A technique of using cells isolated from tissue for tests and examinations is essential in biotechnology-related fields.  Such a technique is widely used for a diagnosis of diseases and pathoses, a search for a new drug and an assessment of its effect, an animal inspection, a plant inspection, a test of an environment pollutant and so on.  Therefore, cells used in the biotechnology field are becoming increasingly diversified. 
Although some isolated cells are immediately used for tests in a floating state, others are cultured in a state of being adherent to a culture dish and used for various tests and examinations in most cases.  Primary cells and cell lines used for cell culture are required to exhibit drug sensitivity, toxicity reaction or the like of a similar level to a test in vivo, so-called an in vivo test.  In other words, an in vivo-like cell function is required in a cell culture container.  Further, because isolation for obtaining primary cells is complicated and cell culture lines used for a cell culture test are expensive, a test method with a small number of cells is desired. 
Recently, discontinuation of development in the clinical testing phase has been an issue.  This is due to an animal species difference in the pharmacokinetics study phase.  Heretofore, in pharmacokinetics studies in the preclinical phase, in vivo pharmacokinetics has been predicted by using an animal such as a rat, a dog or a monkey.  However, it has becoming evident that the prediction is virtually invalid in a clinical testing using a human.  Therefore, in the prediction of pharmacokinetics or the like for humans, using a human sample is the most effective and convenient way, and it is important for conducting efficient drug development and safe clinical testing. 
In the pharmacokinetics study that examines in vivo pharmacokinetics, absorption, metabolism and excretion in the liver are mainly examined, and a human sample to be used is liver slices, liver cells, liver microsomes or the like.  Among those, the liver slices are not easily obtainable, and the liver microsomes can be used only for a metabolism test with limited metabolic enzymes.  Thus, use of the liver cells is considered to be the most effective. 
In screening, a culture dish to be used is a petri dish made of resin or a 6-well, 12-well, 48-well or 96-well plate.  The size of the entire plate is substantially the same, and as the number of wells increases, the size of one well decreases.  One well corresponds to one culture dish.  Further, with the recent trend toward micronization, a 384-well plate made up of a larger number of culture dishes with a smaller diameter has been started to be used, and the one adaptable for a desired screening method is used.  The bottom of such a culture dish is a flat-shaped, and the bottom surface is used as a culture surface. 
However, if a hitherto-used culture dish is used for culture of tissue cells, there are cases where the original function disappears and dedifferentiation occurs and where undifferentiated cells do not differentiate, which raises an issue that a target cell function is not expressed.  For example, if fresh human liver cells are cultured on a normal flat plate, the function of metabolic enzymes when isolated is significantly lowered in one day or so, and therefore a drug metabolism test is conducted in four hours from seeding the cells onto the plate in some cases.  There is thus a problem that it is impossible to make use for a test with long-hours culture and a problem that it is impossible to investigate long-hours metabolic stability. 
To overcome the above problems, an attempt to coat a culture container surface with a biological material (glycoprotein, protein etc.)  of human or animal origin (cf.  Patent Document 1), an attempt to culture in polymer gel (cf.  Patent Document 2), and an attempt to form a liver cell mass in a micro-container (cf.  Patent Document 3) have been made. 
[Patent Document 1]
    Japanese Unexamined Patent Application Publication No.  8-319317[Patent Document 2]    Japanese Unexamined Patent Application Publication No.  8-308562[Patent Document 3]    International Patent Publication No.  WO2008/130025