Wires were characterised using a wireless TRMS multimeter (EX542, Extech Instruments) to measure resistance and imageJ used to measure wire diameter from microscopy images (n=10, randomly chosen). To culture monolayers onto 3D printed electrodes, modified adhesive wells (80828, Ibidi) were utilised and adhered to electrodes, providing a 1cm 2 cell growth area. Electrodes were plasma cleaned and silanized to increase the adhesion of printed structures and prevent detachment in an aqueous solution. Glass slides were immersed in ethanol for 10 minutes before O2 plasma cleaning. Glass slides were placed into a plasma chamber between two copper band electrodes connected to a power source (Coaxial Power Ltd.). The chamber was evacuated, and needle valves (BOC Edwards) were used to control the oxygen pressure. The pressure was monitored with a Pirani gauge (Kurt J. Lesker Ltd.) and a glow-discharged plasma was initiated when the pressure was stabilised to 9x10 -2 Mbar (50W for 3 minutes). Salinisation was performed using 1% 3-(Trimethoxysilyl) propyl methacrylate (TMSPMA) in toluene for 1 hr, followed by washing with dH2O. Cells were seeded at ~5 x 10 5 cells per well in 300µL of culture media. Immediately before wire growth, media and sticky slides were removed, samples were washed with PBS, and substituted with a droplet of diH2O. 3D spheroids were cultured using a Rotary Cell Culture System (RCCS, Synthecon). Cells were incubated in disposable 10 ml culture vessels for 3-4 days and rotated at varying speeds to ensure spheroids were in a constant state of free-fall. Spheroids were characterised using light microscopy (Diaphot 300, Nikon). To initiate wire growth, cultured spheroids were washed in PBS and placed between 3D printed electrodes, where diH2O was added, covering the spheroid.