Fig. 2

Stimuli-responsive nanotechnologies on TNT. a Preparation of TNT by EA, which could only accept the light which wavelength ranges in the ultraviolet spectrum [26]. According to mg-heat treatment, TiO₂ nanotubes were converted into Ti nanotubes to response electric stimulus and release the drug inside [35]; b loading coatings on nanotubes and drugs or nanoparticles inside is the most common application of TNT. There are different coatings to seal the nozzles, like which could response pH [39] and enzyme [43], after receiving the stimuli, the coatings open and contents flow out (1); and loading nanoparticles above the drugs, and release or break after receive the stimuli, for example liposome-rhBMP-2 nanocomplexes which respond USW, and then the liposome break to release the rhBMP-2 (2) [19]; the strategy that nanoparticles loaded on the bottom of TNT with drugs loaded above is another drug delivery way, in which the active nanoparticles could push the drugs out of the TNT (3) [60]; c elements doping such as S, N, metal, etc. could improve the photoresponsive ability of TNT