A versatile PDMS submicrobead/graphene oxide nanocomposite ink for the direct ink writing of wearable micron-scale tactile sensors

Although direct ink writing (DIW) is a versatile 3D printing technique, progress in DIW has been con-strained by the stringent rheological requirements for printable conductive nanocomposites, particularlyat smaller length scales. In this work, we overcome these challenges using an aqueous nanocompositeink with polydimethylsiloxane (PDMS) submicrobeads and an electrochemically derived graphene oxide(EGO) nanofiller. This nanocomposite ink possesses a thixotropic, self-supporting viscoelasticity. It can beeasily extruded through very small nozzle openings (as small as 50 �m) allowing for the highest resolutionPDMS DIW reported to date. With a mild thermal annealing, the DIW-printed device exhibits low resis-tivity (1660 �·cm) at a low percolation threshold of EGO (0.83 vol.%) owing to the unique nanocompositestructure of graphene-wrapped elastomeric beads. The nanocomposite ink was used to print wearable,macro-scale strain sensing patches, as well as remarkably small, micron-scale pressure sensors. Thelarge-scale strain sensors have excellent performance over a large working range (up to 40% strain), withhigh gauge factor (20.3) and fast responsivity (83 ms), while the micron-scale pressure sensors demon-strated high pressure sensitivity (0.31 kPa−1) and operating range (0.248–500 kPa). Ultrahigh resolution,multi-material layer-by-layer deposition allows the engineering of microscale features into the devices,features which can be used to tune the piezoresistive mechanism and degree of piezoresistivit