However, it is usually capable of printing only on to flat surfaces [@Hu2018; @Ng2019a].

Conformal printing is an attractive and emerging field, which can enable specific electronic features such as sensors and circuits directly on to 3D objects. This is especially important in the present-day internet of things (IoT) era where 3D objects are increasingly interconnected. However, functional ink deposition on 3D structures is not a trivial process due to uneven and sometimes, complex topography. To date, several techniques have been explored to achieve conformal functional printing of 2D material, carbon nanotube and metal nanoparticle-based inks. These include aerosol jetting [@Jabari2015] or specially adapted inkjet or screen printing that manipulate arbitrarily-shaped substrates *via* rotary systems around ink nozzle heads or printing mesh[@Krebs2009]. However, these usually require highly complex and expensive printer designs that are capable of only depositing functional patterns on to one object at a time. Thermoforming has also been used in conjunction with other printing techniques such as flexography and gravure where inks are first deposited on planar polymer substrates which are then made pliable *via* the application of heat and formed into a complex 3D shape in a multi-stage, offline process. [@Krebs2009]. Other more esoteric methods such 