Dynamic Structural Change of Plant Epidermal Cell Walls under Strain.

The molecular foundations of epidermal cell wall mechanics are critical for understanding structure-function relationships of primary cell walls in plants and facilitating the design of bioinspired materials. To uncover the molecular mechanisms regulating the high extensibility and strength of the cell wall, the onion epidermal wall is stretched uniaxially to various strains and cell wall structures from mesoscale to atomic scale are characterized. Upon longitudinal stretching to high strain, epidermal walls contract in the transverse direction, resulting in a reduced area. Atomic force microscopy shows that cellulose microfibrils exhibit orientation-dependent rearrangements at high strains: longitudinal microfibrils are straightened out and become highly ordered, while transverse microfibrils curve and kink. Small-angle X-ray scattering detects a 7.4 nm spacing aligned along the stretch direction at high strain, which is attributed to distances between individual cellulose microfibrils. Furthermore, wide-angle X-ray scattering reveals a widening of (004) lattice spacing and contraction of (200) lattice spacing in longitudinally aligned cellulose microfibrils at high strain, which implies longitudinal stretching of the cellulose crystal. These findings provide molecular insights into the ability of the wall to bear additional load after yielding: the aggregation of longitudinal microfibrils impedes sliding and enables further stretching of the cellulose to bear increased loads.

Community and shotgun metagenomic analysis of Alligator mississippiensis oral cavity and GI tracts reveal complex ecosystems and potential reservoirs of antibiotic resistance.

We report here the community structure and functional analysis of the microbiome of the Alligator mississippiensis GI tract from the oral cavity through the entirety of the digestive tract. Although many vertebrate microbiomes have been studied in recent years, the archosaur microbiome has only been given cursory attention. In the oral cavity we used amplicon-based community analysis to examine the structure of the oral microbiome during alligator development. We found a community that diversified over time and showed many of the hallmarks we would expect of a stable oral community. This is a bit surprising given the rapid turnover of alligator teeth but suggests that the stable gumline microbes are able to rapidly colonize the emerging teeth. As we move down the digestive tract, we were able to use both long and short read sequencing approaches to evaluate the community using a shotgun metagenomics approach. Long read sequencing was applied to samples from the stomach/duodenum, and the colorectal region, revealing a fairly uniform and low complexity community made up primarily of proteobacteria at the top of the gut and much more diversity in the colon. We used deep short read sequencing to further interrogate this colorectal community. The two sequencing approaches were concordant with respect to community structure but substantially more detail was available in the short read data, in spite of high levels of host DNA contamination. Using both approaches we were able to show that the colorectal community is a potential reservoir for antibiotic resistance, human pathogens such as Clostridiodes difficile and a possible source of novel antimicrobials or other useful secondary metabolites.

Creating cross-linked lamellar block copolymer supporting layers for biomimetic membranes.

The long-standing goal in membrane development is creating materials with superior transport properties, including both high flux and high selectivity. These properties are common in biological membranes, and thus mimicking nature is a promising strategy towards improved membrane design. In previous studies, we have shown that artificial water channels can have excellent water transport abilities that are comparable to biological water channel proteins, aquaporins. In this study, we propose a strategy for incorporation of artificial channels that mimic biological channels into stable polymeric membranes. Specifically, we synthesized an amphiphilic triblock copolymer, poly(isoprene)-block-poly(ethylene oxide)-block-poly(isoprene), which is a high molecular weight synthetic analog of naturally occurring lipids in terms of its self-assembled structure. This polymer was used to build stacked membranes composed of self-assembled lamellae. The resulting membranes resemble layers of natural lipid bilayers in living systems, but with superior mechanical properties suitable for real-world applications. The procedures used to synthesize the triblock copolymer resulted in membranes with increased stability due to the crosslinkability of the hydrophobic domains. Furthermore, the introduction of bridging hydrophilic domains leads to the preservation of the stacked membrane structure when the membrane is in contact with water, something that is challenging for diblock lamellae that tend to swell, and delaminate in aqueous solutions. This new method of membrane fabrication offers a practical model for making channel-based biomimetic membranes, which may lead to technological applications in reverse osmosis, nanofiltration, and ultrafiltration membranes.

Comparison of a gelatin thrombin versus a modified absorbable polymer as a unique treatment for severe hepatic hemorrhage in swine.

There are many surgical techniques (packing, Pringle maneuver, etc.) and hemostatic agents to manage hepatic bleeding in trauma surgery. This study compares the effectiveness of two different types of hemostatic agents, one is an active flowable hemostat and the other is a passive hemostat made of modified absorbable polymers [MAP]. Both surgical technique and hemostatic agents can be used together as a means of controlling bleeding. We have hypothesized that a single hemostatic agent might be as effective as a unique hemostatic surgical technique. Twenty swine were prospectively randomized to receive either active Flowable (Floseal) or passive MAP powder (PerClot) hemostatic agents. We used a novel severe liver injury model that caused exsanguinating hemorrhage. The main outcome measure was total blood loss volume. The total volume of blood loss, from hepatic injury to minute 120, was significantly lower in the Flowable group (407.5 cm3; IqR: 195.0-805.0 cm3) compared to MAP group (1107.5 cm3; IqR: 822.5 to 1544.5 cm3) (Hodges-Lehmann median difference: - 645.0 cm3; 95% CI: - 1144.0 to - 280.0 cm3; p = 0.0087). The rate of blood loss was significantly lower in the flowable group compared with the MAP group as measured from time of injury to minutes 3, 9, 12, and 120 (except for 6 min). The mean arterial pressure gradually recovered in the flowable group by 24 h, whereas in the MAP group, the mean arterial pressure was consistently stayed below baseline values. Kaplan-Meier survival analysis indicated similar rates of death between study groups (Logrank test p = 0.3395). Both the flowable and the MAP hemostatic agents were able to effectively control surgical bleeding in a novel severe liver injury model, however, the flowable gelatin-thrombin agent provided quicker and better bleed control.

Grazing-incidence diffraction reveals cellulose and pectin organization in hydrated plant primary cell wall.

The primary cell wall is highly hydrated in its native state, yet many structural studies have been conducted on dried samples. Here, we use grazing-incidence wide-angle X-ray scattering (GIWAXS) with a humidity chamber, which enhances scattering and the signal-to-noise ratio while keeping outer onion epidermal peels hydrated, to examine cell wall properties. GIWAXS of hydrated and dried onion reveals that the cellulose ([Formula: see text]) lattice spacing decreases slightly upon drying, while the (200) lattice parameters are unchanged. Additionally, the ([Formula: see text]) diffraction intensity increases relative to (200). Density functional theory models of hydrated and dry cellulose microfibrils corroborate changes in crystalline properties upon drying. GIWAXS also reveals a peak that we attribute to pectin chain aggregation. We speculate that dehydration perturbs the hydrogen bonding network within cellulose crystals and collapses the pectin network without affecting the lateral distribution of pectin chain aggregates.

An insight into microscopy and analytical techniques for morphological, structural, chemical, and thermal characterization of cellulose.

Cellulose obtained from plants is a bio-polysaccharide and the most abundant organic polymer on earth that has immense household and industrial applications. Hence, the characterization of cellulose is important for determining its appropriate applications. In this article, we review the characterization of cellulose morphology, surface topography using microscopic techniques including optical microscopy, transmission electron microscopy, scanning electron microscopy, and atomic force microscopy. Other physicochemical characteristics like crystallinity, chemical composition, and thermal properties are studied using techniques including X-ray diffraction, Fourier transform infrared, Raman spectroscopy, nuclear magnetic resonance, differential scanning calorimetry, and thermogravimetric analysis. This review may contribute to the development of using cellulose as a low-cost raw material with anticipated physicochemical properties. HIGHLIGHTS: Morphology and surface topography of cellulose structure is characterized using microscopy techniques including optical microscopy, transmission electron microscopy, scanning electron microscopy, and atomic force microscopy. Analytical techniques used for physicochemical characterization of cellulose include X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, nuclear magnetic resonance spectroscopy, differential scanning calorimetry, and thermogravimetric analysis.

Preferred crystallographic orientation of cellulose in plant primary cell walls.

Cellulose, the most abundant biopolymer on earth, is a versatile, energy rich material found in the cell walls of plants, bacteria, algae, and tunicates. It is well established that cellulose is crystalline, although the orientational order of cellulose crystallites normal to the plane of the cell wall has not been characterized. A preferred orientational alignment of cellulose crystals could be an important determinant of the mechanical properties of the cell wall and of cellulose-cellulose and cellulose-matrix interactions. Here, the crystalline structures of cellulose in primary cell walls of onion (Allium cepa), the model eudicot Arabidopsis (Arabidopsis thaliana), and moss (Physcomitrella patens) were examined through grazing incidence wide angle X-ray scattering (GIWAXS). We find that GIWAXS can decouple diffraction from cellulose and epicuticular wax crystals in cell walls. Pole figures constructed from a combination of GIWAXS and X-ray rocking scans reveal that cellulose crystals have a preferred crystallographic orientation with the (200) and (110)/([Formula: see text]) planes preferentially stacked parallel to the cell wall. This orientational ordering of cellulose crystals, termed texturing in materials science, represents a previously unreported measure of cellulose organization and contradicts the predominant hypothesis of twisting of microfibrils in plant primary cell walls.

Dental extractions in patients on antiplatelet therapy. A study conducted by the Oral Health Department of the Navarre Health Service (Spain).

OBJECTIVES: Antiplatelet drugs are used to treat and prevent a wide range of cardiovascular pathologies and/or cerebrovascular accidents. Although the use of anticoagulants in dental extractions is highly protocolized, a clear control method has not yet been established for antiplatelet drugs. This study is directed at evaluating the clinical consequences of extractions in patients on antiplatelet therapy. STUDY DESIGN: The Oral Health Department of the Navarre Health Service-Osasunbidea conducted a trial on 155 patients who underwent dental extractions and were receiving antiplatelet therapy. The patients were not requested to interrupt the medication and local measures were taken to control potential haemorrhage. RESULTS: No major haemorrhages were reported. One patient had a moderate haemorrhage that required emergency care. In the remaining patients the bleeding was controlled with local measures. With regard to subsequent bleeding, no differences were observed between the various antiplatelet drugs used. The only statistically significant relationship found was between bleeding and the number of teeth extracted. CONCLUSIONS: It can be concluded that no more than 3 teeth should be removed at any one time, and for multiple extractions, the teeth should be adjacent to each other.

Biomimetic Separation of Transport and Matrix Functions in Lamellar Block Copolymer Channel-Based Membranes.

Cell membranes control mass, energy, and information flow to and from the cell. In the cell membrane a lipid bilayer serves as the barrier layer, with highly efficient molecular machines, membrane proteins, serving as the transport elements. In this way, highly specialized transport properties are achieved by these composite materials by segregating the matrix function from the transport function using different components. For example, cell membranes containing aquaporin proteins can transport ∼4 billion water molecules per second per aquaporin while rejecting all other molecules including salts, a feat unmatched by any synthetic system, while the impermeable lipid bilayer provides the barrier and matrix properties. True separation of functions between the matrix and the transport elements has been difficult to achieve in conventional solute separation synthetic membranes. In this study, we created membranes with distinct matrix and transport elements through designed coassembly of solvent-stable artificial (peptide-appended pillar[5]arene, PAP5) or natural (gramicidin A) model channels with block copolymers into lamellar multilayered membranes. Self-assembly of a lamellar structure from cross-linkable triblock copolymers was used as a scalable replacement for lipid bilayers, offering better stability and mechanical properties. By coassembly of channel molecules with block copolymers, we were able to synthesize nanofiltration membranes with sharp selectivity profiles as well as uncharged ion exchange membranes exhibiting ion selectivity. The developed method can be used for incorporation of different artificial and biological ion and water channels into synthetic polymer membranes. The strategy reported here could promote the construction of a range of channel-based membranes and sensors with desired properties, such as ion separations, stimuli responsiveness, and high sensitivity.

Simple Polymethylglutarimide Microfluidic Channels With Hydrogel-Assisted Fluid Exchange.

We present an experimental protocol for fabricating enclosed microfluidic channels using polymethylglutarimide (PMGI). PMGI is optically transparent, biocompatible, and can be used to readily fabricate micrometer-scale lateral and vertical dimension channels using conventional photolithography. The low auto-fluorescence intensity of PMGI facilitates imaging of analytes without interference. The hydrophilicity of PMGI allows fluid exchange in micrometer-scale channels using a hydrogel as an interface without an external pump. As a demonstration, we assemble fluorescently-labeled lipid bilayers in PMGI microfluidic channels and show that PMGI has negligible auto-fluorescence intensity compared to the lipid bilayer. PMGI channels together with hydrogel-assisted fluidic exchange provides a simple approach to fabricate micrometer and sub-micrometer scale fluidic channels for optofluidics, molecular biology, and other medical diagnostic and sensing applications.

Resonant soft X-ray scattering reveals cellulose microfibril spacing in plant primary cell walls.

Cellulose microfibrils are crucial for many of the remarkable mechanical properties of primary cell walls. Nevertheless, many structural features of cellulose microfibril organization in cell walls are not yet fully described. Microscopy techniques provide direct visualization of cell wall organization, and quantification of some aspects of wall microstructure is possible through image processing. Complementary to microscopy techniques, scattering yields structural information in reciprocal space over large sample areas. Using the onion epidermal wall as a model system, we introduce resonant soft X-ray scattering (RSoXS) to directly quantify the average interfibril spacing. Tuning the X-ray energy to the calcium L-edge enhances the contrast between cellulose and pectin due to the localization of calcium ions to homogalacturonan in the pectin matrix. As a consequence, RSoXS profiles reveal an average center-to-center distance between cellulose microfibrils or microfibril bundles of about 20 nm.

Dehydration-induced physical strains of cellulose microfibrils in plant cell walls.

The effect of dehydration of plant cell walls on the physical status of cellulose microfibrils (CMFs) interspersed in pectin matrices was studied. Vibrational sum frequency generation (SFG) spectroscopy analysis of cellulose revealed reversible changes in spectral features upon dehydration and rehydration of onion epidermal walls used as a model primary cell wall (PCW). Combined with microscopic imaging and indentation modulus data, such changes could be attributed to local strains in CMFs due to the collapse of the pectin matrix upon dehydration. X-ray diffraction (XRD) showed that the (200) spacing of cellulose in dried PCWs is larger than that of cellulose Iß obtained from tunicates. Thus, the modulus of CMFs in PCWs would be lower than those of highly-crystalline cellulose Iß and inhomogeneous local bending or strain of CMFs could occur readily during the physical collapse of pectin matrix due to dehydration.

Survival of hydroxyapatite-coated cups: acetabular screws involve a lower rate of revision surgery due to aseptic loosening.

BACKGROUND: It is believed that the path of acetabular screws may represent a shuttle between hydroxyapatite (HA) particles and the liner. The aim was to assess the relationship between acetabular screws and revision surgery for aseptic loosening in total hip arthroplasties (THAs). MATERIAL AND METHODS: A retrospective multicentric study was performed. Patients older than 18 years and patients who underwent THA with both the stem and cup HA-coated were included. The rate of revision-surgery considering only aseptic loosening was calculated. The proportion of cases in which acetabular screws were used was registered, as well as the proportion of cups that showed osteolysis. The statistical relationship between acetabular screws and osteolysis, as well as acetabular screws and revision-surgery for aseptic loosening were assessed. RESULTS: There were 749 cases. Mean age 62.1 (45-84) years. Mean follow-up 14.19 (8.9-16.7) years. Revision surgery was performed in 12.8% (96/749) of the cups. 73.95% (71/96) of the revised cups showed aseptic loosening. The overall 15-year survival of the cups considering only aseptic loosening was 84.4%. Acetabular screws were used in 47.5% (356/749) of the cups. Acetabular screws were used in 40.44% (55/136) of the cups that showed osteolysis. The use of acetabular screws was associated with less osteolysis (p = 0.006). Acetabular screws were used in 35.21% (25/71) of the cups that were revised for aseptic loosening. The use of acetabular screws was associated with a lower rate of revision surgery (p = 0.020). CONCLUSIONS: In THA with the stem and cup HA-coated, the use of acetabular screws is associated with a lower rate of revision surgery.

Lithographically defined two- and three-dimensional tissue microarrays.

Traditional methods to study normal and pathological development of tissues have been limited by -difficulties in controlling experimental conditions and quantifying biological processes of interest. Here we describe methods to create microarrays of engineered tissues that enable controlled and quantitative investigations. Using soft lithography-based techniques, extracellular matrix proteins can be microcontact printed or micromolded to make two- and three-dimensional micropatterned scaffolds. The ultimate form and resulting properties of the tissue construct are dictated by the geometry of the patterned extracellular matrix components. This chapter describes elastomeric stamp fabrication, microcontact printing and micromolding of extracellular matrix proteins, cell culture in micropatterned substrata, and quantitative immunofluorescence analysis of micropatterned tissues.