Table 3.

A summary characterization of 3D in vitro models.

Type of 3D In Vitro Model	Specific Features	Biomedical Applications	Reference(s)
Co-cultures	direct—different cells are cultured together indirect—the cells are separated by a physical barrier cells of different phenotypes do not grow together even when they are in direct contact	Cell–cell communication Cell–microenvironment interactions Cancer invasion	[89]
Spheroids	non-scaffold-based 3D model round-shaped micro-sized cellular aggregates can be generated either from 2D cell cultures (primary or immortalized cells) or tissue fragments multilayer structure: (i) external layer—proliferative cells, (ii) middle layer—senescent cells, and (iii) core—necrotic cells two types of tumor spheroids: homodymic, containing ex-clusively cancer cells, and heterodymic, containing tumor cells cul-tivated with other cell types ECM consists of proteins produced by the cells during sphe-roid formation	Drug discovery Disease modelling Toxicity screening High-throughput screening	[90,91,92]
Organoids	also known as “organ buds” complex scaffold-free 3D models stem cell organoids (derived from embryonic stem cells/induced pluripotent cells/primary stem cells) tissue organoids (stromal cell-free culture) ‘organ-in-a-dish’ in vivo-like complexity and architecture	Carcinogenesis studies Anticancer drug screen-ing and discovery Development of person-alized anticancer therapies	[12,37,90,92,93,94,95]
Scaffold-based models	3D constructs providing a physical support (matrix) on which cells can proliferate, divide, and migrate specifically designed to recapitulate the in vivo ECM composed of natural (i.e., Matrigel, chitosan, hyaluronic acid, alginate) or synthetic (i.e., polyethylene glycol, polyvinyl alcohol) scaffolds	Drug screening and dis-covery	[92,96,97]
Bioprinted and 3D printed models	layer-by-layer deposed bioinks (i.e., cell pellets; decellularized ECM constituents) with 3D architecture scaffold-free design—bioprinting on sacrificial materials (agarose; alginate), which are eventually discarded, or scaffold-based design—bioprinting of hydrogel-encapsulated bioinks	Tissue engineering Cancer pathology re-search Anticancer drug discov-ery	[97,98]
Organ-on-a-chip	miniature microfluidic devices made of optically clear mate-rials (i.e., plastic, glass, polymers) containing microchannels popu-lated by living cells extended viability of the cultured cells (weeks, months) faithful simulation of the in vivo organ structure and func-tions mimicking both the physiological and pathological features of the organ	Modeling of specific tumoral processes: growth, neovascularization and angiogenesis, progression from early to late stages, invasion, and metastasis	[92,99]