Marko Peura

Changes in Submicrometer Structure of Enzymatically Hydrolyzed Microcrystalline Cellulose

To understand the limitations occurring during enzymatic hydrolysis of cellulosic materials in renewable energy production, we used wide-angle X-ray scattering (WAXS), small-angle X-ray scattering (SAXS), X-ray microtomography, and transmission electron microscopy (TEM) to characterize submicrometer changes in the structure of microcrystalline cellulose (Avicel) digested with the Trichoderma reesei enzyme system. The microtomography measurements showed a clear decrease in particle size in scale of tens of micrometers. In all the TEM pictures, similar elongated and partly ramified structures were observed, independent of the hydrolysis time. The SAXS results of rewetted samples suggested a slight change in the structure in scale of 10-20 nm, whereas the WAXS results confirmed that the degree of crystallinity and the crystal sizes remained unchanged. This indicates that the enzymes act on the surface of cellulose bundles and are unable to penetrate into the nanopores of wet cellulose.

Tablet preformulations of indomethacin-loaded mesoporous silicon microparticles.

In this study, indomethacin-loaded thermally oxidized mesoporous silicon microparticles (TOPSi-IMC) were formulated into tablets with excipients in order to improve the dissolution and permeability properties of the poorly soluble drug. Formulations of TOPSi-IMC particles and excipients were prepared at different TOPSi-IMC particle ratios (25, 30 and 35%). The formulations were compressed by direct compression technique with a single punch tablet machine. For comparison, a formulation containing the bulk IMC (indomethacin) and the same excipients without thermally oxidized mesoporous silicon microparticles particles (TOPSi) was prepared and compressed into tablets. The TOPSi-IMC tablets were characterised according to weight, thickness, crushing strength, disintegration time and dissolution rate. The results of this study show that TOPSi-IMC particles can be compressed to a conventional tablet. The release rate of the drug and its permeation across intestinal cells model (Caco-2) from TOPSi-IMC tablets was improved compared to the bulk IMC tablets. The dissolution rate and permeability of IMC from the tablets decreased with increasing ratio of the TOPSi-IMC particles in the formulation. The phenomenon is, presumably, a result of the loss of unique pore structure of the particles due to deformation of the particles under the compression load.

Effect of amylose content on physical and mechanical properties of potato-starch-based edible films.

The present study investigated the amylose content and the gelatinization properties of various potato starches extracted from different potato cultivars. These potato starches were used to prepare edible films. Physical and mechanical properties of the films were investigated. The crystallinity of selected native starches and edible films made of the same starches were determined by X-ray diffraction. The amylose content of potato starches varied between 11.9 and 20.1%. Gelatinization of potato starches in excess water occurred at temperatures ranging from 58 to 69 degrees C independently of the amylose content. The relative crystallinity was found to be around 10-13% in selected native potato starches with low, medium, and high amylose content. Instead, films prepared from the same potato starches were found to be practically amorphous having the relative crystallinity of 0-4%. The mechanical properties and the water vapor permeability of the films were found to be independent of the amylose content.

X-ray scattering and microtomography study on the structural changes of never-dried silver birch, European aspen and hybrid aspen during drying

Abstract The impact of drying on the structure of the never-dried hardwood cell wall was studied at nanometer level by means of wide- and small-angle X-ray scattering (WAXS, SAXS), and at micrometer level by X-ray microtomography (μCT). Never-dried silver birch, European aspen and hybrid aspen samples were measured by WAXS in situ during drying in air. The samples included juvenile and mature wood, as well as normal and tension wood to allow comparison of the effects of different matrix compositions and microfibril angles. The deformations of cellulose crystallites and amorphous components of the cell wall were detected as changes in the cellulose reflections 200 and 004 and amorphous halo in the WAXS patterns. Especially, the width of the reflection 004, corresponding to the cellulose chain direction, increased due to drying in all the samples, indicating an increase of strain and disorder of the chains. Also, the cellulose unit cell shrank 0.2–0.3% during drying in this direction in all the samples except in hybrid aspen tension wood. According to the SAXS results of silver birch, the distance between micro-fibrils decreased during drying. It was detected by μCT that the mean cross-sectional maximum width of the parenchymatous rays decreased from that of never-dried to air-dried birch by roughly 16%.

Visualizing water-filled versus embolized status of xylem conduits by desktop x-ray microtomography

BackgroundThe hydraulic conductivity of the stem is a major factor limiting the capability of trees to transport water from the soil to transpiring leaves. During drought conditions, the conducting capacity of xylem can be reduced by some conduits being filled with gas, i.e. embolized. In order to understand the dynamics of embolism formation and repair, considerable attention has been given to developing reliable and accurate methods for quantifying the phenomenon. In the past decade, non-destructive imaging of embolism formation in living plants has become possible. Magnetic resonance imaging has been used to visualize the distribution of water within the stem, but in most cases it is not possible to resolve individual cells. Recently, high-resolution synchrotron x-ray microtomography has been introduced as a tool to visualize the water contents of individual cells in vivo, providing unprecedented insight into the dynamics of embolism repair. We have investigated the potential of an x-ray tube -based microtomography setup to visualize and quantify xylem embolism and embolism repair in water-stressed young saplings and shoot tips of Silver and Curly birch (Betula pendula and B. pendula var. carelica).ResultsFrom the microtomography images, the water-filled versus gas-filled status of individual xylem conduits can be seen, and the proportion of stem cross-section that consists of embolized tissue can be calculated. Measuring the number of embolized vessels in the imaged area is a simple counting experiment. In the samples investigated, wood fibers were cavitated in a large proportion of the xylem cross-section shortly after watering of the plant was stopped, but the number of embolized vessels remained low several days into a drought period. Under conditions of low evaporative demand, also refilling of previously embolized conduits was observed.ConclusionsDesktop x-ray microtomography is shown to be an effective method for evaluating the water-filled versus embolized status of the stem xylem in a small living sapling. Due to its non-destructive nature, the risk of inducing embolisms during sampling is greatly reduced. Compared with synchrotron imaging beamlines, desktop microtomography offers easier accessibility, while maintaining sufficient resolution to visualize the water contents of individual cells.

Structure of oak wood from the Swedish warship Vasa revealed by X-ray scattering and microtomography

Abstract The degradation of oak wood of the historical warship Vasa was studied, focusing on cellular structure by X-ray microtomography (μCT) and on the nanostructure of the cell wall by wide- and small-angle X-ray scattering (WAXS, SAXS). Solid samples [polyethylene glycol (PEG)-, impregnated and PEG-extracted] were submitted to X-ray analysis and the results compared to those of recent oak. The cellular structure of the Vasa oak was surprisingly well preserved at the micrometer level, according to the μCT images. As revealed by WAXS, the fraction of crystalline cellulose was lower in the Vasa samples compared with recent oak, but the average length and width of cellulose crystallites (25±2 nm and 3.0±0.1 nm, respectively), and the mean microfibril angles (4–9°), showed no significant differences. Accordingly, the crystalline parts of cellulose microfibrils are well preserved in the Vasa oak. The SAXS results indicated a declined short-range order between the cellulose microfibrils and a higher porosity of the Vasa oak compared with recent oak, which may be explained by modification of the hemicellulose-lignin matrix.

Comparison of microencapsulation properties of spruce galactoglucomannans and arabic gum using a model hydrophobic core compound.

In the present study, microencapsulation and the physical properties of spruce ( Picea abies ) Omicron-acetyl-galactoglucomannans (GGM) were investigated and compared to those of arabic gum (AG). Microcapsules were obtained by freeze-drying oil-in-water emulsions containing 10 wt % capsule materials (AG, GGM, or a 1:1 mixture of GGM-AG) and 2 wt % alpha-tocopherol (a model hydrophobic core compound that oxidizes easily). Microcapsules were stored at relative humidity (RH) of 0, 33, and 66% at 25 degrees C for different time periods, and their alpha-tocopherol content was determined by HPLC. X-ray microtomography analyses showed that the freeze-dried emulsions of GGM had the highest and those of AG the lowest degree of porosity. According to X-ray diffraction patterns, both freeze-dried AG and GGM showed an amorphous nature. The storage test showed that anhydrous AG microcapsules had higher alpha-tocopherol content than GGM-containing capsules, whereas under 33 and 66% RH conditions GGM was superior in relation to the retention of alpha-tocopherol. The good protection ability of GGM was related to its ability to form thicker walls to microcapsules and better physical stability compared to AG. The glass transition temperature of AG was close to the storage temperature (25 degrees C) at RH of 66%, which explains the remarkable losses of alpha-tocopherol in the microcapsules under those conditions.

The elemental composition, the microfibril angle distribution and the shape of the cell cross-section in Norway spruce xylem

Relationships between the elemental composition, the microfibril angle (MFA) distribution and the average shape of the cell cross-section of irrigated-fertilised and untreated Norway spruce (Picea abies [L.] Karst.) earlywood were studied. Sample material was obtained from Flakaliden, Sweden. The elemental composition was studied by determining the relative mass fractions of the elements P, S, Cl, K, Ca and Mn by X-ray fluorescence and by determining the mass absorption coefficients for X-rays. X-ray diffraction was used to determine the MFA distribution and the average shape of the cell cross-section. The latter was also determined by light microscopy. In transition from juvenile wood to mature wood, a decrease of the mode of the MFA distribution from 13°–24° to 3°–6° was connected to a change in the shape of the cell cross-section from circular to rectangular. The irrigation-fertilisation treatment caused no change in the MFA distribution or in the shape of the cell cross-section, whereas the mass absorption coefficient was higher and the density was smaller in irrigated-fertilised wood. Larger proportion of the elements S, Cl and K, but smaller proportion of the element Mn, were observed due to the treatment. The results indicate that the shape of the cell cross-section or the MFA distribution are not directly linked to the growth rate of tracheids or to the nutrient-element content in the xylem and only show notable changes as a function of the cambial age.

Crystallization and shear modulus of a forming biopolymer film determined by in situ x-ray diffraction and ultrasound reflection methods

The structure and the rigidity of a forming biopolymer film were determined using concurrent x-ray diffraction and ultrasonic reflection measurements. Film formation of a xylan solution (de-ionized water, 10g∕l xylan, 4g∕l glycerol) was studied during water evaporation at 24(±2)°C, 37(±5)%RH. X-ray diffraction (XRD) data showed the crystallization and ultrasonic data the increase of the shear modulus (G) during water evaporation. Xylan crystallized into small xylan dihydrate crystallites, the number of which increased as water evaporated. Crystallization began earlier than the increase in G during film formation. The increase in G also continued after the crystallites were fully formed, indicating still ongoing structural changes in the amorphous parts. The maximum value of G was 0.1–0.5GPa. XRD measurements performed ex situ showed a crystallinity of 16%–19% (±5%) and a fairly isotropic crystallite orientation in the surface plane of the films.

Simultaneous X-ray diffraction and X-ray fluorescence microanalysis on secondary xylem of Norway spruce

Secondary xylem of Norway spruce was studied by X-ray microanalysis. Average dimensions of cellulose crystallites, fraction of oriented cellulose, mean microfibril angle, and nutrient element concentrations of K, Ca, Mn, and Zn were simultaneously determined using microfocused synchrotron radiation and a combination of X-ray diffraction and X-ray fluorescence spectroscopy techniques. The variation of these quantities in the microscopic size scale was noticeable, and similar between samples taken from the same annual ring. The mean microfibril angle and the nutrient concentrations of Ca, Mn, and Zn showed a correlation. The mean values of the structural parameters and their variation as a function of the annual ring were similar as reported in previous studies on Norway spruce.