Currently, hundreds of thousands of people are on transplant lists throughout the world hoping to receive a critical organ such as a heart, kidney or liver. Unfortunately, the number of transplantable organs available is only a fraction of those needed. What if we could immediately meet this demand by artificially manufacturing personalised organs from scratch to save lives? This vision drives many scientists worldwide working in bioprinting, a branch within the field of regenerative medicine. Here, customised 3D printers are used to fabricate 3D structures by depositing materials layer by layer according to a digital template. In contrast to materials commonly used in conventional 3D printing, such as metals and plastics, bioprinting implements specially designed bio inks consisting of biological materials. These inks mainly include proteins, which are the main building blocks of organs and tissues. Depending on the application, these bio inks can also include living cells, as well as supplementary components, encouraging cells to grow. Advanced bioprinting techniques even allow for the selective deposition of various bio inks, thus creating more realistic organ and tissue replicates.
So how exactly does it work?
Let us assume that you needed a new lung. Firstly, a digital template is generated which can for instance be based on computer tomography images of your own lung. In the event of your lung already being severely damaged, a vital map of your lung would be recreated based on database details. Secondly, a bio-ink containing lung-specific proteins and cells is assembled. These cells can be derived from donors and are replicated in the lab, as a high number of cells is crucial for a vital organ. Significantly, this allows for the integration of your own cells, making it much more unlikely that your body will eventually reject the transplanted organ. Many bioprinting techniques have been developed and it remains questionable as to which one will enable the printing of functional organs. However, stereolithography methods have produced the highest resolution so far and have thus enabled the fabrication of amazingly accurate organ imitations in regard to shape. These light-based approaches cure a specially designed bio-ink using light. By selectively exposing one layer at a time, a spatially defined chemical reaction is initiated transforming the former liquid bio-ink into a stable, cross-linked gel which matches exactly the selected template. If the print is successful, the cells will start to grow, interact and multiply in the same way as native tissue does. To achieve full functionality, it will be necessary to train the tissue before implantation. This is especially so in the case, for instance, of tendons as these structures must bear high uni-directional loads. This strength is built up by cells reorganising tissue fibres over time according to perceived load stimuli and must therefore be implemented within the fabrication process.
How far are we from 3D printing organs?
Thanks to major advances in generating realistic templates, as well as acquiring and processing biological materials, scientists have been able to print full-sized 3D organs consisting of donor (stem) cells. However, these printed organs are only simplified representations of native organs in that they lack full organ-characteristic functionality. One of the main challenges still remaining in printing genuinely functional organs is to mimic the full complexity of an organ. Native organs are made up of complex biological compositions including various proteins and cells. Furthermore, chemical and physical stimuli, such as growth factors and stiffness significantly guide cellular development. Only by their precise interaction and spatial distribution will physiological functionality arise. Ultimately, the most interesting question will be to do with the minimal set of necessary information which is sufficient for instructing cells to create a functioning organ.
What else can we achieve with this technology?
Fortunately, printing organs is not the only major breakthrough we can achieve with bioprinting. This technology could also signal the end of drug testing on animals and humans. By printing small excerpts of patient specific tissue, the impacts and side effects of drugs can be evaluated on personalised models. In other words, if you were diagnosed with cancer, we could take a small biopsy from your diseased tissue and use that material to print several miniaturised models which exactly replicate your cancer. We could then easily scan the effects of every possible cancer treatment on these miniaturised cancer models to determine which one would represent the best individual choice for you. In contrast to a one-size-fits-all medication, the use of such a personalised approach would allow us to avoid the application of ineffective or even harmful therapies and thus ultimately boost your chances of recovery.
Will this lead to ‘perfect inner bodies’?
Indeed, this technology may also bring people’s aspirations for a ‘perfect body’ to the next level. Besides people with medical problems, healthy individuals may be motivated to replace existing intact organs with more powerful versions. For instance, perhaps athletes would want larger hearts, capable of supplying the body with more oxygen to enhance their performances. Of course, it will still take many more attempts until we are finally capable of replicating fully functional organs. Furthermore, we are still a long way from creating ‘super’ organs which are capable of replacing or even outperforming their natural counterparts. This means that we still have time to devise and introduce the necessary regulations. From an optimistic perspective, bioprinting can certainly be seen as a powerful technology with the potential not only to overcome organ shortages and rejection, but also to eliminate drug testing on animals and humans.
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