Colloidosome
As colloidosomes in are biochemistry active substance-permeable capsules referred consisting colloid composed particles. The term is a word formation that should be based on the concept of liposomes (capsules made of fat-like double layers).
The microscopic capsules can be produced with self-assembling colloidal particles on the surface of emulsion droplets. This creates stable envelopes, the size, permeability and elasticity of which can be varied over a wide range. They can be used to include a large number of active ingredients for technical, medical and biological applications.
As a result, active substances such as drugs , proteins , vitamins , flavorings and small amounts of gases not only reach their desired location, but can also be released there in a controlled manner. The inclusion of living cells is also desirable in order to immunologically separate them from the rest of the tissue. Several research projects have been facing these requirements for several years.
A research group at Harvard University in Cambridge , Massachusetts , developed a universally applicable and flexibly manageable technique for the production of permeable microscopic capsules, which allows the selective and time-delayed release of the active ingredients. The substance to be enclosed is first emulsified with a suitable water or oil-based liquid. If colloidal particles are then added to this liquid, which can be selected in a wide range of sizes from nano- to micrometers, these particles self-organize to form a shell around the emulsion droplets , a process that can be explained by the minimization of the surface energy of the entire system . A spherical, two-dimensional structure is created around the drug drop. The interstices formed by the enveloping particles form the holes that define the permeability of the capsule. It can also be precisely adjusted in a size range between nano- and micrometers through the choice of the colloidal particles used.
Through various techniques such as sintering , careful “baking” of the particles at temperatures just over 100 ° C, or the electrostatic attachment of one or more particle layers, the surface particles are connected to one another in such a way that a stable, but elastic shell is created. The sintering temperature and duration are sensitive to the pore size of the capsule.
The mechanical strength of the colloidosomes can be changed over a wide range. The release of the active ingredients can thus be achieved by mechanical destruction at a precisely defined pressure . In the experiment, the breaking of a 60 mm shell at pressures of 106 to 107 Pa could be demonstrated. Areas of application are the release of flavorings e.g. B. when chewing, in the production of baked goods and special carbonless papers that are equipped with microcapsules. Swellable casings can also be produced in which the substance enclosed in the capsule only gets to the outside when, by slight swelling, e.g. B. a microgel shell in an alkaline environment changes the pore size. Capsules that are subject to chemical or photochemical decomposition at the point of use and then release ingredients are also conceivable.
A large number of inorganic and organic substances, including various polymer and glass particles, are suitable as starting materials for the colloidosomes . Hydrophobic, i.e. water-repellent active ingredients could also be encapsulated by emulsifying oil droplets in an aqueous solution. If the permeability of the colloidosome is in the range of only a few nanometers , so-called “nanosieves” are obtained, which in the case of a cell enable the exchange of small molecules, but do not allow larger molecules of the immune defense to attack the encapsulated cell. In preliminary experiments, living connective tissue cells could be successfully enclosed and their viability could be maintained for several hours. This makes the use of this emulsion technique z. B. possibly of interest in the treatment of diabetes mellitus and in bioreactors .
literature
- AD Dinsmore, Ming F. Hsu, MG Nikolaides, Manuel Marquez, AR Bausch, DA Weitz: Colloidosomes: Selectively Permeable Capsules Composed of Colloidal Particles , Science 298, 1006-1009, 2002. doi: 10.1126 / science.1074868