A modular cell culture device for generating arrays of gradients using stacked microfluidic flows     

Sip CG  Bhattacharjee N  Folch A 《Biomicrofluidics》2011,5(2):22210

Microfluidics has become increasingly important for the study of biochemical cues because it enables exquisite spatiotemporal control of the microenvironment. Well-characterized, stable, and reproducible generation of biochemical gradients is critical for understanding the complex behaviors involved in many biological phenomena. Although many microfluidic devices have been developed which achieve these criteria, the ongoing challenge for these platforms is to provide a suitably benign and physiologically relevant environment for cell culture in a user-friendly format. To achieve this paradigm, microfluidic designs must consider the full scope of cell culture from substrate preparation, cell seeding, and long-term maintenance to properly observe gradient sensing behavior. In addition, designs must address the challenges associated with altered culture conditions and shear forces in flow-based devices. With this consideration, we have designed and characterized a microfluidic device based on the principle of stacked flows to achieve highly stable gradients of diffusible molecules over large areas with extremely low shear forces. The device utilizes a benign vacuum sealing strategy for reversible application to pre-established cell cultures. We apply this device to an existing culture of breast cancer cells to demonstrate the negligible effect of its shear flow on migratory behavior. Lastly, we extend the stacked-flow design to demonstrate its scalable architecture with a prototype device for generating an array of combinatorial gradients.  相似文献   

Ventilatory acclimatisation is beneficial for high-intensity exercise at altitude in elite cyclists     

Nathan E. Townsend  Christopher J. Gore  Tammie R. Ebert  David T. Martin  Allan G. Hahn  Chin-Moi Chow 《European Journal of Sport Science》2016,16(8):895-902

Aim: The aim of this study was to examine the relationship between ventilatory adaptation and performance during altitude training at 2700?m. Methods: Seven elite cyclists (age: 21.2?±?1.1?yr, body mass: 69.9?±?5.6?kg, height 176.3?±?4.9?cm) participated in this study. A hypoxic ventilatory response (HVR) test and a submaximal exercise test were performed at sea level prior to the training camp and again after 15 d at altitude (ALT15). Ventilation (V_E), end-tidal carbon-dioxide partial pressure (P_ETCO₂) and oxyhaemoglobin saturation via pulse oximetry (SpO₂) were measured at rest and during submaximal cycling at 250?W. A hill climb (HC) performance test was conducted at sea level and after 14 d at altitude (ALT14) using a road of similar length (5.5–6?km) and gradient (4.8–5.3%). Power output was measured using SRM cranks. Average HC power at ALT14 was normalised to sea level power (HC%). Multiple regression was used to identify significant predictors of performance at altitude. Results: At ALT15, there was a significant increase in resting V_E (10.3?±?1.9 vs. 12.2?±?2.4?L·min^?1) and HVR (0.34?±?0.24 vs. 0.71?±?0.49?L·min^?1·%^?1), while P_ETCO₂ (38.4?±?2.3 vs. 32.1?±?3.3?mmHg) and SpO₂ (97.9?±?0.7 vs. 94.0?±?1.7%) were reduced (P?V_E at altitude as significant predictors of HC% (adjusted r²?=?0.913; P?=?0.003). Conclusions: Ventilatory acclimatisation occurred during a 2 wk altitude training camp in elite cyclists and a higher HVR was associated with better performance at altitude, relative to sea level. These results suggest that ventilatory acclimatisation is beneficial for cycling performance at altitude.  相似文献   

The development of uncertainty monitoring during kindergarten: Change and longitudinal relations with executive function and vocabulary in children from low-income backgrounds     

Christopher R. Gonzales  Alexis Merculief  Megan M. McClelland  Simona Ghetti 《Child development》2022,93(2):524-539

Children's ability to monitor subjective feelings of uncertainty (i.e., engage in uncertainty monitoring) is a central metacognitive skill. In the current study, we examined the development of uncertainty monitoring as well as its relations with vocabulary and executive function development in children (N = 137, 52% female) from predominately White and Latinx/Hispanic backgrounds when they were 4–6 years old and enrolled in a Head Start preschool and kindergarten between 2018 and 2019. We found that children's uncertainty monitoring improved during the kindergarten year. Children's executive function and vocabulary in preschool and vocabulary growth from preschool to kindergarten predicted uncertainty monitoring at the end of kindergarten, which sheds new light on potential mechanisms supporting children's metacognitive development.  相似文献   

High School Success: A Learning Strategies Intervention to Reduce Drop-Out Rates     

Lowder  Christopher  O’Brien  Chris  Hancock  Dawson  Hachen  Jeremy  Wang  Chuang 《The Urban Review》2022,54(4):509-530

The Urban Review - The transition into high school is a critical time to act for students with a history of academic difficulty. In this study, researchers examined the impact of a learning...  相似文献   

Growth in written academic word use in response to morphology-focused supplemental instruction     

Wood  Carla  Schatschneider  Christopher 《Reading and writing》2022,35(2):399-426

Reading and Writing - The aims of the current project were to: (1) describe average change in the use of academic words across the school year in writing and (2) examine potential predictors of...  相似文献   

Micro- and nanofluidic technologies for epigenetic profiling     

Toshiki Matsuoka  Byoung Choul Kim  Christopher Moraes  Minsub Han  Shuichi Takayama 《Biomicrofluidics》2013,7(4)

This short review provides an overview of the impact micro- and nanotechnologies can make in studying epigenetic structures. The importance of mapping histone modifications on chromatin prompts us to highlight the complexities and challenges associated with histone mapping, as compared to DNA sequencing. First, the histone code comprised over 30 variations, compared to 4 nucleotides for DNA. Second, whereas DNA can be amplified using polymerase chain reaction, chromatin cannot be amplified, creating challenges in obtaining sufficient material for analysis. Third, while every person has only a single genome, there exist multiple epigenomes in cells of different types and origins. Finally, we summarize existing technologies for performing these types of analyses. Although there are still relatively few examples of micro- and nanofluidic technologies for chromatin analysis, the unique advantages of using such technologies to address inherent challenges in epigenetic studies, such as limited sample material, complex readouts, and the need for high-content screens, make this an area of significant growth and opportunity.  相似文献   

The Meaning of Graceful Movement     

Christopher Cordner 《体育哲学杂志》2013,40(2):132-143

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Contributions of local and central sensations to the perception of exertion during cycling: Effects of work rate and cadence     

Christopher Jameson  Christopher Ring 《Journal of sports sciences》2013,31(4):291-298

There is evidence to suggest that perception of exertion during exercise is based on both local and central sensations. The aim of the present experiment was to determine the relative contributions of diff erent sensations to overall perceived exertion during cycling. Eighteen trained cyclists pedalled on a cycle ergometer for 4 min at each of three work rates (100, 150 and 200 W) and cadences (50, 70 and 90 rev. min-1). At the end of each bout, they used Borg's category-ratio (CR-10) scale to rate their overall perceived exertion, leg muscle pain, knee pain, breathlessness and heart beat intensity. The results indicated that cadence only influenced local sensations (muscle pain and knee pain), which were significantly higher at slower pedalling rates. Neither overall perceived exertion nor central sensations (breathlessness and heart beat intensity) were significantly affected by cadence. In contrast, increases in work rate were associated with higher ratings for all sensations. Further analyses revealed that variations in these overall ratings of perceived exertion as a function of work rate were accounted for by variations in ratings of muscle pain and breathlessness. The general implication is that perceived exertion during cycling derives from a combination of muscle and respiratory sensations.  相似文献   

Oxygen uptake kinetics in children and adults after the onset of moderate-intensity exercise     

Samantha G. Fawkner  Neil Armstrong  Christopher R. Potter  Joanne R. Welsman 《Journal of sports sciences》2013,31(4):319-326

The literature suggests that the oxygen uptake ( V O 2 ) response to the onset of moderate-intensity exercise may be both mature from childhood and independent of sex. Yet the cardiorespiratory response to exercise and the metabolic profile of the muscle appear to change with growth and deve . lopment and to differ between the sexes. The aim of this study was to investigate further changes in the V O2 kinetic response with age and sex. Participants completed a series of no less than four step change transitions, from unloaded pedalling to a constant work rate corresponding to 80% of their previously determined ventilatory threshold. Each participant's breath-by-breath responses were interpolated to 1 s intervals, time aligned and then averaged. A single exponential model that included a time delay was used to analyse the averaged response following phase 1 (15 s). Participants with parameter confidence intervals more than - 5 s were removed from the sample; the results for the remaining 13 men and 12 women (age 19-26 years), 12 boys and 11 girls (age 11-12 years) were used for statistical analysis. Children had a significantly shorter time constant than adults, both for males (19.0 - 2.0 and 27.9 - 8.6 s respectively; P ? 0.01) and females (21.0 - 5.5 and 26.0 - 4.5 s respectively; P ? 0.05). There were no significant differences in the time constant between the sexes for either adults or children ( P > 0.05). A significant relationship between the time constant and peak V O 2 was found only in adult males ( P ? 0.05). A shorter time constant in children may reflect an enhanced potential for oxidative metabolism.  相似文献   

The effect of exercise-induced muscle damage on isometric and dynamic knee extensor strength and vertical jump performance     

Christopher Byrne  Roger Eston 《Journal of sports sciences》2013,31(5):417-425

In this study, we assessed the effect of exercise-induced muscle damage on knee extensor muscle strength during isometric, concentric and eccentric actions at 1.57 rad · s -1 and vertical jump performance under conditions of squat jump, countermovement jump and drop jump. The eight participants (5 males, 3 females) were aged 29.5 - 7.1 years (mean - s ). These variables, together with plasma creatine kinase (CK), were measured before, 1 h after and 1, 2, 3, 4 and 7 days after a bout of muscle damaging exercise: 100 barbell squats (10 sets 2 10 repetitions at 70% body mass load). Strength was reduced for 4 days ( P ? 0.05) but no significant differences ( P > 0.05) were apparent in the magnitude or rate of recovery of strength between isometric, concentric and eccentric muscle actions. The overall decline in vertical jump performance was dependent on jump method: squat jump performance was affected to a greater extent than countermovement (91.6 - 1.1% vs 95.2 - 1.3% of pre-exercise values, P ? 0.05) and drop jump (95.2 - 1.4%, P ? 0.05) performance. Creatine kinase was elevated ( P ? 0.05) above baseline 1 h after exercise, peaked on day 1 and remained significantly elevated on days 2 and 3. Strength loss after exercise-induced muscle damage was independent of the muscle action being performed. However, the impairment of muscle function was attenuated when the stretch-shortening cycle was used in vertical jumping performance.  相似文献