From thermally activated to viscosity controlled fracture of biopolymer hydrogels.

We report on rate-dependent fracture energy measurements over three decades of steady crack velocities in alginate and gelatin hydrogels. We evidence that irrespective of gel thermoreversibility, thermally activated "unzipping" of the noncovalent cross-link zones results in slow crack propagation, prevailing against the toughening effect of viscous solvent drag during chain pull-out, which becomes efficient above a few mm s(-1). We extend a previous model [T. Baumberger et al., Nat. Mater. 5, 552 (2006)] to account for both mechanisms and estimate the microscopic unzipping rates.

Lower critical solution temperature type of phase separation in aqueous mixture of polyelectrolytes.

Phase separation behavior in aqueous mixture of different polyelectorolytes having like charges has been investigated as functions of concentration and charge density. When the charge densities of both polyelectorolytes were equally high, the compatibility between different polyelectorolytes was relatively good and the phase separation behavior was a normal upper critical solution temperature (UCST) type. With decreasing the charge density of one polyelectorolyte keeping the charge density of another polyelectrolyte unchanged, the compatibility between different polyelectorolytes became poorer. When the charge density of one polyelectorolyte was lowered below a certain value, the phase separation behavior suddenly changed from the UCST type to a lower critical solution temperature (LCST) type.

The various types of parenteral fluids and their indications.

Assessment of hydration and perfusion is essential in patient evaluation. The acid-base and electrolyte disturbances that accompany many illnesses should also be considered. The duration of illness and body systems involved are also of major importance in patient evaluation. Fluid therapy is an important and potentially life-saving treatment of many and varied problems. The clinician must be able to assess the patient and determine whether the intravascular or extravascular compartments, or both, are deficient. Of primary concern is the status of the intravascular volume, then restoration of total body water and electrolytes. Fluid therapy is divided into three phases; the emergency phase, the rehydration phase, and the maintenance phase; not all patients require the three-phase therapy. The clinician must also be able to select (1) the appropriate solution to treat the volume deficit and correct the acid-base and electrolyte abnormalities and (2) the rate of administration to optimize outcome. Therefore, knowledge of electrolyte composition in plasma and of the various types of commercially available fluids is essential in order to select the appropriate therapy for the individual animal. In addition to the therapeutic aspects of fluid therapy, a knowledge of the side effects and complications of inappropriate fluid selection and rate of delivery is also important. With the individual requirements of each patient seen in a practice, the prescription approach to parenteral fluid therapy will optimize patient response to this extremely important aspect of overall patient management as well as make the practice of fluid therapy intellectually stimulating. This article has introduced the clinician to the parenteral fluids available and their indications in veterinary patients; it also contains a discussion of how to utilize preferred solutions for treatment of specific diseased states. Although there are definite "right" and "wrong" fluids to select for specific problems, there also remains individual preference in fluid choice, which is based on appropriate laboratory data and the practitioner's clinical judgment of the status of the individual patient vis-à-vis the spectrum of its disease. Recommendations for selection of different fluid types to treat similar conditions are usually based on these variables.

Ionization-specific prediction of blood-brain permeability.

This study presents a mechanistic QSAR analysis of passive blood-brain barrier permeability of drugs and drug-like compounds in rats and mice. The experimental data represented in vivo log PS (permeability-surface area product) from in situ perfusion, brain uptake index, and intravenous administration studies. A data set of 280 log PS values was compiled. A subset of 178 compounds was assumed to be driven by passive transport that is free of plasma protein binding and carrier-mediated effects. This subset was described in terms of nonlinear lipophilicity and ionization dependences, that account for multiple kinetic and thermodynamic effects: (i) drug's kinetic diffusion, (ii) ion-specific partitioning between plasma and brain capillary endothelial cell membranes, and (iii) hydrophobic entrapment in phospholipid bilayer. The obtained QSAR model provides both good statistical significance (RMSE < 0.5) and simple physicochemical interpretations (log P and pKa), thus providing a clear route towards property-based design of new CNS drugs.

Ionization-specific analysis of human intestinal absorption.

This study presents a mechanistic QSAR analysis of human intestinal absorption of drugs and drug-like compounds using a data set of 567 %HIA values. Experimental data represent passive diffusion across intestinal membranes, and are considered to be reasonably free of carrier-mediated transport or other unwanted effects. A nonlinear model was developed relating %HIA to physicochemical properties of drugs (lipophilicity, ionization, hydrogen bonding, and molecular size). The model describes ion-specific intestinal permeability of drugs by both transcellular and paracellular routes, and also accounts for unstirred water layer effects. The obtained model was validated on two external data sets consisting of in vivo human jejunal permeability coefficients (P(eff)) and absorption rate constants (K(a)). Validation results demonstrate good predictive power of the model (RMSE = 0.35-0.45 log units for log K(a) and log P(eff)). High prediction accuracy together with clear physicochemical interpretation (log P, pK(a)) makes this model particularly suitable for use in property-based drug design.

Nutrición parenteral: macronutrientes, electrolitos y vitaminas / Parenteral nutrition: macronutrients, electrolytes and vitamins

La indicación de la nutrición parenteral (NP) en niños, está sujeta a enfermedades complejas y/o alteraciones estructurales del tracto gastrointestinal. Su acceso venoso puede ser central o periférico. Existen 2 formas de preparación: la mezcla 2 en 1, que comprende los lípidos por separado y la 3 en 1, donde se encuentran todos los nutrimentos mezclados en la misma bolsa. El agua es el componente esencial e indispensable. La glucosa es la principal fuente de energía. Los aminoácidos cristalinos son la fuente de proteínas. Los lípidos contribuyen como fuente concentrada de energía. Los electrolitos, son agregados separadamente a la solución. El requerimiento de vitaminas parenterales aún no se conoce con exactitud.

The indication for parenteral nutrition (PN) in children, is subject to complex conditions and/or structural abnormalities of the gastrointestinal tract. Its venous Access may be central or peripheral. There are 2 ways to prepare: mix 2 to 1, which includes separate lipids and 3 in 1, where all nutrients are mixed in the same bag. Water is the essential and indispensable. Glucose is the main source of energy. Crystalline amino acids are the source of protein. Lipids contribute as concentrated source of energy. Electrolytes are added separately to the solution. The requirement for parenteral vitamins are not yet understood.

Use of porous membranes modified with polyelectrolyte multilayers as substrates for protein arrays with low nonspecific adsorption.

Coating of substrates with polyelectrolyte multilayers terminated with poly(acrylic acid) (PAA) followed by activation of the free -COOH groups of PAA provides a surface that readily reacts with amine groups to allow covalent immobilization of antibodies. The use of this procedure to prepare arrays of antibodies in porous alumina supports facilitates construction of a flow-through system for analysis of fluorescently labeled antigens. Detection limits in the analysis of Cy5-labeled IgG are 0.02 ng/mL because of the high surface area of the alumina membrane, and the minimal diameter of the substrate pores results in binding limited by kinetics, not mass transport. Moreover, PAA-terminated films resist nonspecific protein adsorption, so blocking of antibody arrays with bovine serum albumin is not necessary. These microarrays are capable of effective analysis in 10% fetal bovine serum.

New class of ultrathin, highly cell-adhesion-resistant polyelectrolyte multilayers with micropatterning capabilities.

Hydrogen-bonded multilayers comprised of polyacrylamide (PAAm) and a weak polyelectrolyte, such as poly(acrylic acid) (PAA) or poly(methacrylic acid) (PMA), were investigated for their surface-cell interactions. The assembled films were lightly cross-linked thermally or photochemically in order to render them stable in a physiological environment. Both PAA/PAAm and PMA/PAAm multilayers were found to exhibit a high resistance to the adhesion (cytophobicity) of mammalian fibroblasts, even with only a single bilayer coating. Protein adsorption to the multilayers, as revealed by surface plasmon resonance measurements, was greatly reduced for fibronectin and serum-containing medium. In situ swelling experiments indicate that the H-bonded multilayers are hydrogellike coatings capable of a high level of swelling in buffered solution. Utilizing the H-bonding nature of these multilayers, we were able to micropattern the films to create more complex cell-resistant/-adhesive surfaces. The long-term stability of the cell-resistant multilayers was found to be exceptionally good even under conditions (pH 7.4, buffered solution) where a high degree of swelling takes place. No degradation of the micropatterned films was observed over a period of a month, during which time the multilayer coatings remained highly resistant to cell-adhesion.

Determinación de enzimas y electrolitos en el líquido cefalorraquídeo de pacientes intervenidos quirúrgicamente por aneurisma cerebral / Determinated of enzimes y electrolyte in the cerebrospinal fluid of patiebts intervened surgical of cerebra aneurym

Con el fin de evaluar qué marcadores bioquímicos del Líquido Cefalorraquídeo son de mayor utilidad en la evolución y pronóstico de los pacientes en postoperatorio inmediato de aneurisma cerebral, se llevó a cabo un estudio de enero-junio 1994, con un total de 20 pacientes, que ingresaron al Hospital Miguel Pérez Carreño, Caracas. Se tomo muestra de líquido cefalorraquídeo, al momento de ser clipado el aneurisma y se determinaron los niveles de CPK, LDH, TGO, TGP, Na y K. La diferencia en los valores obtenidos de K entre los pacientes con evolución satisfactoria y aquellos con evolución tórpida fue estadísticamente significativa concluyendo que dicho marcador puede ayudarnos en el post-operatorio de estos enfermos. El resto de los marcadores no demostraron utilidad alguna