pH-responsive hydrogels from moldable composite microparticles prepared by coaxial electro-spray drying

Physical gelation between two polymers of opposite charges has potential applications in hydrogel delivery systems. However, issues associated with physical gelation, such as gelation control, effective drug loading, and stability before delivery, have limited the application of this technique. We, therefore, investigated gelable composite particles, because drugs can be effectively loaded inside a core with a less hydrophilic protective shell, and, later, the composite particles can be gelled into any shape in water. A modified spray drying apparatus was built by introducing a customized coaxial nozzle and applying a high electric potential between the nozzle and a ground in the air flow channel for convenient preparation of gelable composite particles. The resulting particles were molded into more elastic hydrogels by the addition of water than those prepared by the gelation of powder physical mixtures, and their pH-dependent equilibrium swelling could be tailored to a wide range. The release rate of a model drug (lipoic acid) appears to reflect the composite structures. As the applied voltage was increased, more sustained release and lower equilibrium swelling resulted. This novel preparation technique and the resulting gelable structured particles have potential applications in drug (proteins) delivery systems, wound healing hydrogels, protein-releasing scaffolds, etc.