Self-assembly behaviors of colloidal cellulose nanocrystals: A tale of stabilization mechanisms.

HYPOTHESIS: In solvent casting, colloidal nanocrystal self-assembly patterns are controlled by a mix of cohesive and repulsive interactions that promote destabilization-induced self-assembly (DISA) or evaporation-induced self-assembly (EISA). Tuning the strength and nature of the stabilization mechanisms may allow repulsive interactions to govern self-assembly during the casting of colloidal cellulose nanocrystal (CNC) suspensions. EXPERIMENTS: We propose a tool to classify the level of electrostatic and solvation-induced stabilizations based on two solvent parameters only: dielectric constant, ε, and chemical affinity for CNCs, in terms of Hansen Solubility Parameters, Ra. These criteria are applied to study CNC self-assembly in solvent casting experiments in various media and binary mixtures. FINDINGS: In solvent casting of suspensions stabilized through a combination of electrostatic and solvation effects, the primarily governing mechanism is EISA, which leads to the formation of chiral nematic domains and optically active thin films. In electrostatically-stabilized suspensions, EISA and DISA are in competition and casting may yield anything from a continuous film to a powder. In other suspensions, DISA prevails and evaporation yields a powder of CNC agglomerates. By classifying media according to their stabilization mechanisms, this work establishes that the behavior of CNC suspensions in solvent casting may be predicted from solvent parameters only.

Human arterial responses to isometric exercise: the role of the muscle metaboreflex.

The effects of exercise on the distensibility of large and medium-sized arteries are poorly understood, but can be attributed to a combination of local vasodilator effects of exercise opposed by sympathetic vasoconstrictor tone. We sought to examine this relationship at the conduit artery level, with particular reference to the role of the sympatho-excitatory muscle metaboreflex. The effect of maintained muscle metaboreflex activation on a previously passive or exercised limb femoral artery was investigated. A total of ten healthy volunteers performed 2 min of isometric ankle plantar-flexion at 40% MVC (maximal voluntary force), in conjunction with 2 min of either non-ischaemic isometric HG (handgrip; control condition) or IHG (ischaemic HG) at 40% MVC. IHG was followed by 2 min of PECO (post-exercise circulatory occlusion) to maintain muscle metaboreflex activation. FTPWV [femoral-tibial PWV (pulse wave velocity)] was measured in the exercised or contralateral limb at baseline and immediately following calf exercise. BP (blood pressure) and HR (heart rate) were measured continuously throughout. In the HG condition, BP and HR returned promptly to baseline post-exercise, whereas exercised leg FTPWV was decreased (less stiff) by 0.6 m/s (P<0.05) and the non-exercised leg PWV was not changed from baseline. PECO caused a sustained increase in BP, but not HR, in the IHG condition. Contralateral leg PWV increased (stiffened) during PECO by 0.9 m/s (P<0.05), whereas exercised limb FTPWV was not changed from baseline. In conclusion, muscle metaboreflex activation causes a systemic stiffening of the arterial tree, which can overcome local exercise-induced decreases in arterial PWV.