Polyelectrolyte Characteristics Research Articles

Structural Features, Physicochemical Properties, and In Vitro Digestibility of the Starch-Lipid Complexes Formed between High Amylose Starch and Stearic Acid or Potassium Stearate.

Starch-lipid complexes were prepared from high amylose starch (HAS) with stearic acid (SA) or potassium stearate (PS) at different molar concentrations. The complexes (HAS-PS) formed between HAS and PS showed polyelectrolyte characteristics with ζ-potential ranging from -22.2 to -32.8 mV, and the electrostatic repulsion between anionic charges restricted the starch chain reassociation and facilitated the formation of V-type crystalline structures upon cooling. The hydrophobic effects enabled recrystallization of the SA, and the HAS-SA complexes exhibited weaker V-type crystalline structures than the HAS-PS complexes; both HAS-SA/PS complexes were of a similar "mass fractal" type, with a dimension varied from 2.15 to 2.96. The HAS-SA complexes had a considerable content of resistant starch (RS, 16.1~29.2%), whereas negligible RS was found in the HAS-PS complexes. The findings from the present study imply that the molecular order of starch chains and the macro-structures of starch particles are more important to regulate the digestibility of starch-lipid complexes than the crystalline structures.

From isolated polyelectrolytes to star-like assemblies: the role of sequence heterogeneity on the statistical structure of the intrinsically disordered neurofilament-low tail domain

Intrinsically disordered proteins (IDPs) are a subset of proteins that lack stable secondary structure. Given their polymeric nature, previous mean-field approximations have been used to describe the statistical structure of IDPs. However, the amino-acid sequence heterogeneity and complex intermolecular interaction network have significantly impeded the ability to get proper approximations. One such case is the intrinsically disordered tail domain of neurofilament low (NFLt), which comprises a 50 residue-long uncharged domain followed by a 96 residue-long negatively charged domain. Here, we measure two NFLt variants to identify the impact of the NFLt two main subdomains on its complex interactions and statistical structure. Using synchrotron small-angle x-ray scattering, we find that the uncharged domain of the NFLt induces attractive interactions that cause it to self-assemble into star-like polymer brushes. On the other hand, when the uncharged domain is truncated, the remaining charged N-terminal domains remain isolated in solution with typical polyelectrolyte characteristics. We further discuss how competing long- and short-ranged interactions within the polymer brushes dominate their ensemble structure and, in turn, their implications on previously observed phenomena in NFL native and diseased states.Graphic abstractVisual schematic of the SAXS measurement results of the Neurofilament-low tail domain IDP (NFLt). NFLts assemble into star-like brushes through their hydrophobic N-terminal domains (marked in blue). In increasing salinity, brush height (h) is initially increased following a decrease while gaining additional tails to their assembly. Isolating the charged sub-domain of the NFLt (marked in red) results in isolated polyelectrolytes

Secondary Structure of DNA Aptamer Influences Biomimetic Mineralization of Calcium Carbonate.

Calcium materials, such as calcium carbonate, are produced in natural and industrial settings that range from oceanic to biomedical. An array of biological and biomimetic template molecules have been employed in controlling and understanding the mineralization reaction but have largely focused on small molecule additives or disordered polyelectrolytes. DNA aptamers are synthetic and programmable biomolecules with polyelectrolyte characteristics but with predictable and controllable secondary structure akin to native extracellular moieties. This work demonstrates for the first time the influence of DNA aptamers with known G-quadruplex structures on calcium carbonate mineralization. Aptamers demonstrate kinetic inhibition of mineral formation, sequence and pH-dependent uptake into the mineral, and morphological control of the primarily calcite material in controlled solution conditions. In reactions initiated from the complex matrix of ocean water, DNA aptamers demonstrated enhancement of mineralization kinetics and resulting amorphous material. This work provides new biomimetic tools to employ in controlled mineralization and demonstrates the influence that template secondary structure can have in material formation.

Structure of nanoparticle‐polyelectrolyte complexes: Effects of polyelectrolyte characteristics and charge ratio

AbstractWe present structural and turbidimetric characterizations of aqueous dispersions of oppositely charged nanoparticles and polyelectrolytes that undergo complexation and flocculation to form particle‐rich agglomerates over a wide range of polyelectrolyte and nanoparticle concentrations with varying polyelectrolyte sizes and persistence lengths. Compaction of nanoparticles in the polyelectrolyte–nanoparticle complexes, signified by decreasing internanoparticle spacing until they are brought in near‐contact, is observed upon increasing screening of interparticle repulsion arising from adsorption of polyelectrolytes on the nanoparticle surfaces. We identify the ratio of charge borne by the polyelectrolytes and the nanoparticles as a key parameter dictating the compaction of nanoparticles into complexes as well as densification of complexes into agglomerates. Moreover, the emergence of turbidity in solution is shown to correlate with the initiation of nanoparticle compaction by polyelectrolytes but failing to describe further structural evolution of the complexes, emphasizing the need for alternate characterization techniques.

Chemical stabilization of γ-polyglutamate by chitosan and the effect of co-solvents on the stability

In protein-based formulations, conformational distortions and attractive interactions may cause insoluble and undesired aggregates. In the case of ionic peptides, including cationic or anionic, commonly electrostatic interactions are the main factors that control structure assembling. In this study, it was proposed that grafting of chitosan (CS) to γ-polyglutamic acid (γ-PGA) might exhibit much strong inhibiting effect on the formation of protein aggregates due to multiple amino groups and hydrophilic properties. To guarantee stable and safe biopharmaceutical formulation, the potency of a variety of stabilizers including sugars (glucose, sucrose), polyols (sorbitol, glycerol), surfactant (Tween 20), salting-out salt (PBS), and also different pH values have been evaluated on stabilizing or destabilizing the native state of CS-g-PGA copolymer using FTIR, CD, DLS, and SDS-PAGE. The comparable analysis revealed that the stability of CS-g-PGA was strongly dependent on pH owing to the polyelectrolyte characteristics of the polymers. Altogether these results implied that CS at optimized conditions might be an important precursor for the pharmaceutical industry and function as a new polymer for aggregation suppression and protein stabilization.

Smart, Naturally-Derived Macromolecules for Controlled Drug Release.

A series of troxerutin-based macromolecules with ten poly(acrylic acid) (PAA) or poly(2-dimethylaminoethyl methacrylate) (PDMAEMA) homopolymer side chains were synthesized by a supplemental activator and reducing agent atom transfer radical polymerization (SARA ATRP) approach. The prepared precisely-defined structures with low dispersity (Mw/Mn < 1.09 for PAA-based, and Mw/Mn < 1.71 for PDMAEMA-based macromolecules) exhibited pH-responsive behavior depending on the length of the polymer grafts. The properties of the received polyelectrolytes were investigated by dynamic light scattering (DLS) measurement to determine the hydrodynamic diameter and zeta potential upon pH changes. Additionally, PDMAEMA-based polymers showed thermoresponsive properties and exhibited phase transfer at a lower critical solution temperature (LCST). Thanks to polyelectrolyte characteristics, the prepared polymers were investigated as smart materials for controlled release of quercetin. The influence of the length of the polymer grafts for the quercetin release profile was examined by UV–VIS spectroscopy. The results suggest the strong correlation between the length of the polymer chains and the efficiency of active substance release, thus, the adjustment of the composition of the macromolecules characterized by branched architecture can precisely control the properties of smart delivery systems.

Association between Nonionic Amphiphilic Polymer and Ionic Surfactant in Aqueous Solutions: Effect of Polymer Hydrophobicity and Micellization.

The interaction in aqueous solutions of surfactants with amphiphilic polymers can be more complex than the surfactant interactions with homopolymers. Interactions between the common ionic surfactant sodium dodecyl sulfate (SDS) and nonionic amphiphilic polymers of the poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (PEO-PPO-PEO) type have been probed utilizing a variety of experimental techniques. The polymer amphiphiles studied here are Pluronic F127 (EO100PO65EO100) and Pluronic P123 (EO19PO69EO19), having the same length PPO block but different length PEO blocks and, accordingly, very different critical micellization concentrations (CMC). With increasing surfactant concentration in aqueous solutions of fixed polymer content, SDS interacts with unassociated PEO-PPO-PEO molecules to first form SDS-rich SDS/Pluronic assemblies and then free SDS micelles. SDS interacts with micellized PEO-PPO-PEO to form Pluronic-rich SDS/Pluronic assemblies, which upon further increase in surfactant concentration, break down and transition into SDS-rich SDS/Pluronic assemblies, followed by free SDS micelle formation. The SDS-rich SDS/Pluronic assemblies exhibit polyelectrolyte characteristics. The interactions and mode of association between nonionic macromolecular amphiphiles and short-chain ionic amphiphiles are affected by the polymer hydrophobicity and its concentration in the aqueous solution. For example, SDS binds to Pluronic F127 micelles at much lower concentrations (~0.01 mM) when compared to Pluronic P123 micelles (~1 mM). The critical association concentration (CAC) values of SDS in aqueous PEO-PPO-PEO solutions are much lower than CAC in aqueous PEO homopolymer solutions.

Amylopectin-Sodium Palmitate Complexes as Sustainable Nanohydrogels with Tunable Size and Fractal Dimensions.

Starch-based nanohydrogels with polyelectrolyte characteristics may find unique applications. Herein, the branch chains of amylopectin (AP) were elongated to different extents by amylosucrase, followed by complexation with sodium palmitate (SP) to produce nanohydrogels. Modified AP (mAP) with a longer chain length displayed a better ability to complex with SP, and the mixtures exhibited nanosized particles with an average diameter ranging from 153.5 to 1049.8 nm. The gel strength of bulk nanohydrogels was dependent on the chain length of mAP and SP content, and their fractal dimension was between 1.82 and 2.45. The crystalline structure of native AP was altered from A- to B-type after chain elongation and, subsequently, to B + V-type after complexing with SP. Diffraction peaks of the complexes at 2θ of 7.5°, 12.9°, and 19.8° implied that the AP side chains formed left-handed single helices and the hydrophobic SP was entrapped in the helix cavity.

Synthesis, characterization and toxicological evaluation of pH-sensitive polyelectrolyte Nanogels

Nanogels are polymeric nanoparticles that have similar characteristic to hydrogels, but have the size in nano range. The pH-sensitive nanogel have gained much interest in the field of pharmaceutical nanotechnology as they have potential to be used as nanocarriers in drug delivery system. The aim of the present study was to synthesize pH-sensitive polyelectrolyte MMA/IA nanogels using free radical polymerization containing methyl methacrylate (MMA), itaconic acid (IA), and a crosslinker ethylene glycol dimethacrylate (EGDMA). In the synthesis of nanogels four parameters i.e. ethanol/water ratios (v/v), dilution volume using ethanol/water (v/v), crosslinker EGDMA concentration, and monomers MMA/IA ratios were optimized. Their effect on particle size, PdI, zeta potential and swelling ratio were evaluated. The swelling behaviour of the nanogels was studied by measuring swelling ratio using gravimetric method. The optimized nanogels were characterized by proton nuclear magnetic resonance (1H NMR), Fourier transform infrared spectroscopy (FTIR), liquid chromatography/time-of-flight/mass spectrometry (LC-TOF-MS), X-ray powder diffraction (X-RD) and transmission electron microscopy (TEM). Polyelectrolyte characteristic was confirmed by measuring isoelectric point using aqueous electrophoresis. The in-vitro and in-vivo toxicity studies were performed by MTT assays using Caco-2 cells and Limit test using female Sprague Dawly rats, respectively. The nanogels were amorphous in nature, exhibited pH-responsive property and polyelectrolyte characteristics, which showed an isoelectric point at pH 2.78. They had an average particle size <250 nm, narrow size distribution (PdI < 0.3), and negative zeta potential. The in-vitro MTT assays indicated that the nanogels had no sign of cytotoxicity. The in vivo Limit test showed that the LD50 was greater than 2000 mg/kg body weight. The necrospy, histopathology and hematological studies also revealed no sign of toxicity. These findings suggested that the MMA/IA nanogels are pH-sensitive, non-toxic and have potential to form a polyelectrolyte complex with oppositely charged of macromolecular drugs.

Charge density dependence of elasticity of anionically modified N,N-dimethylacrylamide-based gels with (meth)acrylic acid segments: An insight by quantitative analysis of electrostatic contributions

Swollen state properties of modified polyelectrolyte gels with anionic species is highly dependent on the effective charge density distributions as well as the interactions between the mobile and immobile groups. A more systematic and comparative study of the role of structure and content of the anionic comonomers has been made on poly(N,N-dimethylacrylamide) PDMAAm-based hydrogels attention being focused on their Gaussian elasticity and corresponding swollen state properties. A thermodynamic framework for interpreting gel-swelling model was presented to describe the aqueous equilibrium swelling properties of a series of weakly ionic polyelectrolyte hydrogels based on acidic comonomers; acrylic acid (AAc), methacrylic acid (MAAc), sodium acrylate (NaA) and a base monomer DMAAm as well as the effect of ionizable groups on their resulting mechanical properties. The introduction of the electrostatic interactions decreased the elastic modulus of ionic PDMAAm hydrogels and cryogels. The model predicts well the effect of the gel charge density on the elasticity; however, the correlation of the obtained results with the equilibrium swelling data suggests that a change of the gel microstructure with electrostatic interactions is the responsible of the observed background effect. Although the ionizable functional groups of AAc and MAAc display weak anionic polyelectrolyte characteristics, the swelling ratio is enhanced with respect to homopolymeric PDMAAm, increasing in the order DMAAm<MAAc<AAc<NaA.

Chemical structure and physical-chemical properties of mucilage from the leaves of Pereskia aculeata

Mucilage extracted from leaves of Pereskia aculeata, popularly called Barbados gooseberry (or ora-pro-nobis in Brazil), was investigated in terms of structural, chemical and physical-chemical properties. The mucilage was obtained with a new method using water at room temperature. Analysis of polysaccharide by GC-MS and NMR techniques showed the presence of galactose, arabinose, rhamnose, fucose and partially esterified galacturonic acid, whose main chain consisted of β-d-galactose linked (1 → 4), partially substituted at C-3 by arabinose, making it possible to characterize an arabinogalactan type I, highlighting the presence of fucose units. In water saline solution, the material is highly heterogeneous, as observed by size exclusion chromatography, where the main fraction is dispersed (Đ = 1.3) with weight average molar mass (Mw) of 7.9 × 105 g/mol. In addition, the intrinsic viscosity [η] (26 dL/g), by the Mark-Houwink equation, and the [η] dependence of Mw indicate that the mucilage has random conformation and flexible chains in sodium nitrate solution, with a radius of gyration of 41 nm and critical concentration (c*) of 4.6 mg/mL. Tensiometry allowed determining the critical adsorption concentration (CCA) and the critical self-association concentration (CSAC), as 1 and 6 mg/mL, respectively, and the sample showed mild surfactant characteristics. In aqueous dispersion (30 g/L), the rheological measurement showed pseudoplastic behavior of the mucilage, with polyelectrolyte characteristics. Finally, the pre-heating of the mucilage at 70 °C for 10 min caused an increase in viscosity and improved pseudoplasticity, for better interaction and molecular solubilization after cooling.

Use of a hydrophobic associative four-armed star anionic polymer to create a saline aqueous solution of CO2-switchability

ABSTRACTA four-armed anionic star-shaped block polymer, containing an anionic polymer poly(2-Acrylamido-2-methylpropanesulfonic acid) (PAMPS) as the core group and poly(2-(Dimethylamino)ethyl methacrylate) (PDM) as the terminal group, was synthesized by using the Atom Transfer Radical Polymerization (ATRP) method. The (PAMPS50-PDM50)4 aqueous solution exhibited both polyelectrolyte and hydrophobic associative characteristics, that is, a low concentration of NaCl results in decreasing viscosity but a high concentration of NaCl results in increasing viscosity. The four-armed anionic block polymer shows a CO2-reversible property at high concentrations of brine. Viscosity, pH, and ζ potential demonstrate the switchability jointly; the values could be switched from relatively low to high cyclically. These transitions could actually be attributed to the protonation of tertiary amine groups in PDM blocks, and the mechanism was proved by 1H NMR.

Anionic Polymerization of Oxadiazole-Containing 2-Vinylpyridine by Precisely Tuning Nucleophilicity and the Polyelectrolyte Characteristics of the Resulting Polymers

Anionic polymerization is one of the most powerful techniques for preparation of well-defined polymers. However, this well-known and widely employed polymerization technique encounters major limitations for the polymerization of functional monomers containing heteroatoms. This work presents the anionic polymerization of 2-phenyl-5-(6-vinylpyridin-3-yl)-1,3,4-oxadiazole (VPyOzP), a heteroatom monomer that contains both oxadiazole and pyridine substituents within the same pendant group, using various initiating systems based on diphenylmethyl potassium (DPM-K) and triphenylmethyl potassium (TPM-K). Remarkably, well-defined poly(2-phenyl-5-(6-vinylpyridin-3-yl)-1,3,4-oxadiazole) (PVPyOzP) polymers having predicted molecular weights (MW) ranging from 2200 to 21 100 g/mol and polydispersity indices (PDI) ranging from 1.11 to 1.15 were prepared with TPM-K, without any additional additives, at −78 °C. The effect of temperature on the polymerization of PVPyOzP was also studied at −78, −45, 0, and 25 °C, and it wa...

How does the anionic surfactant SDS affect the association of hydrophobically end-modified PNIPAM chains in aqueous solution?

The studies on the interaction between thermo-responsive polymer PNIPAM and various ionic surfactants have been extensively investigated in the past few years. Unfortunately, the role of the hydrophobic end-group which is inevitably introduced by the initiator or chain transfer agent was generally overlooked in related studies. In this work, to show the interplay between the hydrophobic end-group and the surfactant molecule, five n-dodecyl-terminated poly(N-isopropylacrylamide)s (PNIPAMs-C12H25) with different chain lengths were prepared by RAFT polymerization. The unambiguous molecular parameters were obtained by GPC, LLS, 1H-NMR and UV–Vis measurements. Further study on the association behaviors in SDS aqueous solutions showed that, these PNIPAM-C12H25 chains can form uniform spherical micelles accompanied with a trace amount of large irregular aggregates in pure water at 20 °C, and the size-molar mass relation of aggregates presents a scaling law. The addition of SDS could continuously weaken the association of these alkyl-terminated PNIPAMs, reflected in the decrease of average hydrodynamic radius (<Rh>) and average aggregation number (<Nagg>) of aggregates. Also, it could endow the PNIPAM chains the polyelectrolyte characteristics, reflected in the emergency of a slow relaxation mode in dynamic LLS measurement. More interestingly, the reversal of the dependence of cloud point on the chain length was observed at high SDS concentration, which may be attributed to the preferentially van der Waals interaction between the SDS dodecyl tail and the PNIPAM dodecyl chain end.

Transitions from simple electrolyte to polyelectrolyte in a series of polyphosphates

The dependence of polyelectrolyte characteristics on the number of phosphate groups in a series of polyphosphates was clarified by potentiometric titration and 23Na nuclear magnetic resonance using the Donnan model. Ca2+ ion binding to various polyphosphates was consistently inhibited as supporting electrolyte concentration increased. The electrostatic interactions between polyions and counterions, which is peculiar to polyelectrolytes, was enhanced by an increase in the number of phosphate groups. The polyelectrolyte characteristics increased non-monotonically with the number of phosphate groups that constituted the molecules, that is, (1) gradual emergence with three or four phosphate groups, (2) marked strengthening from four to eight phosphate groups, and (3) saturation with eight or more phosphate groups. The characteristics of polyelectrolyte molecules comprising eight or more phosphate groups were independent of the degree of polymerization. These interesting behaviors were observed to be closely similar using two quite different experimental techniques, electrochemical titration and nuclear magnetic resonance.

Comparative study on the formation and flocculation properties of polyelectrolyte complex dispersions based on synthetic and natural polycations

Nonstoichiometric interpolyelectrolyte complexes (NIPECs) as colloidal dispersions formed by the interaction of synthetic polycations which possess ammonium quaternary centers attached to an acrylic macromolecular chain, derived from poly(N,N-dimethylaminoethyl methacrylate), or a natural polycation, chitosan, with poly(sodium-2-acrylamido-2-methylpropanesulfonate) (PAMPS), and three random copolymers of AMPS with tert-butylacrylamide or methyl methacrylate, were prepared. The effects of polyelectrolyte characteristics and concentration on the complex features were investigated by turbidimetric titration and dynamic light scattering, the molar ratio between the positive and negative charges ranging between 0.05 and 0.4. The nonstoichiometric complex nanoparticles were tested in the destabilization of kaolin model dispersion and proved to be more efficient than polycations alone, especially as concern the broadness of the flocculation window. The highest efficiency of the NIPECs dispersions was found when they have been prepared at very low molar ratios between charges ( n −/ n + < 0.1).

Flocculation by cationic polyelectrolytes: Relating efficiency with polyelectrolyte characteristics

AbstractA series of acrylamide/dimethylaminoethylacrylate methyl chloride copolymers (AM‐co‐DMAEA) was evaluated as flocculants for model Precipitated Calcium Carbonate (PCC) in distilled water. These cationic polyelectrolytes (PEL) differed by their AM/DMAEA ratio, i.e., their charge density, chain architecture (linear and branched), their intrinsic viscosity (IV), and zeta potential of their aqueous solutions. The IV being directly related to the hydrodynamic volume of the PEL and the zeta potential reflecting the effective charges in suspension were selected for practically useful correlations with flocculation performance. The fractal dimension (dF) and the scattering exponent (SE) of the flocs, analyzed by the laser diffraction method, were taken as indication of primary particle and aggregate assembly. For the optimum PEL dosage, SE anddFvaried with the IV and zeta potential. It was observable that floc size, floc resistance, and floc reorganization correlate with the PEL characteristics. Copolymers with lower IV, which is here associated with PEL of similar molar mass but lower charge density, yielded larger and less resistant flocs. Copolymers with higher IV originated smaller more compact flocs being more resistant. In high shear situations, where floc breakage should be avoided, as it is the case in papermaking, polymers with high IV yielding large SE are advantageous. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Complex Nanoparticles Based on Chitosan and Ionic/Nonionic Strong Polyanions: Formation, Stability, and Application

Interpolyelectrolyte complex (IPEC) nanoparticles formed between chitosan having different molar masses (470, 670, and 780 kDa) and two random copolymers of 2-(acrylamido)-2-methylpropanesulfonate (AMPS) with tert-butylacrylamide (TBA) [P(AMPS(54)-co-TBA(46)) and P(AMPS(37)-co-TBA(63))] were prepared by the dropwise addition of polyanion onto the chitosan solution. The effect of polyelectrolyte characteristics and the molar ratio between charges on the morphology of the complex nanoparticles and on their colloidal stability was deeply investigated by turbidimetric titration (optical density at 500 nm), dynamic light scattering, and atomic force microscopy. It was found that the lowest sizes of the IPEC nanoparticles were obtained, with both polyanions, when the chitosan having the lowest molar mass (470 kDa) was used as a major component. In this case, the particle sizes varied in a narrow range, even after the complex stoichiometry; i.e., when the polyanion was added in excess, the colloidal stability of these IPEC dispersions was very high. A mechanism of complex formation as a function of the ratio between charges was proposed. According to this mechanism, the nonstoichiometric complex nanoparticles formed at molar ratios between charges, n(-)/n+, lower than 0.2, i.e., far from the complex stoichiometry, would have a high density of positive charges in excess not only because of the chitosan in excess, which forms the shell, but also because of the mismatch of opposite charges, due to both the differences in the flexibility of complementary polyions and the presence of the hydrophobic comonomer, TBA, in the polyanion structure. Nonstoichiometric IPECs prepared at n(-)/n+ around 0.2 proved to be more efficient than chitosan in the destabilization of kaolin from a model suspension, with a lower optimum concentration flocculation and a much larger flocculation window being found compared with chitosan.

Role, Metabolism, Chemical Modifications and Applications of Hyaluronan

Hyaluronan (hyaluronic acid, HA) is a linear naturally occurring polysaccharide formed from repeating disaccharide units of N-acetyl-D-glucosamine and D-glucuronate. Despite its relatively simple structure, HA is an extraordinarily versatile glycosaminoglycan currently receiving attention across a wide front of research areas. It has a very high molar mass, usually in the order of millions of Daltons, and possesses interesting visco-elastic properties based on its polymeric and polyelectrolyte characteristics. HA is omnipresent in the human body and in other vertebrates, occurring in almost all biological fluids and tissues, although the highest amounts of HA are found in the extracellular matrix of soft connective tissues. HA is involved in several key processes, including cell signaling, wound repair and regeneration, morphogenesis, matrix organization and pathobiology. Clinically, it is used as a diagnostic marker for many disease states including cancer, rheumatoid arthritis, liver pathologies, and as an early marker for impending rejection following organ transplantation. It is also used for supplementation of impaired synovial fluid in arthritic patients, following cataract surgery, as a filler in cosmetic and soft tissue surgery, as a device in several surgical procedures, particularly as an anti-adhesive following abdominal procedures, and also in tissue engineering. This review will provide an overview of the structure and physiological role of HA, as well as of its biomedical and industrial applications. Recent advances in biotechnological approaches for the preparation of HA-based materials, and as a component of tissue scaffolding for artificial organs will also be presented.

Optimization of sewage sludge conditioning and pressure dewatering by statistical modelling

By using a quadratic model, an assessment was made of the relative importance of different sludge and polyelectrolyte variables with respect to sludge pressure dewatering. It was seen that the polyelectrolyte characteristics and dose dominated the cake dry matter content and that sludge properties were less important, especially the electrophoretic mobility of the sludge, which showed a restricted natural variability over the 10-month sampling period. The developed quadratic model in this study appeared very well suited to quantitatively predict the pressure dewatering properties of sludge, allowing the selection of the dose and polyelectrolyte type that yield the best dewatering result. It was further shown that relatively small deviations from the optimal polyelectrolyte dose caused only small changes in cake dry matter values. The model appeared to be applicable on a long-term basis, as it was able to predict the dewaterability of several sludge samples from the studied wastewater treatment plant after more than 3 years. Finally, the model also allowed an (simplified) economic evaluation, indicating that for high cake disposal costs, the polyelectrolyte should be taken that guarantees the best dewatering results, even if it has to be applied in high doses.