A. Demir

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.

Analysis and classification of heterogeneous kidney stones using laser-induced breakdown spectroscopy (LIBS).

Kidney stones were analyzed using laser-induced breakdown spectroscopy (LIBS), utilizing a high resolution multi-channel charge-coupled device (CCD) spectrometer and a nanosecond-pulse Nd: YAG laser. The kidney stones were also characterized using X-ray diffraction (XRD) and X-ray fluorescence (XRF) techniques for comparative analysis. It was found that the ratio of hydrogen (H) to carbon (C) was an important indicator of organic compounds such as uric acid. Advantages of LIBS, especially with regards to amount of sample required and sample preparation as well as the ability to carry out elemental analysis and classification of kidney stones simultaneously, over other analytical techniques such as XRD and XRF are discussed. The common minor elements detected in the kidney stones include P, S, Si, Ti, and Zn. Principal component analysis (PCA) and partial least squares discriminant analysis (PLS-DA) of broadband LIBS spectra were employed for classifying different types of kidney stones. The results are beneficial in understanding kidney stone formation processes, which can lead to preventive therapeutic strategies and treatment methods for urological patients.

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.

Measurement of the duration of X-ray lasing pumped by an optical laser pulse of picosecond duration

Measurements of the duration of X-ray lasing pumped with picosecond pulses from the VULCAN optical laser are obtained using a streak camera with 700 fs temporal resolution. Combined with a temporal smearing due to the spectrometer employed, we have measured X-ray laser pulse durations for Ni-like silver at 13.9 nm with a total time resolution of 1.1 ps. For Ni-like silver, the X-ray laser output has a steep rise followed by an approximately exponential temporal decay with measured full-width at half-maximum (FWHM) of 3.7 (±0.5) ps. For Ne-like nickel lasing at 23.1 nm, the measured duration of lasing is ≈10.7 (±1) ps (FWHM). An estimate of the duration of the X-ray laser gain has been obtained by temporally resolving spectrally integrated continuum and resonance line emission. For Ni-like silver, this time of emission is ≈22 (±2) ps (FWHM), while for Ne-like nickel we measure ≈35 (±2) ps (FWHM). Assuming that these times of emission correspond to the gain duration, we show that a simple model consistently relates the gain durations to the measured durations of X-ray lasing.

Comparison of simulated and experimental time resolved emission for a Ne-like nickel x-ray laser

X-ray laser output at 23.1 nm and the intensity of resonance line and continuum emission between 0.6 and 1.8 nm emitted from a nickel plasma are simulated using a fluid and atomic physics program. The simulations are undertaken for the conditions of a recent experiment using a Nd:glass laser with a ~1.2 ps pulse at 7 × 1015 W cm−2 irradiance pumping a plasma pre-formed by a 280 ps duration pulse at 2 × 1013 W cm−2 with peak-to-peak pulse separation usually set at 300 ps. The simulated duration of x-ray lasing (~12 ps) agrees with the measured laser duration and the temporal output of continuum and resonance lines is in agreement with measurements made using a streak camera.

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.

Quantitative simulations of short pulse x-ray laser experiments

EHYBRID fluid and atomic physics code simulations are compared with experimentally measured Ne-like nickel x-ray laser output at 23.1 nm and emission from nickel and germanium plasmas produced by line focus irradiation into a pre-formed plasma with 1.2 ps pulses of 1.06 µm wavelength and peak irradiance 7 × 1015 W cm−2. A particle-in-cell (PIC) code is used to simulate the laser energy absorption and resulting electron energy distribution in the experiment. It is shown that some absorbed laser energy is distributed to fast electrons that do not produce collisional excitation of the population inversion.

Spectroscopic Investigation of a Double Discharge Pulsed Electron Beam Generator

ABSTRACT The wide range of applications of the plasma-based electron beam generator make it necessary to diagnose the device with a noninterfering method. The results of experimental and modeling studies of neutral helium and hydrogen beta spectral lines emitted from the double discharge pulsed electron beam generator are presented in this paper. Neutral helium lines emitted from the plasma in the pressure range 0.1–0.4 torr are studied and compared with results of the collisional radiative model. The duration of the electron beam is shorter than 100 ns, and the peak current intensity is of order amperes. The full width at half maximum of the H β spectral line is used for the determination of the plasma electron density, found as 3.16 × 1021 m−3 at 0.3 torr, and good agreement is obtained by comparing with the full computer simulation method.

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.