US Patent 7288078 Spring loaded automatic retractable needle syringe

A spring loaded retractable needle syringe comprising a body, a central tube coaxially mounted within said body, a needle carrier and needle slidably mounted within said central tube, a spring mounted within said central tube to bias said needle carrier and needle into said central tube, means for sliding said needle carrier and needle within said central tube to compress said spring and expose said needle, means for retaining said needle carrier and needle in the exposed position against the biasing force of said spring, and means for releasing the needle carrier and needle such that said needle carrier and needle are retracted into said central tube.