Table 2.

Advantages and disadvantages of polymers used in the preparation of biodegradable microspheres and their ophthalmic clinical application.

Polymers used in biodegradable microspheres	polymers	FDA approved for eye use	advantages	disadvantages
Natural biodegradable polymers	Gelatin	Yes	Easily derived, biocompatible, less immunogenic, low cost	Strength depends on source and processing conditions， challenging to safely crosslink
	Alginic acid	Yes	gel forming ability	Poor mechanical strength
	chitosan	No	mucosal adhesion, in-situ gelation, transfection, and permeation-enhancing capabilities	Insoluble in neutral or alkaline, solutions, strong electrostatic behavior
	Pectin	No	gel-forming properties, mucosal adhesion	Lack of clinical data
Synthetic biodegradable polymers	PLA	Yes	Synthesized from natural sources, easily processed, slow degradation rate	Acidic degradation by products
	PLGA	Yes	water soluble, tunable degradation rate	Acidic degradation by products
	PEG	Yes	water soluble, biocompatible	Fast degradation compared to other synthetic polymers
	PCL	No	easily modified, inexpensive	Poor mechanical properties
	PEA	No	Enhanced biocompatibility and excellent mechanical properties	Lack of clinical data
	PCADK	No	excellent biocompatibility and biodegradability properties	Degrades slowly in vivo

Abbreviations：PLA, polylactic-lactic acid; PLGA, polylactic-glycolic acid; PEG, poly (ethylene glycol); PCL, poly (ε-caprolactone); PEA, polyester amide; PCADK, poly (cyclohexane-1,4-diyl acetone dimethylene ketal).