Selective cell response on natural polymer bio-interfaces textured by femtosecond laser

This study reports on the evaluation of laser processed natural polymer-chitosan, which is under consideration as a biointerface used for temporary applications as skin and cartilage substitutes. It is employed for tissue engineering purposes, since it possesses a significant degree of biocompatibility and biodegradability. Chitosan-based thin films were processed by femtosecond laser radiation to enhance the surface properties of the material. Various geometry patterns were produced on polymer surfaces and employed to examine cellular adhesion and orientation. The topography of the modified zones was observed using scanning electron microscopy and confocal microscopy. Test of the material cytotoxicity was performed by evaluating the life/dead cell correlation. The obtained results showed that texturing with femtosecond laser pulses is appropriate method to initiate a predefined cellular response. Formation of surface modifications in the form of foams with an expansion of the material was created under laser irradiation with a number of applied laser pulses from N = 1-5. It is shown that irradiation with N > 5 results in disturbance of microfoam. Material characterization reveals a decrease in water contact angle values after laser irradiation of chitosan films. Consequently, changes in surface roughness of chitosan thin-film surface result in its functionalization. Cultivation of MC3T3 and ATMSC cells show cell orientational migration concerning different surface patterning. The influence of various pulse durations (varying from tau = 30-500 fs) over biofilms surface was examined regarding the evolution of surface morphology. The goal of this study was to define the optimal laser conditions (laser energy, number of applied pulses, and pulse duration) to alter surface wettability properties and porosity to improve material performance. The acquired set of results indicate the way to tune the surface properties to optimize cell-interface interaction

χ (2) -Lens Mode-Locking of a High Average Power Nd:YVO 4 Laser

Abstract: We report over 20 W, 6 ps, 170 MHz, passive mode-locking of a Nd:YVO 4 laser using χ Among laser materials, neodymium-doped vanadate Nd:YVO 4 has been the most extensively studied and widely used in diode-pumped high average power continuous-wave (CW) and mode-locked lasers for the past two decades. Nd:YVO 4 has large emission cross-section and polarized emission attributed to its natural birefringence as well as capacity for being pumped efficiently by laser diodes. The major drawback which limits the output power of Nd:YVO 4 lasers is the poorer thermo-mechanical properties of the crystal in comparison with that of Nd:YAG. Typically, multi-Watt operation of picosecond Nd:YVO 4 lasers has been demonstrated mainly using a modelocking technique based on semiconductor saturable absorber mirrors (SESAMs) In this work we report χ (2) -lens mode-locking of a Nd:YVO 4 laser using a LBO SHG crystal. The laser generates 6 ps transform-limited pulses at 170 MHz with output power of 20.1 W. To our knowledge, it is the maximum output power achieved by a χ (2) -lens mode-locked laser. The design of the mode-locked laser is based on a 810 mm long linear cavity

Improving osteoblasts cells proliferation via femtosecond laser surface modification of 3D-printed poly-ε-caprolactone scaffolds for bone tissue engineering applications

Synthetic polymer biomaterials incorporating cells are a promising technique for treatment of orthopedic injuries. To enhance the integration of biomaterials into the human body, additional functionalization of the scaffold surface should be carried out that would assist one in mimicking the natural cellular environment. In this study, we examined poly-epsilon-caprolactone (PCL) fiber matrices in view of optimizing the porous properties of the constructs. Altering the porosity of a PCL scaffold is expected to improve the material's biocompatibility, thus influencing its osteoconductivity and osteointegration. We produced 3D poly-epsilon-caprolactone (PCL) matrices by a fused deposition modeling method for bone and cartilage tissue engineering and performed femtosecond (fs) laser modification experiments to improve the surface properties of the PCL construct. Femtosecond laser processing is one of the useful tools for creating a vast diversity of surface patterns with reproducibility and precision. The processed surface of the PCL matrix was examined to follow the effect of the laser parameters, namely the laser pulse energy and repetition rate and the number (N) of applied pulses. The modified zones were characterized by scanning electron microscopy (SEM), confocal microscopy, X-ray computed tomography and contact angle measurements. The results obtained demonstrated changes in the morphology of the processed surface. A decrease in the water contact angle was also seen after fs laser processing of fiber meshes. Our work demonstrated that a precise control of material surface properties could be achieved by applying a different number of laser pulses at various laser fluence values. We concluded that the structural features of the matrix remain unaffected and can be successfully modified through laser postmodification. The cells tests indicated that the micro-modifications created induced MG63 and MC3T3 osteoblast cellular orientation. The analysis of the MG63 and MC3T3 osteoblast attachment suggested regulation of cells volume migration

Generation of 40ns laser pulses by a diode-pumped passively Q-switched Tm-Ho:YLF laser

We demonstrate for the first time generation of short pulses from a repetitively passively Q-switched Ho-laser that is diode-pumped near 800 nm by codoping with Tm-ions. The laser material used is the well-known fluoride crystal Tm,Ho:LiYF4 and polycrystalline Cr:ZnSe was employed as a saturable absorber. The maximum peak power achieved was ~640 W and the emission wavelength was ~2050 nm

Base pair motions control the rates and distance dependencies of reductive and oxidative DNA charge transfer

In 1999, Wan et al. [Proc. Natl. Acad. Sci. USA 96, 6014–6019] published a pioneering paper that established the entanglement between DNA base pair motions and the transfer time of the charge carrier. The DNA assemblies contained an ethidium covalently bound via a flexible alkyl chain to the 5′ hydroxyl group of the DNA backbone. Although covalently attached, the loose way in which the ethidium was linked to DNA allowed for large degrees of conformational freedom and thus raised some concern with respect to conformational inhomogeneity. In this letter, we report studies on a different set of ethidium DNA conjugates. In contrast to the “Caltech systems,” these conjugates contain ethidium tightly incorporated (as a base pair surrogate) into the DNA base stack, opposite to an abasic site analog. Despite the tight binding, we found that charge transfer from the photoexcited ethidium base pair surrogate across two or more base pairs is several orders of magnitude slower than in case of the DNA systems bearing the tethered ethidium. To further broaden the scope of this account, we compared (oxidative) electron hole transfer and (reductive) electron transfer using the same ethidium chromophore as a charge donor in combination with two different charge acceptors. We found that both electron and hole transfer are characterized by similar rates and distance dependencies. The results demonstrate the importance of nuclear motions and conformational flexibility and underline the presence of a base gating mechanism, which appears to be generic to electronic transfer processes through π-stacked nucleic acids