The Shape Influence on the Photothermal and Drug Adsorption Performance of Polydopamine Nanoparticles

Abstract

Since first reported in 2007, polydopamine synthesized in weakly alkaline condition has been extensively investigated. Among these studies, polydopamine nanospheres are commonly prepared as drug delivery nanoparticles for chemo-photothermal therapy. However, anisotropic nanostructures such as tubular shaped particles have higher specific surface area and enhanced biodistribution. But owing to the difficulty in preparation, they are rarely studied. In this study, polydopamine were fabricated into spherical and tubular shapes under weakly alkaline conditions. The nanospheres were formed in dopamine solution through a nanoprecipitation process, while hollow polydopamine nanotubes were obtained by forming a polydopamine coating on a sacrificial natural template, halloysite, in dopamine solution. Both the particles were modified with amino terminated polyethylene glycol via Michael addition. Morphology investigation showed distinct shape difference between the both nanoparticles. Under transmission electron microscopy, polydopamine nanoparticles have spherical morphology with diameters of 145-160 nm, while the nanotubes have high aspect ratios in the 4.7-5.9 range with lengths of 532-709 nm and diameters of 104-127 nm. Fourier transform infrared spectroscopy and thermogravimetric analysis were conducted to confirm both nanoparticle composition and that the template was removed completely. The photothermal effect was accessed under near infrared irradiation (808nm, 1W cm-2). The dispersions of the nanotubes, probably due to the higher specific surface, exhibited a higher temperature rise than the nanosphere dispersions. The nanotubes also displayed significantly higher loading capacity, nearly double of that for nanospheres, of an antitumor drug, doxorubicin. The release of the drug was enhanced by both acidic pH and infrared irradiation stimuli.