I am curious to know what is the protocol on how often is saline allowed to be injected into the expander?

Commonly about 50-100cc of saline will be added to the tissue expanders every 7-14 days until the target volume is reached. This is just one of many methods used and each scenario will vary according to specific circumstances (e.g. wound healing, patient health, history of radiation therapy and/or chemotherapy, etc...)

There is no specific protocol that must be followed as to the volume injected or the time in between injections. Each woman has their own set of circumstances as stated by Dr. Neins, that may vary the "protocol".