Biopolymers for medical application

Biopolymers including alginate, chitosan, cellulose, cellulose acetate, silk, etc. that are used for the production of the biocomposite materials for applications in wound management will be presented. Optimized amount of active agents and model drugs, like eosin, PVPI, albumin, curcumin, essential oils of lavender, cinnamon, mint and others, can be incorporated into the biopolymer matrices. It will be presented the realization of smart fibrous mats, films from emulsions, and nanoparticles for wound dressings combining the abovementioned polymers derived from natural sources with the active agents. Electrospun fibers are excellent candidate for wound dressings and scaffolds, due to their characteristics of efficient absorption of wound exudates, gas permeability, protection against bacterial infections and oxidation, easy incorporation of bioactive molecules and drugs, good conformability, and promoted cell attachment and proliferation. Films from emulsions can combine hydrophobic biomatrices with hydrophilic drugs and vice versa, or can combine hydrophilic and hydrophobic drugs in one system. Finally, biocomposite nanoparticles or nanocapsules can be ideal candidates for reaching specific tissues or cells in the human body, which otherwise with conventional methods is very difficult. The controlled delivery in time of the active agents of these system will also be discussed

Optical enhancement by means of concentration tuning of gold precursors in polymer nanocomposite materials

In this work, we propose a new approach regarding the characterization and the enhancement of transmitted light travelling inside a chitosan polymeric film improved by implementation of gold precursors generating nanocomposite materials. Firstly, the experimental optical characterization indicates the influence of the presence of gold particles on the effective refractive index of the chitosan polymer films and, secondly, the influence of their thickness supported by the transmittivity enhancement at precise frequencies for each gold precursor concentration and each polymer film thickness. This developed analysis introduces a basic study for the light enhancement in future complex photonic devices suitable for sensing

Reversibly Light-Switchable Wettability of Hybrid Organic/Inorganic Surfaces With Dual Micro-/ Nanoscale Roughness

Here, an approach to realize ''smart'' solid substrates that can convert their wetting behavior between extreme states under selective light irradiation conditions is described. Hybrid organic/inorganic surfaces are engineered by exploiting photolithographically tailored SU-8 polymer patterns as templates for accommodating closely packed arrays of colloidal anatase TiO2 nanorods, which are able to respond to UV light by reversibly changing their surface chemistry. The TiO2-covered SU-8 substrates are characterized by a dual micro-/nanoscale roughness, arising from the overlapping of surfactantcapped inorganic nanorods onto micrometer-sized polymer pillars. Such combined architectural and chemical surface design enables the achievement of UV-driven reversible transitions from a highly hydrophobic to a highly hydrophilic condition, with excursions in water contact angle values larger than 1008. The influence of the geometric and compositional parameters of the hybrid surfaces on their wettability behavior is examined and discussed within the frame of the available theoretical models

Tuning Concept and Design Criteria of Efficient Planar Metallic Plasmon Waveguides Using Nanocomposite Materials for Electromagnetic Radiation Applications

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Wettability conversion of colloidal TiO2 nanocrystal thin films with UV-switchable hydrophilicity

Under pulsed laser UV irradiation, thin-film coatings made of close-packed TiO2 nanorods individually coated with surfactants can exhibit a temporary increase in their degree of surface hydroxylation without any apparent photocatalytic removal of the capping molecules. This mechanism provides a basis for achieving light-driven conversion from a highly hydrophobic to a highly hydrophilic, metastable state, followed by extremely slow recovery of the original conditions under dark ambient environment. A deeper insight into the wetting dynamics is gained by time-dependent water contact-angle and infrared spectroscopy monitoring of the film properties under different post-UV storage conditions. Our study reveals that, for reversible switchability between extreme wettability excursions and long-term repeatability of such changes to be achieved, specific modifications in the polar and nonpolar components of the TiO2 films need to be guaranteed along with preservation of the original geometric arrangement of the nanocrystal building blocks. The application of moderate vacuum is found to be an effective method for accelerating the post-UV hydrophilic-to-hydrophobic conversion, thereby enabling fast and cyclic hydrophilization/hydrophobicization alternation without any detrimental signs of significant fatigue

Amplified spontaneous emission and waveguiding properties of the colored merocyanine form of (1',3'-dihydro-1',3',3'-trimethyl-6-nitrospiro[2H-1-benzopyran-2,2'-(2H)-indole] molecules

We report a complete study of the properties of amplified spontaneous emission (ASE) of the merocyanine form of the photochromic system, 1',3'-dihydro-1',3',3'-trimethyl-6-nitrospiro[2H-1-benzopyran-2,2'-(2H)-indole], under nanosecond excitation conditions. ASE line narrowing is clearly observed for excitation densities larger than 400 μJ cm-2 with a threshold pumping length in the range 0.5−1.2 mm. Remarkable waveguiding properties were observed, with losses throughout the organic slab of about 5.7 cm-1. The observation of ASE is discussed in terms of a possible S1-dominated photoconversion and excitation/de-excitation dynamics of the photochromic system. These results are important in view of the application of merocyanine-based films as active layers for potentially gateable laser devices

Real time optical pressure sensing for tactile detection using gold nanocomposite material

For the first time, we propose in this work a new concept of optical tactile pressure sensing. We develop a sensor integrating an optical tapered fiber force sensor based on electromagnetic (EM) coupling effect. The sensor consists of a tapered multimode Si fiber which couples the EM field coming from a broad band lamp source with the flexible gold/PDMS nanocomposite material (GNM). PDMS polymer film was used since it is suitable for the generation of gold nanoparticles starting from gold precursors and consecutively is suitable for light coupling: the formed gold nanoparticles increase the effective refractive index of the PDMS and support the EM coupling with the tapered region. By applying different weights that can be translated to pressure forces to the sensor, we experimentally observe in real time the intensity reduction of the transmittivity response at the output of the fiber sensor. This effect is most likely due to displacement of gold nanoparticles near the tapered region during the pressure application

Tuning of the characteristics of Au nanoparticles produced by solid target laser ablation into water by changing the irradiation parameters.

We report the production of Au nanoparticles with different average sizes and size distributions, by laser ablation of a solid Au target into pure deionized water. Tuning laser parameters such as pulse duration, energy, and wavelength is possible to tune the size and the size distributions of the produced nanoparticles into the liquid. We demonstrate the possibility of production of highly monodispersed colloidal solutions, in which the average nanoparticle size ranges from 3 to 10 nm, using laser pulses of ns duration. Laser ablation using fs laser pulses can also produce very small nanoparticles, although a small population of bigger nanoparticles is always present. Low and high-resolution transmission electron microscopy (TEM), in combination with UV-Vis spectroscopy have been employed for the characterization of our samples

Photochemical synthesis: Effect of UV irradiation on gold nanorods morphology

Abstract Gold nanorods (AuNRs) were synthesized by photochemical method, through irradiation of a reaction solution, containing gold precursor, surfactant and a mild reducing agent to speed up the process. The effects of the irradiation parameters on the morphology of the formed AuNRs were investigated by UV–Vis absorption spectra and transmission electron microscopy. Specifically, the control of the UV irradiance (irradiation power per unit area) and irradiation time allowed the preparation of AuNRs with a wide range of sizes. Increase of the irradiation power leads to the formation of smaller AuNRs, with concomitant decrease of length and diameter. Since both axes show a simultaneous size decrease, the produced AuNRs have increased aspect ratio. Overall we show that application of high UV irradiance for short times favors the synthesis of small AuNRs with increased anisotropy. We propose that the rise of the irradiation power primarily accelerates the reduction of the gold precursor, promoting in such way the formation of smaller seeds. Short irradiation times guard against dissolution effects on the formed nanorods