Preparation of hydrogel capsules with thermoresponsive interpenetrating polymer network using concentric two-fluid nozzles

Hydrogel capsules in which shell was composed of thermoresponsive interpenetrating polymer network (IPN) of crosslinked poly(N-isopropylacrylamide) (PNIAPM) and calcium alginate, were prepared using concentric two-fluid nozzles. To introduce different amount of PNIPAM into the capsule shell, the concentrations of the NIPAM monomer and the polymerization initiator were changed in a wide range and the characteristics of the resulting capsules were evaluated. Spherical and uniformly sized capsules were obtained under all conditions. Elemental analyses showed that the PNIPAM/alginate weight ratio increased with the increase of initial concentrations of NIPAM monomer and polymerization initiator and was proportional to the initial rate of polymerization. In addition, the thermoresponsive properties of IPN hydrogel capsule were measured at temperatures from 10 °C to 50 °C and the thermoresponsive volume change ratio was expressed as a function of the PNIPAM/alginate weight ratio raised to a power. From these results, the relationship between the experimental conditions and the amount of PNIPAM in the capsule shell was clarified, and it indicated the magnitude of volume change of IPN hydrogel capsules can be controlled by introducing the desired amount of PNIPAM in the capsules.     

Microcapsules for Enhanced Cargo Retention and Diversity

Prevention of undesired leakage of encapsulated materials prior to triggered release presents a technological challenge for the practical application of microcapsule technologies in agriculture, drug delivery, and cosmetics. A microfluidic approach is reported to fabricate perfluoropolyether (PFPE)‐based microcapsules with a high core‐shell ratio that show enhanced retention of encapsulated actives. For the PFPE capsules, less than 2% leakage of encapsulated model compounds, including Allura Red and CaCl₂, over a four week trial period is observed. In addition, PFPE capsules allow cargo diversity by the fabrication of capsules with either a water‐in‐oil emulsion or an organic solvent as core. Capsules with a toluene‐based core begin a sustained release of hydrophobic model encapsulants immediately upon immersion in an organic continuous phase. The major contribution on the release kinetics stems from the toluene in the core. Furthermore, degradable silica particles are incorporated to confer porosity and functionality to the otherwise chemically inert PFPE‐based polymer shell. These results demonstrate the capability of PFPE capsules with large core–shell ratios to retain diverse sets of cargo for extended periods and make them valuable for controlled release applications that require a low residual footprint of the shell material.     

Effect of capsule addition and healing temperature on the self-healing potential of asphalt mixtures

This paper presents the self-healing results of asphalt mixtures by the action of capsules containing sunflower oil as encapsulated rejuvenator. Three different capsule contents, 0.10, 0.25 and 0.50% by total weight of the mixture, were added to the samples. The mechanical and thermal properties of capsules have been evaluated. In addition, the effect of the capsule addition and the healing temperature on the self-healing properties of asphalt mixtures have been evaluated through three-point bending tests on the cracked asphalt beams with, and without, capsules. The test was implemented by comparing the strength recovery of the broken beams after healing to their original flexural strength. It was proven that the capsules can resist the mixing and compaction processes and break inside the asphalt mixture as a result of applying external mechanical loads, releasing the encapsulated oil. The capsules content in asphalt mixture has a significant influence on the healing level, where a higher capsule content led to obtaining higher healing levels. Likewise, asphalt with, and without, capsules presents an increase of the healing level when the temperature increases. Finally, it was proved that healing temperature has higher influence on the healing levels of the asphalt below 40 °C.     

Influence of process variables and formulation composition on sphericity and diameter of Ca-alginate-chitosan liquid core capsule prepared by extrusion dripping method

ABSTRACT

The influence of process variables and formulation composition on the sphericity and diameter of the alginate capsules which contained dual cations (Ca-and-chitosan) are characterized in this study. Capsule sphericty was not influenced by needle diameter but instead, capsule diameter increased proportionally with the needle diameter. The combined effects of the liquid core solution and alginate solution on the sphericity of the capsules are tabulated. Spherical capsules can be produced when the following criteria were fulfilled: stirring speed is in the range of 240–300 rpm; calcium chloride concentration is >5 g/L; viscosity of liquid core solution is >203 mPa.s; as well as viscosity of alginate solution is in between 47 and 386 mPa.s. The capsule diameter was predicted using a modified Tate’s law equation and an error analysis was conducted to evaluate the equation. The predicted diameter was well correlated with the experimental data with an average absolute deviation <3.6%.     

Delivery Systems for Low Molecular Weight Payloads: Core/Shell Capsules with Composite Coacervate/Polyurea Membranes

Composite polyurea/coacervate core/shell capsules are formed by coupling associative biopolymer phase separation with interfacial polymerization. They combine the excellent chemical stability of synthetic polymer barriers with the strong adhesive properties of protein‐based complex coacervates, inspired by biological underwater glues. To encapsulate volatile oil droplets, a primary coacervate hydrogel capsule is formed by a protein and weak polyanion and is reinforced with a polyurea membrane synthesized in situ at the interface between the coacervate and the oil core. The polyurea layer provides an excellent permeability barrier against diffusion of small volatile molecules while the coacervate portion of the shell enhances adhesion on the targeted substrate.     

The role of metal nanoparticles in remote release of encapsulated materials

Laser mediated remote release of encapsulated fluorescently labeled polymers from nanoengineered polyelectrolyte multilayer capsules containing gold sulfide core/gold shell nanoparticles in their walls is observed in real time on a single capsule level. We have developed a method for measuring the temperature increase and have quantitatively investigated the influence of absorption, size, and surface density of metal nanoparticles using an analytical model. Experimental measurements and numerical simulations agree with the model. The treatment presented in this work is of general nature, and it is applicable to any system where nanoparticles are used as absorbing centers. Potential biomedical applications are highlighted.     

Compound‐Droplet‐Pairs‐Filled Hydrogel Microfiber for Electric‐Field‐Induced Selective Release

The separate co‐encapsulation and selective controlled release of multiple encapsulants in a predetermined sequence has potentially important applications for drug delivery and tissue engineering. However, the selective controlled release of distinct contents upon one triggering event for most existing microcarriers still remains challenging. Here, novel microfluidic fabrication of compound‐droplet‐pairs‐filled hydrogel microfibers (C‐Fibers) is presented for two‐step selective controlled release under AC electric field. The parallel arranged compound droplets enable the separate co‐encapsulation of distinct contents in a single microfiber, and the release sequence is guaranteed by the discrepancy of the shell thickness or core conductivity of the encapsulated droplets. This is demonstrated by using a high‐frequency electric field to trigger the first burst release of droplets with higher conductivity or thinner shell, followed by the second release of the other droplets under low‐frequency electric field. The reported C‐Fibers provide novel multidelivery system for a wide range of applications that require controlled release of multiple ingredients in a prescribed sequence.     

Influence of capsule shell composition on the performance indicators of hypromellose capsule in comparison to hard gelatin capsules

The purpose of this study was to assess the in vitro performances of “vegetable” capsules in comparison to hard gelatin capsules in terms of shell weight variation, reaction to different humidity conditions, resistance to stress in the absence of moisture, powder leakage, disintegration and dissolution. Two types of capsules made of HPMC produced with (Capsule 2) or without (Capsule 3) a gelling agent and hard gelatin capsules (Capsule 1) were assessed. Shell weight variability was relatively low for all tested capsules shells. Although Capsule 1 had the highest moisture content under different humidity conditions, all capsule types were unable to protect the encapsulated hygroscopic polyvinylpyrrolidone (PVP) powder from surrounding humidity. The initial disintegration for all Capsule 1 occurred within 3?min, but for other types of capsules within 6?min (n?=?18). Dissolution of acetaminophen was better when the deionized water (DIW) temperature increased from 32 to 42?°C in case of Capsule 1, but the effect of temperature was not significant for the other types of capsules. Acetaminphen dissolution from Capsule 1 was the fastest (i.e. >90% in 10?min) and independent of the media pH or contents unlike Capsule 2 which was influenced by the pH and dissolution medium contents. It is feasible to use hypromellose capsules shells with or without gelling agent for new lines of pharmaceutical products, however, there is a window for capsule shells manufacturing companies to improve the dissolution of their hypromellose capsules to match the conventional gelatin capsule shells and eventually replace them.     

Improving covalent cell encapsulation with temporarily reactive polyelectrolytes

Calcium alginate/poly-l-lysine beads were coated with either 50% hydrolyzed poly(methyl vinyl ether–alt–maleic anhydride) (PMM₅₀), or with poly(vinyl dimethyl azlactone-co-methacrylic acid) (50:50, PMV₅₀), to form covalently shell-crosslinked capsules, and compared with analogous capsules coated with sodium alginate. All capsule types were prepared with and without C2C12 murine myoblast cells, and implanted into mice for up to 6 weeks. Cell viability, capsule integrity, fibrotic overgrowth, and mechanical strength of the capsules were assessed, and correlated with inflammatory cytokine marker levels in tail vein blood samples taken at different time points. AP-PMM₅₀ capsules displayed the least amount of fibrotic overgrowth, were found to be the strongest, and showed the lowest levels of TNF-α in tail vein serum samples taken at 4 h, 24 h, 1 and 6 weeks post transplantation. The results for APA and AP-PMV₅₀ capsules were more variable and depended on the presence or absence of encapsulated cells.     

Drying oil-in-water Pickering emulsions to make redispersible powders

We report on the formation of powder by drying oil-in-water emulsions stabilized by silanised silica nanoparticles. Drying was achieved by spraying fine droplets (up to a hundred micrometres in diameter) of the emulsions into a chamber of hot, flowing air. We show that the surfaces of droplets of the emulsions become enriched with nanoparticles as the water evaporates in the drying chamber. Controlling the relative amounts of oil and particles in the droplets being dried is the key to encapsulating the oil drops within the powder. Dried Pickering emulsions containing up to 40 wt% encapsulated oil that could be dispersed in water as drops of the same size as in the original emulsion were produced.     

Superamphiphobic Bionic Proboscis for Contamination‐Free Manipulation of Nano and Core–Shell Droplets

Manipulation of nanoliter droplets is a key step for many emerging technologies including ultracompact microfluidics devices, 3D and flexible electronic printing. Despite progress, contamination‐free generation and release of nanoliter droplets by compact low‐cost devices remains elusive. In the present study, inspired by butterflies' minute manipulation of fluids, the authors have engineered a superamphiphobic bionic proboscis (SAP) layout that surpasses synthetic and natural designs. The authors demonstrate the scalable fabrication of SAPs with tunable inner diameters down to 50 µ m by the rapid gas‐phase nanotexturing of the outer and inner surfaces of readily available hypodermic needles. Optimized SAPs achieve contamination‐free manipulation of water and oil droplets down to a liquid surface tension of 26.56 mN m^?1 and a volume of 10 nL. The unique potential of this layout is showcased by the rapid and carefully controlled in‐air synthesis of core‐shell droplets with well‐controlled compositions. These findings provide a new low‐cost tool for high‐precision manipulation of nanoliter droplets, offering a powerful alternative to established thermal‐ and electrodynamic‐based devices.     

Ultrathin Double‐Shell Capsules for High Performance Photon Upconversion

Triplet‐fusion‐based photon upconversion capsules with ultrathin double shells are developed through a single dripping instability in a microfluidic flow‐focusing device. An inner separation layer allows use of a brominated hydrocarbon oil‐based fluidic core, demonstrating significantly enhanced upconversion quantum yield. Furthermore, a perfluorinated photocurable monomer serves as a transparent shell phase with remote motion control through magnetic nanoparticle incorporation.     

Advanced Subcompartmentalized Microreactors: Polymer Hydrogel Carriers Encapsulating Polymer Capsules and Liposomes

The design of compartmentalized carriers for advanced drug delivery systems or artificial cells and organelles is of interest for biomedical applications. Herein, a polymer carrier microreactor that contains two different classes of subcompartments, multilayered polymer capsules and liposomes, is presented. 50 nm‐diameter liposomes and 300 nm‐diameter polymer capsules are encapsulated into a larger polymer carrier capsule, demonstrating control over the spatial positioning of the subcompartments, which are either ‘membrane‐associated’ or 'free‐floating’ in the aqueous interior. Selective and spatially dependent degradation of the 300 nm‐diameter subcompartments (without destroying the structural integrity of the enzyme‐loaded liposomes) is also shown, by performing an encapsulated enzymatic reaction using the liposomal subcompartments. These findings cover several important aspects toward the development of engineered compartmentalized carrier vessels for the creation of artificial cell mimics or advanced therapeutic delivery systems.     

液液两相流法制备海藻酸钠包覆的液态金属微滴

本文以室温液态金属(GaInSn)为分散相、海藻酸钠(NaAlg)溶液(1wt%)为连续相,采用液液两相流方法,在竖直共轴微通道中,制备得到NaAlg凝胶包覆的多个GaInSn微滴,具有单分散、尺寸一致的特点。GaInSn/NaAlg两相流存在四种流型:分散相滴流、分散相柱塞流、连续相滴流和连续相射流。GaInSn微滴的包覆模式三种:Squeezing、Dripping和Compound Jetting,其中Dripping和Compound Jetting是主要的包覆模式。在较低的GaInSn流量下,NaAlg流量增加到一定程度后,包覆模式由Dripping转变Compound Jetting。固定两相流量比,随着两相流量的同比例增加,GaInSn微滴的特征频率呈线性增加、包覆个数增加、特征长度变化不显著。     

The In Vitro Dissolution of Theophylline from Different Types of Hard Shell Capsules

ABSTRACT

The in vitro dissolution of theophylline from two-piece hard shell capsules has been investigated using different types of capsule shells (gelatin, gelatin/polyethylene glycol, hydroxypropyl methylcellulose), different formulations, different capsule fill weights, and different tamping forces. Analysis of variance confirmed that the formulation and the capsule shell materials were the most important factors influencing drug dissolution. The maximum extent of drug dissolution was significantly increased when hydroxypropyl methylcellulose (HPMC) capsules were used. The mean dissolution time (MDT) was significantly reduced, indicating a faster dissolution rate of the drug from HPMC capsules. The addition of microfine cellulose to the formulations as filler reduced the MDT in all cases, whereas the addition of lactose monohydrate did not enhance drug dissolution. The study confirmed that a change from gelatin hard shell capsules to gelatin/PEG or HPMC hard shell capsules should not pose problems with respect to drug absorption or bioavailability.     

The indentation of pressurized elastic shells: from polymeric capsules to yeast cells

Pressurized elastic capsules arise at scales ranging from the 10 m diameter pressure vessels used to store propane at oil refineries to the microscopic polymeric capsules that may be used in drug delivery. Nature also makes extensive use of pressurized elastic capsules: plant cells, bacteria and fungi have stiff walls, which are subject to an internal turgor pressure. Here, we present theoretical, numerical and experimental investigations of the indentation of a linearly elastic shell subject to a constant internal pressure. We show that, unlike unpressurized shells, the relationship between force and displacement demonstrates two linear regimes. We determine analytical expressions for the effective stiffness in each of these regimes in terms of the material properties of the shell and the pressure difference. As a consequence, a single indentation experiment over a range of displacements may be used as a simple assay to determine both the internal pressure and elastic properties of capsules. Our results are relevant for determining the internal pressure in bacterial, fungal or plant cells. As an illustration of this, we apply our results to recent measurements of the stiffness of baker''s yeast and infer from these experiments that the internal osmotic pressure of yeast cells may be regulated in response to changes in the osmotic pressure of the external medium.     

Failure of large-scale pilot evaporator duct nozzle

Failure investigation was carried out on a 12'' water evaporator duct nozzle of a large-scale steam flood pilot which is used to inject steam into a heavy crude oil reservoir. The nozzle contained cracks at the pipe, shell, pad and welds. All the materials are made of UNS31803 grade 2205 duplex stainless steel. The cracks were initially formed at the welds and then propagated through the pipe, pad and shell. The cracks were running almost parallel in a straight manner. The cracks were transgranular in nature in the form of fissures associated with second phase precipitates. The results indicated that the nozzle was subjected to repeated welding thermal cycles and the heat input was relatively high, as manifested by the presence of intense heat tint, high percentage of austenite in the weld region (about 70%), and the presence of embrittling intermetallic phases. The investigation concluded that the primary reason of failure was poor welding practice, which facilitated brittle cracking. Fatigue was the mode of failure, which resulted from vibration in the piping system.     

Calcium pectinate capsules for colon-specific drug delivery

The calcium pectinate (CaP) capsule, a novel, colon-specific delivery system, was designed and developed using 5-fluorouracil (5-FU) as a model drug. Technically, CaP capsules were prepared by dipping a glass or stainless steel rod successively into pectin and calcium chloride solutions, followed by subsequent air-drying and coating. In vitro studies showed that the release of 5-FU from CaP capsules markedly increased in the presence of rat cecal contents, and the release characteristic was mainly associated with some capsule parameters such as calcium content, shell thickness, and coat amount. Gamma scintigraphic studies demonstrated that CaP capsules could pass through the stomach and small intestine intact and could release drug in colon. The 5-FU releasing characteristics acquired both from in vitro biomimic dissolution experiments and from healthy volunteers indicated that the newly developed CaP capsule possessed the ideal colon-specific drug delivery characteristic.     

Calcium Pectinate Capsules for Colon-Specific Drug Delivery

The calcium pectinate (CaP) capsule, a novel, colon-specific delivery system, was designed and developed using 5-fluorouracil (5-FU) as a model drug. Technically, CaP capsules were prepared by dipping a glass or stainless steel rod successively into pectin and calcium chloride solutions, followed by subsequent air-drying and coating. In vitro studies showed that the release of 5-FU from CaP capsules markedly increased in the presence of rat cecal contents, and the release characteristic was mainly associated with some capsule parameters such as calcium content, shell thickness, and coat amount. Gamma scintigraphic studies demonstrated that CaP capsules could pass through the stomach and small intestine intact and could release drug in colon. The 5-FU releasing characteristics acquired both from in vitro biomimic dissolution experiments and from healthy volunteers indicated that the newly developed CaP capsule possessed the ideal colon-specific drug delivery characteristic.     

MONODISPERSE DROPLET GENERATION BY SPONTANEOUS CONDENSATION OF STEAM FLOW IN NOZZLES

ABSTRACT

Spontaneous Condensation (also called homogeneous Condensation)of steam flow in one dimensional nozzle has been numerically modeled. The classical (Frenkel and Volmer) and Deich's nucleation theories were used. Unlike the classical theory, Deich's theory also accounts for the critical droplet size dependence upon the expansion rate in the nozzle. Pressure ratio, mean droplet size and droplet size distributions were obtained along the axial length for various nozzles. Comparisons with experimental data were made. The agreement between the numerical results and the experimental data was good. Both theories predicted the pressure ratio properly but the classical theory tended to underestimate the droplet sizes. Deich's theory is preferred for analyzing and designing new nozzles. The classical theory cannot be used for obtaining a correlation for surface tension ratio, thereby limiting its usage for new nozzles. Effects of Inlet conditions and nozzle expansion rates on mean droplet size and droplet size distributions were examined. The spontaneous condensation process results in relatively monodisperse droplets. The numerical model and the results are discussed in this paper.