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

Abstract

Novel thermoreversible gelation behavior of aqueous solutions of ABA-type triblock copolymers composed of the central polyethylene oxide (PEG) block and two poly(D,L-lactic acid-co-glycolic acid) side blocks was found. Phase transition characteristics, such as critical gel concentration (CGC) and lower and upper critical gel temperature (CGT), are closely related to the molecular structure of the triblock copolymers. The CGC and the lower CGT both increases with increasing PEG/PLGA molecular weight ratio. Increasing the GA content in PLGA block induces a somewhat higher CGC. The copolymer forms micelles with a PLGA loop core and a PEG shell in water. Also grouped micelles are identified seemingly due to the bridging of two micelles sharing two PLGA blocks of a block copolymer chain. As the temperature increases the association of micelles increases, which results in gelation. The ABA-type copolymers exhibit a relatively low CGC (<10%) and low sol-gel transition temperatures compared to BAB-type copolymers. As the temperature increases further gel-sol transition is observed, which would result from the shrinkage of micelles with temperature increase. The hydrodynamic size of the micelles is monitored by dynamic laser scattering, and a possible gelation mechanism was suggested.

Sustained intravitreal delivery of dexamethasone using an injectable and biodegradable thermogel

“…[16,[32][33][34][35][36]. However, the composition window of PLGA-PEG-PLGA triblock copolymers to form a thermogel is quite narrow [37,38]. Otherwise, the polymers are just soluble or precipitate in aqueous medium.…”

The effect of PLGA-PEG-PLGA modification on the sol-gel transition and degradation properties

“…Molar ratio of synthesis was selected based on a literature review about PLGA-PEG-PLGA triblock copolymers [4]. It was assumed that aqueous solutions of these copolymers will change to gel in the vicinity of the body temperature.…”

Synthesis and properties of novel biodegradable triblock copolymers of poly(5-methyl-5-methoxycarbonyl-1,3-dioxan-2-one) and poly(ethylene glycol)

“…PEG is non-biodegradable, however, the lower molecular weight of PEG (less than 10,000) is easily removed from human body through kidney membrane [3]. In recent years, a wide variety of biomedical copolymers containing PEG segment have been reported, such as polycaprolactone/poly(ethylene glycol) (PCL/PEG) [4,5], poly(trimethylene carbonate)/poly(ethylene glycol) (PTMC/PEG) [6], polylactide/poly(ethylene glycol) PLA/ PEG [7,8], polylactide/poly(glycolic acid)/poly(ethylene glycol) (PLA/PGA/PEG) [9] and PGA/PCL/PEG [10].…”