A hollow needle applicator for cartridged drugs etc has provision for automatic needle retraction after cartridge contents expression. Its drugs etc cartridge (125, 225, 325) can itself be at least partially accommodated bodily within a hollow piston actuator (145, 345), and will be released for retraction...http://www.google.com.au/patents/US5957897?utm_source=gb-gplus-sharePatent US5957897 - Hollow needle applicator for cartridged drugs
