Elif Kacar

Femtosecond laser treatment of 316L improves its surface nanoroughness and carbon content and promotes osseointegration: An in vitro evaluation.

Cell-material surface interaction plays a critical role in osseointegration of prosthetic implants used in orthopedic surgeries and dentistry. Different technical approaches exist to improve surface properties of such implants either by coating or by modification of their topography. Femtosecond laser treatment was used in this study to generate microspotted lines separated by 75, 125, or 175μm wide nanostructured interlines on stainless steel (316L) plates. The hydrophobicity and carbon content of the metallic surface were improved simultaneously through this method. In vitro testing of the laser treated plates revealed a significant improvement in adhesion of human endothelial cells and human bone marrow mesenchymal stem cells (hBM MSCs), the cells involved in microvessel and bone formation, respectively, and a significant decrease in fibroblast adhesion, which is implicated in osteolysis and aseptic loosening of prostheses. The hBM MSCs showed an increased bone formation rate on the laser treated plates under osteogenic conditions; the highest mineral deposition was obtained on the surface with 125μm interline distance (292±18mg/cm(2) vs. 228±43mg/cm(2) on untreated surface). Further in vivo testing of these laser treated surfaces in the native prosthetic implant niche would give a real insight into their effectiveness in improving osseointegration and their potential use in clinical applications.

Reduced myofibroblast differentiation on femtosecond laser treated 316LS stainless steel

In-stent restenosis is a common complication after stent surgery which leads to a dangerous wall narrowing of a blood vessel. Laser assisted patterning is one of the effective methods to modify the stent surface to control cell-surface interactions which play a major role in the restenosis. In this current study, 316 LS stainless steel substrates are structured by focusing a femtosecond laser beam down to a spot size of 50 μm. By altering the laser induced spot density three distinct surfaces (low density (LD), medium density (MD) and high density (HD)) were prepared. While such surfaces are composed of primary microstructures, due to fast melting and re-solidification by ultra-short laser pulses, nanofeatures are also observed as secondary structures. Following a detailed surface characterization (chemical and physical properties of the surface), we used a well-established co-culture assay of human microvascular endothelial cells and human fibroblasts to check the cell compatibility of the prepared surfaces. The surfaces were analyzed in terms of cell adherence, proliferation, cell morphology and the differentiation of the fibroblast into the myofibroblast, which is a process indicating a general fibrotic shift within a certain tissue. It is observed that myofibroblast proliferation decreases significantly on laser treated samples in comparison to non-treated ones. On the other hand endothelial cell proliferation is not affected by the surface topography which is composed of micro- and nanostructures. Such surfaces may be used to modify stent surfaces for prevention or at least reduction of restenosis.

Colour-Difference Measurement Method for Evaluation of Quality of Electrolessly Deposited Copper on Polymer after Laser-Induced Selective Activation

In this work a novel colour-difference measurement method for the quality evaluation of copper deposited on a polymer is proposed. Laser-induced selective activation (LISA) was performed onto the surface of the polycarbonate/acrylonitrile butadiene styrene (PC/ABS) polymer by using nanosecond laser irradiation. The laser activated PC/ABS polymer was copper plated by using the electroless copper plating (ECP) procedure. The sheet resistance measured by using a four-point probe technique was found to decrease by the power law with the colour-difference of the sample images after LISA and ECP procedures. The percolation theory of the electrical conductivity of the insulator conductor mixture has been adopted in order to explain the experimental results. The new proposed method was used to determine an optimal set of the laser processing parameters for best plating conditions.

Al2O3 micro- and nanostructures affect vascular cell response

In-stent restenosis (ISR) is one of the most common and serious complications observed after stent implantation. ISR is characterized by the inordinate proliferation of smooth muscle cells (SMC) that leads to narrowing of the blood vessels. To achieve a healthy endothelium, it is critical to selectively enhance the growth of endothelial cells (EC) while suppressing the growth of smooth muscle cells, which is still a major challenge and yet to be achieved. In this study, novel surfaces have been developed to support the selective growth of endothelial cells. Micro- and nanostructured Al2O3 surfaces with unique topographical features were fabricated and tested. Surface characterization and cellular response of endothelial cells (HUVEC) as well as smooth muscle cells (HUVSMC) has been investigated at cellular and molecular levels. A topography driven selective cell response of ECs over SMCs was demonstrated successfully. This selective response of ECs was also analyzed at protein levels in order to understand the basic mechanism.

Longitudinally Pumped Ne-Like Titanium X-Ray Laser Simulation with a Post-Processor Code Coupled to EHYBRID

Longitudinal pumping with a grazing incidence scheme of Ne-like Ti has been modeled by using the EHYBRID and a post-processor code. The atomic data that are required in the simulation are obtained by using the Cowan code. The variation of the Ne-like Ti x-ray laser gain at 32.6 nm is calculated for a fixed delay time with a variation in the incidence angle and a fixed incidence angle with a variation in the delay time. The post processor code has been used to simulate the x-ray resonance lines between 17 and 29 A.

Monitoring of Laser Material Welding Process Using UV‐Visible Spectrometer

UV‐Visible spectrometer is used to record emission from magnesium and titanium metal plates during laser welding processing. Geometrically corrected Czerny‐Turner configurations nearly eliminate defocusing problem. The Optikwerks software is used to find the optimum Czerny‐Turner configuration and to choose optical elements such as grating types, mirrors focal length and diameter, and slit width. The design parameters of the uv‐visible spectrometer in the wavelength range 200–1100 nm for monitoring laser material welding processing.

Percolation effect of a Cu layer on a MWCNT/PP nanocomposite substrate after laser direct structuring and autocatalytic plating

Percolation behavior of a copper (Cu) layer on a multi-walled carbon nanotube/polypropylene (MWCNT/PP) nanocomposite substrate after laser-direct-structuring (LDS) and subsequent autocatalytic Cu deposition (ACD) is presented. The inverse sheet resistance showed percolation type dependence on the area fraction of Cu on MWCNT/PP measured by digital image processing of specimen photos.

Functionalized Hybrid Coatings on ABS Surfaces by PLD and Dip Coatings

It is important to give water-repellent and antibacterial properties to the acrylonitrile butadiene styrene (ABS) surfaces of the hearing aids. In this study, the sol–gel Si and sol–gel Ti solutions were prepared from the reactions of silicon ethoxide, titanium butoxide and methacrylic acid. The catalyst and Dynasylan F8815 were added to the sol–gel solutions to give hydrophobic properties onto the ABS surfaces. Additionally, silver nanoparticles were synthesized by nanosecond laser and added to the coating solutions to give extra antibacterial properties. The surfaces of the ABS targets were coated using the sol–gel dip coating and pulsed laser deposition techniques. The coatings with good adhesion between film and substrate and good water-repellent properties were achieved. The average contact angles for the coated ABS surfaces were measured in the range between 120 and 125 degrees. The obtained sol–gel materials and produced thin films onto the ABS surfaces were also analyzed in terms of the antibacterial properties. The highly antibacterial properties were observed in the sol–gel solutions and the thin films.

Conversion Efficiency Calculations for Soft X-Rays Emitted from Tin Plasma for Lithography Applications

Laser-produced plasmas can be used as extreme ultraviolet (EUV) sources for lithography, operating in the 13.5 nm range. Soft X-rays emitted from laser-produced tin plasma were simulated using the EHYBRID code. Required atomic data for tin ions were calculated using the Cowan code. In the EHYBRID simulations tin slab target is assumed to be irradiated by 1064 nm wavelength Nd:YAG laser. Simulations were performed for different driving laser parameters.

Effects of Double Pulse Configuration on Absorption of Driving Laser Energy for Laser Produced Iron Plasmas

Simulation of the Ne‐like Fe plasma is performed by using hydrodynamic and atomic physics code EHYBRID. The atomic physics data are obtained by using the Cowan code. In the simulation, a slab target is assumed to be irradiated by Nd:glass laser with double pulse configuration for producing Ne‐like Fe plasma. In this study, effects of prepulse duration, prepulse intensity and time interval between prepulse and main pulse on absorption of main pulse energy are investigated. The general plasma properties such as absorbed energy, electron temperature, electron density, plasma expansion velocity distributions are calculated for prepulse duration varying from 0,50 ns to 2,00 ns.