- Regenerative Peripheral Nerve Interfaces (RPNI): RPNI offers an alternative version of an innervated biological interface. An RPNI is a surgical construct that consists of a non-vascularized segment of muscle that is coapted to a distal motor or sensory nerve ending. Unlike TMR, the RPNI muscle is not recruited from an otherwise normally innervated proximal muscle; instead, it is constructed as a free graft from orthotopically sourced donor tissue. The muscle segment is gradually reinnervated by the redirected nerve ending, which then promotes volitional activation of the muscle segment when triggered by the central nervous system. As in TMR, intuitive control occurs because the reinnervated muscles are controlled by the same nerves that once innervated the amputated limb. Unlike TMR, however, there are no limitations on anatomic sites and there does not appear to be problems with long-term signal fidelity.