Self-aligning plunger rod

A self-aligning reinforced plunger rod and non-elastomeric plastic plunger insert assembly for use with an elastomeric plunger in a cartridge or syringe barrel for manual or power-assisted withdrawing of fluid from a site or expelling fluid from the cartridge or syringe barrel:

• a) a plunger rod having a first, second, third and fourth sides, a distal end and a proximal end comprising:
• an end disc at the distal end;
• a plunger rod tip extending from said end disc adapted to engage a plastic plunger insert, said plunger rod tip comprising a neck portion and a ball portion, said ball portion having slots therein extending axially from said neck portion;
• a thumb rest at the proximal end for facilitating exertion of external pressure on the plunger rod;
• a central disc at about the midpoint between the end disc and the thumb rest to provide additional reinforcement between the end disc and the thumb rest;
• four longitudinal radially extending rectangular vanes spaced about 90° from each other and connected to said end disc, to said central disc, and to said thumb rest;
• on the first side of said plunger rod:
• a first pair of longitudinal radially extending reinforcing vanes;
• a second pair of longitudinal radially extending reinforcing vanes, both the first pair and the second pair of longitudinal radially extending reinforcing vanes being connected to said end disc, to said central disc, and to said thumb rest;
• on the third side opposite to said first side of said plunger rod;
• a first pair of longitudinal radially extending reinforcing vanes;
• a second pair of longitudinal radially extending reinforcing vanes, both said first pair and said second pair of longitudinal radially extending reinforcing vanes being connected to said end disc, to said central disc, and to said thumb rest,
• wherein:
• each of said first and second pairs of the longitudinal radially extending reinforcing vanes on the first side of said plunger rod, and each of said first and second pairs of the longitudinal radially extending reinforcing vanes on the third side of said plunger rod forms an obtuse triangle with one of the longitudinal radially extending rectangular vanes, wherein the obtuse angle of the so-formed triangle is at the midpoint between said end disc and said thumb rest;
• on the second side of said plunger rod:
• a first pair of longitudinal radially extending reinforcing vanes forming a two-dimensional hourglass-shape surface extending from said end disc to said central disc, and from said central disc to said thumb rest;
• and
• on the fourth side of said plunger rod:
• a second pair of longitudinal radially extending reinforcing vanes forming a two-dimensional hourglass-shape surface extending from said end disc to said central disc, and from said central disc to said thumb rest;
• b) a non-elastomeric plastic plunger insert comprising:
• a cylindrical shaft having a distal end and a proximal end;
• a cone-shaped head extending from the distal end of said cylindrical shaft having an inside surface and an outside surface;
• a cavity in the cone-shaped head defined by a cylindrical rim and the inside surface of the cone-shaped head;
• a plurality of tabs extending from the cylindrical rim into the cavity;
• and
• a plurality of notches or openings between the tabs designed to receive the slotted ball portion of said plunger rod tip.