Although the underlying molecular causes of aging are not entirely clear, hormetic agents like exercise, heat, and calorie restriction may generate a mild pro-oxidant stress that induces cell protective responses to promote healthy aging. As an individual ages, many cellular and physiological processes decline, including wound healing and reparative angiogenesis. This is particularly critical in patients with chronic non-healing wounds who tend to be older. We are interested in the potential beneficial effects of hyperbaric oxygen as a mild hormetic stress on human microvascular endothelial cells. We analyzed global gene expression changes in human endothelial cells following a hyperbaric exposure comparable to a clinical treatment. Our analysis revealed an upregulation of antioxidant, cytoprotective, and immediate early genes. This increase coincided with an increased resistance to a lethal oxidative stress. Our data indicate that hyperbaric oxygen can induce protection against oxidative insults in endothelial cells and may provide an easily administered hormetic treatment to help promote healthy aging.
Monodisperse thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) microgel particles having a diameter of 520 nm were synthesized by free-radical precipitation polymerization and centrifuged to obtain a concentrated suspension. The centrifuged mother suspension was made to self-order into a crystalline state by repeated annealing beyond the volume phase transition (VPT) of the particles. We report here the three-dimensional (3D) real space structure, determined using a confocal laser scanning microscope, of PNIPAM microgel crystal samples prepared by two different recrystallized routes: (1) solidifying a shear melted colloidal liquid (referred as as-prepared sample) and (2) slow cooling of a colloidal liquid (referred as recrystallized sample). We have recorded images of several regions of the crystal with each region containing 15 horizontal crystal planes for determining the in-plane [two-dimensional (2D)] and 3D pair-correlation functions. The 2D pair-correlation function g(r) revealed hexagonal long-range order of particles in the layers with a lattice constant of 620 nm. The analysis of stacking sequence of layers recorded on as-prepared sample has revealed the existence of stacking disorder with an average stacking probability alpha approximately 0.42. This value of alpha together with the analysis of 3D pair-correlation function determined from particle positions revealed the structure of microgel crystals in the as-prepared sample to be random hexagonal close packing. We report the first observation of a split second peak in the 3D g(r) of the microgel crystals obtained from a shear melted liquid. Upon melting the sample above VPT and recrystallizing it the split second peak disappeared and the crystals are found to have a face centered cubic (fcc) structure with alpha approximately 0.95. From simulations, the split second peak is shown to arise from the displacement of some of the B-planes from the ideal hcp positions. The present results are discussed in light of those reported for charged and hard sphere colloidal crystals and plausible reasons for observing two different structures are also explained.
Nanocrystals having single-band red emission under near-infrared (NIR) excitation through the upconversion process offer great advantages in terms of enhanced cellular imaging in in vitro and in vivo experiments in the biological window (600−900 nm), as a security ink, in photothermal therapy (PTT), in photodynamic therapy (PDT), and so forth but are challenging for materials scientists. In this work, we report for the first time the preparation of a super bright red emitter at 655 nm from monodispersed NaErF 4 :0.5%Tm@ NaYF 4 :20%Yb nanocrystals (core@active shell). This phosphor exhibits 35 times stronger photoluminescence as compared to NaErF 4 :0.5%Tm@NaYF 4 (core@inactive shell). Here, an Er 3+ -enriched host matrix works simultaneously as an activator and a sensitizer under NIR excitation. Upconversion red emission at 655 nm arises due to the electronic transition of Er 3+ via the involvement of a three-photon absorption (expected to be a two-photon absorption), which has been confirmed via a power-dependent luminescence study. Tm 3+ ions incorporated into the core with the active shell act as trapping centers, which promote the red band emission via the back-energy transfer process. Moreover, the active shell containing Yb 3+ ions efficiently transfers the energy to the Er 3+ -enriched core, which suppresses the nonradiative channel rate, and Tm 3+ ions act as trapping centers, which reduce the luminescence quenching via reduction of energy migration to the surface of the host lattice. Also, we have shown the potential applications of these nanocrystals: cellular imaging through downconversion and upconversion processes and security ink.
Nearly monodispersed NaGdF4/Ho–Yb upconversion nanoparticles (UCNPs) are synthesized by thermolysis of respective rare earth oleates. UCNPs are made biocompatible by mesoporous silica (m-SiO2) coating. These particles exhibit red and green bands in the visible range upon excitation at 980 nm laser. Interestingly, because of the presence of Ho3+ ions, these UCNPs can be excited via UV–vis light in addition to the 980 nm near infrared light. A systematic study is carried out to demonstrate the use of these UCNPs as drug (DOX) carriers. Toxicity studies and bio-imaging using DOX-loaded UCNPs have been demonstrated. UCNPs are also radiolabeled with 177Lu using m-SiO2 coating to demonstrate its potential application as a carrier of the therapeutic radionuclide in vivo for radionuclide therapy. Lu-177 adsorption studies are carried out extensively in order to understand the nature of adsorption, and it is found to be a combination of Langmuir and Freundlich isotherm models. Kinetics of adsorption of Lu3+ ions on the m-SiO2 coating of UCNPs is studied. Overall, the synthesis and physicochemical characterization of NaGdF4/Ho–Yb@m-SiO2 upconversion nanocrystals and their potential utilities in multimodal biomedical applications are amply demonstrated.
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