cyber physical production systems, where the integrity of production processes has to be maintained (e.g. in the implementation of Industry 4.0). Key characteristics of laser processing, such as the ablation threshold was commonly related to the fundamental parameters (fluence, pulse number, and irradiated area) by empirical adaptation and optimization. The description of the pulse number dependence (incubation, laser-induced defects) and the irradiation area dependence (intrinsic defects) of the threshold fluence still resorts to phenomenological models. This deficit can be resolved by a combined description of pulse number and beam radius based on a model involving high density and low density defects in the solid material. This extended defect model can describe single and multiple nanosecond and femtosecond pulse ablation experiments on various technological materials such as polystyrene, monocrystalline silicon, and stainless steel. While this model allows a quantification of the laser-induced threshold fluence in dependence of pulse number (incubation) and irradiated area (beam radius), the physical mechanisms involved in the interaction between light and defects, be it intrinsic or laser-generated, are still marginally understood. Further experimental and theoretical effort in this direction is aiming at the provision of the deterministic understanding required in any field applying intense laser light with multiple pulses and various spot sizes, which is essential in e.g. laser cutting, drilling, marking, engraving, hardening, and welding.

A non-destructive, in-line, and low-cost focusing device based on an image sensor has been developed and demonstrated. It allows an in situ focus determination for a broad variety of laser types (e.g. cw and pulsed lasers). It provides stringent focusing conditions with high numerical apertures. This approach does not require sub-picosecond and/or auxiliary lasers, or high fluences above damage thresholds. Applications of this system include, but are not limited to the laser-illumination of micro-electrodes, pump-probe microscopy on thin films, and laser ablation of small samples without sufficient surface area for focus determination by ablation. An uncertainty of the focus position by an order of magnitude less than the respective Rayleigh length could be demonstrated.

Nowadays, multimodal diagnosis by combining several imaging techniques, such as mammography, magnetic resonance imaging and computed X-ray tomography is playing a leading role in the diagnosis of breast cancer. [1] However clinical application of this multimodal approach is still problematic due the lack of appropriate commercial contrast agents showing capabilities to distinguish between malignant tumours and benign abnormal masses. Hybrid nanoparticles, which contain both magnetic and radiopaque elements are a promising alternative for the generation of these multimodal contrast agents due to their unique characteristics, such as: high biocompatibility, contrast enhancement efficacy, cost effectiveness and colloidal stability in the physiological environment.[2] Unfortunately, conventional chemical procedures to synthesize multimodal nanoparticles in liquid media used in laboratory are not well standardized and cost-effective methods to produce large quantities of nanoparticles.[3]