Capsule Shell Thickness Research Articles

Encapsulation of octadecane through crosslinking of cellulose nanofibrils at the interface of Pickering emulsion: Effect of ionic strength on cellulose assembly and capsule shell properties

Emulsion interfacial polymerization is a versatile approach for the encapsulation of organic phase-change materials to improve their stability and prevent their elution and leakage. Herein, we report the successful octadecane encapsulation by the preparation of Pickering emulsions stabilized with carboxylated cellulose nanofibrils (CNF) at various ionic strengths of the dispersive medium. The stable capsule shells were obtained through the formation of amide bonds in the reaction with polymeric isocyanate dissolved in the oil phase. The addition of 5–200 mM NaCl resulted in different adsorption behaviors of carboxylated CNF, which led to an increase in capsule shell thickness (up to 530 nm), improved octadecane encapsulation efficiency (up to 78 %) and thermal stability, as well as reduced elution in organic medium with increasing ionic strength. The study presents a new strategy for the encapsulation of phase-change materials by surfactant-free emulsion interfacial polymerization into containers with defined and adjustable properties.

A dual wide-band ingestible antenna design for wireless capsule endoscopy

In this paper, we present a dual wide-band ingestible antenna design for wireless capsule endoscopy (WCE) biotelemetry applications. The design process employs Characteristic Mode Analysis (CMA) and driven modal analysis. The effectiveness of the prototype antenna is afterward assessed through measurements using a tissue-equivalent phantom liquid model. We investigate the effects of antenna implantation depth and capsule shell thickness on its performance, providing insights into practical considerations. The proposed dual-band antenna demonstrates good performance in both the 1.4 GHz Wireless Medical Telemetry Services (WMTS) and 2.45 GHz Industrial, Scientific, and Medical (ISM) bands, exhibiting measured impedance bandwidths of 36% and 22%, respectively. The measured peak realized gains are −22.9 dBi and −25.3 dBi for the WMTS and ISM bands, respectively, with a compact footprint of 78.5 mm2. To ensure health and safety and optimal performance, we evaluate the antenna's specific absorption rate (SAR) and link margin (LM). Additionally, we assess the performance of the proposed antenna in comparison with the state-of-the-art design for capsule antennas in WCE applications.

Predetermination of burst times of elastoplastic osmotic capsules

“Pulsed drug release” for dosing drugs such as vaccines, hormones etc. that require multiple, predetermined release events can be obtained by using capsules that exploit the principle of osmosis to achieve a delayed burst release of their payload. An objective of this study was to precisely determine the lag time before burst which occurs when the hydrostatic pressure developed due to water influx expands the capsule shell to rupture. A novel ‘dip coating’ technique was used to encapsulate osmotic agent solution or solid within biodegradable poly(lactic acid-co-glycolic) (PLGA) spherical capsule shells. As a prelude to determine the hydrostatic pressure to burst, first, elastoplastic and failure characterization of PLGA was conducted by a novel “beach ball inflation” technique. The lag time before burst of various capsule configurations was predetermined by modeling the rate of water uptake by the capsule core as a function of capsule shell thickness, radius of the sphere, core osmotic pressure, and the membrane's hydraulic permeability and tensile properties. In vitro release was studied with capsules of different configurations to determine their actual time to burst. The time to rupture predetermined from the mathematical model corroborated with the in vitro results and was found to increase with increases in capsule radius and shell thickness and decrease in osmotic pressure. Pulsatile drug delivery can be achieved by using a multitude of these osmotic capsules consolidated in a single system, each programmed to release the drug payload after a pre-determined time lag.

A 3D pore-scale model for macro-encapsulated phase change material-metal foam hybrid energy storage system

A 3D pore-scale model is presented to predict the energy storage characteristics of a macro-encapsulated phase change material (PCM)-metal foam hybrid energy storage system. A single capsule with metallic shell filled with PCM-metal foam composite is considered. The energy transfer from a heat transfer fluid (HTF) flowing over the capsule, the evolution of temperature, and the melting of PCM in the metal foam pores within the capsule are simulated using the model. The model resolves the geometry of the individual pores in the metal foam and thus captures the local heat transfer between the metal foam and PCM, and the movement of PCM solid-liquid interface during melting inside each pore. Heat transfer from the HTF to the metal shell, metal foam, and PCM, and the resulting melting and energy storage characteristics are predicted by using the model. The effects of important geometrical parameters such as capsule size, capsule shell thickness, pore size distribution and porosity of the foam are studied. As a significant fraction of energy storage is in the form of sensible energy, the total energy storage with the variation of these parameters are quantitatively compared. For the range of parameters considered in the study, it is found that the increase in foam porosity from 50 % to 70 % increases the total energy storage by 5.41 % while increasing the average pore radius from 0.5 mm to 0.9 mm keeping the porosity 60 %, increases the total energy storage by only 1.54 %. Change in capsule inner diameter from 7 to 11 mm increases the total energy storage by 211.99 % although the energy stored per unit volume is reduced by 7.55 %. Similar effect is also observed for increase in shell thickness from 0.5 to 1.5 mm.

Effect of Elasticity of Silica Capsules on Cellular Uptake.

Understanding the impact of the physicochemical properties of nanoparticles (NPs) on cellular uptake is important to design optimal drug-delivery nanocarriers. Therein, the influence of NP elasticity on bio-nano-interactions remains elusive due to the complexity of factors affecting cellular uptake. Herein, we synthesized SiO2 capsules with tunable elasticity using metal-organic frameworks as templates to investigate their interactions with cells. Young's moduli of the resultant water-filled SiO2 capsules with identical size, shape, composition, and surface charge can be controlled from 3.8 MPa to 4.7 GPa via the variation of capsule shell thickness. As a result, increased elasticity of SiO2 capsules results in higher cellular uptake. Stiff SiO2 capsules have almost 9 times as much cellular uptake as the soft ones. In addition, the elasticity of SiO2 capsules influences cellular uptake pathways, where the clathrin-mediated pathway is preferred for stiff capsules while the uptake of the soft capsules is mostly mediated by a caveolae-dependent pathway. This work confirms the important role of NP elasticity in nonspecific cell interactions, which can provide a foundational understanding for engineering drug-delivery nanocarriers.

Microencapsulation of lambda-cyhalothrin with polyurethane-urea and application on peppermint plant leaves containing a two-spotted red spider mite (tetranychus urticae)

In this study, lambda-cyhalothrin (LC) used as a pesticide was microencapsulated with polyurethaneurea (PUU) at 55°C temperature for 180 min. Wall thickness and dimensions of the microcapsules, the effect of mixing speed on the capsule size, active substance release times of LC-PUU microencapsules under UV rays and alcohol/water medium, microencapsulation yields and the effect of microencapsulated active substance on the red spider on peppermint plant leaves (mentha piperita) were investigated. The microcapsule yield was found 77.4–85.5%, also capsule shell thickness was 512.3–724.5 nm. The highest release percentage of the microcapsules was found to be 35.00% at 20°C for 4 h under UV light. When the LC-PUU microcapsules applied to the peppermint plant leaves (mentha piperita) which contained a two-spotted red spider mites (tetranychus urticae), it remained active for 8 weeks and during this period no insect formation was observed on the peppermint leaves.

Analytical models to estimate efficiency of capsule-based self-healing cementitious materials considering effect of capsule shell thickness

Capsule-based self-healing materials are a promising solution for maintaining the mechanical properties and durability performance of concrete structures. To assess the efficiency of capsule-based self-healing cementitious material, analytical models considering the effect of the capsule shell thickness were derived for three common capsule shapes: sphere (SPH), cylinder (CYL), and a cylinder with spherical tips (CST). A numerical simulation method was used to validate the proposed analytical models. A parametric study was conducted to investigate the effect of the capsule diameter, aspect ratio, and shell thickness on the self-healing efficiency. Simplified analytical models were derived to calculate the capsule diameter, aspect ratio, and shell thickness for the shape design and manufacturing of the capsule. The results of this study show that: (1) the self-healing efficiency is proportional to the diameter of the capsule; (2) the self-healing efficiency increases approximately linearly with an increase in the aspect ratio for CYL and CST capsules; (3) the self-healing efficiency may be greatly over-estimated without considering the shell thickness, especially for spherical capsules.

Engineering of Nebulized Metal-Phenolic Capsules for Controlled Pulmonary Deposition.

Particle‐based pulmonary delivery has great potential for delivering inhalable therapeutics for local or systemic applications. The design of particles with enhanced aerodynamic properties can improve lung distribution and deposition, and hence the efficacy of encapsulated inhaled drugs. This study describes the nanoengineering and nebulization of metal–phenolic capsules as pulmonary carriers of small molecule drugs and macromolecular drugs in lung cell lines, a human lung model, and mice. Tuning the aerodynamic diameter by increasing the capsule shell thickness (from ≈100 to 200 nm in increments of ≈50 nm) through repeated film deposition on a sacrificial template allows precise control of capsule deposition in a human lung model, corresponding to a shift from the alveolar region to the bronchi as aerodynamic diameter increases. The capsules are biocompatible and biodegradable, as assessed following intratracheal administration in mice, showing >85% of the capsules in the lung after 20 h, but <4% remaining after 30 days without causing lung inflammation or toxicity. Single‐cell analysis from lung digests using mass cytometry shows association primarily with alveolar macrophages, with >90% of capsules remaining nonassociated with cells. The amenability to nebulization, capacity for loading, tunable aerodynamic properties, high biocompatibility, and biodegradability make these capsules attractive for controlled pulmonary delivery.

Mechano-responsive microcapsules with uniform thin shells.

Capsules often prolong the shelf-life of active ingredients, such as many types of drugs, food additives, or cosmetic substances, because they delay oxidation of these substances or prevent their reactions with molecules contained in the surrounding. If capsules are appropriately designed, they can offer an additional benefit: they allow close control over the timing and location of the release of active ingredients. To take advantage of these features, capsules must possess shells whose thickness and composition are well-defined. However, the shell thickness of capsules often varies considerably even within a single capsule, thereby hampering good control over the release kinetics of encapsulants. These variations can be reduced, and hence the degree of control over the release kinetics increased, if shells are made thin. Unfortunately, the controlled fabrication of mechanically stable microcapsules with well-defined sub-μm thick shells is difficult. Here, we introduce a method to fabricate capsules with uniform semi-permeable shells with a thickness as low as 400 nm. This is achieved using water-oil-water double emulsions with 800 nm thick shells as templates to fabricate capsules with uniform 400 nm thin shells. These shells occupy less than 2% of the capsule volume, thereby minimizing their footprint. Despite their thin shells, these capsules are mechanically robust: they withstand pressures up to 1.3 MPa without deformation and remain intact if exposed to pressures up to 2.75 MPa. Moreover, while they are permeable towards water, they retain low molecular weight encapsulants even if dried and re-dispersed. The thin shells of the capsules open up new possibilities of their use to functionalize materials with at least one dimension that is small, such as coatings, where thick shells introduce defects, or as building blocks of new types of functional materials.

Silica layer-dependent leakage of cadmium from CdSe/ZnS quantum dots and comparison of cytotoxicity with polymer-coated analogues

The cytotoxicity of cadmium-containing quantum dots (QDs) is reportedly caused by released Cd2+ as well as other factors such as ligand, size, and surface modification. The tolerated concentration of QDs therefore deviates from ~ 1 to 1000 nM. However, the concentration of Cd2+ released from QDs has seldom been correctly and systematically measured. We prepared highly emitting silica capsules with incorporated multiple CdSe/ZnS QDs through a sol-gel-derived wet method. The concentration of released Cd2+ in buffer solution was measured as a function of the preparation conditions of the capsules. When the shell thickness of the capsule was 15 nm, the release was effectively suppressed compared with a capsule shell thickness of 10 nm. Heat treatment at 40 °C further suppressed the leakage. When the silicon alkoxide hydrolysis time was increased from 3 to 15 h, and the surface was modified with COOH groups, the leakage reached a minimum of ~ 0.01 ppb for a QD concentration of 10 nM after 15 h of dispersion. This was two orders of magnitude less than polymer-coated analogues with the same surface functional groups. These silica capsules did not show any toxicity to culture cells, whereas the polymer-coated ones showed high toxicity with the same QD concentration. Silica capsules are therefore not only the expected ideal, but show significantly superior performance when correctly prepared for biomedical application with CdSe/ZnS QDs, owing to their strong suppression of Cd2+ leakage into solution.

Towards Microcapsules with Improved Barrier Properties.

Microencapsulation is the generic term for numerous technologies, which are often used when the release rate of an active substance in a medium has to be controlled and/or contact between the active substance and the medium has to be prevented. This is achieved by wrapping the tiny particles or droplets of the active substance (capsule core) with a thin layer, or membrane, of another material (capsule shell). The permeability of the membrane determines whether, how fast and under which conditions the active material will be released and/or the components of the medium will enter the inner part of the capsule. Insofar as application is concerned, premature release of an active substance from microcapsules during storage is a very common problem. Prevention of diffusion of an active component or components of the outer medium through the capsule membrane is a complex challenge, which so far cannot be considered as solved. This review briefly covers the theoretical aspects of release kinetics from microcapsules and discusses how such parameters as capsule average size, capsule shell thickness as well as the chemical composition of active material and medium can influence the release profiles. All theoretical considerations are based on the dissolution-diffusion mechanism classically used for the explanation of diffusion trough flat membranes/films. In the second part of the manuscript it is discussed, which strategies have been used for the improvement of the barrier properties of microcapsules up to date and to which extent those strategies were successful.

Using HT and DT gamma rays to diagnose mix in Omega capsule implosions

Experimental evidence [1] indicates that shell material can be driven into the core of Omega capsule implosions on the same time scale as the initial convergent shock. It has been hypothesized that shock-generated temperatures at the fuel/shell interface in thin exploding pusher capsules diffusively drives shell material into the gas core between the time of shock passage and bang time. We propose a method to temporally resolve and observe the evolution of shell material into the capsule core as a function of fuel/shell interface temperature (which can be varied by varying the capsule shell thickness). Our proposed method uses a CD plastic capsule filled with 50/50 HT gas and diagnosed using gas Cherenkov detection (GCD) to temporally resolve both the HT “clean” and DT “mix” gamma ray burn histories. Simulations using Hydra [2] for an Omega CD-lined capsule with a sub-micron layer of the inside surface of the shell pre-mixed into a fraction of the gas region produce gamma reaction history profiles that are sensitive to the depth to which this material is mixed. An experiment to observe these differences as a function of capsule shell thickness is proposed to determine if interface mixing is consistent with thermal diffusion λii∼T2/Z2ρ at the gas/shell interface. Since hydrodynamic mixing from shell perturbations, such as the mounting stalk and glue, could complicate these types of capsule-averaged temporal measurements, simulations including their effects also have been performed showing minimal perturbation of the hot spot geometry.

Preparation of polydopamine nanocapsules in a miscible tetrahydrofuran-buffer mixture.

A miscible tetrahydrofuran-tris buffer mixture has been used to fabricate polydopamine hollow capsules with a size of 200 nm and with a shell thickness of 40 nm. An unusual non-emulsion soft template mechanism has been disclosed to explain the formation of capsules. The results indicate that the capsule structure is highly dependent on the volume fraction of tetrahydrofuran as well as the solvent, and the shell thickness of capsules can be controlled by adjusting the reaction time and dopamine concentration.

Fabrication of polylactic acid (PLA) microcapsules and release of the internal hydrophilic substance under ultrasound irradiation

Hollow microcapsules have been considered for potential application as drug or gene carriers. Targeted drug or gene release to tumor vascular can be achieved by destroying the capsules by high-intensity ultrasound. This report investigates fabrication of microcapsules having biocompatible polylactic acid (PLA) shell and the mechanical property for the destruction under ultrasound irradiation. The PLA hollow microcapsules with the diameter of 1 to 35 μm were fabricated by double emulsion method. Red fluorescent dye which is substitute for drug was enclosed into the capsules. The capsules have trilaminar structure. Inner air is surrounded by red fluorescent, and the PLA shell encloses them. Shell thickness of capsules was distributed from 100 nm to 3 μm. Destruction of the fabricated capsules was investigated by using ultrasound pulse with the center frequencies from 500 kHz to 2 MHz. The behavior of capsule was observed by using an optical microscope under ultrasound irradiation. The frequency dependence of the capsule destruction was investigated and 35% of the capsules with the resonance size was destroyed with 400 kPa at 700 kHz. The capsule shell was ruptured by the ultrasound, and then the inner dye was released; the dye was completely released for 120 seconds under ultrasound irradiation.

Size and Microstructure Control of Calcium Aluminate Microcapsules

Microencapsulation is nowadays widely applied for the separation or controlled and targeted release of substances. In the present work we propose using particle‐stabilized water‐in‐oil emulsions to produce microcapsules from calcium aluminate cement. First, we investigate the parameters determining the capsule size and size distribution. Then, the anhydrous particles at the water‐oil contact line are hydrated resulting in the formation of a layer of precipitated calcium aluminate hydrate that strengthens the capsule shells. By manipulating the hydration reaction of the cement particles, the capsule shell thickness is varied between 200 and 1300 nm. For hydration temperatures of 3°C and 25°C, the capsule walls are mainly formed from Ca2Al2O5·8H2O, whereas Ca2Al2O5·8H2O and the stable γ‐Al(OH)3 and Ca3Al2O6·6H2O phases are precipitated at 60°C. In addition, the impact of these manipulations on the yield of dry microcapsules is discussed. The highest yield of intact capsules observed in this study is 72 ± 3%. We believe that such microcapsules can lead to new applications, particularly in environments with harsh conditions or in inorganic matrixes.

Use of d-H3e proton spectroscopy as a diagnostic of shell ρr in capsule implosion experiments with ∼0.2 NIF scale high temperature Hohlraums at Omega

We present the calculations and preliminary results from experiments on the Omega laser facility using d-(3)He filled plastic capsule implosions in gold Hohlraums. These experiments aim to develop a technique to measure shell rho r and capsule unablated mass with proton spectroscopy and will be applied to future National Ignition Facility (NIF) experiments with ignition scale capsules. The Omega Hohlraums are 1900 microm length x 1200 microm diameter and have a 70% laser entrance hole. This is approximately a 0.2 NIF scale ignition Hohlraum and reaches temperatures of 265-275 eV similar to those during the peak of the NIF drive. These capsules can be used as a diagnostic of shell rho r, since the d-(3)He gas fill produces 14.7 MeV protons in the implosion, which escape through the shell and produce a proton spectrum that depends on the integrated rho r of the remaining shell mass. The neutron yield, proton yield, and spectra change with capsule shell thickness as the unablated mass or remaining capsule rho r changes. Proton stopping models are used to infer shell unablated mass and shell rho r from the proton spectra measured with different filter thicknesses. The experiment is well modeled with respect to Hohlraum energetics, neutron yields, and x-ray imploded core image size, but there are discrepancies between the observed and simulated proton spectra.

Fabrication of Hollow Melamine−Formaldehyde Microcapsules from Microbubble Templates

A fabrication method for hollow melamine-formaldehyde microcapsules from microbubble templates is presented. This method is based on the direct encapsulation of microbubbles, and thus does not require a liquid- or solid-core decomposition process. This study determined the conditions for controlling the surface morphology, shell thickness, and diameter distribution of hollow microcapsules. Results showed that the surface morphology of these hollow microcapsules depended on the reaction time, glycine concentration (pH of aqueous continuous phase) and pre-polymer concentration. The capsule shell thickness could be controlled by adjusting the concentration of aniline that had adsorbed on the microbubble surface and reacted with pre-polymer. The capsule diameter depended on the dissolution rate of gases, and the diameter of the hollow microcapsules fabricated from air microbubble templates ranged from 5 to 200 microm.

Theoretical analysis of microcapsule mass transport behavior

Fundamental microcapsule mass balance equations are used to describe the mass transport behavior of a diffusing species into or out of a microcapsule with a continuous, spherical core/shell structure. These equations demonstrate that a capsule shell thickness of 1 6 the capsule outer diameter maximizes the time required for the diffusing species to reach a specified concentration within the inner core region of the microcapsule. This optimum capsule thickness depends solely upon capsule geometry and corresponds to an active agent loading well below that often found in current microcapsules.

Photostability of indomethacin in model gelatin capsules: effects of film thickness and concentration of titanium dioxide on the coloration and photolytic degradation.

The dependence of the photostability of indomethacin on the capsule shell thickness and on the concentration of titanium dioxide used as an opacificient was investigated using gelatin films prepared by casting as models of hard gelatin capsules. The film thickness and concentration of opacificient were varied in the ranges of 50-150μm and 0-1.5% of the amount of dried films, respectively. Films and indomethacin tablets were exposed to a 400 W mercury vapor lamp for 120 min, then coloration of the enclosed indomethacin was measured by tristimulus colorimetry, and evaluated as Hunter's color difference. The chemical stability of the drug was determined by following the ultraviolet spectrophotometric change of a solid sample. There was a good linear relationship between color difference values and the square root of exposure time at all concentrations and thicknesses. The coloration rate constants calculated from the slopes of these lines were affected by both parameters, and decreased significantly as the film thickness was increased at every concentration of opacificient. However, the effect of concentration seemed to disappear above 1% addition. The coloration rate was directly dependent on the average transmittance of films over the wavelength range relating to the photostability of indomethacin. Degradation of indomethacin followed apparently sequential first-order kinetics. Apparent conversions after 120-min exposure as determined from the UV spectra were also affected by both parameters and were below 3% at thicknesses above 80μm at every opacificient concentration tested ; this represents excellent protection of indomethacin.