Self-assembly of polysaccharides gives rise to distinct mechanical signatures in marine gels.

Marine-gel biopolymers were recently visualized at the molecular level using atomic force microscopy (AFM) to reveal fine fibril-forming networks with low to high degrees of cross-linking. In this work, we use force spectroscopy to quantify the intra- and intermolecular forces within the marine-gel network. Combining force measurements, AFM imaging, and the known chemical composition of marine gels allows us to identify the microscopic origins of distinct mechanical responses. At the single-fibril level, we uncover force-extension curves that resemble those of individual polysaccharide fibrils. They exhibit entropic elasticity followed by extensions associated with chair-to-boat transitions specific to the type of polysaccharide at high forces. Surprisingly, a low degree of cross-linking leads to sawtooth patterns that we attribute to the unraveling of polysaccharide entanglements. At a high degree of cross-linking, we observe force plateaus that arise from unzipping, as well as unwinding, of helical bundles. Finally, the complex 3D network structure gives rise to force staircases of increasing height that correspond to the hierarchical peeling of fibrils away from the junction zones. In addition, we show that these diverse mechanical responses also arise in reconstituted polysaccharide gels, which highlights their dominant role in the mechanical architecture of marine gels.

Force-clamp experiments reveal the free-energy profile and diffusion coefficient of the collapse of protein molecules.

We present force-clamp data on the collapse of ubiquitin polyproteins from a highly extended state to the folded length, in response to a quench in the force from 110 pN to 5 or 10 pN. Using a recent method for free-energy reconstruction from the observed nonequilibrium trajectories, we find that their statistics is captured by simple diffusion along the end-to-end length. The estimated diffusion coefficient of ∼ 100 nm(2) s(-1) is significantly slower than expected from viscous effects alone, possibly because of the internal degrees of freedom of the protein. The free-energy profiles give validity to a physical model in which the multiple protein domains collapse all at once and the role of the force is approximately captured by the Bell model.

Meta-analysis of the effects of nonnutritive sucking on heart rate and peripheral oxygenation: research from the past 30 years.

A meta-analysis of the effects of nonnutritive sucking (NNS) on heart rate and transcutaneous oxygen tension (TcPaO2) was performed. Four studies of NNS on heart rate without stimulations, three studies on heart rate during painful stimulations, and three studies on TcPaO2--all conducted over the past 30 years--were found through a computer search. Using the Fisher combined test, NNS significantly decreased heart rate without stimulations (p = .002) and during painful stimulations (p = .0001), and significantly increased TcPaO2 (p = .0001). The total weighted effect size for heart rate without stimulations was small (0.17); however, it was large for heart rate during painful stimulations (1.05) and TcPaO2 (0.69). Larger effects were noticed for preterm infants than for term infants and for longer NNS. More studies of NNS effects with independent treatment and control groups, using the physiological outcome variables of heart rate and oxygenation for different age groups of preterm infants, are needed to examine the fundamental mechanisms of NNS effects. Clinically, a low-risk intervention such as NNS can be more broadly used during any painful procedures to decrease infant distress.