BackgroundHuman induced pluripotent stem cell-derived mesenchymal stem cells (hiPSC-MSCs) have emerged as a promising alternative for stem cell transplantation therapy. Exosomes derived from mesenchymal stem cells (MSC-Exos) can play important roles in repairing injured tissues. However, to date, no reports have demonstrated the use of hiPSC-MSC-Exos in cutaneous wound healing, and little is known regarding their underlying mechanisms in tissue repair.MethodshiPSC-MSC-Exos were injected subcutaneously around wound sites in a rat model and the efficacy of hiPSC-MSC-Exos was assessed by measuring wound closure areas, by histological and immunofluorescence examinations. We also evaluated the in vitro effects of hiPSC-MSC-Exos on both the proliferation and migration of human dermal fibroblasts and human umbilical vein endothelial cells (HUVECs) by cell-counting and scratch assays, respectively. The effects of exosomes on fibroblast collagen and elastin secretion were studied in enzyme-linked immunosorbent assays and quantitative reverse-transcriptase–polymerase chain reaction (qRT-PCR). In vitro capillary network formation was determined in tube-formation assays.ResultsTransplanting hiPSC-MSC-Exos to wound sites resulted in accelerated re-epithelialization, reduced scar widths, and the promotion of collagen maturity. Moreover, hiPSC-MSC-Exos not only promoted the generation of newly formed vessels, but also accelerated their maturation in wound sites. We found that hiPSC-MSC-Exos stimulated the proliferation and migration of human dermal fibroblasts and HUVECs in a dose-dependent manner in vitro. Similarly, Type I, III collagen and elastin secretion and mRNA expression by fibroblasts and tube formation by HUVECs were also increased with increasing hiPSC-MSC-Exos concentrations.ConclusionsOur findings suggest that hiPSC-MSC-Exos can facilitate cutaneous wound healing by promoting collagen synthesis and angiogenesis. These data provide the first evidence for the potential of hiPSC-MSC-Exos in treating cutaneous wounds.

Limonene has a high emission rate both from biogenic sources and from household solvents. Here we examine the limonene + ozone reaction as a source for secondary organic aerosol (SOA). Our data show that limonene has very high potential to form SOA and that NO(x) levels, O(3) levels, and UV radiation all influence SOA formation. High SOA formation is observed under conditions where both double bonds in limonene are oxidized, but those conditions depend strongly on NO(x). At low NO(x), heterogeneous oxidation of the terminal double bond follows the initial limonene ozonolysis (at the endocyclic double bond) almost immediately, making the initial reaction rate limiting. This requires a high uptake coefficient between ozone and the first-generation, unsaturated organic particles. However, at high NO(x), this heterogeneous processing is inhibited and gas-phase oxidation of the terminal double bond dominates. Although this chemistry is slower, it also yields products with low volatility. UV light suppresses production of the lowest volatility products, as we have shown in earlier studies of the alpha-pinene + ozone reaction.

Chronic skin wounds represent one of the most common and disabling complications of diabetes. Endothelial progenitor cells (EPCs) are precursors of endothelial cells and can enhance diabetic wound repair by facilitating neovascularization. Recent studies indicate that the transplanted cells exert therapeutic effects primarily via a paracrine mechanism and exosomes are an important paracrine factor that can be directly used as therapeutic agents for regenerative medicine. However, application of exosomes in diabetic wound repair has been rarely reported. In this study, we demonstrated that the exosomes derived from human umbilical cord blood-derived EPCs (EPC-Exos) possessed robust pro-angiogenic and wound healing effects in streptozotocin-induced diabetic rats. By using a series of in vitro functional assays, we found that EPC-Exos could be incorporated into endothelial cells and significantly enhance endothelial cells' proliferation, migration, and angiogenic tubule formation. Moreover, microarray analyses indicated that exosomes treatment markedly altered the expression of a class of genes involved in Erk1/2 signaling pathway. It was further confirmed with functional study that this signaling process was the critical mediator during the exosomes-induced angiogenic responses of endothelial cells. Therefore, EPC-Exos are able to stimulate angiogenic activities of endothelial cells by activating Erk1/2 signaling, which finally facilitates cutaneous wound repair and regeneration.

Master equation calculations on a computational potential energy surface reveal that collisional stabilization at atmospheric pressure becomes important in the gas-phase ozonolysis of endocyclic alkenes for a carbon number between 8 and 15. Because the reaction products from endocyclic ozonolysis are tethered, this system is ideal for consideration of collisional energy transfer, as chemical activation is confined to a single reaction product. Collisional stabilization of the Criegee intermediate precedes collisional stabilization of the primary ozonide by roughly an order of magnitude in pressure. The stabilization of the Criegee intermediate leads to a dramatic transformation in the dominant oxidation pathway from a radical-forming process at low carbon number to a secondary ozonide-forming process at high carbon number. Secondary ozonide formation is important even for syn-isomer Criegee intermediates, contrary to previous speculation. We use substituted cyclohexenes as analogues for atmospherically important mono- and sesquiterpenes, which are major precursors for secondary organic aerosol formation in the atmosphere. Combining these calculations with literature experimental data, we conclude that the transformation from chemically activated to collisionally stabilized behavior most probably occurs between the mono- and sesquiterpenes, thus causing dramatically different atmospheric behavior.

We present a master equation study of organic nitrate formation from the peroxy radical (RO2) + NO reaction. The mechanism is constrained by both quantum chemical calculations of the potential energy surface and existing yield data. This mechanism displays heretofore unrecognized features of the system, including distinct conformers of a critical peroxynitrite (ROONO) intermediate that do not interconvert and a dual falloff behavior driven by collisional stabilization in multiple wells. These features have significant implications for atmospheric chemistry; in particular, only a fraction of the ROONO intermediates may easily isomerize to nitrates, resulting in a limit to total nitrate production. Existing mechanisms, extrapolated to low temperature and high pressure, produce nitrate almost exclusively. As a consequence, hydrocarbon oxidation sequences based on these mechanisms do not propagate radical chemistry, which is inconsistent with available experimental data. To reproduce observed nitrate yields, we model a transition state from the ROONO intermediate to RONO2 that differs considerably from the few found in computational studies. Specifically, the data require that this transition state energy lie well below the energy of separated radical products (RO + NO2), while computational studies find the transition state at higher energies. A second feature of yield data is difficult to model; to enable collisional stabilization of C5 systems, as observed, we reduce the unimolecular decomposition rate constants from the ROONO intermediate by a factor that is at the far end of the plausible range. However, with these experimental constraints in place, the model successfully reproduces multiple features of existing data quantitatively, including both high- and low-pressure asymptotes to nitrate production as well as the observed shifting of pressure falloff curves with carbon number. Consequently, we present a new parametrization of nitrate yields, providing interpolation equivalent to existing parametrizations but dramatically improved extrapolation behavior.

We present a novel method for continuous, stable OH radical production for use in smog chamber studies, especially those focused on organic aerosol aging. Our source produces OH radicals from the reaction of 2,3-dimethyl-2-butene and ozone and is unique as a method that requires neither NOx nor UV photolysis of a radical precursor. Typical radical concentrations are in the range of (4-8) x 10(6) molec cm(-3) and are easily sustainable over experimental time scales of several hours. We discuss design considerations, radical production capability under different operating conditions, and the core source chemistry. As a proof of concept we present preliminary results from oxidation of n-hexacosane aerosol observed with an Aerodyne Aerosol Mass Spectrometer. The extent of hexacosane oxidation is sufficient to significantly change the organic aerosol mass spectrum by virtue of fast heterogeneous uptake of OH radicals at the particle surface, with a calculated uptake coefficient gamma = 1.04 +/-0.21.

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Summary We present a systematic study of laboratory tests of alternative chemical formulations for a chemical flood design and application. Aqueous and microemulsion phase behavior tests have previously been shown to be a rapid, inexpensive, and highly effective means to select the best chemicals and minimize the need for relatively expensive coreflood tests. Microemulsion phase behavior testing was therefore conducted using various combinations of surfactants, cosolvents, and alkalis with a particular crude oil and in reservoir conditions of interest. Branched alcohol propoxy sulfates and internal olefin sulfonates showed high performance in these tests, even when mixed with both conventional and novel alkali agents. Systematic screening methods helped tailor and fine tune chemical mixtures to perform well under the given design constraints. The best chemical formulations were validated in coreflood experiments, and compared in terms of both oil recovery and surfactant retention in cores. Each of the four best formulations tested in corefloods gave nearly 100% oil recovery and very low surfactant adsorption. The two formulations with conventional and novel alkali agents gave almost zero surfactant retention. In standard practice, soft water must be used with alkali, but we show how alkali-surfactant-polymer (ASP) flooding can be used in this case even with very hard saline brine. Introduction Many mature reservoirs under waterflood have low economic production rates despite having as much as 50 to 75% of the original oil still in place. These reservoirs are viable candidates for chemical enhanced oil recovery (EOR) that uses both surfactant to reduce oil/water interfacial tension (IFT) and polymer to improve sweep efficiency. However, designing these aqueous chemical mixtures is complex and must be tailored to the reservoir rock and fluid (i.e., crude oil and formation brine) properties of the application. The early success of a systematic laboratory approach to low-cost, high performance chemical flooding depends on the efficiency of designing a formula for coreflood injection in accordance with sound evaluation criteria. A general, a three-stage procedure has been developed previously to screen hundreds of potential chemicals (i.e., surfactant, cosurfactant, cosolvent, alkali, polymer, and electrolytes), and arrive at a mixture having good recovery of residual oil in cores (Jackson 2006; Levitt 2006; Levitt et al. 2006). Additionally, furthering laboratory and field-testing in this area contributes to an expanding research database to help broaden reservoir types that can become candidates for routine chemical EOR application. This paper describes a systematic laboratory approach to low cost, high performance chemical flooding, and explores novel approaches to ASP flooding in reservoirs containing very hard saline brines. The design strategy first uses microemulsion phase behavior experiments to quickly select and optimize concentrations of injected chemicals. Assessment of formula optimization strategies are carried out through varying surfactant-to-cosurfactant ratio, reducing cosolvent concentration, reducing total surfactant concentration, selecting a suitable alkali, and using formation brine in the injection mixture. Formulations performing well in phase behavior are validated in coreflood experiments that adhere to necessary design criteria such as pressure and salinity gradients, surfactant adsorption, and capillary effects. We illustrate the application of our design approach in prepared Berea sandstone cores previously waterflooded with very hard saline brine, and show how ASP flooding can use some of the same brine in the chemical formulation. Conventional ASP flooding requires soft water that may not always be available, and softening hard brines can be very costly or infeasible in many cases depending on the location and other factors. These new results demonstrate high tolerance to both salinity and hardness of the high performance surfactants, and how novel alkalis--in particular sodium metaborate--can provide similar benefits in such harsh environments as sodium carbonate has shown in environments without divalent cations. This experimental success begins to vastly increase the range of conditions for economical EOR using chemicals.