The present application relates to a modular injection system for administration of dermal filler compositions, the system comprising: a handheld injector unit (101) including a grippable housing (124) including a distal end having a coupling portion (614), and a drive system contained within the housing, a separate control unit (102), remote from the injector unit (101), the control unit (102) including a controller/processor (310) configured to control the drive system and a cartridge (121), couplable to the coupling portion (614) of the grippable housing (124), and containing an injectable fluid the drive system using a pump to cause extrusion of the injectable fluid from the cartridge when the cartridge (121) is coupled to the coupling portion (614), or the drive system using a pressurized syringe to cause extrusion of the injectable fluid from the cartridge when the cartridge (121) is coupled to the coupling portion (614), wherein the extrusion of the injectable fluid is controlled with a valve.
