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PubMed2003

Capillary electrochromatography and preconcentration of neutral compounds on poly(dimethylsiloxane) microchips.

Capillary electrochromatography (CEC) and preconcentration of neutral compounds have been realized on poly(dimethylsiloxane) (PDMS) microchips. The channels are coated with polyelectrolyte multilayers to avoid absorption of hydrophobic analytes into PDMS. The structures of a microchip include an injector and a bead chamber with integrated frits, where the particles of the stationary phase are completely retained. Dimensions of the frit structures are 25 micro mx20 micro m, and the space between the structures is 3 micro m. A neutral compound, BODIPY, that is strongly absorbed into native PDMS, is successfully and selectively retained on octadecylsilane-coated silica beads in the bead chamber with a concentration enhancement of up to 100 times and eluted with elution buffer solution containing 70% acetonitrile. Preconcentrations and CEC separations of coumarins have been conducted with the same device and achieved complete separations in less than 50 s.

Acetonitriles↗
PubMed2003

Open-tubular capillary electrochromatography using a polymeric surfactant coating.

A stable polyelectrolyte multilayer (PEM) coating was investigated for use in open-tubular capillary electrochromatography (o-CEC). In this approach, the PEM consisted of the cationic polymer of a quaternary ammonium salt, poly(diallyldimethylammonium chloride) and the anionic polymeric surfactant, poly(sodium undecylenic sulfate). Both the cationic and anionic polymers were physically adsorbed to the surface of a fused-silica capillary by use of a simple coating procedure. This procedure involved an alternate rinse of the positively and negatively charged polymers. The performance of the PEM coating as a dynamic stationary phase was evaluated by use of electrochromatographic experiments and showed good selectivity for both phenols and benzodiazepines. Reproducibility of the PEM coating was also evaluated by calculating the relative standard deviations (RSDs) of the electroosomotic flow (EOF). The run-to-run and capillary-to-capillary RSD values of the EOF were less than 1.5%. The endurance of the coating was more than 100 runs. The importance of the PEM coating was illustrated by comparing separations on a bare uncoated capillary with the coated capillary. In addition, the chromatographic performance using o-CEC and micellar electrokinetic chromatography (MEKC) was compared for the separation of benzodiazepines.

Benzodiazepines↗
PubMed2005

End-labeled free-solution electrophoresis of DNA.

DNA is a free-draining polymer. This subtle but "unfortunate" property of highly charged polyelectrolytes makes it impossible to separate nucleic acids by free-flow electrophoresis. This is why one must typically use a sieving matrix, such as a gel or an entangled polymer solution, in order to obtain some electrophoretic size separation. An alternative approach consists of breaking the charge to friction balance of free-draining DNA molecules. This can be achieved by labeling the DNA with a large, uncharged molecule (essentially a hydrodynamic parachute, which we also call a drag-tag) prior to electrophoresis; the resulting methodology is called end-labeled free-solution electrophoresis (ELFSE). In this article, we review the development of ELFSE over the last decade. In particular, we examine the theoretical concepts used to predict the ultimate performance of ELFSE for single-stranded (ssDNA) sequencing, the experimental results showing that ELFSE can indeed overcome the free-draining issue raised above, and the technological advances that are needed to speed the development of competitive ELFSE-based sequencing and separation technologies. Finally, we also review the reverse process, called free-solution conjugate electrophoresis (FSCE), wherein uncharged polymers of different sizes can be analyzed using a short DNA molecule as an electrophoretic engine.

DNA↗
PubMed2006

Electrophoretic mobility of linear and star-branched DNA in semidilute polymer solutions.

Electrophoresis of large linear T2 (162 kbp) and 3-arm star-branched (N(Arm) = 48.5 kbp) DNA in linear polyacrylamide (LPA) solutions above the overlap concentration c* has been investigated using a fluorescence visualization technique that allows both the conformation and mobility mu of the DNA to be determined. LPA solutions of moderate polydispersity index (PI approximately 1.7-2.1) and variable polymer molecular weight Mw (0.59-2.05 MDa) are used as the sieving media. In unentangled semidilute solutions (c* < c < c(e)), we find that the conformational dynamics of linear and star-branched DNA in electric fields are strikingly different; the former migrating in predominantly U- or I-shaped conformations, depending on electric field strength E, and the latter migrating in a squid-like profile with the star-arms outstretched in the direction opposite to E and dragging the branch point through the sieving medium. Despite these visual differences, mu for linear and star-branched DNA of comparable size are found to be nearly identical in semidilute, unentangled LPA solutions. For LPA concentrations above the entanglement threshold (c > c(e)), the conformation of migrating linear and star-shaped DNA manifest only subtle changes from their unentangled solution features, but mu for the stars decreases strongly with increasing LPA concentration and molecular weight, while mu for linear DNA becomes nearly independent of c and Mw. These findings are discussed in the context of current theories for electrophoresis of large polyelectrolytes.

Acrylic Resins↗
PubMedDate not supplied

Problems in treating experimentally induced acute hepatic failure by hemoperfusion or cross circulation.

Acute hepatic failure was induced in rats by galactosamine injection intraperitoneally (1 gm per kg). Twenty-four hours later rats were treated by hemoperfusion (HP) over encapsulated sorbents: cellulose acetate-coated charcoal, polyelectrolyte-coated XAD4, a combination of both, or cross circulation with a healthy donor. Compared with control treatment (prevention of hypoglycemia by glucose infusion), the survival rate was not improved by HP or cross circulation: controls 19% vs. treated animals 0 to 17%. Extension of duration or increased frequency of HP gave the same survival rates. Computer simulation based on zero-order introduction of a possible toxin into a two-compartment model shows that HP up to 5 hr per day is not able to clear the body effectively from the assumed toxin if its partition coefficient exceeds a value of 50.

Animals↗
PubMed2002

Thin film rheology and lubricity of hyaluronic acid solutions at a normal physiological concentration.

Using a surface forces apparatus to measure forces, and optical (multiple beam) interferometry to measure surface shapes and separations (to +/-1 A), the normal, viscous, and shear (lubrication) forces between smooth mica surfaces in aqueous hyaluronic acid (HA) solutions were measured. The experimental conditions of loading pressures, pH, and HA concentration were set to closely correspond to physiological human knee-joint conditions. From the force and optical (refractive index) measurements, it was concluded that, like other negatively charged polyelectrolytes, HA does not naturally adsorb on the mica surface which is hydrophilic and weakly negatively charged at physiological conditions: the polymer solution exhibits the bulk viscosity (22.5 +/- 1.5 cP) for films thicker than about 0.4 miccrom of the polymer, whereas for thinner films, the viscosity decreases monotonically toward the value of the pure electrolyte solution (1 cP) as HA is extruded from between the surfaces. This is indicative of a repulsive "depletion" interaction of HA with each mica surface and to a weakly attractive polymer-mediated force between the two surfaces. Thus, free HA in synovial fluid is not expected to act as a good "boundary lubricant." Relaxation measurements on approaching and receding surfaces in HA solutions were also performed, and it is shown that the presence of HA in the bulk solution can improve "hydrodynamic" modes of lubrication, for example, by assuaging the compression stroke. The study includes information that is beneficial to researchers working with biomaterials viscosupplementation devices.

Adsorption↗
PubMed2002

Polymer--calcium phosphate cement composites for bone substitutes.

The use of self-setting calcium phosphate cements (CPCs) as bioresorbable bone-replacement implant materials presently is limited to non-load-bearing applications because of their low compressive strength relative to natural bone. The present study investigated the possibility of strengthening a commercially available CPC, alpha-BSM, by incorporating various water-soluble polymers into the cement paste during setting. Several polyelectrolytes, poly(ethylene oxide), and the protein bovine serum albumin (BSA) were added in solution to the cement paste to create calcium phosphate-polymer composites. Composites formulated with the polycations poly(ethylenimine) and poly(allylamine hydrochloride) exhibited compressive strengths up to six times greater than that of pure alpha-BSM material, with a maximum value reached at intermediate polymer content and for the highest molecular weight studied. Composites containing BSA developed compressive strengths twice that of the original cement at protein concentrations of 13-25% by weight. In each case, XRD studies correlate the improvement in compressive strength with reduced crystallite dimensions, as evidenced by a broadening of the (0,0,2) reflection. This suggests that polycation or BSA adsorption inhibits crystal growth and possibly leads to a larger crystal aspect ratio. SEM results indicate a denser, more interdigitated microstructure. The increased strength was attributed to the polymer's capacity to bridge between multiple crystallites (thus forming a more cohesive composite) and to absorb energy through plastic flow.

Animals↗
PubMed2002

Superabsorbent materials from shellfish waste--a review.

Increasing global demand for improved absorbent materials for body fluids in disposable medical and personal-care articles creates an incentive for new basic research and development of efficient absorbent materials and systems with additional benefits such as biodegradability or certain biomedical functions. Highly absorbing materials based on polyelectrolyte polymers can absorb up to 50 grams of body fluid per gram of dry mass. Currently available synthetic superabsorbents are not biodegradable in landfills and do not offer any value-added functions to personal and medical-care products. Various academic and industrial research groups have put considerable amounts of effort and resources toward development of new absorbent materials from natural polymers, which would decompose in landfills. The basic substrates in these studies have been mainly polysaccharides, particularly cellulose and starch. The most common approach has involved converting these polymers into carboxymethyl derivatives followed by structural cross-linking. Commercial synthetic superabsorbent polymers as well as those derived from cellulose and starch are essentially polyanionic. On the other hand, polycationic absorbers seem to have potential functional advantages over the polyanionic counterparts. Chitin is the second abundant natural polymer, whose main derivative, chitosan, becomes polycationic in acid media. Currently, the main source of this polysaccharide is shellfish waste. This review provides basic information about new superabsorbent materials based on chitosan salts, their properties and preparation.

Absorbent Pads↗
PubMed2001

Chitosan-alginate films prepared with chitosans of different molecular weights.

Chitosan-alginate polyelectrolyte complex (CS-AL PEC) is water insoluble and more effective in limiting the release of encapsulated materials compared to chitosan or alginate. Coherent CS-AL PEC films have been prepared in our laboratory by casting and drying suspensions of chitosan-alginate coacervates. The objective of this study was to evaluate the properties of the CS-AL PEC films prepared with chitosans of different molecular weights. Films prepared with low-molecular-weight chitosan (Mv 1.30 x 10(5)) were twice as thin and transparent, as well as 55% less permeable to water vapor, compared to films prepared with high-molecular-weight chitosan (Mv 10.0 x 10(5)). It may be inferred that the low-molecular-weight chitosan reacted more completely with the sodium alginate (M(v) 1.04 x 10(5)) than chitosan of higher molecular weight. A threshold molecular weight may be required, because chitosans of Mv 10.0 x 10(5) and 5.33 x 10(5) yielded films with similar physical properties. The PEC films exhibited different surface properties from the parent films, and contained a higher degree of chain alignment with the possible formation of new crystal types. The PEC films exhibited good in vitro biocompatibility with mouse and human fibroblasts, suggesting that they can be further explored for biomedical applications.

Animals↗
PubMed2002

Chitosan-alginate PEC membrane as a wound dressing: Assessment of incisional wound healing.

Flexible, thin, transparent, novel chitosan-alginate polyelectrolyte complex (PEC) membranes, cast from aqueous suspensions of chitosan-alginate coacervates with CaCl(2), were evaluated as potential wound-dressing materials. MTT and NR assays suggested that the chitosan-alginate PEC membranes and their aqueous extracts were nontoxic towards mouse and human fibroblast cells. Cell growth was also not hindered by co-incubation with the membranes. Compared to conventional gauze dressing, the PEC membranes caused an accelerated healing of incision wounds in a rat model. Wounds closed at 14 days postoperatively, and histological observations showed mature epidermal architecture with keratinized surface of normal thickness and a subsided inflammation in the dermis. This was followed by an excellent remodeling phase with organized thicker collagen bundles and mature fibroblasts at 21 days postoperative. Control wounds continued to show signs of an active inflammatory phase under scab on Day 21. Closure rate and appearance of PEC membrane-treated wounds were comparable with Opsite(R)-treated wounds. On the basis of its biocompatibility and wound-healing efficacy, the chitosan-alginate PEC membrane can be considered for wound-dressing applications.

Alginates↗
PubMed1979

13C NMR spectroscopic analysis of poly(electrolyte) cement liquids.

13C NMR spectroscopy has been applied to the analysis of carboxylic poly-acid cement liquids. Monomer incorporation, composition ratio, sequence statistics, and stereochemical configuration have been considered theoretically, and determined experimentally, from the spectra. Conventionally polymerized poly(acrylic acid) has an approximately random configuration, but other varieties may be synthesized. Two commercial glass-ionomer cement liquids both contain tartaric acid as a chelating additive but the composition of their poly-acids are different. Itaconic acid units, distributed randomly, constitute 21% of the repeating units in one of these polyelectrolytes.

Acrylic Resins↗
PubMed1987

Prostacyclin immobilized albuminated surfaces.

The adhered platelets on artificial surfaces play a crucial role in inducing thrombosis. Therefore, it is very much desirable to have surfaces which can effectively retard platelet adhesion and aggregation. Prostaglandins like PGE2, PGE1 and PGD2 possess potent antiplatelet activity, but have very short half life. A chemically stable prostacyclin analog, 10,10-difluoro-13-dehydroprostacyclin (DF2-PGI2) seems to be promising. Polyelectrolyte (PE) synthesized from natural poly cis-1,4 isoprene has also been found to possess outstanding anticoagulant and antiplatelet activity. Modification of polyetherurethane urea (PEUU) by immobilizing DF2-PGI2 and poly-electrolyte in various combinations using glow discharge technique has been attempted. Surfaces thus modified showed negligible platelet adherence. The inhibition of platelet adherence in presence of inducing agents like fibrinogen, thrombin and ADP was also remarkable. The interactions of albumin and fibrinogen with the modified surfaces were studied using 125I labelled proteins.

Adenosine Diphosphate↗
PubMed1992

Organoapatites: materials for artificial bone. I. Synthesis and microstructure.

We have synthesized a new family of materials we termed organoapatites which may be useful in the formulation of artificial bone. These materials are synthesized by nucleation and growth of apatite crystals in media containing poly(amino acids) or synthetic organic polyelectrolytes using strict atmospheric, temperature, and pH control. The macromolecules used to synthesize the organoapatites include poly(L-lysine), poly(L-glutamic acid), and poly(sodium acrylate). The products were characterized by x-ray diffraction, scanning electron microscopy, surface area measurements, elemental analysis, and spectroscopic techniques. Organoapatites were found to contain large surface area morphologies with small crystallites which mature slowly based on analysis of Ca/P ratios. The organic macromolecules are thought to induce nucleation of crystals but also to quench their growth, thus becoming intimately dispersed in a mineral network. The organomineral particles harvested from the reaction medium contain polymer-netted microcrystals, and for this reason the synthetic approach can be used to modulate crystal maturation and biological response. It is likely that the preparative approach mimics some aspects of natural bone matrix synthesis and could be specially useful in the preparation of mineral implants containing intimate dispersions of small amounts of biomolecules such as growth factors, special drugs, or bioadhesives.

Apatites↗
PubMed1993

Organoapatites: materials for artificial bone. II. Hardening reactions and properties.

This article reports on chemical reactions and the properties they generated in artificial bone materials termed "organoapatites." These materials are synthesized using methodology we reported in the previous article of this series. Two different processes were studied here for the transition from organoapatite particles to implants suitable for the restoration of the skeletal system. One process involved the hardening of powder compacts by beams of blue light derived from a lamp or a laser and the other involved pressure-induced interdiffusion of polymers. In both cases, the hardening reaction involved the formation of a polyion complex between two polyelectrolytes. In the photo-induced reaction an anionic electrolyte polymerizes to form the coulombic network and in the pressure-induced one, pressure forms the complex by interdiffusion of two polyions. Model reactions were studied using various polycations. Based on these results the organoapatite selected for the study was that containing dispersed poly(L-lysine) and sodium acrylate as the anionic monomer. The organomineral particles can be pressed at room temperature into objects of great physical integrity and hydrolytic stability relative to anorganic controls. The remarkable fact about these objects is that intimate molecular dispersion of only 2-3% by weight organic material provides integrity to the mineral network in an aqueous medium and also doubles its tensile strength. This integrity is essentially nonexistent in "anorganic" samples prepared by the same methodology used in organoapatite synthesis. The improvement in properties was most effectively produced by molecular bridges formed by photopolymerization. The photopolymerization leads to the "hardening" of pellets prepared by pressing of organoapatite powders. The reaction was found to be more facile in the microstructure of the organomineral, and it is potentially useful in the surgical application of organoapatites as artificial bone.

Apatites↗
PubMed1993

Organoapatites: materials for artificial bone. III. Biological testing.

This article reports on the in vivo testing of new artificial bone materials we have termed "organoapatites." These materials consist of mineral networks in which organic polymers are intimately dispersed by nucleation and growth of apatite crystals from a mother liquor containing the organic substances. Organoapatites were tested as implants in adult canine cortical bone for periods in the range from 12-35 weeks and fluorochromes were used in the model to investigate the kinetics of bone growth or repair. The analysis of histological samples was carried out using histomorphometric methods as well as fluorescence microscopy. Results showed excellent apposition of poly(amino acid) organoapatites with mineralized bone and fibrous encapsulation when a synthetic polyelectrolyte was the only organic component. This observation suggests that the molecularly dispersed organic dopant amounting to only 2-3% by weight of the microstructure can play a critical role in the tissue response to the implant. Relative to apatite controls, organoapatites were also found to have greater resistance to fragmentation in vivo and those containing amino acid units revealed interfacial bioerosion accompanied by regeneration of mineralized tissue. Design of organoapatite compositions and microstructures may therefore be useful in achieving the specific rate of biological response which is clinically desired.

Animals↗
PubMed2003

Biomedical application of a superabsorbent hydrogel for body water elimination in the treatment of edemas.

A novel system of body water elimination to be used for the treatment of edemas, based on superabsorbent cellulose derivatives able to absorb large amounts of water and water solutions, has been investigated. Hydrogels have been synthesized starting from water solutions of carboxymethylcellulose sodium salt and hydroxyethylcellulose, chemically crosslinked with divinylsulphone. Polyelectrolyte hydrogels displayed high sensitivity in sorption capacity to variations of the ionic strength and pH of the external solution, which is a key parameter for the application under investigation. Further, swelling properties have been modulated acting on the degree of crosslinking of the macromolecular network, and a direct method for the measurement of this parameter based on NMR solid-state analysis has been provided. The hydrogel biocompatibility has been studied in terms of its capacity either to induce nitric oxide and lactate dehydrogenase release by macrophages or influence their viability. The eventual release of toxic substances from the hydrogel was also investigated using Swiss 3T3 fibroblasts. The results obtained from the biocompatibility studies carried out in this work are consistent with the hypothesis that this gel may represent an alternative to diuretic therapies in those pathologic conditions in which edemas occur.

Absorption↗
PubMed2005

Influence of channel width on alignment of smooth muscle cells by high-aspect-ratio microfabricated elastomeric cell culture scaffolds.

Engineered smooth muscle tissue requires ordered configurations of cells to reproduce native function, and microtechnology offers possibilities for physically and chemically controlling cell organization with high spatial resolution. In this work, poly(dimethylsiloxane) microchannel scaffolds, modified by layer-by-layer self-assembly of polyelectrolytes to promote cell adhesion, were evaluated for use as substrates for the culture of aligned smooth muscle cells. The hypothesis that narrower channels would result in better alignment was tested using channel width dimensions of 20, 30, 40, 50, and 60 microm, in addition to flat (control) surfaces. Alignment of cells was assessed by two different methods, each sensitive to a different aspect of cell alignment from fluorescence micrographs. Two-dimensional fast Fourier transform analysis was performed to analyze the orientation distribution of actin filaments in cells. This was complemented by connectivity analysis of stained nuclei to obtain nuclear orientation distributions. Both methods produced consistent data that support the hypothesis that narrow microchannels promote a highly aligned culture of smooth muscle cells, and the degree of alignment is dependent on the microchannel width. Precise replication of in vivo cell alignment in engineered tissue, with the ability to tailor specific surface chemistries of the scaffold to the desired application, will potentially allow the production of artificial tissue that more closely duplicates the structure and function of native tissue.

Actins↗
PubMed2007

Water soluble complexes of chitosan-g-MPEG and hyaluronic acid.

Novel water soluble, biocompatible, and highly viscoelastic polyelectrolyte complexes were prepared by mixing of positively charged chitosan grafted with poly (ethylene glycol) monomethyl ether (CS-g-MPEG) and negatively charged hyaluronic acid (HA). CS-g-MPEGs having different degrees of substitution were synthesized by reacting chitosan with MPEG-aldehyde. The molecular structure, thermal and rheological properties, as well as biocompatibility of CS-g-MPEG/HA complexes were characterized. Rheological results showed that a small amount of HA could greatly enhance the viscosity of CS-g-MPEG solution. The highest viscosity was obtained when the charge ratio of CS-g-MPEG/HA was close to 1.0. Small-angle X-ray scattering measurements provided some insights into the lamellar structure of the CS-g-MPEG/HA complex. The CS-g-MPEG/HA complex system offers promising potentials in pharmaceutical, cosmetic, and biotechnology applications (e.g., cell scaffold, artificial synovial fluid, and drug/gene delivery medium).

Biocompatible Materials↗