Influence of Different Magnetic Nanoheaters on the Thermoresponsive Deswelling of pNIPAM/Alginate Ferrogels for Remotely Activated Release Devices

Abstract

Smart ferrogels composed of the thermoresponsive polymer poly(N-isopropylacrylamide) (pNIPAM) and iron oxide nanoparticles are excellent candidates for designing remotely activated controlled release devices as they can synergize the deswelling ability of pNIPAM with the magnetic heating capacity of the nanoparticles. However, the synthesis of these nanocomposites presents several challenges that require careful optimization to ensure optimal integration and function of the entire system. In this work, we present the preparation, characterization, and technological performance of thermoresponsive ferrogels composed of pNIPAM/alginate and citrate-stabilized iron oxide nanoparticles. In particular, we focus on testing three types of nanoparticles of different mean sizes to find the nanoheaters that best integrate with the polymer matrix and give rise to the best thermosensitive response of the material against the application of the external magnetic field. We found that the incorporation of any of the three nanoparticles and alginate does not significantly alter the thermosensitive response of the system compared to that of pure pNIPAM hydrogels; in all cases, we observed a deswelling (water release) close to 80% over 30 min when heated in a water bath above their transition temperature. However, when testing the heat generated by the external magnetic field due to the presence of the nanoheaters, only the ferrogel with nanoparticles of 10 nm was able to generate the appropriate thermosensitive response and deswelling. In this system, the deswelling rate by magnetic heating even exceeded the rate measured during external heating in the bath, indicating that this ferrogel can act as a stimulus-responsive and ″smart″ nanocomposite with potential uses as a remotely activated release device for drug delivery, gel actuators, and other technological applications.