Degradable and Thermosensitive Microgels with Tannic Acid as the Sole Cross-Linker

Abstract

Poly(N-isopropylacrylamide) (PNIPAM)− tannic acid (TA) microgels were successfully prepared via surfactant-free emulsion polymerization (SFEP) at 70 °C in aqueous solution using N-isopropylacrylamide (NIPAM) as the monomer and a natural polyphenol macromolecule, TA, as the sole cross-linker. The cross-linking network of the PNIPAM−TA microgels was confirmed to contain both physical cross-linking structures formed via hydrogen-bonding interactions between TA and PNIPAM chains and chemical cross-linking structures formed via capturing the radicals of propagating polymer chains by catechol and pyrogallol groups of TA. Furthermore, TA was applied to modify the surface of hydrophobic Fe 3 O 4 nanoparticles, leading to hydrophilic Fe 3 O 4 @TA composite nanoparticles, which were successfully used as the cross-linker to fabricate PNIPAM−Fe 3 O 4 @TA organic−inorganic hybrid microgels. The obtained PNIPAM−TA and PNIPAM−Fe 3 O 4 @TA organic−inorganic hybrid microgels had a uniform spherical shape with a relatively narrow size distribution and exhibited thermosensitive behavior and pH-tunable degradation. The PNIPAM−TA microgels were stable in the pH range of 1.3−11.1 but underwent complete degradation with pH above 11.4. The PNIPAM−Fe 3 O 4 @TA hybrid microgels were partially degraded at pH values of 1.3 and 2.1, stable in the pH range of 3.1−11.1, and underwent complete degradation at pH above 11.4. The partial degradation of PNIPAM−Fe 3 O 4 @TA organic−inorganic hybrid microgels under strong acidic conditions was attributed to the disintegration of Fe 3 O 4 nanoparticles. The complete degradation of both microgels at pH above 11.4 was attributed to the hydrolysis of ester groups of TA under strong alkali conditions.

A stretchable, environmentally stable, and mechanically robust nanocomposite polyurethane organohydrogel with anti-freezing, anti-dehydration, and electromagnetic shielding properties for strain sensors and magnetic actuators

“…TA possesses multiple phenolic hydroxyl and galloyl groups and exhibits strong adhesion on the surfaces of various metals and metal oxides. 24 Thus, stable Fe 3 O 4 @TA nanoparticles can be synthesized based on the coordination reaction of iron ions and galloyl groups. Fig.…”

Aggressive strategies for regenerating intervertebral discs: stimulus-responsive composite hydrogels from single to multiscale delivery systems

“…, PNIPAAM-Fe 3 O 4 @TA composite microgels formed by hydrophilic Fe 3 O 4 @TA nanoparticles through hydrogen bonding are thermosensitive, pH-tunable, and degradable and exhibit a homogeneous spherical shape with a narrow particle size distribution. 237…”

“…236 Hydrogen bonding breaks are heat-absorbing reactions, and the phase transition and degradation of microgels synthesized based on hydrogen bonding can be regulated by temperature; e.g., PNIPAAM-Fe 3 O 4 @TA composite microgels formed by hydrophilic Fe 3 O 4 @TA nanoparticles through hydrogen bonding are thermosensitive, pH-tunable, and degradable and exhibit a homogeneous spherical shape with a narrow particle size distribution. 237 Cell-to-cell interaction-driven microgel assembly mostly occurs on the microgel surface, e.g., PEGDA microgels with low surface adhesion can lead to cell shedding and are not suitable for longterm culture. However, GelMA is able to maintain cellular integrity and exhibit high expression of morphogenetic elements over time.…”

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

“…[54] Moreover, PNIPAAm-based microgels crosslinked with TA as a physical crosslinker have been prepared using surfactant-free emulsion polymerization to serve as carriers for iron oxide nanoparticles. [55] In the present work, we performed a detailed analysis of the polymerization conditions (pH, temperature, addition mode of TA) to improve the microgels yield and achieve control of the chemical composition (VCL:TA ratio). In addition, we present systematic studies of the microgel disassembly in aqueous, alkaline solutions.…”

“…[ 54 ] Moreover, PNIPAAm‐based microgels crosslinked with TA as a physical crosslinker have been prepared using surfactant‐free emulsion polymerization to serve as carriers for iron oxide nanoparticles. [ 55 ]…”