Table 1. Summary of Hydrogel Properties and Their Application in Generation of Topological Microtissues (TM).

hydrogel	gelation methods	Young’s modulus	cell–matrix interactions	biodegradability	cell types	application in TM
agarose	temperature (cooling)72,166	10–800 kPa163,164	possible after modification	possible after modification	mouse embryonic stem cells167	microdroplets for cell coculture,72 shell in core–shell droplets270 or Janus structures166
alginate	ionic95,132,271	5–50 kPa,177 0.2–20 kPa132,177 (microgels), 150–540 kPa178 (nonphysiological conditions)	possible after modification	possible after modification	stem cells,66,205,215,272,273 HUVECs,203,205 PC12,274 rat neural Schwann cells (RSC 96),114 rat embryonic neurons,82 osteosarcoma cells,255 cardiomyocytes,203 human liver cancer cell line (HepG2)194	inner185 and outer phase108 in core–shell droplets, bead-loaded,198 core–shell67 and Janus199 microfibers, porous hydrogel films,71 porous scaffolds214
chitosan	pH, ionic,196,275 chemical146,218	6–20 MPa219	possible after modification	yes	PC1250,221	bead-loaded fibers,221 porous foams218
collagen	thermal229	0.1–10 kPa226,227 (physiological conditions), 10–50 kPa227 (nonphysiological conditions)	yes	yes	HUVECs,45,115,208 stem cells,95,106,110,112,231 PC12,276 preantral follicles,52,95 C2C12,195 cortical neurons45	coculture systems,231 core–shell microspheres,230 scaffold for cell culture229
decellularized ECM	thermal238,239	depends on tissue	yes	yes	stem cells,110,192 cardiomiocytes,45 HUVECs,45,262 smooth muscle cells,262 MCF-7 cancer cells,115 cortical neurons45	scaffold for tissue culture238,239
fibrin	enzymatic144,244,275	0.1–30 kPa241,242	yes	yes	cardiomiocytes,45,277 C2C12,73 HUVECs,277 fibroblasts73	microbead generation,244 inner phase in core–shell fibers,110 hybrid hydrogels for cell culture with PEG144
gelatin	thermal,246 enzymatic,246,278 Michael addition247	0.5–81 kPa248,249	yes	yes	rat H9c2 myoblasts279	core–shell structures,280 porous foam127
GelMa	photoinitiated,253 thermal84	3–185 kPa254	yes	yes	Schwann cells (RSC 96),221 PC12,50,221 stem cells,192,272 HUVECs,203,281 cardiac precursor cells,282 osteosarcoma cells,255 cardiomiocytes,203 fibroblasts281	core–shell microdroplets,253 core–shell and Janus microfibers,67 microrods,84 porous foams256
hyaluronic acid + derivatives	photoinitiated,283 Michael-type addition247	10–500 kPa257 10–25 kPa136 (microgels)	possible after modification	yes	HUVECs255	scaffolds for cell culture,247 microfibers255
matrigel	thermal20,84	400–480 Pa260	yes	yes	stem cells106,108	core–shell microstructures,108 microrods,84 microscaffold material20
PEG and derivatives	photoinitiated,93,266 Michael-type addition264,265	5–500 kPa267 1–3 kPa131 (microgels)	possible after modification	possible after modification	stem cells,131,284 C2C12,285 HUVECs131	beads in bulk hydrogel,269 jammed beads,72 porous hydrogel films,71 core–shell structures265