A common question is why use biodegradable PEG-PLGA when other thermogels are available which are comprised of PEG and other polymers such as polybutylene oxide and polypropylene oxide? One of the advantages of a biodegradable system in an injectable application is that the lactide and glycolide degrade away to eventually metabolize to carbon dioxide and water while PEG chains with MW's less than 5000Da are screened away by the kidneys. The same is not true for non-degradable thermogels. Studies have shown that accumulation of non-degradable thermogels based on hydrophobic PBO and PPO induced toxic enhancement of plasma cholesterol and triglyceral after intraperitional infection. Additionally to biocompatibility issues there is a difference in the form between the micelles. PPO-PEG-PPO tend to form into ball-micelles with no linkage between the micelles while PLGA-PEG-PLGA forms into micellular structure which has PLGA chains bridging from one micelle to another(1). See full-text here.
(1) Shim, Myung Seob, Hyung Tak Lee, Woo Sun Shim, Insun Park, Hyunjung Lee, Taihyun Chang, Sung Wan Kim, and Doo Sung Lee. "Poly (D, L‐lactic acid‐co‐glycolic acid)‐b‐poly (ethylene glycol)‐b‐poly (D, L‐lactic acid‐co‐glycolic acid) triblock copolymer and thermoreversible phase transition in water." Journal of biomedical materials research 61, no. 2 (2002): 188-196.