ATP:Mg2+ shapes condensate properties of rRNA-NPM1 in vitro nucleolus model and its partitioning of ribosomes

Nucleoli have viscoelastic gel-like condensate dynamics that are not well represented in vitro. Nucleoli models, such as those formed by nucleophosmin 1 (NPM1) and ribosomal RNA (rRNA), exhibit condensate dynamics orders of magnitude faster than in vivo nucleoli. Here we show that an interplay between magnesium ions (Mg2+) and ATP governs rRNA dynamics, and this ultimately shapes the physical state of these condensates. Using quantitative fluorescence microscopy, we demonstrate that increased RNA compaction occurs in the condensates at high Mg2+ concentrations, contributing to the slowed RNA dynamics. At Mg2+ concentrations above 7 mM, rRNA is fully arrested and the condensates are gels. Below the critical gel point, NPM1-rRNA droplets age in a temperature-dependent manner, suggesting that condensates are viscoelastic materials, undergoing maturation driven by weak multivalent interactions. ATP addition reverses the dynamic arrest of rRNA, resulting in liquefaction of these gel-like structures. Surprisingly, ATP and Mg2+ both act to increase partitioning of NPM1-proteins as well as rRNA, which influences the partitioning of small client molecules. By contrast, larger ribosomes form a halo around NPM1-rRNA coacervates when Mg2+ concentrations are higher than ATP concentrations. Within cells, ATP levels fluctuate due to biomolecular reactions, and we demonstrate that a dissipative enzymatic reaction can control the biophysical properties of in vitro condensates through depletion of ATP. This enzymatic ATP depletion also reverses the formation of the ribosome halos. Our results illustrate how cells, by changing local ATP concentrations, may regulate the state and client partitioning of RNA-containing condensates such as the nucleolus.

Effects of the Temperature–Time Regime of Curing of Composite Patch on Repair Process Efficiency

Repair procedures with the use of composite patches are considered to be the most effective among the current technologies of repair of the structures of various applications. In the process of moulding-on of a patch made of polymeric composite material by means of curing, technological stresses arise in the patch. Determination of residual technological stresses is a priority task for the modelling of the repair process. Reduction of residual stresses can be achieved by optimization of the mode of repair patch curing. For meeting this objective, the method for determination of technological stresses, which arise in the structure under repair in the process of curing of a composite patch, has been developed. The method takes into account the shrinkage, change in physico-mechanical characteristics, rheological processes occurring in the binder during moulding process, and determination of stresses in the structure under repair at any time. Therefore, premature failure of the repair joint at the stage of repair can be avoided. It is shown that the method adequately describes the level of deformations and stresses in the structure being repaired at the stage of heating and holding of the composite patch. Increase in the moulding temperature leads to a reduction in residual stresses in the structure under repair. However, current stresses at the stages of heating and temperature holding are increased significantly. Reliability of assumptions and developed method is confirmed by the comparison with the experimental data. The obtained experimental graph of total deformation of the composite patch allowed us to clearly determine the moment of residual stress occurrence in the structure under repair. This moment matches quite exactly (with the discrepancy not exceeding 5 min) the gel point determined analytically based on dependence of the degree of curing on the moulding mode. Consequently, the research together with the results previously obtained allows making an integrated choice of geometric parameters of the repair composite patch and temperature–time regime of its curing in order to ensure the specified level of strength and stiffness of the structure under repair.

Rheological Analysis of the Synthesis of High-Molecular-Weight Epoxy Resins from Modified Soybean Oil and Bisphenol A or BPA-Based Epoxy Resins

The research undertaken in this work is one of the examples of the engineering of modern polymer materials. This manuscript presents studies on the gelation process which might occur during the synthesis of epoxy resin using the modified vegetable oil via the epoxy fusion process conducted in bulk. Based on obtained results we determined rheological parameters related to the properties of reacting mixture during the polyaddition process, especially before and after occurring the phenomenon of gelation (via (1) theoretical determination of the gel point using the degree of conversion of reactants before occurring the gelation process of reacting mixture and (2) experimentally—the dynamic mechanical properties such as storage modulus, G′; loss modulus, G″; and loss tangent, tg δ). Theoretical investigations show that for both systems: epoxidized soybean oil and bisphenol A (ESBO_BPA), as well as the hydroxylated soybean oil and low molecular weight epoxy resin (SMEG_EPR), theoretical values of the degree of conversion at the gel point are characterized by similar values (ESBO_BPA: xgel-theoretical = 0.620, xgel-theoretical = 0.620 and SMEG_EPR: xgel-theoretical = 0.614, xgel-experiment = 0.630, respectively), while the one determined based on the initial assumptions are greater than the above-mentioned (ESBO_BPA: xgel-assumed = 0.696 and SMEG_EPR: xgel-assumed = 0.667). Moreover, experimental studies in the viscoelastic fluid stage showed that the SMEG_EPR system is characterized by lower values of G′ and G″, which indicates lower elasticity and lower viscosity than the epoxidized derivative. It was found that alike during the conventional polyaddition reaction, both systems initially are homogeneous liquids of increasing viscosity. Wherein gradual increase in viscosity of the reaction mixture is related to the fusion of oligomer molecules and the formation of higher molecular weight products. In the critical stage of the process, known as the gelation point, the reaction mixture converts into the solid form, containing an insoluble cross-linked polymer.

The Use of the ATD Technique to Measure the Gelation Time of Epoxy Resins

In this paper, we investigated the thermodynamics of the resin curing process, when it was a part of composition with graphite powder and cut carbon fibers, to precisely determine the time and temperature of gelation. The material for the research is a set of commercial epoxy resins with a gelation time not exceeding 100 min. The curing process was characterized for the neat resins and for resins with 10% by weight of flake graphite and cut carbon fibers. The results recorded in the analysis of temperature derivative (ATD) method unequivocally showed that the largest first derivative registered during the test is the gel point of the resin. The innovative approach to measuring the gelation time of resins facilitates the measurements while ensuring the stability of the curing process compared to the normative tests that introduce mechanical interaction. In addition, it was found during the research that the introduction of 10% by weight of carbon particles in the form of graphite and cut carbon fibers rather shortens the gelation time and lowers the temperature peak due to the effective absorption and storage of heat from the cross-linking system. The inhibiting (or accelerating) action of fillers is probably dependent on chemical activity of the cross-linking system.

Long-Term Thermal Aging of Modified Sylgard 184 Formulations

Primarily used as an encapsulant and soft adhesive, Sylgard 184 is an engineered, high-performance silicone polymer that has applications spanning microfluidics, microelectromechanical systems, mechanobiology, and protecting electronic and non-electronic devices and equipment. Despite its ubiquity, there are improvements to be considered, namely, decreasing its gel point at room temperature, understanding volatile gas products upon aging, and determining how material properties change over its lifespan. In this work, these aspects were investigated by incorporating well-defined compounds (the Ashby–Karstedt catalyst and tetrakis (dimethylsiloxy) silane) into Sylgard 184 to make modified formulations. As a result of these additions, the curing time at room temperature was accelerated, which allowed for Sylgard 184 to be useful within a much shorter time frame. Additionally, long-term thermal accelerated aging was performed on Sylgard 184 and its modifications in order to create predictive lifetime models for its volatile gas generation and material properties.

The effect of type and concentration of acid on the characteristics of gelatine from bones of milkfish (Chanos chanos)

Gelatin is derived from the hydrolysis of the animal collagen contained in the bones and skin. Milkfish bones have the potential to be used as raw materials for gelatine production because it is estimated to be 15–20% of the total body weight of the fish. The extraction of gelatine from fish bones is a solution in utilizing the waste of the fish processing industry. Hydrolysis or soaking in an acidic solution against collagen is aimed to eliminate the salt of calcium and other minerals in the cartilage. This research was conducted to determine the influence of acid types and concentration on the milkfish bones gelatine production. This study used a completely randomized factorial design with two factors. The first factor was the type of acid (citric acid, acetic acid, and a mixture of citric and acetic acids), while the second factor was the concentration of acid (5%, 9%, and 13%). The data obtained were analysed using Analysis of Variance (ANOVA) and Duncan Multiple Range Test (DMRT) Advanced test. The results showed that the type and concentration of acid affected the yield, gel strength, viscosity, melting point, and gelling point. The best treatment in this study was extraction using a 9% concentration of citric acid to produce gelatine with a yield of 10.48%, gel strength 283.1 g bloom, viscosity 4.35 cP, melting point 60.1°C, gel point 16.9°C. Identification of gelatine functional groups was carried out on gelatine from the best treatment using FT-IR Spectrophotometer. From the results of FT-IR spectra analysis, it is known that the functional groups present in the sample are – OH, C-O, N-H, C-H, C-N, C=O which are the main functional groups of gelatine. This study showed that the type and concentration of acid affected the characteristics of milkfish bone gelatine

Enhanced Morphological Characterization of Cellulose Nano/Microfibers through Image Skeleton Analysis

The present paper proposes a novel approach for the morphological characterization of cellulose nano and microfibers suspensions (CMF/CNFs) based on the analysis of eroded CMF/CNF microscopy images. This approach offers a detailed morphological characterization and quantification of the micro and nanofibers networks present in the product, which allows the mode of fibrillation associated to the different CMF/CNF extraction conditions to be discerned. This information is needed to control CMF/CNF quality during industrial production. Five cellulose raw materials, from wood and non-wood sources, were subjected to mechanical, enzymatic, and (2,2,6,6-Tetramethylpiperidin-1-yl)oxyl (TEMPO)-mediated oxidative pre-treatments followed by different homogenization sequences to obtain products of different morphologies. Skeleton analysis of microscopy images provided in-depth morphological information of CMF/CNFs that, complemented with aspect ratio information, estimated from gel point data, allowed the quantification of: (i) fibers peeling after mechanical pretreatment; (ii) fibers shortening induced by enzymes, and (iii) CMF/CNF entanglement from TEMPO-mediated oxidation. Being mostly based on optical microscopy and image analysis, the present method is easy to implement at industrial scale as a tool to monitor and control CMF/CNF quality and homogeneity.

Printability Study of a Conductive Polyaniline/Acrylic Formulation for 3D Printing

There is need for developing novel conductive polymers for Digital Light Processing (DLP) 3D printing. In this work, photorheology, in combination with Jacobs working curves, efficaciously predict the printability of polyaniline (PANI)/acrylate formulations with different contents of PANI and photoinitiator. The adjustment of the layer thickness according to cure depth values (Cd) allows printing of most formulations, except those with the highest gel point times determined by photorheology. In the working conditions, the maximum amount of PANI embedded within the resin was ≃3 wt% with a conductivity of 10−5 S cm−1, three orders of magnitude higher than the pure resin. Higher PANI loadings hinder printing quality without improving electrical conductivity. The optimal photoinitiator concentration was found between 6 and 7 wt%. The mechanical properties of the acrylic matrix are maintained in the composites, confirming the viability of these simple, low-cost, conductive composites for applications in flexible electronic devices.

Simplification of gel point characterization of cellulose nano and microfiber suspensions

Nanocellulose is an emerging material that needs to be well characterized to control its performance during industrial applications. Gel point (Øg) is a convenient parameter commonly used to estimate the aspect ratio (AR) of cellulose nano/microfibers (CNFs/CMFs), providing critical information on the nanofiber network. However, its estimation requires many sedimentation experiments, tedious and time consuming. In this study, a simpler and faster technique is presented to estimate Øg, based on one or two sedimentation experiments, reducing the experiments by a factor of at least 2.5. Here, this new methodology is successfully validated by using the Øg of different CNF/CMF hydrogels calculated with the traditional methodology, showing an error lower than 7%. The error in the estimation of the AR is lower than 3% in all cases. Furthermore, the two mathematical models currently used to estimate Øg, the smoothing spline and the quadratic fit, are compared and the mathematical assumptions improved. Graphical abstract