Fig. 3.

Commonly used formation methods and advanced engineering formation methods for stem cell spheroids. (a) Representative schematic of hanging drop culture method and engineered hanging drop methods using bio-inspired superhydrophobic surfaces with palladium layer onto vertically aligned silicon nanowires. Reproduced with permission from Ref. [17]. (b) Representative schematic of microwell plate formation method and engineered microwell plate using lotus seedpod-structured Tet-TA polymer hydrogel coated with fibronectin. Reproduced with permission from Ref. [133]. (c) Representative schematic of spinner flask levitation culture method and engineered levitation formation method using multi-trap acoustic levitation platforms using a PDMS chip and an ultrasound transducer. Reproduced with permission from Ref. [139]. (d) Representative schematic of hydrogel matrix formation method and engineered hydrogel matrix formation method using the 3D-printed matrix of chitosan methacrylate and polyvinyl alcohol hybrid hydrogel microparticles. Reproduced with permission from Ref. [147]. (e) Representative schematic of magnetic force-derived formation method and engineered magnetic-based formation method using microfabricated magnetic patterns and magnetic nanoparticles. Reproduced with permission from Ref. [19]. (f) Representative schematic of microfluidic chip-based formation method and engineered method using a droplet-trapping microfluidic chip. Reproduced with permission from Ref. [18].