Controlled release of anti-cancer drug from the shell and hollow cavities of poly(N-isopropylacrylamide) hydrogel particles synthesized via reversible addition-fragmentation chain transfer polymerization

Abstract

Temperature-responsive poly(N-isopropylacrylamid) (PNIPAAm) hydrogels with two different crosslinking densities were coated on silica nanoparticles via surface-initiated reversible addition-fragmentation chain transfer network formation method in an inverse emulsion medium. The temperature-responsive hollow hydrogel particles were also prepared by etching of the silica cores using hydrofluoric acid. The hybrid and hollow hydrogel particles were used as doxorubicin (DOX) delivery systems. The synthesis process was evaluated by proton magnetic nuclear resonance and Fourier-transform infrared spectroscopies, thermogravimetric analysis, and scanning and transmission electron microscopies. Dynamic light scattering and turbidimetry by UV–vis spectroscopy were also used to study responsivity of the hybrid and hollow PNIPAAm hydrogels to temperature. Gel collapse temperature (GCT) of the hydrogels was studied using UV transmittance curves. UV transmittance and the GCT value of the hollow hydrogels were higher than the hybrid samples. The hollow hydrogel particles with higher crosslinking density showed higher hydrodynamic diameter (Dh) at temperatures of above the GCT, whereas the hollow cavity and lower crosslinking densities resulted in higher Dh at temperatures below GCT. Release of DOX from the hybrid and hollow hydrogel particles with two different crosslinking densities was investigated by using UV–vis spectroscopy at below and above GCT of the hydrogel particles (25 and 45 °C, respectively). The hollow particles with low crosslinking density showed the lowest release percent due to its higher loading capacity. In addition, the DOX release percent was reduced by increasing temperature from 25 to 40 °C.