SYRINGE ASSEMBLY

A syringe assembly includes a barrel and a plunger slidably placed in the barrel. The plunger includes a shaft with a distal piston. The piston has a distal sealing portion with a distal surface including a central section and an outside section and a guide portion. The sealing portion has an outside diameter greater than the inside diameter of the barrel before the piston is placed in the barrel. The sealing portion has a groove in the distal surface where the central section flexibly joins the outside section. When the piston is placed in the barrel, the outside section contacts the barrel wall distally, deflecting the outside section with respect to the central section, forming a fluid tight seal with the barrel wall for facilitating drawing and expelling fluid with movement of the piston. The guide portion contacts the barrel wall to coaxially maintain the plunger in the barrel. The area of reduced thickness in the plunger sealing portion is formed as a living hinge by the part being distally flexed at the area of reduced thickness as the mold is opened. The plunger molding tool has a primary and a secondary opening mode. In the method of forming the plunger, the mold first opens in the secondary mode forming the living hinge, and then opens in the primary mode providing access to the part.