Research / 2020 / Article / Fig 3

Review Article

Requirement and Development of Hydrogel Micromotors towards Biomedical Applications

Figure 3

Different propulsion strategies of hydrogel micromotors. (a) Bubble-propelled hydrogel micromotor including a catalyst (KMnO4). Reproduced with permission from ref. [84], American Chemical Society 2016. (b) Bubble-propelled emulsion-based hydrogel micromotor due to absorbing fuel (CH2Cl2 liquid). The inset shows a typical trajectory of an emulsion-based hydrogel micromotor (scale bar 20 mm). Reproduced with permission from ref. [32], American Chemical Society 2017. (c) Schematics (I)~(IV) illustrate an organic solvent-driven motion of an oval-shaped PNIPAM gel. Dark red circles represent ethanol, and the light blue circles are water. Different movements are observed with different shapes of hydrogel micromotors. Reproduced with permission from ref. [87], American Chemical Society 2008. (d) The autonomous movement of a fish-like enzymeless motor, caused by the Marangoni effect, which appears due to an interaction between the glucose and the hydrogel with phenylboronic acid (I); the corresponding trajectory of a hydrogel micromotor is shown (II). Reproduced with permission from ref. [82], The Royal Society of Chemistry 2017. (e) Magnetic propulsion of a star-like hydrogel microswimmer by including ferromagnetic Fe3O4 nanoparticles in the hydrogel. Reproduced with permission from ref. [55], Wiley-VCH 2018. (f) Bubble propulsion of the asymmetric hydrogel motor by the catalase contained in the hydrogel matrix, which converts hydrogen peroxide into water and oxygen. The trajectory of the motor is either circular or linear, depending on the direction of bubble recoil (scale bar 20 μm). Reproduced with permission from ref. [89], Wiley-VCH 2018.