A neuromodulation system is described in which electrodes are mounted within a neural interface device configured to include elastic self-pulsatile or IPG-controlled pneumatic/hydraulic collars in a distal end of the system. One or more electrodes are mounted in each collar. Each collar is connected to an implanted pulse generator (IPG) at the proximal end of the neuromodulation system via a lead body that includes pneumatic/hydraulic lines to the collars and electrical wiring to the electrodes. Gas or fluid pressure supplied to each collar can be controlled by one or more precision step motors inside the IPG. Proximal connectors to the lead body have one or more gas or liquid (biocompatible) reservoirs whose pressure is individually or collectively controlled by the one or more precision motors inside the IPG. The IPG can drive one common or multiple independent precision motors lined around each reservoir to drive one or more collars in the neural interface device.