Fig. 3.

Different types of internal and external stimuli used to enable diverse biofunctionalities of biomaterials. a In-body/internal biomaterials respond to signals or stimuli in the immediate vicinity of the implanted biomaterial. Some examples of these signals include enzymes, antigens, proteins, pH levels, and ionic factors. b Out-body/external signals are located distally from the biomaterial (e.g., outside the body) and could include electromagnetic fields, mechanical stresses, or temperature changes. Some signals, including temperature, can be found both in-body and out-body