Table 1.

Biodegradable polymers: sources, merits, and demerits.

Biodegradable Polymers	Name	Sources	Merits	Demerits
Natural biodegradable polymers	Chitosan	Exoskeleton of crustaceans	Biodegradability, low cost biocompatibility, mucosal immune [103].	Soluble in acidic solutions, limited application [130].
	Zein	Corn	Biodegradability, low toxicity, biocompatibility, low cost [107].	Soluble in water containing organic solvents, limited application [106].
	Alginate	Algae	Low toxicity, low cost, used in mucous membranes and traverse body [111].	Tedious preparation process, no targeting [131].
	Hyaluronic acid	Animal tissue, microbial	Biocompatibility, low toxicity [132].	Mass-production may lead to impurity, high price of biological extraction [133].
Synthetic biodegradable polymers	Poly(lactide-co- glycolide acid)	Polymerization of lactic acid and glycolic acid	Loading multiple antigens and immune modulators, used in mucous membranes and traverse body [134].	Organic solvents are required, lack of stability, mucosal administration is ineffective [135].
	Poly (ε-caprolactone)	Polymerization of ε-caprolactone	Biodegradability, colloidal stable, low toxicity, facile celluar uptake [122].	Slow degradation rate, poor mechanical properties, low cell adhesion [123].
	Dendrigraft poly-L-lysine	Lysine polycondensation synthesis	Low toxicity, targeted [136].	Preparation requires complex coupling processes, immunogenicity may interfere with booster immunity [125].
	Polyanhydride	Methyl vinyl ether-maleic hydride synthesis	Sustained release, surface erosion [137].	Highly sensitive to hydrolysis, limited application [138].