Polymeric Microcapsules Research Articles

One‐step building of molecularly imprinted polymer microcapsules with multicore structure by Pickering emulsion polymerization

AbstractNovel molecularly imprinted polymer (MIP) microcapsules with multicore structure were prepared through one step Pickering emulsion polymerization combined with the polymerization driven phase separation. Bisphenol A (BPA) is found to play the part of heterogeneous nuclei besides template molecule, which offers opportunity for the building of the multicore structure inside of MIP microcapsules. The internal structure of MIP microcapsules could be regulated by choosing different kinds of template molecules. Rebinding experiments showed that the MIP with multicore structure possessed excellent binding properties toward BPA. The imprinting factor of MIP toward BPA is 1.96. The binding could reach equilibrium within 30 min. The fast rebinding kinetics was attributed to the unique multicore structure which reduced largely the mass transfer resistance of BPA in the MIP.

Polymer Capsules with Tunable Shell Thickness Synthesized via Janus-to-core shell Transition of Biphasic Droplets Produced in a Microfluidic Flow-Focusing Device

Droplet microfluidics has enabled the synthesis of polymeric particles with controlled sizes, shell thickness, and morphologies. Here, we report the Janus to core-shell structural evolution of biphasic droplets formed in a microfluidic flow-focusing device (MFFD) for the synthesis of polymer microcapsules with oil core/thickness-tunable shell via off-chip photo- and thermally induced polymerization. First, nanoliter-sized biphasic Janus droplets comprising an acrylate monomer and silicone oil were generated in a co-flowing aqueous polyvinyl alcohol (PVA) solution in an MFFD on a glass chip. Immediately following their break-off, the produced Janus droplets started to change their geometry from Janus to core-shell structure comprising a single silicone-oil core and an acrylate-monomer shell by the minimization of interfacial energy. Thus, we could produce monodisperse core-shell drops with average diameters of 105–325 μm, coefficient of variation (CV) values of 1.0–4.5%, and shell thickness of 1–67 μm. Subsequently, these drops were synthesized to fabricate polymeric microcapsules with tunable shell thickness via photo- and thermally induced polymerization. By increasing the concentration of the photo- and thermal initiator, we successfully produced thinner and ultra-thin shell (800 nm thickness) microcapsules. The surface structure of resulting particles was smooth in photopolymerization and porous in thermal polymerization.

Inkjet‐Based Technology for Microencapsulation of Gold Nanoparticles within Biocompatible Hydrogels

AbstractHerein, an inkjet‐based technology as a versatile high throughput methodology for the microencapsulation of gold nanoparticles (AuNPs) inside a biocompatible chitosan hydrogel is described. This continuous automated inkjet production approach generates 30 µm diameter polymeric microcapsules and offers a high rate of production and nanoparticle encapsulation efficiency of 14 nm diameter AuNPs, precise control of the microcapsule size, and ease of scale‐up. The hybrid microcapsules demonstrate biocompatible cell‐adhesion properties and resist degradation over a large range of pH, making them particularly relevant for a variety of potential health applications.

Polymer capsules modified with iron oxide nanoparticles as an effective platform for MRI visualization and drug delivery

Efficiency of existing (usually toxic) drugs can be increased substantially with the targeted effect on the site of the disease. A potential platform for the targeted drug delivery can be polymer capsules. This will help reduce side effects on the human body and start treatment at the early stages of the disease. Modification of such capsules with the magnetic nanoparticles allows their visualization using magnetic resonance imaging (MRI). In this study the use of polymer microcapsules modified with iron oxide nanoparticles are employed as contrast agents for T2-weighted magnetic resonance (MR) images, the possibility of their implementation as for drug delivery carriers are discussed. For this, two different types of polymer capsules are synthesized. The results on the spin-spin and spin-lattice relaxivities were obtained.

Quantification of Residual Perfume by Py-GC-MS in Fragrance Encapsulate Polymeric Materials Intended for Biodegradation Tests

Perfume encapsulates are widely used in commercial products to control the kinetic release of odorant molecules, increase storage stability and/or improve deposition on different substrates. In most of the cases, they consist of core-shell polymeric microcapsules that contain fragrance molecules. A current challenge is to design and produce polymeric materials for encapsulation that are both resistant and non-persistent. The selection of such eco-friendly formulations is linked to a deep understanding of the polymeric material used for encapsulation and its biodegradation profile. To collect this information, pure samples of capsule shells are needed. In this article we present an innovative quantification method for residual volatiles based on pyrolysis-GC-MS to enable validation of sample quality prior to further testing. The presented analytical method also led to the development of a robust and comprehensive purification protocol for polymers from commercial samples. Standard techniques are not suited for this kind of measurement due to the non-covalent embedding of volatiles in the 3D structure of the polymers. We demonstrated the confounding impact of residual volatiles on the estimated biodegradability of fragrance encapsulates.

Multinuclear solid-state NMR of complex nitrogen-rich polymeric microcapsules: Weight fractions, spectral editing, component mixing, and persistent radicals

The molecular structure of a crosslinked nitrogen-rich resin made from melamine, urea, and aldehydes, and of microcapsules made from the reactive resin with multiple polymeric components in aqueous dispersion, has been analyzed by 13C, 13C{1H}, 1H–13C, 1H, 13C{14N}, and 15N solid-state NMR without isotopic enrichment. Quantitative 13C NMR spectra of the microcapsules and three precursor materials enable determination of the fractions of different components. Spectral editing of non-protonated carbons by recoupled dipolar dephasing, of CH by dipolar DEPT, and of C–N by 13C{14N} SPIDER resolves peak overlap and helps with peak assignment. It reveals that the N- and O-rich resin “imitates” the spectrum of polysaccharides such as chitin, cellulose, or Ambergum to an astonishing degree. 15N NMR can distinguish melamine from urea and guanazole, NC=O from COO, and primary from secondary amines. Such a comprehensive and quantitative analysis enables prediction of the elemental composition of the resin, to be compared with combustion analysis for validation. It also provides a reliable reference for iterative simulations of 13C NMR spectra from structural models. The conversion from quantitative NMR peak areas of structural components to the weight fractions of interest in industrial practice is derived and demonstrated. Upon microcapsule formation, 15N and 13C NMR consistently show loss of urea and aldehyde and an increase in primary amines while melamine is retained. NMR also made unexpected findings, such as imbedded crystallites in one of the resins, as well as persistent radicals in the microcapsules. The crystallites produce distinct sharp lines and are distinguished from liquid-like components by their strong dipolar couplings, resulting in fast dipolar dephasing. Fast 1H spin–lattice relaxation on the 35-ms time scale and characteristically non-exponential 13C spin–lattice relaxation indicate persistent radicals, confirmed by EPR. Through 1H spin diffusion, the mixing of components on the 5-nm scale was documented.

Polymer microcapsules and microbeads as cell carriers for in vivo biomedical applications.

Polymer microcarriers are being extensively explored as cell delivery vehicles in cell-based therapies and hybrid tissue and organ engineering. Spherical microcarriers are of particular interest due to easy fabrication and injectability. They include microbeads, composed of a porous matrix, and microcapsules, where matrix core is additionally covered with a semipermeable membrane. Microcarriers provide cell containment at implantation site and protect the cells from host immunoresponse, degradation and shear stress. Immobilized cells may be genetically altered to release a specific therapeutic product directly at the target site, eliminating side effects of systemic therapies. Cell microcarriers need to fulfil a number of extremely high standards regarding their biocompatibility, cytocompatibility, immunoisolating capacity, transport, mechanical and chemical properties. To obtain cell microcarriers of specified parameters, a wide variety of polymers, both natural and synthetic, and immobilization methods can be applied. Yet so far, only a few approaches based on cell-laden microcarriers have reached clinical trials. The main issue that still impedes progress of these systems towards clinical application is limited cell survival in vivo. Herein, we review polymer biomaterials and methods used for fabrication of cell microcarriers for in vivo biomedical applications. We describe their key limitations and modifications aiming at improvement of microcarrier in vivo performance. We also present the main applications of polymer cell microcarriers in regenerative medicine, pancreatic islet and hepatocyte transplantation and in the treatment of cancer. Lastly, we outline the main challenges in cell microimmobilization for biomedical purposes, the strategies to overcome these issues and potential future improvements in this area.

Facile fabrication of shell crosslinked microcapsule by visible light induced graft polymerization for enzyme encapsulation.

Immobilization of enzymes can effectively improve their stability, facilitate their recycling and reduce the cost, which is of great significance for the development of highly efficient biocatalysis technology. Here a simple strategy to encapsulate enzymes into polymeric microcapsules fabricated by visible light induced graft polymerization on a removable template was developed. The strategy showed a high degree of enzyme loading and excellent reusability of the immobilized enzyme.

Non-invasive cell counting of adherent, suspended and encapsulated mammalian cells using optical density.

In situ measurement to determine mammalian cell number in a non-invasive, non-destructive and reagent-free manner is needed to enable continuous cell manufacturing. An analytical method is presented for non-invasive cell counting by conducting multiwavelength spectral analysis of mammalian cells achieving a minimal detectable cell count of 62,500 at 295 nm. Light absorbance was insensitive to culture volume, giving an absolute cell count rather than a concentration. The activation state of cells was also considered. The study was extended to quantification within polymeric microcapsules as an advanced substrate for mammalian cell growth in bioreactor formats and resulted in an offset directly correlating with the absorbance maxima of the polymer. These studies provide feasibility for optical density as a simple end point to indirectly quantify mammalian cell number for continuous monitoring of cell cultures.

Autonomous Self-Healing of Electrical Degradation in Dielectric Polymers Using In Situ Electroluminescence

Summary Dielectric polymers are ubiquitous as electrical insulation in electrical power systems and electronic devices. Electrical treeing is typically regarded as an irreversible degradation process of dielectric polymers subjected to high electric stresses, which significantly limits their lifespan and endangers the reliability of electronics and electrical power systems. Here, we report self-healing polymers consisting of microcapsules that are capable of completely restoring the dielectric properties as a direct response to electrical tree degradation. We design the microcapsules with a relatively higher dielectric constant than polymer matrix to guide the propagation of electrical trees. The electroluminescence generated in situ during electrical treeing of polymers triggers crosslinking of the healing agents released from the capsules to repair the electrically damaged areas under ambient conditions. Notably, the breakdown strength of the mended region is largely enhanced upon healing, which was initiated at different locations. The integration of autonomous healing capability into dielectric materials opens new avenues to smart polymers for electronics and energy applications.

Preparation and characterization of vetiver oil encapsulated polymeric microcapsules for sedative and hypnotic activity

In the present work, in view of the medicinal properties of vetiver oil (extracted from the roots of Vetiveria zizanioides L.), we made an attempt to encapsulate vetiver oil in a biocompatible polymeric system made of sodium alginate with gellan gum or karaya gum. Sodium alginate and gellan gum or karaya gum were ionotropically cross-linked to encapsulate vetiver oil. Vetiver oil encapsulations in these microcapsules were 35.92 ± 3.18 % to 78.55 ± 3.35%. Vetiver oil encapsulated microcapsules were of spherically shaped with 656-769 µm mean diameter. This vetiver oil encapsulated microcapsules made of alginate-gellan gum blends were found capable of providing a long release of encapsulated oil, showing the potential for the sustained release application. These microcapsules were analyzed by FTIR, DSC, and SEM, etc. In addition, sedative and hypnotic activities of vetiver oil encapsulated polymeric microcapsules in the male Swiss albino mice were evaluated. The sedative-hypnotic activity of vetiver oil encapsulated polymeric microcapsules in rats was observing the number of crossing and motilities. The results proves that vetiver oil encapsulated polymeric microcapsules decreased motility when compared to the control group.

Trigger efficiency enhancement of polymeric microcapsules for self-healing cementitious materials

In this work, silane coupling agent, [3-(2-Aminoethylamino)propyl]trimethoxysilane (KH792), was applied to improve the trigger efficiency of poly(phenol-formaldehyde) (PPF) microcapsules in the cementitious materials. Two schemes of reaction procedure were proposed based on different chemical reaction mechanism. The chemical structure of surface modified microcapsules was investigated by attenuated total reflection-Fourier transformation infrared spectrometry (ATR-FTIR) and then further proofed by X-ray photoelectron spectroscopy (XPS). The thermal properties and the decomposition temperature of the modified microcapsules were characterized by thermal gravimetric analysis (TGA). The morphology of the surface modified microcapsules and the crack surface of microcapsule-embedded cement paste were observed by environmental scanning electron microscope (ESEM). Finally, the influence of microcapsules incorporation and surface modification on the compressive strength of the self-healing cementitious system was evaluated. It was found that the microcapsules modified with reaction scheme 1 possess significantly higher trigger efficiency in cement matrix (41% for S1-10 sample and 63% for S1-30 sample) than the plain microcapsule (22%) and microcapsules modified with reaction scheme 2 (less than 10%). Although the incorporation of PPF microcapsules has an overall negative effect on the mechanical property of cement matrix, longer reaction time of surface modification could slightly mitigate this impact.

Immobilisation of bifidobacteria in biodegradable food-grade microparticles

The present research features a natural polymer that can be used for immobilisation of bifidobacteria as well as a method of immobilisation. We described a modified method of microencapsulation of probiotics using sodi- um alginate. The experiment studied the effect of encapsulation on probiotic stability and involved an in vitro model of human digestive tract. The test sample of microencapsulated Bifi obacterium bifi um 791 showed a decrease in the activity from 3.0×107 to 2.2×105 CFU/ml in a mouse model with pH 1.2. By contrast, the control sample, unprotected by biodegradable polymer microcapsules, demonstrated a higher death rate of bifidobacteria: from 2.6×108 CFU/ml to 5.0×103 CFU/ml. The control sample demonstrated the same downward trend in in vitro gastrointestinal models with pH values of 4.5, 6.8, 7.2, and 5.8. Because the total plate count fell down to 4.0l g CFU/ml in acidity gradients, the titres of the initial microencapsulated biomass had to be increased up to > 109 CFU/ml. According to the results of scanning electron microscopy, the new type of microcapsules obtained by using a resistant starch had a closed sur- face. Prebiotics increased the resistance of bacteria to low pH and bile salts. Bifidobacteria encapsulated with natural biodegradable polymers proved to be well-tolerated and harmless for mice. The experiment revealed that biodegrad- able polymer microcapsules did not cause any chronic or acute toxicity when administered orally at 2×107 CFU per 1 gram of animal mass. The microcapsules demonstrated neither dermonecrotic properties nor any irritant effect on the ocular mucosa and, thus, can be used for food enforcement.

In Situ Fabrication of Polymeric Microcapsules by Ink-Jet Printing of Emulsions.

Phase separation driven by solvent evaporation of emulsions can be used to create polymeric microcapsules. The combination of emulsion solvent evaporation with ink-jet printing allows the rapid fabrication of polymeric microcapsules at a target location on a surface. The ink is an oil-in-water emulsion containing in the dispersed phase a shell-forming polymer, a core-forming fluid that is a poor solvent for the polymer, and a low-boiling good solvent. After the emulsion is printed onto the substrate, the good solvent evaporates by diffusion through the aqueous phase, and the polymer and the poor solvent phase separate to form microcapsules. The continuous aqueous phase contains polyvinyl alcohol that serves as an emulsifier and a binder of the capsules to the substrate. This method is demonstrated for microcapsules with various shell-forming polymers (polystyrene, poly(methylmethacrylate) and poly(l-lactide)) and core-forming poor solvents (hexadecane and a 4-heptanone/sunflower oil mixture). Cargoes such as fluorescent dyes (Nile Red and tetracyanoquinodimethane) or active ingredients (e.g., the fungicide tebuconazole) can be encapsulated. Uniform microcapsules are obtained by printing emulsions containing monodisperse oil droplets produced in a microfluidic device. We discuss the physical parameters that need to be controlled for the successful fabrication of microcapsules in inkjet printing. The method for rapid, in situ encapsulation could be useful for controlled-release applications such as in agrochemical sprays, fragrances, functional coatings, and topical medicines.

One-step microencapsulation and spraying of pesticide formulations for improved adhesion and sustained release

Aim: To reduce the contamination arising from abuse of commercial pesticide formulations, the coaxial electrospray (CES) method was used for one-step microencapsulation and spraying of pesticides.Methods: After optimisation of process parameters, polymeric microcapsules with different structures were fabricated as the carriers of azoxystrobin (AZS). For the resultant microcapsules, the sustained pesticide release was verified in vitro and the adhesion properties were investigated through a normalised rinsing test.Results: The maximum encapsulation efficiency of the fabricated AZS-loaded microcapsules was 99.14%. Compared to commercial AZS aqueous suspension, the microcapsules fabricated by the CES method exhibited improved sustained release performance of AZS, which could be readily controlled by adjusting the shell thicknesses. Moreover, highly enhanced adhesion performance was observed for the AZS-loaded microcapsules directly sprayed in CES process.Conclusions: The CES process is promising to be applied as a one-step microencapsulation and spraying technology for improving pesticide utilisation and reducing environmental pollution.

Versatile biomanufacturing through stimulus-responsive cell-material feedback.

Small-scale production of biologics has great potential for enhancing the accessibility of biomanufacturing. By exploiting cell-material feedback, we have designed a concise platform to achieve versatile production, analysis and purification of diverse proteins and protein complexes. The core of our technology is a microbial swarmbot, which consists of a stimulus-sensitive polymeric microcapsule encapsulating engineered bacteria. By sensing the confinement, the bacteria undergo programmed partial lysis at a high local density. Conversely, the encapsulating material shrinks responding to the changing chemical environment caused by cell growth, squeezing out the protein products released by bacterial lysis. This platform is then integrated with downstream modules to enable quantification of enzymatic kinetics, purification of diverse proteins, quantitative control of protein interactions and assembly of functional protein complexes and multienzyme metabolic pathways. Our work demonstrates the use of the cell-material feedback to engineer a modular and flexible platform with sophisticated yet well-defined programmed functions.

Synthesis of Polyurethane/Poly(urea-formaldehyde) Double-shelled Microcapsules for Self-healing Anticorrosion Coatings

One-component, catalyst-free self-healing coatings with double-shelled polymer microcapsules have drawn considerable attention due to wide applications. In this work, the synthesis parameters of double-shelled polymer microcapsules and the mechanism of the self-healing process were systematically investigated. Apart from the chemical structure of the microcapsule shell, the shell thickness, the microcapsule size, and the core fraction could affect the self-healing anticorrosion properties. The synthesis parameters were further optimized in terms of the agitation rate, pH, weight ratio of core to shell, and temperature. Under these conditions, the microcapsule shell consisting of a rough surface formed by poly(urea-formaldehyde) and a smooth inner wall by polyurethane was prepared. The size of the microcapsules and core fraction were calculated to be approximately 30 μm and 75%, respectively. The self-healing anticorrosion coating incorporating as-synthesized microcapsules exhibited corrosion resistance in artificially scratched areas, which was further characterized by electrochemical impedance spectroscopy.

Real-Time Imaging of Ammonia Release from Single Live Cells via Liquid Crystal Droplets Immobilized on the Cell Membrane.

Tumor cells exhibit prominent metabolic alterations through which they acclimatize to their stressful microenvironment. These cells have a high rate of glutaminolysis and release ammonia (NH3) as a byproduct, which may function as a diffusible signal among cancer cells and can reveal cellular heterogeneity. E7, a nematic liquid crystal (LC), is doped with 4‐pentyl‐4′‐biphenyl carboxylic acid (PBA) and encapsulated in polymeric microcapsules (P‐E7PBA), which are then immobilized on cells in a microfluidic channel. Normal human umbilical vein endothelial cells (HUVECs) and myeloma, human primary glioblastoma (U87), human colon carcinoma (Caco‐2), and human breast adenocarcinoma (MCF‐7) cells are investigated for the release of NH3. The P‐E7PBA is able to visualize NH3 release from the cell via a radial‐to‐bipolar (R‐B) orientation change, observed through a polarized optical microscope. The various cell lines significantly differ in their response time required for an R‐B change. The mean response times for Caco‐2, U87, and MCF‐7 cells are 277, 155, and 121 s, respectively. NH3 release from a single cell captured in a microwell flow chip shows a similar R‐B change. The P‐E7PBA droplets technology could be applied to other multiple targets by functionalizing LCs with different probes.

Preparation and characterization of polymer microcapsules containing ammonium persulfate with controlled burst release

Microcapsules containing water-soluble ammonium persulfate (APS) cores as gel breakers that offer controlled burst release, are become increasingly important in improving the gel breaking efficiency of fracturing fluids in oil fields. To date, microcapsules with various control slow release behaviors have been thoroughly investigated, but microcapsules with burst release properties are rarely studied. Here, we reported a novel inverse emulsion polymerization method to exploit this new type of microcapsule. The microcapsules were composed of APS cores and stimuli-responsive P(MMA-co-AA) copolymer shells. The microcapsules have spherical structures with diameters of 10 to 16 μm. The encapsulated cores offer controlled burst release from the microcapsules and their beginning time of burst release could be delayed up to 42 h. Moreover, all of the cores could be completely released within 1 h from the microcapsules. The temperature, pH, and salt concentration change could stimulate the release. These novel microcapsules might have promising applications in oil exploration, batteries, monomer polymerization, fiber printing, and grease.

Rigidity-Dependent Placental Cells Uptake of Silk-Based Microcapsules.

Polymeric microcapsules have begun to attract significant interest in biomedical fields. As the interactions between cells and materials are influenced by both cell type and elasticity, silk-based microcapsules are synthesized with desirable mechanical features using layer-by-layer assembly and then the uptake of these microcapsules by BeWo b30 placental cells is investigated. Cellular uptake is enhanced with increasing of elastic modulus of the silk-based microcapsules. More importantly, the distinct microvilli of these cells behaves in a diverse manner when exposed to microcapsules with different mechanical features, including grabbing (rigidity) or random touching (soft) behavior; these factors affect the final uptake. Inspired by oocyte pickup, the grabbing behavior of the microvilli may provide valuable information with which to elucidate the specific characteristics of uptake between cells and man-made particles, particularly in the reproductive system.