Table 1.

Stimuli-responsive smart biomaterials for the types of response, materials, principles, and characteristics.

Type of response	Material	Principle	Characteristic	Ref.
Electricity	CA–CS–HA and PCL/PDMS/PCL–FA	Converting mechanical energy into electrical energy to promote chondrocyte proliferation	Implantable; self-powered, anti-interference; highly sensitive; intelligentically degradable	[87]
	Nanofibrous scaffold of PLLA	Generating adjustable piezoelectric charges under applied force; altering calcium signaling pathways to induce endogenous TGF-β	Biodegradable; controlled mechanical activation	[89]
Temperature	PAF-PEG-PAF	The enlarged pore size and enhanced mechanical strength generate the cartilage and reduce the formation of fibrous tissue	Excellent temperature responsiveness; minimally invasive implantation in situ	[94]
	stereocomplex 4-arm PEG–PLA	The cartilaginous-specific matrix, biomechanical property, and gene expressions	Improved mechanical properties; larger pore size; better chondrocyte adhesion	[29]
NIR light	E@Au–Ag	Anti-oxidative stress to reduce chondrocyte apoptosis; up-regulating col II expression in chondrocytes and decreasing apoptosis marker proteins p-caspase-3 and MMP13 expression	Antibacterial; NIR-sensitive; synergistic therapy	[95]
Light	CM-NTU	Increasing intracellular ATP and NADPH levels and improving anabolism in degenerating chondrocytes	The natural photosynthetic system controls cell behavior; the cross-species system	[100]
Magnetism	WY-CMC-MnOx	Promoting chondrogenesis of MSCs	Precise ability to target cartilage; ultrasmall sizes	[96]
	MNPs (CAG)	Upregulating the chondrogenesis-related genes of COL2A1 and ACAN	3D magnetic scaffolds; operating under a dynamic magnetic field	[101]
Enzyme	PEG-KGN	Quickly fill with bone marrow blood shortly after implantation, enabling maximal absorption and retention of ESPCs	Fast absorption of protein solution through capillarity