Refractive index of adipose tissue and lipid droplet measured in wide spectral and temperature ranges.

This study presents refractive index measurements of human and porcine adipose tissues and lipid droplet content in the visible and near-infrared. The coefficients of the Sellmeier formula were calculated for approximation of tissue dispersion. For the first time, to the best of our knowledge, the phase transition temperatures and temperature increments dn/dT of adipose tissue were quantified for a wide wavelength range from 480 to 1550 nm and from room temperature up to 50°C. For human abdominal adipose tissue, the refractive index increment averaged across all wavelengths is dn/dT=-(3.54±0.15)×10-4°C-1, for porcine tissue dn/dT=-7.92(0.74)×10-4°C-1, and for porcine lipid droplet dn/dT=-6.01(0.29)×10-4°C-1. Data available in literature for refractive indices of adipose tissues measured by different techniques are summarized and compared with the received data.

Multimodal Diagnostics of Changes in Rat Lungs after Vaping.

(1) Background: The use of electronic cigarettes has become widespread in recent years. The use of e-cigarettes leads to milder pathological conditions compared to traditional cigarette smoking. Nevertheless, e-liquid vaping can cause morphological changes in lung tissue, which affects and impairs gas exchange. This work studied the changes in morphological and optical properties of lung tissue under the action of an e-liquid aerosol. To do this, we implemented the "passive smoking" model and created the specified concentration of aerosol of the glycerol/propylene glycol mixture in the chamber with the animal. (2) Methods: In ex vivo studies, the lungs of Wistar rats are placed in the e-liquid for 1 h. For in vivo studies, Wistar rats were exposed to the e-liquid vapor in an aerosol administration chamber. After that, lung tissue samples were examined ex vivo using optical coherence tomography (OCT) and spectrometry with an integrating sphere. Absorption and reduced scattering coefficients were estimated for the control and experimental groups. Histological sections were made according to the standard protocol, followed by hematoxylin and eosin staining. (3) Results: Exposure to e-liquid in ex vivo and aerosol in in vivo studies was found to result in the optical clearing of lung tissue. Histological examination of the lung samples showed areas of emphysematous expansion of the alveoli, thickening of the alveolar septa, and the phenomenon of plasma permeation, which is less pronounced in in vivo studies than for the exposure of e-liquid ex vivo. E-liquid aerosol application allows for an increased resolution and improved imaging of lung tissues using OCT. Spectral studies showed significant differences between the control group and the ex vivo group in the spectral range of water absorption. It can be associated with dehydration of lung tissue owing to the hyperosmotic properties of glycerol and propylene glycol, which are the main components of e-liquids. (4) Conclusions: A decrease in the volume of air in lung tissue and higher packing of its structure under e-liquid vaping causes a better contrast of OCT images compared to intact lung tissue.

Light distribution in fat cell layers at physiological temperatures.

Adipose tissue (AT) optical properties for physiological temperatures and in vivo conditions are still insufficiently studied. The AT is composed mainly of packed cells close to spherical shape. It is a possible reason that AT demonstrates a very complicated spatial structure of reflected or transmitted light. It was shown with a cellular tissue phantom, is split into a fan of narrow tracks, originating from the insertion point and representing filament-like light distribution. The development of suitable approaches for describing light propagation in a AT is urgently needed. A mathematical model of the propagation of light through the layers of fat cells is proposed. It has been shown that the sharp local focusing of optical radiation (light localized near the shadow surface of the cells) and its cleavage by coupling whispering gallery modes depends on the optical thickness of the cell layer. The optical coherence tomography numerical simulation and experimental studies results demonstrate the importance of sharp local focusing in AT for understanding its optical properties for physiological conditions and at AT heating.

Optical clearing and testing of lung tissue using inhalation aerosols: prospects for monitoring the action of viral infections.

Optical clearing of the lung tissue aims to make it more transparent to light by minimizing light scattering, thus allowing reconstruction of the three-dimensional structure of the tissue with a much better resolution. This is of great importance for monitoring of viral infection impact on the alveolar structure of the tissue and oxygen transport. Optical clearing agents (OCAs) can provide not only lesser light scattering of tissue components but also may influence the molecular transport function of the alveolar membrane. Air-filled lungs present significant challenges for optical imaging including optical coherence tomography (OCT), confocal and two-photon microscopy, and Raman spectroscopy, because of the large refractive-index mismatch between alveoli walls and the enclosed air-filled region. During OCT imaging, the light is strongly backscattered at each air-tissue interface, such that image reconstruction is typically limited to a single alveolus. At the same time, the filling of these cavities with an OCA, to which water (physiological solution) can also be attributed since its refractive index is much higher than that of air will lead to much better tissue optical transmittance. This review presents general principles and advances in the field of tissue optical clearing (TOC) technology, OCA delivery mechanisms in lung tissue, studies of the impact of microbial and viral infections on tissue response, and antimicrobial and antiviral photodynamic therapies using methylene blue (MB) and indocyanine green (ICG) dyes as photosensitizers.

Immersion optical clearing of adipose tissue in rats: ex vivo and in vivo studies.

Optical clearing (OC) of adipose tissue has not been studied enough, although it can be promising in medical applications, including surgery and cosmetology, for example, to visualize blood vessels or increase the permeability of tissues to laser beams. The main objective of this work is to develop technology for OC of abdominal adipose tissue in vivo using hyperosmotic optical clearing agents (OCAs). The maximum OC effect (77%) was observed for ex vivo rat adipose tissue samples exposed to OCA on fructose basis for 90 minutes. For in vivo studies, the maximum effect of OC (65%) was observed when using OCA based on diatrizoic acid and dimethylsulfoxide for 120 minutes. Histological analysis showed that in vivo application of OCAs may induce a limited local necrosis of fat cells. The efficiency of OC correlated with local tissue damage through cell necrosis due to accompanied cell lipolysis.

Optical monitoring of adipose tissue destruction under encapsulated lipase action.

Enzymatic destruction of adipose tissue has been achieved by encapsulation of lipase into the polymeric microcapsules. Adipose tissue destruction was delayed while lipase is encapsulated comparing with the direct lipase action as demonstrated by optical microscopy and optical coherence tomography in in vitro studies. Raman spectroscopy confirms that triglycerides in fat tissue were cleaved into free fatty acids, glycerol, and possible di- and monoglyceride residues. The results underpin the concept of local and controlled treatment of tissues via encapsulation. Effect of lipase encapsulation into the polymeric microcapsules on adipose tissue destruction compared to free lipase application.

Measurement of tissue optical properties in the context of tissue optical clearing.

Nowadays, dynamically developing optical (photonic) technologies play an ever-increasing role in medicine. Their adequate and effective implementation in diagnostics, surgery, and therapy needs reliable data on optical properties of human tissues, including skin. This paper presents an overview of recent results on the measurements and control of tissue optical properties. The issues reported comprise a brief review of optical properties of biological tissues and efficacy of optical clearing (OC) method in application to monitoring of diabetic complications and visualization of blood vessels and microcirculation using a number of optical imaging technologies, including spectroscopic, optical coherence tomography, and polarization- and speckle-based ones. Molecular modeling of immersion OC of skin and specific technique of OC of adipose tissue by its heating and photodynamic treatment are also discussed.

Delivery and reveal of localization of upconversion luminescent microparticles and quantum dots in the skin in vivo by fractional laser microablation, multimodal imaging, and optical clearing.

Delivery and spatial localization of upconversion luminescent microparticles [Y2O3:Yb, Er] (mean size ∼1.6 µm) and quantum dots (QDs) (CuInS2/ZnS nanoparticles coated with polyethylene glycol-based amphiphilic polymer, mean size ∼20 nm) inside rat skin was studied in vivo using a multimodal optical imaging approach. The particles were embedded into the skin dermis to the depth from 300 to 500 µm through microchannels performed by fractional laser microablation. Low-frequency ultrasound was applied to enhance penetration of the particles into the skin. Visualization of the particles was revealed using a combination of luminescent spectroscopy, optical coherence tomography, confocal microscopy, and histochemical analysis. Optical clearing was used to enhance the image contrast of the luminescent signal from the particles. It was demonstrated that the penetration depth of particles depends on their size, resulting in a different detection time interval (days) of the luminescent signal from microparticles and QDs inside the rat skin in vivo. We show that luminescent signal from the upconversion microparticles and QDs was detected after the particle delivery into the rat skin in vivo during eighth and fourth days, respectively. We hypothesize that the upconversion microparticles have created a long-time depot localized in the laser-created channels, as the QDs spread over the surrounding tissues.

Morphology alterations of skin and subcutaneous fat at NIR laser irradiation combined with delivery of encapsulated indocyanine green.

The goal of this study is to quantify the impact of the in vivo photochemical treatment of rats with obesity using indocyanine green (ICG) dissolved in saline or dispersed in an encapsulated form at NIR laser irradiation, which was monitored by tissue sampling and histochemistry. The subcutaneous injection of the ICG solution or ICG encapsulated into polyelectrolyte microcapsules, followed by diode laser irradiation (808 nm, 8 ?? W / cm 2 , 1 min), resulted in substantial differences in lipolysis of subcutaneous fat. Most of the morphology alterations occurred in response to the laser irradiation if a free-ICG solution had been injected. In such conditions, membrane disruption, stretching, and even delamination in some cases were observed for a number of cells. The encapsulated ICG aroused similar morphology changes but with weakly expressed adipocyte destruction under the laser irradiation. The Cochran Q test rendered the difference between the treatment alternatives statistically significant. By this means, laser treatment using the encapsulated form of ICG seems more promising and could be used for safe layerwise laser treatment of obesity and cellulite.

In vivo optical monitoring of transcutaneous delivery of calcium carbonate microcontainers.

We have developed a method for delivery of biocompatible CaCO3 microcontainers (4.0 ± 0.8 µm) containing Fe3O4 nanoparticles (14 ± 5 nm) into skin in vivo using fractional laser microablation (FLMA) provided by a pulsed Er:YAG laser system. Six laboratory rats have been used for the microcontainer delivery and weekly monitoring implemented using an optical coherence tomography and a standard histological analysis. The use of FLMA allowed for delivery of the microcontainers to the depth about 300 µm and creation of a depot in dermis. On the seventh day we have observed the dissolving of the microcontainers and the release of nanoparticles into dermis.

Photoinduced cell morphology alterations quantified within adipose tissues by spectral optical coherence tomography.

Morphological changes of the adipose tissue at phototreatment are studied in vitro using optical coherence tomography. The 200 to 600 µm fat tissue slices are used in the experiments. The observed change in the tissue structure was associated with fat cell lipolysis and destruction caused by the photodynamic effect. It is found that overall heating of a sample from room to physiological temperature leads to deeper and faster morphology tissue changes if other processing conditions are kept constant. These data support the hypothesis that photodynamic/photothermal treatment induces fat cell lipolysis during some period after treatment.

Fat tissue histological study at indocyanine green-mediated photothermal/photodynamic treatment of the skin in vivo.

Histological slices of skin samples with the subcutaneous adipose tissue after photothermal/photodynamic treatment are analyzed. In the case of subcutaneous indocyanine green injection and 808-nm diode laser exposure of the rat skin site in vivo, the greatest changes in tissue condition were observed. Processes were characterized by dystrophy, necrosis, and desquamation of the epithelial cells, swelling and necrosis of the connective tissue, and widespread necrosis of the subcutaneous adipose tissue. The obtained data are useful for safe layer-by-layer dosimetry of laser illumination of ICG-stained adipose tissue for treatment of obesity and cellulite.