Printed electronics has emerged as a pathway for large scale, flexible, and wearable devices enabled by graphene and two-dimensional (2D) materials. Solution processing of graphite and layered materials demonstrated mass production of inks allowing techniques such as inkjet printing to be used for device fabrication. However, the complexity of the ink formulations and the polycrystalline nature of the thin films, together with the metal, semimetal, and semiconducting behaviour of different 2D materials, have impeded the investigation of charge transport in inkjet printed 2D material devices. Here we unveil the charge transport mechanisms of surfactant-and solvent-free inkjet-printed thin-film devices of representative few-layer graphene (semi-metal), molybdenum disulfide (MoS2, semiconductor) and titanium carbide MXene (Ti3C2, metal) by investigating the temperature (T ), gate and magnetic field dependencies of their electrical conductivity. We find that charge transport in printed few-layer MXene and MoS2 devices is dominated by the intrinsic transport mechanism of the constituent flakes: MXene devices exhibit a weakly-localized 2D metallic behavior at any T , whereas MoS2 devices behave as insulators with a crossover from 3D-Mott variable-range hopping at low T to nearest-neighbor hopping around at ∼ 200 K. The charge transport in printed few-layer graphene devices is dominated by the transport mechanism between different flakes, which exhibit 3D-Mott variable range hopping conduction at any T . These findings reveal and finally establish the fundamental mechanisms responsible for charge transport in inkjet-printed devices with 2D materials, paving the way for a reliable design of high performance printed electronics.

Electroconductive biomaterials are gaining significant consideration for regeneration in tissues where electrical functionality is of crucial importance, such as myocardium, neural, musculoskeletal, and bone tissue. In this work, conductive biohybrid platforms were engineered by blending collagen type I and 2D MXene (Ti3C2Tx) and afterwards covalently crosslinking; to harness the biofunctionality of the protein component and the increased stiffness and enhanced electrical conductivity (matching and even surpassing native tissues) that two-dimensional titanium carbide provides. These MXene platforms were highly biocompatible and resulted in increased proliferation and cell spreading when seeded with fibroblasts. Conversely, they limited bacterial attachment (Staphylococcus aureus) and proliferation. When neonatal rat cardiomyocytes (nrCMs) were cultured on the substrates increased spreading and viability up to day 7 were studied when compared to control collagen substrates. Human induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) were seeded and stimulated using electric-field generation in a custom-made bioreactor. The combination of an electroconductive substrate with an external electrical field enhanced cell growth, and significantly increased cx43 expression. This in vitro study convincingly demonstrates the potential of this engineered conductive biohybrid platform for cardiac tissue regeneration.

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