Alginate: properties and biomedical applications

This review concerns the applications of some polysaccharides in the domain of biomaterials and bioactive polymers. Natural polysaccharides from different sources have been studied for a long time, and their main properties are summarized in this paper; some of their derivatives obtained by chemical modification are also described. The main polysaccharides currently used in the biomedical and pharmaceutical domains are chitin and its derivative chitosan, hyaluronan and alginates. Alginates are well known for their property of forming a physical gel in the presence of divalent counterions (Ca, Ba, Sr) whereas carrageenans form a thermoreversible gel; these seaweed polysaccharides are mainly used to encapsulate different materials (cells, bacteria, fungi). Other promising systems are the electrostatic complexes formed when an anionic polysaccharide is mixed with a cationic polysaccharide (e.g. alginate/chitosan or hyaluronan/chitosan). An important development of the applications of polysaccharides can be predicted for the next few years in relation to their intrinsic properties such as biocompatibility and biodegradability in the human body for some of them; they are also renewable and have interesting physical properties (film-forming, gelling and thickening properties). In addition, they are easily processed in different forms such as beads, films, capsules and fibres. Copyright © 2007 Society of Chemical Industry

Main properties and current applications of some polysaccharides as biomaterials

Alginate composites for bone tissue engineering: a review.

http://www.cchem.berkeley.edu/schaffer/2009%20Publications/Banerjee_NSCmodulusAlginate_Biomats_09.pdf

The Influence of Hydrogel Modulus on the Proliferation and Differentiation of Encapsulated Neural Stem Cells

The intent of this paper is to bring up to date an earlier theory of equilibrium selectivity [23, 24], with emphasis on making it applicable to the permeation of membrane channels and carriers, which involve kinetic considerations [8, 56]. We will review critically and unify a number of conceptual advances that have occurred since 1961, particularly the recognition by Hille [56] of how the same energetic principles that describe equilibrium selectivity of binding sites also apply to the peaks of the energy barriers (the so-called selectivity filters) involved in the kinetics of permeation. In the process, the precision of the term selectivity will gradually be increased. We will start with the intuitively simple comparison of effects of one ion versus another. Then we will proceed through more theoretically based classical concepts such as permeability ratios, conductance ratios, and ratios of binding affinities, all of which can be interrelated quite directly in sufficiently simple channels. It will become clear that these concepts lose their crispness and usefulness in multi-barrier channels as a consequence of asymmetry and/or possible multiple occupancy. Our formulation is influenced by a number of useful concepts from classical rate theory [40, 48, 126, 128], where the channel is viewed as having a static energy profile for a given state of ion occupancy; but we will also consider the consequences of viewing the channel as a dynamic structure with a fluctuating energy profile [83, 851. Besides presenting a topical review of selectivity, we have found it necessary to consider two subjects which are so new that they have received little attention as yet in a selectivity context. These are the effects in multi-barrier channels of asymmetry and multiple occupancy. This is because a number of classical concepts, and even ways of thinking about selectivity, are implicitly conditioned by conclusions that have been reached from considerations heretofore largely restricted to channels occupiable by no more than one ion at a time, or to channels with only one significantly rate determining barrier 1, or to channels which are symmetrical. To exemplify the effects of channel asymmetry, we examine in a simple two-barrier one-site model the consequences of asymmetry for reversal potential selectivity. To exemplify the effects of multiple rate-determining barriers, we also examine some implications of the energy profile which can be inferred for the gramicidin channel. In the process of presenting this material, we describe certain relationships between selectivity as seen in different phenomena such as conductance, reversal potential, and binding at least in systems which are simple enough for these classical concepts to retain their utility. This should lead to an understanding of why different measures of selectivity sometimes lead to different apparent selectivities, even in very simple channels. We also will define some guidelines for the applicability of these classical concepts and give some suggestions as to how to define selectivity when they fail, as fail they must, in those biological channels which are asymmetric and/or occupied by more than one ion at a time.

Ionic selectivity revisited: The role of kinetic and equilibrium processes in ion permeation through channels

The promotion of oriented axonal regrowth in the injured spinal cord by alginate-based anisotropic capillary hydrogels.

Unidirectional fluxes in saturated single-file pores of biological and artificial membranes. I. Pores containing no more than one vacancy.

Determination of Krafft point and CMC of hexadecylpyridinium salts in electrolyte solutions

New primer molecules have been synthesized to increase the adhesion strength between a copper leadframe and an epoxy molding compound in microelectronical devices. The coupling agents were preliminarily chemisorbed at the surface of copper plates via special binding groups like thiol, disulfide, ethylene diamine and phthalocyanine. Binding to the epoxy resin was performed via an hydroxyl group. Linear hydrocarbon spacers with various chain lengths connected the copper- and epoxy-binding groups. The self-assembled layers of the organic coupling agents at the metal surface were characterized by X-ray photoelectron spectroscopy. Thermogravimetric analysis was used to study the coating with respect to its corrosion oxidation inhibition. Shear tests clearly indicated that the coupling agents increase adhesion strength and are stable even in extreme humidity and thermal conditions in analogy to IPC-Level-1 pretreatment. Thus, delamination of the microelectronical packages was prevented.

New Adhesion Promoters for Copper Leadframes and Epoxy Resin

Nonspecific adsorption of surfactants on polycrystalline gold electrodes, covered by a chemically adsorbed monomolecular layer of octadecanethiol, was studied by means of capacitive measurements. Homologous series of fatty acids (from decane to tetradecane acids) and dodecanepyridinium chloride were used as surfactants. The behavior of the electrode was completely different in the first and subsequent cycles of adsorption/desorption. In the first adsorption cycle, an initial capacitance jump at low concentrations (<10 μM) occurs, while later the curves show the usual saturation behavior. The first surfactant layer could not be completely desorbed; only the electrode capacitance shown after the jump was reached. Subsequent cycles do not reveal any capacitance jumps and were completely reversible. Adsorption curves in the series of monoalkyl acids are shifted according to the Traube rule. A comparison with the surfactant adsorption at the air/water interface has been done.

Klaus Heckmann

Papers

The promotion of oriented axonal regrowth in the injured spinal cord by alginate-based anisotropic capillary hydrogels.

Unidirectional fluxes in saturated single-file pores of biological and artificial membranes. I. Pores containing no more than one vacancy.

Determination of Krafft point and CMC of hexadecylpyridinium salts in electrolyte solutions

New Adhesion Promoters for Copper Leadframes and Epoxy Resin

Capacitive detection of surfactant adsorption on hydrophobized gold electrodes