The creation of microporous surface modification of chitosan thin films irradiated by ultrashort laser pulses are studied. For this purpose, chitosan substrates were treated by using an amplified Ti:sapphire laser system at 800 nm central wavelength with 30 fs and 150 fs pulse duration and repetition rate 1 kHz and 50 Hz, respectively. Formation of surface modifications for both cases (30 fs and 150 fs) after femtosecond laser irradiation were observed. The threshold values for single-pulse (N = 1) and multi-pulse (N > 1) modification were evaluated by studying the linear relationship between the squared crater diameter D2 and the logarithm of the laser fluence (F) for N = 1, 2, 5, 10, 20, 30 and 50 number of laser pulses. The coefficient of incubation ξ, a major parameter in the process of surface modification and ablation of materials also was calculated for multi - pulse fluence threshold estimation by power - law relationship Fth (N) = Fth (1) Nξ-1, where N is the number of applied laser pulses. The surface properties of chitosan based thin films before and after femtosecond laser irradiation were investigated. The aim of this work is to determine the optimal morphological characteristics of the created structures for tailoring of protein adsorption and cell behavior.
The collagen – elastin biopolymer thin films treated by CPA Ti:Sapphire laser (Femtopower – Compact Pro) at 800nm central wavelength with 30fs and 1kHz repetition rate are investigated. A process of surface modifications and microporous scaffold creation after ultrashort laser irradiation has been observed. The single–shot (N=1) and multi–shot (N<1) ablation threshold values were estimated by studying the linear relationship between the square of the crater diameter D2 and the logarithm of the laser fluence F for determination of the threshold fluences for N=1, 2, 5, 10, 15 and 30 number of laser pulses. The incubation analysis by calculation of the incubation coefficient ξ for multi – shot fluence threshold for selected materials by power – law relationship form Fth(N)=Fth(1)Nξ-1 was also obtained. In this paper, we have also shown another consideration of the multi – shot ablation threshold calculation by logarithmic dependence of the ablation rate d on the laser fluence. The morphological surface changes of the modified regions were characterized by scanning electron microscopy to estimate the generated variations after the laser treatment.
The propagation is investigated of a continuous laser beam through homogeneous tissue-like turbid media such as diluted
emulsions of Intralipid or milk having presumably sharply forward directed Henyey-Greenstein or Gaussian indicatrices.
The cross sectional radial distributions of the detected forward-propagating light power at different depths along the
beam axis in each medium of interest are experimentally determined. The detected-power spatial distribution, for both
the types of indicatrices, is also described analytically by a solution of the radiative transfer equation in the so-called
small-angle approximation. The experimental results are consistent with the analytical expressions obtained that are
shown to allow one to estimate the extinction ( αt), reduced-scattering (αrs) and absorption (αa) coefficients and the gfactor
of the investigated media. The values obtained of α quite reasonable and
behave, depending on the dilution turbidity, in a way observed formerly in other similar experiments. The comparative
analysis of the estimated characteristics of the dilutions shows that in the case of Henyey-Greenstein indicatrix we have a
smaller value of the g-factor and larger value of αrs with respect to the case of Gaussian indicatrix. At equal g-factors, in
the former case we shall have a narrower forward-propagating scattered-light beam with higher on-axis intensity as
compared with the latter case.
Fluorescent analysis of basal cell carcinoma (BCC), squamous cell carcinoma (SCC), keratoacanthoma and benign
cutaneous lesions is carried out under initial phase of clinical trial in the National Oncological Center - Sofia. Excitation
sources with maximum of emission at 365, 380, 405, 450 and 630 nm are applied for better differentiation between nonmelanoma
malignant cutaneous lesions fluorescence and spectral discrimination from the benign pathologies. Major
spectral features are addressed and diagnostic discrimination algorithms based on lesions' emission properties are
proposed. The diagnostic algorithms and evaluation procedures found will be applied for development of an optical
biopsy clinical system for skin cancer detection in the frames of National Oncological Center and other university
hospital dermatological departments in our country.
The spatial parameters of scattered light in turbid media with different degrees of turbidity and at various depths are
studied in this work. The measurements are made at two wavelengths (687 nm and 850 nm). A collimated laser radiation
is used in the experiments in order to avoid the effect of input laser beam structure on the measured optical fields. The
radial and in depth distribution is measured of the intensity of the forward-scattered optical beam radiation in turbid
(tissue-like) media. The influence of small ingredients within the turbid media is also analyzed. The optical properties of
the ingredients are different from those of the surrounding turbid medium. Milk-water mixtures are used as a test
medium. The intensity distribution within milk solutions with concentrations ranging from 3.3% to 16.5% is measured in
depth of more than 10 cm. The experimental results indicate that the presence of small ingredients within the phantom
leads to characteristic changes of the intensity distribution. These preliminary results are evaluated as promising for
developing a novel technique for determination of optical characteristics of small embedded ingredients in turbid media.
Light-induced autofluorescence spectroscopy provides many possibilities for medical diagnostics needs for
differentiation of tissue pathologies including cancer. For the needs of clinical practice scientists collect spectral data
from patients in vivo or they study different tumor models to obtain objective information for fluorescent properties of
every kind of normal and diseased tissue. Therefore it is very important to find the most appropriate and close to the
human skin samples from the point of view of laser-induced fluorescence spectroscopy, which will give the possibility
for easier transfer of data obtained in animal models to spectroscopic medical diagnostics in humans. In this study are
presented some results for in vitro detection of the autofluorescence signals of the animal skin (pig and chicken) with
using of LEDs as excitation sources (maximum emission at 365, 375, 385 and 400 nm). The autofluorescence signals
from in vivo human skin were also detected for comparison with the models' results. Specific features of the spectra
measured are discussed and there are proposed some of the origins of the fluorescence signals obtained. Fluorescence
maxima detected are addressed to the typical fluorophores existing in the cutaneous tissues. Influence of main skin
absorbers, namely melanin and hemoglobin, is also discussed.
In this study are presented some initial results using LEDs as excitation sources for the needs of fluorescence
spectroscopy of the skin, which are compared with the results obtained by nitrogen laser used as excitation source for
cutaneous fluorescence. The main studies are made by developed in IE-BAS experimental fibro-optic system for
fluorescence spectroscopy. Several volunteers, representative of each skin phototype typical for Bulgarian region,
namely--phototypes I, II and III were investigated by the methods of fluorescence spectroscopy of the human skin on
several anatomic sites, typical for this type of measurements--palm, medial part of the forearm and lateral part of the
forearm. Fluorescence maxima detected are addressed to the typical fluorophores existing in the cutaneous tissues.
Influence of main skin absorbers, namely melanin and hemoglobin, is also discussed and their impact on the
fluorescence signals received from different anatomical areas and skin phototypes is determined.
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