Polydopamine Coatings in Confined Nanopore Space: Toward Improved Retention and Release of Hydrophilic Cargo

Abstract

A composite nanocarrier system integrating the porous structure of mesoporous silica nanoparticles (MSNs) and the adhesive property of polydopamine for loading and release of hydrophilic drugs is reported. Amino group functionalization facilitates the oxidant-induced surface polymerization of dopamine in the confined space of mesopores by Schiff base/Michael addition reaction in a mild synthesis. As a consequence, to MSN@PDA particles with an average pore size of 4.0 nm, a particle diameter of ~ 70 nm, as well as a thin layer of polydopamine coating on the surfaces of MSNs. The MSN@PDA nanocarriers can effectively adsorb hydrophilic drugs with high loading capacities (380 µg/mg for doxorubicin hydrochloride (DOX)and 320 µg/mg for calcein), facilitated by the π-π stacking interactions between the abundant aromatic rings of PDA and the aromatic backbones of drugs. Interestingly, sustained and pHdependent drug release was observed for these drug loaded MSN@PDA particles, owing to the adhesive property of polydopamine like "molecular glue". Moreover, a catechol-metal-drug coordination system can be easily constructed on the basis of the coordination bonding between catechols in polydopamine and transition metal ions (Fe 3+ , Zn 2+ ), as well as that between metal ions and anthracycline drugs (i.e. DOX), resulting in an acid-triggered drug release.

Chemistry of polydopamine analogues

“…PDA can also be modified in a non‐covalent way by aromatic compounds via π – π interactions. This attitude has been successfully applied in the nano‐medicine field to immobilize hydrophobic drugs like doxorubicin …”

Mussel‐inspired decoration of Ni(OH)2 nanosheets on 2D MoS2 towards enhancing thermal and flame retardancy properties of poly(lactic acid)

“…In comparison with MoS 2 , the adsorption peaks of MoS 2 ‐PDA at 3431 and 883 cm −1 are attributed to the symmetric stretching vibration of NH 2 and N–H out‐of‐plane bending vibration, respectively. It can be seen that the band at 1621 cm −1 can correspond to the vibration of O–H from the catechol groups (a basic constituent of the PDA molecule) . In addition, the FTIR spectra of MoS 2 ‐PDA@Ni(OH) 2 exhibit some notable differences with MoS 2 ‐PDA, which give the evidence to the successful incorporation of PDA on MoS 2 and the decoration with Ni(OH) 2 .…”

Versatile Surface Modification Using Polydopamine and Related Polycatecholamines: Chemistry, Structure, and Applications

“…This is because catechol coordination complexes are strong, have rapid rates of formation, and are reversible and so can imbue materials with desirable properties such as toughness, self‐repair, adhesion, and hardness . These qualities can be tuned by varying the density of complexation, and the pH of reaction as well as the coordination state and type of metal ion . Metal ions coordinated to catecholamine can also oxidize catechol groups, enhancing the cyclization reaction, promoting polymerization, and facilitating further covalent cross‐linking within the structure of the material .…”

“…Further, polydopamine coatings on both organic and inorganic nanoparticles containing drugs have enhanced stability and controlled release of internalized active ingredients . This includes pH, near‐infrared, and redox chemistry mediated release of drugs . Related polydopamine coatings have also been used to functionalize the drug containing nanoparticles with both stealth coatings to reduce clearance from body and with ligands to target delivery …”