Most veteran amputees incurred from trauma while on active duty receive their care and prostheses paid for by the Veteran's Administration (VA). The requirements are that your husband enroll in a VA clinic and attend regular follow-up care.
Taking part in formal studies is not required but certainly helpful for others. Information gathered from these studies helps the VA provide better care for war veterans wounded in the line of duty. If it's an ongoing study you may be able to enter at a later date when it's more convenient for your family.
Talk to the study coordinator and find out what are your options.