Complexes of Charged-Neutral Block Copolymers and Surfactants: Process-Dependent Features and Long-Term Stability of Their Aqueous Dispersions.

Aqueous dispersions of charged-neutral block copolymers (poly(acrylamide)-b-poly(acrylate)) complexed with an oppositely charged surfactant (dodecyltrimethylammonium) have been prepared by different approaches: the simple mixing of two solutions (MS approach) containing the block copolymer and surfactant, with their respective simple counterions, and dispersion of a freeze-dried complex salt prepared in the absence of simple counterions (CS approach). The CS particles were investigated under different conditions: dispersion of a CS in salt-free water and dispersion of a CS in a dilute salt solution, the latter condition yielding dispersions with the same composition as the MS process. Additionally, aged dispersions (up to 6 months) and dispersed complexes of the polyacrylate homopolymer and dodecyltrimethylammonium surfactant were evaluated. By employing different characterization techniques, it was seen that dispersions prepared by the MS approach display nanometric spherical particles with disordered cores, and poor colloidal stability, partially caused by the absence of surface charge (ζ-potential close to zero). Oppositely, anisometric particles were formed in CS dispersions and were large enough to sustain micellar cubic cores. The CS particles presented long-time colloidal stability, partially due to a net negative surface charge, but the stability varied with the length of the neutral block composing the corona. Our results demonstrate that all dispersed particles are metastable structures, with physicochemical properties strongly dependent on the preparation procedure, thus making these particles suitable for fundamental studies and potential applications where accurate control of their properties, including size, shape, internal structure, and stability, is desired.

Adequacy of glyphosate doses in the Merremia cissoides (Lam.) Hallier f. control as a function of light intensity in the growth environments.

Shading interferes with the weed's biology, which can change their sensitivity to post-emergence herbicides. The objective was to evaluate the control of Merremia cissoides with glyphosate in full sunlight and shade conditions in two plant growth stages (30 and 73 days after sowing (DAS)). At 30 and 73 DAS, treatments were established in a 2 × 5 and 2 × 6 factorial scheme, respectively. In both experiments, the growth environments constituted the first factor, and the glyphosate doses the second factor. Shading promoted 50 and 40% reductions in glyphosate doses at 30 and 73 DAS, respectively. At 73 DAS, M. cissoides is 177.77 and 131.48% more tolerant to glyphosate than 30 DAS in shading and full sunlight, respectively. Due to the increase in glyphosate tolerance as the plant grows, the management of M. cissoides should be carried out until the stage of six fully expanded leaves. Increasing glyphosate doses reduced the quantum yield of photosystem II and electron transport rate (ETR) in both growth environments, with ETR data showing a high negative correlation with the control. The doses reductions promoted by shading and glyphosate application in the initial growth stage of M. cissoides reduces costs and the negative environmental impacts of this herbicide use.

Airflow restriction mask induces greater central fatigue after a non-exhaustive high-intensity interval exercise.

The airflow restriction mask (ARM) is a practical and inexpensive device for respiratory muscle training. Wearing an ARM has recently been combined with high-intensity interval exercise (HIIE), but its effect on neuromuscular fatigue is unknown. The present study investigated the effects of ARM wearing on neuromuscular fatigue after an HIIE session. Fourteen healthy men performed two HIIE sessions (4 × 4 min at 90% HRmax , 3 min recovery at 70% HRmax ) with or without an ARM. Neuromuscular fatigue was quantified via pre- to post-HIIE changes in maximal voluntary contraction (MVC), voluntary activation (VA, central fatigue), and potentialized evoked twitch force at 100, 10, and 1 Hz (peripheral fatigue). Blood pH and lactate were measured before and after the HIIE session, while HR, SpO2 , dyspnea, physical sensation of effort (P-RPE), and Task Effort and Awareness (TEA) were recorded every bout. The exercise-induced decrease in MVC was higher (p < 0.05) in the ARM (-28 ± 12%) than in the Control condition (-20 ± 11%). The VA decreased (p < 0.05) in the ARM (-11 ± 11%) but not in the control condition (-4 ± 5%, p > 0.05). Pre- to post-HIIE declines in evoked twitch at 100, 10, and 1 Hz were similar (p > 0.05) between ARM and control conditions (ARM: -18 ± 10, -43 ± 11 and -38 ± 12%; Control: -18 ± 14, -43 ± 12 and -37 ± 17%). When compared with the control, the HIIE bout wearing ARM was marked by higher heart rate, plasma lactate concentration, dyspnea, P-RPE and TEA, as well as lower SpO2 and blood pH. In conclusion, ARM increases perceptual and physiological stress during a HIIE, which may lead to a greater post-exercise central fatigue.

Molecular Assembly in Block Copolymer-Surfactant Nanoparticle Dispersions: Information on Molecular Exchange and Apparent Solubility from High-Resolution and PFG NMR.

Internally structured block copolymer-surfactant particles are formed when the complex salts of ionic-neutral block copolymers neutralized by surfactant counterions are dispersed in aqueous media. Here, we report the 1H NMR signal intensities and self-diffusion coefficients (D, from pulsed field gradient nuclear magnetic resonance, PFG NMR) of trimethyl alkylammonium surfactant ions and the poly(acrylamide)-block-poly(acrylate) (PAAm-b-PA) polyions forming such particles. The results reveal the presence of an "NMR-invisible" (slowly exchanging) fraction of aggregated surfactant ions in the particle core and an "NMR-visible" fraction consisting of surface surfactant ions in rapid exchange with the surfactant ions dissociated into the aqueous domain. They also confirm that the neutral PAAm blocks are exposed to water at the particle surface, while the PA blocks are buried in the particle core. The self-diffusion of the polyions closely agree with the self-diffusion of a hydrophobic probe molecule solubilized in the particles, showing that essentially all copolymer chains are incorporated in the aggregates. Through centrifugation, we prepared macroscopically phase-separated systems with a phase concentrated in particles separated from a clear dilute phase. D values for the surfactant and block copolymer indicated that the dilute phase contained small aggregates (ca. 5 nm) of surfactant ions and a few anionic-neutral block copolymer chains. Regardless of the overall concentration of the sample, the fraction of block copolymer found in the dilute phase was nearly constant. This indicates that the dilute fraction represented a tail of small particles created by the dispersion process rather than a true thermodynamic solubility of the complex salts.

Maytenus ilicifolia Extract Increases Oxygen Uptake without Changes in Neuromuscular Fatigue Development during a High-Intensity Interval Exercise.

OBJECTIVE: We investigated the effects of acute ingestion of Maytenus ilicifolia extract on metabolic and cardiopulmonary responses during a high-intensity interval exercise (HIIE), and its consequence on neuromuscular fatigue. METHODS: Ten healthy men underwent a HIIE (4 x 4 min, 3 min recovery) one hour after ingesting 400 mg of Maytenus ilicifolia extract (MIE) or placebo. Oxygen uptake (V̇O2), dioxide carbon production (V̇CO2), ventilation (V̇E) and heart rate (HR) were measured throughout the HIIE. Maximal voluntary contraction (MVC), voluntary activation (VA), and evoked 1, 10 and 100 Hz force twitch were measured before supplementation (baseline), and before (pre-HIIE) and after the HIIE (post-HIIE). RESULTS: The V̇O2, V̇E, V̇E/V̇O2 ratio and HR increased progressively throughout the HIIE under both conditions (p < 0.05). MIE increased HR, however, at bouts 1 and 2 and mean V̇O2 during HIIE. The mean respiratory exchange ratio during recovery was also reduced with MIE (p < 0.05). MVC and evoked force at 1, 10 and 100 Hz declined similarly after HIIE, regardless of the condition (MIE: -18 ± 17%, -50 ± 15%, -61 ± 13% and -34 ± 10% vs. placebo: -19 ± 15%, -48 ± 16%, -58 ± 12 and -29 ± 11%, respectively, p < 0.05). There was no effect of exercise or MIE on VA (p > 0.05). CONCLUSION: MIE increases heart rate in the first bouts and mean oxygen uptake during HIIE without changes in neuromuscular fatigue development.

Inclusion Complexation between α-Cyclodextrin and Oligo(ethylene glycol) Methyl Ether Methacrylate.

The preparation of inclusion complexes based on α-cyclodextrin (α-CD) and oligo(ethylene glycol) methyl ether methacrylate (OEGMA) was investigated aiming to reveal complexation particularities and thermodynamic and kinetic aspects as a function of the oligomer architecture. Small-angle X-ray scattering and isothermal titration calorimetry measurements revealed that oligomer molecular weight controls both the kinetics and thermodynamics of inclusion. Unlike linear ethylene glycol polymers, OEGMA groups possess a methacrylate group, which seems to act as a stopper, affecting their mode of complexation. Nuclear magnetic resonance spectra and relaxation measurements support the fact that methacrylate groups lie outside the α-CD ring and that a full sequential complexation of the oligomer ethylene oxide groups is not observed. These results allied to the temperature sensitivity of these oligomers and enable possible routes for chemical modifications and design of new stimuli-responsive materials.

Caffeine increases peripheral fatigue in low- but not in high-performing cyclists.

The influence of cyclists' performance levels on caffeine-induced increases in neuromuscular fatigue after a 4-km cycling time trial (TT) was investigated. Nineteen cyclists performed a 4-km cycling TT 1 h after ingesting caffeine (5 mg·kg-1) or placebo (cellulose). Changes from baseline to after exercise in voluntary activation (VA) and potentiated 1 Hz force twitch (Qtw,pot) were used as markers of central and peripheral fatigue, respectively. Participants were classified as "high performing" (HP, n = 8) or "low performing" (LP, n = 8) in accordance with their performance in a placebo trial. Compared with placebo, caffeine increased the power, anaerobic mechanical power, and anaerobic work, reducing the time to complete the trial in both groups (p < 0.05). There was a group versus supplement and a group versus supplement versus trial interaction for Qtw,pot, in which the postexercise reduction was greater after caffeine compared with placebo in the LP group (Qtw,pot = -34% ± 17% vs. -21% ± 11%, p = 0.02) but not in the HP group (Qtw,pot = -22% ± 8% vs. -23% ± 10%, p = 0.64). There was no effect of caffeine on VA, but there was a group versus trial interaction with lower postexercise values in the LP group than in the HP group (p = 0.03). Caffeine-induced improvement in 4-km cycling TT performance seems to come at the expense of greater locomotor muscle fatigue in LP but not in HP cyclists. Novelty Caffeine improves exercise performance at the expense of a greater end-exercise peripheral fatigue in low-performing athletes. Caffeine-induced improvement in exercise performance does not affect end-exercise peripheral fatigue in high-performing athletes. High-performing athletes seem to have augmented tolerance to central fatigue during a high-intensity time trial.

The Effects of Acute and Chronic Sprint-Interval Training on Cytokine Responses Are Independent of Prior Caffeine Intake.

We examined the effect of acute and chronic sprint interval training (SIT), with or without prior caffeine intake, on levels of exercise-induced inflammatory plasma cytokines [interleukin (IL)-6, IL-10, tumor necrosis factor (TNF)-α]. Twenty physically-active men ingested either a placebo (n = 10) or caffeine (n = 10) 1 h before each SIT session(13-s × 30-s sprint/15 s of rest) during six training sessions (2 weeks). The early (before, immediately after, and 45 min after the exercise) and late (24 and 48 h after the exercise) cytokine and creatine kinase (CK) responses were analyzed for the first and last training sessions. Plasma IL-6 and IL-10 peaked 45 min after the exercise, and then returned to basal values within 24 h (p < 0.05) in both groups on both occasions (p > 0.05). On both occasions, and for both groups, plasma TNF-α increased from rest to immediately after the exercise and then decreased at 45 min before reaching values at or below basal levels 48 h after the exercise (p < 0.05). Serum CK increased from rest to 24 and 48 h post-exercise in the first training session (p < 0.05), but did not alter in the last training session for the PLA group (p > 0.05). Serum CK was unchanged in both the first and last training sessions for the CAF group (p > 0.05). Two weeks of SIT induced a late decrease in the IL-6/IL-10 ratio (p < 0.05) regardless of caffeine intake, suggesting an improved overall inflammatory status after training. In conclusion, a single session of SIT induces muscle damage that seems to be mitigated by caffeine intake. Two weeks of SIT improves the late SIT-induced muscle damage and inflammatory status, which seems to be independent of caffeine intake.

Phase Behavior Controlled by the Addition of Long-Chain n-Alcohols in Systems of Cationic Surfactant/Anionic Polyion Complex Salts and Water.

Phase behavior of surfactants in water may be affected by the addition of a third component, and the present study discusses how long-chain n-alcohols affect phase transitions of systems formed by the surfactant hexadecyltrimethylammonium bromide, C16TAB, or its complex salts formed with polyacrylate, C16TAPA30, as well as other previously reported complex salts/water/alcohol systems. Structural characterization by X-ray diffraction patterns at small and wide angles and different temperatures was performed for samples containing n-decanol, n-dodecanol, or n-tetradecanol. Differential scanning calorimetry (DSC) was also used to study the phase transition. The results allowed us to observe and understand the coexistence of lamellar gel (Lß) and lamellar liquid-crystal (Lα) phases, elucidating the structure of a previously reported mesophase, proposing an alternative assignment. Whereas the chain-melting transition is well-known to be sharp for lipids, we have found that it is broader for C16TAB and C16TAPA in the presence of these n-alcohols. We have investigated the effects of their composition and chain length on the temperature and enthalpy of transition. This elucidates why the addition of n-alcohols with chains slightly shorter than that of the surfactants leads to the formation of an ordered gel-like lamellar phase (Lß). n-Alcohols act as neutral cosurfactants, leading to more packing, and all of the factors converge to a limit situation, associated with a common critical area occupied by each alkyl chain. We compared our results with other mesophase systems from the literature, demonstrating that the same trends of phase behavior occur for complex salts of other polyelectrolytes with alkyltrimethylammonium surfactants.

Gender-related cardiac dimension differences between female and male professional soccer players.

BACKGROUND: The aim of this study was to determine if cardiac hypertrophy differs between professional female and male soccer players. METHODS: Twenty-two female and 20 male professional soccer players, and their respective non-athlete controls (22 females and 19 males) were submitted to an echocardiogram. RESULTS: Females had a shorter left ventricular intracavitary diameter and wall thicknesses than males in both groups. However, these differences disappeared when cardiac dimensions were expressed relative to body mass area (P>0.05). Compared to their respective controls, female and male soccer players had a longer (P<0.05) left ventricular end-systolic diameter (female: 1.87±0.16 vs. 1.77±0.15 cm/m2 and male: 1.83±0.21 vs. 1.73±0.16 cm/m2), left ventricular end-diastolic diameter (female: 2.86±0.25 vs. 2.74±0.22 cm/m2 and male: 2.81±0.26 vs. 2.55±0.66 cm/m2), left ventricular posterior wall thickness (female: 0.44±0.06 vs. 0.39±0.04 cm/m2 and male: 0.43±0.04 vs. 0.39±0.10 cm/m2), left ventricular septal wall thickness (female: 0.47±0.06 vs. 0.41±0.04 cm/m2 and male: 0.45±0.04 vs. 0.40±0.11 cm/m2), and left ventricular mass index (female: 91.8±22.1 vs. 72.3±10.5 g/m2 and male: 121.7±20.3 vs. 99.8±13.8 g/m2 ). CONCLUSIONS: Part of the gender differences in cardiac dimensions might be attributed to differences in body dimension. Soccer training increases cardiac dimensions even with BSA correction and females seem to have similar left ventricle remodeling compared to males.

Arterialized and venous blood lactate concentration difference during different exercise intensities.

OBJECTIVE: The purpose of this study was to investigate the difference between arterialized and venous blood lactate concentrations [La] during constant-load exercises at different intensities. METHODS: Fifteen physically active men cycled for 30 minutes (or until exhaustion) at the first lactate threshold (LT1), at 50% of the difference between the first and second lactate threshold (TT50%), at the second lactate threshold (LT2), and at 25% of the difference between LT2 and maximal aerobic power output (TW25%). Samples of both arterialized and venous blood were collected simultaneously at rest and every 5 minutes during the exercise. RESULTS: The arterialized blood [La] was higher at minute 5 than venous blood [La] for all exercise intensities (p < 0.05). After this period, the arterialized and venous [La] samples became similar until the end of the exercise (p > 0.05). The arterialized-venous difference during the first 10 minutes was greater for the two highest exercise intensities (LT2 and TW25%) compared with the two lowest (LT1 and TT50%, p < 0.05). Thereafter, arterialized-venous difference decreased progressively, reaching values close to zero for all exercise intensities (p > 0.05). CONCLUSION: These results suggest a delayed lactate appearance in the venous blood, which is accentuated at higher exercise intensities. The lactate measured in arterialized and venous blood is interchangeable only when blood samples are collected at least 10 minutes after the exercise starts.

Labeling mesenchymal cells with DMSA-coated gold and iron oxide nanoparticles: assessment of biocompatibility and potential applications.

BACKGROUND: Nanoparticles' unique features have been highly explored in cellular therapies. However, nanoparticles can be cytotoxic. The cytotoxicity can be overcome by coating the nanoparticles with an appropriated surface modification. Nanoparticle coating influences biocompatibility between nanoparticles and cells and may affect some cell properties. Here, we evaluated the biocompatibility of gold and maghemite nanoparticles functionalized with 2,3-dimercaptosuccinic acid (DMSA), Au-DMSA and γ-Fe2O3-DMSA respectively, with human mesenchymal stem cells. Also, we tested these nanoparticles as tracers for mesenchymal stem cells in vivo tracking by computed tomography and as agents for mesenchymal stem cells magnetic targeting. RESULTS: Significant cell death was not observed in MTT, Trypan Blue and light microscopy analyses. However, ultra-structural alterations as swollen and degenerated mitochondria, high amounts of myelin figures and structures similar to apoptotic bodies were detected in some mesenchymal stem cells. Au-DMSA and γ-Fe2O3-DMSA labeling did not affect mesenchymal stem cells adipogenesis and osteogenesis differentiation, proliferation rates or lymphocyte suppression capability. The uptake measurements indicated that both inorganic nanoparticles were well uptaken by mesenchymal stem cells. However, Au-DMSA could not be detected in microtomograph after being incorporated by mesenchymal stem cells. γ-Fe2O3-DMSA labeled cells were magnetically responsive in vitro and after infused in vivo in an experimental model of lung silicosis. CONCLUSION: In terms of biocompatibility, the use of γ-Fe2O3-DMSA and Au-DMSA as tracers for mesenchymal stem cells was assured. However, Au-DMSA shown to be not suitable for visualization and tracking of these cells in vivo by standard computed microtomography. Otherwise, γ-Fe2O3-DMSA shows to be a promising agent for mesenchymal stem cells magnetic targeting.

The Placenta as an Organ and a Source of Stem Cells and Extracellular Matrix: A Review.

The placenta is a temporal, dynamic and diverse organ with important immunological features that facilitate embryonic and fetal development and survival, notwithstanding the fact that several aspects of its formation and function closely resemble tumor progression. Placentation in mammals is commonly used to characterize the evolution of species, including insights into human evolution. Although most placentas are discarded after birth, they are a high-yield source for the isolation of stem/progenitor cells and are rich in extracellular matrix (ECM), representing an important resource for regenerative medicine purposes. Interactions among cells, ECM and bioactive molecules regulate tissue and organ generation and comprise the foundation of tissue engineering. In the present article, differences among several mammalian species regarding the placental types and classifications, phenotypes and potency of placenta-derived stem/progenitor cells, placental ECM components and current placental ECM applications were reviewed to highlight their potential clinical and biomedical relevance.

Identification of training status differences using perceived exertion threshold.

We investigated if the rate of perceived exertion (RPE) threshold is as sensitive as the lactate threshold to detect training differences. Lactate and RPE thresholds were identified in well-trained cyclists and physically active males. Power output was higher in well-trained cyclists than in physically active individuals for both thresholds (p < 0.05). Our results suggest that RPE threshold is successful in discriminating differences between well-trained cyclists and physically active individuals.

Addition of n-Alcohols Induces a Variety of Liquid-Crystalline Structures in Surfactant-Rich Cores of Dispersed Block Copolymer/Surfactant Nanoparticles.

Poly(acrylamide)-b-complex salts made from a symmetric poly(acrylate-b-acrylamide) block copolymer, where the acrylate charges are neutralized by cationic surfactant counterions, form kinetically stable aqueous dispersions of hierarchical aggregates with a liquid-crystalline complex salt core and a diffuse hydrated shell. By the addition of suitable amounts of long-chain alcohols, such as octanol or decanol, the structure of the internal phase can be varied, producing micellar cubic, hexagonal, lamellar, or reverse hexagonal liquid-crystalline phases. In addition, a disordered reverse micellar phase forms at the highest content of octanol. These core structures are the same as those previously obtained for macroscopic homopolymer poly(acrylate) complex salt/water/n-alcohol systems at the corresponding compositions. The poly(acrylamide)-b-complex salt dispersions are kinetically stable for several weeks, with their colloidal properties and internal structures remaining unchanged. The methodology described here establishes an easy and robust protocol for the preparation of colloidal nanoparticles with variable but controlled internal structures.