Table 1.

Properties of different 4D printing polymers.

Polymers	Physicochemical properties	Stimulation	Advantages	Disadvantages	Ref.
PNIPAAm	Temperature-sensitive	Temperature	The response temperature is close to the body temperature	Low mechanical strength	[141]
PVA	Water-soluble polymer with good adhesion and film-forming properties	Temperature, Water	Good water solubility; easy to process; good biocompatibility	Low mechanical strength; poor stability	[[142], [143], [144],145]
PCL	Semi-crystalline polymer with low melting point and glass transition temperature	Temperature, pH	Good biocompatibility, biodegradability, and flexibility; slow degradation rate; suitable for long-term application	Low mechanical strength; general thermal stability; printing accuracy may be limited	[146,147,148]
PLA	High crystallinity	Temperature, pH	Good biocompatibility and degradability; good mechanical properties	Great brittleness and insufficient toughness; degradation products may result in a locally acidic environment	[149,150,151,152]
PU	Good mechanical properties, flexibility, and wear resistance	Temperature	Adjustable properties by changing the molecular structure and composition	Relatively poor biodegradability	[153,154,155]
Alginate	Natural polymer with good biocompatibility and gel formation ability	Ion, pH	Rich source; low cost; good biocompatibility and gel properties.	Limited mechanical strength; the rate of degradation is difficult to control precisely	[156,157,158]
Chitosan	Natural polysaccharide with good biocompatibility and biodegradability	Enzyme, pH	Good biocompatibility and bioactivity; antibiosis	Poor mechanical properties; difficult to process	[159,160,161]