Convenient one-step approach based on stimuli-responsive sol-gel transition properties to directly build chitosan-alginate core-shell beads

Polysaccharide-based sustainable hydrogel spheres for controlled release of agricultural inputs

Producing food in quantity and quality to meet the growing population demand is a challenge for the coming years. In addition to the need to improve the use and efficiency of conventional agricultural inputs, we face climate change and disparity in access to food. In this context, creating innovative, efficient, and ecologically approaches is necessary to transform this global scenario. Several delivery systems are being developed to encapsulate agrochemicals, aiming to improve the controlled release of active ingredients and protect them against environmental biotic and abiotic factors. Among these systems, hydrogel spheres are particularly notable for their ability to be fabricated from biodegradable materials, allowing the encapsulation of molecules, nanomaterials, and even organisms (e.g., bacteria and fungi). This review provides an overview of the latest progress in developing polysaccharide-based hydrogel spheres for agriculture. In addition, we describe methods for preparing hydrogel spheres and discuss the encapsulation and release of agricultural inputs in the field. Finally, we put hydrogel spheres into perspective and seek to highlight some current challenges in the field to spark new inspiration and improve the development of environmentally friendly and cost-effective delivery systems for the agricultural sector.

Alginate functionalized sugarcane cellulose-based beads to improve methylene blue adsorption from aqueous solution

The study was carried out with the goal of synthesizing composite bead of cellulose, chitosan functionalized by sodium alginate using as an efficient and applicable adsorbent for methylene blue removal. Fabricating parameters of the material synthesis process like cellulose mass, sodium hydroxide concentration, immersing time and sodium alginate concentration were assessed in detail. The dye adsorption performance in water under the influence of pH, contact time, dye initial concentration, the material mass, shaking speed, temperature was also thoroughly evaluated. The results of advanced analyses showed that the beads were successfully synthesized with a rough surface and mesoporous structure. The adsorption isotherm and adsorption kinetics of dye adsorption process exhibited that the process was consistent with the Freundlich adsorption isotherm and the pseudo-second-order kinetic model, indicating a favorable physical adsorption process with multilayer of the dye on the adsorbent surface. The intra-particle diffusion model showed the strong dye adsorption by the beads occurred during the first two and half hours. The adsorbent could maintain its adsorption performance of 86 % for three times of regeneration. Finally, this study provided a recyclable and effective adsorbent for dyes separation from water.

Compressive elasticity of epoxy functionalized Chitosan-based semi-IPN cryobeads of N-alkyl methacrylate esters: Validity of the Hertzian model with experiments

In situ forming poly(dimethylaminoethyl methacrylate-co-glycidylmethacrylate)/Chitosan, P(DMAEMA-co-GMA)/Chitosan, (PDG/CS) cryobeads based on "dropwise freezing into cryogenic liquid method" combined with "blending with polymer method" are promising for applications due to their pH-responsiveness and stability under physiological conditions. Based on classical contact mechanics, Hertzian elasticity of semi-interpenetrated network (semi-IPN) cryobeads was analyzed to examine whether there is a direct correlation between elastic properties of single particle and its macroscopic behavior. A one-step procedure has been proposed to design chitosan-interpenetrated cryobeads with a cationic nature via combination of structural properties as well as functionality of chitosan containing primary and secondary hydroxyl and amino groups. The study is focused on characterization of network formation kinetics in different shapes and how different production variables affect the elasticity/swelling performance of cross-linked system. The elastic properties of semi-IPN cryobeads were improved by both adding chitosan to copolymer PDG structure and lowering the gelation temperature to cryogelation conditions. The results obtained highlighted the importance of composition to modulate elasticity, the influence of preparation temperature and shape of cryobeads on their elasticity. Findings regarding the topography-dependent local elastic properties of chitosan-incorporated semi-IPN gels offer possibilities for modulating the behavior of chitosan-based soft materials.

Recent studies on proteins and polysaccharides-based pH-responsive fluorescent materials

Polymer-based pH-responsive fluorescent materials have the characteristics of fast response, real-time monitoring, visualisation, and easy forming. Consequently, they have attracted widespread attention in wound healing, sweat monitoring, security and anti-counterfeiting, freshness detection of aquatic products, metal-ion sensing and bioimaging. This paper analyses the preparation principles and characteristics of pH-responsive fluorescent materials based on cellulose, chitosan and proteins. It then outlines the fluorescence properties, environmental response mechanisms and applications of various luminescent materials. Next, the research indicates that amines, N-heterocyclic rings, carboxyl groups and amino plasmonic groups on the fluorescent molecule structure and polymer skeleton appear to change the degree of ionisation under acid or alkali stimulation, which affects the light absorption ability of chromophore electrons, thus producing fluorescence changes in fluorescent materials under different pH stimuli. On this basis, the challenges and growth encountered in the development of proteins and polysaccharides-based pH-responsive fluorescent materials were prospected to provide theoretical references and technical support for constructing pH-responsive fluorescent materials with high stability, high sensitivity, long-lasting pH-response and wide detection range.

Rationally designed chitosan-interpenetrated cryobeads functionalized with polyacrylamide chains: Comparative analysis by Hertzian model and rubber elasticity

Optimization of the synthesis of polymer microspheres and millimeter-sized gel beads has gained importance due to efficiency and design advantages in applications. A systematic study is presented to allow for a molecular-based understanding of elasticity of crosslinked-chitosan (CS) beads. Unique results were obtained examining the effect of polymerization temperature and gel-preparation form on physico-mechanical properties of CS-incorporated poly (N-isopropylacrylamide‑sodium acrylate)/polyacrylamide, PNIPA/PAAm-CS, beads. ATR-FTIR, and thermogravimetric analysis results confirmed the successful preparation and enhanced thermal stability of CS-based gel beads in the form of semi-IPN. The structural changes of semi-IPN gels were studied based on powder X-ray diffraction analysis. After being incorporated with CS, the cryopolymerization was carried out under cryo-conditions, and PNIPA/PAAm structure became much more resistant to mechanical load. Addition of CS to semi-IPN structure caused a 2-fold increase in compressive elastic modulus, while the gel preparation under cryoconditions also improved the mechanical properties considerably by lowering the polymerization temperature. The scaling parameter calculations estimated by Hertz model for PNIPA/PAAm-CS semi-IPN cryobeads are related to displacement of compression force with an exponent of 1.63 ± 0.19. As cryobead diameter increased, swelling degree tendency increased, while a decrease in modulus was observed with increasing swelling. The presence of CS in semi-IPNs improved pH-response in an acidic environment, but stiffness of CS reduced the shrinkage ability of cryobeads upon increasing swelling temperature. Based on the interaction between semi-IPN structure and salt solutions, an improvement in elastic modulus was observed in various ammonium salts and sodium tripolyphosphate solution. On-off switching of cryobeads was a reversible process that was consistent with changes in ammonium salt concentration. Qualitative comparisons with experimental results showed that the prepared cryobeads can be designed as drug release carriers by ionic strength-switching modulation.

Application of Sol–Gels for Treatment of Gynaecological Conditions—Physiological Perspectives and Emerging Concepts in Intravaginal Drug Delivery

Approaches for effective and sustained drug delivery to the female reproductive tract (FRT) for treating a range of gynaecological conditions remain limited. The development of versatile delivery platforms, such as soluble gels (sol–gels) coupled with applicators/devices, holds considerable therapeutic potential for gynaecological conditions. Sol–gel systems, which undergo solution-to-gel transition, triggered by physiological conditions such as changes in temperature, pH, or ion composition, offer advantages of both solution- and gel-based drug formulations. Furthermore, they have potential to be used as a suitable drug delivery vehicle for other novel drug formulations, including micro- and nano-particulate systems, enabling the delivery of drug molecules of diverse physicochemical character. We provide an anatomical and physiological perspective of the significant challenges and opportunities in attaining optimal drug delivery to the upper and lower FRT. Discussion then focuses on attributes of sol–gels that can vastly improve the treatment of gynaecological conditions. The review concludes by showcasing recent advances in vaginal formulation design, and proposes novel formulation strategies enabling the infusion of a wide range of therapeutics into sol–gels, paving the way for patient-friendly treatment regimens for acute and chronic FRT-related conditions such as bacterial/viral infection control (e.g., STDs), contraception, hormone replacement therapy (HRT), infertility, and cancer.

The Layered Encapsulation of Vitamin B2 and β-Carotene in Multilayer Alginate/Chitosan Gel Microspheres: Improving the Bioaccessibility of Vitamin B2 and β-Carotene

This research underlines the potential of alginate multilayered gel microspheres for the layered encapsulation and the simultaneous delivery of vitamin B₂ (VB) and β-carotene (BC). Chitosan was used to improve the stability and controlled release ability of alginate-based gel microspheres. It was shown that a clear multilayered structure possessed the characteristics of pH response, and excellent thermal stability. The sodium alginate concentration and the number of layers had notable effects on mechanical properties and particle size of gel microspheres. Fourier-transform infrared spectroscopy and X-ray diffraction analyses further proved that VB and BC were encapsulated within the gel microspheres. Compared with the three-layer VB-loaded gel microspheres, the total release of VB from the three-layer VB and BC-loaded gel decreased from 93.23% to 85.58%. The total release of BC from the three-layer VB and BC-loaded gel increased from 66.11% to 69.24% compared with three-layer BC-loaded gel. The simultaneous encapsulation of VB and BC in multilayered gel microspheres can markedly improve their bioaccessibility and bioavailability. These results showed the multilayer gel microspheres synthesized herein have potential for applications in the layered encapsulation and simultaneous delivery of various bioactive substances to the intestinal tract.

Ultrasonic Synthesis of Nanochitosan and Its Size Effects on Turbidity Removal and Dealkalization in Wastewater Treatment

A detailed study on the synthesis of chitosan nanoparticles under ultrasonication is reported in this paper. By using this simple technique, chitosan particles in nanometer range can be easily prepared without using any harmful and expensive chemicals. The results show that increasing the ultrasonic irradiation time and ultrasonic wave amplitude are the key factors for producing discrete chitosan nanoparticles with narrow particle size distribution. The resulting nanoparticles show superior turbidity removal efficiency (75.4%) and dealkalization (58.3%) in wastewater treatment than the bulk chitosan solid (35.4% and 11.1%, respectively), thus offering an eco-friendly and promising approach for treating wastewater via the coagulation/flocculation process.

Alginate-based delivery systems for food bioactive ingredients: An overview of recent advances and future trends

Due to its advantagessuch as ionic crosslinking, pH responsiveness, excellent biocompatibility, biodegradability and low price, alginate has become one of the most important natural polysaccharides extensively used in constructing desired delivery systems for food bioactive ingredients. In this review, the fundamental knowledge of alginate as a building block for construction of nutraceutical delivery systems is introduced. Then, various types of alginate-based nutraceutical delivery systems are classified and summarized. Furthermore, the future trends of alginate-based delivery systems are highlighted. Currently, alginate-based delivery systems include hydrogel, emulsion, emulsion-filled alginate hydrogel, nanoparticle, microparticle, core-shell particle, liposome, edible film, and aerogel. Although alginate has been widely used in the fabrication of food bioactive ingredient delivery systems, further efforts and improvements are still needed. For this purpose, the future perspectives of alginate-based delivery systems are discussed. The feasible research trends of alginate-based delivery systems include the development of novel large-scale commercial preparation technology, multifunctional delivery system based on alginate, alginate oligosaccharide-based delivery system and alginate-based oleogel. Overall, the objective of this review is to provide useful guidance for rational design and application of alginate-based nutraceutical delivery systems in the future.

Electrostatic Interaction-Based Fabrication of Calcium Alginate-Zein Core-Shell Microcapsules of Regulable Shapes and Sizes

Core-shell microcapsules with combined features of hydrophilicity and hydrophobicity have become much popular. However, the assembly of biocompatible and edible materials in hydrophilic-hydrophobic core-shell microcapsules is not easy. In this work, based on electrostatic interactions, we prepared controllable calcium alginate (ALG)-zein core-shell particles of different shapes and sizes using hydrophilic ALG and hydrophobic zein by a two-step extrusion method. Negatively charged hydrogel beads of spherical, ellipsoidal, or fibrous shape were added into a positively charged zein solution (dissolved in 70% (v/v) aqueous ethanol solution) to achieve different-shaped core-shell particles. Interestingly, the size, shape, and shell thickness of the particles can be regulated by the needle diameter, stirring speed, and zein concentration. Moreover, for simplification, the core-shell particles were also synthesized by a one-step extrusion method, in which an ALG solution was added dropwise into a 70% (v/v) aqueous ethanol solution containing zein and CaCl₂. The particles synthesized in this work showed controlled digestion of encapsulated medium-chain triglyceride (MCT) and sustained release of encapsulated thiamine and ethyl maltol. Our preparation method is simplistic and can be extended to fabricate a variety of hydrophilic and hydrophobic core-shell structures to encapsulate a broad spectrum of materials.

A double-layer hydrogel based on alginate-carboxymethyl cellulose and synthetic polymer as sustained drug delivery system

A new double-layer, pH-sensitive, composite hydrogel sustained-release system based on polysaccharides and synthetic polymers with combined functions of different inner/outer hydrogels was prepared. The polysaccharides inner core based on sodium alginate (SA) and carboxymethyl cellulose (CMC), was formed by physical crosslinking with pH-sensitive property. The synthetic polymer out-layer with enhanced stability was introduced by chemical crosslinking to eliminate the expansion of inner core and the diffusion of inner content. The physicochemical structure of the double-layer hydrogels was characterized. The drug-release results demonstrated that the sustained-release effect of the hydrogels for different model drugs could be regulated by changing the composition or thickness of the hydrogel layer. The significant sustained-release effect for BSA and indomethacin indicated that the bilayer hydrogel can be developed into a novel sustained delivery system for bioactive substance or drugs with potential applications in drugs and functional foods.

Chitosan/carbon nanotube hybrids: recent progress and achievements for industrial applications

This review focuses on the state-of-the-art of the recent research development on chitosan/CNT nanomaterials in biomedicine, (bio)sensors, and pollution management.

Effective passivation of lead by phosphate solubilizing bacteria capsules containing tricalcium phosphate

Phosphate solubilizing bacteria (PSBs) shows high potential to be used for lead passivation in sediments due to the abilities of releasing phosphate and the subsequent formation of insoluble Pb-phosphate compounds. In this research, microbial capsules implemented with sodium alginate and CaCl₂, containing Leclercia adecarboxylata L15 (a lead resistant PSB) and Ca₃(PO₄)₂, were developed and the performance on lead passivation under different conditions was examined. The optimal concentrations of sodium alginate and CaCl₂ for formulating the capsules were determined to be 0.3% and 10%, respectively. The removal efficiency of Pb²⁺ by capsules containing L15 and Ca₃(PO₄)₂ was up to 98% with a capsule dosage of 2%, initial Pb²⁺ concentration of 1mM and pH of 3.0, which was better than that of free L15 (18%) and capsules containing only L15 (34%). Lead was immobilized via the formation of Pb₅(PO₄)₃Cl on the surface and Pb₃(PO₄)₂ in the interior of the capsules. The simulated sediment remediation experiments showed that the acid soluble fraction of lead reduced from 28% to 14% and transformed into more stable fractions after 10 days. The experiment results indicated that PSBs capsules coupled with phosphate materials have a great promise for application in remediation of lead contaminated sediments.

Ionotropic Gelation Synthesis of Chitosan-Alginate Nanodisks for Delivery System and In Vitro Assessment of Prostate Cancer Cytotoxicity

We report on the synthesis of chitosan-alginate nanodisks (Cs-Al NDs) using a simple approach consisting of the ionotropic gelation method. Sodium tripolyphosphate (STPP) was used as crosslinking agent to promote the electrostatic interaction between amine groups the chitosan and hydroxyl and carboxyl groups of alginate. Scanning electron microscopy (SEM) images provided direct evidence of the morphology of the nanodisks where agglomeration was observed due to the electrostatic interaction between the functional groups. Furthermore, dynamic light scattering (DLS) showed that the hydrodynamic size of the Cs-Al NDs was 227 nm and 152 nm in pH 1.2 and pH 7.4, respectively, which is in agreement with the information observed in the SEM images. The chemical structure is presented mainly the amine and carboxyl groups due to the presence of chitosan and alginate in the nanodisks, respectively, which allow the electrostatic interaction through N-H linkages. According to the X-ray diffraction, we found that the Cs-Al NDs exhibited the typical structure of chitosan and alginate, which lead the formation of polyelectrolyte complexes. We also evaluated the encapsulation of amoxicillin in the nanodisk, obtaining a loading efficiency of 74.98%, as well as a maximum in vitro release amount of 63.2 and 52.3% at pH 1.2 and 7.4, respectively. Finally, the cytotoxicity effect of the Cs-Al nanodisks was performed in human prostatic epithelial PWR-1E and Caucasian prostate adenocarcinoma PC-3 cell lines, in which the cell viability was above 80% indicating low inhibition and determining the Cs-Al NDs as a promising technology for controlled delivery systems.

All-Natural Food-Grade Hydrophilic-Hydrophobic Core-Shell Microparticles: Facile Fabrication Based on Gel-Network-Restricted Antisolvent Method

Hydrophilic-hydrophobic core-shell microparticles are highly appealing for a variety of industrial applications (foods, pharmaceutics, cosmetics, biomedicines, etc.) owing to their unique properties of moisture resistance and controlled release. However, the fabrication of such structured microparticles proves to be nontrivial due to the difficulty in assembling two materials of distinctly different hydrophilicities and hydrophobicities. This paper reports a facile method to fabricate hydrophilic-hydrophobic core-shell microparticles using all-natural food-grade polysaccharides and proteins, based on a novel principle of gel-network-restricted antisolvent precipitation. Immersion of microgel beads prepared from hydrophilic polysaccharides (i.e., alginates, κ-carrageenan, agarose) into a hydrophobic protein solution (i.e., zein in 70% aqueous ethanol) enables slow and controllable antisolvent precipitation of a protein layer around the microbead surface, leading to the formation of a hydrophilic-hydrophobic core-shell structure. The method applies to various gelling systems and can easily tailor the particle size and shell thickness. The resulting freeze-dried microparticles demonstrate restricted swelling in water, improved moisture resistance, and sustained release of encapsulants, with great potential in applications such as protection of unstable and/or hygroscopic compounds and delivery and controlled release of drugs, bioactives, flavors, etc. The method is rather universal and can be extended to prepare more versatile core-shell structures using a large variety of hydrophilic and hydrophobic materials.