M.Eng. Alexander May

A new water-based silica sol was developed to provide single-layer anti-reflective (AR) coatings. The combination of nanoparticle-based aqueous coating and wiping-coating method facilitated to reduce the solvent waste. The wiping-coating process requires only 35 ml sol to cover a large glass substrate (80 × 160 cm). Samples coated on one side show an improvement in light transmission in the visible range: the maximum transmission is 95.12 ± 0.33% on float glass and 92.48 ± 0.25% on display glass. This is an excellent performance compared to the extra 99.04% maximum transmission of samples coated on both sides. The layer thickness distribution defined by the ellipsometry of 98 samples (10 × 10 cm) shows homogeneity (77.4 ± 2.2 nm) over the total area. Homogeneous films with good surface wetting were applied on glass, polycarbonate (PC), and acrylic glass (PMMA). The cured layers were successfully tested against dry heat, damp heat (40 °C/98% RH), and climatic change (−40 °C–40 °C/98% RH) on all three substrate materials. No delamination from the substrate was observed. The changes in the minimum reflection after exposure to damp heat and climatic change were minimal (ΔR = ±0.6%) in the wavelength range of 400–1000 nm. The addition of Levasil nanoparticles into the water-based silica sol improved coating hardness on glass sheets up to 3H pencil hardness without significant loss in transmission.

Coating on large surfaces is a critical issue in both academic studies and industrial production. This work proposes a novel method of coating a large flat substrate (50 × 100 cm2) via a wet chemical process using a very small amount (20 ml) of coating solution. The sol material consisted of surface-modified silicon dioxide (SiO2) nanoparticles (10–30 nm), which have the optimal antireflective (AR) function in the visible spectral range for thin films with a thickness ranging from 110 to 120 nm. Ellipsometry results demonstrate a homogeneous thickness of the AR coating on glass (109.4 ± 2.7 nm). A deviation of less than 3% over a large coated surface was observed. Crack-free coatings with homogeneous morphology on the surface of the coatings were observed using scanning electron microscopy. The AR effect was confirmed with UV–vis measurements, with an average transmittance of 91.1% and 94.7%, respectively, in visible wavelengths for the one-sided and double-sided AR coatings (in comparison to 88% for uncoated glass).

Purpose The aim of this study was to compare the proliferation and attachment behavior of fibroblasts and epithelial cells on differently structured abutment materials. Materials and Methods Three different surface topographies were prepared on zirconia and titanium alloy specimens and defined as follows: machined (as delivered without further surface modification), smooth (polished), and rough (sandblasted). Energy-dispersive X-ray spectroscopy, topographical analysis, and water contact angle measurements were used to analyze the surface properties. Fibroblasts (HGF1) and epithelial cells (HNEpC) grown on the specimens were investigated 24 hours and 72 hours after seeding and counted using fluorescence imaging. To investigate adhesion, the abundance and arrangement of the focal adhesion protein vinculin were evaluated by immunocytochemistry. Results Similar surface topographies were created on both materials. Fibroblasts exhibited significant higher proliferation rates on comparable surface topographies of zirconia compared with the titanium alloy. The proliferation of fibroblasts and epithelial cells was optimal on different substrate/topography combinations. Cell spreading was generally higher on polished and machined surfaces than on sandblasted surfaces. Rough surfaces provided favorable properties in terms of cellular adhesion of fibroblasts but not of epithelial cells. Conclusions Our data support complex soft tissue cell-substrate interactions: the fibroblast and epithelial cell response is influenced by both the material and surface topography.

The surface of the medical grade titanium alloy (Ti–6Al–4V) was modified using a millisecond laser to alter the topography and wetting behavior. We combined anisotropic surface patterning with a nitriding process which is essential for the protection of dental implants against corrosion and wear. While a homogenous nitride layer was achieved, the laser induced a surface topography composed of both micro- and nano-structures. The surface topography leads to anisotropy in wetting which is desired in next generation implant applications such as nature-analogue anisotropic dental restoration.

Pulsed laser deposition (PLD) is one of the well-established physical vapor deposition methods used for synthesis of ultra-thin layers. Especially PLD is suitable for the preparation of thin films of complex alloys and ceramics where the conservation of the stoichiometry is critical. Beside several advantages of PLD, inhomogeneity in thickness limits use of PLD in some applications. There are several approaches such as rotation of the substrate or scanning of the laser beam over the target to achieve homogenous layers. On the other hand movement and transition create further complexity in process parameters. Here we present a new approach which we call Matrix Shaped PLD to control the thickness and homogeneity of deposited layers precisely. This new approach is based on shaping of the incoming laser beam by a microlens array and a Fourier lens. The beam is split into much smaller multi-beam array over the target and this leads to a homogenous plasma formation. The uniform intensity distribution over the target yields a very uniform deposit on the substrate. This approach is used to deposit carbide and oxide thin films for biomedical applications. As a case study coating of a stent which has a complex geometry is presented briefly.

Polyetheretherketone (PEEK) is considered as a substitute for metallic implant materials due to its extremely low elastic modulus (3-4 GPa). Despite its good mechanical properties, PEEK exhibits a slow integration with the bone tissue due to its relatively inert surface and low biocompatibility. We introduced a dual modification method, which combines the laser and plasma surface treatments to achieve hierarchically patterned PEEK surfaces. While the plasma treatment leads to nanotopography, the laser treatment induces microstructures over the PEEK surface. On the other hand, plasma and laser treatments induce inhomogeneity in the surface chemistry in addition to the tailored surface topography. Therefore, we coated the structured PEEK surfaces with a thin alumina layer by pulsed laser deposition (PLD) to get identical surface chemistry on each substrate. Such alumina-coated PEEK surfaces are used as a model to investigate the effect of the surface topography on the wetting independent from the surface chemistry. Prepared surfaces bring advantages of enhanced wetting, multiscaled topography, proven biocompatibility (alumina layer), and low elastic modulus (PEEK as substrate), which together may trigger the use of PEEK in bone and other implant applications.

Ag nanoparticles with a narrow size distribution down to 3-4 nm have been embedded in an Al2O3 matrix by a single step pulsed laser co-deposition. A two-beam laser setup and a single target which is composed of Ag and Al2O3 are used for achieving a controlled deposition. This approach allows the control of the laser fuency on each target independently. The resulting Ag/Al2O3 nanocomposite thin films exhibit a specific plasmon absorption. This easy-to-apply single step method allows precise particle size and distribution control at room temperature. Therefore the approach can be used for synthesis of various nanocomposite thin films of more complex materials on various substrates.