Coaxial nanotubes of stimuli responsive polymers with tunable release kinetics.

Stimuli responsive polymeric (SRP) nanotubes have great potential as nanocarriers of macromolecules due to their large surface areas and release mechanisms that can be activated externally. In this work, we demonstrate vapor phase synthesis of coaxial nanotubes with layers of different SRP polymers for improved release kinetics. Temperature responsive poly(N-isopropylacrylamide) (pNIPAAm), pH responsive poly(methacrylic acid) (pMAA) and poly(hydroxyethyl methacrylate) (pHEMA) are used to fabricate the responsive coaxial nanotubes and the phloroglucinol dye is used as the model molecule to study the release kinetics. Fastest release is observed with single layer pNIPAAm nanotubes with rates of 0.134 min(-1), whereas introducing pHEMA or pMAA as inner layers slows down the release, enabling tuning of the response. Furthermore, repeating the release studies multiple times shows that the release rates remain similar after each run, confirming the stability of the nanotubes.