Fig. 1. (Color online) Wound healing phases: (a) inflammation, (b) proliferation, and (c) remodeling. Reprinted with permission from Ref. [5]. The time course of pH milieu in different wounds such as (d) acute and (e) chronic wounds^[18].

Fig. 2. (Color online) (a) Flexible array-type pH sensor. (b) Color change on the pH from acidic to basic^[36]. (c) The flexible pH sensor can be fixed on the skin, and (d) change color when the pH varied^[37]. (e) Photographic images of the hydrogel patch under pH values from 5 to 9. (f) and (g) Electrospun PCL-curcumin nanofibers under pH 6 and 9^[49].

Fig. 3. (Color online) (a) Fabrication process to create the pH-sensitive bandage. (b) A real-time pH changes in a simulated wound^[59]. (c) Fabrication process of paper based pH sensor array. (d) Relationship between the potential and pH values for the paper based pH sensor array^[66].

Fig. 4. (Color online) (a) Design of a pH sensitive gel placed between two inductive coils. Relationship between the resonant frequency, the gap and the pH^[68]. (b) Schematic diagram of the fabrication of OPSBs and the magnitude relation to pH^[69]. (c) Fabrication process of pH sensor on ITO film and potential related to pH^[70].

Fig. 5. (Color online) (a) Optical image of pH sensing bandage (left) and SEM of the pH sensitive threads. (b) Open circuit voltage versus pH for the threads. (c) Data acquisition setup for pH sensing smart bandage. (d) Smart bandage pH map^[72].