Fabrication Of Microcapsules Research Articles

Mechanisms of Forming Hollow Microspheres from Solid Granules

Problems in fabrication of large-size hollow microspheres with specific properties and ideal geometric parameters for inertial confinement fusion and other applications require profound knowledge of their formation processes. In this work, we analyze experimentally and analytically the formation of hollow microspheres from solid spherical granules by high-temperature foaming and formulate the conditions for fabrication of microcapsules with high parameters in high-temperature processes.

Fabrication of Microcapsules by the Combination of Biomass Porous Carbon and Polydopamine for Dual Self-Healing Hydrogels.

Artificial development of smart materials from agricultural waste or food residues is particularly desirable for green chemistry. In this paper, dual-network self-healing hydrogels were successfully fabricated by using functional microcapsules. These microcapsules were established by biomass porous carbon (PC) after recycling of apple residues. Glutaraldehyde (GA) as the healing agent was embedded in the porous carbon, and the outer surface was coated with polydopamine (PDA). After the microcapsules were added, modifying guar gum-type hydrogels were successfully obtained with dual self-healing performance by the combination of a healing agent and metal-ligand coordination. The self-healing efficiency was about 89.9% from the tension test, and the fracture strength was measured as 7.68 MPa. These results not only highlight a new idea for the utilization of apple residues but also provide a new method for the preparation of excellent self-healing hydrogels.

The Search for Ways to Improve the Catalytic Activity of Encapsulated Horseradish Peroxidase

Abstract—We consider a previously proposed method for encapsulation of enzymes, which employs the layer-by-layer adsorption of oppositely charged polyelectrolytes onto composite spherulites (calcium carbonate/protein) followed by dissolution of the calcium carbonate support. The goal of this work is to choose conditions for encapsulation of the enzyme horseradish peroxidase by the method so that the catalytic activity of the encapsulated enzyme would be comparable with that of the soluble one. The steps of the fabrication of polyelectrolyte microcapsules with the studied enzyme have been tested. A protocol for obtaining composite spherulites of the desired size ranging from 2 to 10 µm has been developed. It is shown that the catalytic activity of horseradish peroxidase encapsulated in a microcapsule with a positively charged inner surface of the microcapsule envelope (the inner layer modified by polycation polyallylamine hydrochloride) is significantly higher than that of the enzyme encapsulated in a microcapsule with a negatively charged inner layer (modified by polyanion sodium polystyrene sulfonate). At the support dissolution step, ethylene glycol bis-(β-aminoethyl) tetraacetic acid (EGTA), a decalcifying agent used to dissolve CaCO3 from horseradish peroxidase microcapsules, is significantly less detrimental to enzymes than ethylene diamine tetraacetic acid. The catalytic activity of horseradish peroxidase encapsulated in polyallylamine hydrochloride/sodium polystyrene sulfonate/polyallylamine hydrochloride microcapsules (with positively charged inner surface of the microcapsule envelope) is 60–70% of the activity of the soluble enzyme (in experiments where the calcium-carbonate support of the composite spherulites is dissolved with EGTA).

Comparison of different cationic polymers efficacy in fabrication of alginate multilayer microcapsules

In past decades, alginate-based multilayer microcapsules have been given important attention in various pharmaceutical investigations. Alginate-poly l lysine-alginate (APA) is studied the most. Due to the similarity between the structure of polyethyleneimine (PEI) and poly-L-lysine (PLL) and also lower price of PEI than PLL, this study was conducted to compare the efficacy of linear (LPEI) and branch (BPEI) forms of PEI with PLL as covering layers in fabrication of microcapsules. The microcapsules were fabricated using electrostatic bead generator and their shape/size, surface roughness, mechanical strength, and interlayer interactions were also investigated using optical microscopy, AFM, explosion test and FTIR, respectively. Furthermore, cytotoxicity was evaluated by comparing the two anionic final covering layers alginate (Alg) and sodium cellulose sulphate (NCS) using MTT test. BPEI was excluded from the rest of the study due to its less capacity to strengthen the microcapsules and also the aggregation of the resultant alginate-BPEI-alginate microcapsules, while LPEI showed properties similar to PLL. MTT test also showed that NCS has no superiority over Alg as final covering layer. Therefore, it is concluded that, LPEI could be considered as a more cost effective alternative to PLL and a promising subject for future studies.

Fabrication of silk microcapsules by layer-by-layer desolvation

The procedure to increase shell thickness of multilayer silk microcapsules fabricated by layer-by-layer assembly (LbL assembly) are tedious and time-consuming. To address this, layer-by-layer desolvation (LbL desolvation), a more efficient technique, was developed with PLGA microspheres as sacrificial templates. Due to high efficiency of desolvation in increasing the shell thickness, self-supporting structures were obtained with merely seven silk layers. Permeability of the microcapsules was manipulated with high efficiency as well. Moreover, crosslinking was found to reduce surface charge of the shell. We attributed this to crosslinking-induced conformational change of silk fibroin based on secondary structure analysis. The LbL desolvation technique will facilitate fabrication of multilayer silk microcapsules for biomedical applications.

Microfluidic fabrication of wrinkled protein microcapsules and their nanomechanical properties affected by protein secondary structure

Wrinkled microcapsules have attracted great interest due to their distinguished features, including enhanced adhesion propensity and release profiles. These features could be beneficial for food-related applications and improve the bioavailability of encapsulated compounds by promoting their attachment to epithelium. However, the fabrication of such microcapsules with food-grade materials has been met with limited success. In this study, a facile approach to produce wrinkled microcapsules using a food-grade protein, zein, is proposed. Internal phase separation was used to form zein microcapsules and three acids (phytic acid, citric acid, and succinic acid) were incorporated at two concentration levels (10 mM and 20 mM) to modify the secondary structure of zein in the microcapsules. The results showed that the mechanical properties of the microcapsules, which were characterized by nanoindentation, were greatly dependent on the protein secondary structure, particularly the α-helix structure. The morphology of the microcapsules was evaluated by image analysis. An extensive wrinkle was observed on the surfaces of the microcapsules with high viscoplasticity. Among the three acids used in this study, phytic acid significantly increased the degree of wrinkling and viscoplasticity of the microcapsules. Further characterization with circular dichroism and wide-angle X-ray scattering suggested that a less ordered zein secondary structure was formed in the samples prepared using phytic acid than in those prepared using other acids or without acid, which further supports the hypothesis that the nanomechanical properties and degree of wrinkling are associated with the protein secondary structures.

Fabrication of Protease-Sensitive and Light-Responsive Microcapsules Encompassed with Single Layer of Gold Nanoparticles by Using Self-Assembly Protein of α-Synuclein.

A bioapplicable cargo delivery system requires the following characteristics of biocompatibility, in vivo stability, and selective cargo release at target sites. We introduce herein the microcapsules enclosed with a single-layered shell of gold nanoparticles (AuNPs) mutually connected by an amyloidogenic protein of α-synuclein (αS). The microcapsules were fabricated by producing oil(chloroform)-in-water Pickering emulsions of the αS-encapsulated AuNPs and subsequent molecular engagement of the outlying αS molecules, leading to formidable β-sheet formation in the presence of chloroform. The wrinkled skin of microcapsules obtained after evaporation of the internal chloroform also reflects robustness of the protein-protein interaction, which was experimentally confirmed by their rheological stability. For the emulsions loaded with rhodamine 6G, their dye release was demonstrated to be controlled by proteases. Along with their photothermal activity, the AuNP-containing microcapsules and their proteolyzed fragments were therefore suggested to be capable of eliminating aberrant cells in the protease-activated pathologically affected areas. Orthogonal cargo loading was also achieved by encapsulating both hydrophobic and hydrophilic substances either directly dissolved in chloroform or prepackaged in inverted micelles, respectively. Microcapsule's functionality was further expanded by localizing quantum dots, magnetic nanoparticles, and antibodies inside or on the surface of the microcapsules. Taken together, these multimodal AuNP microcapsules are suggested to be an ideal cargo carrier system, which could be employed in not only biomedical theranostic applications as they exhibit structural robustness, specific targeting, triggered release, and photothermal activity but also sensor development in general.

Microfluidic fabrication of microcapsules tailored for self-healing in cementitious materials

Autonomic self-healing in cement-based infrastructure materials has recently emerged as a promising strategy for extending the service life of concrete infrastructure. Amongst the various self-healing systems being developed, the use of microcapsules has received significant attention partly because of its ease implementation. Up to date, microcapsules for self-healing applications have been mainly manufactured using bulk emulsifications polymerisation techniques. However this methodology raises concerns regarding shell dimensions and interfacial bonding. This study proposes for the first time the fabrication of microcapsules with tailored characteristics for mechanically triggered self-healing action in cement-based composites. For this, a microfluidic device was used to produce a double emulsion template for the formation of microcapsules, containing both aqueous and organic liquid core. In addition, a novel method has been proposed to functionalize the microcapsules' surface with hydrophilic groups in order to increase the interfacial bond with the cementitious host matrix. The core retention was studied using EDX and TGA, and their mechanical triggering was investigated via SEM of the microcapsules embedded in the cement paste. The results demonstrated the capability of microfluidics to produce microcapsules with liquid organic core, thin shell, hydrophilic surface and appropriate fracture strength for use in mechanically triggered self-healing of cementitious materials.

Improving survivability of Lactobacillus plantarum in alginate-chitosan beads reinforced by Na-tripolyphosphate dual cross-linking

In the present study, Lactobacillus plantarum PTCC 1058 was microencapsulated in Alginate-chitosan blended beads based on ionically dual cross-linking by Na-tripolyphosphate (Na-TPP). The homogenous solution of bacteria and alginate was dripped into the gelling bath of calcium chloride. After 30 min hardening, filtrate beads were transferred into the solution of chitosan. Dual cross-linked gel beads were prepared by employing Na-TPP solution to the chitosan coated beads. Morphology, particle size, alginate-chitosan interaction, characterizing the structure of single and dual cross-linked beads were determined by using scanning electron microscopy SEM, FTIR and XRD analysis. FTIR analysis demonstrated fabrication of the Na-tripolyphosphate dual cross-linked microcapsules. X-ray diffractograms revealed less amorphous nature of Ag/Cs/TPP microcapsules compared to Ag/Cs ones. Survivability of probiotics and swelling behavior of microcapsules were also evaluated under simulated gastrointestinal conditions. Based on the results, the highest viability corresponds to the dual cross-linked beads (by only 1.58 ± 0.03 log reduction) compared to single cross-linked alginate (2.26 ± 0.09 log) and chitosan-coated alginate beads (1.78 ± 0.1 log). Thus, the reinforced microcapsules could be suitable for improving the capsule stability in site-specific delivery applications.

Microcapsule Technology for Controlled Growth Factor Release in Musculoskeletal Tissue Engineering.

Tissue engineering strategies have relied on engineered 3-dimensional (3D) scaffolds to provide architectural templates that can mimic the native cell environment. Among the several technologies proposed for the fabrication of 3D scaffold, that can be attractive for stem cell cultivation and differentiation, moulding or bioplotting of hydrogels allow the stratification of layers loaded with cells and with specific additives to obtain a predefined microstructural organization. Particularly with bioplotting technology, living cells, named bio-ink, and additives, such as biopolymer microdevices/nanodevices for the controlled delivery of growth factors or biosignals, can be organized spatially into a predesigned 3D pattern by automated fabrication with computer-aided digital files. The technologies for biopolymer microcarrier/nanocarrier fabrication can be strategic to provide a controlled spatiotemporal delivery of specific biosignals within a microenvironment that can better or faster address the stem cells loaded within it. In this review, some examples of growth factor-controlled delivery by biopolymer microdevices/nanodevices embedded within 3D hydrogel scaffolds will be described, to achieve a bioengineered 3D interactive microenvironment for stem cell differentiation. Conventional and recently proposed technologies for biopolymer microcapsule fabrication for controlled delivery over several days will also be illustrated and critically discussed.

Fabrication of dye-doped liquid crystal microcapsules for electro-stimulated responsive smart textiles

Electrochromic dye-doped liquid crystal microcapsules were prepared via emulsion polymerization and further fabricated into a dye-doped liquid crystal-based smart fabric. The optimal preparation condition of electrochromic dye-doped liquid crystal microcapsules was determined by a serial of designed experiments. Transmission electron microscope images showed that dye-doped liquid crystal microcapsules possessed a spherical core-shell structure with a diameter of about 3 μm. The core loading was around 70 wt% and confirmed by thermogravimetric analysis. The color of fabric coated with dye-doped liquid crystal microcapsules were changed under direct current/voltage due to the Frederick transformation. We found that driving voltages of dye-doped liquid crystal and electrochromic dye-doped liquid crystal microcapsule were below human safety voltage. Whiles, service life of dye-doped liquid crystal was significantly improved after encapsulated by PMMA shell, but without reducing its transmittance.

Fabrication and Release Behavior of Microcapsules with Double-Layered Shell Containing Clove Oil for Antibacterial Applications.

In this study, double-layer polyurethane/poly(urea-formaldehyde) (PU/PUF) shell microcapsules containing clove oil with antibacterial properties were successfully synthesized via in situ and interfacial polymerization reactions in an oil-in-water emulsion. The morphology, core-shell structure, and composition of the microcapsules were investigated systematically. Additionally, the release behaviors of microcapsules synthesized under different reaction parameters were studied. It was found that the release rate of clove oil can be controlled by tuning the amount of PU reactants and the length of PUF deposition time. The release profile fitted well against the Baker-Lonsdale model, which indicates diffusion as the primary release mechanism. Experimental results based on the ASTM E2315 time kill test revealed that the fabricated microcapsules have great antibacterial activities against the marine bacteria Vibrio coralliilyticus, Escherichia coli, Exiguobacterium aestuarii, and marine biofilm-forming bacteria isolated from the on-site contaminated samples, showing their great potential as an eco-friendly solution to replace existing toxic antifouling agent.

Layer-by-layer hollow photosensitizer microcapsule design via a manganese carbonate hard template for photodynamic therapy in cells

Microcapsules fabricated using layer-by-layer self-assembly have unique properties, making them attractive for drug delivery applications. The technique has been improved, allowing the deposition of multiple layers of oppositely charged polyelectrolytes on spherical, colloidal templates. These templates can be decomposed by coating multiple layers, resulting in hollow shells. In this paper, we describe a novel drug delivery system for loading photosensitizer drugs into hollow multilayered microcapsules for photoprocess applications. Manganese carbonate particles were prepared by mixing NH4HCO3 and MnSO4 and performing consecutive polyelectrolyte adsorption processes onto these templates using poly-(sodium 4-styrene sulfonate) and poly-(allylamine hydrocholoride). A photosensitizer was also incorporated into the layers. Hollow spheres were fabricated by removing the cores in the acidic solution. The hollow, multilayered microcapsules were studied by scanning electron microscopy, steady-state, and time-resolved techniques. Their biological activity was evaluated in vitro with cancer cells using a conventional MTT assay. The synthesized CaCO3 microparticles were uniform, non-aggregated, and highly porous spheres. The phthalocyanine derivatives loaded in the microcapsules maintained their photophysical behaviour after encapsulation. The spectroscopic results presented here showed excellent photophysical behaviour of the studied drug. We observed a desirable increase in singlet oxygen production, which is favourable for the PDT protocol. Cell viability after treatment was determined and the proposed microcapsules caused 80% cell death compared to the control. The results demonstrate that photosensitizer adsorption into the CaCO3 microparticle voids together with the layer-by-layer assembly of biopolymers provide a method for the fabrication of biocompatible microcapsules for use as biomaterials.

Fabrication of Protein Microparticles and Microcapsules with Biomolecular Tools

Abstract Microparticles have attracted much attention for medical, analytical and biological applications. Calcium carbonate (CaCO3) templating method with the advantages of having narrow size distribution, controlled morphology and good biocompatibility that has been widely used for the synthesis of various protein-based microparticles. Despite CaCO3 template is biocompatible, most of the conventional methods to create stable protein microparticles are mainly driven by chemical crosslink reagents which may induce potential harmful effect and remains undesirable especially for biomedical or clinical applications. In this article, we demonstrate the fabrication of protein microparticles and microcapsules with an innovative method using biomolecular tools such as enzymes and affinity molecules to trigger the assembling of protein molecules within a porous CaCO3 template followed by a template removal step. We demonstrated the enzyme-assisted fabrication of collagen microparticles triggered by transglutaminase, as well as the affinity-assisted fabrication of BSA-biotin avidin microcapsules triggered by biotin-avidin affinity interaction, respectively. Based on the different protein assemble mechanisms, the collagen microparticles appeared as a solid-structured particles, while the BSA-biotin avidin microcapsules appeared as hollow-structured morphology. The fabrication procedures are simple and robust that allows producing protein microparticles or microcapsules under mild conditions at physiological pH and temperature. In addition, the microparticle morphologies, protein compositions and the assemble mechanisms were studied. Our technology provides a facile approach to design and fabricate protein microparticles and microcapsules that are useful in the area of biomaterials, pharmaceuticals and analytical chemistry.

Microencapsulation of a sunlight-curable silicon-based resin in the presence of polyvinylpyrrolidone

PurposeThe purpose of this investigation is to develop a facile method to encapsulate a sunlight-curable silicone-based resin into a melamine–urea–formaldehyde (MUF) shell in the presence of polyvinylpyrrolidone (PVP) as an emulsifier. These microcapsules can be used in self-healing coating formulations.Design/methodology/approachMUF microcapsules containing a sunlight-curable core (methacryloxypropyl-terminated polydimethylsiloxane, MAT-PDMS) have been fabricated by means of in situ polymerisation of an oil-in-water emulsion using PVP as an efficient and environmentally advantageous stabiliser. The effects of agitation rate and PVP concentration on the microencapsulation process have been investigated using optical microscopy (OM) and scanning electron microscopy (SEM). The chemical structure and thermal stability of the microcapsules have been studied using Fourier transform infrared (FTIR) spectroscopy and thermogravimetric analysis (TGA). The solvent resistance of the microcapsules has been determined as well.FindingsIt has been revealed that the pH of the reaction mixture remained almost constant during the reaction, which simplified the process. It has also been observed that the microencapsulation yield improved and the microcapsules’ surface morphology became smoother when a high PVP content was used. With an increase in stirring rate from 600 to 1,200 rpm, the surface roughness and the average particle size decreased. The mean diameter of the prepared microcapsules ranged from 32.1 to 327.1 µm depending on the synthesis conditions. It was demonstrated that the microcapsules had a high capacity for MAT-PDMS encapsulation (more than 88 Wt.%). The solvent stability of the microcapsules against different polar, semi-polar and non-polar solvents was also evaluated.Research limitations/implicationsThis research is limited to the encapsulation of a hydrophobic and sunlight curable liquid (such as MAT-PDMS) by means of in situ polymerisation of amino resins.Practical implicationsThe results can be used by researchers working on the fabrication of microcapsules for applications such as drugs, electrophoretic inks, electrophoretic displays, intumescent fire-retardant coatings and self-healing materials.Social implicationsIn self-healing coatings, healing agents which can be cured by UV irradiation or sunlight are envisaged attractive because they are catalyst-free, environmentally friendly and relatively inexpensive. PVP is an environmentally friendly emulsifier. The prepared microcapsules can be used in self-healing coatings to help in reducing maintenance costs for buildings and steel structures.Originality/valueThe novel aspect of this work is the development of a sunlight-curable silicone-based resin that was encapsulated in a MUF shell in the presence of PVP. A simple method was used to fabricate MUF microcapsules containing MAT-PDMS without the need to control pH during the reaction. Conventional methods for the preparation of amino resin microcapsules require an intensive and precise pH control to obtain favourable microcapsules. MAT-PDMS can be cured by sunlight and is catalyst-free, environmentally friendly and relatively inexpensive.

Strong Dual-Compartment Microcapsules Loaded with High Cargo Contents.

Compartmentalized microcapsules are useful for the release of multiple cargos in medicine, agriculture, and advanced responsive materials. Although several encapsulation strategies that involve more than one cargo have been proposed, dual- or multicompartment capsules with high cargo loadings and sufficient mechanical stability are rarely reported. Here, we propose a single-step emulsification route for the preparation of strong dual-compartment capsules that can host the main cargo in their core in combination with another liquid cargo stored within their thick shell. Capsules are produced through the polymerization of the middle oil phase of water-oil-water double emulsions made by microfluidics. Compartmentalization results from the phase separation of monomers within the middle phase of the double emulsion. We investigate the effect of such phase separation process on the microstructure and mechanical properties of the capsules and eventually illustrate the potential of this approach by creating thermosensitive capsules with programmable bursting temperature. The large variety of possible mixtures of monomers and cargos that can be added in the oil and aqueous phases of the double emulsion templates makes this encapsulation approach a promising route for the fabrication of robust microcapsules for on-demand release of multiple cargos.

Fabrication of microcapsules containing dual-functional tung oil and properties suitable for self-healing and self-lubricating coatings

Abstract Tung oil-loaded microcapsules with the protection of Poly(urea-formaldehyde) (PUF) shells were prepared by in-situ polymerization method. Microcapsules keep the spherical shape with core content of more than 80.0 wt%. The average diameter was approximately 105 μm. Microcapsules exhibit excellent thermal stability. Dual-functional coatings were prepared by incorporating tung oil-loaded microcapsules into epoxy. Self-healing and self-lubricating function of coatings were realized by the releasing of tung oil from microcapsules under the scarp or wear condition. Tung oil has excellent film-forming property when they contact with oxygen. self-healing anti-corrosion and self-lubricating anti-wear properties were evaluated by salt-immersed corrosion tests and wear tests. Results demonstrated the coatings have an excellent corrosion resistance performance, the corrosion resistance get better as the increasing of microcapsules content. Besides, epoxy coatings demonstrated a favorable self-lubricating performance with the add of microcapsules. The friction coefficient and wear rate were the lowest at the microcapsules content of 10 wt%, there were 17.3% and 78.6% decrease respectively compared to the pure epoxy. The self-healing and self-lubricating mechanism were also discussed.

One-Step Bulk Fabrication of Polymer-Based Microcapsules with Hard-Soft Bilayer Thick Shells.

Microcapsules are important for the protection, transport, and delivery of cargo in a variety of fields but are often too weak to withstand the high mechanical stresses that arise during the preparation and formulation of products. Although thick-shell strong capsules have been developed to circumvent this issue, the microfluidic or multistep methods utilized thus far limit the ease of fabrication and encapsulation throughput. Here, we exploit the phase separation of ternary liquid mixtures to achieve a high-throughput fabrication of strong bilayer microcapsules using a one-step bulk emulsification process. Phase separation is induced by the diffusion of water from the continuous phase into droplets that initially contain a mixture of monomers, cross-linkers, an initiator, and cosolvent γ-butyrolactone. The double emulsions generated via such a phase separation are converted into microcapsules through a polymerization reaction triggered by UV illumination. Surprisingly, the shells of the consolidated capsules exhibit a hard-soft bilayer structure that can be designed to show a resilient eggshell-like fracture behavior. Our method allows for the production of large volumes of microcapsules with such a strong bilayer shell within a time scale of only a few minutes, thus offering an enticing pathway toward the high-throughput fabrication of mechanically robust encapsulation systems.

Fabrication of polyurethane microcapsules with different shapes and their influence on cellular internalization

The shape of particles is recognized as an important parameter to influence their interactions with cells. In this study, spherical and discal polyurethane microcapsules were prepared via an adsorption and crosslinking method on the templates with corresponding shapes in organic solvent. Both types of capsules could be well dispersed in aqueous medium and maintain their original shapes. The internalization behaviors of the microcapsules were investigated by co-incubation with RAW 264.7 and HepG2 cells. Compared with the spherical capsules, the discal microcapsules could be internalized with faster rate and higher amount by both types of cells. Both types of capsules did not show significant cytotoxicity even after co-incubation for 72h at a high ratio of capsule to cell.

Low-Ceiling-Temperature Polymer Microcapsules with Hydrophobic Payloads via Rapid Emulsion-Solvent Evaporation.

We report a microencapsulation procedure based on rapid solvent evaporation to prepare microcapsules with hydrophobic core materials and low-ceiling-temperature polymer shell wall of cyclic poly(phthalaldehyde) (cPPA). We use and compare microfluidic and bulk emulsions. In both methods, rapid solvent evaporation following emulsification resulted in kinetically trapped core-shell microcapsules, whereas slow evaporation resulted in acorn morphology. Through the systematic variation of encapsulation parameters, we found that polymer-to-core weight ratios higher than 1 and polymer concentrations higher than 4.5 wt % in the oil phase were required to obtain a core-shell structure. This microencapsulation procedure enabled the fabrication of microcapsules with high core loading, controlled size, morphology, and stability. This procedure is versatile, allowing for the encapsulation of other hydrophobic core materials, i.e., mineral oil and organotin catalyst, or using an alternative low-ceiling-temperature polymer shell wall, poly(vinyl tert-butyl carbonate sulfone).