On the origins of apparent fragile-to-strong transition of protein hydration waters

2H NMR is used to study the mechanisms for the reorientation of protein hydration water. In the past, crossovers in temperature-dependent correlation times were reported at T_x1=225K (X1) and T_x2=200K (X2). We show that neither X1 nor X2 are related to a fragile-to-strong transition. Our results rule out an existence of X1. Also, they indicate that water performs thermally activated and distorted tetrahedral jumps at T<T_x2, implying that X2 originates in an onset of this motion, which may be related to a universal defect diffusion in materials with defined hydrogen-bond networks.Comment: 4 pages, 3 figure

Enteroendocrine K-cells exert complementary effects to control bone quality and mass in mice

International audienceThe involvement of a gut-bone axis in controlling bone physiology has been long suspected, although the exact mechanisms are unclear. We explored whether glucose-dependent insulinotropic polypeptide (GIP)-producing enteroendocrine K-cells were involved in this process. The bone phenotype of transgenic mouse models lacking GIP secretion (GIP-GFP-KI) or enteroendocrine K-cells (GIP-DT) was investigated. Mice deficient in GIP secretion exhibited lower bone strength, trabecular bone mass, trabecula number and cortical thickness, notably due to higher bone resorption. Alterations of microstructure, modifications of bone compositional parameters, represented by lower collagen cross-linking were also apparent. None of these alterations were observed in GIP-DT mice lacking enteroendocrine K-cells, suggesting that other K-cell secretory product acts to counteract GIP action. To assess this, stable analogues of the known K-cell peptide hormones, xenin and GIP, were administered to mature NIH Swiss male mice. Both were capable of modulating bone strength mostly by altering bone microstructure, bone gene expression and bone compositional parameters. However, the two molecules exhibited opposite actions on bone physiology, with evidence that xenin effects are mediated indirectly, possibly via neural networks. Our data highlight a previously unknown interaction between GIP and xenin, which both moderate gut-bone connectivity

Advances in tenascin-C biology

Tenascin-C is an extracellular matrix glycoprotein that is specifically and transiently expressed upon tissue injury. Upon tissue damage, tenascin-C plays a multitude of different roles that mediate both inflammatory and fibrotic processes to enable effective tissue repair. In the last decade, emerging evidence has demonstrated a vital role for tenascin-C in cardiac and arterial injury, tumor angiogenesis and metastasis, as well as in modulating stem cell behavior. Here we highlight the molecular mechanisms by which tenascin-C mediates these effects and discuss the implications of mis-regulated tenascin-C expression in driving disease pathology

The Advancement of Biomaterials in Regulating Stem Cell Fate.

Stem cells are well-known to have prominent roles in tissue engineering applications. Embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs) can differentiate into every cell type in the body while adult stem cells such as mesenchymal stem cells (MSCs) can be isolated from various sources. Nevertheless, an utmost limitation in harnessing stem cells for tissue engineering is the supply of cells. The advances in biomaterial technology allows the establishment of ex vivo expansion systems to overcome this bottleneck. The progress of various scaffold fabrication could direct stem cell fate decisions including cell proliferation and differentiation into specific lineages in vitro. Stem cell biology and biomaterial technology promote synergistic effect on stem cell-based regenerative therapies. Therefore, understanding the interaction of stem cell and biomaterials would allow the designation of new biomaterials for future clinical therapeutic applications for tissue regeneration. This review focuses mainly on the advances of natural and synthetic biomaterials in regulating stem cell fate decisions. We have also briefly discussed how biological and biophysical properties of biomaterials including wettability, chemical functionality, biodegradability and stiffness play their roles

Zero order release from swollen hydrogels

In vitro release studies of theophylline from a series of swollen poly (2-hydroxyethyl methacrylate-co-glycidyl methacrylate), p (HEMA-GMA), hydrogels in water and in 0.05 N sulphuric acid are reported. Release in water follows the conventional Higuchi relationship. In acidic medium, the release index is found to vary between 0.7 and 0.9. The results are attributed to the structural changes taking place in the matrix during the course of release in acidic medium

On the Maximum Rate of Networked Computation in a Capacitated Network

We are given a capacitated communication network and several infinite sequences of source data each of which is available at some node in the network. A function of the source data is to be computed in the network and made available at a sink node that is also on the network. The schema to compute the function is given as a directed acyclic graph (DAG). We want to generate a computation and communication schedule in the network to maximize the rate of computation of the function for an arbitrary function (represented by DAG). We first analyze the complexity of finding the rate maximizing schedule for the general DAG. We show that finding an optimal schedule is equivalent to solving a packing linear program (LP). We then prove that finding the maximum rate is MAX SNP-hard (by analyzing this packing LP) even when the DAG has bounded degree, bounded edge weights and the network has three vertices. We then consider special cases arising in practical situations. First, a polynomial time algorithm for the network with two vertices is presented. This algorithm is a reduction to a version of a submodular function minimization problem. Next, for the general network we describe a restricted class of schedules and its equivalent packing LP. By relating this LP to minimum cost embedding problem, we present approximation algorithms for special classes of DAGs

Matrix systems for zero-order release: facile erosion of crosslinked hydrogels

Bioerodible matrices are particularly suited for the systemic administration of drugs over extended time periods. Type I-A bioerodible matrices reported in the past degrade either too slowly or too rapidly. The rate of erosion, therefore, has no influence on the kinetics of release. This paper reports kinetics of release of theophylline from a series of crosslinked glassy/swollen hydrogel matrices based on a novel crosslinking monomer, viz. 2-hydroxyethyl glycolate dimethacrylate. The release of theophylline in an alkaline medium is accompanied by the erosion of the crosslinks. Under appropriate conditions, theophylline is released at a constant rate by the erosion of the crosslinks in the bulk of the swollen polymer as well as by the surface erosion of the glassy polymer. The release behaviour has been explained on the basis of the concept of time-dependent diffusivity of the active ingredient and swelling-controlled zero-order release, respectively

Zero order release from glassy hydrogels. II. Matrix effects

A series of copolymers of 2 -hydroxyethyl methacrylate (HEMA) with a hydrophobic monomer, methoxyethyl methacrylate (MEMA), and a hydrophilic monomer, methoxyethoxyethyl methacrylate (MEEMA), was evaluated as matrices for the release of benzoic acid and theophylline. The results are discussed in the context of the criteria developed in the literature for zero order release from glassy hydrogels. Release of theophylline from a p (HEMA-MEMA) matrix containing 22% MEMA followed zero order kinetics. Benzoic acid was released at constant rate from all the matrices