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.
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.
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