Effectively manipulating nanoscale graphene materials to assemble macroscopic, functional objects is a significant challenge for integrating graphene into next-generation devices. In recent years, graphene has been patterned at low concentrations onto substrates to create flexible and conducting features using 2D printing techniques. In addition, graphene has been employed as an additive in 3D printing polymer composites, enabling self-supporting structures on the multi-mm and cm scale which utilize its unique properties, although not as the primary component. We present a new 3D-printable, graphene-based liquid ink, as well as comprehensive characterization of the mechanical, electrical and biological properties of the printed graphene structures. The ink composed of majority graphene particles can be rapidly patterned at room temperature into self-supporting, user-defined constructs with feature sizes from 90-1000 µm. Although comprised primarily of graphene, the resulting objects are soft and robust due to the biocompatible elastomer minority component, which percolates, preferentially carries mechanical loads, while allowing graphene flakes to translate. The flexible 3D-printed graphene fibers and constructs have high electrical conductivity, through which is maintained after cyclic bending over many cycles. This conductivity is improved without compromising the mechanical properties following a low temperature thermal anneal. We also present what we believe to be the first in vitro and in vivobiological studies on graphene scaffolds, which is not in the form of two-dimensional patterns or low concentration graphene composites, such as doped hydrogels. The response of induced pluripotent stem cell (iPSC) derived human neurons as well as human mesenchymal stem cells (hMSCs) seeded onto 3D-printed graphene scaffolds is monitored over the course of several weeks, and shows that neurons attach and interact with the graphene environment much more intimately than with a biocompatible elastomer control. Additionally, hMSCs on 3D-printed graphene are highly viable, proliferate rapidly, and quickly develop morphologies reminiscent of neuronal cells without the inclusion of any differentiation-inducing factors in the media. To determine the biocompatibility of 3D-printed graphene, scaffolds were subcutaneously implanted into mice and analyzed at 7 and 30 days post implantation. Standard histology combined with “electron-histological” imaging techniques illustrate that host tissue readily integrates within the 3D-printed graphene, elicits no observable immune response, host tissue integration with 3D-printed graphene, and apparent vascularization within the graphene constructs. This suite of mechanical, electrical, and biological properties position this scalable3D-printingprintable graphene ink for significant potential impacts in the emergent the fields of flexible electronics, tissue engineering, and bioelectronics.
Northwestern University, Northwestern University
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