A Human Machine Interface (HMI) and a handheld 3D printing apparatus , the Human Machine Interface comprising: • an on/off power button configured to power on or power off the handheld 3D printing apparatus ; • a speed indicator configured to indicate a speed of extrusion of material from the handheld 3D printing apparatus ; • a setting control button configured to select one or more settings of the handheld 3D printing apparatus ; • a first indicator lamp configured to indicate a purge operation of a first reagent; and • a second indicator lamp configured to indicate a purge operation of a second reagent; wherein the HMI is located at the upper housing of the handheld 3D printing apparatus ; wherein the HMI drives custom software that controls all apparatus functions; and wherein the handheld 3D printing apparatus comprises: a housing comprising: a first reagent container support arrangement which in use receives and supports a first reagent container containing a cell supporting reagent; a second reagent container support arrangement which in use receives and supports a second reagent container containing a light curable reagent; a power supply ; an electric drive train arrangement configured to drive a first reagent piston into a distal end of the first reagent container, and to drive a second reagent piston into a distal end of the second reagent container; an electronic control circuit to control the electric drive train to control extrusion of the reagents from the first and second reagent containers; and a nozzle connected at a distal end to the housing and comprising a coextrusion tip comprising a core aperture and an annular aperture in a coaxial arrangement, and a first conduit for receiving the first reagent driven out of a proximal end of the first reagent container and directing the first reagent out of the core aperture in the tip , and a second conduit for receiving the second reagent driven out of a proximal end of the second reagent container and directing the second reagent out of the annular aperture in the tip. • an on/off power button configured to power on or power off the handheld 3D printing apparatus ; • a speed indicator configured to indicate a speed of extrusion of material from the handheld 3D printing apparatus ; • a setting control button configured to select one or more settings of the handheld 3D printing apparatus ; • a first indicator lamp configured to indicate a purge operation of a first reagent; and • a second indicator lamp configured to indicate a purge operation of a second reagent; a first reagent container support arrangement which in use receives and supports a first reagent container containing a cell supporting reagent; a second reagent container support arrangement which in use receives and supports a second reagent container containing a light curable reagent; a power supply ; an electric drive train arrangement configured to drive a first reagent piston into a distal end of the first reagent container, and to drive a second reagent piston into a distal end of the second reagent container; an electronic control circuit to control the electric drive train to control extrusion of the reagents from the first and second reagent containers; and a nozzle connected at a distal end to the housing and comprising a coextrusion tip comprising a core aperture and an annular aperture in a coaxial arrangement, and a first conduit for receiving the first reagent driven out of a proximal end of the first reagent container and directing the first reagent out of the core aperture in the tip , and a second conduit for receiving the second reagent driven out of a proximal end of the second reagent container and directing the second reagent out of the annular aperture in the tip. <EOS>