Rheological properties of PLGA-PEG-PLGA copolymers for ophthalmic injection

Polymer rheological property is one of intrinsic properties for the design and preparation of intravitreal injection systems. Rheological behaviors of thermosensitive poly(lactic acid-co-glycolic acid)-poly(ethylene glycol)-poly(lactic acid-co-glycolic acid) (PLGA-PEG-PLGA) triblock copolymers were investigated in this article. The rigidity phase angle (d), elastic modulus (G'), viscous modulus (G?), and complex viscosity (?*) were determined. The injectability of polymers was evaluated as well. The results indicated both temperature and concentration were key parameters influencing elasticity of polymers. Owing to low complex viscosity (below 1 Pa s), PLGA-PEG-PLGA polymers can be successfully injected at room temperature. When the temperature was raised to 37 degrees C, the complex viscosity increased (over 4 Pa s). Thus, suitable rheological properties (G' > G?; tan d < 1) were obtained for injection administration. Elastic modulus (G'), viscous modulus (G?), and complex viscosity (?*) were diminished when polymer solutions were ejected through syringe needles (25 gauge, G). Ejection force (from 4.21 to 19.42 N) was required in the process of injecting administration through syringe needles (24, 25, and 26 G) for polymer solutions at 20, 25, and 30% (w/v) concentration. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012