Fig. 1. Schematic diagrams of single-photon and two-photon excitation processes. (a) Single-photon excitation process; (b) two-photon excitation process

Fig. 2. Scheme of femtosecond laser two-photon micro-nano manufacturing^[17]

Fig. 3. TPP photoinitiator with C_2v symmetric structure^[23]. (a) Anthraquinone TPP photoinitiator; (b) carbazole TPP photoinitiator; (c) anthracene TPP photoinitiator; (d) water-soluble TPP photoinitiator assembled by anthraquinone TPP photoinitiator and cyclodextrin

Fig. 4. Configuration of water-soluble two-photon initiator obtained from the host-guest chemical interaction simulated by quantum chemistry^[26]. (a) Optimized binding configurations of BMVMC; (b) bird view of CB7; (c) side view of CB7; (d) bird view of CB7/BMVMC with optimized geometrical configuration; (e) side view of CB7/BMVMC

Fig. 5. Chemical structure of water-soluble TPP initiator with ionic groups^[30]

Fig. 6. Scanning electron microscopy (SEM) images of three-dimensional (3D) hydrogel microstructure prepared by TPP. (a) Adenovirus hydrogel microstructure^[28]; (b) red blood cell microstructure^[35]; (c) lotus-like microstructure, cube frame microstructure with suspended spheres inside and hydrogel “bridge” microstructure on the micro column array^[36]; (d) 3D woodpile microstructure^[24]; (e) single-layer spider web microstructure^[37]

Fig. 7. Microstructures with stimulus-response fabricated by TPP. (a) SEM images of reversible ion responsive hydrogel microcantilever in water, 1 mol/L NaCl solution, again in water and dry microcantilever^[43];^{(b) microstructures of imitated coronavirus, plum blossom and tortoise[27];(c) schematic diagrams and bright field images of capture and release behavior of biomimetic hydrogel micro actuator[44];(d) schematic and optical micrographs of the micropillar cilia with and without light stimulation[45];(e) optical micrograph of the micro heart without and with light stimulation[45]}

Fig. 8. Bionic micro-device with stimulus-response. (a) Dynamic reversible 3D trap structure of BSA protein was detected by optical microscope and 3D Raman imaging (the structure was upright and “open” when pH was 5, and four double-column structures bent inward and closed to each other when pH changed from 5 to 11)^[46];^{(b) confocal fluorescence images of the 3D panda relief with reversible deformation at changing pH values[47]; (c) actuation of the micro-spider when the pH value was switched from 13 to 5[48];(d) actual process of manipulation (positioning, driving, handling, and releasing)[48]}

Fig. 9. Structural color micro-device with stimulus-response^[52]. (a) SEM image of the woodpile structure;^{(b) different colors of woodpile structures in original or deformed status were observed by the objective lens in transmittance mode; (c) the color change of red and blue woodpile fish in original, deformed, and recover status, respectively;(d) images showing the pH-responsive butterfly painting}

Fig. 10. Application of TPP technology in drug delivery. (a) Comparison between traditional PEG and S30 microrobots when they encountered macrophages^[54]; (b) schematic illustration of magnetic SMMFs for targeted DOX release to treat cancer cells by shape morphing, and snapshots of the viability of HeLa cells in the DOX-releasing area and the control area^[55]

Fig. 11. PEGDA 3D hydrogel scaffold. (a) Dark-field image of co-culture of scaffold and cell by LIFT, fluorescence image of different types of cells and detailed image of boundary area after LIFT^[57];^{(b) cell growth and adhesion behavior on PEGDA hydrogel scaffold[58]; (c) oblique SEM image, confocal fluorescence image and bright field image of a complete hexagonal grid scaffold, and confocal fluorescence image and bright field image of HeLa cells co-culturing with the grid scaffold[25]}

Fig. 12. Confocal fluorescent microscopy images of scaffold and cells grown on 3D microscaffolds with strut spacing of 10, 15, 20, 25, 30 μm, and schematic of the mechanism for regulating F-actin synthesis through sensing information by filopodia^[14]