Tracer Penetration Research Articles

Estimation of Effective Fracture Aperture in Glacial Tills by Analysis of Dye Tracer Penetration.

This study advances a methodology to estimate effective apertures of fractures in glacial tills based on dye tracer infiltration tests and numerical simulations. The approach uses the visible penetration depth of the dye tracer along fracture flow paths as primary information to calculate effective fracture apertures. Further data used in the calculation are the dye tracer input concentration and retardation, the duration of the tracer injection, and the hydraulic gradient applied to control the infiltrating water fluxes. The method does not require measurement of hydraulic conductivity for the fractured till and enables direct observation of flow and transport patterns within the fractures (e.g., uniform flow and dye tracer distribution, channeling due to aperture variability, and presence of biogenic macropores in fractures). The approach was successfully verified by using the estimated effective fracture aperture values in Large Undisturbed Columns (LUCs) to consistently simulate both the observed LUC effluent breakthrough of a conservative bromide tracer and the water fluxes with the hydraulic gradient applied in the experiments. Sensitivity analyses revealed that estimation of small effective fracture apertures (<10 μm) required accurate determination of the dye tracer retardation factor. By contrast, in the case of larger effective apertures (>20 μm), the sensitivity of the estimated effective fracture aperture to variations in the porous material and solute transport parameters was low compared to the dominant sensitivity to the water flow through the fractures (cubic relation between flow and aperture). The proposed approach may be extended beyond laboratory applications and assist in characterizing field-scale fracture networks.

Recovery of denitrification and dissimilatory nitrate reduction to ammonium following reoxygenation of sediments from a periodically hypoxic temperate lagoon

AbstractEutrophication and stratification events have increased the incidences of hypoxia and anoxia in coastal environments. The depletion of oxygen in these environments can lead to a shift in biogeochemical processes such as denitrification and dissimilatory nitrate reduction to ammonium (DNRA). The balance between denitrification and DNRA is critical because denitrification leads to a loss of bioavailable nitrogen and DNRA maintains it within the system. This study examined the effects of reoxygenation on denitrification and DNRA in sediments collected from a periodically hypoxic system (Gippsland Lakes, Australia) and subjected to experimental hypoxia using a modified 15N‐isotope pairing technique. For freshly collected sediments, the ratio of denitrification : DNRA was generally &lt; 1 indicating a dominance of DNRA. After 3–4 weeks of oxygenation, denitrification increased relative to DNRA resulting in a denitrification : DNRA ratio &gt; 1. Profiles of 15N‐N2 and accumulation in these experiments showed denitrification and DNRA generally only took place in the surface ~ 2 cm of sediment. Prolonged experiments with reoxygenated sediments showed a decrease in the denitrification : DNRA to &lt; 1 after 56 d coincident with deep accumulation of within the sediment (2–5 cm) suggesting faunal irrigation enhanced DNRA deep in the sediment. An experiment with bromide tracer confirmed the occurrence of DNRA deep within the sediment at 2–6 cm was coincident with tracer penetration, and there was a significant positive relationship between bioirrigation and DNRA. We suggest DNRA deep within the sediment was enhanced by increased availability of organic carbon, reduced solutes, and possibly exposure of reworked sediment to .

Serum from rats subjected to traumatic brain injury and hemorrhagic shock induces profound endothelial barrier dysfunction

IntroductionTraumatic brain injury (TBI) has been associated with development of indirect acute respiratory distress syndrome (ARDS). However, the causative relationship between TBI and lung injury remains unclear. To explore potential mechanism linking TBI with development of ARDS, we characterized effects of serum factors released during TBI and hemorrhagic shock (HS) in a rat model on the pulmonary endothelial cell (EC) barrier dysfunction, a key feature of ARDS.MethodsThe adult male rat polytrauma model consisted of controlled cortical impact (CCI)–induced TBI followed by 30 minutes of hemorrhage shock (HS) induced by blood withdrawal. The HS phase was followed by a 1‐hour “prehospital” Hextend fluid resuscitation phase and then a 1‐hour “hospital phase” when shed blood was reinfused. 48 hours after the TBI, blood was drawn from right ventricle and serum samples were obtained. Serum was collected from the TBI or sham rats, and its effects on barrier properties of pulmonary endothelial cell culture were assessed by measurements of transendothelial electrical resistance (TER) using the electrical cell impedance sensor and visualization of fluorescent tracer penetration through EC monolayer using XPerT assay.ResultsWe found pronounced barrier‐disruptive effects of serum samples from animals exposed to controlled cortical impact (CCI) and HS, but not from sham operated rats. Rapid and sustained decrease in EC monolayer transendothelial resistance was observed within minutes after serum addition and remained below basal TER levels after incubation with CCI‐HS sera. Thrombin has been implicated in the early‐phase barrier disruptive activity of CCI‐HS serum, as both thrombin inhibitor and thrombin receptor antagonist attenuated the acute phase of serum‐induced TER decline, but did not affect TER decline at later time points. These findings suggest that thrombin elevation may play a role in early‐phase barrier disruptive activity of CCI‐HS serum. However, both the early and late phases of CCI‐HS‐induced EC permeability were inhibited by heparin. The late phase barrier disruptive effect of CCI‐HS was also prevented by serum preincubation with heparin‐sepharose. Pulmonary EC treated with serum from CCI‐HS rats for 3 hours have demonstrated significant decline in expression of EC junctional protein, VE‐Cadherin, and disassembly of peripheral EC adherens junction complexes monitored by immunostaining with VE‐cadherin antibody.ConclusionThese results suggest that exposure to CCI‐HS leads to production of humoral factors causing early and late‐phase barrier disruptive effects in lung vascular endothelium. While thrombin‐PAR1 signaling has been identified as mechanism of acute EC permeability increase by CCI‐HS serum, the factor(s) defining long‐term EC barrier disruption in CCI‐HS model remain to be determined.

Repetitive transcranial magnetic stimulation ameliorates the pathology and cognitive dysfunction in a mouse model of Alzheimer's disease through increased drainage efficiency of meningeal lymphatic system

AbstractBackgroundAlzheimer’s disease (AD) is a progressive neurodegenerative disease with high prevalence rate among elderly population. Given numerous studies that have shown promising outcomes in delaying or reversing the disease at preclinical stage, however, successful translation into clinical applications has been rare. Repetitive transcranial magnetic stimulation (rTMS) is a non‐invasive, painless technique that has been clinically proven to improve cognitive function in AD patients, but the underlying cellular and molecular mechanisms remain largely uninvestigated.Method5xFAD mice, an AD mouse model that overexpresses human familiar APP and presenilin 1 mutations under regulated expression of mouse neuronal‐specific Thy1 promotor, were stimulated by rTMS for 2 weeks. The stimulation contained a total of 4000 magnetic stimulation pulses given daily, which consisted of 100 burst trains and 40 pulses of each train at 20 Hz with a 5 sec intertrain interval. At the end of rTMS treatment, mice underwent memory tests including Y‐maze, novel object recognition and novel location recognition. A 10kD Dextran‐AlexaFluo647 tracer was injected into the cisterna magna compartment and mice were perfused 30 minutes later. Brains, meninges and deep cervical lymph nodes were resected for subsequent immunofluorescent analysis.Result5xFAD mice treated with high frequency rTMS for two weeks showed improved long‐term object and spatial memory, increased neuronal activity as revealed by the elevation of c‐fos‐positive neurons in the prefrontal cortex and the hippocampus, and reduced pathological features of AD, which included enhanced clearance of β‐amyloid deposit and reduced glial activation. Importantly, rTMS significantly enhanced the drainage of the intra‐cisterna magna injected tracer in 5xFAD mice, as revealed by tracer penetration and clearance in the brain parenchyma, dura mater, and deep cervical lymph nodes.ConclusionOur findings provide the novel mechanistic insight of the regulatory role of rTMS in the drainage efficiency of brain lymphatic system and the clearance of β‐amyloid in the 5xFAD mouse model, suggesting rTMS as a potential tool for the intervention of neurodegenerative and other disorders related to meningeal lymphatic dysfunction.

Evaluation of Fluorinated Cromolyn Derivatives as Potential Therapeutics for Alzheimer's Disease.

Cromolyn is an anti-neuroinflammatory modulator with a multifactorial mechanism of action that has been shown to inhibit amyloid-β (Aβ) aggregation and enhance microglial uptake and clearance of Aβ. We report the effects of fluoro-cromolyn derivatives on microglial cell toxicity and microglial clearance of Aβ42. Microglial cell toxicity for cromolyn derivatives were determined in naive BV2 microglial cells. Microglial clearance assays were performed with Aβ42 in naive BV2 microglial cell line and single cell clone BV2 line expressing CD33WT. PET imaging was performed for three F-18 analogs in a rhesus macaque. All compounds but derivative 8 exhibited low microglial cell toxicity. Cromolyn 1 and derivatives 2, 4, and 7 displayed an increased uptake on Aβ42 in naïve BV2 microglial cells. Derivative 4 increased Aβ42 uptake in a dose-dependent manner and at 75μM resulted in a one-fold increase in Aβ42 uptake in BV2-CD33WT. PET imaging for three [18F]cromolyn analogs revealed the order of brain tracer penetration to be 4a > 10 > 2a. Tracer 4a exhibited enhanced uptake in areas of high perfusion (putamen, grey matter, and cerebellum) and lower signal in areas of lower perfusion (caudate, thalamus, and white matter). Substantial uptake of Aβ42 in both naïve BV2 and BV2-CD33WT cells observed with 4 indicate conversion of microglial cells from a pro-inflammatory to an activation state favoring Aβ phagocytosis/clearance. These findings suggest that a fluoro-cromolyn analog could reduce fibril-prone Aβ42in vivo and thereby serve as a therapeutic for the treatment and prevention of AD.

Acute systemic LPS-exposure impairs perivascular CSF distribution in mice

BackgroundThe exchange of cerebrospinal (CSF) and interstitial fluid is believed to be vital for waste clearance in the brain. The sleep-dependent glymphatic system, which is comprised of perivascular flow of CSF and is largely dependent on arterial pulsatility and astrocytic aquaporin-4 (AQP4) expression, facilitates much of this brain clearance. During the last decade, several observations have indicated that impaired glymphatic function goes hand in hand with neurodegenerative diseases. Since pathologies of the brain carry inflammatory components, we wanted to know how acute inflammation, e.g., with lipopolysaccharide (LPS) injections, would affect the glymphatic system. In this study, we aim to measure the effect of LPS on perivascular CSF distribution as a measure of glymphatic function.MethodsThree hours after injection of LPS (1 mg/kg i.p.), C57bl/6 mice were (1) imaged for two CSF tracers, injected into cisterna magna, (2) transcardially perfused with buffer, or (3) used for physiological readouts. Tracer flow was imaged using a low magnification microscope on fixed brains, as well as using vibratome-cut slices for measuring tracer penetration in the brain. Cytokines, glial, and BBB-permeability markers were measured with ELISAs, Western blots, and immunohistochemistry. Cerebral blood flow was approximated using laser Doppler flowmetry, respiration and heart rate with a surgical monitor, and AQP4-polarization was quantified using confocal microscopy of immunolabeled brain sections.ResultsLPS-injections significantly lowered perivascular CSF tracer flow and penetration into the parenchyma. No differences in AQP4 polarization, cytokines, astroglial and BBB markers, cerebral blood flow, or respiration were detected in LPS-injected mice, although LPS did elevate cortical Iba1+ area and heart rate.ConclusionsThis study reports another physiological response after acute exposure to the bacterial endotoxin LPS, namely the statistically significant decrease in perivascular distribution of CSF. These observations may benefit our understanding of the role of systemic inflammation in brain clearance.

PET imaging of P2X7R in the experimental autoimmune encephalomyelitis model of multiple sclerosis using [11C]SMW139

BackgroundNon-invasive imaging of the activation status of microglia and the ability to identify a pro- or anti-inflammatory environment can provide valuable insights not only into pathogenesis of neuro-inflammatory and neurodegenerative diseases but also the monitoring of the efficacy of immunomodulatory therapies. P2X7R is highly expressed on pro-inflammatory microglia and [11C]SMW139, a specific P2X7R tracer for positron emission tomography imaging, showed good pharmacokinetics, stability, and brain permeability in vivo. Our objective was to evaluate the potential of [11C]SMW139 for PET imaging of neuroinflammation in vivo in the experimental autoimmune encephalomyelitis (EAE) model.MethodsWe induced EAE in Lewis rats by immunization with MBP 69-88 in complete Freund’s adjuvant (CFA). We determined the affinity of [11C]SMW139 to human and rat P2X7R using saturation binding assay. Using this tracer, PET imaging was performed at the peak of disease and in the recovery phase. In vivo blocking experiments were conducted to validate the specific brain uptake of the tracer. Immunohistochemistry staining and autoradiography were performed to evaluate the level of neuroinflammation and validate the specific binding of [11C]SMW139.Results[11C]SMW139 showed good affinity for the rat P2X7R with a Kd of 20.6 ± 1.7 nM. The uptake of [11C]SMW139 was significantly higher in EAE animals at the peak of disease compared to the recovery phase but not in CFA control animals. The amplitude of increase of [11C]SMW139 uptake showed significant positive correlation with clinical scores mainly in the spinal cord (Pearson = 0.75, Spearman = 0.76; p < 0.0001). Treating EAE animals with P2X7R antagonist JNJ-47965567 blocked the uptake of [11C]SMW139 in the spinal cord, cerebellum, and brain stem, demonstrating specific accumulation of the tracer. P-glycoprotein blocking with tariquidar (30 mg/kg) did not affect tracer penetration in the brain showing that [11C]SMW139 is not a Pgp substrate.ConclusionOur data shows that [11C]SMW139 is a promising PET tracer for imaging neuroinflammation and evaluating the dynamics of pro-inflammatory microglia in the brain. This can provide crucial insights into the role of microglia in disease progression and enables the development of novel treatment strategies aimed at modulating the immune response in order to promote neuroprotection.

Insight into the influence of local streambed heterogeneity on hyporheic-zone flow characteristics

Interaction between surface water and groundwater plays a fundamental role in influencing aquatic chemistry, where hyporheic exchange processes, distribution of flow paths and residence times within the hyporheic zone will influence the transport of mass and energy in the surface-water/groundwater system. Geomorphological conditions greatly influence hyporheic exchange, and heterogeneities such as rocks and clay lenses will be a key factor for delineating the hyporheic zone. Electrical resistivity tomography (ERT) and ground-penetrating radar (GPR) were used to investigate the streambed along a 6.3-m-long reach in order to characterise geological layering and distinct features which may influence parameters such as hydraulic conductivity. Time-lapse ERT measurements taken during a tracer injection demonstrated that geological features at the meter-scale played a determining role for the hyporheic flow field. The penetration depth of the tracer into the streambed sediment displayed a variable spatial pattern in areas where the presence of highly resistive anomalies was detected. In areas with more homogeneous sediments, the penetration depth was much more uniformly distributed than observed in more heterogeneous sections, demonstrating that ERT can play a vital role in identifying critical hydraulic features that may influence hyporheic exchange processes. Reciprocal ERT measurements linked variability and thus uncertainty in the modelled resistivity to the spatial locations, which also demonstrated larger variability in the tracer penetration depth, likely due to local heterogeneity in the hydraulic conductivity field.

Quantitative Determination of Glymphatic Flow Using Spectrophotofluorometry.

Following intrathecal injection of fluorescent tracers, ex vivo imaging of brain vibratome slices has been widely used to study the glymphatic system in the rodent brain. Tracer penetration into the brain is usually quantified by image-processing, even though this approach requires much time and manual operation. Here, we illustrate a simple protocol for the quantitative determination of glymphatic activity using spectrophotofluorometry. At specific time-points following intracisternal or intrastriatal injection of fluorescent tracers, certain brain regions and the spinal cord were harvested and tracers were extracted from the tissue. The intensity of tracers was analyzed spectrophotometrically and their concentrations were quantified from standard curves. Using this approach, the regional and dynamic delivery of subarachnoid CSF tracers into the brain parenchyma was assessed, and the clearance of tracers from the brain was also determined. Furthermore, the impairment of glymphatic influx in the brains of old mice was confirmed using our approach. Our method is more accurate and efficient than the imaging approach in terms of the quantitativedetermination of glymphatic activity, and this will be useful in preclinical studies.

Enhanced junctional epithelial permeability in TRPV4-deficient mice.

Background and ObjectiveAs the interface between the oral cavity and the teeth, the junctional epithelial barrier is critical for gingival defense. The junctional epithelium is subject to mechanical stresses from biting force or external insults such as bacterial attacks, but little is known about the effects of mechanical stimuli on epithelial functions. Transient receptor potential vanilloid 4 (TRPV4) functions as a mechanosensitive nonselective cation channel. In the present study, based on marked expression of TRPV4 in the mouse junctional epithelium, we aimed to clarify the putative links between TRPV4 and junctional complexes in the junctional epithelium.Methods and ResultsHistological observations revealed that the junctional epithelium in TRPV4‐deficient (TRPV4−/−) mice had wider intercellular spaces than that in wild‐type (TRPV4+/+) mice. Exogenous tracer penetration in the junctional epithelium was greater in TRPV4−/− mice than in TRPV4+/+ mice, and immunoreactivity for adherens junction proteins was suppressed in TRPV4−/− mice compared with TRPV4+/+ mice. Analysis of a mouse periodontitis model showed greater bone volume loss in TRPV4−/− mice compared with TRPV4+/+ mice, indicating that an epithelial barrier deficiency in TRPV4−/− mice may be associated with periodontal complications.ConclusionThe present findings identify a crucial role for TRPV4 in the formation of adherens junctions in the junctional epithelium, which could regulate its permeability. TRPV4 may be a candidate pharmacological target to combat periodontal diseases.

Pore Structure and Fluid Uptake of the Springer/Goddard Shale Formation in Southeastern Oklahoma, USA

Hosting an emerging play of the Springer/Goddard shale, the South Central Oklahoma Oil Province (SCOOP), is also the main production field for the underlying Woodford Formation. Understanding the reservoir quality of the Chesterian-age Goddard shale, currently little has been achieved, is vital to sustainable hydrocarbon production and exploration. Using polar (DI water and/or API brine) and nonpolar (n-decane) fluids to probe hydrophilic and hydrophobic pore networks, the purpose of this study is to examine wettability, pore connectivity, fluid imbibition, and tracer migration of the Springer shale. To achieve this, we collected core samples from two wells located at the heart of the play and performed mercury injection capillary pressure, wettability, fluid imbibition, and vapor absorption tests. Results from these studies show that the Springer shale has a stronger affinity to oil (n-decane in this study), compared to DI water and API brine. With porosity values averaging at 6.32 ± 0.75% and permeability of 20.0 ± 6.52 nD, the majority of pore-throat sizes for the Springer shale are 5–50 nm. The utility of wettability tracers of different molecular sizes helps tease out the intertwined relationship of pore-throat sizes, connectivity, and associated wettability of shale. The imbibition results suggest a molecular entanglement effect at the scale of 0.5 nm, even for the tracer penetration of a wetting fluid of n-decane. A petrophysical analysis of the Springer shale presented in this work is beneficial to further understand the pore structure and fluid movement within the shale to facilitate increased production and accurate economic evaluations.

Quantification of the vertical translocation rate of soil solid-phase material by the magnetic tracer method

Approaches to the quantification of the vertical translocation rate of soil solid-phase material by the magnetic tracer method have been developed; the tracer penetration depth and rate have been determined, as well as the radial distribution of the tracer in chernozems (Chernozems) and dark gray forest soils (Luvisols) of Belgorod oblast under natural steppe and forest vegetation and in arable lands under agricultural use of different durations. It has been found that the penetration depth of spherical magnetic particles (SMPs) during their 150-year-occurrence in soils of a forest plot is 68 cm under forest, 58 cm on a 100-year old plowland, and only 49 cm on a 150-year-old plowland. In the chernozems of the steppe plot, the penetration depth of SMPs exceeds the studied depth of 70 cm both under natural vegetation and on the plowlands. The penetration rates of SMPs deep into the soil vary significantly among the key plots: 0.92–1.32 mm/year on the forest plot and 1.47–1.63 mm/year on the steppe plot, probably because of the more active recent turbation activity of soil animals.

The use of micro-Raman imaging to measure 18O tracer distribution in thermally grown zirconia scales

High temperature Zircaloy-4 oxidation has been studied through two-stage oxidation experiments using 18O isotope. 18O distribution in the oxidation scales was investigated by micro-Raman imaging. First, zirconia standards with known 18O content were prepared and analyzed for calibration purposes. Then, to assess the method on a simple case, 18O tracer penetration patterns were recorded after a 800°C two-stage oxidation. Finally, oxidation at 850°C of a Zircaloy4 cladding tube pre-corroded at 425°C to simulate corrosion during normal reactor operation was studied. These preliminary results give insights on the protective nature of the first formed zirconia scale in case of an accident.

Adaptation and penetration of resin-based root canal sealers in root canals irradiated with high-intensity lasers.

This research analyzed the quality of resin-based sealer adaptation after intracanal laser irradiation. Extracted teeth (n = 168) were root canal treated and divided into four groups, according to dentin surface treatment: no laser; Nd:YAG laser (1.5 W, 100 mJ, 15 Hz); diode laser (2.5 W in CW), and Er:YAG laser (1 W, 100 mJ, 10 Hz). The teeth were divided into four subgroups according to the sealer used: AH Plus, EndoREZ, Epiphany, and EpiphanySE. For testing the sealing after root canal obturation, the penetration of silver nitrate solution was measured, whereas to evaluate the adaptation and penetration of the sealer into the dentin, environmental scanning electron microscopy (ESEM) was used. The ESEM images were analyzed using a four-grade criteria score by three evaluators. The inter-examiner agreement was confirmed by Kappa test and the scores statistically compared by the Kruskal-Wallis' test (p < 0.05). Both adaptation and sealer penetration in root canals were not affected by the laser irradiation. Nd:YAG and diode laser decreased the tracer penetration for AH Plus, whereas EndoREZ and EpiphanySE performances were affected by Nd:YAG irradiation (p < 0.05). It can be concluded that intracanal laser irradiation can be used as an adjunct in endodontic treatment; however, the use of hydrophilic resin sealers should be avoided when root canals were irradiated with Nd:YAG laser.

Stroke literature synopses: basic science.

Stroke literature synopses: basic science.

Imaging and quantifying solute transport across periosteum: Implications for muscle–bone crosstalk

Muscle and bone are known to act as a functional unit and communicate biochemically during tissue development and maintenance. Muscle-derived factors (myokines) have been found to affect bone functions in vitro. However, the transport times of myokines to penetrate into bone, a critical step required for local muscle–bone crosstalk, have not been quantified in situ or in vivo. In this study, we investigated the permeability of the periosteum, a major barrier to muscle–bone crosstalk by tracking and modeling fluorescent tracers that mimic myokines under confocal microscopy. Periosteal surface boundaries and tracer penetration within the boundaries were imaged in intact murine tibiae using reflected light and time-series xz confocal imaging, respectively. Four fluorescent tracers including sodium fluorescein (376Da) and dextrans (3kDa, 10kDa and 40kDa) were chosen because they represented a wide range of molecular weights (MW) of myokines. We found that i) murine periosteum was permeable to the three smaller tracers while the 40kDa could not penetrate beyond 40% of the outer periosteum within 8h, suggesting that periosteum is semi-permeable with a cut-off MW of approximately 40kDa, and ii) the characteristic penetration time through the periosteum (~60μm thick) increased with tracer MW and fit well with a relationship tcs=−4.43×104−0.57×MWDa−4×104−8.65×108MWDa−4×104, from which, the characteristic penetration times of various myokines were extrapolated. To achieve effective muscle–bone crosstalk, likely signaling candidates should have shorter penetration time than their bioactive time, which we assumed to be 5 times of the molecule's half-lifetime in the body. Myokines such as PGE2, IGF-1, IL-15 and FGF-2 were predicted to satisfy this requirement. In summary, a novel imaging approach was developed and used to investigate the transport of myokine mimicking-tracers through the periosteum, enabling further quantitative studies of muscle–bone communication in physiologically normal and pathological conditions.

Universal Scaling of Polymer Diffusion in Nanocomposites.

Nanoparticles are new and valuable additives that can favorably tune thermomechanical, electric, optical, and magnetic properties of polymeric materials. The addition of nanoparticles can also enhance or slow down polymer dynamics depending on the mixture thermodynamics and key length scales, namely, nanoparticle size, interparticle spacing (ID), and the polymer radius of gyration (Rg). Presently, a framework for understanding how nanoparticles affect polymer dynamics is not available, in part, because of a lack of wide-ranging experimental studies. Here, tracer diffusion is studied in model nanocomposites containing silica nanoparticles grafted with either polymer brushes (soft nanoparticles) or short ligands (hard nanoparticles). Over a wide range of tracer molecular weights and nanoparticle loadings, the normalized diffusion coefficient collapses onto a universal curve for both soft and hard nanoparticles when plotted against a confinement parameter, defined as ID/Rg, which accounts for tracer penetration into the brush. These experimental results provide new insights into the fundamental principles required to construct predictive models of polymer dynamics in nanocomposites.

Clinical relevance of tests on bond strength, microleakage and marginal adaptation

Dental adhesive systems should provide a variety of capabilities, such as bonding of artificial materials to dentin and enamel, sealing of dentinal tubules, reduction of post-operative sensitivity and marginal sealing to reduce marginal staining and caries. In the laboratory, numerous surrogate parameters that should predict the performance of different materials, material combinations and operative techniques are assessed. These surrogate parameters include bond strength tests of various kinds, evaluation of microleakage with tracer penetration between restorative and tooth, two-dimensional analysis of marginal quality with microscopes and mapping of the micromorphology of the bonding interface. Many of these tests are not systematically validated and show therefore different results between different research institutes. The correlation with clinical phenomena has only partly been established to date. There is some evidence, that macrotensile and microtensile bond strength tests correlate better with clinical retention of cervical restorations than macroshear and microshear bond tests but only if data from different test institutes are pooled. Also there is some evidence that marginal adaptation has a moderate correlation in cervical restorations with clinical retention and in Class II restorations (proximal enamel) with clinical marginal staining. There is moderate evidence that microleakage tests with dye penetration does not correlate with any of the clinical parameters (post-operative hypersensitivity, retention, marginal staining). A rationale which helps the researcher to select and apply clinically relevant test methods in the laboratory is presented in the paper.

Endothelial Glycocalyx: Permeability Barrier and Mechanosensor

Endothelial cells are covered with a polysaccharide rich layer more than 400 nm thick, mechanical properties of which limit access of circulating plasma components to endothelial cell membranes. The barrier properties of this endothelial surface layer are deduced from the rate of tracer penetration into the layer and the mechanics of red and white cell movement through capillary microvessels. This review compares the mechanosensor and permeability properties of an inner layer (100-150 nm, close to the endothelial membrane) characterized as a quasi-periodic structure which accounts for key aspects of transvascular exchange and vascular permeability with those of the whole endothelial surface layers. We conclude that many of the barrier properties of the whole surface layer are not representative of the primary fiber matrix forming the molecular filter determining transvascular exchange. The differences between the properties of the whole layer and the inner glycocalyx structures likely reflect dynamic aspects of the endothelial surface layer including tracer binding to specific components, synthesis and degradation of key components, activation of signaling pathways in the endothelial cells when components of the surface layer are lost or degraded, and the spatial distribution of adhesion proteins in microdomains of the endothelial cell membrane.

In vitro dentin permeability after application of Gluma® desensitizer as aqueous solution or aqueous fumed silica dispersion

ObjectivesTo assess and to compare the effects of Gluma® Desensitizer (GDL) with an experimental glutaraldehyde and HEMA containing fumed silica dispersion (GDG) on dentin permeability using a chemiluminous tracer penetration test.Material and MethodsTwenty disc-shaped dentin specimens were dissected from extracted human third molars. The dentin specimens were mounted in a split chamber device for determination of permeability under liquid pressure using a photochemical method. Ten specimens were randomly selected and allocated to the evaluation groups Gluma® Desensitizer as aqueous solution and glutaraldehyde/HEMA as fumed silica dispersion, respectively. Dentin disc permeability was determined at two pressure levels after removal of smear with EDTA, after albumin soaking, and after application of the desensitizing agents. Two desensitizer-treated and rinsed specimens of each group were examined by scanning electron microscopy (SEM) for surface remnants.ResultsComparatively large standard deviations of the mean EDTA reference and albumin soaked samples permeability values reflected the differences of the dentin substrates. The mean chemiluminescence values of specimen treated with GDL and GDG, respectively, were significantly reduced after topical application of the desensitizing agents on albumin-soaked dentin. The effects of GDL and GDG on permeability were not significantly different. Treated specimens showed no surface remnants after rinsing.ConclusionsThe experimental desensitizer gel formulation reduced dentin permeability as effectively as the original Gluma® Desensitizer solution.