The point integrated practice summarizes how our work on human practices influenced the design and planing of our project. This is an important point for us as we are developing a solution for that may ultimately be applied in patients and it is thus important to know what patients and medical doctors are concerned with.

The kill-switch was implemented into our project as we were asked several times in discussions with experts (such as medical doctors or life science professors) what would happen if we would have some malignant cells in our printed organs. As this case is potentially possible and may also be a factor patients or healthcare officials would probably be sensitized, we started to plan a kill switch. We decided to integrate as very solid and simple kill switch that features a constantly expressed prodrug-convertase enzyme. The prodrug-convertase expressed in the printed organ is generally not harmful as long as no problems for the patient occur. In an emergency case in which a doctor decides that the synthetic tissue needs to be removed from the patient he gives the patient a single pill with the prodrug (which is Famciclovir in our case) and all transgenic cells in the patient will suffer from a reduced viability and die in only a few days.

The second point we identified from our interviews with experts to be crucial was the printed extracellular matrix composed of recombinant proteins. Some of the experts worried about immunogenicity of these components especially if it was somehow mentioned in the discussion that in the future it could be an aim for the bioprinting sector to print replacement organs. Our answer for such questions was always, that the Avidin & Biotin mesh is only used to give the cells initial mechanical stability until they can start to divide and differentiate. From this imput we came to the idea that it would be a great point for our bioprinting approach if we could dissolve the synthetic tissues upon addition of a substance. We found this substance when we read about biotinidase, which is an enzyme that recycles biotin, which is quite value vitamin for mammals. As it cleaves-off biotin molecules from proteins in the blood it is also capable of dissolving our bioprinted tissue as soon as it is added to the petri dish with the synthetic tissue. In our Linker Chemistry subproject we then developed extended linkers that were expected to be easier or harder to cleave by the biotinidase. This approach was successful and we found two additional linkers that are easily accessible by means of organic synthesis and the biotin-valin-NHS linker proved to be much more resistant towards biotinidase cleavage.