Parametric localized modes in quadratic nonlinear photonic structures

We analyze two-color spatially localized modes formed by parametrically coupled fundamental and second-harmonic fields excited at quadratic (or chi-2) nonlinear interfaces embedded into a linear layered structure --- a quasi-one-dimensional quadratic nonlinear photonic crystal. For a periodic lattice of nonlinear interfaces, we derive an effective discrete model for the amplitudes of the fundamental and second-harmonic waves at the interfaces (the so-called discrete chi-2 equations), and find, numerically and analytically, the spatially localized solutions --- discrete gap solitons. For a single nonlinear interface in a linear superlattice, we study the properties of two-color localized modes, and describe both similarities and differences with quadratic solitons in homogeneous media.Comment: 9 pages, 8 figure

Synthesis of Co-Ni Alloy Particles with the Structure of a Solid Substitution Solution by Precipitation in a Supercritical Carbon Dioxide

Mixed Co-Ni bimetallic systems with the structure of a solid substitution solution have been synthesized using the supercritical antisolvent precipitation (SAS) method, which uses supercritical CO2 as an antisolvent. The systems obtained have been characterized in detail using X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), Fourier-transform infrared (FTIR) spectroscopy, and magnetostatic measurements. It has been found that Co-enriched systems have a defective hexagonal close-packed (hcp) structure, which was described by a model which embedded cubic fragments of packaging into a hexagonal close-packed (hcp) structure. It has been shown that an increase in water content at the precipitation stage leads to a decrease in the size of cubic fragments and a more uniform distribution of them in Co-enriched systems. It has also been shown that mixed systems have the greatest coercivity in the line of samples. Ni-enriched bimetallic systems have a cubic close-packed (ccp) structure with modified crystal lattice parameters

Synthesis and Characterization of Novel Succinyl Chitosan-Dexamethasone Conjugates for Potential Intravitreal Dexamethasone Delivery

The development of intravitreal glucocorticoid delivery systems is a current global challenge for the treatment of inflammatory diseases of the posterior segment of the eye. The main advantages of these systems are that they can overcome anatomical and physiological ophthalmic barriers and increase local bioavailability while prolonging and controlling drug release over several months to improve the safety and effectiveness of glucocorticoid therapy. One approach to the development of optimal delivery systems for intravitreal injections is the conjugation of low-molecular-weight drugs with natural polymers to prevent their rapid elimination and provide targeted and controlled release. This study focuses on the development of a procedure for a two-step synthesis of dexamethasone (DEX) conjugates based on the natural polysaccharide chitosan (CS). We first used carbodiimide chemistry to conjugate DEX to CS via a succinyl linker, and we then modified the obtained systems with succinic anhydride to impart a negative ζ-potential to the polymer particle surface. The resulting polysaccharide carriers had a degree of substitution with DEX moieties of 2–4%, a DEX content of 50–85 μg/mg, and a degree of succinylation of 64–68%. The size of the obtained particles was 400–1100 nm, and the ζ-potential was −30 to −33 mV. In vitro release studies at pH 7.4 showed slow hydrolysis of the amide and ester bonds in the synthesized systems, with a total release of 8–10% for both DEX and succinyl dexamethasone (SucDEX) after 1 month. The developed conjugates showed a significant anti-inflammatory effect in TNFα-induced and LPS-induced inflammation models, suppressing CD54 expression in THP-1 cells by 2- and 4-fold, respectively. Thus, these novel succinyl chitosan-dexamethasone (SucCS-DEX) conjugates are promising ophthalmic carriers for intravitreal delivery

Succinyl Chitosan-Colistin Conjugates as Promising Drug Delivery Systems

The growth of microbial multidrug resistance is a problem in modern clinical medicine. Chemical modification of active pharmaceutical ingredients is an attractive strategy to improve their biopharmaceutical properties by increasing bioavailability and reducing drug toxicity. Conjugation of antimicrobial drugs with natural polysaccharides provides high efficiency of these systems due to targeted delivery, controlled drug release and reduced toxicity. This paper reports a two-step synthesis of colistin conjugates (CT) with succinyl chitosan (SucCS); first, we modified chitosan with succinyl anhydride to introduce a carboxyl function into the polymer molecule, which was then used for chemical grafting with amino groups of the peptide antibiotic CT using carbodiimide chemistry. The resulting polymeric delivery systems had a degree of substitution (DS) by CT of 3–8%, with conjugation efficiencies ranging from 54 to 100% and CT contents ranging from 130–318 μg/mg. The size of the obtained particles was 100–200 nm, and the ζ-potential varied from −22 to −28 mV. In vitro release studies at pH 7.4 demonstrated ultra-slow hydrolysis of amide bonds, with a CT release of 0.1–0.5% after 12 h; at pH 5.2, the hydrolysis rate slightly increased; however, it remained extremely low (1.5% of CT was released after 12 h). The antimicrobial activity of the conjugates depended on the DS. At DS 8%, the minimum inhibitory concentration (MIC) of the conjugate was equal to the MIC of native CT (1 µg/mL); at DS of 3 and 5%, the MIC increased 8-fold. In addition, the developed systems reduced CT nephrotoxicity by 20–60%; they also demonstrated the ability to reduce bacterial lipopolysaccharide-induced inflammation in vitro. Thus, these promising CT-SucCS conjugates are prospective for developing safe and effective nanoantibiotics

Succinyl Chitosan-Colistin Conjugates as Promising Drug Delivery Systems

The growth of microbial multidrug resistance is a problem in modern clinical medicine. Chemical modification of active pharmaceutical ingredients is an attractive strategy to improve their biopharmaceutical properties by increasing bioavailability and reducing drug toxicity. Conjugation of antimicrobial drugs with natural polysaccharides provides high efficiency of these systems due to targeted delivery, controlled drug release and reduced toxicity. This paper reports a two-step synthesis of colistin conjugates (CT) with succinyl chitosan (SucCS); first, we modified chitosan with succinyl anhydride to introduce a carboxyl function into the polymer molecule, which was then used for chemical grafting with amino groups of the peptide antibiotic CT using carbodiimide chemistry. The resulting polymeric delivery systems had a degree of substitution (DS) by CT of 3–8%, with conjugation efficiencies ranging from 54 to 100% and CT contents ranging from 130–318 μg/mg. The size of the obtained particles was 100–200 nm, and the ζ-potential varied from −22 to −28 mV. In vitro release studies at pH 7.4 demonstrated ultra-slow hydrolysis of amide bonds, with a CT release of 0.1–0.5% after 12 h; at pH 5.2, the hydrolysis rate slightly increased; however, it remained extremely low (1.5% of CT was released after 12 h). The antimicrobial activity of the conjugates depended on the DS. At DS 8%, the minimum inhibitory concentration (MIC) of the conjugate was equal to the MIC of native CT (1 µg/mL); at DS of 3 and 5%, the MIC increased 8-fold. In addition, the developed systems reduced CT nephrotoxicity by 20–60%; they also demonstrated the ability to reduce bacterial lipopolysaccharide-induced inflammation in vitro. Thus, these promising CT-SucCS conjugates are prospective for developing safe and effective nanoantibiotics

Night Photostimulation of Clearance of Beta-Amyloid from Mouse Brain: New Strategies in Preventing Alzheimer’s Disease

The deposition of amyloid-β (Aβ) in the brain is a risk factor for Alzheimer’s disease (AD). Therefore, new strategies for the stimulation of Aβ clearance from the brain can be useful in preventing AD. Transcranial photostimulation (PS) is considered a promising method for AD therapy. In our previous studies, we clearly demonstrated the PS-mediated stimulation of lymphatic clearing functions, including Aβ removal from the brain. There is increasing evidence that sleep plays an important role in Aβ clearance. Here, we tested our hypothesis that PS at night can stimulate Aβ clearance from the brain more effectively than PS during the day. Our results on healthy mice show that Aβ clearance from the brain occurs faster at night than during wakefulness. The PS course at night improves memory and reduces Aβ accumulation in the brain of AD mice more effectively than the PS course during the day. Our results suggest that night PS is a more promising candidate as an effective method in preventing AD than daytime PS. These data are an important informative platform for the development of new noninvasive and nonpharmacological technologies for AD therapy as well as for preventing Aβ accumulation in the brain of people with disorder of Aβ metabolism, sleep deficit, elderly age, and jet lag.Peer Reviewe