Competing Effects of Hydration and Cation Complexation in Single-Chain Alginate

Mechanism Study on the Immobilization of Cu2+/Pb2+ in Aqueous Phase by Mineral Co-Milling-Modified Biochar

A large number of studies have shown that the modification of biochar can greatly improve its adsorption capacity. This study adopts a one-step ball milling technology without solvent medium, using sawdust biochar (600 °C) and attapulgite/diatomaceous earth to prepare MABC10%/MDBC10% (mass ratio: 10% attapulgite/diatomite +90% biochar coabrasive). Characterization experiments show that attapulgite/diatomite was successfully loaded on biochar and has more C/O functional groups and wider adsorption pore sizes. Adsorption kinetics and isotherm experiments show that the adsorption process of MABC10% and MDBC10% on Cu2+/Pb2+ was mainly multilayer chemical adsorption. The adsorption capacities of MABC10% and MDBC10% for Cu2+ were 40.85 and 65.20 mg·L-1, respectively. The adsorption amounts of Pb2+ were 82.63 and 71.32 mg·L-1, respectively. The particle diffusion model shows that the adsorption process was controlled by both the surface adsorption rate limitation and boundary layer diffusion. The higher acidity in the solution will cause part of the negative charges on the surface of attapulgite/diatomite to be neutralized, thereby hindering its adsorption of Cu2+/Pb2+. The presence of coexisting ions did not significantly affect the adsorption performance. Mechanistic studies have shown that pore diffusion, active sites provided by C/O functional groups, electrostatic interactions, and cation exchange are the main mechanisms of MABC10% adsorption of Cu2+/Pb2+. In summary, MABC10% has a significant adsorption synergistic effect compared to MBC. It was an economical and effective adsorbent, and the higher the pH value of the wastewater, the more significant the adsorption effect.

Glyoxal crosslinking of electro-responsive alginate-based hydrogels: Effects on the properties

To improve the features of alginate-based hydrogels in physiological conditions, Ca2+-crosslinked semi-interpenetrated hydrogels formed by poly(3,4-ethylenedioxythiophene):polystyrene sulfonic acid and alginate (PEDOT/Alg) were subjected to a treatment with glyoxal to form a dual ionic/covalent network. The covalent network density was systematically varied by considering different glyoxalization times (tG). The content of Ca2+ was significantly higher for the untreated hydrogel than for the glyoxalized ones, while the properties of the hydrogels were found to largely depend on tG. The porosity and swelling capacity decreased with increasing tG, while the stiffness and electrical conductance retention capacity increased with tG. The potentiodynamic response of the hydrogels notably depended on the amount of conformational restraints introduced by the glyoxal, which is a very short crosslinker. Thus, the re-accommodation of the polymer chains during the cyclic potential scans became more difficult with increasing number of covalent crosslinks. This information was used to improve the performance of untreated PEDOT/Alg as electrochemical sensor of hydrogen peroxide by simply applying a tG of 5 min. Overall, the control of the properties of glyoxalized hydrogels through tG is very advantageous and can be used as an on-demand strategy to improve the performance of such materials depending on the application.

Facile wound dressing replacement: Carbon dots for dissolving alginate hydrogels via competitive complexation

Dissolvable hydrogels have shown great potentials in removing the exudes and alleviating pain during wound dressing replacement. Herein, a series of carbon dots (CDs) composing high complexation ability with Cu²⁺ were prepared for capturing Cu²⁺ from Cu²⁺-alginate hydrogels. CDs were prepared using biocompatible lysine as the main starting material, while ethylenediamine was chosen as the other starting material for its extremely high complexation ability with Cu²⁺. The complexation ability increased with the increasing amount of ethylenediamine, while the cell viability decreased. When the mass ratio of ethylenediamine to lysine in CDs was above 1/4, six-coordinate copper centers could be formed. CD_1/4 at the concentration of 90 mg/mL could dissolve Cu²⁺-alginate hydrogels within 16 min, which was about twice faster than lysine. In vivo results showed the replaced hydrogels could ameliorate hypoxic conditions, alleviate local inflammatory reactions and promote the healing speed of burn wounds. Thus, the above results suggested the competitive complexation of CDs with Cu²⁺ could effectively dissolve Cu²⁺-alginate hydrogels, which have much potential in realizing facile wound dressing replacement.

A review on the synthesis and development of alginate hydrogels for wound therapy

Convenient and low-cost dressings can reduce the difficulty of wound treatment. Alginate gel dressings have the advantages of low cost and safe usage, and they have obvious potential for development in biomedical materials. Alginate gel dressings are currently a research area of great interest owing to their versatility, intelligent, and their application attempts in treating complex wounds. We present a detailed summary of the preparation of alginate hydrogels and a study of their performance improvement. Herein, we summarize the various applications of alginate hydrogels. The research focuses in this area mainly include designing multifunctional dressings for the treatment of various wounds and fabricating specialized dressings to assist physicians in the treatment of complex wounds (TOC). This review gives an outlook for future directions in the field of alginate hydrogel dressings. We hope to attract more research interest and studies in alginate hydrogel dressings, thus contributing to the creation of low-cost and highly effective wound treatment materials.

Swelling of Homogeneous Alginate Gels with Multi-Stimuli Sensitivity

A new two-step method is suggested for the preparation of homogeneous alginate gels. In the first step, alginate chains are weakly bonded by Ca2+ ions in an aqueous solution with a low pH. In the next step, the gel is immersed into a strong solution of CaCl2 to finalize the cross-linking process. Homogeneous alginate gels preserve their integrity in aqueous solutions with a pH ranging from 2 to 7 and ionic strength in the interval from 0 to 0.2 M, at temperatures ranging from room temperature up to 50 °C, and can be used in biomedical applications. The immersion of these gels into aqueous solutions with low pH induces the partial breakage of ionic bonds between chains (treated as gel degradation). This degradation affects the equilibrium and transient swelling of homogeneous alginate gels and makes them sensitive to the history of loading and environmental conditions (pH, ionic strength and temperature of aqueous solutions). As sensitivity to the environmental stimuli is a characteristic feature of polymer networks connected by catch bonds, homogeneous alginate gels may serve as a simple model, mimicking the behavior of more sophisticated structures in living matter.

3D printing of complicated GelMA-coated Alginate/Tri-calcium silicate scaffold for accelerated bone regeneration

Polymer-based composite scaffolds are an attractive class of biomaterials due to their suitable physical and mechanical performance as well as appropriate biological properties. When such composites contain osteoinductive ceramic nanopowders, it is possible, in principle, to stimulate the seeded cells to differentiate into osteoblasts. However, reproducibly fabricating and developing an appropriate niche for cells' activities in three-dimensional (3D) scaffolds remains a challenge using conventional fabrication techniques. Additive manufacturing provides a new strategy for the fabrication of complex 3D structures. Here, an extrusion-based 3D printing method was used to fabricate the Alginate (Alg)/Tri-calcium silicate (C₃S) bone scaffolds. To improve physical and biological attributes, scaffolds were coated with gelatin methacryloyl (GelMA), a biocompatible viscose hydrogel. Conducting a combination of experimental techniques and molecular dynamics simulations, it is found that the composition ratio of Alg/C₃S governs intermolecular interactions among the polymer and ceramic, affecting the product performance. Investigating the effects of various C₃S amounts in the bioinks, the 90/10 composition ratio of Alg/C₃S is known as the optimum content in developed bioinks. Accordingly, the printability of high-viscosity inks is boosted by improved hierarchical interactions among assemblies, which in turn leads to better nanoscale alignment in extruded macroscopic filaments. Conducting multiple tests on specimens, the GelMA-coated Alg/C₃S scaffolds (with a composition ratio of 90/10) were shown to have improved mechanical qualities and cell adhesion, spreading, proliferation, and osteogenic differentiation, compared to the bare scaffolds, making them better candidates for further future research. Overall, the in-silico and in vitro studies of GelMA-coated 3D-printed Alg/C₃S scaffolds open new aspects for biomaterials aimed at the regeneration of large- and complicated-bone defects through modifying the extrusion-based 3D-printed constructs.

How Accurate Is the Egg-Box Model in Describing the Binding of Calcium to Polygalacturonate? A Molecular Dynamics Simulation Study

We performed molecular dynamics (MD) simulations of octameric galacturonate, GalA₈, chains in the presence of Ca²⁺ in a ratio of R = [Ca²⁺]/[GalA] = 0.25 in order to determine to which extent the popular "egg-box model" (EBM) is able to describe the association between Ca²⁺ cations and polygalacturonate (polyGalA) chains. To this aim, we slightly revised the empirical parameters for the interaction between Ca²⁺ and the carboxylate oxygen atoms of GalA units so as to reproduce the experimental Ca²⁺-GalA association constant. We also defined an ad hoc order parameter, referred to as the egg-box score (EBS), that quantifies any deviation of the local coordination geometry of calcium cations with respect to an "ideal" EBM coordination geometry. The results reveal that the local coordination geometry of Ca²⁺ cations bound to polyGalA chains differs from that of the EBM. Moreover, polyGalA chains exhibit significant conformational disorder, and the cross-link angles formed between polyGalA chain axes are broadly distributed. Overall, the present study suggests that the EBM fails to describe accurately the association modes between calcium and polyGalA chains at a molar ratio R of 0.25.

Quantum Chemical Calculation for Intermolecular Interactions of Alginate Dimer-Water Molecules

The abundance of applications of alginates in aqueous surroundings created by their interactions with water is a fascinating area of research. In this paper, computational analysis was used to evaluate the conformation, hydrogen bond network, and stabilities for putative intermolecular interactions between alginate dimers and water molecules. Two structural forms of alginate (alginic acid, alg, and sodium alginate, SA) were evaluated for their interactions with water molecules. The density functional theory (DFT-D3) method at the B3LYP functional and the basis set 6-31++G** was chosen for calculating the data. Hydrogen bonds were formed in the Alg-(H₂O)_n complexes, while the SA-(H₂O)_n complexes showed an increase in Van der Walls interactions and hydrogen bonds. Moreover, in the SA-(H₂O)_n complexes, metal-nonmetal bonds existed between the sodium atom in SA and the oxygen atom in water (Na…O). All computational data in this study demonstrated that alginate dimers and water molecules had moderate to high levels of interaction, giving more stability to their complex structure.