Non-invasive quality control for production processes of artificial skin equivalents by optical coherence tomography

The engineering of artificial tissue and organs is widely gaining relevance in biotechnological and biomedical research. Particularly by the law enforced reduction of animal testing, alternative methods need to be developed to simulate and test the effects of chemical substances on human organs. Regarding the branches for pharmaceuticals, chemicals and cosmetics most products need to be tested on penetration of the human skin tissue. As an alternative method to animal testing, skin equivalents (SEs) based on tissue engineering may be used to test the skin barrier function. In the framework of a large scale research project, we built a fully automated production process based on the adaption of manual laboratory protocols to carry out the biological process steps for the manufacturing of SEs. In a first step, keratinocytes are mechanically and enzymatic isolated from human foreskin biopsies. In a second process, the cells are cultivated in MTP format cultivation dishes und undergo a series of passages. In a last process step, the keratinocytes are concentrated and dispensed in 24 well membrane based MTPs. Due to biological fluctuations in cell and tissue growth, the production process faces major challenges to control and process a vast variety in batch duration and timing. This results in a strong impact in the final tissue quality. For quality control in the manual process, histologies of the SEs are prepared followed by staining and microscopic imaging. To overcome this time intensive process, we developed a fully automated optical coherence tomography OCT system. OCT is a non- invasive and non-destructive imaging technique based on the interferometric detection of optical light feedback from the probe tissue in the near infrared light. OCT generates 2D and 3D tomographic images with a micron resolution and a tissue penetration up to 2 mm. We developed custom image processing algorithms, to detect the individual layer structure and corresponding layer thicknesses. The OCT results show a high degree of correlation with the histological findings regarding structure and layer thicknesses. Further, we show in a first study a method to use this OCT layer detection technique as a potential substitution measurement to the ET50 test used for analyzing the in vitro skin barrier function.