This study reports the effects of substrate temperature and laser ablation wavelength on the structural and bioactivity properties of hydroxyapatite (HAP) coatings. The coatings were obtained using a pulsed laser deposition technique on Ti6Al4V and Si(100) substrates. Different substrate temperatures were used ranging from 25°C to 800°C. Three wavelengths of Nd:YAG pulsed laser (1064 nm, 532 nm, and 355 nm) were employed to study the ablation mechanisms and their effects on film morphology. Surface morphology was investigated by SEM with EDX Analysis and AFM. All coatings were confirmed to be grown in a granular system and it was observed that 355 nm and 532 nm produce smoother coatings. The XRD measurements showed the transition from amorphous to crystalline HAP beyond 500°C. The adhesion strength of the coatings to the substrates was analyzed by pull-out tests. Although as substrate temperature increased, adhesion also got better, further increase of temperature to 800 °C resulted in a significant decrease in bonding. Finally, the bioactivity of the coatings was assessed on multiple levels such as protein adsorption, dissolution in simulated body fluid, and cell proliferation.
Bacterial antibiotic resistance poses a pressing global health crisis, challenging conventional therapies. Efflux pumps diminish antimicrobial effectiveness by expelling drugs from bacterial cells. Multidrug efflux pumps (MEPs) have been found to transport diverse compounds, including phenothiazinium dyes like methylene blue, out of bacteria. Inhibition of MEPs offers a promising strategy to bolster the efficacy of antimicrobial photodynamic inactivation (PDT). This research adopts a synergistic approach, combining the efflux pump inhibitor (EPI) , reserpine, with silver nanoparticles (Ag NPs) and methylene blue (MB) to enhance PDT efficiency. Ag NPs were synthesized via pulsed laser ablation and characterized using TEM, UV-Vis, and PL spectra. E. coli was treated with MB, Ag NPs, and reserpine, followed by LED light irradiation. MB was twice as effective, and AgNPs/MB was six times more effective with reserpine during a sixminute irradiation. Ongoing experiments on morphological changes will be presented. AgNPs/MB with reserpine could effectively combat bacterial pathogens in open wounds and prosthetic joint infections.
Using Pulsed Laser Deposition (PLD), Zr films were deposited on silicon with laser wavelengths of 1064 nm and 532 nm, at substrate temperatures of 25 °C, 300 °C, and 500 °C, and fluences of 0.25, 0.5, and 1.0 J/cm2. The 1064 nm wavelength yielded smoother films, with surface roughness growing at higher fluences. The 300 °C temperature was ideal for crystal quality. Analyses through XRD, SEM, and AFM showed unique morphologies due to laser variables. Computations using a thin film growth model matched the empirical data, underscoring the factors critical to Zr film deposition and guiding PLD optimization for superior film quality.
Zirconia is known to be a hard-to-machine in the sintered state. In this study, the zirconia samples were patterned and then sintered. A nanosecond Nd:YAG laser operating at 1064 and was used to pattern the zirconia surface. A confined plasma was formed through the interaction between the laser beam and a copper grid template. The template was covered by a sacrificial aluminum layer, and the plasma was confined using a glass slide. The size and depth of the pattern were shown to be dependent on the shape of the grid, fluence, exposure time, confinement medium, wavelength, and beam spot size. We successfully achieved patterns ranging in size from 7 μm to 40 μm with depths of up to 3 μm. The resulting patterned surfaces were characterized using Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM). The findings on the nature of the patterning will help in controlling functionality of zirconia, such as hardness, biofilm formation, and osteointegration.
This conference presentation was prepared for the Optical Methods for Tumor Treatment and Detection: Mechanisms and Techniques in Photodynamic Therapy XXXI conference at SPIE BiOS, SPIE Photonics West 2023.
Photosensitizing agents play an essential role in deactivation process of multidrug resistant pathogens and tumor treatments. In this work, methylene blue (MB) functionalized silver nanoparticles (Ag NPs) are used as an effective photodynamic therapy (PDT) agent for deactivating different strains of bacteria. Ag NPs were synthesized by pulsed laser ablation technique in different aqueous solutions like polyvinylpyrrolidone (PVP), citrate and polyvinyl alcohol (PVA) at different wavelength and power. With 1064nm wavelength, Ag NPs average size distribution in citrate, PVP, and PVA were found to be 6nm, 10nm, and 12nm respectively. Further, when 532nm wavelength is used, the average size was found to be 4nm, 7nm, and 10nm respectively. The synthesized Ag NPs were characterized using a transmission electron microscopy (TEM), UV–vis, and photoluminescence (PL) spectra. These Ag NPs were combined with MB and used to deactivate the Gram-negative bacteria, Escherichia coli (E. coli), and Gram-positive bacteria, Staphylococcus aureus (S. aureus). MB and Ag NPs combination was found to possess higher antimicrobial activity in comparison to MB and Ag NPs alone. Within 6 min of irradiation time with 660 nm LED, the MB/Ag NPs deactivated entire ~108 CFU/mL concentrated S. aureus and E. coli, bacteria. MB/Ag NPs used in PDT could be effective in killing bacterial pathogens in open wounds, prosthetic joint infections, in vivo cancer and tumor treatments.
Shape Memory Alloys (SMA) have unique characteristics to memorize their original structure and retain them when activated by heat or stress, however, there still much to be done in terms of fatigue life and phase modifiability. In this project, we propose a tunable treatment method using shockwaves created by nanosecond and picosecond pulsed lasers assisted with magnetic field to create 3-D structures on NiTi SMA. When the laser pulse hits the surface, its energy is partially absorbed, which ablates the surface resulting a plasma plume. By confining the plasma using dielectric medium and magnetic field, the shockwave is tuned for vertical transfer of the pressure gradient on the surface. Optical profilometer and SEM results confirm that the shockwave pressure became uniform when magnetic field was used. The less heat affected zones on the crater, and equal depth across the crater indicates a stable surface morphology due to magnetic field. Moreover, Shape-memory properties were also investigated with differential scanning calorimetry (DSC) measurements of NiTi samples, and the results indicate significant phase broadening, reaching up to 33% from the initial, and shifts in austenitic and martensitic phases of 5 °C. The tunability of the shockwave using magnetic field and water confinement expands the usage in treatment and imprinting of SMAs for biomedical and industrial applications.
An advanced direct imprinting method with low cost, quick, and minimal environmental impact to create a thermally controllable surface pattern using nanosecond and picosecond laser pulses is reported. Patterned micro indents were generated on shape memory alloys (SMA) and aluminum using nanosecond and picosecond laser operating at various wavelengths combined with suitable transparent overlay, a sacrificial layer of graphite, and copper grid. Laser pulses at different energy densities which generate pressure pulses up to a few GPA on the surface were focused through the confinement medium, ablating the copper grid to create plasma and transferring the grid pattern onto the surface. Scanning electron microscope (SEM), atomic force microscope (AFM), and optical microscope images show that various patterns were obtained on the surface with high fidelity. Optical profile analysis indicates that the depth of the patterned sample initially increases with the laser energy and later levels off. Our simulations of the laser irradiation process also confirm that high temperature and high pressure (up to 10 GPA) could be generated when laser energy of 2 J/cm2 is used. Experimental data is in good agreement with a theoretical simulation of laser-induced shock wave propagation inside the material. Stress wave closely followed the rise time of the laser pulse to its peak values and initial decay. Ongoing experiments on a different wavelength and confinement medium conditions and recovery ratio (ratio of the depth of cold indent to the depth of the initial indent) will also be presented.
Graphene quantum dots (GQD) are one of the most promising antimicrobial agents since they possess high germicidal activity against a broad range of microbes. In our project, we aim to investigate GQD with methylene blue (MB) as an effective, inexpensive and available compound which will hold even higher antimicrobial activity and lower toxicity toward human blood. GQDs were grown by focusing nanosecond laser pulses into benzene and were later combined with MB. The Gram-negative bacteria, Escherichia coli, and Gram-positive bacteria, Micrococcus luteus, were deactivated by GQD/MB. Detailed characterization was performed with transmission electron microscopy (TEM), scanning electron microscopy (SEM), Fourier-transform infrared (FTIR), UV-Visible (UV-Vis), and photoluminescence (PL) spectra. Furthermore, MBGQD singlet oxygen generation was investigated by measuring the rate of photobleaching. Combining MB with GQDs caused enhanced singlet oxygen generation. Our results show that the MB-GQD combination is more effective than QGD and MB alone in destroying bacteria. MTT assay was used to determine if GQDs in dark conditions caused human cellular side-effects and affected cancer and non-cancer cellular viability. We found that even high concentrations of GQDs do not alter viability under dark conditions. These results suggest that the MB-GQD combination is a promising form of photodynamic therapy. Further, the cytotoxicity of GQDs, MB and MB-GQD mixture toward MCF-7 breast cancer cells were evaluated.
we use a nanosecond laser pulses to create shock waves on material surface. using those shock waves, we are able to generate any three dimensional template with high fidelity. Currently, we use this technique to create shape memory effect on shape memory alloys and other materials. This is a fast environmental friendly and low cost technique.
An advanced direct imprinting method with low cost, quick, and minimal environmental impact to create a thermally controllable surface pattern using the laser pulses is reported. Patterned microindents were generated on Ni50Ti50 shape memory alloys and aluminum using an Nd: YAG laser operating at 1064 nm combined with a suitable transparent overlay, a sacrificial layer of graphite, and copper grid. Laser pulses at different energy densities, which generate pressure pulses up to a few GPa on the surface, were focused through the confinement medium, ablating the copper grid to create plasma and transferring the grid pattern onto the surface. Scanning electron microscope and optical microscope images show that various patterns were obtained on the surface with high fidelity. One-dimensional profile analysis indicates that the depth of the patterned sample initially increases with the laser energy and later levels off. Our simulations of laser irradiation process also confirm that high temperature and high pressure could be generated when the laser energy density of 2 J/cm2 is used.
Shape memory alloys (SMAs) are a unique class of smart materials and they were employed in various applications in engineering, biomedical, and aerospace technologies. Here, we report an advanced, efficient, and low-cost direct imprinting method with low environmental impact to create thermally controllable surface patterns. Patterned microindents were generated on Ni50Ti50 (at. %) SMAs using an Nd:YAG laser with 1064 nm wavelength at 10 Hz. Laser pulses at selected fluences were focused on the NiTi surface and generated pressure pulses of up to a few GPa. Optical microscope images showed that surface patterns with tailorable sizes can be obtained. The depth of the patterns increases with laser power and irradiation time. Upon heating, the depth profile of SMA surfaces changed where the maximum depth recovery ratio of 30 % was observed. Recovery ratio decreased and saturated at about 15 % when the amount of time and thus the indent depth was increased. Laser-induced shock wave propagation inside the material was simulated and showed a good agreement with the experimental results. The stress wave closely followed the rise time of the laser pulse to its peak value and initial decay. Rapid attenuation and dispersion of the stress wave were observed.
An advanced direct imprinting method with low cost, quick, and less environmental impact to create thermally controllable surface pattern using the laser pulses is reported. Patterned micro indents were generated on Ni50Ti50 shape memory alloys (SMA) using an Nd:YAG laser operating at 1064 nm combined with suitable transparent overlay, a sacrificial layer of graphite, and copper grid. Laser pulses at different energy densities which generates pressure pulses up to 10 GPa on the surface was focused through the confinement medium, ablating the copper grid to create plasma and transferring the grid pattern onto the NiTi surface. Scanning electron microscope (SEM) and optical microscope images of square pattern with different sizes were studied. One dimensional profile analysis shows that the depth of the patterned sample initially increase linearly with the laser energy until 125 mJ/pulse where the plasma further absorbs and reflects the laser beam. In addition, light the microscope image show that the surface of NiTi alloy was damaged due to the high power laser energy which removes the graphite layer.
The surfaces of Ni50Ti50 shape memory alloys (SMAs) were patterned by laser scribing. This method is more simplistic and efficient than traditional indentation techniques, and has also shown to be an effective method in patterning these materials. Different laser energy densities ranging from 5 mJ/pulse to 56 mJ/pulse were used to observe recovery on SMA surface. The temperature dependent heat profiles of the NiTi surfaces after laser scribing at 56 mJ/pulse show the partially-recovered indents, which indicate a "shape memory effect (SME)" Experimental data is in good agreement with theoretical simulation of laser induced shock wave propagation inside NiTi SMAs. Stress wave closely followed the rise time of the laser pulse to its peak values and initial decay. Further investigations are underway to improve the SME such that the indents are recovered to a greater extent.
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