Immobilization of rhodamine 6G in calcium alginate microcapsules based on aromatic–aromatic interactions with poly(sodium 4-styrenesulfonate)

Transforming the Stability, Encapsulation, and Sustained Release Properties of Calcium Alginate Beads through Gel-Confined Coacervation

Calcium alginate (Ca2+/alginate) gel beads find use in diverse applications, ranging from drug delivery and tissue engineering to bioprocessing, food formulation, and agriculture. Unless modified, however, these gels have limited stability in alkaline media (including phosphate buffers), and their high solute permeability limits their ability to efficiently encapsulate and slowly release water-soluble small molecules. Here, we show how these limitations can be addressed by mixing the alginate solutions used in the bead preparation with the nontoxic anionic polymer polyphosphate (PP). Upon complexing Ca2+ ions, PP undergoes complex coacervation (i.e., liquid/liquid phase separation into a Ca2+/PP-rich coacervate phase and a dilute supernatant phase). At lower PP concentrations, the Ca2+/PP coacervate appears to simply remain dispersed within the beads. Though its presence makes the beads more stable in alkaline media (phosphate-buffered saline and seawater), it has little impact on the bead stiffness, morphology, and (at least in the absence of substantial payload/coacervate association) encapsulation and release properties. When the PP concentrations exceed a critical value, however, Ca2+/PP coacervation within the gelling Ca2+/alginate beads collapses the resulting beads into more compact, interpenetrating polymer networks. Besides their enhanced stability to alkaline environments, these hybrid beads exhibit irregular morphologies with wrinkled and dimpled surface structures and macroscopic (closed) internal pores, and their collapse into these polymer-rich networks also makes them significantly stiffer than their PP-free counterparts. Crucially, these beads also exhibit a much lower solute permeability, which enables highly efficient encapsulation and multiday release of water-soluble small molecules (with the beads encapsulating >90% of the added model payload and sustaining its release over 3-5 d). Collectively, these findings provide a mild and simple (single-step) pathway to generating ionically cross-linked alginate beads with significantly enhanced stability, encapsulation efficiency, and sustained release.

One-Pot Synthesis of Pyrite Nanoplates Supported on Chitosan Hydrochar as Fenton Catalysts for Organics Removal from Water

The Fenton reaction is a powerful method for removing refractory pollutants from water, yet it is restricted by shortcomings such as pH adjustments and generation of iron-containing sludge. In this study, a highly dispersed pyrite nanoplate supported on chitosan hydrochar was prepared through a simple one-pot hydrothermal method. The interactions between chitosan and Fe3+ suppressed the accumulation of FeS2 in the crystal growth period and led to the formation of pyrite nanoplates with many exposed (210) facets. Thus, it showed excellent Fenton-like activity and the removal efficiency of AR 73 reached 99.9% within 60 min. The catalyst could be used in a wide pH range of 3~10. Hydroxyl radicals are the main reactive oxygen species in this catalytic system. The self-reduction of generated Fe(III) species by sulfur via inner electron transfer promoted the Fe(II)/Fe(III) redox cycle, and the presence of graphene facilitated the adsorption of pollutants. This catalyst also showed good reuse performances as well as stability, which has promising prospects for practical use in wastewater treatment.

Alginate beads as a highly versatile test-sample for optoacoustic imaging

Test-samples are necessary for the development of emerging imaging approaches such as optoacoustics (OA); these can be used to benchmark new labeling agents and instrumentation, or to characterize image analysis algorithms or the inversion required to form the three-dimensional reconstructions. Alginate beads (AlBes) loaded with labeled mammalian or bacterial cells provide a method of creating defined structures of controllable size and photophysical characteristics and are well-suited for both in vitro and in vivo use. Here we describe a simple and rapid method for efficient and reproducible production of AlBes with specific characteristics and show three example applications with multispectral OA tomography imaging. We show the advantage of AlBes for studying and eventually improving photo-switching OA imaging approaches. As highly defined, homogeneous, quasi point-like signal sources, AlBes might hold similar advantages for studying other agents, light-fluence models, or the impact of detection geometries on correct image formation in the near future.

Concentration Dependent Single Chain Properties of Poly(sodium 4-styrenesulfonate) Subjected to Aromatic Interactions with Chlorpheniramine Maleate Studied by Diafiltration and Synchrotron-SAXS

The polyelectrolyte poly(sodium 4-styrenesulfonate) undergoes aromatic–aromatic interaction with the drug chlorpheniramine, which acts as an aromatic counterion. In this work, we show that an increase in the concentration in the dilute and semidilute regimes of a complex polyelectrolyte/drug 2:1 produces the increasing confinement of the drug in hydrophobic domains, with implications in single chain thermodynamic behavior. Diafiltration analysis at polymer concentrations between 0.5 and 2.5 mM show an increase in the fraction of the aromatic counterion irreversibly bound to the polyelectrolyte, as well as a decrease in the electrostatic reversible interaction forces with the remaining fraction of drug molecules as the total concentration of the system increases. Synchrotron-SAXS results performed in the semidilute regimes show a fractal chain conformation pattern with a fractal dimension of 1.7, similar to uncharged polymers. Interestingly, static and fractal correlation lengths increase with increasing complex concentration, due to the increase in the amount of the confined drug. Nanoprecipitates are found in the range of 30–40 mM, and macroprecipitates are found at a higher system concentration. A model of molecular complexation between the two species is proposed as the total concentration increases, which involves ion pair formation and aggregation, producing increasingly confined aromatic counterions in hydrophobic domains, as well as a decreasing number of charged polymer segments at the hydrophobic/hydrophilic interphase. All of these features are of pivotal importance to the general knowledge of polyelectrolytes, with implications both in fundamental knowledge and potential technological applications considering aromatic-aromatic binding between aromatic polyelectrolytes and aromatic counterions, such as in the production of pharmaceutical formulations.

Dynamic cross-linking of an alginate-acrylamide tough hydrogel system: time-resolved in situ mapping of gel self-assembly

Hydrogels are a popular class of biomaterial that are used in a number of commercial applications (e.g.; contact lenses, drug delivery, and prophylactics). Alginate-based tough hydrogel systems, interpenetrated with acrylamide, reportedly form both ionic and covalent cross-links, giving rise to their remarkable mechanical properties. In this work, we explore the nature, onset and extent of such hybrid bonding interactions between the complementary networks in a model double-network alginate-acrylamide system, using a host of characterisation techniques (e.g.; FTIR, Raman, UV-vis, and fluorescence spectroscopies), in a time-resolved manner. Further, due to the similarity of bonding effects across many such complementary, interpenetrating hydrogel networks, the broad bonding interactions and mechanisms observed during gelation in this model system, are thought to be commonly replicated across alginate-based and broader double-network hydrogels, where both physical and chemical bonding effects are present. Analytical techniques followed real-time bond formation, environmental changes and re-organisational processes that occurred. Experiments broadly identified two phases of reaction; phase I where covalent interaction and physical entanglements predominate, and; phase II where ionic cross-linking effects are dominant. Contrary to past reports, ionic cross-linking occurred more favourably via mannuronate blocks of the alginate chain, initially. Evolution of such bonding interactions was also correlated with the developing tensile and compressive properties. These structure-property findings provide mechanistic insights and future synthetic intervention routes to manipulate the chemo-physico-mechanical properties of dynamically-forming tough hydrogel structures according to need (i.e.; durability, biocompatibility, adhesion, etc.), allowing expansion to a broader range of more physically and/or environmentally demanding biomaterials applications.

Conjugated Polymer for Voltage-Controlled Release of Molecules

Conjugated polymers are attractive in numerous biological applications because they are flexible, biocompatible, cost-effective, solution-processable, and electronic/ionic conductive. One interesting application is for controllable drug release, and this has been realized previously using organic electronic ion pumps. However, organic electronic ion pumps show high operating voltages and limited transportation efficiency. Here, the first report of low-voltage-controlled molecular release with a novel organic device based on a conjugated polymer poly(3-hexylthiophene) is presented. The releasing rate of molecules can be accurately controlled by the duration of the voltage applied on the device. The use of a handy mobile phone to remotely control the releasing process and its application in delivering an anticancer drug to treat cancer cells are also successfully demonstrated. The working mechanism of the device is attributed to the unique switchable permeability of poly(3-hexylthiophene) in aqueous solutions under a bias voltage that can tune the wettability of poly(3-hexylthiophene) via oxidation or reduction processes. The organic devices are expected to find many promising applications for controllable drug delivery in biological systems.

Dispersion of the Photosensitizer 5,10,15,20-Tetrakis(4-Sulfonatophenyl)-porphyrin by the Amphiphilic Polymer Poly(vinylpirrolidone) in Highly Porous Solid Materials Designed for Photodynamic Therapy

The ability of the amphiphilic and biocompatible poly(vinylpyrrolidone) to avoid self-aggregation of the photosensitizer 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin in aqueous solution in the presence of the biocompatible polycation chitosan, polymer that induces the dye self-aggregation, is shown. This is related to the tendency of the dye to undergo preferential solvation by the amphiphilic polymer. Importantly, the dispersant ability of this polymer is transferred to the solid state. Thus, aerogels made of the biocompatible polymers chitosan and chondroitin sulfate, and containing the photosensitizer dispersed by the amphiphilic polymer have been synthesized. Production of reactive oxygen species by the aerogel containing the amphiphilic polymer was faster than when the polymer was absent, correlating with the relative concentration of dyes dispersed as monomers. The aerogels presented here constitute low cost biocompatible materials bearing a conventional photosensitizer for photodynamic therapy, easy to produce, store, transport, and manage in clinical practice.

Immobilization of hydrophilic low molecular-weight molecules in nanoparticles of chitosan/poly(sodium 4-styrenesulfonate) assisted by aromatic-aromatic interactions

The immobilization of the hydrophilic low molecular-weight cationic molecules rhodamine 6G, methylene blue, and citidine in nanoparticles composed of two opposite charged polyelectrolytes, poly(sodium 4-styrenesulfonate) and chitosan, is studied, and the results correlated with their physicochemical properties. Nanoparticles containing both polyelectrolytes have been synthesized showing hydrodynamic diameters of around 200 nm and tunable zeta potential. It was found that the strength of binding of the cationic molecules to the polyanion bearing charged aromatic groups poly(sodium 4-styrenesulfonate) by means of short-range aromatic-aromatic interactions increases with their hydrophobicity and polarizability, as seen by (1)H NMR and UV-vis spectroscopies, and diafiltration. Consequently, association efficiencies of 45, 21, and 12% have been found for the three molecules, respectively, revealing the different ability of the molecules to be immobilized in the nanoparticles. These results provide a proof of concept on a new strategy of immobilization of hydrophilic low molecular-weight molecules based on aromatic-aromatic interactions between polyelectrolytes and their aromatic counterions.