High Concentrations Of Tannic Acid Research Articles

Effects of Chemical Cleaning on the Ageing of Polyvinylidene Fluoride Microfiltration and Ultrafiltration Membranes Fouled with Organic and Inorganic Matter.

Herein, the effects of cleaning with sodium hydroxide and citric acid solutions as cleaning reagents on the changes in the properties of two hollow-fiber PVDF microfiltration (MF) and ultrafiltration (UF) membranes fouled with organic and inorganic matter were investigated. Accelerated membrane ageing was induced by use of high concentrations of tannic acid and iron oxide (Fe2O3) particles in the feed water; these conditions were kept with different membrane soaking times to observe temporal effects. It was found that tannic acid molecules adsorb onto the membrane surface that results in changes in surface characteristics, particularly surface functional groups that are responsible for enhancing membrane’s hydrophilicity. Experimental results demonstrate that NaOH had a stronger effect on the tensile strength and surface chemistry of the fouled MF and UF membranes than citric acid. Prediction of lifetime by an exponential (decay) model confirmed that the UF membrane cleaned with NaOH would be aged within about 1.8 years and the MF membrane after about 5 years, at cleaning every 15 days, downtime 2 h per cleaning, when a 10% tensile strength decrease against the original membrane is allowed.

The Physical Adsorption of Gelatinized Starch with Tannic Acid Decreases the Inhibitory Activity of the Polyphenol against α-Amylase.

The effects of mixing orders of tannic acid (TA), starch, and α-amylase on the enzyme inhibition of TA were studied, including mixing TA with α-amylase before starch addition (order 1), mixing TA with pre-gelatinized starch before α-amylase addition (order 2) and co-gelatinizing TA with starch before α-amylase addition (order 3). It was found that the enzyme inhibition was always highest for order 1 because TA could bind with the enzyme active site thoroughly before digestion occurred. Both order 2 and 3 reduced α-amylase inhibition through decreasing binding of TA with the enzyme, which resulted from the non-covalent physical adsorption of TA with gelatinized starch. Interestingly, at low TA concentration, α-amylase inhibition for order 2 was higher than order 3, while at high TA concentration, the inhibition was shown with the opposite trend, which arose from the difference in the adsorption property between the pre-gelatinized and co-gelatinized starch at the corresponding TA concentrations. Moreover, both the crystalline structures and apparent morphology of starch were not significantly altered by TA addition for order 2 and 3. Conclusively, although a polyphenol has an acceptable inhibitory activity in vitro, the actual effect may not reach the expected one when taking processing procedures into account.

Characterization of collagen type I/tannic acid beads as a cell scaffold

Breast cancer is the most commonly diagnosed cancer among women worldwide. Surgical removal of tumors is often necessary and many patients suffer complications due to subsequent breast reconstruction. A safe and effective breast reconstructive material is needed for patients recovering from surgical removal of small breast cancer tumors. Our lab has developed injectable collagen/tannic acid beads seeded with patient-derived preadipocytes for regeneration of healthy breast tissue in patients post-lumpectomy. Previous research indicates that the inclusion of tannic acid in the matrix imparts an anticancer property. This research seeks to determine the variables needed to control collagen/tannic acid bead diameter and seeded cell attachment, which are essential to proper bead implantation and function. We found that as tannic acid concentration increases within the beads, cell attachment decreases. Bead diameter is controlled by bead generator voltage, solution osmolality, the degree of cell attachment, and tannic acid concentrations. Higher voltages resulted in significant decrease in bead diameter. Collagen/tannic acid beads decreased in diameter when placed in solutions of increasing osmolality. Higher degrees of cell attachment across the surface of the beads were associated with a significant decrease in diameter. In beads made with high concentrations of tannic acid, bead diameter was found to decrease. Collagen/TA beads are a promising subdermal tissue regenerative matrix with anticancer activity as an alternative to simple lipofilling in breast reconstructive procedures. This study was conducted to better understand the properties of collagen/TA beads in order to improve injection efficacy and tissue regenerative activity.

Feed intake and dietary composition of iron (Fe), copper (Cu), vitamin E, and tannic acid of five captive black rhinoceros (Diceros bicornis) in a UK collection.

The black rhinoceros (Diceros bicornis) is a critically endangered species facing multiple anthropogenic pressures in its natural home range across Africa. Black rhinoceros are difficult to maintain ex situ and subject to diseases that are linked with captive dietary factors. Hemochromatosis is of particular concern, as it is a common finding at necropsy of captive adults, and has been linked to excessive dietary iron intake. This intake study investigates the select nutrient composition of the diets offered to and consumed by five captive black rhinoceros in a UK zoo to evaluate, ensure adequacy, and/or make adjustments if necessary. Alfalfa hay, pellets and six browse species offered were analyzed for iron (Fe), copper (Cu), vitamin E, and tannic acid content. Intakes were quantified and evaluated against levels found in wild diets and the currently available feeding guidelines for black rhinoceros. Diets eaten by five individual rhinoceros (1.4%–2.3% of bodyweight dry matter [DM] intake), comprising 68%–82% hay, 6%–13% pellets, and 13%–27% browse, contained 76–98 mg/kg Fe (on a DM basis), fell within the ranges of plants eaten by free‐ranging rhinoceros (45–140 mg/kg DM), as well as values recommended for captive‐fed browsing rhinoceros (50–100 mg/kg DM). Consumed diets were found to be marginal to adequate in Cu (9–11 mg/kg DM) compared with the recommended 10 mg/kg DM; dietary vitamin E ranged from 54 to 79 IU/kg DM, and tannic acid measured 13–14 g/kg DM. Commercial pellets were the primary contributor of dietary Fe, Cu, and vitamin E, containing up to 10 times more of each of those nutrients than the forages. Native browses were important sources of lower Fe ingredients, as well as appropriate levels of dietary Cu and vitamin E (dependent on species). Interestingly, pellets (23 g/kg) and alfalfa hay (14 g/kg) contained higher concentrations of tannic acid compared with any of the browses fed (4–13 g/kg). All nutritional parameters evaluated were close to recommended dietary levels, diets resembled values consumed in the wild, and the animals remained clinically healthy throughout the study. Overall, diets were considered nutritionally adequate for captive feeding of black rhinoceros; evaluating the nutrient composition of all ingredients, including browse plants in diets, provides important information for achieving optimal nutrient balance.

Facile Synthesis of Monodispersed Ag NPs in Ethylene Glycol Using Mixed Capping Agents.

Capping agents play an important role in the synthesis of silver nanostructures in polyol solvents. In this work, we demonstrate that using a small amount of tannic acid (TA), a reducing capping agent, in addition to poly(vinylpyrrolidone) (PVP), a protective capping agent, can lead to the production of monodisperse spherical silver nanoparticles (Ag NPs) that are stable with respect to particle aggregation for at least 100 days and have particle sizes ranging from 16 to 28 nm depending on the TA concentration. We hypothesize that the complexation between PVP and TA can lead to the formation of a stable particle coating and a fast Ag+ reduction rate at a relatively high TA concentration. Both effects can benefit the formation of small spherical Ag NPs with narrow size distribution.

Denitrifying Woodchip Bioreactor Leachate Tannic Acid and True Color: Lab and Field Studies

HighlightsOak leached more tannic acid, true color, and chemical oxygen demand (COD) than ash and mixed hardwood chips.The factors became similar (tannic acid, COD) or below stream levels (true color) after flushing.Eleven site-years of field bioreactor data showed decreasing tannic acid and true color over time.Post-startup tannic acid was lower in bioreactor outflow than in area streams.True color did not appear to be a reliable indicator of leachate tannic acid at low concentrations.Abstract. Woodchips have been a preferred denitrifying bioreactor medium to date, but concerns about potential harmful effects of tannins in the leachate have precluded the use of oak chips in many installations. A study was conducted to compare the suitability of oak (genus Quercus) woodchips as a denitrifying bioreactor medium relative to other types of woodchips, both in lab leachate tests and in the context of observed bioreactor leaching in the field. Assessment measures included the content of tannic acid and other compounds in the leachate, as well as leachate color, which can often be high during startup. An 84-day leaching test using rectangular bioreactor cells filled with either oak (Quercus rubra), ash (Fraxinus spp. L.), or a generic hardwood blend showed that oak initially leached higher concentrations of tannic acid, true color, and chemical oxygen demand (COD) than the other two media. The significant differences in leached concentrations among the three wood types were eliminated after a finite leaching period. Tannic acid and true color in 11 site-years of field bioreactor outflow data generally decreased over time, except following a dry period when one of the bioreactors received no drainage inflow for more than two months. The lab and field results indicated the capability of woodchip bioreactors to flush at least these two analytes to ambient stream levels. True color did not appear to be the best parameter for estimating the tannin content of woodchip leachate due to discrepancies at low concentrations. Mass normalized tannic acid leaching ranged from 0.03 to approximately 40 mg tannic acid g-1 woodchip across the lab and field assessments. Oak initially leached more tannic acid, color, and COD than the other wood types, but the eventual similarity among the wood types after flushing with a sufficient number of pore volumes meant that any potentially negative environmental impacts would likely be limited to the startup period or possibly after dry periods. Oak initially eluted higher mean total nitrogen (TN) concentrations than the other wood types, but the treatments were not significantly different by day 3, indicating that biological N removal was not significantly inhibited, even with high concentrations of tannic acid. Keywords: Chemical oxygen demand, Oak, Tannin, Water quality, Wood leachate.

Effect of tannic acid on blood components and functions

Tannic acid (TA) has become increasingly important as a biomaterial because of its ability to capture free radicals and form complexes with metal ions. Nevertheless, a systematic evaluation of the blood safety of TA has not been done. Therefore, we studied the effect of TA on erythrocyte morphology and hemolysis at different time points, and the fluorescence and circular dichroism (CD) spectroscopy of TA and fibrinogen. The blood coagulation time of TA was measured by the activated partial thromboplastin time (APTT), plasma prothrombin time (PT), and thrombelastogram (TEG) experiments. We found that higher concentrations of TA could lead to crinkling and hemolysis of erythrocytes, which may have been mediated by the hydrogen bond in TA. Spectroscopic results showed that TA influenced the structure and conformation of fibrinogen. Higher concentrations of TA could shorten the activated partial thromboplastin and plasma prothrombin times, and various concentrations of TA could affect the reaction time, clotting time, clot aggregation speed, and maximum clot strength of whole blood coagulation. These findings provide a basis for the design of TA molecules and the possible application of TA in biomedicine.

The allelochemical tannic acid affects the locomotion and feeding behaviour of the pond snail, Lymnaea stagnalis, by inhibiting peripheral pathways

(1) The effect of tannic acid (TA), a dominant component of plant allelochemicals, was investigated on the locomotion and feeding of the pond snail, Lymnaea stagnalis. The effect of TA on the neuronal background underlying feeding activity was also analysed. (2) TA affected the spontaneous locomotion and of juvenile snails in a concentration-dependent way. Low (10 μM) TA concentration resulted in an increased (sliding or swimming) activity compared to the control; meanwhile, high (100 μM) TA concentration inhibited the locomotion of the animals. (3) Low (10 μM) TA concentration increased the frequency of sucrose-evoked feeding of intact animals, whereas high (100 μM) TA concentration resulted in significantly longer feeding latency and decreased feeding rate. The feeding changes proved to be partially irreversible, since after 48 h maintained in clear water, the animals tested in 100 μM TA previously still showed lower feeding rate in sucrose. (4) Electrophysiological experiments on semi-intact preparations showed that application of 100 μM TA to the lip area inhibited the fictive feeding pattern of central neurons, the cellular response to sucrose. (5) On isolated CNS preparation, 100 μM TA applied in the bathing solution, however, failed to inhibit the activation of the central feeding (CPG) interneurons following application of extracellular dopamine. Our results suggest that TA affects both afferent and efferent peripheral functions in Lymnaea. TA reduces feeding activity by primarily blocking feeding sensory pathways, and its negative effect on locomotion may imply sensory pathways and/or ciliary activity.

Adsorption of bisphenol A on dispersed carbon nanotubes: Role of different dispersing agents

Although the adsorption of organic contaminants on carbon nanotubes (CNTs) and the dispersion of CNTs have been extensively investigated separately, the adsorption behavior of organic contaminants on dispersed CNTs, which may be a missing link to understanding their environmental behavior and risks, remain unclear yet rarely studied. In this study, the effect of the dispersing agent structure on the adsorption characteristics of BPA (a representative organic contaminant) on dispersed CNTs were investigated using tannic acid (TA), sodium dodecylbenzenesulfonate (SDBS), and gallic acid (GA) as model dispersing agents. Our results showed that at low dispersing agent concentrations, adsorption of TA could lead to higher CNT suspension than adsorption of SDBS and GA due to greater steric hindrance. However, the presence of TA reduced the adsorption of BPA due to strong competitive adsorption on dispersed CNTs. At high concentrations of TA, the suspension of CNTs was reduced by the “bridging effect,” in which adjacent dispersed CNTs form hydrogen bonds and re-aggregate. However, the adsorption of BPA dramatically increased due to the enhanced partition of BPA into pseudomicelles of TA on dispersed CNTs, as indicated by the significantly increased index of heterogeneity at high TA concentration. Transmission electron microscopy images confirmed the formation of TA pseudomicelles. This study highlights the key role of the dispersing agent structure on CNT dispersion and adsorption of organic contaminants. The high mobility and transport of CNT-adsorbed contaminants may lead to higher environmental risks compared with aggregated CNTs.

Tannic acid modulates the activity of bombyxin- and PTTH-producing neurons in Lymantria dispar L. (Insecta: Lepidoptera) caterpillars

Lymantria dispar caterpillars were exposed for 3 days to tannic acid, added to the artificial diet in the following concentrations: 1, 2.5 and 5%. Changes in the morphometric parameters of medial A2 bombyxin immunopositive and dorsolateral L2` prothoracicotropic (PTTH) immunopositive neurosecretory neurons (nsn; sizes of six nsn, the size of their nuclei, and quantification of cytoplasm density) were analysed upon caterpillars’ exposure to this allelochemical. Protein band density, obtained by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS PAGE) electrophoresis, from regions of bombyxin and PTTH molecular mass (Mr) were estimated. A2 nsn decreased in size, while the size of their nuclei did not change significantly. Relative cytoplasm density and relative band density from the bombyxin Mr region (Mr 4–5 kD) were decreased upon exposure to 1% and 2.5% tannic acid, while the addition of 5% tannic acid to artificial diet increased all of these parameters. Results suggested that lower concentrations of tannic acid stimulate the release of neurosecretory material from A2 nsn, most probably bombyxin-like protein. High tannic acid concentration (5%) probably allocates resources towards induction of other stress protective components instead of bombyxin-mediated metabolic stress response mechanisms. In L2` nsn, the size of nsn, nuclei and the relative cytoplasm density were increased, and relative band density from the region of big PTTH form (Mr 11–15 kD) was higher in all treatments in comparison to control. Results indicate that PTTH is synthesised and stored in the cytoplasm of L2` nsn.

Adjustment of L1 neurosecretory neuron activity in response to different stressors in gypsy moth caterpillars

Gypsy moth caterpillars were exposed to an increased rearing temperature of 35?C and diet, supplemented with Cd, a heavy metal pollutant, and tannic acid, a plant secondary metabolite. After 3 days? exposure to stressors, changes in the number, morphometric parameters of L1 neurosecretory neurons (nsn) (sizes of the nsn and their nuclei), and the quantity of neurosecretory material in the cytoplasm of the neurons were estimated. Acute exposure to the high temperature of 35?C induced increases in the number of L1 nsn, their size and the size of their nuclei with prolonged exposure time. After acute exposure to different Cd concentrations, the number of L1 nsn was reduced, their size increased and the size of their nuclei decreased. Together with the enhanced relative density of the cytoplasm, our results point to an intensive synthesis and retention of neurosecretory material in the neurons. The relative density of the neurosecretory material in the cytoplasm increased at the thermal treatment, suggesting intensive synthesis and secretory activity in L1 nsn. Caterpillars reared on an artificial substrate with the addition of high concentrations of tannic acid (TA) showed a decreased number of nsn, increased cell size and decreased size of their nuclei. The reduction in the relative density of the cytoplasm led us to conclude that this treatment induced a high synthetic activity of L1 nsn.

Klebsiellasp. strain C2A isolated from olive oil mill waste is able to tolerate and degrade tannic acid in very high concentrations

Four bacterial strains capable of growing in the presence of tannic acid as sole carbon and energy source were isolated from olive mill waste mixtures. 16S rRNA gene sequencing assigned them to the genus Klebsiella. The most efficient strain, Klebsiella sp. strain C2A, was able to degrade 3.5gL(-1) tannic acid within 35h with synthesizing gallic acid as main product. The capability of Klebsiella sp. strain C2A to produce tannase was evidenced at high concentrations of tannic acid up to 50gL(-1) . The bacteria adapted to the toxicity of tannic acids by an increase in the membrane lipid fatty acids degree of saturation, especially in the presence of concentrations higher than 20gL(-1) . The highly tolerant and adaptable bacterial strain characterized in this study could be used in bioremediation processes of wastes rich in polyphenols such as those derived from olive mills, winery or tanneries.

Antioxidant and pro-oxidant challenge of tannic acid in mussel hemocytes exposed to cadmium

The present study investigates the antioxidant and pro-oxidant behavior of tannic acid (TA) in hemocytes of mussel Mytilus galloprovincialis, in the presence or the absence of cadmium (Cd). TA at concentrations up to 20 μM, primarily found to be no toxic (in terms of cell viability, superoxide anions, nitric oxide and lipid peroxidation products currently estimated), significantly diminished the cytotoxic and oxidative effects induced by the metal (50 and/or 100 μM) in all cases. On the other hand, higher concentrations of TA (40 and 60 μM) were toxic, thus enhancing Cd-mediated cytotoxic and oxidative effects. The present study showed TA beneficiary properties in hemocytes of mussels, at least at low concentrations, while TA at concentrations higher than 20 μM could serve as an excellent oxidized substrate, thus enhancing toxic effects either alone or with the presence of micromolar concentrations of non transition metals, such as Cd.

Optimization of Tannase Production by Aspergillus niger in Solid-State Packed-Bed Bioreactor

Tannin acyl hydrolase, also known as tannase, is an enzyme with important applications in the food, feed, pharmaceutical, and chemical industries. However, despite a growing interest in the catalytic properties of tannase, its practical use is very limited owing to high production costs. Several studies have already demonstrated the advantages of solid-state fermentation (SSF) for the production of fungal tannase, yet the optimal conditions for enzyme production strongly depend on the microbial strain utilized. Therefore, the aim of this study was to improve the tannase production by a locally isolated A. niger strain in an SSF system. The SSF was carried out in packed-bed bioreactors using polyurethane foam as an inert support impregnated with defined culture media. The process parameters influencing the enzyme production were identified using a Plackett–Burman design, where the substrate concentration, initial pH, and incubation temperature were determined as the most significant. These parameters were then further optimized using a Box-Behnken design. The maximum tannase production was obtained with a high tannic acid concentration (50 g/l), relatively low incubation temperature (30°C), and unique low initial pH (4.0). The statistical strategy aided in increasing the enzyme activity nearly 1.97-fold, from 4,030 to 7,955 U/l. Consequently, these findings can lead to the development of a fermentation system that is able to produce large amounts of tannase in economical, compact, and scalable reactors.

Effect of phenolic compounds on the properties of porcine plasma protein-based film

Properties of porcine plasma protein-based film incorporated with tannic acid, caffeic acid and ferulic acid at different concentrations (1–3% (w/w) of protein content) were studied. Film-forming solution (FFS) containing 3% protein (w/v) and 70% glycerol (w/w of protein content) was preheated at 70 °C for 30 min and adjusted pH to 10 followed by the addition of phenols and film casting. Tensile strength (TS) of resulting film increased by 123.3, 194.3 and 19.5% and elongation at break (EAB) increased by 71.1, 86.3 and 10.2%, respectively, compared with the control film, when tannic acid, caffeic acid and ferulic acid at a level of 3% was added. The use of all phenolic compounds slightly increased water vapor permeability (WVP) of resulting films ( p < 0.05). The increases in a ∗- and b ∗-values of films were observed as the higher concentrations of tannic acid and caffeic acid were used. This was associated with the lowered transparency of resulting films. FFS containing 3% caffeic acid with prior oxygenation, especially with pH 10, yielded the film with increased TS but lowered EAB ( p < 0.05). Oxygenation of FFS was associated with the lower L ∗-value and higher a ∗-value of resulting films. Therefore, phenolic compounds could be used as natural cross-linkers which affected the properties of porcine plasma protein-based film differently.

The use of tannic acid to remove adhesiveness from pikeperch, Sander lucioperca, eggs

The studies conducted in 2003–2004 focused on the possibilities of applying a tannic solution to remove adhesiveness from pikeperch eggs. Spawners were caught in Lake Pątnowskie (central Poland) and then transported to the Goslawice Fish Farm. After initial selection, the fish were weighed, measured and stimulated with human chorionic gonadotropin. Gametes were obtained 5 days after the first injection. The weight and diameter of the eggs, and the commercial fecundity of individual females were determined. The eggs were fertilized with the dry method. After the addition of water, the eggs were mixed for 4 min, and then divided into 20 g portions. After determining the number of eggs in the various portions, the adhesiveness removal procedure was performed. Three concentrations of tannic acid solution (500, 1000, 1500 mg L−1) and three exposure times (0.5, 2, 5 min) were applied. The eggs were incubated in Weiss jars. The studies indicated that both the solution concentration and the exposure time significantly (P<0.05) impacted pikeperch egg hardening, the degree of adhesive removal and embryo survival. The tannic acid solution concentration of ≤500 mg L−1 applied for 0.5–2 min was not effective; the eggs clumped and it was impossible to separate them even with intensive mixing. Better results were obtained using higher tannic acid concentrations and/or by lengthening exposure time. The adhesiveness of pikeperch eggs disappeared completely after 5 min exposure to tannic acid solution concentrations of 500–1500 mg L−1 or after 2 min exposure to solution concentrations of 1000–1500 mg L−1. In these variants, the embryo survival rate to the eyed-egg stage was 78.0–84.0% (2003) and 82.3–84.7% (2004). However, high tannic acid concentration had a negative impact on the pikeperch larvae hatching. The greatest decrease in survival rate was observed in groups exposed to a tannic acid solution of 1500 mg L−1 for 2 and 5 min periods. Thus, the optimum method for removing pikeperch egg adhesiveness was to apply a solution of tannic acid at a concentration of 500 mg L−1 for 5 min or 1000 mg L−1 for 2–5 min.

Efficient degradation of tannic acid by black Aspergillus species

A set of aspergillus strains from culture collections and wild-type black aspergilli isolated on non-selective media were used to validate the use of media with 20% tannic acid for exclusive and complete selection of the black aspergilli. The 20% tannic acid medium proved useful for both quantitative and qualitative selection of all different black aspergilli, including all recognized species: A. carbonarius, A. japonicus, A. aculeatus, A foetidus, A. heteromorphus, A. niger, A. tubingensis and A. brasiliensis haplotypes. Even higher concentrations of tannic acid can be utilized by the black aspergilli suggesting a very efficient tannic acid-degrading system. Colour mutants show that the characteristic ability to grow on high tannic acid concentrations is not causally linked to the other typical feature of these aspergilli, i.e. the formation of brown-black pigments. Sequence analysis of the A. niger genome using the A. oryzae tannase gene yielded eleven tannase-like genes, far more than in related species. Therefore, a unique ecological niche in the degradation of tannic acid and connected nitrogen release seems to be reserved for these black-spored cosmopolitans.

Induction and repression patterns of fungal tannase in solid-state and submerged cultures

Induction and repression patterns of tannase production by Aspergillus niger Aa-20 in solid-state (SSC) and submerged culture (SmC) were established. Tannic acid and glucose were used as carbon sources. Induction and repression ratios were obtained with different concentrations of tannic acid and glucose, respectively. Tolerance to high concentrations of tannic acid by A. niger Aa-20 was lower in SmC than in SSC. In SSC an increase in tannic acid enhanced the expression of tannase activity. The addition of glucose (>20 g l −1) resulted in strong catabolite repression in SmC system. The tannase/biomass yield in SSC was at least 2 times higher than in SmC. The results presented demonstrate the capacity of SSC to minimize catabolite repression. The role of gallic acid in tannase regulation was also studied.

Effect of tannic acid concentration on development of the western treehole mosquito,Aedes sierrensis (Diptera: Culicidae)

Populations ofAedes sierrensis (Ludlow) completed development in tannic acid solutions over a wide concentration range (i.e., 0-1.0 g/liter) in artificial microcosms exposed to field conditions. The most notable effects of high tannic acid concentration were to slow larval developmental rates and to reduce numbers of adults produced; adult size and sex ratio were minimally affected. Vector potential of the western treehole mosquito is discussed in terms of tannin concentration.

Rapid Contrasting of Extracellular Elements in Thin Sections

Standard methods for contrasting ultrathin sections generally have their greatest effect on cells and cellular components, whereas extracellular elements remain relatively electron-lucent. Occasionally, some extracellular elements even fail completely to react with the staining solutions. We describe a method for rendering a uniformly high contrast to extracellular tissue components. This consists of a brief prestaining of grids with diluted tannic acid in distilled water. Simple, rapid, and versatile, this procedure can be routinely applied to all tissue samples examined by electron microscopy. As an additional advantage, the method greatly enhances the electron density of intracellular glycogen. Higher concentrations of tannic acid give increased electron density, especially to elastin, and can therefore be used as an elastin stain.