Patent ID: 6981963

Claim:
A medical device, comprising: a barrel having an open proximal end and a distal end; a needle having a first sharpened tip and being operable between an extended position in which the first sharpened tip projects forwardly from the barrel and a shielded position in which the first sharpened tip is shielded to prevent inadvertent contact with the first sharpened tip; a cartridge in fluid communication with the needle, comprising: a first chamber containing a first substance; a second chamber containing a second substance; a fluid flow controller between the first chamber and the second chamber; and a plunger slidably disposed within the cartridge; a biasing element imparting a force capable of displacing the needle relative to the barrel to shield the first sharpened tip; and a needle retainer releasably retaining the needle in the extended position; wherein axially advancing the plunger within the first chamber advances the first substance through the fluid flow controller and into the second chamber where said first substance combines with the second substance to form a medicinal mixture, and continued advancement of the plunger and cartridge relative to the barrel after the mixture is expelled from the cartridge actuates the needle retainer to release the needle, whereupon the biasing element displaces the needle relative to the barrel to shield the first sharpened tip.