Rheological Characterization as an Alternative Method to Indentation for Determining the Setting Time of Restorative and Endodontic Cements.

This study explored an alternative approach using rheology to assess setting time. The following cements were tested: ProRoot® MTA (Dentsply, Tulsa, OK, USA), Biodentine® (Septodont, Saint Maur des Fosses, France), Fuji VII®, FujiVII® EP, and Fuji IX® (from GC Corporation, Tokyo, Japan), RealSeal SE™ Sealer (SybronEndo, Amersfoort, The Netherlands), AH 26® and AH Plus (both from Dentsply DeTrey, Konstanz, Germany). Freshly mixed cements were placed into a strain-controlled rheometer (1 rad·s-1 with an applied strain of 0.01%). From measurements of elastic modulus over time, the time taken to reach 90% of the plateau elastic modulus (designated as the setting time) was determined for each cement. In increasing order, the setting times were as follows: Fuji VII EP 3.3 min, Fuji VII 3.6 min, Fuji IX 3.7 min, ProRoot MTA 5.1 min, Biodentine 15.9 min, RealSeal 22.2 min, AH Plus 5933 min, and AH 26 5067 min. However, ProRoot MTA did not yield reliable results. The time to reach the 90% plateau elastic modulus correlates well with the setting time of glass ionomer cements and Biodentine. Using this approach gives much longer setting times for endodontic sealers than previously recognized.

The molecular structural features controlling stickiness in cooked rice, a major palatability determinant.

The stickiness of cooked rice is important for eating quality and consumer acceptance. The first molecular understanding of stickiness is obtained from leaching and molecular structural characteristics during cooking. Starch is a highly branched glucose polymer. We find (i) the molecular size of leached amylopectin is 30 times smaller than that of native amylopectin while (ii) that of leached amylose is 5 times smaller than that of native amylose, (iii) the chain-length distribution (CLD: the number of monomer units in a chain on the branched polymer) of leached amylopectin is similar to native amylopectin while (iv) the CLD of leached amylose is much narrower than that of the native amylose, and (v) mainly amylopectin, not amylose, leaches out of the granule and rice kernel during cooking. Stickiness is found to increase with decreasing amylose content in the whole grain, and, in the leachate, with increasing total amount of amylopectin, the proportion of short amylopectin chains, and amylopectin molecular size. Molecular adhesion mechanisms are put forward to explain this result. This molecular structural mechanism provides a new tool for rice breeders to select cultivars with desirable palatability by quantifying the components and molecular structure of leached starch.

Instrumental measurement of cooked rice texture by dynamic rheological testing and its relation to the fine structure of rice starch.

Increasing demands for better instrumental methods to evaluate cooked rice texture is driving innovations in rice texture research. This study characterized cooked rice texture by descriptive sensory analysis and two instrumental methods (texture profile analysis (TPA) and dynamic rheological testing) using a set of 18 varieties of rice with a wide range in amylose content (0-30%). The panellists' results indicated that hardness and stickiness were the two most discriminating attributes among 13 tested textural attributes. The consistency coefficient (K(*)) and loss tangent (tan δ) from a dynamic frequency sweep were used to compare with hardness and stickiness tested by TPA and sensory panellists, showing that using K(*) to express hardness, and tan δ to express stickiness, are both statistically and mechanistically meaningful. The instrumental method is rationalized in terms of starch structural differences between rices: a higher proportion of both amylose and long amylopectin branches with DP 70-100 causes a more elastic and less viscous texture, which is readily understood in terms of polymer dynamics in solution.

The importance of amylose and amylopectin fine structure for textural properties of cooked rice grains.

Statistically and causally meaningful relationships are established between starch molecular structure (the molecular distribution of branched starch and the chain length distribution of debranched starch) and texture (hardness and stickiness) of cooked rice grains. The amounts of amylose chains with degree of polymerization (DP) 100-20,000, and of long amylopectin chains, positively correlated with hardness, while amylopectin chains with DP<70 and amylose molecular size both showed negative correlations with hardness (p<0.05). There was also a significant negative correlation between stickiness and the amounts of long amylopectin chains (p<0.01). For rices with similar amylose content, the amount of amylose chains with DP 1000-2000 positively correlated with hardness while size negatively correlated with hardness (p<0.05). This indicates for the first time that, regardless of amylose content, rice varieties with smaller amylose molecular sizes and with higher proportions of long amylose chains have a harder texture after cooking.

Identification of the primary lesion of toxic aluminum in plant roots.

Despite the rhizotoxicity of aluminum (Al) being identified over 100 years ago, there is still no consensus regarding the mechanisms whereby root elongation rate is initially reduced in the approximately 40% of arable soils worldwide that are acidic. We used high-resolution kinematic analyses, molecular biology, rheology, and advanced imaging techniques to examine soybean (Glycine max) roots exposed to Al. Using this multidisciplinary approach, we have conclusively shown that the primary lesion of Al is apoplastic. In particular, it was found that 75 µm Al reduced root growth after only 5 min (or 30 min at 30 µm Al), with Al being toxic by binding to the walls of outer cells, which directly inhibited their loosening in the elongation zone. An alteration in the biosynthesis and distribution of ethylene and auxin was a second, slower effect, causing both a transient decrease in the rate of cell elongation after 1.5 h but also a longer term gradual reduction in the length of the elongation zone. These findings show the importance of focusing on traits related to cell wall composition as well as mechanisms involved in wall loosening to overcome the deleterious effects of soluble Al.

Implications of changing the amount of thickener in thickened infant formula for infants with dysphagia.

When a dysphagic infant is prescribed thickened infant formula (TIF) as a treatment method, some clinicians determine their own addition rates of thickener to meet the specific needs of the infant rather than relying on the directions on the tin. In this study the rheological behaviour of a TIF at different addition levels of thickener was measured to determine whether there was a difference in full rheological response and in viscosity. In addition, the time taken for the TIF to reach a near-stable viscosity was also measured. One hundred grams of Karicare® infant formula was made up according to the manufacturer's instructions and Karicare® feed thickener was added at levels of 2, 3, 4, 5, and 6 g, respectively. A strain-controlled rheometer (ARES) with Couette geometry was used to rheologically characterise the TIF at the different levels of thickener addition. There was a significant difference in viscosity between the low levels and the higher levels of addition thickener (p < 0.05). Also, the low levels of thickener addition showed Newtonian-like behaviour, whereas the higher levels of addition were shear-thinning. The time taken for the thickener to reach a near-stable viscosity was found to be 10 min. Guidelines for thickened infant formula need to take into account the different levels of thickener addition rates.

Effect of the ionic liquid 1-ethyl-3-methylimidazolium acetate on the phase transition of starch: dissolution or gelatinization?

This work revealed that the interactions between starch, the ionic liquid 1-ethyl-3-methylimidazolium acetate ([Emim][OAc]), and water might contribute to the phase transition (gelatinization, dissolution, or both) of native starch at reduced temperature. Using mixtures of water and [Emim][OAc] at certain ratios (7.2/1 and 10.8/1 mol/mol), both the gelatinization and dissolution of the starch occur competitively, but also in a synergistic manner. At lower [Emim][OAc] concentration (water/[Emim][OAc] molar ratio≥25.0/1), mainly gelatinization occurs which is slightly impeded by the strong interaction between water and [Emim][OAc]; while at higher [Emim][OAc] concentration (water/[Emim][OAc] molar ratio≤2.8/1), the dissolution of starch is the major form of phase transition, possibly restricted by the difficulty of [Emim][OAc] to interact with starch.

Control of the orientation of symmetric poly(styrene)-block-poly(D,L-lactide) block copolymers using statistical copolymers of dissimilar composition.

The interactions of block copolymers with surfaces can be controlled by coating those surfaces with appropriate statistical copolymers. Usually, a statistical copolymer comprised of monomer units identical to those of the block copolymer is used; that is, typically a poly(styrene)-stat-poly(methyl methacrylate) (PS-stat-PMMA) is used to direct the alignment of poly(styrene)-block-poly(methyl methacrylate) (PS-block-PMMA), and poly(styrene)-stat-poly(2-vinylpyridine) (PS-stat-P2VP) has been used for poly(styrene)-block-poly(2-vinylpyridine) (PS-block-P2VP). Reports of controlling the orientation of block copolymers with statistical copolymers with a dissimilar composition are limited. Here, we demonstrate that this method can be further extended to show that PS-stat-PMMA can be used to control the wetting properties of poly(styrene)-block-poly(D,L-lactide) (PS-block-PDLA). Surfaces were modified with a series of cross-linked PS-stat-PMMA-stat-glycidyl methacrylate terpolymers, and the surface chemistries and energies were assessed using angle-dependent X-ray photoelectron spectroscopy and the two-liquid harmonic method, respectively. From these experiments, an expected neutral compositional window was identified for symmetrical PS-block-PDLA. Moreover, high-resolution SEM, AD-XPS, and grazing-incidence SAXS measurements were used to evaluate the morphology of PS-block-PDLA as a function of the surface composition of the underlying cross-linked copolymer films, and the neutral composition was found to range from 32 to 38 mol % of PS, in the bulk polymer. Ultimately, we demonstrated the determination of nonpreferential surface compositions that allow the self-assembly of lamellae with sizes in the sub-10 nm regime that are oriented perpendicular to the substrate. These findings have important implications for the use of PS-block-PDLA block copolymers in directed self-assembly, most specifically in advanced lithographic processes.

Effects of Ca, Cu, Al and La on pectin gel strength: implications for plant cell walls.

Rheology of Ca-pectate gels is widely studied, but the behaviour of pectate gels formed by Cu, Al and La is largely unknown. It is well known that gel strength increases with increasing Ca concentration, and it is hypothesised that this would also be the case for other cations. Pectins are a critical component of plant cell walls, imparting various physicochemical properties. Furthermore, the mechanism of metal toxicity in plants is hypothesised to be, in the short term, related to metal interactions with cell wall pectin. This study investigated the influence of Ca, Cu, Al and La ion concentrations at pH 4 on the storage modulus as a function of frequency for metal-pectin gels prepared from pectin (1%) with a degree of esterification of 30%. Gels were formed in situ over 6d in metal chloride solution adjusted daily to pH 4. Cation concentration was varied to develop a relationship between gel strength and cation concentration. At similar levels of cation saturation, gel strength increased in the order of La

Electrostatically mediated specific adsorption of small molecules in metallo-organic frameworks.

We investigate the interaction of ethylene and ethane with a Cu-tricarboxylate complex and show that at low loadings the lighter molecule has a higher binding energy as a result of an increased interaction with the framework Cu and stronger hydrogen bonding with the basic framework oxygens. This leads to selective adsorption of ethylene by a factor of about 2 at low pressure, which is overcome by the stronger van der Waals interaction of ethane at high loadings, explaining recent literature data. The results suggest the possibility of separation of light hydrocarbons at low pressures or in trace amounts.