The bioreactor contains a substrate consisting of nine wells (diameter 1.5 mm), in which the liver cells and microparticles are embedded.
The microbioreactor was developed by researchers at the Fraunhofer Institute for Cell Therapy and Immunology IZI in Potsdam in collaboration with partners at the Hebrew University of Jerusalem as part of the HeMiBio (Hepatic Microfluidic Bioreactor) project, building on previous work on cultured liver cells.
These have often been viewed as one of the most promising approaches in this area as given the liver’s importance in eliminating toxins from the body, it makes sense to use its cells to test the toxicity of substances.
This has hit problems in the past however, as liver cells rarely survive for longer than a few days in a laboratory environment making it virtually impossible to carry out experiments to determine the long-term effect of toxic substances on a living organism.
However, in this new development, the Fraunhofer Institute claims that its microbioreactor can keep liver cells alive and observed for a period of one month, allowing researchers to watch how liver cells react to toxic substances directly and in real time.
“Up to now, both in animal testing and in conventional lab tests, measurements have usually only been made at the end of the test,” says Dr Claus Duschl, head of the cellular biotechnology department at the IZI.
“The procedure consists of administering different doses of an active ingredient and subsequently analyzing the areas of dead tissue or the dead animal. It is not possible to determine the precise effect of the active ingredient on the cells using this method.”
Measuring metabolic processes
The microbioreactor has miniature sensors that gather real-time data which measure the amount of oxygen being taken up by the liver cells at any time and can then precisely identify the stages of the metabolic process that are affected or halted by an active ingredient, thus rating its toxicity.
“We have been able to verify various hypotheses by selectively replacing specific metabolic products whose synthesis had been blocked by the toxic substance,” Duschl explains. “As we had surmised, the metabolic process then continued unaffected to the next stage.”
The reactor also uses tiny polymer particles containing a luminescent dye which can help indicate the presence of metabolic activity, and can be used to measure the effect of the toxic substance, enabling scientists to gain a better understanding of the way certain substances affect the human organism and understand why some are toxic while others have a therapeutic effect.
So far all of the research has worked as intended, but Duschl admits there is still a way to go.
Researchers at the Fraunhofer Institute are collaborating with colleagues in Belgium, and have developed a more advanced reactor based on highly complex microfluidic structures. The first tests are underway, and the results are very promising.
Over the last few years serious efforts have been underway to significantly reduce the number of animal tests carried out for research purposes.
The latest EU Cosmetics Regulation, which came into force in 2013, bans the sale of cosmetic products containing ingredients that have been tested on animals; but the challenge has been that it is difficult to find alternatives, for pharmaceutical purposes as well as for the cosmetics industry.
In many cases, there are no other suitable methods of toxicity testing available. Numerous research groups are therefore working on the development of new, viable test formats.