The technique using cells isolated from a tissue in testing or examination is now an essential method in the biotechnology-related fields. It is widely used in diagnosing a disease or morbid condition, searching for a new drug and evaluating the efficacy of a drug, or in animal inspection, plant inspection and testing for environment pollutants, among others.
The cells isolated are sometimes immediately subjected to testing but, in many cases, they are cultured in culture dishes or test tubes in the manner of cell culture. Various assays are carried out in such culture systems.
Generally, in these assays, a uniform culture system is established and, for example, the amount or concentration of a drug or the like to be evaluated in that system is varied to estimate the effect thereof. Therefore, the culture vessels used for such culture are made uniform and constant in shape. As the culture vessels, use is generally made of the so-called culture dishes or plates.
Generally used as such culture dishes or plates are petri dishes and 6-well, 12-well, 48-well and 96-well plates (cf. Patent Document 1). In response to the recent trend toward miniaturization, the use of 384-well plates smaller in well diameter and increased in the number of culture wells has also been started.
However, when the culture of tissue cells is carried out in those cell culture dishes or plates which are commercially available, there arises a problem that cells extend thinly to take a form showing no directionality and no longer show one or more functions they have in vivo.
For confirming certain cell activities, it is possible to measure the change in pH due to discharge of a waste material or the level of carbon dioxide emission by means of an electrochemical sensor, for instance. Attempts have been made to compare the measured data for a vital tissue with the measured data for cells cultured on culture dishes or plates. Under present conditions, however, the values reproducing the data for vital tissues cannot be reproduced on culture dishes or plates. A plausible reason is that while each plate well has a vessel-like form, it means nothing but plate culture to cells several microns to several tens of microns in size. In particular, in the case of proliferation of tissue cells such as hepatocytes which are difficult to culture, it becomes more difficult to allow them to function as in vivo.
As a means for solving such problems, an attempt has been made to form, on culture plates, a fine vessel pattern suited for the growth of tissue cells and culture cells within such fine vessel pattern (cf. Patent Document 2). Namely, it is intended to culture cells in each fine vessel pattern to propagate cells three-dimensionally so that they may perform a function(s) they have in vivo.
Currently, however, this means can be applied only to cell culture for certain bioassays or for certain therapeutic purposes alone. For example, cardiac myocytes of a living individual beat in response to an electric signal transmitted from the brain. For performing their pulsating function, cardiac myocytes in a living body are constituted so that the arrangement thereof may have directionality. Therefore, in the field of biotechnology, tissue culture under regulation of the extension direction, like in the case of living tissues, is required in studying tissue regeneration in artificial organs. To the contrary, the culture on the conventional culture plates has a problem that, in addition to the difficulty of three-dimensional culture, it cannot regulate the extension direction, so that it cannot be applied for purposes of research and testing.
As an example of cardiac muscle culture for a therapeutic purpose, transplantation of a cultured cardiac muscle tissue partly into the cardiac muscle tissue necrotized by cardiac infarction for lifesaving has been studied. The whole heart pulsates greatly in response to an electric signal from the brain. Upon necrosis of a part of the cardiac muscle tissue due to myocardial infarction, the signal transduction within the cardiac muscle is blocked, with the result that the heart repeats small contractions called fibrillation. Accordingly, thrombi are formed as a result of residence of blood in the heart and, in the case of their being carried to the brain tissue, such a secondary case as cerebral infarction may be induced. Prolonged fibrillation may possibly lead to death. In the treatment of such condition, the object is not the completion of an artificial organ but the substitution of a part of the tissue. Therefore, it is desired that such cardiac tissue culture be realized as early as possible.
Under the existing circumstances, however, the culture on the conventional culture plates cannot regulate the extension direction, in addition to the difficulty in three-dimensional culture, hence has a problem that it cannot be applied for this purpose, either.
Patent Document 1: Japanese Kokai (Laid-open) Publication H11-169166
Patent Document 2: Japanese Kokai Publication