3D-Printing Biopolymer Gels with an Electric Field—A Simple Route that Avoids Nozzles, Heat and UV Light

3D-printing of hydrogels has attracted great interest in recent years. In particular, gels of biopolymers such as proteins (e.g., gelatin) or polysaccharides (e.g., alginate) are used to encapsulate cells, and these can serve as scaffolds for tissue engineering. The promise of 3D-bioprinting lies in custom-printing a body part, potentially using a patient’s own cells. However, current 3D-bioprinting is a cumbersome operation that requires a large ‘printer’ and expensive ‘inks’. The inks, i.e., suspensions of cells in a pre-polymer, are typically pumped through fine nozzles in the printer. As soon as drops of this suspension emerge out of the nozzle, they are converted into gels by heat or UV light. By rastering the nozzle in 3D, a solid gel is built from the ground up (in layer-by-layer fashion) in a desired shape. Issues with this approach include the fact that the use of high shear (in the nozzle) or UV light can damage sensitive cells. Moreover, conventional 3D-bioprinting is slow and requires hours to create a custom part.<br/><br/>Here, we introduce an alternative method for 3D-printing gels of biopolymers such as alginate. Our method uses moderate electric fields (DC voltages around 5 to 15 V) and a solution of the above biopolymer. The central idea is that the biopolymer is gelled at a precise location by applying the electric field through fine metal electrodes. By moving the electrode(s) in 3D space using an externally controlled XYZ stage, we can build a gel in a specific shape. A gel that is 2 to 3 cm tall can be formed in a matter of minutes with our technique. The gel is also highly robust and it can be lifted out of the solution and manipulated by hand within seconds after the printing is complete. Layered gels with different internal contents can be readily created by this technique. Thus, this electro-gelation strategy could serve as a rapid, inexpensive, and powerful alternative to conventional 3D-printing of hydrogels.