Esterification influence in thermosensitive behavior of copolymers PNIPAm-co-PAA and PNVCL-co-PAA in magnetic nanoparticles surface

The ability to generate heat from magnetic nanoparticle and the response of thermosensitive polymers poly(n-isopropylacrylamide) (PNIPAm) and poly(n-vinyl caprolactam) (PNVCL) are properties that have promoted several studies in controlled drug release systems. As the lower critical solution temperatures (LCST) of PNIPAm and PNVCL are between 32–35 °C and close to the temperature of the human body these polymers are adequate for biomedical applications. The LCST could be increased by copolymerizing the thermoresponsive polymer with a monomer with greater water affinity as poly(acrylic acid) (PAA), which was studied copolymerized with PNIPAm and PNVCL in aqueous solution. Cancer treatment is possible using the ability to generate heat from magnetic nanoparticles. Magnetic hyperthermia can be combined with controlled drug release and improve the treatment. In this work iron oxide nanoparticles were surface modified with a copolymer of acrylic acid with PNIPAm or PNVCL and then modified by esterification. Infrared spectroscopy indicated the presence of the polymer in the magnetic nanoparticles and showed the bound of carboxylic groups to the magnetite surface. The temperature-time experiments showed that magnetic nanoparticles coated with thermoresponsive polymers can heat from 20 °C to 40 °C, in a suspension of 15 mg of magnetite in 1 ml of water under an alternating magnetic field of 14 kA m−1 and frequency of 420 kHz. The polymer onto magnetic nanoparticle surface has a high release rate of methotrexate at 43 °C, but low at 37 °C. PNIPAm-co-PAA or PNVCL-co-PAA showed different behavior in methotrexate (MTX) release, as the esterified copolymer of PNIPAm showed an increase in MTX release in 43 °C and PNVCL esterification decreases the release rate. The LCST of PINIPAm-co-PAA and PNVCL-co-PAA decreased with the esterification since the reaction added hydrophilic groups in the polymer chain. These results suggest that the platform developed in this work can be used for drug delivery in cancer treatment, since its LSCT can be tuned in function of esterification and composition to temperatures well above the human body.