E. Akman

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.

Optimizatin Of Pulsed Nd:YAG Laser Parameters For Titanium Seam‐Welding

Titanium alloys are the most advantageous metals for the medical and aerospace industry because of their light weight and excellent corrosion resistance. Several techniques were investigated to achieve reliable welds with optimal distortion for the fabrication components used in industry. Laser welding is the most important joining technique because of its precision, rapid processing. For pulse mode Nd:YAG laser; pulse shape, energy, duration, repetition rate and peak power are the most important parameters effects the weld quality. And also the combinations of these parameters are very important for pulsed laser seam‐welding. In this study, an experimental work has been done to determine the pulsed laser seam‐welding parameters for 3mm thick titanium alloys using the Lumonics JK760TR Nd:YAG pulsed laser.

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.

Effect of Pulsed Nd: YAG Laser Powers On 304 Stainless Steel Welding

In this study, optimum welding parameters are obtained for 1mm thickness type 304 stainless steel welding using the Lumonics JK760TR pulsed Nd:YAG laser. The influences of laser welding parameters such as pulse duration, focal position, frequency, laser power, welding speed, and shielding gas (N2) pressure on penetration defining welding quality are investigated. Also comparisons of overlap ratios are presented between theory and experiment for pulse duration, frequency and welding speed.

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.

Progresses on the Theoretical and Experimental Studies in Laser Technologies Research and Application Center In Kocaeli

Laser Technologies Research and Application Center (LATARUM) was established in 2005 with interdisciplinary cooperation to obtain product based on projects, to train personnel with at highest academic level with knowledge to use latest technology. There are electro‐optics, laser material processing and modelling and simulation groups working on projects. Theoretical modeling studies are performed for x‐ray laser media. Ne‐like nickel and iron and Ni‐like tin and molybdenum x‐ray laser media for different pumping laser configurations have been modeled using EHYBRID. Theoretical and experimental studies on spectrometer design for wavelength range between X‐ray and IR are carried out by electro‐optic group. Material processing studies using Nd‐YAG laser are performed. Materials of titanium, aluminum and stainless steel have been welded in different laser pulse, power, and repetition rate conditions. Optimum parameters for these welding processes have been obtained.

Effects of Shielding Gas on Absorption Energy of Nd-YAG Laser for Aluminium Welding

Aluminium is the one of the most abundant element situated in Earth’s crust and using in thousands of industrial applications. In this study spectroscopic analysis for 1mm thick aluminium plates investigated and electron temperatures were calculated with using emission spectra obtained from plasma. The relation between electron temperature and shielding gas pressure, type, pulse energy, beam focus position and flow direction were observed. With using shielding gases Ar, He, N2 at different pressures the bead widths was measured.

Theoretical and experimental investigation of soft x-rays emitted from TIN plasmas for lithographic application

Extreme ultraviolet lithography (EUVL) requires an emission of soft x-rays around a wavelength region of 13.5 nm. EHYBRID simulation was made under the laser operation at 1064 nm with a pulse duration of 6 ns. Intensity was changed between 1 x 10 12 W/cm2 and 5 x 10 12 W/cm2. Soft X-rays emitted from Sn XII and Sn XIII ions were simulated by using the EHYBRID code. Ion fractions of the tin ions and the line intensities for different electron temperatures were calculated by using the collisional radiative code NeF.