Arnold Gillner

Fabrication of 2D protein microstructures and 3D polymer–protein hybrid microstructures by two-photon polymerization

Two-photon polymerization (TPP) offers the possibility of creating artificial cell scaffolds composed of micro- and nanostructures with spatial resolutions of less than 1 µm. For use in tissue engineering, the identification of a TPP-processable polymer that provides biocompatibility, biofunctionality and appropriate mechanical properties is a difficult task. ECM proteins such as collagen or fibronectin, which could mimic native tissues best, often lack the mechanical stability. Hence, by generating polymer-protein hybrid structures, the beneficial properties of proteins can be combined with the advantageous characteristics of polymers, such as sufficient mechanical stability. This study describes three steps toward facilitated application of TPP for biomaterial generation. (1) The efficiency of a low-cost ps-laser source is compared to a fs-laser source by testing several materials. A novel photoinitiator for polymerization with a ps-laser source is synthesized and proved to enable increased fabrication throughput. (2) The fabrication of 3D-microstructures with both systems and the fabrication of polymer-protein hybrid structures are demonstrated. (3) The tissue engineering capabilities of TPP are demonstrated by creating cross-linked gelatin microstructures, which clearly forced porcine chondrocytes to adapt their cell morphology.

Locally selective bonding of silicon and glass with laser

Abstract A novel method for joining silicon and glass wafers with laser radiation is described. In order to characterize the locally selective bonding with laser (SBL) process, variations of laser parameters have been correlated with temperature measurements during bonding and the achieved bonding results. It was found that the temperature load outside the laser irradiated zone only lasted for seconds and remained below 300°C. The result of the investigations was a parameter field producing reproducible and strong silicon glass bonds. Basic knowledge for the thermal process of bonding and a understanding of the recognized bond defects was developed. Finally advantages and disadvantages of SBL with silicon and glass are discussed with respect to the anodic bonding technology putting emphasis on the low temperature and locally selective bonding capability of SBL.

Tunable surface texturing by polarization-controlled three-beam interference

For the fabrication of periodic microstructures, a high-precision and highly efficient polarization-controlled three-beam interference technology (PoTBI) has been developed. With the theory of superposition of multiple laser beams, simulations on the influence of polarization upon the intensity distribution in the overlapped area have been carried out. By controlling the polarization of the interfering beams, various intensity patterns can be obtained. An optical setup for PoTBI has been realized and used to generate microstructures in polyimide foil. Micro cavities, micro bumps, eye-like cavities and rectangular columns of hexagonal symmetry and one-dimensional lines are produced. Compared with other multi-beam interference technologies, different surface textures of hexagonal symmetry with the same periodicity can be obtained only by changing the polarization status of the interfering beams without changing the geometrical interference setup. Thus, PoTBI provides a simply tunable texturing technology with a wide range of applications in surface structuring.

Nano structures via laser interference patterning for guided cell growth of neuronal cells

Laser interference patterning is a versatile tool for the fabrication of nano patterns. For this study, regular nano line patterns with feature sizes between 100 and 1000 nm were produced on polymers polyimide, polyetheretherketone, and polydimethylsiloxane. Cell culture experiments with B35 neuronal cells revealed the alignment of cellular extensions along nano grooves of different feature sizes. Especially, when feature depth exceeds a distinct threshold (aspect ratio > 0.6), more than 50% of cells are oriented parallel, i.e., within angles of 0°–30° to the direction of the line pattern. The presented techniques enable new materials to be processed and offer a promising approach for nerve repair in the central nervous system.

Laser bonding of micro-optical components

A novel method for bonding micro optical components using a new joining process of silicon with glass is described. The process is based on selective heating with laser radiation forming a chemical bond at the interface of both joining partners. In order to characterize the locally selective bonding with laser (SLB) process, variations of laser parameters have been correlated with temperature measurements during bonding and the achieved bonding results. It was found that the temperature load outside the laser irradiated zone only lasted for seconds and remained below 300°C, so minimizing the heat load of the entire component. The result of the investigations was a parameter field producing reproducible and strong silicon glass bonds. Basic knowledge for the thermal process of bonding and an understanding of the recognized bond defects was developed. Finally advantages and disadvantages of SBL with silicon and glass are discussed with respect to micro assembly of optical parts for telecommunication components.

Photochemistry with laser radiation in condensed phase using miniaturized photoreactors

Summary Miniaturized microreactors enable photochemistry with laser irradiation in flow mode to convert azidobiphenyl into carbazole with high efficiency.

Advances in silicon-to-glass bonding with laser

In this work low temperature bonding of silicon and glass wafers for MEMS applications by the application of a Nd:YAG Laser using the transmission welding principle is examined. With this method the Laser beam is transmitted through the glass wafer and absorbed by the silicon at the silicon-glass interface. The resulting heated zone leads to locally selective bonding in spot and line shape with line width of 300 micrometers and less. The scope of the work is to characterize the Laser bonding (LB) technology and the quality of the produced silicon-glass joints. The continuous Laser power applied was between 12 and 30 W and the scribing velocity was between 50 and 500 mm/min. The measurements of the thermal load in the silicon during LB performed with micro-thermocouples show temperatures near the bonding zone around 300 degree(s)C for less than one second. The produced joints were found to have tensile strength between 5 and 10 MPa, which is comparable with other bonding methods. Hermetic tightness was proved with a helium leak detector and leak rates around 3(DOT)10-8 mbar(DOT)l(DOT)s-1 were found. Finally it will be discussed in which cases LB could be a supplement to anodic bonding, which is the state of the art bonding method for silicon-glass couples. Conclusively it can be said that locally selective LB is a novel method for MEMS packaging, with high bonding velocity, low thermal load for the joining partners and high bonding quality concerning strength and hermetic tightness.

High-accuracy micromachining of ceramics by frequency-tripled Nd:YAG lasers

Ceramics like Si3N4, Al2O3 and ZrO2 and also diamonds can be hardly machined by conventional methods. Short pulse lasers, especially frequency-tripled, diode pumped Nd:YAG-lasers with a high beam quality offer the possibility to ablate these materials with high quality. With a spot size of about 10 micrometers , high fluences can be achieved, so that the materials are vaporized without or with only a small holes with diameters >= 5 micrometers and cutting of thin ceramic substrates. The edges are sharp and the face of the cut is very smooth. Furthermore it is possible to ablate three dimensional microstructures. Therefore the laser beam is scanned over the surface and the materials is ablated pulse beside optimized machining parameters the surface roughness can be reduced to R <EQ 0.1 micrometers . Due to the low ablation rate of around 0.05 (mu) g/pulse the ablation depth of a single slice can be controlled very precisely. Depending on the material and the machining parameters the depth is in the range of 1 to 10 micrometers .

Block copolymer supramolecular assemblies hierarchically structured by three-beam interference laser ablation

We report the fabrication of hierarchical structures by combining bottom-up self-assembly of block copolymer supramolecular assemblies with top-down three-beam interference laser ablation methods. To fabricate the shorter length scale in the hierarchical structures, we use supramolecular assemblies (SMAs) of azobenzene compounds hydrogen bonded with poly(vinyl pyridine) blocks of polystyrene-block-poly(vinyl pyridine) block copolymers. The SMAs form phase separation nanostructures by solvent vapor annealing. The longer length scale of the hierarchical structures is fabricated by three-beam interference laser ablation on the phase separated nanostructures of the SMAs. The ablation process is induced by single laser shots with 35 ns pulse duration. Tuning of both length scales is feasible by changing the interference conditions and chemical composition of the SMAs, which enables efficient and straightforward fabrication of hierarchical photonic structures.

All-optical fabrication of ellipsoidal caps on azobenzene functional polymers.

We have fabricated an azobenzene (azo) polymer microellipsoidal cap array of hexagonal symmetry with high-power laser ablation and subsequent single-beam-induced mass migration. High-power interference with polarization-controlled triple beams is utilized to inscribe a circular bump array directly on the surface of the azo polymer film. The produced circular cap array is exposed to the linearly polarized beam, and the caps are stretched along the polarization direction of the irradiating beam. A model of gradient force emerged by the interaction of the polarized beam and azo polymer is constructed to explain the mechanism of such polarization-induced microscale shape deformation.