The present invention relates to a composite body for long-term delivery of effective substances, such as multi-layer membranes, multi-layer hollow fibers, or porous powder provided with a skin or a membrane layer, etc., which deliver over a long period effective material in identical quantities, such as pharmaceutics, hormones, chemicals, etc.
New and improved effective materials are always developed for the pharmaceuticals industry. In contrast, the methods of application of such effective materials have not been changed. The majority of medicaments are always applied orally or, more seldom, under the skin, intramuscularly or intravenously. The dosing of the effective substance for a successive therapy often has the same great importance as the effective substance itself.
For eliminating the disadvantages of the conventional application, it has been proposed to deliver the effective substance from a storage with a certain rate. There are, for example, so-called microcapsules in which the effective material, in general a medicament, is surrounded by a membrane. In this case, it is possible to control the discharge speed of the medicament, for example, by the structure of the membrane, its thickness, selection of the polymer for the membrane, and the like. It has also been proposed to load microporous powder with effective substances, such as fertilizers, insecticides, etc., which deliver in the course of time the effective material to its surroundings.
In all the above described methods, it cannot be in many cases avoided that at least in the initial period an increased delivery of the effective substance takes place, or a so-called "burst" effect. During the course of time, frequently the quantity of delivered effective substance decreases, despite the fact that the storage has not been exhausted.
It is also known to use in such processes composite membranes or porous grains which contain an effective material and are provided with an impregnating substance. The European Pat. No. 5,302 discloses, for example, a process in accordance with which the grains are loaded with an effective material, and a polyurethane skin is formed by chemical reaction to close the pores. Such a method is complicated and difficult. Despite the fact that a whole range of bodies for the long-term delivery of effective materials is known, there is a demand for improved bodies for the long-term delivery.