Versatile preparation of spherically and mechanically controllable liquid-core-shell alginate-based bead through interfacial gelation

Preparation of hyaluronic acid-loaded liquid-core hydrogel beads with acceptable mechanical properties and thermal stability

BACKGROUND

Hyaluronic acid liquid-core hydrogel beads (HA-LHB) is a good way for oral intake of HA. However, HA may affect the reaction-diffusion of sodium alginate (SA) and Ca2+ leading to poor mechanical properties, since HA is a polyanionic electrolyte having electrostatic effect and a certain spatial site-blocking effect.

RESULTS

The mechanical properties of HA-LHB were modified from bathing solution, core solution and secondary calcium bath time. The mechanical properties varied with the SA structure and concentration in bathing solution, where SA with high G (guluronic acid) segment compounded with SA with high M (mannuronic acid) segment at a mass ratio of 7:3 with a 11 g kg-1 concentration showed the best mechanical properties. The secondary calcium bath can greatly improve the mechanical properties due to the tight network formed by bidirectional crosslinking, and 15 min reaction reached the plateau if Ca2+ is sufficient. And the mechanical properties were positively correlated with calcium lactate concentration only at <70 g kg-1 in core solution, but the diffusion of Ca2+ was hindered by the tight gel network at higher concentrations. Moreover, the mechanical properties can be maintained during heat treatment, due to the rearrangement of alginate network structure.

CONCLUSION

Our results suggested that the problem of poor mechanical properties of LHB in the presence of high HA concentration can be avoided by process control, which may broaden the development of HA and popping boba market. © 2024 Society of Chemical Industry.

Polyethylenimine Inclusion to Develop Aqueous Alginate-Based Core-Shell Capsules for Biomedical Applications

Aqueous core-shell structures can serve as an efficient approach that allows cells to generate 3D spheroids with in vivo-like cell-to-cell contacts. Here, a novel strategy for fabricating liquid-core-shell capsules is proposed by inverse gelation of alginate (ALG) and layer-by-layer (LbL) coating. We hypothesized that the unique properties of polyethylenimine (PEI) could be utilized to overcome the low structural stability and the limited cell recognition motifs of ALG. In the next step, alginate dialdehyde (ADA) enabled the Schiff-base reaction with free amine groups of PEI to reduce its possible toxic effects. Scanning electron microscopy and light microscopy images proved the formation of spherical hollow capsules with outer diameters of 3.0 ± 0.1 mm for ALG, 3.2 ± 0.1 mm for ALG/PEI, and 4.0 ± 0.2 mm for ALG/PEI/ADA capsules. The effective modulus increased by 3-fold and 5-fold when comparing ALG/PEI/ADA and ALG/PEI to ALG capsules, respectively. Moreover, PEI-coated capsules showed potential antibacterial properties against both Staphylococcus aureus and Escherichia coli, with an apparent inhibition zone. The cell viability results showed that all capsules were cytocompatible (above 75.5%). Cells could proliferate and form spheroids when encapsulated within the ALG/PEI/ADA capsules. Monitoring the spheroid thickness over 5 days of incubation indicated an increasing trend from 39.50 μm after 1 day to 66.86 μm after 5 days. The proposed encapsulation protocol represents a new in vitro platform for developing 3D cell cultivation and can be adapted to fulfill the requirements of various biomedical applications.

The pH-responsiveness carrier of sanxan gel beads crosslinked with CaCl2 to control drug release

Natural polysaccharide-based gel carriers have been widely studied for their potential to provide slow and controlled release. Sanxan is an edible polysaccharide produced by Sphingomonas sanxanigenens. In this study, gel beads were prepared using the extrusion dripping method with sanxan as the carrier material and HCl and CaCl2 as the fixing solution. The molecular structure, texture profile, and microstructure of the bead were analyzed. And the swelling characterization and in vitro release of beads were evaluated. The results of Fourier-transform infrared analysis indicate that Ca2+ was used to create an ionically crosslinked structure of sanxan. Texture analyzer and scanning electron microscope studies showed that the acid‑calcium gel exhibited physical resistance and resilience, as well as a distinct gel pore structure. The swelling, dissolution, and drug release of the beads decreased as the amount of CaCl2 increased. Compared to the control (without CaCl2), the release of sanxan beads when 0.5 CaCl2 was added (sanxan carboxyl/Ca2+, by the number of moles M/M) in the stomach and small intestine release decreased by 40.9 % and 49.5 %, respectively. This study indicates that the fabrication of sanxan-Ca2+ crosslinked gel had sustained release characteristics, indicating that sanxan carriers have great potential for gradual and regulated medication delivery.

Stability improvement of carboxymethyl cellulose/chitosan complex beads by thermal treatment

Carboxymethyl cellulose (CMC) and chitosan (CHI) are two well-known natural polymer derivatives, as such the CMC@CHI complex beads fulfill many requirements for bio-related and safety-required applications. However, poor mechanical properties of CMC@CHI beads hinder their applications. We managed to improve the beads stability by a simple thermal treatment during the bead preparation. The effects of temperature, changing from 25 °C to 75 °C, on the stability of the formed beads were investigated. The morphology, diameter, shell thickness and structure of the beads treated at different temperature were analyzed using SEM, XPS and FTIR. The mechanical test and swelling experiments showed that the thermal treatment enhanced the bead's ability to withstand pressure and swelling. The beads treated at 75 °C showed the best pressure resistance, while the beads treated at 55 °C exhibited the highest swelling capability without losing integrity. This method is convenient to implement, not only improves the stability, but also controls the swelling capacity and mechanical properties of the beads, which are important for their potential applications in adsorption and controlled release. More importantly, this work offered insights on the effects of thermal treatment on the complexation process of the two polysaccharide molecular chains.

Design of Environmentally Friendly Ca-Alginate Beads for Self-Healing Cement-Based Materials

Ca-alginate beads have strong hygroscopicity, which have been used for the self-healing and internal curing of cement-based materials. However, ca-alginate beads in cement will chelate with calcium ions, which decreases the swelling rate of ca-alginate beads in the healing environment and is detrimental to the self-healing of cement-based materials. In this paper, the mechanism and steps for preparing ca-alginate beads with a lower ability to chelate with calcium ions were proposed based on protonation theory. In addition, the molecular structure and the swelling rates in cement filtrate and healing environment of ca-alginate beads prepared by the proposed method were characterized. The results showed that the ca-alginate beads prepared by the proposed method had higher molecular density and a lower ability to chelate with calcium ions. The swelling rate in the healing environment is not decreased. Furthermore, the equilibrium swelling rate in cement filtrate can satisfy the need for internal curing of cement-based materials.

3D hydrogel-based microcapsules as an in vitro model to study tumorigenicity, cell migration and drug resistance

In this work, we analyzed the reliability of alginate-gelatin microcapsules as artificial tumor model. These tumor-like scaffolds are characterized by their composition and stiffness (∼25 kPa), and their capability to restrict -but not hinder- cell migration, proliferation and release from confinement. Hydrogel-based microcapsules were initially utilized to detect differences in mechano-sensitivity between MCF7 and MDA-MB-231 breast cancer cells, and the endothelial cell line EA.hy926. Additionally, we used RNA-seq and transcriptomic methods to determine how the culture strategy (i.e. 2D v/s 3D) may pre-set the expression of genes involved in multidrug resistance, being then validated by performing cytotoxicological tests and assays of cell morphology. Our results show that both breast cancer cells can generate elongated multicellular spheroids inside the microcapsules, prior being released (mimicking intravasation stages), a behavior which was not observed in endothelial cells. Further, we demonstrate that cells isolated from 3D scaffolds show resistance to cisplatin, a process which seems to be strongly influenced by mechanical stress, instead of hypoxia. We finally discuss the role played by aneuploidy in malignancy and resistance to anticancer drugs, based on the increased number of polynucleated cells found within these microcapsules. Overall, our outcomes demonstrate that alginate-gelatin microcapsules represent a simple, yet very accurate tumor-like model, enabling us to mimic the most relevant malignant hints described in vivo, suggesting that confinement and mechanical stress need to be considered when studying pathogenicity and drug resistance of cancer cells in vitro. STATEMENT OF SIGNIFICANCE: In this work, we analyzed the reliability of alginate-gelatin microcapsules as an artificial tumor model. These scaffolds are characterized by their composition, elastic properties, and their ability to restrict cell migration, proliferation, and release from confinement. Our results demonstrate four novel outcomes: (i) studying cell migration and proliferation in 3D enabled discrimination between malignant and non-pathogenic cells, (ii) studying the cell morphology of cancer aggregates entrapped in alginate-gelatin microcapsules enabled determination of malignancy degree in vitro, (iii) determination that confinement and mechanical stress, instead of hypoxia, are required to generate clones resistant to anticancer drugs (i.e. cisplatin), and (iv) evidence that resistance to anticancer drugs could be due to the presence of polynucleated cells localized inside polymer-based artificial tumors.

Reducing synthetic colorants release from alginate-based liquid-core beads with a zein shell

An innovative method to reduce hydrophilic synthetic colorant release at interface was presented in this work, based on the anti-solvent effect at the membrane outside surface of liquid-core beads manufactured by reverse spherification between alginate and calcium ion. Zein, a hydrophobic protein which formed precipitation shell ensured the stability of colorant. Acidification of solvent made zein particles more kinetically stable, allowed zein stretching and collated more orderly secondary structures even in high polarity solvents. Colorants that hydrogen bonded or electrostatically interacted with zein could have optimized release properties. The zein/erythrosine samples had the most orderly secondary structure from circular dichroism and had the highest stability among all zein/colorant systems. The release rate of erythrosine was only 2.76% after 48 h storage after soaking in zein shell solution. This study demonstrated a promising clean and scalable strategy to encapsulate hydrophilic compounds in zein-based shells of liquid-core beads for food, supplement and pharmaceutical applications.

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.

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.