Additive Manufacturing and Physicomechanical Characteristics of PEGDA Hydrogels: Recent Advances and Perspective for Tissue Engineering

In this brief review, we discuss the recent advancements in using poly(ethylene glycol) diacrylate (PEGDA) hydrogels for tissue engineering applications. PEGDA hydrogels are highly attractive in biomedical and biotechnology fields due to their soft and hydrated properties that can replicate living tissues. These hydrogels can be manipulated using light, heat, and cross-linkers to achieve desirable functionalities. Unlike previous reviews that focused solely on material design and fabrication of bioactive hydrogels and their cell viability and interactions with the extracellular matrix (ECM), we compare the traditional bulk photo-crosslinking method with the latest three-dimensional (3D) printing of PEGDA hydrogels. We present detailed evidence combining the physical, chemical, bulk, and localized mechanical characteristics, including their composition, fabrication methods, experimental conditions, and reported mechanical properties of bulk and 3D printed PEGDA hydrogels. Furthermore, we highlight the current state of biomedical applications of 3D PEGDA hydrogels in tissue engineering and organ-on-chip devices over the last 20 years. Finally, we delve into the current obstacles and future possibilities in the field of engineering 3D layer-by-layer (LbL) PEGDA hydrogels for tissue engineering and organ-on-chip devices

Internal states, stress-strain behavior and elasticity in oedometrically compressed model granular materials

International audienceThe behaviour of a model granular material (an assembly of slightly poly-disperse spherical beads, with Hertz-Mindlin elastic and frictional contacts) subjected to one dimensional (oedometric) compressions is studied by DEM simulations. We systematically investigate the influence of the (idealized) packing process on the microstructure and stresses in the initial, weakly confined equilibrium state. Such characteristics as density (ranging from maximally dense to moderately loose), coordination number (which might vary independently of solid fraction, especially in dense systems), fabric and stress anisotropies are monitored in oedometric loading cycles in which the major principal stress varies by up to 5 orders of magnitude. The evolution of the solid fraction (or the void ratio) versus the imposed vertical (principal) stress as observed in the loading and unloading paths, like in the case of isotropic compression [2] and unlike laboratory tests on sands, the behaviour shows only very limited plastic strain and is very nearly reversible in dense samples (which tend nevertheless to lose contacts in a loading cycle if the initial coordination number was large). The irreversibility observed in sands should thus be attributed to plasticity or damage within inter granular contacts. The anisotropy of the microstructure is described by the angular distributions of contacts and forces. It is explicitly linked to the stresses in the loading history, by semi-quantitative relations. One of the important characteristics measured during the compression is the ratio of lateral to controlled ('vertical') stress, K0. We discuss conditions in which K0 might be regarded as constant. We calculate, via a static (matrix) method [1], the complete tensor of elastic moduli, expressing response to very small stress increments about the transversely isotropic equilibrium states along the loading path

A new method for measuring grain displacements in granular materials by X-ray computed tomography

International audienceWe aim to measure the individual grain displacements in a granular material under constant load (creep). X-ray computed tomography imaging provides images of the granular medium microstructure during the experiment, and discrete volumetric image correlation (DV-DIC) [1] allows the determination of the grain individual rigid body motion from the reconstructed tomography images. However, for short-term creep, and time-resolved experiments in general, the sample evolutions can be very quick and occur before the full tomography scan is complete. This constitutes a serious limitation of standard experimental procedures for the investigation of the micromechanics of the creep of granular media at the grain scale. We present a new method for measuring grain displacements, that overcomes the above-mentioned limitation. Indeed, in a granular material, assuming no breakage occurs, each grain undergoes a rigid body motion. Therefore, the displacement field reduces to a set of six degrees of freedom per grain. This suggests that the information contained in a full set of projections (necessary to perform an accurate 3D reconstruction) is excessively redundant for the determination of the grain displacements. Our method requires only few projections of the sample at its current state, thus reducing dramatically the acquisition time. Displacements are estimated from the projections directly, without 3D reconstruction. Our method is formulated as an inverse problem. A forward model based on Beer-Lambert's law is developed to efficiently perform numerical projections. The grain displacements are estimated by fitting the numerical projections to experimental projections of the current state of the sample. We also study the sensitivity of the estimated displacements to image noise, both numerically and through a theoretical model which highlights the influence of the setup parameters on the measurements. The method has been validated and its accuracy assessed against 2D and 3D numerical experiments on virtual microstructures

Knowledge and practices of safe use of pesticides among a group of farmers in Northern Iran

Background: The unsafe use of chemical pesticides, along with the lack of appropriate preventive protocols and equipment may damage the health of users. Objective: To determine the knowledge and practice of the safe use of chemical pesticides by farm workers in northern Iran. Methods: The present cross-sectional study was conducted on 300 farmers in Mazandaran province, in 2017. The data collection instrument was a two-part questionnaire: The first part was concentrated on demographic and agricultural characteristics of the participants; the second part dealt with the farmers' knowledge and practice of the safe use of pesticides. Results: The mean knowledge and practice scores (out of 100) of the participating farmers in the safe use of pesticides were 84.8 (SD 13.5) and 50.8 (13.2), respectively. There was a significant positive correlation (r=0.466, p<0.001) between their knowledge and practice. Wearing protective clothes, while applying pesticides, was among safe practices. Although more than 60 of farmers had a sufficient level of knowledge of the safe use of pesticides, they did not implement their knowledge in practice. There was a significant (p<0.001) association between the education level and knowledge of the safe use of pesticides. Conclusion: There was a significant correlation between knowledge and practices of the safe use of pesticides among farmers in northern Iran. There was a clear know-do gap�al-though the majority of the participants possessed a sufficient level of knowledge of the safe use of pesticides, they did not implement it in practice. © 2019, NIOC Health Organization. All rights reserved

Nanoindentation Response of 3D Printed PEGDA Hydrogels in a Hydrated Environment

Hydrogels are commonly used materials in tissue engineering and organ-on-chip devices. This study investigated the nanomechanical properties of monolithic and multilayered poly(ethylene glycol) diacrylate (PEGDA) hydrogels manufactured using bulk polymerization and layer-by-layer projection lithography processes, respectively. An increase in the number of layers (or reduction in layer thickness) from 1 to 8 and further to 60 results in a reduction in the elastic modulus from 5.53 to 1.69 and further to 0.67 MPa, respectively. It was found that a decrease in the number of layers induces a lower creep index (CIT) in three-dimensional (3D) printed PEGDA hydrogels. This reduction is attributed to mesoscale imperfections that appear as pockets of voids at the interfaces of the multilayered hydrogels attributed to localized regions of unreacted prepolymers, resulting in variations in defect density in the samples examined. An increase in the degree of cross-linking introduced by a higher dosage of ultraviolet (UV) exposure leads to a higher elastic modulus. This implies that the elastic modulus and creep behavior of hydrogels are governed and influenced by the degree of cross-linking and defect density of the layers and interfaces. These findings can guide an optimal manufacturing pathway to obtain the desirable nanomechanical properties in 3D printed PEGDA hydrogels, critical for the performance of living cells and tissues, which can be engineered through control of the fabrication parameters

Monogenic Primary Immunodeficiency Disorder Associated with Common Variable Immunodeficiency and Autoimmunity

Background: Common variable immunodeficiency (CVID) is the most frequent primary immunodeficiency disorder mainly characterized by recurrent bacterial infections besides other immunological defects including loss of or dysfunction of B cells and decreased immunoglobulin levels. In this study, our aim is to evaluate clinical, immunological, and molecular data of patients with a primary clinical diagnosis of CVID and autoimmune phenotype with a confirmed genetic diagnosis. Methods: Among 297 patients with CVID, who were registered in the Iranian Primary Immunodeficiency Registry at Children's Medical Center Hospital in Iran, 83 patients have been genetically examined and 27 patients with autoimmunity and confirmed genetic mutations were selected for analysis. Whole-exome sequencing and confirmatory Sanger sequencing methods were used for the study population. A questionnaire was retrospectively filled for all patients to evaluate demographic, laboratory, clinical, and genetic data. Results: In the 27 studied patients, 11 different genetic defects were identified, and the most common mutated gene was LRBA, reported in 17 (63.0) patients. Two patients (7.7) showed autoimmune complications as the first presentation of immunodeficiency. Eleven patients (40.7) developed one type of autoimmunity, and 16 patients (59.3) progressed to poly-autoimmunity. Most of the patients with mono-autoimmunity (n = 9, 90.0) primarily developed infectious complications, while in patients with poly-autoimmunity, the most common first presentation was enteropathy (n = 6, 37.6). In 13 patients (61.9), the diagnosis of autoimmune disorders preceded the diagnosis of primary immunodeficiency. The most frequent autoimmune manifestations were hematologic (40.7), gastrointestinal (48.1), rheumatologic (25.9), and dermatologic (22.2) disorders. Patients with poly-autoimmunity had lower regulatory T cells than patients with mono-autoimmunity. Conclusion: In our cohort, the diagnosis of autoimmune disorders preceded the diagnosis of primary immunodeficiency in most patients. This association highlights the fact that patients referring with autoimmune manifestations should be evaluated for humoral immunity. © 2020 Georg Thieme Verlag. All rights reserved

All-sky search for long-duration gravitational wave transients with initial LIGO

We present the results of a search for long-duration gravitational wave transients in two sets of data collected by the LIGO Hanford and LIGO Livingston detectors between November 5, 2005 and September 30, 2007, and July 7, 2009 and October 20, 2010, with a total observational time of 283.0 days and 132.9 days, respectively. The search targets gravitational wave transients of duration 10-500 s in a frequency band of 40-1000 Hz, with minimal assumptions about the signal waveform, polarization, source direction, or time of occurrence. All candidate triggers were consistent with the expected background; as a result we set 90% confidence upper limits on the rate of long-duration gravitational wave transients for different types of gravitational wave signals. For signals from black hole accretion disk instabilities, we set upper limits on the source rate density between 3.4×10-5 and 9.4×10-4 Mpc-3 yr-1 at 90% confidence. These are the first results from an all-sky search for unmodeled long-duration transient gravitational waves. © 2016 American Physical Society

All-sky search for long-duration gravitational wave transients with initial LIGO

We present the results of a search for long-duration gravitational wave transients in two sets of data collected by the LIGO Hanford and LIGO Livingston detectors between November 5, 2005 and September 30, 2007, and July 7, 2009 and October 20, 2010, with a total observational time of 283.0 days and 132.9 days, respectively. The search targets gravitational wave transients of duration 10-500 s in a frequency band of 40-1000 Hz, with minimal assumptions about the signal waveform, polarization, source direction, or time of occurrence. All candidate triggers were consistent with the expected background; as a result we set 90% confidence upper limits on the rate of long-duration gravitational wave transients for different types of gravitational wave signals. For signals from black hole accretion disk instabilities, we set upper limits on the source rate density between 3.4×10-5 and 9.4×10-4 Mpc-3 yr-1 at 90% confidence. These are the first results from an all-sky search for unmodeled long-duration transient gravitational waves. © 2016 American Physical Society