Newly developed drugs need to be tested by using cell culture and in vivo using animals. Following these experiments, medicines can then enter into clinical trials to first assess their safety and then efficacy. After appropriate acceptable results obtained, producers apply for approvals from concerned bodies, such as the FDA in the United States. In many cases even with medicines that are approved, complications may occur. 1, 2 Because of the failure of two-dimensional (2D) cell culture system to recapitulate in vivo events and failure of animal models to be representative of a different species, that is, human, 3 it remains necessary to search for new possibilities and be able to overcome limitations related to current drug testing methods. 4 Given also the fact of demanding that all medicines and chemicals undergo animal testing, the cost of development will be tremendously huge, and will be reflected in the prices of developed drugs and time they take before they become available. With new EU regulation (REACH Policy for Registration, Evaluation, and Authorization of Chemicals) requesting the testing for toxicity of c. 30,000 chemicals, we will need about 2.5 to 54 million animals 5 to use for testing (costing about 1.3–9.3 trillion Euros). 6, 7 The development of a single drug formulation can take up to 13.5 years 8 and cost 2.5 billion USD. 9

With the advent of organ-on-a-chip technology which evolved from lab-on-a-chip 10 by culturing cells into microchannels, it seems that an alterative to 2D culture and animals is emerging with promises to be more biomimetic to human physiology. So far, various tissue models were developed to represent lung, 11 gut, 12, 13 kidney, 14 heart, 15 liver, 16, 17 and bone marrow. 18 Multiorgan-on-achip devices were also connected to develop a more biomimetic system to test for studying systemic 19 and secondary 20 toxicity where kidney, liver gut, and so on can interact and provide more reliable results regarding drug absorption, metabolism, clearance, and toxicity. With a more complex level, where about 10 organ-ona-chip organ types are connected, human-on-a chip is developed to study systemic toxicity. 21