Water absorption of poly(methyl methacrylate) measured by vertical interference microscopy

PMMA (poly(methyl methacrylate)) is widely used to prepare orthopedic cements. They are in direct contact with cells and body fluids. PMMA, despite its hydrophobic nature, can absorb ~2% w/w water. We have evaluated by vertical interference microscopy if water absorption can produce a significant swelling in different types of PMMA blocks: pure, with a plasticizer, with a cross-linker, and in two types of commercial bone cements. Graphite rods which do not swell in water were used as internal standard. Hardness, indentation modulus, plastic, and elastic works were determined by nanoindentation under a 25mN fixed force. Vertical interference microscopy was used to image the polymer in the dry state and hydrated states (after 24 h in distilled water). On the surface of the polished polymers (before and after hydration), we measured roughness by the fractal dimension, the swelling in the vertical and the lateral directions. For each polymer block, four images were obtained and values were averaged. Comparison and standardization of the images in the dry and hydrated states were done with Matlab software. The average value measured on the graphite rod between the two images (dried and hydrated) was used for standardization of the images which were visualized in 3D. After grinding, a small retraction was noticeable between the surface of the rod and the polymers. A retraction ring was also visible around the graphite rod. After hydration, only the pure PMMA and bone cements had a significant swelling in the vertical direction. The presence of polymer beads in the cements limited the swelling in the lateral direction. Swelling parameters correlated with the nanoindentation data. PMMA can swell by absorbing a small amount of water and this induces a swelling that varies with the polymer composition and particle inclusions.

Molecular crowding of collagen: a pathway to produce highly-organized collagenous structures

Collagen in vertebrate animals is often arranged in alternating lamellae or in bundles of aligned fibrils which are designed to withstand in vivo mechanical loads. The formation of these organized structures is thought to result from a complex, large-area integration of individual cell motion and locally-controlled synthesis of fibrillar arrays via cell-surface fibripositors (direct matrix printing). The difficulty of reproducing such a process in vitro has prevented tissue engineers from constructing clinically useful load-bearing connective tissue directly from collagen. However, we and others have taken the view that long-range organizational information is potentially encoded into the structure of the collagen molecule itself, allowing the control of fibril organization to extend far from cell (or bounding) surfaces. We here demonstrate a simple, fast, cell-free method capable of producing highly-organized, anistropic collagen fibrillar lamellae de novo which persist over relatively long-distances (tens to hundreds of microns). Our approach to nanoscale organizational control takes advantage of the intrinsic physiochemical properties of collagen molecules by inducing collagen association through molecular crowding and geometric confinement. To mimic biological tissues which comprise planar, aligned collagen lamellae (e.g. cornea, lamellar bone or annulus fibrosus), type I collagen was confined to a thin, planar geometry, concentrated through molecular crowding and polymerized. The resulting fibrillar lamellae show a striking resemblance to native load-bearing lamellae in that the fibrils are small, generally aligned in the plane of the confining space and change direction en masse throughout the thickness of the construct. The process of organizational control is consistent with embryonic development where the bounded planar cell sheets produced by fibroblasts suggest a similar confinement/concentration strategy. Such a simple approach to nanoscale organizational control of structure not only makes de novo tissue engineering a possibility, but also suggests a clearer pathway to organization for fibroblasts than direct matrix printing.

Targeted gene inactivation reveals a functional role of calpain-1 in platelet spreading

BACKGROUND

Calpains are implicated in a wide range of cellular functions including the maintenance of hemostasis via the regulation of cytoskeletal modifications in platelets.

OBJECTIVES

Determine the functional role of calpain isoforms in platelet spreading.

METHODS AND RESULTS

Platelets from calpain-1(-/-) mice show enhanced spreading on collagen- and fibrinogen-coated surfaces as revealed by immunofluorescence, differential interference contrast (DIC) and scanning electron microscopy. The treatment of mouse platelets with MDL, a cell permeable inhibitor of calpains 1/2, resulted in increased spreading. The PTP1B-mediated enhanced tyrosine dephosphorylation in calpain-1(-/-) platelets did not fully account for the enhanced spreading as platelets from the double knockout mice lacking calpain-1 and PTP1B showed only a partial rescue of the spreading phenotype. In non-adherent platelets, proteolysis and GTPase activity of RhoA and Rac1 were indistinguishable between the wild-type (WT) and calpain-1(-/-) platelets. In contrast, the ECM-adherent calpain-1(-/-) platelets showed higher Rac1 activity at the beginning of spreading, whereas RhoA was more active at later time points. The ECM-adherent calpain-1(-/-) platelets showed an elevated level of RhoA protein but not Rac1 and Cdc42. Proteolysis of recombinant RhoA, but not Rac1 and Cdc42, indicates that RhoA is a calpain-1 substrate in vitro.

CONCLUSIONS

Potentiation of the platelet spreading phenotype in calpain-1(-/-) mice suggests a novel role of calpain-1 in hemostasis, and may explain the normal bleeding time observed in the calpain-1(-/-) mice.

Nondestructive monitoring of the repair of enamel artificial lesions by an acidic remineralization model using polarization-sensitive optical coherence tomography

OBJECTIVES

It is difficult to completely remineralize carious lesions because diffusion into the interior of the lesion is inhibited as new mineral is deposited in the outermost layers. In previous remineralization studies employing polarization sensitive optical coherence tomography (PS-OCT), two models of remineralization were employed and in both models there was preferential deposition of mineral in the outer most layer. In this study we attempted to remineralize the entire lesion using an acidic remineralization model and demonstrate that this remineralization can be monitored using PS-OCT.

METHODS

Artificial lesions approximately 100-150 μm in-depth were exposed to an acidic remineralization regimen and the integrated reflectivity from the lesions was measured before and after remineralization using PS-OCT.

RESULTS

Automated integration routines worked well for assessing the integrated reflectivity for the lesion areas after remineralization. Although there was a high degree of remineralization, there was still incomplete remineralization of the body of the lesion.

CONCLUSION

This study demonstrated that PS-OCT can be used to non-destructively measure changes in lesion structure and severity upon exposure to an acidic remineralization model. This study also demonstrated that automated algorithms can be used to assess the lesion severity even with the presence of a weakly reflective surface zone.

Single nanoparticle detectors for biological applications

Nanoparticle research has become increasingly important in the context of bioscience and biotechnology. Practical use of nanoparticles in biology has significantly advanced our understanding about biological processes in the nanoscale as well as led to many novel diagnostic and therapeutic applications. Besides, synthetic and natural nanoparticles are of concern for their potential adverse effect on human health. Development of novel detection and characterization tools for nanoparticles will impact a broad range of disciplines in biological research from nanomedicine to nanotoxicology. In this article, we discuss the recent progress and future directions in the area of single nanoparticle detectors with an emphasis on their biological applications. A brief critical overview of electrical and mechanical detection techniques is given and a more in-depth discussion of label-free optical detection techniques is presented.

The α-glucanase Agn1p is required for cell separation in Schizosaccharomyces pombe

BACKGROUND INFORMATION

In animal cells, cytokinesis occurs by constriction of an actomyosin ring. In fission yeast, ring constriction is followed by deposition of a multilayered division septum that must be cleaved to release the two daughter cells. Although many studies have focused on the actomyosin ring and septum assembly, little is known about the later steps involving the cleavage of the cell wall.

RESULTS

We identified a novel gene in Schizosaccharomyces pombe, namely the agn1(+) gene that has homology to fungal 1,3-alpha-glucanases (mutanases). Disruption of the agn1(+) gene is not lethal to the cells, but does interfere with their separation, whereas overexpression of Agn1p is toxic and causes cell lysis. Agn1p levels reach a peak during septation and the protein localizes to the septum region before cell separation. Moreover, agn1(+) is responsible for the 1,3-alpha-glucanase activity, which shows a maximum at the end of septation.

CONCLUSIONS

Our results clearly suggest the existence of a relationship between agn1(+), 1,3-alpha-glucanase activity and the completion of septation in S. pombe. Agn1p could be involved in the cleavage of the cylinder of the old wall that surrounds the primary septum, a region rich in alpha-glucans.

One-dimensional deterministic transport in neurons measured by dispersion-relation phase spectroscopy

We studied the active transport of intracellular components along neuron processes using a new method developed in our laboratory: dispersion-relation phase spectroscopy. This method is able to quantitatively map spatially the heterogeneous dynamics of the concentration field of the cargos at submicron resolution without the need for tracking individual components. The results in terms of density correlation function reveal that the decay rate is linear in wavenumber, which is consistent with a narrow Lorentzian distribution of cargo velocity.

Quantitative cell imaging using single beam phase retrieval method

Quantitative three-dimensional imaging of cells can provide important information about their morphology as well as their dynamics, which will be useful in studying their behavior under various conditions. There are several microscopic techniques to image unstained, semi-transparent specimens, by converting the phase information into intensity information. But most of the quantitative phase contrast imaging techniques is realized either by using interference of the object wavefront with a known reference beam or using phase shifting interferometry. A two-beam interferometric method is challenging to implement especially with low coherent sources and it also requires a fine adjustment of beams to achieve high contrast fringes. In this letter, the development of a single beam phase retrieval microscopy technique for quantitative phase contrast imaging of cells using multiple intensity samplings of a volume speckle field in the axial direction is described. Single beam illumination with multiple intensity samplings provides fast convergence and a unique solution of the object wavefront. Three-dimensional thickness profiles of different cells such as red blood cells and onion skin cells were reconstructed using this technique with an axial resolution of the order of several nanometers.

Arachnids secrete a fluid over their adhesive pads

Background

Many arachnids possess adhesive pads on their feet that help them climb smooth surfaces and capture prey. Spider and gecko adhesives have converged on a branched, hairy structure, which theoretically allows them to adhere solely by dry (solid-solid) intermolecular interactions. Indeed, the consensus in the literature is that spiders and their smooth-padded relatives, the solifugids, adhere without the aid of a secretion.

Methodology and Principal Findings

We investigated the adhesive contact zone of living spiders, solifugids and mites using interference reflection microscopy, which allows the detection of thin liquid films. Like insects, all the arachnids we studied left behind hydrophobic fluid footprints on glass (mean refractive index: 1.48–1.50; contact angle: 3.7–11.2°). Fluid was not always secreted continuously, suggesting that pads can function in both wet and dry modes. We measured the attachment forces of single adhesive setae from tarantulas (Grammostola rosea) by attaching them to a bending beam with a known spring constant and filming the resulting deflection. Individual spider setae showed a lower static friction at rest (26%±2.8 SE of the peak friction) than single gecko setae (Thecadactylus rapicauda; 96%±1.7 SE). This may be explained by the fact that spider setae continued to release fluid after isolation from the animal, lubricating the contact zone.

Significance

This finding implies that tarsal secretions occur within all major groups of terrestrial arthropods with adhesive pads. The presence of liquid in an adhesive contact zone has important consequences for attachment performance, improving adhesion to rough surfaces and introducing rate-dependent effects. Our results leave geckos and anoles as the only known representatives of truly dry adhesive pads in nature. Engineers seeking biological inspiration for synthetic adhesives should consider whether model species with fluid secretions are appropriate to their design goals.

Morphological redescriptions of four marine ciliates (Ciliophora: Cyrtophorida: Dysteriidae) from Qingdao, China

The morphology and infraciliature of four marine cyrtophorid ciliates isolated from Qingdao, China, were investigated. Based on the present work and on previous data, improved diagnoses for three rarely known species are provided: (1) Mirodysteria decora; small-sized marine Mirodysteria about 35-60 × 25-35 μm in vivo, oval in outline; body surface with two or three conspicuous dorsal spines and one caudal spine; three right kineties, the rightmost one extending dorso-apically; left frontal kineties reduced, each consisting of three basal bodies only; podite subcaudally positioned; two ventrally located contractile vacuoles. (2) Dysteria legumen; body oval with two longitudinal grooves on different plates; six right kineties, the rightmost two of which extend dorso-apically; two left frontal kineties and two ventrally located contractile vacuoles. (3) Dysteria proraefrons; body about 60×35 μm in vivo; six right kineties, the two rightmost of which extend dorso-apically and the leftmost one is considerably shortened; three left frontal kineties; two ventrally located contractile vacuoles. A population of D. derouxi with eight or nine right kineties is also briefly described. The current investigation further demonstrates high diversity and cosmopolitan distribution of this highly specialized group of benthic ciliates.

Germination of individual Bacillus subtilis spores with alterations in the GerD and SpoVA proteins, which are important in spore germination

Release of Ca(2+) with dipicolinic acid (CaDPA) was monitored by Raman spectroscopy and differential interference contrast microscopy during germination of individual spores of Bacillus subtilis strains with alterations in GerD and SpoVA proteins. Notable conclusions about germination after the addition of nutrient were as follows. (i) Following L-alanine addition, wild-type and gerD spores and spores with elevated SpoVA protein levels (↑SpoVA spores) slowly released ∼10% of their CaDPA during a variable (6- to 55-min) period ending at T(lag), the time when faster CaDPA release began. (ii) T(lag) times were lower for ↑SpoVA spores than for wild-type spores and were higher for gerD spores. (iii) The long T(lag) times of gerD spores were partially due to slow commitment to germinate. (iv) The intervals between the commitment to germinate and CaDPA release were similar for wild-type and ↑SpoVA spores but longer for gerD spores. (v) The times for rapid CaDPA release, ΔT(release) = T(release) - T(lag) (with T(release) being the time at which CaDPA release was complete), were similar for wild-type, gerD, and ↑SpoVA spores. (vi) Spores with either one of two point mutations in the spoVA operon (spoVA(1) and spoVA(2) spores) exhibited a more rapid rate of CaDPA release beginning immediately after L-alanine addition leading to ∼65% CaDPA release prior to T(lag). (vii) T(lag) times for spoVA(1) and spoVA(2) spores were longer than for wild-type spores. (viii) The intervals between spoVA(1) and spoVA(2) spores' commitment and CaDPA release were similar to those for wild-type spores, but commitment occurred later. In contrast to germination after the addition of nutrient, T(lag) and ΔT(release) times were relatively similar during dodecylamine germination of spores of the five strains. These findings suggest the following. (i) GerD plays no role in CaDPA release during spore germination. (ii) SpoVA proteins are involved in CaDPA release during germination with nutrients, and probably with dodecylamine. (iii) Spores release significant CaDPA before commitment. (iv) CaDPA release during T(lag) and ΔT(release) may signal subsequent germination events.

Dynamic analysis of pathogen-infected host cells using quantitative phase microscopy

We present the real-time quantitative analysis of Vibrio vulnificus-infected host cells using quantitative phase microscopy (QPM) based on interferometric techniques. This provides the ability to retrieve the phase or optical path-length distribution over the cell with nanometer path-length sensitivity from a single interferogram image. We have used QPM to study dynamic cell morphologic changes and to noninvasively quantify the cell volumes of rat basophilic leukemia RBL-2H3 cells infected with V. vulnificus strains: wild type (MO6-24∕O) and RtxA1 toxin mutant (CMM770). During the process of V. vulnificus infection in RBL-2H3 cells, the dynamic changes of quantitative phase images, cell volumes, and areas were observed in real time using QPM. In contrast, dramatic changes were not detected in RBL-2H3 cells infected with the noncytotoxic RtxA1 toxin mutant. The results showed good correlation between QPM analysis and biochemical assays, such as lactate dehydrogenase assay or β-hexosaminidase release assay. We suggest that QPM is a powerful quantitative method to study the dynamic process of host cells infected with pathogens in a noninvasive manner.

Noninvasive identification of subcellular organization and nuclear morphology features associated with leukemic cells using light-scattering spectroscopy

Leukemia is the most common and deadly cancer among children and one of the most prevalent cancers among adults. Improvements in its diagnosis and monitoring of leukemic patients could have a significant impact in their long-term treatment. We demonstrate that light-scattering spectroscopy (LSS)-based approaches could serve as a tool to achieve this goal. Specifically, we characterize the light scattering properties of leukemic (NALM-6) cells and compare them to those of normal lymphocytes and granulocytes in the 440-710 nm range, over ±4 deg about the exact backscattering direction. We find that the LSS spectra are well described by an inverse power-law wavelength dependence, with a power exponent insensitive to the scattering angle but significantly higher for leukemic cells than for normal leukocytes. This is consistent with differences in the subcellular morphology of these cells, detected in differential interference contrast images. Furthermore, the residual light-scattering signal, extracted after subtracting the inverse power-law fit from the data, can be analyzed assuming a Gaussian distribution of spherical scatterers using Mie theory. This analysis yields scatterer sizes that are consistent with the diameters of cell nuclei and allows the detection of the larger nuclei of NALM-6 cells compared to those of lymphocytes and granulocytes.

Titanium dioxide nanoparticles impair lung mitochondrial function

Titanium dioxide nanoparticles (TiO(2) NPs) are used in an increasing number of human products such as cosmetics, sunscreen, toothpaste and paints. However, there is clear evidence about effects associated to TiO(2) NPs exposure, which include lung inflammation and tumor formation and these effects are related to reactive oxygen species (ROS) formation. The ROS generation could be attributed to a mitochondrial dysfunction. Even though, it has been shown that TiO(2) NPs exposure can induce some alterations in mitochondria including cytochrome c release to cytosol, change in mitochondrial permeability and decrease of mitochondrial membrane potential (ΔΨ(m)), there is no information about the changes in mitochondrial function induced by TiO(2) NPs. We hypothesized that TiO(2) NPs effects are associated with mitochondrial dysfunction and redox unbalance. To test our hypothesis we isolated mitochondria from lung tissue of rats and exposed them to 10(g TiO(2) NPs (particle size<25nm)/mg protein for 1h. Our results showed that TiO(2) NPs decreases NADH levels and impairs ΔΨ(m) and mitochondrial function accompanied by ROS generation during mitochondrial respiration.

Cellular responses to cobalt-chrome and CP titanium--an in vitro comparison of frameworks for implant-retained oral prostheses

The responses of cell types in peri-implant tissues to cobalt-chrome and titanium were studied in vitro. Cylinders were made from both a cobalt-chrome alloy and commercially pure titanium (length 6 mm, diameter 7.9 mm). Plastic tubes were placed over the cylinders to create cell culture wells, in which human epithelial cells or mouse fibroblasts were cultivated. Cell viability was studied using the Alamar Blue method. The surface structure of two samples of each material was analyzed with optical interferometry. The morphology of cells grown on cylinders of each material was studied with scanning electronic microscopy. Epithelial cells and fibroblasts in the titanium group were more viable than those in the cobalt-chrome group (p = 0.001 and p = 0.000, respectively). The titanium surfaces had a greater height deviation (S(a), p = 0.027) but were less dense (S(ds), p = 0.044) than the cobalt-chrome group. The scanning electronic microscopy revealed no major deviations from normal cell morphology. Within the limitations of the present study, the findings indicate that epithelial cells as well as fibroblasts have a stronger negative response to cobalt-chrome alloy than to titanium. We suggest that these differences can be explained only bythe material per se and not by the minor differences in surface structure. Further and clinical studies are needed to confirm the significance of these findings.

The sense of water in the blowfly Protophormia terraenovae

The gustatory system of the blowfly, Protophormia terraenovae, is a relatively simple biological model for studies on chemosensory input and behavioral output. It appears to have renewed interest as a model for studies on the role of water channels, namely aquaporins or aquaglyceroporins, in water detection. To this end, we investigated the presence of water channels, their role in "water" and "salt" cell responsiveness and the transduction mechanism involved. For the first time our electrophysiological results point to the presence of an aquaglyceroporin in the chemoreceptor membrane of the "water" cell in the blowfly taste chemosensilla whose transduction mechanism ultimately involves an intracellular calcium increase and consequently cell depolarization. This hypothesis is also supported by calcium imaging data following proper stimulation. This mechanism is triggered by "water" cell stimulation with hypotonic solutions and/or solutes such as glycerol which crosses the membrane by way of aquaglyceroporins. Behavioral output indicates that the "sense" of water in blowflies is definitely not dependent on the "water" cell only, but also on the "salt" cell sensitivity. These findings also hypothesize a new role for aquaglyceroporin in spiking cell excitability.

[Morphometric analysis of the differentiation process of hippocampal neurons in vitro]

Neuronal cultures of the central nervous system are widely used to study the molecular mechanisms that rule the differentiation process. These cultures have also been used to evaluate drugs and to develop new therapies. From this we can infer the relevance of performing an extended characterization that involves the main aspects driving such process. To carry out such characterization in the present study we prepared primary cultures from hippocampal cells to study cell identity, development of neuronal processes (dendrites and axons), density of synaptic vesicles and development of growth cones. Using immunofluorescence techniques, specific antibodies and non-immunological probes, we studied the changes experienced by the structures under study during different temporal stages (1-21 days). We observed a major proportion of neurons over glia, normal development of neuronal networks (formed by dendrites and axons), increase in the length of dendrites and axons and establishment of synaptic connections. Synaptic vesicles also showed an increase in their densities as long as the time of the culture progressed. Finally, we studied the morphological changes of the growth cones and observed that those were mostly closed at the beginning of the culture period. As neurons matured we observed an increase in the proportion of open growth cones. This work represents an advance in the morphometric characterization of neuronal cultures, since it gathers the main aspects that outline the neuronal differentiation process. In this study, measurement of these morphological features made possible to establish quantitative markers that will allow establishing more precisely the different stages of neuronal differentiation.

Influence of estradiol analogue on cell growth, morphology and death in esophageal carcinoma cells

2-Methoxyestradiol-bis-sulphamate is a bis-sulphamoylated derivative of the naturally occurring 17-beta-estradiol metabolite namely 2-methoxyestradiol. 2-Methoxyestradiol-bis-sulphamate is regarded as a potential anticancer drug with increased antiproliferative activity when compared to 2-methoxyestradiol. The aim of this pilot in vitro study was to determine the influence of 2-methoxyestradiol-bis-sulphamate on cell growth, morphology and possible induction of certain types of cell death in the SNO esophageal carcinoma cell line. A dose-dependent study (0.2-1.0 microM) was conducted with an exposure time of 24 hours. Data revealed that 2-methoxyestradiol-bis-sulphamate reduced cell numbers statistically significantly to 74% after exposure to 0.4 microM of the drug. Morphological studies including light microscopy demonstrated hallmarks of apoptosis, while fluorescent microscopy revealed both the presence of apoptosis and autophagy as types of cell death being induced in SNO cells after 24 hours of exposure to 0.4 microM 2-methoxyestradiol-bis-sulphamate.

Imaging with total internal reflection fluorescence microscopy for the cell biologist

Total internal reflection fluorescence (TIRF) microscopy can be used in a wide range of cell biological applications, and is particularly well suited to analysis of the localization and dynamics of molecules and events near the plasma membrane. The TIRF excitation field decreases exponentially with distance from the cover slip on which cells are grown. This means that fluorophores close to the cover slip (e.g. within ~100 nm) are selectively illuminated, highlighting events that occur within this region. The advantages of using TIRF include the ability to obtain high-contrast images of fluorophores near the plasma membrane, very low background from the bulk of the cell, reduced cellular photodamage and rapid exposure times. In this Commentary, we discuss the applications of TIRF to the study of cell biology, the physical basis of TIRF, experimental setup and troubleshooting.

Variation in epidermal morphology in human skin at different body sites as measured by reflectance confocal microscopy

Two methods of estimating stratum corneum thickness using reflectance confocal microscopy were examined, and epidermal thickness measurements at multiple body sites were compared. Measurements of stratum corneum thickness were made using the derivative method, which is based on the rate of change of image intensity as a proxy for keratin concentration, and simple visual analysis of confocal images. To compare epidermal thickness we collected 1491 z-axis stacks of confocal images from 10 body sites in 39 subjects. An artefact associated with the imaging process interfered with the derivative method for stratum corneum thickness, and simple visual analysis is to be preferred. Although some epidermal properties varied by site, the most striking finding was the degree of within-site variation, which accounted for between 50% and 74% of the total variation observed. The majority of this variation was not due to measurement error, and represents genuine topographical irregularity. This fine-scale variation limits the ease of use of reflectance confocal microscopy for quantitative studies of the epidermis and stratum corneum.

Microtubule dynamics analysis using kymographs and variable-rate particle filters

Studying intracellular dynamics is of fundamental importance for understanding healthy life at the molecular level and for developing drugs to target disease processes. One of the key technologies to enable this research is the automated tracking and motion analysis of these objects in microscopy image sequences. To make better use of the spatiotemporal information than common frame-by-frame tracking methods, two alternative approaches have recently been proposed, based upon either Bayesian estimation or space-time segmentation. In this paper, we propose to combine the power of both approaches, and develop a new probabilistic method to segment the traces of the moving objects in kymograph representations of the image data. It is based on variable-rate particle filtering and uses multiscale trend analysis of the extracted traces to estimate the relevant kinematic parameters. Experiments on realistic synthetically generated images as well as on real biological image data demonstrate the improved potential of the new method for the analysis of microtubule dynamics in vitro.