Liposome-type artificial red blood cells stabilized with carboxymethylchitin (mean diameter 310 nm) were prepared by a two-step emulsification technique. Sheep haemolysate was dispersed as fine droplets in a lecithin solution in dichloromethane to yield a W/O-type emulsion. The W/O emulsion thus obtained was then dispersed in an aqueous carboxymethylchitin solution to give a W/O/W-type complex emulsion. Removal of the organic solvent by evaporation from the complex emulsion left an aqueous suspension of the artificial red blood cells. The haemoglobin-trapping efficiency of the cells was found strongly dependent on the pH of the carboxymethylchitin solution used.The artificial red blood cells underwent disintegration by the action of surfactants. When a comparison was made among those surfactants which have the same alkyl chain length, the degree of cell disintegration was in the increasing order, anionic cationic nonionic. Globulin and fibrinogen produced no disintegration of the cells while albumin disrupted the cells to a slight extent.
This paper describes the effect of pH on the phase behaviour of an amphoteric surfactant (N α , N α -dimethyl-N α -lauroyl lysine, DMLL) in electrolyte (NaCl)/alkane (n-octane)/cosurfactant (n-pentanol) systems which are of possible pertinence to enhanced oil recovery. Three-phase microemulsion systems, which are composed of water, alkane, and microemulsion phases, are formed with n-octane containing/i-pentanol over the entire pH range of 1-9. The pH of the aqueous surfactant solutions is found to have a considerable effect on the cosurfactant requirement for middle phase microemulsion formation. The optimal cosurfactant requirement for middle phase microemulsion formation shows two minima at two pH values, where different types of DMLL coexist in the multiphase microemulsion system, but is almost independent of temperature in the vicinity of the isoelectric region (net charge of DMLL molecules becomes almost zero). It is found that the change of optimal concentration of cosurfactant with changing pH is caused by the dissociation of the surfactant and the binding of ions (Na+ and Cl - ) with the hydrophilic groups of DMLL molecules.
Two types of microcapsules with different negative surface potentials, poly (1, 4-piperazinediylterephthaloyl) microcapsules containing various concentrations of sodium polystyrene sulfonate solution and hemolysate-loaded polyamide microcapsules of different degrees of carboxylation, were prepared by using an interfacial polymerization technique, and the interactions of these microcapsules with human polymorphonulcear leucocytes (PMNs) were investigated as a function of the surface potential of the microcapsules in the absence and presence of plasma proteins. The rate of oxygen consumption by PMNs was taken as a measure of the interaction. In the absence of plasma proteins, the rate of oxygen consumption by PMNs increased with increasing difference in surface potential between the microcapsules and PMNs. The presence of plasma proteins affected the rate of oxygen consumption, which was dependent on the protein species present and related to the surface potential of the microcapsules. This was interpreted as showing that the surface potential of the microcapsules exerts a great influence on the mode and amount of protein adsorption on the microcapsule surface.
Polylactide (PLA) microcapsules with an average diameter of 1.5μm were prepared by an interfacial deposition technique. The degree of degradation of PLA microcapsules was estimated by determination of the amount of lactic acid as a final product in bulk solution and from the molecular weight distribution of PLA of the microcapsules remaining undegraded by means of gel permeation chromatography using chloroform as the eluent. The rate of hydrolytic degradation of PLA microcapsules prepared by using poly (D, L-lactide) or poly (L-lactide) was extremely pH-dependent ; it was slowest at pH around 5.0 and it increased in both strongly acidic and strongly alkaline solutions. The activation energy of deesterification at pH 7.4 and ionic strength 0.15 was calculated to be 19.9kcal/mol for poly (D, L-lactide) microcapsules and 20.0 kcal/mol for poly (L-lactide) microcapsules, when the initial weight-average molecular weight was about 100000 for both polymers. These values are comparable to those found for the hydrolysis of alkyl acetates.1) In buffer solution (pH 9.6), the hydrolytic degradation was enhanced when the ionic strength of the medium was increased. Chromatographic analysis of the products of hydrolytic degradation suggested that OH- or H3O+ attacks the ester bonds located in the crystalline zone, followed by further cleavage of the initial products into fractions with lower molecular weights. Carboxylic esterase promoted the degradation by cleaving the ester bonds located in the crystalline zone directly. Urea and NaSCN accelerated the degradation effectively, while AlCl3, CaCl2, and KCl had no or little effect on the degradation rate. Poly (L-lactide) microcapsules were degraded less rapidly than poly (D, L-lactide) microcapsules.
Methods of microcapsule preparation are described. They are roughly classified into chemical, physicochemical, and physical methods. Fundamentals and examples of preparation are given for each of the methods.
Conditions for preparing tiny biodegradable capsules were examined using electrocapillary emulsification that allows one to prepare monodisperse emulsions with ease by applying a DC potential between oil and water phases without mechanical agitation. The results obtained showed that a 1 : 4 mixture of polysorbate 80 (TO-10), a hydrophilic non-ionic surfactant, and sorbitan monooleate (SO-10), an oleophilic surfactant, is appropriate as the surfactant to be added to oil phase, cyclohexane is acceptable as the oil phase and 1000 V is optimum as the DC potential to be applied. The capsules prepared had sizes ranging from 100–300 nm and a surface roughness of ∼10 nm and degraded in model intestinal juice more easily and rapidly than in model gastric juice. In addition, the capsules containing lactoferrin, an anti-carcinogenic protein, were found to keep 12.5% of the protein used in encapsulation without losing its activity.
