Throughout the years jet injectors have been redesigned to overcome the risk of carrying contamination to subsequent subjects. To try to stop the risk, researchers placed a single-use protective cap over the reusable nozzle. The protective cap was intended to act as a shield between the reusable nozzle and the patient's skin. After each injection the cap would be discarded and replaced with a sterile one. These devices were known as protector cap needle-free injectors or PCNFI. A safety test by Kelly and colleagues (2008) found a PCNFI device failed to prevent contamination. After administering injections to hepatitis B patients, researchers found hepatitis B had penetrated the protective cap and contaminated the internal components of the jet injector, showing that the internal fluid pathway and patient contacting parts cannot safely be reused.