Ultrasonic monitoring of drug loaded Pluronic F127 micellular hydrogel phase behaviour

Pluronic hydrogels composed of PEO–PPO–PEO tri-block copolymers have received a lot of attention for their applicability to drug delivery. These systems can be injected into the body in a liquid form and then, in response to temperature changes, self-assemble into nano-sized micelles which ultimately aggregate to form a gel. The phase behaviour and effectiveness of Pluronic hydrogels as drug carriers is affected by the local thermal and ionic environment which is likely to be different from patient to patient. There is a current need for in vivo techniques to study the phase behaviour of Pluronic hydrogels and this work demonstrates an ultrasound approach for the study of drug loaded Pluronic F127 hydrogels. Ultrasound velocity and attenuation were both found to change with temperature and through validation with fluorescence spectroscopy it was determined that the temperature dependent micellation transition in the Pluronic solutions could be identified through relative changes in ultrasound velocity and attenuation as a function of temperature. This phase transition was more clearly detected through examination of the first and second derivatives of both ultrasound parameters with respect to temperature. Further this work demonstrates for the first time to our knowledge ultrasound characterisation studies on drug loaded Pluronics.