Development of chitosan-coated polydopamine nanoparticles for skin delivery applications

Polydopamine nanoparticles (PDA) have shown promising results due to their functional versatility as innovative nanocarriers. However, PDA bioadhesive and skin permeation properties are still points of care. Then, PDA were developed and coated with CHI (Chitosan) aiming skin delivery applications. PDA were synthesized via oxidative self-polymerization (at pH 8.5 and 10) and temperatures from 25 to 70 °C. The material was dispersed in ultrapure water and sonicated (1 min cycles at 20 kHz). PDA exhibited different hydrodynamic diameters (Dh, nm) at pH 8.5: 390 ± 47 (25 °C), 463 ± 117 (50 °C), 242 ± 19 (70 °C). At pH 10, Dh were 419 ± 106 (25 °C), 447 ± 196 (50 °C), and 435 ± 184 (70 °C), indicating that PDA adequate size was obtained at pH 8.5 and 70 °C. CHI-coating was performed by using low, medium, and high molecular masses (pH 8.5 and 70 °C, 120, 275, and 340 kDa CHI, respectively) at concentrations from 250 to 1000 µg/mL. Dh values after CHI-coating were 204 ± 79 (PDA); 393 ± 75 (PDA-CHI-low); 347 ± 113 (PDA-CHI-medium) and 321 ± 82 (PDA-CHI-high) while zeta potential (ZP) values shifted from –44.0 mV (PDA) to +44, +24, and +20 mV, for low, medium and high, respectively. Additionally, CHI-coating was also confirmed by FTIR, by identification of functional groups from PDA (catechol and amine) and CHI (amine and hydroxyl). AFM analysis showed rough surface topographies and uniformly distributed clusters. Phase mapping indicated surface heterogeneity. SEM revealed spherical nanoparticles with smooth surfaces and uniform distribution, without dense aggregate formation, consistent with synthesis under alkaline conditions. Rheological assays showed that samples exhibited similar G’/G” (~25-fold), confirming a dominant elastic behavior, but with no influence from CHI molecular masses. In summary, the optimized synthesis of PDA nanoparticles and their coating with CHI resulted in improved colloidal stability, confirming the effectiveness of the synthesis process and its potential bioadhesive properties for application as skin delivery systems.