4. The promises of tissue engineering for organ building and banking

With aging population, increase in longevity and decrease in the number of qualified donors, the need to find alternative solutions to current organ replacement methods is rapidly becoming a critical issue. Tissue engineering has appeared as a potentially viable solution. Classical tissue engineering is based on culturing cells in scaffolds, artificial extracellular matrix mimics, with the hope that the process leads to tissues and organs, that upon implantation can replace damaged, dysfunctional ones and lead to regeneration. However, building extensive living structures, such as tissues and organs is a task of monumental complexity. A recent approach to aid this endeavor is bioprinting. In this technique bioink particles, minitissues in the particular method to be described, are deposited into the biopaper, the temporary support structure, with the aid of special-purpose three-dimensional printer, the bioprinter. However, contrary to 3D printing of acellular materials, in the case of bioprinting deposition in itself does not lead to the final product. The functional biological structure results from the post-printing maturation, under near physiological conditions in bioreactors, a process that relies on fundamental early developmental processes akin to those used in embryonic morphogenesis and with no counterpart in the case of printing inanimate substance. With the recent advances in tissue engineering in general and bioprinting in particular, preservation of the biological structures will soon become an indispensable part of the process. Three possible approaches to the preservation of the engineered tissues and organs seem to emerge, depending on their location in the body or the specific method of their preparation. One approach is to establish a depository of ready-to-use, of-the-shelf replacement organs. This will require the same preservation solutions that are currently used or under development for donor organs. In particular, this approach will benefit from efficient ways of storing and managing organs. This in turn would increase the demand for tissue engineered products, lead to increased funding of the field and eventually result in saving more lives or improving the quality of many patients’ lives. Another possible approach is that the postprinting maturation process takes place in vivo, utilizing the body, the ultimate bioreactor. This approach is limited to non-vital organs or cases where the original organ is not yet fully dysfunctional. Here, it is the recipient organism that carries out the preservation function until the engineered structure becomes fully functional. Finally, in case of in vivo bioprinting, the deposition of the cellular material is performed directly in the recipient. This approach is limited to parts of the body that are accessible for printing, such as skin. The latter two solutions are inherent to tissue engineering. Novel methods of biofabricating functional tissues and organs, based on tissue engineering technologies thus may offer an alternative solution to mitigating the chronic shortage of donor organs including their preservation.