Araldite as an Embedding Medium for Electron Microscopy

Epoxy resins are suitable media for embedding for electron microscopy, as they set uniformly with virtually no shrinkage. A mixture of araldite epoxy resins has been developed which is soluble in ethanol, and which yields a block of the required hardness for thin sectioning. The critical modifications to the conventional mixtures are the choice of a plasticized resin in conjunction with an aliphatic anhydride as the hardener. The hardness of the final block can be varied by incorporating additional plasticizer, and the rate of setting can be controlled by the use of an amine accelerator. The properties of the araldite mixture can be varied quite widely by adjusting the proportions of the various constituents. The procedure for embedding biological specimens is similar to that employed with methacrylates, although longer soaking times are recommended to ensure the complete penetration of the more viscous epoxy resin. An improvement in the preservation of the fine structure of a variety of specimens has already been reported, and a typical electron microgram illustrates the present paper.     

Dental composite resin porosity and effect on water absorption

The aims of this study were: 1) to characterize the solubility and water absorption of different composite resins used as dental restorative materials; 2) to analyse their surface morphology using S.E.M. The resins tested were a mixture of glycidyl methacrylate (Bis-GMA) and TEGMA filled with silane-coated particles of inorganic fillers, and Bis-GMA and urethane resin. Cylindrical samples of composite resin were polymerized and stored in distilled water and weighed after different times. SEM analysis demonstrated voids and porous in several samples. The present study shows that dental restorative composite loose a small percentage of their components during storage time and that the type of resin, the nature of fillers and the methods of polymerization greatly influence water uptake and solubility of dental composite resin materials. These findings could explain the loss of anatomic form and the occlusal degradation of dental composites in "in vivo" conditions.     

Hexadecanedionic acid-sepharose 4B: A new tool for preparation of albumin-depleted plasma

Serum and plasma are the major sources of human material for clinical molecular diagnostics and drug discovery. However, due to the high abundance of some proteins, of which serum albumin (SA) is most prominent, lower-abundance proteins often remain undetectable in proteomic analysis of these body fluids. We have used hexadecanedionic acid (HDA) immobilized to Sepharose 4B to develop an affinity resin that is effective in the removal of SA from plasma. Two-dimensional gel analysis of the SA-depleted samples shows a significant enhancement of the low-abundance proteins and highly specific capture of serum albumin. The HDA resin shows better performance in terms of specificity than dye-based resins.     

Secondary ion mass spectrometry (SIMS) of standards for analysis of soft biological tissue.

Gelatin films containing water-soluble salts of lithium, rubidium, strontium, or copper were analyzed by secondary ion mass spectrometry. Calcium and vanadium organometallic compounds in an epoxy resin were similarly analyzed. A linear relationship between positive secondary ion intensity and ion concentration was observed over several decades of ion concentration and at absolute concentrations as low as 1 wt ppm. These standards can be used for quantitative analysis of tissue or other biological material in epoxy resins, providing a highly sensitive method for simultaneous quantitation and localization of elements.     

Novolak PF resins prepared from phenol liquefied Cryptomeria japonica and used in manufacturing moldings

The wood of Japanese cedar (Cryptomeria japonica) was liquefied in phenol with H2SO4 and HCl as catalysts. The liquefied wood was reacted with formalin to prepare the novolak PF resin. The results showed that the reaction of liquefied Japanese cedar with formalin was an exothermic reaction, and formed a solid-like resin without extra heating. Two novolak PF resins were prepared from the liquefied wood which were identified as SF and CF that using the liquefied wood with H2SO4 and HCl as catalyst respectively. The novolak PF powder displayed thermo-melting characteristic. The resins of SF and CF had weight average molecular weight of 3638 and 3941 respectively and melting temperature of 149.4 degrees C and 127.5 degrees C respectively. Both of the novolak resins could be used to make moldings with good performance by mixing the novolak resin with wood powder, hardener and zinc stearate at the weight ratio of 60:30:10:1 and hot-pressed under 200 degrees C for 10min.     

Diversity matters: how bees benefit from different resin sources

Biodiverse environments provide a variety of resources that can be exploited by consumers. While many studies revealed a positive correlation between biodiversity and consumer biomass and richness, only few studies have investigated how resource diversity affects single consumers. To better understand whether a single consumer species benefits from diverse resources, we tested how the protective function of a defensive plant resource (i.e. resin exploited by social bees) varied among different sources and target organisms (predators, parasites and pathogens). To assess synergistic effects, resins from different plant genera were tested separately and in combination. We found that resin diversity is beneficial for bees, with its functional properties depending on the target organisms, type and composition of resin. Different resins showed different effects, and mixtures were more effective than some of the single resins (functional complementarity). We conclude that resins of different plant species target different organisms and act synergistically where combined. Bees that rely on resin for protection benefit more when they have access to diverse resin sources. Loss of biodiversity may in turn destabilize consumer populations due to restricted access to a variety of resources.     

微波加热时基托树脂收缩量的研究

目的,针对基托树脂固化的特性,探讨微波加热对树脂收缩量的影响。方法:采用四种常用基托树脂,分别采取单纯微波固化和微波加压固化聚合后,测定开盒后一周内树脂的聚合收缩情况。结果:两种固化方法收缩量均较小,适应性强。微波加压固化虽收缩量相对稍大但收缩均匀各树脂间无显著差异。结论:微波加热固化清洁高效,基托树脂结构致密,收缩量小,是今后树脂固化的一个发展方向。     

Characteristics of novel dental composites containing 2,2-bis[4-(2-methoxy-3-methacryloyloxy propoxy) phenyl] propane as a base resin

Many dental restorative dental composites still utilize 2,2-bis[4-(2-hydroxy-3-methacryloyloxy propoxy) phenyl] propane (Bis-GMA) as base resin. The high viscosity of Bis-GMA necessitates dilution with dimethacrylate ethers of low viscosity such as triethylene glycol dimethacrylate (TEGDMA). However, increased amounts of the TEGDMA have adverse effects on properties such as water uptake and curing shrinkage. The viscosity of the base resin should be as low as possible to enable the preparation of dental composites with a minimum content of diluent. To overcome the disadvantage of Bis-GMA, i.e., its high viscosity caused by hydrogen bonding between hydroxyl groups, 2,2-bis[4-(2-methoxy-3-methacryloyloxy propoxy) phenyl propane (Bis-M-GMA) was prepared by substituting methoxy groups for hydroxyl groups in Bis-GMA. The viscosity of Bis-GMA was dramatically decreased from 574 (Pa.s) to 3.7 (Pa.s) by substitution of methoxy group. Consequently, the amount of TEGDMA included in the resin matrix could be minimized. Dental composites were prepared from Bis-M-GMA (or Bis-GMA) mixtures with TEGDMA filled with 75 wt % filler. Comparing the curing shrinkage of dental composite containing Bis-M-GMA with that prepared from Bis-GMA, the reduction in curing shrinkage was about 47%. Dental composites prepared from new resin matrixes also exhibited low water uptake and better properties in mechanical strength.     

A novel tight cylindrical mold for epoxy resin embedding allows enhanced microscopic analysis of microcores extracted from woody plants

A novel mold was devised to embed microcores extracted from stems of trees in epoxy resin, which has been widely used for optical and electron microscopic analysis of xylem formation. The embedding mold of a tight cylindrical shaped tube was designed to avoid displacement of microcores from the right position during the process of resin embedding. Microcores of a ring-porous hardwood species, Quercus crispula, with higher wood density and much larger differentiating vessel elements laid down on the boundary between the current xylem and the previous one, which generally cause difficulty in thin sectioning and breaks in sections, respectively, were embedded in the cylindrical molds full of epoxy resin. Locations of the three principal planes of wood anatomy could be determined in cylindrical resin-embedded microcores as follows: the transverse plane could be found on their side of cylinder, the radial one was vertical to the transverse, and the tangential ones were their circular ends of cylinder. The present embedding mold, therefore, can provide all three principal sections for microscopic wood anatomy from the side or ends of the same cylindrical microcore in principle. To confirm the usefulness of the resin-embedded microcores, we examined the differentiation of vessel elements during the period of earlywood formation on their transverse sections under microscopes, consequently could observe cell division in the cambial zone and sequential stages of vessel element differentiation, including cell expansion and deposition of the secondary cell wall. The present embedding mold for epoxy resin is simple but highly useful and innovative for a wide range of applications of microcores in microscopy for studies on tree-ring formation.     

The partition of cholesterol between ordered and fluid bilayers of phosphatidylcholine: a synchrotron X-ray diffraction study

The structure and composition of coexisting bilayer phases separated in binary mixtures of dipalmitoylphosphatidylcholine and cholesterol and ternary mixtures of equimolar proportions of dipalmitoyl- and dioleoylphosphatidycholines containing different proportions of cholesterol have been characterized by synchrotron X-ray diffraction methods. The liquid-ordered phase is distinguished from gel and fluid phases by a disordering of the hydrocarbon chains intermediate between the two phases as judged from the wide-angle X-ray scattering profiles. Electron density distribution calculated in coexisting bilayer phases shows that liquid-ordered phase is enriched in dipalmitoylphosphatidylcholine and cholesterol and a higher electron density in the methylene chain region of the bilayer ascribed to the location of the sterol ring of cholesterol. The ratio of the two constituents in the liquid-ordered phase is not constant because the stoichiometry is temperature-dependent as seen by respective changes in bilayer thickness over the range 20 degrees to 36 degrees C where coexisting phases are observed. Three coexisting phases were deconvolved in the ternary mixture at 20 degrees C. From an analysis of the ternary mixtures containing mole fractions of cholesterol from 0.09 to 0.15 it was found that the liquid-crystal and gel phases each contained about 10% of the cholesterol molecules and the liquid-ordered phase was comprised of 30% cholesterol molecules.     

The role of microorganisms in the formation of pitch deposits in pulp and paper mills

The cause of pitch deposit formation seems still not fully understood. The work reported here demonstrates that microorganisms effect the agglomeration of emulgated resin droplets and the formation of sticky precipitates.

Pitch deposits from mills consist mainly of ethanol-soluble resins. It is also the ethanol-soluble fraction of wood resins which forms stable emulsions and which is easily agglomerated by microorganisms.

Pitch deposits, collected from various pulp and paper mills, were all found to contain large amounts of microorganisms. Sterile resin emulsions prepared from pitch deposits remained stable over long periods. After inoculation with microorganisms the emulsions were destabilized and the resins completely precipitated as sticky lumps.

Various bacteria and fungi are capable of agglomerating the resins, but species isolated from water, pulp and slime in paper mills were usually most effective. Resins from fresh wood were precipitated at a faster rate than aged resins.

Problems of pitch formation can be considerably reduced when microbial growth is kept under control in the production system. To be effective, the control measures, e.g. slimicides, must be applied at the right place and time, and in the correct concentrations. This presupposes a thorough knowledge of the plant's microbiological condition which can only be obtained by microbiological examination. Practical cases of the appropriate application of biocides in pulp and paper mill systems are discussed.     

Epoxy Resins in Electron Microscopy

A method of embedding biological specimens in araldite 502 (Ciba) has been developed for materials available in the United States. Araldite-embedded tissues are suitable for electron microscopy, but the cutting qualities of the resin necessitates more than routine attention during microtomy. The rather high viscosity of araldite 502 also seems to be an unnecessary handicap. The less viscous epoxy epon 812 (Shell) produces specimens with improved cutting qualities, and has several features—low shrinkage and absence of specimen damage during cure, minimal compression of sections, relative absence of electron beam-induced section damage, etc.—which recommends it as a routine embedding material. The hardness of the cured resin can be easily adjusted by several methods to suit the materials embedded in it. Several problems and advantages of working with sections of epoxy resins are also discussed.     

The effect of hemicelluloses on wood pulp nanofibrillation and nanofiber network characteristics

Hemicelluloses as matrix substances showed an important role in nanofibrillation of wood pulp. Never-dried and once-dried pulps with different amounts of hemicelluloses were fibrillated using a grinding treatment. The degree of fibrillation was evaluated by scanning electron microscopy observation of the fibrillated pulps and light transmittance measurements of the fibrillated pulp/acrylic resin composites. With a one-pass grinding treatment, the once-dried pulp with higher hemicellulose content was fibrillated into 10-20 nm wide fibers as easily as the never-dried pulps, while the once-dried pulp with lower hemicellulose content was not fibrillated into uniform nanosized fibers. This result indicates that hemicelluloses act as inhibitors of the coalescence of microfibrils during drying and facilitate the nanofibrillation of once-dried pulp. Furthermore, hemicelluloses provide adhesion between nanofibers, contributing to reduction of thermal expansion and enhancement of mechanical properties in the composites.     

The partition of cholesterol between ordered and fluid bilayers of phosphatidylcholine: A synchrotron X-ray diffraction study

The structure and composition of coexisting bilayer phases separated in binary mixtures of dipalmitoylphosphatidylcholine and cholesterol and ternary mixtures of equimolar proportions of dipalmitoyl- and dioleoylphosphatidycholines containing different proportions of cholesterol have been characterized by synchrotron X-ray diffraction methods. The liquid-ordered phase is distinguished from gel and fluid phases by a disordering of the hydrocarbon chains intermediate between the two phases as judged from the wide-angle X-ray scattering profiles. Electron density distribution calculated in coexisting bilayer phases shows that liquid-ordered phase is enriched in dipalmitoylphosphatidylcholine and cholesterol and a higher electron density in the methylene chain region of the bilayer ascribed to the location of the sterol ring of cholesterol. The ratio of the two constituents in the liquid-ordered phase is not constant because the stoichiometry is temperature-dependent as seen by respective changes in bilayer thickness over the range 20° to 36 °C where coexisting phases are observed. Three coexisting phases were deconvolved in the ternary mixture at 20 °C. From an analysis of the ternary mixtures containing mole fractions of cholesterol from 0.09 to 0.15 it was found that the liquid-crystal and gel phases each contained about 10% of the cholesterol molecules and the liquid-ordered phase was comprised of 30% cholesterol molecules.     

CO2 reduction potentials by utilizing waste plastics in steel works

Background, aim, and scope  Feedstock recycling has received attention as an effective method to recycle waste plastics. However, estimating the reduction potential by life cycle assessment using coke oven and blast furnace in steel works has been a challenging task due to the complex structure of energy flow in steel works. Municipal waste plastics consist of several plastic resins. Previous studies have generally disregarded the composition of waste plastics, which varies significantly depending on the geographical area. If the reduction potentials by using each plastic resin in steel works can be quantified, the potential of municipal waste plastics (mixtures of plastic resins) can be estimated by summing up the potential of each resin multiplied by the composition of each resin in municipal waste plastics. Therefore, the goal of this study is to investigate the reduction potentials of CO₂ emissions by using individual plastic resins (polyethylene (PE), polypropylene (PP), polystyrene (PS), polyethylene terephthalate (PET)) and those for municipal waste plastics in the coke oven and blast furnace. Materials and methods  A model was developed to clarify the energy flow in steel works. In order to estimate the changes in energy and material balance in coke ovens when waste plastics are charged, the equations to calculate the coke product yield, gas product yield, and oil product yields of each plastic resin were derived from previous studies. The Rist model was adopted to quantify the changes in the inputs and outputs when plastics were fed into a blast furnace. Then, a matrix calculation method was used to calculate the change in energy balance before and after plastics are fed into a coke oven. Results  It was confirmed that product yields of municipal waste plastics (mixtures of plastic resins) could be estimated by summing up the product yield of each plastic resin multiplied by the composition of each resin in municipal waste plastics. In both cases of coke oven and blast furnace feedstock recycling, the reduction potential of CO₂ emissions varies significantly depending on the plastic resins. For example, in the case of coke oven chemical feedstock recycling, the reduction potential of PS and PP is larger than that of PE. On the other hand, in the case of blast furnace feedstock recycling, PE has the largest CO₂ emissions reduction potential, whereas the CO₂ emission reduction potential of PP is smaller than those of PE and PS. In both cases, PET has negative CO₂ emission reduction potentials, i.e., there is an increase of CO₂ emissions. In addition, the reduction potentials of CO₂ emissions are slightly different in each city. Discussions  The differences in the reduction potentials of CO₂ emissions by coke oven chemical feedstock recycling of each plastic resin is attributable to the differences in calorific values and coke product yields of each plastic resin. On the other hand, the difference in the CO₂ emission reduction potential for each plastic resin in blast furnace feedstock recycling is attributable to the difference in calorific values and the carbon and hydrogen content of each plastic resin, which leads to a difference in the coke substitution effect by each plastic resin. In both cases, the difference in those of municipal waste plastics is mostly attributable to the amount of impurities (e.g., ash, water) in the municipal waste plastics. Conclusions  It was found that the reduction potential of CO₂ emissions by coke oven and blast furnace feedstock recycling of municipal waste plastics (mixtures of plastic resins) could be estimated by summing up the potential of each resin multiplied by the composition of each resin in municipal waste plastics. It was also clarified that feedstock recycling of waste plastic in steel works is effective for avoiding the increase in CO₂ emissions by incinerating waste plastics, such as those from household mixtures of different resins. Recommendations and perspectives  With the results obtained in this study, reduction potentials of CO₂ emissions can be calculated for any waste plastics because differences in composition are taken into account.     

Polyester Sheeting (Melinex O), a Tissue-Culture Support Easily Separable from Epoxy Resins after Flat-Face Embedding

Pieces of Melinex O polyester films (0.003 in. thick) can be used as substitute for glass in flat-face embedding in epoxy resins for electron microscopy. Melinex sheeting can be obtained from Imperial Chemical Industries. It can be sterilized by alcohol or by autoclaving. It is transparent and it is resistant to customary cytological processing fluids. It separates readily from the resin block wihout the use of water and without cooling.     

On the dual role of starch,cellulose and their dialdehydes as fillers and accelerators in the tertiary amine catalysed curing of epoxy resin

Gel time studies of epoxy resins containing varying concentrations of water, starch, cellulose, or their dialdehydes were carried out at 120°C using the tertiary amines triethylamine (TEA) and hexamethylenetetramine (HEXA) as catalysts. In the 40 parts per 100 parts of resin (phr) polysaccharide-filled epoxy-HEXA system it was found that ～50% oxidised starch or cellulose produced unexpectedly high curing rate enhancements and gel times of 13 and 22 min, respectively, were obtained. With 100% oxidised starch the gel time increased to 37 min, while with 10% oxidised cellulose the gel time obtained was 91 min. The non-oxidised starch and cellulose gave even higher gel times. Thus, there seems to be some sort of a synergistic mechanism operating when the degree of oxidation of the polysaccharide is ～50% of the glucose monomer units. The difference in the effects of TEA and HEXA on the polysaccharide-filled epoxy curing reaction is explained on the basis of the decomposition of HEXA into its constituents (formaldehyde and ammonia/ammonia derivatives) under the reaction conditions employed, the formation of intermolecular and intramolecular hemiacetal and/or various hydrated aldehyde structures, and the difference in crystallinity and rigidity of the different polysaccharides affecting the availability of hydroxyl groups.     

Characterization of nano-clay reinforced phytagel-modified soy protein concentrate resin

Phytagel and nano-clay particles were used to improve the mechanical and thermal properties and moisture resistance of soy protein concentrate (SPC) resin successfully. SPC and Phytagel were mixed together to form a cross-linked structure. The Phytagel-modified SPC resin (PH-SPC) showed improved tensile strength, modulus, moisture resistance, and thermal stability as compared to the unmodified SPC resin. The incorporation of 40% Phytagel and 20% glycerol led to an overall 340% increase in the tensile strength (over 50 MPa) and approximately 360% increase in the Young's modulus (over 710 MPa) of the SPC resin. Nano-clay was uniformly dispersed into PH-SPC resin to further improve the properties. The PH-SPC (40% Phytagel) resin modified with 7% clay nanoparticles (CPH-SPC) had a modulus of 2.1 GPa and a strength of 72.5 MPa. The dynamic mechanical properties such as storage modulus together with the glass transition temperature of the modified resins were also increased by the addition of clay nanoparticles. The moisture resistance of the CPH-SPC resin was higher as compared to both SPC and PH-SPC resins. The thermal stability of the CPH-SPC resin was seen to be higher as compared to the unmodified SPC.     

Microwave-assisted acid extraction methodology for trace elements determination in mastic gum of Pistacia lentiscus using inductively coupled plasma atomic emission spectrometry

Introduction – To ensure food safety, accurate knowledge of the levels of several trace elements is necessary. This is also true for natural products of plants and resins used for human consumption or therapeutic treatment, like the mastic gum of Pistacia lentiscus. The rapid analysis of gum and resin matrices is a challenge because there are problems with the decomposition of such complicated matrices. Objective – To develop an efficient multielemental analytical method for the determination of trace elements and to compare different procedures for analyte extraction when microwave‐assisted digestion is applied. Methodology – The inductively coupled plasma atomic emission spectrometric (ICP‐AES) technique was applied and the optimum ICP conditions like radiofrequency power, argon flow rate and nebuliser sample uptake flowrate were found. The microwave‐assisted procedure was compared with that with conventional heating. Since mastic and resinous materials are difficult for dissolution and extraction of trace element, influential acid mixtures containing hydrofluoric acid proved to be capable of quantitative extraction of the analytes. Results – The digestion of mastic resin or similar matrices is significantly facilitated by using microwave radiation instead of conventional heating since the obtained recovery for several analytes is much higher. It was proved that the acid mixture of HCl–HNO₃–HF was the most efficient for complete sample digestion and recovery of the analytes. Conclusions The performance characteristics of the developed method were evaluated against certified reference material and the method was proved reliable and applicable to the analysis of mastic gum and possibly to similar resinous matrices. Copyright © 2010 John Wiley & Sons, Ltd.     

Formation of ceramide/sphingomyelin gel domains in the presence of an unsaturated phospholipid: a quantitative multiprobe approach

To better understand how ceramide modulates the biophysical properties of the membrane, the interactions between palmitoyl-ceramide (PCer) and palmitoyl-sphingomyelin (PSM) were studied in the presence of the fluid phospholipid palmitoyl-oleoyl-phosphatidylcholine (POPC) in membrane model systems. The use of two fluorescent membrane probes distinctly sensitive to lipid phases allowed a thorough biophysical characterization of the ternary system. In these mixtures, PCer recruits POPC and PSM in the fluid phase to form extremely ordered and compact gel domains. Gel domain formation by low PCer mol fraction (up to 12 mol %) is enhanced by physiological PSM levels (approximately 20-30 mol % total lipid). For higher PSM content, a three-phase situation, consisting of fluid (POPC-rich)/gel (PSM-rich)/gel (PCer-rich) coexistence, is clearly shown. To determine the fraction of each phase a quantitative method was developed. This allowed establishing the complete ternary phase diagram, which helps to predict PCer-rich gel domain formation and explains its enhancement through PSM/PCer interactions.