Single Microcapsules Research Articles

Oral administration of biochemically active microcapsules to treat uremia: new insights into an old approach

This paper begins with an extensive review of previous research on the degradation of non-protein nitrogen compounds for improved therapy of renal failure. During the 1970s, Malchesky established that naturally occurring strains of microorganisms were highly effective for the in vitro degradation of urea and other compounds found in urine, and that these bacteria could be conditioned with selected media to enhance growth and degradation efficiency. A few years later, Setala introduced the concept of oral delivery of lyophilized bacteria, harvested from soil, to uremic patients, for degradation of non-protein nitrogen compounds. In the 1990s, Chang proposed delivery of encapsulated genetically modified bacteria for removal of uremic waste products in vitro and in vivo. Recently, our group has pursued the idea of orally delivering formulated combinations of enzymes or modified bacteria. A new study is also described, which characterizes the capacity of a single alginate microcapsule containing a mixture of genetically modified cells and enzyme to degrade urea, uric acid and creatinine. The combination capsules were found to be effective in vitro and in vivo in a rodent model of chemically-induced renal failure. Reduction of urea concentration in vivo required co-administration of a cation exchange resin to adsorb ammonia. Increased investigative effort is warranted for these approaches which offer significant potential as an adjunct to conventional forms of dialysis.

Shell Effects on Vibration Behavior of a Microcapsule in an Acoustic Field

The shell effects on the vibration behavior of a microcapsule in an acoustic field are discussed. Shell elasticity parameter Sp is applied to the quantitative evaluation of the shell effects. In this work, the behaviors of a single microcapsule in an acoustic standing wave are observed using a high-speed video camera. By changing the driving-sound pressure, the dependence of the vibration mode of a microcapsule on the driving-sound pressure is confirmed. Measurements of impulse response of the microcapsules are also carried out, and then it is found that microcapsules have higher resonant frequencies than free bubbles which do not have a shell. A comparison between the experimental and calculated results is carried out by applying the modified RPNNP equation, and the shell elasticity parameter Sp of a microcapsule is estimated.

Mechanical strength of microcapsules made of different wall materials.

The mechanical strength of microcapsules made of three different wall materials, including melamine-formaldehyde resin, urea-formaldehyde resin and gelatin-gum arabic coacervate, were measured by a micromanipulation technique. Single microcapsules were compressed to large deformations or rupture and the force being imposed on them were measured simultaneously. Melamine-formaldehyde and urea-formaldehyde microcapsules showed clear bursting under compression, and their bursting force, deformation at bursting and deformation at a pesudo yield point were determined. Gelatin microcapsules did not show clear bursting under compression, and their mechanical strength was characterized by the force required to cause their deformation to 50%. The mechanical strengths of these three types of microcapsules are compared in this paper.

Parameters to be Considered in the Simulation of Drug Release from Aspirin Crystals and their Microcapsules

Purpose: Drug microparticles may be microencapsulated with water-insoluble po lymers to obtain controlled release, which may be further determined by the pa rticle d istribution. The purpose o f t his s tudy was to de termine the drug release pa rameters needed for the theoretical prediction of the release profiles of single aspirin crystals and their microcapsules. Method: Four single crystals of aspirin of varied weight and orthorhombic in shape or their microcapsules also of varied weights were randomly selected for the study. The microcapsules were walled with an acrylatemethacrylate copolymer ( wall thickness, 11 i m). The following parameters were evaluated: the order of release, the dissolution rate constant, k (crystals), the diffusion coefficient, D (microcapsules), the maximum release m∞ and time to attain it t∞. These parameters were in turn used to simulate the release profiles of hypothetical single particles of a wide range size distribution, 0.3 ‐ 1.4 mm at 0.1mm intervals. Results: The e mpirical single crystals exhibited an initial zero o rder ( 93%; dissolution constant = 4.4 min -1 ) followed by a first order release (6%; dissolution constant = 0.38 min -1 ). Maximum release from each of the crystals was 99% of the initial particle weight; thus m∞ was a constant fraction of the initial particle weight. A zero order release consistent with a Fickian diffusion model was displayed b y the single microcapsules (diffusion coefficient, 5.4x10 -4 mm 2 min -1 ). At same particle weight the release parameters m∞, t∞, and the slopes of the rate order plots compared favourably with the theoretical data. Conclusion: The study indicates that the empirical release data on a few single particles can be used to predict the release profiles of single particles of a wide range of size distribution. This finding may be exploited in the prediction of drug release from polydisperse systems.

Mechanical properties of melamine-formaldehyde microcapsules

The mechanical properties of melamine-formaldehyde (M-F) microcapsules were studied using a micromanipulation technique. Single microcapsules with diameters of 1-12 microm were compressed and held between two parallel planes, compressed and released, and compressed to burst at different speeds, whilst the force being imposed on the microcapsules and their deformation were measured simultaneously. This force increased as single microcapsules were compressed and then relaxed slightly as they were held. When the microcapsules were repeatedly compressed and released, a pseudo yield point was found for each microcapsule. Before the microcapsules were compressed to this point, the deformed microcapsules recovered to their original shape once the force was removed. However, when the deformation was beyond the 'yield point' there was profound hysteresis and the microcapsules showed plastic behaviour. As the microcapsules were compressed to burst at different speeds, ranging from 0.5-6.0 microm/s, it was found that their mean bursting forces did not change significantly. The deformations at the pseudo yield point and at bursting were also independent of the compression speed. On average, these melamine-formaldehyde microcapsules reached their 'yield point' at a deformation of about 19 +/- 1%, and burst at a deformation of 70 +/- 1%.

Study of the Theophylline Content of Single Coated Particles by Gas Chromatography/Mass Spectrometry

The aim of the present study was to determine by gas chromatography/mass spectrometry (GC/MS) the content uniformity of single theophylline microcapsules of different particle size ranges. Microencapsulation was carried out in a laboratory fluidized bed system using Eudragit L30D aqueous dispersion. Scanning electron microscopy was applied for the characterization of the surface morphology of the prepared theophylline microcapsules of two different particle size ranges. The theophylline content of single particles was determined by GC/MS analysis. It was found that the particle size of microcapsules greatly influenced their theophylline content. The GC/MS analysis was successfully applied to indicate the changes in the content uniformity and thus the interparticular coating distribution of single theophylline microcapsules in the presence of several excipients.

Raman spectroscopic investigation of polycyanacrylate capsules

Raman spectroscopy is used for the characterization of different polycyanacrylates. The influence of pH-value and temperature on polymer properties is examined for bulk material as well as for single microcapsules. The technique of optical trapping in combination with Raman spectroscopy enables the study of the polymerization process in one single emulsion particle.

Mechanical strength of single microcapsules determined by a novel micromanipulation technique

A micromanipulation technique has been developed to measure the bursting force of single dry microcapsules coated onto a surface, such as those normally used in carbonless copying paper. For measuring the bursting force of a given microcapsule, a single fine probe with a flat end about 10mum in diameter was used to squeeze the microcapsule against a flat surface until it burst. The force being imposed on the microcapsule was measured by a transducer connected to the probe. The bursting force and diameter of single dry microcapsules in two samples, different in size and wall thickness, were measured by this technique. The bursting force of the microcapsules in one sample ranged from 50 to 220muN and the diameter from 1.3 to 7.0mum, whilst the bursting force in the other was from 20 to 175muN and the diameter from 0.7 to 3.7mum. This technique makes it possible to compare the mechanical strength of microcapsules made of different formulations, and to infer information about microcapsule mechanical properties.

Raman spectroscopic monitoring of the polymerization of cyanacrylate

Micro Raman spectroscopy is used to investigate the polymerization reaction kinetics of cyanacrylates. Polycyanacrylates have important applications in medical and pharmaceutical research (polycyanacrylate capsules are used as drug carriers in the pharmaceutical industry). The reaction of the acrylate-monomers in both bulk as well as in single trapped microcapsules has been monitored by Raman spectroscopy recording the decrease of the CC stretching band as a function of time. The polymerization process is followed through reaction parameters such as ester function of the monomer (methyl/ethyl, butyl), the reaction medium (bulk, emulsion), temperature, and pH value.

Light Scattering of a Single Microcapsule with a Hydrogel Membrane

We have developed a light-scattering apparatus using a capillary tubing sample cell that is particularly suitable for investigating the structure of a single microcapsule. This approach is capable of determining the individual structures of polydisperse particles because the scattering function of each individual microcapsule can be measured independently. The apparatus was used to determine the outer diameter d and the membrane thickness δ of poly(l-lysine-alt-terephthalic acid) microcapsules as a function of pH. The values of both d and δ were found to be the lowest at pH 4 and increased as the pH value was shifted to either side of pH 4. The change in δ was roughly proportional to the change in d, suggesting an isotropic volumetric phase transition of the hydrogel membrane of the microcapsule. Diffusion coefficients of anionic and cationic electrolyte ions in the microcapsule membrane changed in parallel with δ.

Microspectroscopic Analyses of Dye Distribution Characteristics in Single Microcapsules

The distribution characteristics of a dye in single melamine resin wall microcapsules containing a dye/toluene solution are studied by a laser trapping-absorption microspectroscopy technique. In the case of Disperse Orange 13 as a dye, the molar absorptivity determined from the slope of a dye absorbance-capsule diameter (d) plot agrees well with that observed in a homogeneous toluene solution, indicating that the dye is solubilized homogeneously in the inner toluene solution of the capsule. For tetraphenylporphyrins (MTPP: Zn(II)TPP, Co(II)TPP, or H(2)TPP), however, the d dependence of absorbance shows a sigmoidal curve. Since absorbance of a ZnTPP/toluene droplet before polymerization of the melamine resin increases linearly with an increase in the droplet diameter, the sigmoidal d dependence of the absorbance is concluded to originate from distribution of the dye into the resin wall. Detailed analyses of the data indicate that the partitioning ratio of the dye between the toluene and resin phases is dependent on the capsule diameter. Size-dependent distribution of MTPP in single microcapsules is discussed on the basis of a proposed model and the d dependence of the dye absorbance, and it is concluded that the distribution of MTPP to the melamine resin wall is facilitated for larger microcapsules.

Compressive deformation of a single microcapsule

This paper reports an experimental and theoretical study of the compressive behavior of single microcapsules; that is, liquid-filled cellular entities (approximately 65 \ensuremath{\mu}m in diameter) with a thin polymeric membrane wall. An experimental technique which allows the simultaneous measurement of both the compressive displacement and the reaction forces of individual microcapsules deformed between two parallel plates up to a dimensionless approach [(compressive displacement)/(initial particle diameter)] of 60% is described. The corresponding major geometric parameters of the deformed microcapsule, such as central lateral extension as well as the failure phenomena, are reported and recorded through a microscopic visualization system. The elastic modulus, the bursting strength of the membrane, and the pressure difference across the membrane are computed by using a theoretical analysis which is also presented in this paper. This theoretical model, which was developed by Feng and Yang [J. Appl. Mech. 40, 209 (1973)] and then modified by Lardner and Pujara [in Mechanics Today, edited by S. Nemat-Nasser (Pergamon, New York, 1980), Vol. 5], considers the deformation of a nonlinear elastic spherical membrane which is filled with an incompressible fluid. The predictions of the theory are consistent with the experimental observations.

Distribution of Zinc Tetraphenylporphine in Single Melamine-Resin/Toluene Microcapsules Studied by Laser Trapping-Microspectroscopy

Abstract Absorption microspectroscopy has been conducted to study chemical properties of single melamine-resin microcapsules containing a zinc tetraphenylporphine (ZnTPP)/toluene solution. Although absorbance of ZnTPP in the capsule increased with increasing the capsule diameter, its tendency was much smaller than that expected from a homogeneous distribution of ZnTPP in the inner toluene solution. The results were discussed in terms of a distribution of ZnTPP in both the melamine-resin and toluene phases.

Gradation of microcapsule wall porosity by deposition of polymer mixtures (Eudragit RL and Eudragit RS). Phase separation of polymer mixtures and effects of external media and conditions on release.

With the aim of increasing flexibility in controlling release from microcapsules, mixtures of wall polymers varying in porosity were investigated by phase separation. Eudragit RL and RS (polymethylmethacrylate linear backbone polymers) mixtures differing in polar substituent content and porosity were used as the wall material and were deposited using a non-solvent addition method. Release rates increased with polar group content of the mixtures, using theophylline, potassium dichromate or sodium chloride as model core materials. Theophylline release rate had the same relationship to polar group content as found earlier for urea permeation of cast mixed-polymer films. Release was generally accelerated in these systems when the external medium contained sodium lauryl sulphate as a wetting agent but not consistently, decreasing unexpectedly for RL-theophylline microcapsules. Localized dissolution of core substance was visible microscopically during release from single microcapsules. The release rate was sensitive to agitation intensity only at low wall to core ratios. Temperature change revealed only a single release mechanism for sodium chloride by Arrhenius equation treatment. Buffer ions penetrated coatings readily, changing theophylline release rates and providing clear evidence of diffusion via a pore-capillary mechanism.

The preparation of microcapsules which include silicon carbide particles in a wall material

Microcapsules, of which the wall material was made of polystyrene, with a core material of water were prepared by the drying-in-liquid method. In order to improve the thermal conductivity of the wall material, an attempt was made to get silicon carbide (SiC) particles to disperse in it. SiC powder had been treated with a silane coupling agent to change its affinity for an oil phase. When untreated SiC powder was added, spherical-shaped single cellular microcapsules were obtained and SiC particles were localized at the surface of the wall material. When treated SiC powder was added, irregular-shaped multicellular microcapsules were obtained and SiC particles were dispersed in the wall material. The formation mechanism of the microcapsules was proposed on the basis of stabilizing effect of SiC particles on coalescence between water-in-oil droplets.

壁膜に炭化ケイ素粒子を含有するマイクロカプセルの調製

Microcapsules, of which the wall was made of polystyrene, with a core material of water were prepared by the drying-in-liquid method. In order to improve the thermal conductivity of the wall material, an attempt was made to get silicon carbide (SiC) particles to disperse in it. SiC powder had been treated with a silane coupling agent to change its affinity for an oil phase. When untreated SiC powder was added, spherical shaped single cellular microcapsules were obtained and SiC particles were localized at the surface of the wall material. When treated SiC powder was added, irregular shaped multicellular microcapsules were obtained and SiC particles were dispersed in the wall material. The formation mechanism of the microcapsules was proposed on the basis of the stabilizing effect of the SiC particles on coalescence between the (w/o) -droplets.

Dielectric measurement of a single sub-millimeter size microcapsule

A new technique is described for measuring dielectric dispersion of a single microcapsule in suspension over a frequency range from 1 kHz to 10 MHz. It was applied to polystyrene microcapsules which showed a two-step dielectric dispersion, that is, a superposition of two Debye type dispersions. The dielectric dispersion was analyzed by an electrical model in which a spherical core covered with a shell is immersed in a continuous phase, yielding the phase parameters related to the microcapsule: the wall thickness, the permittivity and conductivity of the core phase. The advantage of this technique is that it can characterize individual microcapsules, whereas the conventional method provides average properties of many microcapsules. Hence, the technique enables us to directly determine the distributions of the phase parameters and to exactly examine the relationship between the dielectric behavior and the microcapsule structure simultaneously observed by microscopy.

Pyrene excimer formation dynamics in a single microcapsule by space- and time-resolved fluorescence spectroscopy

Pyrene excimer formation dynamics in a single microcapsule by space- and time-resolved fluorescence spectroscopy

Laser manipulation and ablation of a single microcapsule in water

Laser manipulation and ablation of a single microcapsule in water

Toward Microphotoconversion. Laser Manipulation of a Fine Particle.

By introducing CW and pulsed lasers into optical microscope, we have set up a laser trapping spectroscopy-ablation system which enables us to study spectroscopic and dynamic properties of an individual single particle in solution. We demonstrated three-dimensional laser trapping of various, μm-order particles and determined the trapping force to be in the order of pN. When a laser-trapped particle was further irradiated by a pulsed laser, ablative penetration of the particle by a minute hole was observed. It was demonstrated, furthermore, that a single microcapsule containing organic reagents was chosen, transferred, and ablated to eject the inner organic solution in an arbitrary spatial position by the present technique. A manipulation tool for controlling chemical reactions in the μm-size volume is now realized by this technique.