Conformation and cooperative order-disorder transition in aqueous solutions of ß-1,3-d-glucan with different degree of branching varied by the Smith degradation.

ß-1,3-d-glucan with different degrees of branching were obtained by selectively and gradually removing side chains from schizophyllan, a water-soluble triple helical polysaccharide, using the Smith degradation. Size exclusion chromatography combined with a multi-angle light scattering detection was performed in aqueous 0.1 M NaCl. The degree of branching decreased after the Smith degradation, while the molar mass distributions were almost unchanged. The molecular conformation of the Smith-degraded ß-1,3-d-glucan was analyzed on the basis of the molar mass dependency of the radius gyration, and found to be comparable to the original triple helix of schizophyllan. Differential scanning calorimetry in deuterium oxide-hexadeuterodimethylsulfoxide mixtures was performed to investigate the effects of the degree of branching on the cooperative order-disorder transition. Removal of side chains affects both the transition temperature and transition enthalpy. The ordered structure is formed by the residual side chains in the triplex unit, so that the linear cooperative system of the triplex is maintained after the Smith degradation.

Adsorption dynamics of tannin on deacetylated electrospun Konjac glucomannan fabric.

A nonwoven fabric of Konjac glucomannan (KGM) for the adsorption of tannin was fabricated by using electrospinning and then followed by deacetylation with alkaline solution. To analyze the adsorption dynamics of tannin, the time course of the adsorption of tannin on the nonwoven KGM fabric was measured by immersing the fabric in tannin solution at different concentrations of tannin and amounts of the fabric. The initial and late stages of the adsorption behavior could be expressed, respectively, by using a diffusion-limited equation and a stoichiometric equation. A discussion on the dependence of the control parameters on the adsorption behavior is presented. The results represent the first step to provide an effective adsorption procedure for tannin in the use of modified KGM fabric.

Study of plasma coagulation induced by contact with calcium chloride solution.

Blood coagulation capability is one of the most important factors for the diagnosis of patients with thrombosis. Regarding the blood coagulation as an example of gelation of soft matter, we can apply an analytical method to this phenomenon and pick up some relevant parameters. In various systems, gelation dynamics induced by contact between a polymer solution and a crosslinker solution are well explained by the "moving boundary picture" (Yamamoto et al., J. Phys. Chem. B, 2010, 114, 10002-10009). The aim of this paper is to clarify whether this picture can be applied to a clinically important biological system used for blood coagulation tests. We have measured the time course of the thickness of a plasma gel layer formed when plasma comes in contact with calcium chloride solution in a rectangular cell and analyzed theoretically on the basis of the moving boundary picture. The entire process was well expressed using a scaled equation involving three parameters characterizing the plasma, k, Kin, and ß, where k is the time required to reach the incipient stage of three-dimensional network formation, the parameter Kin is proportional to calcium chloride concentration and ß is a constant. These results indicate the direct applicability of the general theory of gelation dynamics induced by contact between two solutions to the in vitro coagulation (gelation) of plasma, and the fitting parameters may be used for diagnosis.

Glassy Behavior of a Tin Dioxide Nanoparticle Suspension.

Dilute suspensions of charged colloidal particles with a short-range attraction and long-range repulsion can exhibit a variety of arrested states. In many applications using suspensions of charged nanoparticles, the optimization of the process requires the understanding of the mechanism underlying the stability and the rheological properties of the suspensions. In an attempt to clarify the solidification mechanism for dilute suspensions of tin dioxide (SnO2) nanoparticles, we present dynamic viscoelasticity, dynamic and static light scattering, and small-angle X-ray scattering experiments on a SnO2 nanoparticle suspension with a nanoparticle concentration of 25.0 wt % (volume fraction φ = 0.045). The behaviors of the observed dynamic and static structure factors reveal that the aging of SnO2 nanoparticles is Wigner glassy rather than gel-like.

Shaping and Structuring of Polymer Gels.

Most industrial gels are prepared as apparently isotropic and homogeneous materials through a preparation process encompassing alterations in temperature, application of isotropic mechanical stress, exposure to high-energy electromagnetic waves, and mixing with cross-linkers (gelators) [...].

Gelation and Orientation Dynamics Induced by Contact of Protein Solution with Transglutaminase Solution.

Gel growth induced by contact of polymer solutions with crosslinker solutions yields an emerging class of anisotropic materials with many potential applications. Here, we report the case of a study on the dynamics in forming anisotropic gels using this approach with an enzyme as a trigger of gelation and gelatin as the polymer. Unlike the previously studied cases of gelation, the isotropic gelation was followed by gel polymer orientation after a lag time. The isotropic gelation dynamics did not depend on concentrations of the polymer turning into gel and of the enzyme inducing gelation, whereas, for the anisotropic gelation, the square of the gel thickness was a linear function of the elapsed time, and the slope increased with polymer concentration. The gelation dynamics of the present system was explained by a combination of diffusion-limited gelation followed by free-energy-limited orientation of polymer molecules.

Studies on the formation mechanism and the structure of the anisotropic collagen gel prepared by dialysis-induced anisotropic gelation.

We have found that dialysis of 5 mg/mL collagen solution into the phosphate solution with a pH of 7.1 and an ionic strength of 151 mM [corrected] at 25 °C results in a collagen gel with a birefringence and tubular pores aligned parallel to the growth direction of the gel. The time course of averaged diameter of tubular pores during the anisotropic gelation was expressed by a power law with an exponent of 1/3, suggesting that the formation of tubular pores is attributed to a spinodal decomposition-like phase separation. Small angle light scattering patterns and high resolution confocal laser scanning microscope images of the anisotropic collagen gel suggested that the collagen fibrils are aligned perpendicular to the growth direction of the gel. The positional dependence of the order parameter of the collagen fibrils showed that the anisotropic collagen gel has an orientation gradient.

Anisotropic structure of calcium-induced alginate gels by optical and small-angle X-ray scattering measurements.

It was more than 50 years ago that an appearance of birefringence in alginate gels prepared under cation flow was reported for the first time, however, the anisotropic structure of the alginate gel has not been studied in detail. In the present study, anisotropic Ca-alginate gels were prepared within dialysis tubing in a high Ca(2+)-concentration external bath, and optical and small-angle X-ray scattering (SAXS) measurements were performed to characterize the structure of the gel. The observations of the gel with crossed polarizers and with circular polarizers revealed the molecular orientation perpendicular to the direction of Ca(2+) flow. Analyses of the SAXS intensity profiles indicated the formation of rod-like fibrils consisting of a few tens of alginate molecules and that the anisotropy of the gel was caused by the circumferential orientation of the large fibrils. From the observed asymmetric SAXS pattern, it was found that the axis of rotational symmetry of the anisotropic structure was parallel to the direction of Ca(2+) flow. The alignment factor (A(f)) calculated from the SAXS intensity data confirmed that the orientation of the fibrils was perpendicular to the direction of Ca(2+) flow.

A galactosamine-mediated drug delivery carrier for targeted liver cancer therapy.

In order to minimize the side effect of cancer chemotherapy, a novel galactosamine-mediated drug delivery carrier, galactosamine-conjugated albumin nanoparticles (GAL-AN), was developed for targeted liver cancer therapy. The albumin nanoparticles (AN) and doxorubicin-loaded AN (DOX-AN) were prepared by the desolvation of albumin in the presence of glutaraldehyde crosslinker. Morphological study indicated the spherical structure of these synthesized particles with an average diameter of around 200 nm. The functional ligand of galactosamine (GAL) was introduced onto the surfaces of AN and DOX-AN via carbodiimide chemistry to obtain GAL-AN and GAL-DOX-AN. Cellular uptake and kinetic studies showed that GAL-AN is able to be selectively incorporated into the HepG2 cells rather than AoSMC cells due to the existence of asialoglycoprotein receptors on HepG2 cell surface. The cytotoxicity, measured by MTT test, indicated that AN and GAL-AN are non-toxic and GAL-DOX-AN is more effective in HepG2 cell killing than that of DOX-AN. As such, our results implied that GAL-AN and GAL-DOX-AN have specific interaction with HepG2 cells via the recognition of GAL and asialoglycoprotein receptor, which renders GAL-AN a promising anticancer drug delivery carrier for liver cancer therapy.

Gel growth of aqueous konjac glucomannan solution containing sodium trimetaphosphate dialyzed with dilute sodium hydroxide.

The growth rate of the hydrogel of the aqueous konjac glucomannan (KGM) solution containing sodium trimetaphosphate (STMP) dialyzed with aqueous NaOH was investigated in a rectangular cell. The growth rate of the KGM-STMP gel depended on both the KGM and STMP concentrations in addition to the NaOH concentration. The initial growth rate of the KGM-STMP gel was closely related to the diffusion of NaOH into the KGM-STMP solution, leading to the ring-opening reaction of STMP and the deacetylation of KGM at the interface. The time course of the gelation of the KGM-STMP solution was analyzed on the basis of the moving boundary picture theory by introducing the characteristic length to express the consumption of NaOH in the gel layer accompanying the decomposition of STMP. Dynamic mechanical measurements were performed to compare the gelation of the KGM-STMP solution mixed homogeneously with dilute NaOH and the gel dynamics by the dialysis method.

Crossover of Rate-Limiting Process in Plasma Gel Growth by Contact with Source of Gelator.

Plasma is regarded as a solution of precursor polymers specifically transformed to gel-forming polymers by a reaction with initiators. We developed a theory for the gel growth dynamics of plasma induced by contact with a source of gelators that are yielded by the initiation. In developing the theory, we combined the Ginzburg-Landau type dynamics with the gelator diffusion dynamics expressed by the moving boundary picture. The theory predicts the crossover of the rate-limiting process in the time course of the thickness of the gel layer X from the energy-limited process expressed by X∼t to the diffusion-limited process expressed by X∼t, where t is the time elapsed from when the plasma comes into contact with the source of gelators. A demonstration experiment was performed by placing a tissue factor coating plate as the initiator in plasma. Log-log plot of X vs. t showed a crossover as predicted by the theory, and the parameters characterizing plasma were determined.

Gel Volume Near the Critical Point of Binary Mixture Isobutyric Acid-Water.

The volume of a cylindrical polyacrylamide gel was measured when immersed in a binary mixture of isobutyric acid-water at different temperatures and weight fractions of isobutyric acid. Near the upper critical solution temperature of the binary mixture, the curve for gel volume vs. isobutyric acid weight fraction has a shoulder or a peak near the critical weight fraction. On the other hand, in a region away from the critical temperature, the gel volume decreased monotonically with increasing isobutyric acid weight fraction. The cloud point temperature of the binary mixture inside the gel was lower than that outside the gel. Thermodynamic description for the gel in the critical mixture is derived on the basis of the Ising model. By the description, the experimental results are explained consistently. The theoretical analysis shows that the shoulder and the peak appearing in the swelling behavior of the gel are respectively induced by the criticalities of the binary mixture outside and inside the gel. It also shows that the cloud point temperature lowering of the binary mixture inside the gel is attributed to the effective enhancement of the temperature of the binary mixture inside the gel induced by the presence of the gel polymer.

Thermosensitive polymer-conjugated albumin nanospheres as thermal targeting anti-cancer drug carrier.

Thermosensitive Poly(N-isopropylacrylamide-co-acrylamide-co-allylamine) (PNIPAM-AAm-AA)-conjugated albumin nanospheres (PAN) was developed as a new thermal targeting anti-cancer drug carrier by conjugating PNIPAM-AAm-AA on the surface of albumin nanospheres (AN). AN with diameter below 200nm and narrow size distribution was successfully prepared in the first step with desolvation technique. PNIPAM-AAm-AA with different molecular weight (M(w)) was synthesized in the second step by radical polymerization and conjugated onto the surface of AN. Anti-cancer drug adriamycin (ADR) was then entrapped into the AN and PAN during the particle preparation. Compared with AN, the release rate of ADR from PAN in trypsin solution was slower, and decreased with increasing the conjugation amounts (hairy density) or M(w) of PNIPAM-AAm-AA (hairy length). Moreover, the release of ADR from PAN above the cloud-point temperature (T(cp)) of PNIPAM-AAm-AA became faster due to shrinkage of hairy thermosensitive polymer. To testify the thermal targetability in vivo, PAN was incubated with HepG2 cells. As expected, PAN can target cancer cells above the T(cp) of PNIPAM-AAm-AA, whereas it cannot below the T(cp). These results might reflect that PAN may selectively accumulate onto solid tumors that are maintained above physiological temperature due to local hyperthermia.

Preparation and characterization of thermo-responsive albumin nanospheres.

Thermo-responsive poly(N-isopropylacrylamide-co-acrylamide)-block-polyallylamine-conjugated albumin nanospheres (PAN), new thermal targeting anti-cancer drug carrier, was developed by conjugating poly(N-isopropylacrylamide-co-acrylamide)-block-polyallylamine (PNIPAM-AAm-b-PAA) on the surface of albumin nanospheres (AN). PAN may selectively accumulate onto solid tumors that are maintained above physiological temperature due to local hyperthermia. PNIPAM-AAm-b-PAA was synthesized by radical polymerization, and AN was prepared by ultrasonic emulsification. AN with diameter below 200 nm and narrow size distribution was obtained by optimizing the preparative conditions. Rose Bengal (RB) was used as model drug for entrapment into the AN and PAN during the particle preparation. The release rate of RB from PAN compared with AN in trypsin solution was slower, and decreased with the increase of PNIPAM-AAm-b-PAA molecular weight, which suggested that the existence of a steric hydrophilic barrier on AN made digestion of AN more difficult. Moreover, the release of RB from PAN above the cloud-point temperature (T(cp)) of PNIPAM-AAm-b-PAA became faster. This was because the density of temperature-responsive polymers on AN was not so high, so that the interspace between the polymer chains increased after they shrunk due to the high temperature. As a result, the biodegradable AN was attacked more easily by trypsin. The design of PAN overcame the disadvantages of temperature-responsive polymeric micelles.

Comparison of the kinetics of chain aggregation and chain collapse in dilute polymer solutions.

The rates of chain aggregation of poly(methyl methacrylate) (PMMA) in acetonitrile (AcN) and in the mixed solvent of AcN+water (10 vol%) were determined by static light scattering and compared with the rates of chain collapse [Maki, J. Chem. Phys. 126, 134901 (2007)]. Dilute solutions of PMMA with the molecular weight m{w}=6.4 x 10{6} and in the concentration range of (0.8-5)x10;{-4}gcm;{3} were quenched below the cloud point, and the weight-average molecular weight M{w} and z -average square radius of gyration S;{2}_{z} for clusters of PMMA chains were measured as a function of the time t after the quench and the concentration c . The measurement of chain aggregation was carried out up to the cluster size of M{w}m{w} approximately 30 , which required time periods of hours to several days depending on the concentration and solvent. The chain aggregation in AcN+water occurred much faster than that in AcN. The growth of clusters in both the solvents was represented by the exponential function as M{w} approximately e;{gct} and S;{2}_{z} approximately e{hct} , where g and h represent the intrinsic rate of chain aggregation. The ratio sigma of the intrinsic rate in AcN+water to that in AcN was estimated to be 9 by taking a rough average of the ratios 9.4 obtained from g and 8.8 from h . This value is comparable to the ratio 11 of the rate of chain collapse of PMMA in AcN+water (10 vol%) to that in AcN. This close value of the ratios indicates that the nature of solvent would affect the rates of chain collapse and chain aggregation through a similar mechanism.

Analysis of Heterogeneous Gelation Dynamics and Their Application to Blood Coagulation.

We present a scaling model based on a moving boundary picture to describe heterogeneous gelation dynamics. The dynamics of gelation induced by different gelation mechanisms is expressed by the scaled equation for the time taken for development of the gel layer with a few kinetic coefficients characterizing the system. The physical meaning obtained by the analysis for a simple boundary condition from the standpoint of the phase transition shows that the time development of the gelation layer depends on whether the dynamics of the order parameter expressing the gelation of the polymer solution is fast or slow compared with the diffusion of the gelators in the heterogeneous gelation. The analytical method is used to understand the coagulation of blood from various animals. An experiment using systems with plasma coagulation occurring at interfaces with calcium chloride solution and with packed erythrocytes is performed to provide the data for model fitting and it is clarified that a few key kinetic coefficients in plasma coagulation can be estimated from the analysis of gelation dynamics.

Cooperative Order-Disorder Transition of Carboxylated Schizophyllan in Water-Dimethylsulfoxide Mixtures.

Carboxylated schizophyllan ("sclerox") is a chemically modified polysaccharide obtained by partial periodate oxidation and subsequent chlorite oxidation of schizophyllan, a water-soluble neutral polysaccharide having a ß-1,3-linked glucan backbone and a ß-1,6-linked d-glucose residue side chain at every third residue of the main chain. The triple helix of schizophyllan in water has a cooperative order-disorder transition associated with the side chains. The transition is strongly affected by the presence (mole fraction) of dimethylsulfoxide (DMSO). In the present study, the solvent effects on the order-disorder transition of sclerox with different degrees of carboxylation (DS) in water-DMSO mixtures were investigated with differential scanning calorimetry and optical rotation. The transition temperature ( Tr) and transition enthalpy (Δ Hr) strongly depended on the mole fraction of DMSO ( xD). Data were further analyzed with the statistical theory for the linear cooperative transition, taking into account the solvent effect, where DMSO molecules are selectively associated with the unmodified side chains. The modified side chain does not contribute to the transition; hence, Δ Hr decreases with increasing DS. The dependence of Tr on the DMSO content becomes weaker than that for unmodified schizophyllan. The theoretical analyses indicated that the number of sites binding with the DMSO molecule and the successive ordered sequence of the ordered unit of the triple helix are changed by carboxylation.

Small-angle X-ray and light scattering analysis of multi-layered Curdlan gels prepared by a diffusion method.

Curdlan, a microbial polysaccharide, forms a multi-layered gel consisting of four layers with different turbidity when its alkaline solution is dialyzed against aqueous solutions containing Ca2+ (diffusion-set gel). The present study clarified the microstructure of each layer of the diffusion-set Curdlan gel by small-angle X-ray scattering (SAXS) and small-angle light scattering (SALS). The SAXS data showed that Curdlan chains assume a helical ordered conformation in the gel and that the gel consists of the fibrils formed by the association of Curdlan chains and the aggregates of fibrils. The SAXS results also indicated that the gelation is induced by the formation of a network of Ca2+-cross-linked fibrils in the outer region of the gel, whereas by the network formation of the aggregation of fibrils in the neutralization process in the inner region of the gel. A structural anisotropy of the gel was investigated by analysis of two-dimensional SAXS images, showing that the fibril is oriented circumferentially in the outer region of the cylindrical gel, whereas it is oriented randomly in the inner region of the gel. The SALS data showed that a characteristic length of an inhomogeneous structure in the turbid layers is of the order of micrometers. The observed spatial variation of the microscopic structure is caused by the difference in the paths of pH and [Ca2+] traced in the gelation process.

Effects of carboxylation of the side chains on the order-disorder transition in aqueous solution of schizophyllan, a triple helical polysaccharide.

Schizophyllan and scleroglucan are water-soluble polysaccharides having repeating units consisting of three ß-1,3-linked glucose residues in the main chain and a single ß-1,6-linked glucose residue as the side chain. This polysaccharide dissolves as a triple helix in an aqueous solution and shows a cooperative order-disorder transition between the side chain and solvent molecules while retaining the triple helical conformation. Periodate and subsequent chlorite oxidations selectively modify the side chain glucose to provide the corresponding dicarboxylate units. Optical rotation measurements and differential scanning calorimetry were performed on carboxylated schizophyllan/scleroglucan ('sclerox') samples to investigate the effects of the degree of carboxylation on the order-disorder transition in deuterium oxide with 0.1M NaCl. The transition curves for the sclerox samples are strongly dependent on the degree of carboxylation. The modified side chains cannot take the ordered structure, resulting in a reduction of the transition enthalpy. The transition temperature for carboxylated schizophyllan becomes lowered and the transition curve broadens with increasing the degree of carboxylation. The permanent disordered units are included in a trimer by the carboxylation to inhibit a long sequence of the ordered units.

Erythrocyte aggregation under high pressure studied by laser photometry and mathematical analysis.

The effects of hydrostatic pressure on erythrocyte aggregation have been studied by laser photometry and analysis based on a phenomenological theory. Samples were prepared by suspending swine erythrocytes in their own plasma. A high-pressure vessel consisting of a stainless-steel block with a hole to hold a sample cell and two sapphire windows to allows the passage of a He-Ne laser beam was used in the experimental setup. The suspension was stirred at 1500 rpm to disperse the erythrocytes homogeneously. Immediately after reducing the stirring rate from 1500 rpm to 300 rpm, the transmitted light intensity (I) was recorded every 10 ms under a high pressure of 40-200 MPa. The value of I increased with time (t) owing to erythrocyte aggregation. From the phenomenological theory, the equation ΔI(t)=ΔIeq[1-e(-Kt)/(1-B(1-e(-Kt)))] was derived for the change in the transmitted light intensity (ΔI) due to erythrocyte aggregation, where ΔIeq is the transmitted light intensity in the steady state, K is a time constant and B is a constant that represents the ratio of the number of interaction sites on erythrocyte aggregates at time t to that in the steady state. The observed time courses of ΔI obtained at all pressures could be closely fitted to the theoretical equation. ΔIeq roughly increased with increasing pressure. On the other hand, K and B abruptly decreased above 120 MPa. The growth rate of aggregates decreased above 120 MPa. These results suggest a change in the mechanism of erythrocyte aggregation at approximately 120 MPa. We discuss the physical meaning of the parameters.