Brigita Abakevičienė

Femtosecond laser micro‐machined polyimide films for cell scaffold applications

Engineering of sophisticated synthetic 3D scaffolds that allow controlling behaviour and location of the cells requires advanced micro/nano‐fabrication techniques. Ultrafast laser micro‐machining employing a 1030‐nm wavelength Yb:KGW femtosecond laser and a micro‐fabrication workstation for micro‐machining of commercially available 12.7 and 25.4 μm thickness polyimide (PI) film was applied. Mechanical properties of the fabricated scaffolds, i.e. arrays of differently spaced holes, were examined via custom‐built uniaxial micro‐tensile testing and finite element method simulations. We demonstrate that experimental micro‐tensile testing results could be numerically simulated and explained by two‐material model, assuming that 2–6 μm width rings around the holes possessed up to five times higher Youngs modulus and yield stress compared with the rest of the laser intacted PI film areas of ‘dog‐bone’‐shaped specimens. That was attributed to material modification around the micro‐machined holes in the vicinity of the position of the focused laser beam track during trepanning drilling. We demonstrate that virgin PI films provide a suitable environment for the mobility, proliferation and intercellular communication of human bone marrow mesenchymal stem cells, and discuss how cell behaviour varies on the micro‐machined PI films with holes of different diameters (3.1, 8.4 and 16.7 μm) and hole spacing (30, 35, 40 and 45 μm). We conclude that the holes of 3.1 μm diameter were sufficient for metabolic and genetic communication through membranous tunneling tubes between cells residing on the opposite sides of PI film, but prevented the trans‐migration of cells through the holes. Copyright

Inhomogeneity of phase transition in lead titanate thin films formed by magnetron layer-by-layer deposition

The formation of deposited ferroelectric perovskite PbTiO3 thin films using layer-by-layer reactive magnetron sputtering was investigated in this work. Deposition rates of each layer (PbO and TiO2) for 7.2 and 9.2 nm/min, respectively, were chosen there. Silicon (110) substrate with the heater was moved periodically and parallel to the magnetron cathodes during deposition. The heater temperature (380 °C–700 °C) has influence on the stoichiometry of thin films. Perovskite phase of lead titanate was not obtained without post annealing. The reasons for this are discussed in the work. The results of the structure of thin layers deposited on silicon substrates at 380 °C and annealed for one hour at 700 °C in air have shown that a pure perovskite phase of PbTiO3 is formed there.

Micro-channel drilling of Ni and Pt films on silicon by using laser beam interference ablation for solid oxide fuel cells

Solid oxide fuel cells (SOFC) are widely studied because of their potential usage in power source applications. At present huge attention is paid to micro solid oxide fuel cells (μ-SOFC) based on thin film technologies with power capacity in the range of several watts. Porous nickel is an important part in many types of solid oxide fuel cells. This work presents experimental results of laser micro-channel formation in the 200 nm thick nickel and platinum films for the fuel cell membranes. The four-beam interference ablation was applied for fast and parallel formation of microchannel over a large area in thin metal film on a silicon substrate for μ-SOFC. Using this technique, regularly arranged circular holes with a period of 4.2 μm were formed in the 200 nm thick nickel and platinum films. The diameter of the holes ranged from 1.7 to 2.7 μm. The area where holes were ablated by a single laser exposure was approximately 250x250 μm. A silicon substrate was chemically etched from backside to release the patterned nickel film.