Metal-phenolic networks as a novel filler to advance multi-functional immunomodulatory biocomposites

Here, we exploited the potential applications of metal-phenolic networks (MPNs) as a novel type of filler for next-generation multi-functional immunomodulatory biocomposites. Tannic acid (TA) and Mg2+ were selected as the model phenolic ligand and metal ion, respectively, and used to assemble MPN particles, and a TA-Mg/polycaprolactone (PCL) composite nanofibrous scaffold was then prepared by blending electrospinning. Measurements of the resultant composite scaffold verified strong hydrogen-bonding interactions between TA motifs and PCL chains and the good dispersity of MPN particles throughout the substrate. Due to the pH-responsive disassembly kinetics of MPN complexes, both TA and Mg2+ displayed pH-responsive sustained release behaviour, thus eliciting significant biological effects. Specifically, TA and Mg2+ synergistically generated an anti-inflammatory micro-environment, which was beneficial for osteogenesis, and Mg2+ directly stimulated the osteogenic differentiation of stem cells. Consequently, the composite membrane significantly enhanced in vivo osteogenic performance when used as a barrier membrane to guide bone tissue regeneration. One unique advantage of this filler is that it combines the functions of both metal ions and phenolic ligands. By selecting different phenolic ligands and metal ions, a series of novel MPN-based fillers with unique functions could be easily obtained, suggesting that this system has a wide range of potential applications for next-generation multi-functional biocomposites.