FIGURE 4.

Rapid release of exosomes mediated by soft hydrogels inhibits macrophage inflammation. (A) After 24 h, the hydrogel-embedded sciatic nerves were collected, and the frozen sections were imaged under a fluorescence microscope. Image analysis showed that compared with the stiff hydrogel–embedded sciatic nerves, the sciatic nerves embedded in the soft hydrogels had a larger fluorescent area (p = 0.00162, n = 5) and higher IOD (p = 0.01827, n = 5; bar = 200 μm). (B) Hydrogels with different stiffnesses were loaded with PKH26-labeled exosomes and incubated with THP1 cells and PMA (100 ng/ml). After 24 h, the cells were imaged under a laser confocal microscope (bar = 250 μm). Image analysis shows that compared with the cells grown on stiff hydrogels, the cells grown on soft hydrogels had a larger fluorescent area (p = 0.00101, n = 15) and higher IOD (p = 0.00201, n = 15). (C) After PMA (100 ng/ml) induced THP1 to adhere to the wall (con), LPS (100 ng/ml) was used to induce the cells to differentiate into M1 for 12 h (LPS). Then, the cells were treated with different concentrations of exosomes to detect the expression of the related genes, IL-1β and TNF-α (IL-1β: con vs. LPS p = 6.57496E-5, LPS vs. 10 μg/ml p = 7.66959E-4, 10 μg/ml vs. 100 μg/ml p = 3.2624E-4; TNF-α: con vs. LPS p = 9.737936E-4, LPS vs. 10 μg/ml p = 0.00355, 10 μg/ml vs. 100 μg/ml p = 1.63632E-4; n = 3). (D) Schematic diagram of the mechanism by which exosome release affects damaged nerve repair. The rapid release of exosomes from the soft hydrogel can reduce macrophages and the expression of proinflammatory IL-1β and TNF-α in M1 macrophages, thereby promoting the repair of the injured nerve. *p < 0.05; **p < 0.01; and ***p < 0.001, t test.