Increasing the antioxidant capacity of ceria nanoparticles with catechol-grafted poly(ethylene glycol).

Ceria nanoparticles are remarkable antioxidants due to their large cerium(III) content and the possibility of recovering cerium(III) from cerium(IV) after reaction. Here we increase the cerium(III) content of colloidally stable nanoparticles (e.g., nanocrystals) using a reactive polymeric surface coating. Catechol-grafted poly(ethylene glycols) (PEG) polymers of varying lengths and architectures yield materials that are non-aggregating in a variety of aqueous media. Cerium(IV) on the ceria surface both binds and oxidizes the catechol functionality, generating a dark-red colour emblematic of surface-oxidized catechols with a concomitant increase in cerium(III) revealed by X-ray photoemission spectroscopy (XPS). The extent of ceria reduction depends sensitively on the architecture of the coating polymer; small and compact polymer chains pack with high density at the nanoparticle surface yielding the most cerium(III). Nanoparticles with increased surface reduction, quantified by the intensity of their optical absorption and thermogravimetric measures of polymer grafting densities, were more potent antioxidants as measured by a standard TEAC antioxidant assay. For the same core composition nanoparticle antioxidant capacities could be increased over an order of magnitude by tailoring the length and architecture of the reactive surface coatings.

When function is biological: Discerning how silver nanoparticle structure dictates antimicrobial activity.

Silver nanomaterials have potent antibacterial properties that are the foundation for their wide commercial use as well as for concerns about their unintended environmental impact. The nanoparticles themselves are relatively biologically inert but they can undergo oxidative dissolution yielding toxic silver ions. A quantitative relationship between silver material structure and dissolution, and thus antimicrobial activity, has yet to be established. Here, this dissolution process and associated biological activity is characterized using uniform nanoparticles with variable dimension, shape, and surface chemistry. From this, a phenomenological model emerges that quantitatively relates material structure to both silver dissolution and microbial toxicity. Shape has the most profound influence on antibacterial activity, and surprisingly, surface coatings the least. These results illustrate how material structure may be optimized for antimicrobial properties and suggest strategies for minimizing silver nanoparticle effects on microbes.

Validating Tackle Mechanics in American Football: Improving Safety and Performance.

Research has helped to understand the risks of injuries of tackling in American football and rugby; however, approaches to teaching and analysis are not well-documented. Shoulder-led tackling has been proposed as a safer approach to tackling even though data on the effectiveness for safety and defensive performance is limited. Additionally, some have argued that safety and effectiveness are incompatible. The purpose of the study was to validate a specific sequence of tackling actions as a tool for teaching safer and more effective tackling skills. Results suggested tackle scores help predict presence of head contact, and that higher tackle scores were associated with reductions in Yards After Contact (YAC). Eight hundred and thirty-two (832) American high school football tackles were rated using a 12-element rating system. Estimated Structural Equation Modeling (ESEM) was employed to identify the factor structure of the elements with three factors identified: Track, Engage, and Finish. ANOVA, along with logistic and linear equation models were run to determine relationships between tackle scores and outcomes. Tackle scores predicted head-contact category (binary logistic regression accuracy = .76). Yards after contact (YAC) were significantly reduced [Finish factor: MANOVA F(3, 828) = 105.825, p < .001]. Construct and predictive validity were demonstrated and show that these tackle elements provide valid foci for teaching better tackling as well as analyzing both teaching effectiveness and performance.

Sleep and stress in the acute phase of concussion in youth.

This study sought to address the complex interplay between both biological and psychological perceptions of stress and sleep in the acute stages following a mild traumatic brain injury. A secondary goal was to identify potential targets for intervention. Eleven acutely injured youth (mean age 12 years) were studied at home with overnight actigraphy, salivary cortisol and melatonin assays, and subjective ratings of stress and fatigue (injured group). Nine matched control youth also were assessed (control group). Results suggested longer sleep latencies (time to fall asleep) and higher levels of fatigue in the injured group exist (p = 0.025 and p = 0.004, respectively). In the injured group, stress and sleep onset were significantly related with most subjects meeting criteria for Acute Stress Disorder. Melatonin levels were lower at bedtime in the injured group. Saliva samples were collected via passive drool at three time points: ∼1 h before bed ("bedtime" or T1), immediately upon waking (time 2: T2), and 30 min post-waking (time 3: T3). Overnight increases in cortisol (T1 to T2) were greater for the injured group; however, post-sleep changes in cortisol (T2 to T3) were reversed with control concentrations increasing. These findings are unique in using actigraphy and salivary hormone levels in an acutely injured youth while in their homes. The differences in sleep latency and the presence of injury-related stress point to potential treatment targets in acute concussion.

Confirmatory factor analysis of two computerized neuropsychological test batteries: Immediate post-concussion assessment and cognitive test (ImPACT) and C3 logix.

Introduction: Tests of memory and speed of cognitive and motor responses have been the primary foci in sports-related concussion assessment. This study sought to assess the construct validity of neuropsychological tests within C3 Logix. Method: Results of both baseline C3 Logix and the Immediate Post-Concussion Assessment and Cognitive Test (ImPACT) computerized tests from 86 Division I collegiate athletes were submitted to a two-factor confirmatory analysis using structural equation modeling. The two factors of Speed and Memory have been confirmed in previous studies of ImPACT. Results: Results confirmed the two-factor model of ImPACT, whereas C3 Logix did not conform to a pure two-factor model. Instead, along with additional error terms, a cross-loading was required between Speed and Memory factors in order to obtain the best model fit (χ2 = 22.91, p= 0.12, CFI = 0.94, TLI = .90, RMSEA = 0.07 (90% CI [0.00, 0.13], SRMR = .06)): all factor loadings exceeded 0.30. Conclusions: The final model suggested C3 Logix employs three pure indicators of Speed and one indicator of both Speed and Memory. The lack of a pure indicator of Memory in C3 Logix raises a concern about its specificity and ultimately, its sensitivity to a sports-related concussion.

Test-retest, retest, and retest: Growth curve models of repeat testing with Immediate Post-Concussion Assessment and Cognitive Testing (ImPACT).

Computerized neuropsychological testing has become an important tool in the identification and management of sports-related concussions; however, the psychometric effect of repeat testing has not been studied extensively beyond test-retest statistics. The current study analyzed data from Division I collegiate athletes who completed Immediate Post-Concussion Assessment and Cognitive Testing (ImPACT) baseline assessments at four sequential time points that varied over the course of their athletic careers. Administrations were part of a larger National Institutes of Health (NIH) study. Growth curve modeling showed that the two memory composite scores increased significantly with successive administrations: Change in Verbal Memory was best represented with a quadratic model, while a linear model best fit Visual Memory. Visual Motor Speed and Reaction Time composites showed no significant linear or quadratic growth. The results demonstrate the effect of repeated test administrations for memory composite scores, while speed composites were not significantly impacted by repeat testing. Acceptable test-retest reliability was demonstrated for all four composites as well.

Electroless plating of thin gold films directly onto silicon nitride thin films and into micropores.

A method to directly electrolessly plate silicon-rich silicon nitride with thin gold films was developed and characterized. Films with thicknesses <100 nm were grown at 3 and 10 °C between 0.5 and 3 h, with mean grain sizes between ∼20 and 30 nm. The method is compatible with plating free-standing ultrathin silicon nitride membranes, and we successfully plated the interior walls of micropore arrays in 200 nm thick silicon nitride membranes. The method is thus amenable to coating planar, curved, and line-of-sight-obscured silicon nitride surfaces.