[Show abstract][Hide abstract] ABSTRACT: Spherical silicon nanoparticles with the sizes of 100–200 nm exhibit strong electric and magnetic dipole responses in the visible spectral range due to Mie resonances. At the resonance conditions, electromagnetic energy is accumulated inside Si nanoparticles, which can be used for the realization of efficient nanoantennas, nanolasers, and novel metamaterials. In this paper, modification of optical properties of Si nanoparticles by metal nanoinclusions, randomly distributed inside them, is theoretically investigated. The method is based on the recently developed, so-called, decomposed discrete dipole approximation (DDDA) allowing multipole analysis of light scattering by arbitrary shaped inhomogeneous nanoparticles. Particularly, the influence of metal nanoinclusions, their concentration and distribution, on the excitation of magnetic and electric dipole modes in Si nanoparticles is studied.
[Show abstract][Hide abstract] ABSTRACT: Calcium phosphates, functionalized with nano-sized metal particles, are a promising material class for the treatment of bone defects. However, a sintering process is required in principle to achieve sufficient strength of calcium phosphate scaffolds. In this work laser-generated nano-sized silver, gold and platinum particles were adsorbed on micro-sized β-tricalcium phosphate particles and further heat treated at temperatures between 600 and 1200 °C. Gold and platinum nanoparticles underwent exponential growth starting at about 600 °C, while sintering of β-tricalcium phosphate started at 800 °C. We hypothesise that this phenomenon is caused by a heat-induced evaporation and growth process where the decrease of the particle number is directly correlated with the size increase. The silver nanoparticles on the other hand formed a new phase with the calcium phosphate (AgCa10(PO4)7) during the heat treatments and could not be observed within the ceramic scaffold anymore. Addressing the lack of information in nanoparticle-combined calcium phosphate scaffolds, this study contributes to the further modification of bone replacement materials with biologically relevant functions and molecules.
[Show abstract][Hide abstract] ABSTRACT: Aim: In this study, the suitability of a mixture containing riboflavin (vitamin B2) and triethanolamine (TEOHA) as a novel biocompatible photoinitiator for two-photon polymerization (2PP) processing was investigated. Materials & methods: Polyethylene glycol diacrylate was crosslinked using Irgacure(®) 369, Irgacure 2959 or a riboflavin-TEOHA mixture; biocompatibility of the photopolymer extract solutions was subsequently assessed via endothelial cell proliferation assay, endothelial cell viability assay and single-cell gel electrophoresis (comet) assay. Use of a riboflavin-TEOHA mixture as a photoinitiator for 2PP processing of a tissue engineering scaffold and subsequent seeding of this scaffold with GM-7373 bovine aortic endothelial cells was also demonstrated. Results: The riboflavin-TEOHA mixture was found to produce much more biocompatible scaffolds than those produced with Irgacure 369 or Irgacure 2959. Conclusion: The results suggest that riboflavin is a promising component of photoinitiators for 2PP fabrication of tissue engineering scaffolds and other medically relevant structures (e.g., biomicroelectromechanical systems).
Regenerative Medicine 11/2013; 8(6):725-38. · 3.87 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The unique optical properties of nanoparticles are highly sensitive in respect to particle shapes, sizes, and localization on a sample. This demands for a fully controlled fabrication process. The use of femtosecond laser pulses to generate and transfer nanoparticles from a bulk target towards a collector substrate is a promising approach. This process allows a controlled fabrication of spherical nanoparticles with a very smooth surface. Several process parameters can be varied to achieve the desired nanoparticle characteristics. In this paper, the influence of two of these parameters, i.e. the applied pulse energy and the laser beam shape, on the generation of Si nanoparticles from a bulk Si target are studied in detail. By changing the laser intensity distribution on the target surface one can influence the dynamics of molten material inducing its flow to the edges or to the center of the focal spot. Due to this dynamics of molten material, a single femtosecond laser pulse with a Gaussian beam shape generates multiple spherical nanoparticles from a bulk Si target. The statistical properties of this process, with respect to number of generated nanoparticles and laser pulse energy are investigated. We demonstrate for the first time that a ring-shaped intensity distribution on the target surface results in the generation of a single silicon nanoparticle with a controllable size. Furthermore, the generated silicon nanoparticles presented in this paper show strong electric and magnetic dipole resonances in the visible and near-infrared spectral range. Theoretical simulations as well as optical scattering measurements of single silicon nanoparticles are discussed and compared.
[Show abstract][Hide abstract] ABSTRACT: In industrialized countries glaucoma is one of the most common causes that leads to blindness. It is also the most common cause of irreversible blindness worldwide. In addition to local treatment of intraocular pressure and filtering glaucoma surgery, alloplastic implants are increasingly being used in glaucoma therapy. As long-term results published in the literature of commonly used implants are unsatisfactory, it seems useful to search for new concepts. In order to avoid the well-known short-term and long-term postoperative complications a pressure-controlled microstent with antiproliferative surface modifications was developed. Additionally, the functionality of such a microstent should be investigated using an animal glaucoma model. This paper describes the concept of a microstent which drains aquous humour from the anterior chamber into the suprachoroidal space. In addition, the glaucoma models described in the literature are discussed. Unfortunately, none of the methods could be reproduced permanently. First results show a correct implantation of a coated microstent with valve where the anti-proliferative effect could be demonstrated histologically. The promising results should lead to further investigations and the final goal will be the testing of the stent in the human eye.
[Show abstract][Hide abstract] ABSTRACT: The spatiotemporal evolution of a SPP wave packet with femtosecond duration is experimentally investigated in two different plasmonic focusing structures. A two-dimensional reconstruction of the plasmonic field in space and time is possible by the numerical analysis of interferometric time-resolved photoemission electron microscopy data. We show that the time-integrated and time-resolved view onto the wave packet dynamics allow one to characterize and compare the capabilities of two-dimensional components for use in plasmonic devices operating with ultrafast pulses.
[Show abstract][Hide abstract] ABSTRACT: Computer assisted biofabrication of fully functional living tissue for regenerative medicine involves generation of complex three-dimensional constructs consisting of living cells and biomaterials. Laser BioPrinting (LaBP) based on laser-induced forward-transfer provides unique possibilities for the deposition of different living cells and biomaterials in a well-defined 3D structure. LaBP can be applied to generate scaffold-free 3D cell systems through a layer-by-layer technique by combining cell solutions with materials that are able to form stable gels. Also, it is used to precisely populate scaffolds with different cells and different cell densities. It was proven that printed cells are not affected by the laser printing procedure and that a differentiation of printed stem cells is not induced. Thus, LaBP is demonstrated as a promising tool for the ex vivo generation of tissue replacements.
Current pharmaceutical biotechnology 01/2013; 14(1):91-7. · 3.40 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Nanoprocessing of materials using ultrashort laser pulses involves a number of concurrent fundamental physical processes. Due to different time and spatial scales of activation, however, these processes are difficult to study within the frames of a single computational model on one hand, and yet not possible to isolate in the experimental analysis on the other hand. In their detailed investigation, the transient character of the nonequilibrium states of matter induced with a short laser pulse hampers the applicability of continuum approaches, but classical molecular dynamics simulations are usually limited in the system sizes. In this work, a molecular dynamics based model coupled to a continuum description of the photo-excited free carrier’s dynamics and implemented in parallel algorithm is extended to the scale directly accessible in the experiment. This allows for the first time a direct comparison to experimental data. The essential mechanisms responsible for the short laser pulse surface nanostructuring are analyzed in the complex dynamics of competing processes simultaneously involved into the nanostructures generation process. The modeling and experiment show a very good agreement and predict a new opportunity for fabrication of nanoparticle structures and the surface subpatterning.
Applied Physics A 01/2013; 111(3). · 1.69 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We apply femtosecond laser direct writing in photopolymers for manufacturing of conical microlenses and closely packed arrays thereof. We demonstrate the fabrication of high optical quality axicons of 15 µm in radius, having 150°, 160°, and 170° cone angles. Their optical properties and performance are modeled using the finite-difference time-domain method and compared with experimentally measured data. Additionally, optimization of the laser direct writing parameters regarding these types of micro-objects is presented. Possible applications of closely packed arrays of axicon microlenses are discussed, having potential attractivity in the fields of modern microscopy, light-based material processing, particle manipulation in microfluidic, and optofluidic applications.
[Show abstract][Hide abstract] ABSTRACT: In this paper, the authors report on the formation of nanobumps and nanojets on thin gold films, induced by single fs-laser pulse irradiation. Experimental results on the structure size and shape depending on the pulse energy and the pulse duration are presented. For the first time, the process of short laser pulse nanostructuring on thin metal films was modeled by molecular dynamic simulations on the scale directly accessible in the experiments. Additionally, pump-probe experiments were performed for in-situ visualization of the structure formation.
Journal of Laser Applications 07/2012; 24(4). · 0.57 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Superhydrophobic titanium surfaces fabricated by femtosecond laser ablation to mimic the structure of lotus leaves were assessed for their ability to retain coccoid bacteria. Staphylococcus aureus CIP 65.8T, S. aureus ATCC 25923, S. epidermidis ATCC 14990T and Planococcus maritimus KMM 3738 were retained by the surface, to varying degrees. However, each strain was found to preferentially attach to the crevices located between the microscale surface features. The upper regions of the microscale features remained essentially cell-free. It was hypothesised that air entrapped by the topographical features inhibited contact between the cells and the titanium substratum. Synchrotron SAXS revealed that even after immersion for 50 min, nano-sized air bubbles covered 45% of the titanium surface. After 1 h the number of cells of S. aureus CIP 65.8T attached to the lotus-like titanium increased to 1.27×10(5) mm(-2), coinciding with the replacement of trapped air by the incubation medium.
[Show abstract][Hide abstract] ABSTRACT: Strong resonant light scattering by individual spherical Si nanoparticles is experimentally demonstrated, revealing pronounced resonances associated with the excitation of magnetic and electric modes in these nanoparticles. It is shown that the low-frequency resonance corresponds to the magnetic dipole excitation. Due to high permittivity, the magnetic dipole resonance is observed in the visible spectral range for Si nanoparticles with diameters of ∼200 nm, thereby opening a way to the realization of isotropic optical metamaterials with strong magnetic responses in the visible region.
[Show abstract][Hide abstract] ABSTRACT: In this study, we explore the production of well-defined macroscopic scaffolds with two-photon polymerization (2PP) and their use as neural tissue engineering scaffolds. We also demonstrate that these 3D scaffolds can be replicated via soft lithography, which increases production efficiency. Photopolymerizable polylactic acid (PLA) was used to produce scaffolds by 2PP and soft lithography. We assessed the biocompatibility of these scaffolds using an SH-SY5Y human neuronal cell line and primary cultured rat Schwann cells (of direct relevance to the repair of nerve injuries). A Comet assay with SH-SY5Y human neuronal cells revealed minimal DNA damage after washing the photocured material for 7 days in ethanol. Additionally, thin films and 3D scaffolds of the photocured PLA sustained a high degree of Schwann cell purity (99%), enabled proliferation over 7 days and provided a suitable substrate for supporting Schwann cell adhesion such that bi-polar and tri-polar morphologies were observed. Evidence of orthogonally aligned and organized actin thin filaments and the formation of focal contacts were observed for the majority of Schwann cells. In summary, this work supports the use of PLA as a suitable material for supporting Schwann cell growth and in turn use of 3D soft lithography for the synthesis of neural scaffolds in nerve repair.