Self-Assembly of Metal–Phenolic Networks as Functional Coatings for Preparation of Antioxidant, Antimicrobial, and pH-Sensitive-Modified Starch Nanoparticles

Metal–phenolic network (MPN) coatings have generated increased interest because of their facile fabrication and biocompatibility, especially for safe and nontoxic. How to synthesize a novel, safe, biodegradable, and biocompatible material to replace synthetic materials is of interest in fields of food, biomedicine, and material science. In this study, we successfully fabricated two series of novel and multifunctional-modified starch nanoparticles (MPN@DBS-NPs and MPN@SNCs) by introducing MPN coatings to debranched starch nanoparticles (DBS-NPs) or starch nanocrystals (SNCs) based on the reaction coordinates of the tannic acid (TA) and iron ions. The resulting MPN@DBS-NP and MPN@SNC, each with a spherical shape, measured approximately 75–95 and 110–125 nm in diameter, respectively. Moreover, these nanoparticles provided a negligible release of TA at both a neutral pH (7.4) and an alkaline pH (9.0), as well as a highly efficient release at physiologically relevant acidic pH levels (1.2, 3.0, and 5.0). By utilizing the unique nature of TA, the functionalized surface modification strategy provided the DBS-NP and SNC with excellent antioxidant bioactivity. Notably, significant effects against Gram-positive and Gram-negative bacteria were observed. Cell assays confirmed that MPN@DBS-NP exhibited nontoxicity and high biocompatibility. Together, the cytocompatibility, antioxidant, and antibacterial characteristics of the novel pH-sensitive-modified starch make them promising candidates for food and biomedical applications.