Responsive Polyphenol‐Crosslinked Supramacromolecular Microgels with pH‐Triggered Disassembly in Aqueous Solution

Abstract

This work focuses on the pH‐triggered disassembly of supramacromolecular microgels, which are composed of the temperature‐responsive poly(N‐vinylcaprolactam) (PVCL) and the natural polyphenol tannic acid (TA). A systematic investigation of the microgel formation demonstrates that a retarded addition of tannic acid during semi‐batch precipitation polymerization influences the yield, chemical composition, and properties of the microgels to a great extent. Microgel properties, such as size, deformability, and chemical stability, can be easily tuned by varying the ratio between both building blocks PVCL and TA. Finally, the pH‐triggered disassembly of supramacromolecular microgels at different pH and temperatures demonstrates that their chemical structure can precisely control the degradation profile. Temperatures lower than the volume phase transition temperature (VPTT) of PVCL (T < 32 °C) and a pH > 10 result in a complete disassembly of the microgels into PVCL chains and TA due to the destruction of the hydrogen bonds responsible for the formation of a colloidal microgel. Interestingly, at temperatures above VPTT, the microgels keep their integrity due to enhanced hydrophobic interactions between the polymer chains of the microgel and are no longer affected by pH changes.

Tuning the Porosity of Dextran Microgels with Supramacromolecular Nanogels as Soft Sacrificial Templates

“…To remove the ST out of the microgel, the pH of the microgel environment was adjusted to pH 12 for 24 h to deprotonate all phenolic groups of TA, which induces the ST to degrade. [ 33 ] The microgels were then washed with water after 24 h. The remaining low‐intensity fluorescence after template removal can be explained by the fact, that the dye is covalently attached to 2,2′‐azobis(2‐amidinopropane) dihydrochloride (V‐50) used during the preparation of the ST and not all the long pVCL chains can diffuse out of the dex‐MA microgel within 24 h since there will be interactions between both hydrophilic polymer chains.…”

“…The synthesis of the pH‐degradable, supramacromolecular microgels was performed accordingly to the recently published literature. [ 23,33 ] Stock solutions of TA (0.1633 g) were prepared in pure, deionized water (3 mL) and a second solution of CTAB (0.2135 g) was prepared in pure deionized water (13 mL). VCL (0.800 g, 100 mol%, 139.19 g mol −1 ) was dissolved in pure, deionized water (60 mL) and filled into a 100 mL round‐bottom flask equipped with a stirrer bar.…”

“…Those sacrificial colloidal templates have been synthesized by semi-batch precipitation polymerization according to recently published literature. [23,33] Different concentrations of the surfactant cetyltrimethylammonium bromide (CTAB) were used to vary the size of the resulting sacrificial nanogels to achieve different pore sizes within the dextran-based microgels. Raman spectroscopy was used to characterize their chemical composition, as well as to quantify the content of the bio-based cross-linker TA (Figure S3 and Table S1, Supporting Information).…”

Supramolecular assemblies of multifunctional microgels for biomedical applications

“…The microgels exhibit reversible temperature-dependent swelling/deswelling and undergo pH-triggered degradation in aqueous solutions. 101 PNIPAM–TA microgels contain both physical cross-linking via hydrogen bonding between TA and PNIPAM chains and chemical cross-linking via capturing the radicals of propagating polymer chains by catechol and pyrogallol groups of TA (Fig. 6).…”

Hexyl Gallate Loaded Microgels Enable Efficient Protection Against Citrus Canker

“…Tannic acid (TA) has already been described as an efficient organic agent in the inhibition of a wide variety of bacteria, [54] being effective against pathogens of clinical interest such as Staphylococcus aureus, [55] and Penicillium digitatum, which is an important phytopathogen of citrus. [56] However, the incorporation of TA in some of the microgels synthesized in the present work was aimed only to cross-link the polymer network, [57,58] with no focus on its possible bactericidal action against X. citri. It is noteworthy that the microgels pVCL/pGMA/TA and pVCL/pGMA/TA/hDerm at the concentration of 2.75 mg mL −1 showed growth inhibition values of 33.67 % and 36.99 %, respectively.…”