Bio-inspired synthesis of PEGylated polypyrrole@polydopamine nanocomposites as theranostic agents for T₁-weighted MR imaging guided photothermal therapy

Polypyrrole nanoparticle (PPy) based theranostic agents for magnetic resonance imaging (MRI) guided photothermal therapy (PTT) have received increasing attention in recent years. However, the limitations of cost and biocompability still offer us opportunities to improve these agents. Considering the versatile character of polydopamine (PDA), PEGylated PPy@Fe³⁺-chelated PDA nanocomposites (PPDEs) were designed and prepared in an easy way. PPDE with a uniform core–shell structure could be obtained by adjusting the ratio of dopamine and PPys. In this nanocomplex, the shells confer the nanoparticles with good biocompability and MRI signal enhancing ability. Moreover, the PPy cores play a role in photothermal ablation of tumors. Compared with pure PDA nanoparticles, the PPDEs have higher NIR absorbance and better photothermal capability benefitting from the high photothermal conversion of the cores. Additionally, the obtained PPDEs provide significant MRI signal enhancement for both in vitro and in vivo imaging with high longitudinal relaxivity (r₁ = 5.055 mM⁻¹ s⁻¹). After intravenous injection, the PPDEs exhibited valid tumor accumulation, as revealed by MRI and verified by biodistribution analysis. Under NIR irradiation, the PPDEs showed highly effective photothermal ablation of 4T1 cells. Notably, excellent biocompability of the PPDEs was confirmed by a relevant MTT assay and histologic analysis. This work achieved an example of exploiting the inherent advantages of PPy and PDA within a single unit and exploring its potential for T₁ MRI-guided PTT.