Table 2.

Summary of the factors influencing cell fate that should be taken into account when designing a scaffold.

Factors	Example	Effects/applications	Important notes	Ref.
Biological cues	Full-length proteins, cell adhesion motifs, HA binding domain, ECM constituents, etc.	Biological cues provide a desirable microenvironment for cell attachment, spread, migration, proliferation, and differentiation. The local density of RGD supports cell adhesion and condensation and regulates early chondrogenic differentiation of MSCs. Cell adhesion motifs are used to enhance cell motility and hydrogel adhesion. ECM components of MSCs can induce MSC proliferation, migration, and multilineage differentiation. MSC-derived ECM can provide a proper substrate for expansion, proliferation, and maintenance of the chondrogenic phenotype.	The composition of the MSC-derived ECM greatly depends on the stage of the chondrogenic differentiation of MSCs. MSC-derived ECM has an undefined composition and may elicit unwanted immunological responses or cause an improper cell commitment.	[149–152]
Surface chemistry	—	Surface chemistry plays an important role in cell adhesion, proliferation, and morphology. Surface chemistry can control phenotype and promote the expression of lineage-specific markers in differentiated MSCs.	—	[153–157]
Geometry	Curvature, porosity, pore size, and pore shape.	Scaffold geometry plays a key role in chondrocyte adhesion and regulates their phenotype and function. The geometry regulates the orientation of the tubulin and actin cytoskeleton and affects the mechanical behavior and Ca2+ signaling of chondrocytes. The tissue regeneration rate is proportional to the surface curvature and could be significantly influenced by the pore shape. The chondrocyte density considerably increases with scaffold pore size and porosity, while ECM synthesis significantly decreases. The pore diameter correlates negatively with the metabolic and anabolic activities of chondrocytes. An effective strategy to promote chondrogenesis at the beginning of in vitro cartilage engineering is the combination of small pores with low porosity.	While other parameters of the porous structure are fixed, the change in pore size often leads to a change in the mechanical properties of the porous scaffold.	[158–162]
Microtopography	Microgrooves, microgrids, microholes, and micropillars.	Cell structure, morphology, and migration are affected by microtopography. The depth, width, and direction of microtopography influence migration rate, directional movement, and size of aggregates. Microtopography can promote MSC growth and differentiation. A microgroove topography can retain the phenotype of chondrocytes and improve their adhesion and proliferation.	The size of the ridges plays a more important role than the grooves in determining the MSC fate. The impact of surface topography on cell behavior strongly depends on surface chemistry.	[163–168]
Nano-topography	Nanogrooves, nanogrids, nanoholes, and nanopillars.	Nanopatterned surfaces can induce and enhance receptor-mediated cellular responses. The nanoscale topography could promote epigenetic changes.	The nanoscale topography alone cannot significantly improve the chondrogenic differentiation and its impact depends on surface chemistry.	[169–172]
Surface stiffness		Surface stiffness arises from substrate chemistry and controls stem cell differentiation. Mild stiffness would induce the ROCK pathway that is responsible for the promotion of the chondrocyte phenotype. The combination of surface stiffness and exogenous TGF-β can support the redifferentiation capacity of chondrocytes to generate cartilage.	There is no widely accepted value for stiffness modulus that specifically determines the fate of stem cells.	[173–176]