A casing may be configured to envelop at least a portion of a plunger arm attached to a plunger head located in a reservoir. A plunger head moveable in a reservoir may have a front portion comprising a first material compatible with fluidic media in an interior volume of the reservoir. A seal member having a first end and a second end that taper to a mid-portion may be positioned between a reservoir and a plunger head. A bias member may be configured to force a plunger arm operatively connected to a plunger head against a drive member to operatively engage the plunger arm to the drive member. A plunger head moveable in a reservoir may have a first ridge, a second ridge, a seal member adjacent at least one of the ridges, and protrusions arranged around at least one of the ridges.