Tuning the properties of pH-responsive and redox sensitive hollow particles and gels using copolymer composition

Biodegradable pH-responsive hollow polymer particles offer excellent potential for preparing high performance biomaterials. Unfortunately, the established methods for pH-responsive hollow particle preparation are laborious and difficult to scale up. Recently, we reported that pH-responsive hollow particles could be prepared using solvent evaporation [Bird et al., Chem. Commun., 2011, 47, 1443]. Here, we greatly expand and extend that work by investigating four new pH-responsive hollow particle systems based on poly(MMA-co-MAA) (methyl methacrylate and methacrylic acid) and poly(EA-co-MAA) (EA is ethyl acrylate). The hollow polymer particles were crosslinked with cystamine after preparation to give redox sensitive, biodegradable, hollow particles. For one of the systems a remarkable particle-in-hollow particle morphology was observed. The pH-triggered swelling of the hollow particles was studied and pH-triggered release of a model solute from these new hollow particles was demonstrated. The dispersions formed physical gels in the physiological pH range. The hollow particle physical gels had elastic modulus values as high as 4000 Pa at low total polymer concentrations. The swelling properties of the particles and the mechanical properties of the gels were tuneable using copolymer composition. The particles and gels could be disassembled with glutathione. The properties of these new gel-forming dispersions imply they have good potential for future application as injectable gels for regenerative medicine.