We are living in an aging society that is facing a decreasing supply of donor organs. To confront this pressing issue, Munichs iGEM Team 2016 developed a game-changing approach to bioprint tissues for biomedical applications. The interdisciplinary work aimed to create a unique ink, named biotINK, to revolutionize bioprinting. The printing process uses a hijacked 3D printer and two components of biotINK to induce an instantaneous polymerization reaction, creating three-dimensional multi-cellular structures in a user-definable manner. The principle of this two-component glue relies on the rapid and specific interaction of biotin and its tetrameric binding protein avidin. To make use of this high biotin-avidin affinity for cell-cell cross-linking, they engineered cells presenting biotin moieties or biotin-binding proteins on their surfaces as well as recombinant matrix proteins, which co-polymerize upon printing.

Altogether, this system is a novel approach to Bioprinting and provides the necessary means to advance the SynBio community to the next level – the tissue level.

Visit their wiki for details: http://2016.igem.org/Team:LMU-TUM_Munich

Technology in Detail 

The project consists of two parts: a biology and a hardware part.

Biology

The following extracellular domains were constructed and tested: A biotinylated receptor containing an extracellular biotin acceptor peptide that is endogenously biotinylated by a coexpressed biotin ligase (BirA) and thus presents biotin groups at the cell surface.

Receptors presenting an extracellular avidin variant: These avidin derivates, by design, allow the functional fusion of the otherwise tetrameric avidin molecule with the receptor. Two different variants were used here: The so-called enhanced monomeric avidin, a single subunit avidin that is able to bind biotin as a monomer, and a "single-chain avidin", which resembles the naturally occuring avidin tetramer, but has the subunits being connected via polypeptide linkers. By linking the C-terminus with the N-terminus of the adjacent monomer the whole tetravalent avidin has only one N- and one C-terminus and can thus be fused to a type-I membrane protein for surface presentation.

Both receptor types generally serve the same purpose: By interacting with the complementary component in the printing reservoir, cells are being cross-linked due to the polyvalent binding of streptavidin molecules to polyvalent biotinylated proteins. Since the basis of the polymerization reaction is the interaction of Streptavidin and its binding partner Biotin they used biotinylated proteins to convey the polymerization between the cells. As one alternative for a linker molecule they biotinylated PAS-Lysine, which is an amino acid sequence consisting of Prolin-Alanin-Serin repeats with a Lysin at about every 20th position. As part of the bioink the polymer's biotin binds to the single chain Avidin, enhanced monomeric Avidin or respectively Streptavidin and is able to crosslink the cells.

Based on this whole new approach for Bioprinting the team managed to precisely print cells. Here you see the printing of their universities logo.

Hardware

They aimed to provide a open-source platform in order to make 3D tissue printing available for everyone. Therefore they modified an Ultimaker 2+ plastic printer to become a Bioprinter. All bioprinter-parts are made out of plastic and can be printed right from the CAD files they provide on their project wiki: https://2016.igem.org/wiki/images/b/b4/ MUC16_T--LMU-TUM_Munich--All_Parts.zip. The syringe pump is the main part of their printer extension. Its purpose is to deliver a precise and constant volume flow of liquid according to the printer's information. The syringe pump is supplemented by the printer head and the dish retainer. Furthermore they provide a detailed description how to assemble the printer with the printed plastic parts. Even the software files can be downloaded from their wiki.

 Videos

Who Developed this Technology?

The idea was developed by Munichs iGEM Team 2016. They presented their project at 2016 iGEM competition in Boston to 300 teams from all over the world. Their achievements in the competition:

• Grand Prize "Overgrad" (Best project of the competition)
• Best Manufacturing Project
• Best Hardware Project
• Best Software Project
• Nominated for Best Modelling
• Nominated for Best Entrepreneurship
• Nominated for Best Presentation
• Nominated for Best Composite Part

Companies working on this

There are several companies out there trying to develop conventional bioprinting products. Their extraordinary market cap reflects the promises that are linked to Bioprinting: Organovo Inc. (NASDAQ,  318 Mio. USD market cap.) and Cellink (NASDAQ, 519 Mio. USD merket cap.) are the two major players in this market.

Until now no company is utilizing this novel approach to bioprinting.

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