Abstract: A three-dimensional printing pen includes a barrel open on a first end and having an opening for receiving a melt-substrate on a second end, opposite to the first end. A nozzle is configured to receive and melt said melt-substrate and arranged to be connected to the first open end of the barrel The pen further includes a channel inside the barrel with a first opening adjacent and aligned with the opening in the barrel for receiving said melt-substrate and a second opening, opposite to said first opening, adjacent to the nozzle. A transport mechanism has a rotatable transport member which is, in use, in contact with the melt-substrate for moving the melt-substrate through towards the nozzle.