Artefacts arising during preparation of hydrated paper pulp samples for low-temperature SEM

Beating, a pulp treatment widely used in the paper industry, causes disruption of cell wall layers and fibrillation. Previous studies of the effects of beating on fibre morphology have used conventional methods of specimen preparation, with all the attendant problems of shrinkage and distortion during dehydration. Low-temperature scanning electron microscopy (LTSEM) therefore seemed to offer an ideal method for examining fully hydrated wood pulp fibres. Cryofixation of pulp followed by sublimation of superficial ice, however, is shown to generate artefacts indistinguishable from structures present in the samples. Fibrillar and membranous structures were generated in LTSEM-prepared sugar solutions; their presence in pulp samples was therefore attributed to the dissolved carbohydrates inherent in pulp suspensions. Since artefact and fact are currently impossible to distinguish in LTSEM-prepared pulp samples, it seems that the technique should be applied to wet paper or pulp samples with considerable circumspection.     

Effects of ultramorphological changes on adhesion to lased dentin-Scanning electron microscopy and transmission electron microscopy analysis

Dentin irradiation with erbium lasers has been reported to alter the composite resin bond to this treated surface. There is still a lack of studies reporting the effect of erbium lasers on dentin organic content and elucidating how laser treatment could interfere in the quality of the resin-dentin interface. This study aimed to evaluate the effect of erbium laser irradiation on dentin morphology and microtensile bond strength (μTBS) of an adhesive to dentin. Seventy-two dentin disks were divided into nine groups (n = 8): G1-Control (600-grit SiC paper); Er:YAG groups: G2- 250 mJ/4 Hz; G3- 200 mJ/4 Hz; G4- 180 mJ/10 Hz; G5- 160 mJ/10 Hz; Er,Cr:YSGG groups: G6- 2 W/20 Hz; G7- 2.5 W/20 Hz; G8- 3 W/20 Hz; G9- 4 W/20 Hz. Specimens were processed for cross-sectional analysis by scanning electron microscopy (SEM) (n = 3), transmission electron microscopy (TEM) (n = 2), and adhesive interface (n = 3). Forty-five dentin samples (n = 5) were restored and submitted to μTBS testing. ANOVA (α = 5%) revealed that G1 presented the highest μTBS values and irradiated groups did not differ from each other. TEM micrographs showed a superficial layer of denatured collagen fibrils. For SEM micrographs, it was possible to verify the laser effects extending to dentin subsurface presenting a rough aspect. Cross-sectional dentin micrographs of this hybridized surface revealed a pattern of modified tags with ringlike structures around it. This in vitro study showed that erbium laser irradiation interacts with the dental hard tissue resulting in a specific morphological pattern of dentin and collagen fibrils that negatively affected the bond strength to composite resin.     

Evaluation of nanoparticle tracking for characterization of fibrillar protein aggregates

Amyloidogenesis is the process of formation of protein aggregates with fibrillar morphology. Because amyloidogenesis is linked to neurodegenerative disease, there is interest in understanding the mechanism of fibril growth. Kinetic models of amyloidogenesis require data on the number concentration and size distribution of aggregates, but this information is difficult to obtain using conventional methods. Nanoparticle tracking analysis (NTA) is a relatively new technique that may be uniquely suited for obtaining these data. In NTA, the two‐dimensional (2‐D) trajectory of individual particles is tracked, from which the diffusion coefficient, and, hence, hydrodynamic radius is obtained. Here we examine the validity of NTA in tracking number concentration and size of DNA, as a model of a fibrillar macromolecule. We use NTA to examine three amyloidogenic materials: beta‐amyloid, transthyretin, and polyglutamine‐containing peptides. Our results are instructive in demonstrating the advantages and some limitations of single‐particle diffusion measurements for investigating aggregation in protein systems. © 2014 American Institute of Chemical Engineers AIChE J, 60: 1236–1244, 2014     

Oriented Strontium Carbonate Nanocrystals within Collagen Films for Flexible Piezoelectric Sensors

Bone, assembled by mineralized collagen fibrils, displays piezoelectric properties under external stimulation to affect tissue growth. The mineralized collagen fibrils consist of collagen and oriented inorganic nanocrystals. Inspired from the unique structures and piezoelectric effect of mineralized collagen fibrils, the intrafibrillar mineralization of oriented strontium carbonate nanocrystals is achieved in vitro, which also exhibits good piezoelectric properties. The amorphous strontium carbonate precursors penetrate from the gap zones and fill gradually into the whole space within the collagen fibrils, and transform into a co-oriented crystalline phase. Isolated mineralized collagen fibrils with organized SrCO₃ nanocrystals acquire good flexible properties and inverse piezoelectric responses with an effective piezoelectric coefficient of 3.45 pm V⁻¹, much higher than individual collagen (1.12 pm V⁻¹) and SrCO₃ crystals (0.092 pm V⁻¹). These results may indicate that the organic and inorganic components synergistically contribute to the piezoelectric effect of bone. Furthermore, devices of flexible piezoelectric thin films assembled by SrCO₃ mineralized collagen fibrils exhibit a regular open-circuit voltage of 1.2 V under compressive stress and a stable cycling short-circuit current of 80 nA under a bending mode. It can also facilitate the development of promising piezoelectric sensors.     

碳纳米管/导电聚苯胺纳米复合纤维的合成与表征

为实现碳纳米管在树脂内形成一体化导电网络，从而制备出透明导电性能最优的有机透明导电涂层，必须把导电性的碳纳米管纤维在树脂内有效地组装成一体化导电结构网络。本文报道运用在树脂内可以自组装的导电苯胺来实现碳纳米管纤维自组装的方法．合成出了导电聚苯胺纳米薄膜均匀包覆的碳纳米管/导电聚苯胺纳米复合纤维．并运用透射电镜、傅立叶红外光谱以及四探针法表面电阻测试仪对合成出的具有精细微观结构的纳米复合纤维进行了表征．发现合成出了理想的碳纳米管/导电聚苯胺纳米复合纤维，并且其导电性较碳纳米管和导电聚苯胺自身都有大幅度的提高。这种特殊结构的纳米复合纤维的制备为组装高性能的聚合物基透明导电涂层奠定了坚实基础，而且这种自组装方法为各种纳米纤维的组装提供了可能。     

Orientational Ordering within Semiconducting Polymer Fibrils

Due to a general paucity of suitable characterization methods, the internal orientational ordering of polymer fibrils has rarely been measured despite its importance particularly for semi-conducting polymers. An emerging tool with sensitivity to bond orientation is polarized resonant soft X-ray scattering (P-RSoXS). Here, P-RSoXS reveals the molecular arrangement within fibrils (if type I or type II fibrils), the extent of orientation in the fibril crystal, and an explicit crystal-amorphous interphase. Neat films as well as binary blends with a fullerene derivative are characterized for three different polymers, that are prototypical materials widely used in organic electronics applications. Anisotropic P-RSoXS patterns reveal two different fibril types. Analysis of the q-dependence of the anisotropy from simulated and experimental scattering patterns reveal that neat polymer fibrillar systems likely comprise more than two phases, with the third phase in addition to crystal and amorphous likely being an interphase with distinct density and orientation. Intriguingly, the fibril type correlates to the H- or J-aggregation signature in ultraviolet-visible (UV–vis) spectroscopy, revealing insight into the fibril formation. Together, the results will open the door to develop more sophisticated structure-function relationships between chemical design, fibril type, formation pathways and kinetics, interfacial ordering, and eventually device functions.     

Composite Gels Containing Whey Protein Fibrils and Bacterial Cellulose Microfibrils

In this study, we investigated the gelation of WPI fibrils in the presence of bacterial cellulose (BC) microfibrils at pH 2 upon prolonged heating. Rheology and microstructure were investigated as a function of BC microfibril concentration. The presence of BC microfibrils did not influence the gelation dynamics and resulting overall structure of the WPI fibrillar gel. The storage modulus and loss modulus of the mixed WPI‐BC microfibril gels increased with increasing BC microfibril concentration, whereas the ratio between loss modulus and storage modulus remained constant. The WPI fibrils and BC microfibrils independently form two coexisting gel networks. Interestingly, near to the BC microfibrils more aligned WPI fibrils seemed to be formed, with individual WPI fibrils clearly distinguishable. The level of alignment of the WPI fibrils seemed to be dependent on the distance between BC microfibrils and WPI fibrils. This also is in line with our observation that with more BC microfibrils present, WPI fibrils are more aligned than in a WPI fibrillar gel without BC microfibrils. The large deformation response of the gels at different BC microfibril concentration and NaCl concentration is mainly influenced by the concentration of NaCl, which affects the WPI fibrillar gel structures, changing form linear fibrillar to a particulate gel. The WPI fibrillar gel yields the dominant contribution to the gel strength.     

Buckling of sheared and compressed microfibrils

In this paper, we study the stability of an initially straight elastic fibril clamped at one end, while the other end is subjected to a constant normal compressive force and a prescribed shear displacement. We found the buckling load of a sheared fibril to be always less than the Euler buckling load. Furthermore, if the end of the fibril loses adhesion, then the buckling load can be considerably less. Our result suggests that the static friction of microfibre arrays can decrease with increasing normal compressive load and, in some cases, friction force can actually become negative.