Polymer Capsules Research Articles

Tunable morphologies of polymer capsules templated from cuprous oxide particles for control over cell association

Over the past two decades, layer-by-layer (LbL) assembly of micro/nanocapsules has been of interest for the investigation of bio-nano interactions to explore bio-applications, such as drug delivery. The choice of an appropriate template that can be easily dissolved under mild conditions is one of the challenges for the assembly of LbL capsules. Herein, we report the engineering of LbL capsules with tunable morphologies using cuprous oxide (Cu2O) particles as templates. Cu2O particles with cubic, tetradecahedral or spherical morphologies were synthesized via hydrothermal processes, which can be dissolved under mild condition (e.g., sodium thiosulfate solution). The influence of capsule morphologies on cell association was investigated, which indicates that LbL capsules with cubic geometry promoted cell association up to 4 and 9-fold than tetradecahedral and spherical capsules, respectively. The reported method provides a new avenue for the assembly of LbL capsules with different morphologies, which has the potential for better understanding of biological interactions of LbL capsules.

Degradable Protein-loaded Polymer Capsules Fabricated by Thiol-disulfide Cross-linking Reaction at Liquid-liquid Interface

In these years, the encapsulation of proteins for protection and delivery purpose has attracted great interest. In this research, W/O emulsion droplets were used as soft templates and bovine serum albumin (BSA) encapsulated hollow capsules were prepared by liquid-liquid interfacial thiol-disulfide exchange reaction. Block copolymer chains with pendant pyridyl disulfide groups are located at liquid-liquid interface, and upon addition of a macromolecular crosslinking agent with multiple pendant thiol groups into an emulsion, thiol-disulfide interfacial crosslinking reactions lead to the formation of BSA encapsulated hollow capsules. The cleavage of disulfides on the membranes results in the degradation of hollow structures and the release of encapsulated protein molecules. Transmission electron microscopy, scanning electron microscopy, atomic force microscopy, and confocal laser scanning microscopy were employed to characterize the hollow capsules. In comparison with native BSA, BSA molecules encapsulated in the hollow structures show higher catalytic efficiency due to higher local concentration of reactants in the structures. The membranes of the hollow capsules can efficiently protect the encapsulated BSA from hydrolysis by trypsin.

Hybrids of Polymeric Capsules, Lipids, and Nanoparticles: Thermodynamics and Temperature Rise at the Nanoscale and Emerging Applications.

The importance of thermodynamics does not need to be emphasized. Indeed, elevated temperature processes govern not only industrial scale production but also self-assembly, chemical reaction, interaction between molecules, etc. Not surprisingly, biological processes typically take place at a specific temperature. Here, we look at possibilities to raise the localized temperature by a laser around noble-metal nanoparticles incorporated into shells of layer-by-layer polyelectrolyte microcapsules-freely suspended delivery vehicles in an aqueous solution, developed in the Department of Interfaces, Max Planck Institute of Colloids and Interfaces, headed by Helmuth Möhwald. Understanding the mechanisms of localized temperature rise is essential, that is why we analyze the influence of incident intensity, nanoparticle size, their distribution and aggregation state, as well as thermodynamics at the nanoscale. This leads us to scrutinize "global" (used for thermal encapsulation) versus "local" (used for release of encapsulated materials) temperature rise. Similar analysis is extended to planar polymeric coatings, the lipid membrane system of vesicles and cells, on which nanoparticles are adsorbed. Insights are provided into the mechanisms of physicochemical and biological effects, the nature of which has always been profoundly, interactively, and engagingly discussed in the Department of Interfaces. This analysis is combined with recent developments providing outlook and highlighting a broad range of emerging applications.

Preparation and Investigation of Intelligent Polymeric Nanocapsule for Enhanced Oil Recovery.

Micro-/nanomotors colloidal particles have attracted increasing interest as composite surfactants, owing to the combined advantages of both Janus solid surfactants and micro-/nanomotors. Here we put micro-/nanomotors colloidal particles into hollow polymeric micro-encapsulates. An intelligent polymeric nanocapsule was prepared for enhanced oil recovery by the self-assembly method. The particle size range of the polymeric capsule can be controlled between 20 to 1000 nm by adjusting the cross-linking thickness of the capsule’s outer membrane. The average particle size of polymeric capsules prepared in the study was 300 nm. The structure and properties of the Intelligent polymeric nanocapsule was characterized by a wide range of technics such as Fourier transform infrared spectroscopy, scanning electron microscopy by laser diffraction, fluorescence microscopy, pendant drop tensiometer, laser particle size instrument, and interface tension analyzer. It was found that the intelligent polymeric nanocapsule exhibited significant interfacial activity at the oil-water interface. When the Janus particles’ concentration reached saturation concentration, the adsorption of the amphiphilic nanoparticles at the interface was saturated, and the equilibrium surface tension dropped to around 31 mN/m. When the particles’ concentration reached a critical concentration of aggregation, the Gibbs stability criterion was fulfilled. The intelligent polymeric nanocapsule system has a better plugging and enhanced oil recovery capacity. The results obtained provide fundamental insights into the understanding of the assembly behavior and emulsifying properties of the intelligent polymeric nanocapsule, and further demonstrate the future potential of the intelligent polymeric nanocapsule used as colloid surfactants for enhanced oil recovery applications.

Fabrication of Water Soluble Polymer Capsules for Protecting Mineral Admixtures in Groundwater for Emergency Recovery of Sinkhole.

Polyethylene glycol (PEG) based water-soluble polymer composites were fabricated for mineral admixture encapsulants to be used in underground sinkhole restoration. Linear low-density polyethylene (LLDPE) and talc were added to the composites to increase their mechanical strengths and heat resistances. PEG/LLDPE/Talc composites were manufactured via melt mixing using a twin extruder. Blending PEG and LLDPE increased the mechanical properties and heat resistances of the composite, but decreased the water solubility. Talc was added to the composite to increase mechanical properties and heat resistance. The addition of talc increased the water solubilities of PEG-based composites. The highest tensile strength and impact strength were 2.89 MPa and 2.86, respectively, the increase rate being 9.63-fold relative to that of pristine PEG.

Magnetically Navigated Core-Shell Polymer Capsules as Nanoreactors Loadable at the Oil/Water Interface.

Polymer core-shell nanocapsules with magnetic nanoparticles embedded in their oil cores were fabricated and applied as nano(photo)reactors. Superparamagnetic iron oxide nanoparticles (SPIONs) coated with oleic acid were first synthesized and characterized structurally, and their magnetic properties were determined. The capsules with chitosan-based shells were then formed in a one-step process by sonication-assisted mixing of (1) an aqueous solution of the hydrophobically derived chitosan and (2) oleic acid containing the dispersed SPIONs. In this way, magnetic capsules with a diameter of approximately 500-600 nm containing encapsulated SPIONs with an average diameter of approximately 20-30 nm were formed as revealed by dynamic light scattering and scanning transmission electron microscopy measurements. The composition and magnetic properties of the formed capsules were also followed using dynamic light scattering, electron microscopies, and magnetic force microscopy. The water-dispersible capsules, thanks to their magnetic properties, were then navigated in a static magnetic field gradient and transferred between the water and oil phases, as evidenced by fluorescence microscopy. In this way, the capsules could be loaded in a controlled way with a hydrophobic reactant, perylene, which was later photooxidized upon transferring the capsules to the aqueous phase. The capsules were shown to serve as robust reloadable nanoreactors/nanocontainers that via magnetic navigation can be transferred between immiscible phases without disruption. These features make them promising reusable systems not only for loading and carrying lipophilic actives, conducting useful reactions in the confined environment of the capsules, but also for magnetically separating and guiding the encapsulated active molecules to the site of action.

Ceria/polymer nanocontainers for high-performance encapsulation of fluorophores.

We report the synthesis of high-performance organic–inorganic hybrid fluorescent nanocapsules comprising a polymer shell armored with an inorganic layer and a liquid core containing a fluorophore. The polymeric capsules are synthesized by free radical miniemulsion polymerization and contain covalently bound carboxylate surface functionalities that allow for the binding of metal ions through electrostatic interaction. A cerium(IV) oxide nanoparticle layer, formed in situ at the surface of the hybrid nanocapsules, acts as oxygen scavenger and keeps external reactive molecular oxygen from entering into the capsules, eventually resulting in a reduction of the photooxidation of encapsulated fluorescent molecules. This approach shows an increase in the fluorescence of the model organic fluorophore terrylene diimide by avoiding the ground-state molecular oxygen to react with electronically excited states of the fluorescent hydrocarbon molecule.

The construction of thiol-functionalized DNAsomes with small molecules response and protein release

In this work, a poly(N-isopropylacrylamide) polymer (PNIPAAm) was prepared via the photoinduced reversible addition-fragmentation chain transfer (RAFT) polymerization using Ru(bpy)3Cl2·6H2O as photoinitiator. The design and spontaneous assembly of thiol-functionalized DNA-Thiol/PNIPAAm polymeric capsule (DNAsomes) by water-in-oil Pickering emulsion method and effective response with small molecules (Sybr green and phenanthrene) were described. The intermediate product, DNA-Thiol/PNIPAAm conjugates and DNAsomes were characterized by using 1H NMR, dynamic light scattering (DLS), SEM, TEM and UV–vis methods. The obtained results indicated that DNA-Thiol/PNIPAAm constructs assembled in a Pickering emulsion could produce DNA-based spherical DNAsomes with typically 3.3–267.7 μm in diameter. The DNAsomes showed a vesicle formation approximately 2 μm in diameter, resulting in phenanthrene molecule intercalating with DNAsomes. The phenomenon indicated that the DNA-Thiol/PNIPAAm conjugates may have potential applications in recognition polycyclic aromatic hydrocarbon molecules. The membrane of the DNAsomes could effective response toward small molecules such as Sybr green or phenanthrene, and DNAsomes has release capability of protein (BSA) under reductive agent glutathione (GSH). Our results highlight the potential of integrating aspects of supramolecular and polymer chemistry into the design and construction of DNA-polymeric capsule, guest molecule encapsulation, control delivery of drugs, recognition organic polycyclic aromatic hydrocarbon molecules and gene-directed capsule synthesis.

Neem oil-loaded cross-linked biodegradable polymeric capsules: Its larvicidal activity against Culex quinquefasciatuss larvae.

Background:Pesticide delivery system has been formulated in the form of emulsifiable concentrates, water solutions, aerosols, or spray formulations. However, such formulations showed health hazards. Encapsulation technique is the more suitable method to reduce health hazard and to deliver and release the pesticides. Natural biopolymers have been widely studied for encapsulation of pesticide compounds, as they are biodegradable, biocompatible, and low toxic to mammalian. Neem oil has been reported for controlling of the mosquitoes and more eco-friendly insecticide than synthetic insecticides. The present study was designed to prepare a cross-linked polymeric network capsules loaded with neem oil as effective controlled release formulation against Culex quinquefasciatus larvae.Materials and Methods:Neem oil-loaded chitosan/alginate/gelatin capsules were prepared by cross-linking method. Neem oil-loaded capsules were characterized with respect to their capsule size, scanning electron microscopy (SEM) analysis, and swelling property. In vitro larvicidal activity of neem oil-loaded polymeric capsules was studied against C. quinquefasciatus larvae.Results:The cross-linking method produced spherical shape of neem oil-loaded capsules. Ultraviolet spectroscopy analysis indicated that 10% of neem oil was loaded with capsule. A swelling study indicated that swelling of the loaded capsules tends to be more stable. SEM analysis showed that loading of the neem oil with the capsules fills all pores and capsules were found with good compatibility between chitosan, alginate, and gelatin due to the uniform shape of the capsule. Formulated neem oil-loaded capsules showed potential larvicidal activity (100% of mortality) against C. quinquefasciatus larvae in an in vitro model.Conclusion:Formulated neem oil-loaded capsules showed a simple method of preparation and eco-friendly. These polymeric capsule containing neem oil exhibited potential larvicidal activity against C. quinquefasciatus larvae.

Microfluidic probing of the complex interfacial rheology of multilayer capsules.

Encapsulation of chemicals using polymer membranes enables control of their transport and delivery for applications such as agrochemistry or detergency. To rationalize the design of polymer capsules, it is necessary to understand how the membranes' mechanical properties control the transport and release of the cargo. In this article, we use microfluidics to produce model polymer capsules and study in situ their behavior in controlled divergent flows. Our model capsules are obtained by assembling polymer mono and hydrogen-bonded bilayers at the surface of an oil droplet in water. We also use microfluidics to probe in situ the mechanical properties of the membranes in a controlled divergent flow generated by introducing the capsules through a constriction and then in a larger chamber. The deformation and relaxation of the capsules depend on their composition and especially on the molecular interactions between the polymer chains that form the membranes and the anchoring energy of the first layer. We develop a model and perform numerical simulations to extract the main interfacial properties of the capsules from the measurement of their deformations in the microchannels.

Polymer Capsules for Enzymatic Catalysis in Confined Environments

Catalysis is at the base of a series of biological and technological application processes. In recent years, the tendency has developed to carry out catalyzed reactions within confined structures, thus forming systems called micro or nanoreactors. Compartmentalized structures are cavities delimited by a wall where specific functions are introduced with a defined concentration and in the desired sites. These containers are generally referred to as nano or microcapsules, assuming the function of reactors in the presence of chemical reactions. Among the various types of existing structures, one of the most interesting is represented by systems made with polymers. This review aims to highlight some of the current advances in the use of functionalized structures that are useful for catalysis reactions, paying particular attention to polymer capsules and enzymes. The built-up methods used for the production of polymer capsules, as well as the aspects that influence membrane permeability and reactivity to environmental conditions, are discussed. Recent advances on biocatalysis confined in polymeric capsules are illustrated, and the strengths and weaknesses of the principal nanoreactors are considered.

Effect of a lipopeptide biosurfactant on the precipitation of calcium carbonate.

Observing flora and fauna, it can be said that nature is a great architect. Nature can create amazing structures with unique properties that may find potential applications in industry. This phenomenon is why the biomimetic synthesis of calcium carbonate with various polymorphs, sizes and morphologies using natural biomolecules, such as proteins and polysaccharides, has become an interesting topic in recent years. This novel work uses natural surfactants produced by Bacillus species (surfactins) in the formation of calcium carbonate particles. Calcium carbonate was synthesized by the reaction of Na2CO3 and CaCl2. The effects of surfactin concentration and pH on calcium carbonate crystal growth were investigated. Precipitated calcium carbonate was characterized by powder X-ray diffraction (XRD), Fourier transform infrared (FTIR) analysis, scanning electron microscopy (SEM) and atomic force microscopy (AFM). The pore size and specific surface area were measured via the BET isotherm method. Surfactin molecules were observed to prevent the transformation of vaterite into calcite in the reaction system, especially at pH 8. Surfactin possesses two negatively charged groups (COO-), which have strong affinity towards metal ions at pH 8. When the surfactin concentration was 20 ppm, the surfaces of calcite crystals were punctuated by spherical and oval depressions. Surface roughness may substantially improve the properties of the obtained structures, for example, as inorganic templates for polymeric capsules.

Internal Structure of Matrix-Type Multilayer Capsules Templated on Porous Vaterite CaCO₃ Crystals as Probed by Staining with a Fluorescence Dye.

Multilayer capsules templated on decomposable vaterite CaCO3 crystals are widely used as vehicles for drug delivery. The capsule represents typically not a hollow but matrix-like structure due to polymer diffusion into the porous crystals during multilayer deposition. The capsule formation mechanism is not well-studied but its understanding is crucial to tune capsule structure for a proper drug release performance. This study proposes new approach to noninvasively probe and adjust internal capsule structure. Polymer capsules made of poly(styrene-sulfonate) (PSS) and poly(diallyldimethylammonium chloride) (PDAD) have been stained with fluorescence dye rhodamine 6G. Physical-chemical aspects of intermolecular interactions required to validate the approach and adjust capsule structure are addressed. The capsules consist of a defined shell (typically 0.5–2 µm) and an internal matrix of PSS-PDAD complex (typically 10–40% of a total capsule volume). An increase of ionic strength and polymer deposition time leads to the thickening of the capsule shell and formation of a denser internal matrix, respectively. This is explained by effects of a polymer conformation and limitations in polymer diffusion through the crystal pores. We believe that the design of the capsules with desired internal structure will allow achieving effective encapsulation and controlled/programmed release of bioactives for advanced drug delivery applications.

Remotely controlled opening of delivery vehicles and release of cargo by external triggers.

Tremendous efforts have been devoted to the development of future nanomedicines that can be specifically designed to incorporate responsive elements that undergo modification in structural properties upon external triggers. One potential use of such stimuli-responsive materials is to release encapsulated cargo upon excitation by an external trigger. Today, such stimuli-response materials allow for spatial and temporal tunability, which enables the controlled delivery of compounds in a specific and dose-dependent manner. This potentially is of great interest for medicine (e.g. allowing for remotely controlled drug delivery to cells, etc.). Among the different external exogenous and endogenous stimuli used to control the desired release, light and magnetic fields offer interesting possibilities, allowing defined, real time control of intracellular releases. In this review we highlight the use of stimuli-responsive controlled release systems that are able to respond to light and magnetic field triggers for controlling the release of encapsulated cargo inside cells. We discuss established approaches and technologies and describe prominent examples. Special attention is devoted towards polymer capsules and polymer vesicles as containers for encapsulated cargo molecules. The advantages and disadvantages of this methodology in both, in vitro and in vivo models are discussed. An overview of challenges associate with the successful translation of those stimuli-responsive materials towards future applications in the direction of potential clinical use is given.

Polymer@MOFs capsules prepared through controlled interfacial mineralization for switching on/off enzymatic reactions

Engineering MOFs nanocrystals into hierarchical/macroscopic structures is critical for many applications. However, defects between MOFs nanocrystals often exist due to the uncontrollable nucleation and growth in MOFs crystallization. In our study, inspired by biomineralization processes in nature, we report a facile and generic method to prepare polymer@MOFs capsules with defect-free MOFs layer through controlled interfacial mineralization. Specifically, zeolitic imidazolate framework-8 (ZIF-8) and polydopamine (PDA) capsules are used to prepare the polymer@MOFs capsules. The PDA capsules are exploited to confine Zn2+ ions within the capsule lumen and on the capsule wall. When incubated into a solution of 2-methylimidazole (2-MeIm), Zn2+ ions on the capsule wall will trigger the interfacial nucleation of ZIF-8, while Zn2+ ions in the capsule lumen will diffuse into the capsule wall and react with 2-MeIm, enabling the growth and formation of defect-free ZIF-8 nanolayer. The molecule-sieving property of polymer@MOFs capsules is tested by the controlled permeation of small molecules (methylene blue, 6.0×13.8Å2) through the capsule wall, conferring the enzyme-embedded polymer@MOFs capsules with the unique features of on/off control of enzymatic reactions over multiple reaction cycles, and high stability of entrapped enzymes against long-term storage. Through changing the species of polymer capsules, shapes of polymer capsules and species of MOFs, a series of polymer@MOFs capsules are prepared, highlighting the versatility and functionality extension of this interfacial mineralization method.

A review study on encapsulation‐based self‐healing for cementitious materials

Encapsulation‐based self‐healing technology is an effective method for healing the crack‐deteriorated cementitious material. Encapsulation‐based self‐healing initiates by crack occurrence and progresses by chemical reaction of released self‐healing agents in the cracks, which are contained in capsules. In this paper, a review has been conducted on various healing agents, encapsulation techniques, as well as experimental approaches, basing on existing substantial studies. Recently, there is no consistent agreement on the effective criteria for evaluating encapsulation‐based self‐healing and mature solution for increasing the survival ratio of capsules during mixing. However, the polyurethane‐based healing agents filled in glass or ceramic tubes are popularly applied for self‐healing cementitious materials. Besides, the polymer capsules present promising attractions for engineering application. Mechanical strength and durability are the most widely used self‐healing efficiency assessment indexes. On the other hand, nondestructive technique and numerical modeling have also extensively adopted to visualize and evaluate the self‐healing behavior of cementitious materials. However, there are still some challenges, which require further investigations, such as behavior of crack propagation, kinetics of healing agent in discrete crack surfaces, effect of inserted capsules on the mechanical properties of self‐healed cementitious materials.

Fabrication and characterization of aluminum nanoparticles entrapped in hollow polymer capsules

In this study, we report on the in situ synthesis of aluminum nanoparticles within the cavity of hollow polymer nanocapsules. A novel titanium (IV) benzyloxide initiator was synthesized within and trapped inside the nanocapsule. The initiator and nanocapsule complex formed a nano-reactor environment in which alane was decomposed to form the nanoparticles, producing reactive metal–polymer nanorattles. The synthetic protocol resulted in air-stable nanoparticles with crystalline active core sizes of 18–23 nm. Thermal analysis showed combustion and metal ignition exotherms associated with the presence of aluminum confirming successful fabrication of Al NPs. The ratio of active aluminum (Al0) to total aluminum present in any oxidation state was determined to be 85 %.

2D Particles at Fluid-Fluid Interfaces: Assembly and Templating of Hybrid Structures for Advanced Applications.

Fluid-fluid interfaces have widespread applications in personal care products, the food industry, oil recovery, mineral processes, etc. and are also important and versatile platforms for generating advanced materials. In Pickering emulsions, particles stabilize the fluid-fluid interface, and their presence reduces the interfacial energy between the two fluids. To date, most Pickering emulsions stabilized by 2D particles make use of clay platelets or GO nanosheets. These systems have been used to template higher order hybrid, functional materials, most commonly, armored polymer particles, capsules, and Janus nanosheets. This review discusses the experimental and computational study of the assembly of sheet-like 2D particles at fluid-fluid interfaces, with an emphasis on the impact of chemical composition, and the use of these assemblies to prepare composite structures of dissimilar materials. The review culminates in a perspective on the future of Pickering emulsions using 2D particle surfactants, including new chemical modification and types of particles as well as the realization of properties and applications not possible with currently accessible systems, such as lubricants, porous structures, delivery, coatings, etc.

Influence of Heat Treatment on Loading of Polymeric Multilayer Microcapsules with Rhodamine B.

Layer-by-layer assembled polymeric multilayer capsules (PMC) of micrometer sizes are permeable for molecules below 1 KDa; therefore, the efficacy of such capsules in the delivery of low molecular weight water soluble bioactive compounds and drugs is frequently challenged. Thermally induced contraction of hollow PMC is explored here to enhance their loading efficacy with model compound, fluorescent rhodamine B (RhB). Four bilayered capsules obtained of poly(diallyldimethylammonium chloride)/polystyrene sulfonate ([PDADMAC/PSS]4 ) or poly-l-arginine/dextran sulfate ([PARG/DS]4 ) on sacrificial CaCO3 spherical microparticles are postloaded with RhB at ambient or elevated temperatures. The influence of heat on capsule loading is determined quantitatively by varying the amounts of capsules in the batch and keeping the concentration of RhB constant. The applied heat improves the loading efficacy of [PDADMAC/PSS]4 capsules at concentrations up to 2.25 × 109 capsules mL-1 , but has a reversed effect on [PARG/DS]4 capsules at all studied concentrations ((0-3.5) × 109 capsules mL-1 ).

A note on using VOF method for polymer bead manufacturing

The production of mono-dispersed spherical and non-spherical polymer beads and capsules using micro-fluidics requires precise control of dispersed phase which are distributed in a continuous phase. The prediction of two phase or three phase flow patterns in the mini/micro channels finds its application in production process of such spherical polymers. In the present work a numerical model based flow analysis is done for creation of the spherical/non spherical dispersed air bubbles in a continuous liquid phase. The results are validated with experiments done in a similar liquid–gas flow experiments carried out in a glass mini channel of size 2.05 mm. The flow regime is recorded with a high speed camera. The volume of fluid model in ANSYS Fluent software is used to predict the flow pattern details numerically. The model can be effectively used for predicting the size behavior in such spherical/non-spherical polymer bead production.