Needle-free connector

A needle-free connector for accessing a patient's intravenous line, the needle-free connector comprising:

• a hollow body having a first end with a first opening, a second end with a second opening, and an inner wall defining a chamber;
• and
• a hollow piston disposed in the chamber, the hollow piston comprising an inner surface, an outer surface, a longitudinal axis and a void inside the hollow piston,
• the hollow piston being axially collapsible in the chamber to allow fluid to flow between the inner wall of the hollow body and the outer surface of the hollow piston, wherein the void extends from a base end of the hollow piston to a midsection of the hollow piston,
• the inner surface of the hollow piston comprising a fluted section having a radial array of axial slots that extend parallel to the longitudinal axis,
• the fluted section having a first radial thickness that is configured to buckle in response to axial force applied to the hollow piston, wherein the fluted section extends from the base end of the hollow piston to the midsection of the hollow piston,
• the hollow piston further comprising a retrograde-reducing stiffener,
• the retrograde-reducing stiffener having a second radial thickness that is greater than the first radial thickness, wherein the retrograde-reducing stiffener comprises a resilient member housed inside of the void.