Rheological and textural analysis as tools for investigation of drug-polymer and polymer–polymer interactions on the example of low-acyl gellan gum and mesalazine

Purpose. In the performed study, the rheological and textural parameters of gellan-based hydrogels were investigated and their dependence on three factors was taken into consideration: ( i) The presence of the model drug, ( ii) The presence and type of the ionic crosslinking agent, and ( iii) the composition of the polymer network. The objective was to compare two analytical methods, regarded as complementary, and define to what extent the obtained results correlate with each other. Methods. The hydrogels contained low-acyl gellan gum or its mixtures with hydroxyethyl cellulose or κ-carrageenan. CaCl2 and MgCl2 were used as gelling agents. Mesalazine was used as a model drug. The rheological analysis included oscillatory stress and frequency sweeping. The texture profile analysis was performed to calculate texture parameters. Results. Placebo gels without the addition of gelling agents had the weakest structure. The drug had the strongest ability to increase the stiffness of the polymer network. The weakest structure revealed the placebo samples without the addition of gelling agents. Texture analysis revealed no significant influence of the drug on the strength of the gels, while rheological measurements indicated clear differences. Conclusions. It can be concluded that in the case of some parameters methods correlate, that is, the effect related to gelling ions. However, the rheological analysis seems to be more precise and sensitive to some changes in the mechanical properties of the gels.

Alginates –A Seaweed product: Its Properties and Applications

Alginates are natural polysaccharides available as seaweed products. They possess several properties due to their molecular structure made of bipolymeric α-L-Guluronic acid and β-D-Mannuronic acid polymers. Alginates have several properties such as film-forming ability, pH responsiveness, and gelling, hydrophilicity, biocompatibility, biodegradability, non-toxic, processability and ionic crosslinking. They’re commonly used in several industries, including food, pharmaceuticals, dental applications, welding rods and scaffolding. Due to their gelling and non-toxic properties, as well as their abundance in nature, the cosmetics and healthcare industries have shown a great deal of interest in biodegradable polymers in general and alginates particularly over the last few decades.

A thermogelling organic-inorganic hybrid hydrogel with excellent printability, shape fidelity and cytocompatibility for 3D bioprinting

Alginates are the most commonly used bioink in biofabrication, but their rheological profiles makes it very challenging to perform real 3D printing. In this study, an advanced hybrid hydrogel ink was developed, a mixture of thermogelling diblock copolymer, alginate and clay i.e. Laponite XLG. The reversible thermogelling and shear thinning properties of the diblock copolymer in the ink system improves handling and 3D printability significantly. Various three-dimensional constructs, including suspended filaments, were printed successfully with high shape fidelity and excellent stackability. Subsequent ionic crosslinking of alginate fixates the printed scaffolds, while the diblock copolymer is washed out of the structure, acting as a fugitive material on the (macro)molecular level. Finally, cell-laden printing and culture over 21 days demonstrated good cytocompatibility and feasibility of the novel hybrid hydrogels for 3D bioprinting. We believe that the developed material could be interesting for a wide range of bioprinting applications including tissue engineering and drug screening, potentially enabling also other biological bioinks such as collagen, hyaluronic acid, decellularized extracellular matrix or cellulose based bioinks.

Crosslinking Strategies for the Microfluidic Production of Microgels

This article provides a systematic review of the crosslinking strategies used to produce microgel particles in microfluidic chips. Various ionic crosslinking methods for the gelation of charged polymers are discussed, including external gelation via crosslinkers dissolved or dispersed in the oil phase; internal gelation methods using crosslinkers added to the dispersed phase in their non-active forms, such as chelating agents, photo-acid generators, sparingly soluble or slowly hydrolyzing compounds, and methods involving competitive ligand exchange; rapid mixing of polymer and crosslinking streams; and merging polymer and crosslinker droplets. Covalent crosslinking methods using enzymatic oxidation of modified biopolymers, photo-polymerization of crosslinkable monomers or polymers, and thiol-ene “click” reactions are also discussed, as well as methods based on the sol−gel transitions of stimuli responsive polymers triggered by pH or temperature change. In addition to homogeneous microgel particles, the production of structurally heterogeneous particles such as composite hydrogel particles entrapping droplet interface bilayers, core−shell particles, organoids, and Janus particles are also discussed. Microfluidics offers the ability to precisely tune the chemical composition, size, shape, surface morphology, and internal structure of microgels by bringing multiple fluid streams in contact in a highly controlled fashion using versatile channel geometries and flow configurations, and allowing for controlled crosslinking.

Recent Advances in Chemically-Modified and Hybrid Carrageenan-Based Platforms for Drug Delivery, Wound Healing, and Tissue Engineering

Recently, many studies have focused on carrageenan-based hydrogels for biomedical applications thanks to their intrinsic properties, including biodegradability, biocompatibility, resembling native glycosaminoglycans, antioxidants, antitumor, immunomodulatory, and anticoagulant properties. They can easily change to three-dimensional hydrogels using a simple ionic crosslinking process. However, there are some limitations, including the uncontrollable exchange of ions and the formation of a brittle hydrogel, which can be overcome via simple chemical modifications of polymer networks to form chemically crosslinked hydrogels with significant mechanical properties and a controlled degradation rate. Additionally, the incorporation of various types of nanoparticles and polymer networks into carrageenan hydrogels has resulted in the formation of hybrid platforms with significant mechanical, chemical and biological properties, making them suitable biomaterials for drug delivery (DD), tissue engineering (TE), and wound healing applications. Herein, we aim to overview the recent advances in various chemical modification approaches and hybrid carrageenan-based platforms for tissue engineering and drug delivery applications.

REINFORCEMENT EFFECT OF IN SITU DEVELOPED ITACONIC ACID BASED METAL SALT NANO-CRYSTALS IN ACRYLONITRILE-BUTADIENE COPOLYMER

ABSTRACT Itaconic acid has been employed as a special facilitator to construct divalent metal ion based ionic crosslinking framework in the acrylonitrile butadiene rubber matrix. Readily accessible double bonds in itaconic acid could directly react with the elastomer to form effective covalent bonds. On the other hand, presence of easily dissociable protons in itaconic acid enables them to form ionic bonds that leads to an increase in crosslinking density of the vulcanizates. The synergistic effect of covalent crosslinking induced by peroxide and ionic crosslinking induced by metal carboxylate could effectively enhance the overall mechanical and dynamic mechanical properties of the rubber composites. In this study, three metal oxides, that is, zinc oxide, magnesium oxide, and calcium oxide, have been selected for this purpose. Tensile strength of nitrile rubber composites depends on the strength of ionic crosslinks, which in turn is influenced by the size of the alkaline earth metals, such as Mg, Ca, etc., and stoichiometric quantity of itaconic acid, which is at par in the formulation of this study. The novelty of this study is that the introduction of a dicarboxylic acid in combination with metal oxides enhances the crosslink density and tensile strength of nitrile rubber composites which could result from the metal organic framework.

Crosslinking Strategies for Microfluidic Production of Microgels

This article provides a systematic review of the crosslinking strategies used to produce microgel particles in microfluidic chips. Various ionic crosslinking methods for gelation of charged pol-ymers are discussed, including external gelation via crosslinkers dissolved or dispersed in the oil phase, internal gelation methods using crosslinkers added to the dispersed phase in their non-active forms, such as chelating agents, photo-acid generators, sparingly soluble or slowly hydrolyzing compounds, and methods involving competitive ligand exchange, rapid mixing of polymer and crosslinking streams, and merging polymer and crosslinker droplets. Covalent crosslinking methods using enzymatic oxidation of modified biopolymers, photo-polymerization of crosslinkable monomers or polymers, and thiol-ene “click” reactions are also discussed, as well as the methods based on sol-gel transitions of stimuli responsive polymers triggered by pH or temperature change. In addition to homogeneous microgel particles, the production of structurally heterogeneous particles such as composite hydrogel particles entrapping droplet interface bi-layers, core-shell particles, organoids, and Janus particles are also discussed. Microfluidics offers the ability to precisely tune chemical composition, size, shape, surface morphology, and internal structure of microgels by bringing in contact multiple fluid streams in a highly controlled fashion using versatile channel geometries and flow configurations and allowing controlled crosslinking.