Preparation of Multicore Colloidosomes: Nanoparticle-Assembled Capsules with Adjustable Size, Internal Structure, and Functionalities for Oil Encapsulation

Colloidosomes, also known as Pickering emulsion capsules, have attracted attention for encapsulation of hydrophilic and hydrophobic actives. However, current preparation methods are limited to single core structures and require the use of modified/engineered nanoparticles for forming the shell. Here, we report a fast, simple, and versatile method for producing multi-oil core silica colloidosomes via salt-driven assembly of purely hydrophilic commercial nanoparticles dispersed within an oil-in-water-in-oil (O/W/O) double emulsion template. The internal structure and overall diameter of the capsules can be adjusted by altering the primary and secondary emulsification conditions. With this approach, 7-35 μm diameter multicore colloidosomes containing 0.9-4.2 μm large oil cores were produced. The capsules can easily be functionalized depending on the type of nanoparticles used in the preparation process. Here, metal oxide nanoparticles, such as Fe₃O₄, TiO₂, and ZnO, were successfully incorporated within the structure, conferring specific functional properties (i.e., magnetism and photocatalysis) to the final microcapsules. These capsules can also be ruptured by using ultrasound, enabling easy access to the internal core environments. Therefore, we believe this work offers a promising approach for producing multicore colloidosomes with adjustable structure and functionalities for the encapsulation of hydrophobic actives.

Engineered Multilayer Microcapsules Based on Polysaccharides Nanomaterials

The preparation of microcapsules composed by natural materials have received great attention, as they represent promising systems for the fabrication of micro-containers for controlled loading and release of active compounds, and for other applications. Using polysaccharides as the main materials is receiving increasing interest, as they constitute the main components of the plant cell wall, which represent an ideal platform to mimic for creating biocompatible systems with specific responsive properties. Several researchers have recently described methods for the preparation of microcapsules with various sizes and properties using cell wall polysaccharide nanomaterials. Researchers have focused mostly in using cellulose nanomaterials as structural components in a bio-mimetic approach, as cellulose constitutes the main structural component of the plant cell wall. In this review, we describe the microcapsules systems presented in the literature, focusing on the works where polysaccharide nanomaterials were used as the main structural components. We present the methods and the principles behind the preparation of these systems, and the interactions involved in stabilizing the structures. We show the specific and stimuli-responsive properties of the reported microcapsules, and we describe how these characteristics can be exploited for specific applications.

Enzymatically Disulfide-Crosslinked Chitosan/Hyaluronic Acid Layer-by-Layer Self-Assembled Microcapsules for Redox-Responsive Controlled Release of Protein

Disulfide-crosslinked hollow polyelectrolyte microcapsules composed of thiolated chitosan (CS-SH) and hyaluronic acid (HA-SH) were prepared by combining the layer-by-layer (LBL) technique and horseradish peroxidase (HRP)-mediated oxidative cross-linking reaction in mild conditions. FITC-dextran-doped CaCO₃ microspheres were used as template core and removed after LBL depositing CS-SH and HA-SH on the surface. The disulfide-crosslinked (CS/HA) microcapsules were readily fabricated by HRP-mediated oxidative coupling of the thiol groups in CS/HA shell layer in the presence of HRP (10 units/mL) and Tyramine hydrochloride (Tyr, 35 mmol/L). The kinetics of enzymatic disulfide-crosslinking reaction was investigated through the real-time monitoring of the consumption of thiol groups by UV absorption spectra. It found that the formation of disulfide linkages by the enzymatic thiol oxidation reaction showed a gradual acceleration. The disulfide-crosslinked CS/HA hydrogel were rapidly formed in gelation time between approximately 17 and 30 min, which were dependent on the concentrations of HRP and Tyr. The disulfide linkages endowed the microcapsule-enhanced physical stability and low permeability under physiological conditions and redox-responsive degradability in reducing environments. The structural stability of disulfide-crosslinked (CS/HA) microcapsules was visualized by confocal laser scanning microscopy in phosphate-buffered saline containing 5.0 mmol/L dithiothreitol (DTT) to evaluate the redox-responsive disassembly process. Redox-responsive controlled release of encapsulated FITC-dextran from the disulfide-crosslinked (CS/HA) microcapsules were obtained. The release profiles of FITC-dextran could be manipulated by controlling the shell thickness and the concentration of DTT. The conformational stability analyses and more than 94% esterase activity of released bovine serum albumin (BSA) from (CS/HA) microcapsules conformed that the structural integrity and bioactivity were well preserved during the encapsulation and release process. The microcapsules exhibited excellent cytocompatibility for HEK 293 cells up to a concentration of 1.0 mg/mL. The microcapsules efficiently delivered loaded FITC-BSA into HeLa cells and released the protein in the reducing cytosol. This study proposed a novel approach for producing disulfide-crosslinked microcarriers for intracellular delivery and redox-responsive controlled release of protein.

Hybrid microcapsules with tunable properties via Pickering emulsion templates for the encapsulation of bioactive volatiles

Hybrid microcapsules with tunable properties and low permeability were fabricated via Pickering emulsion templates for the encapsulation of bioactive volatiles.