Functionalization of nanoporous poly (L-lactic acid) microspheres using light-activated chlorine dioxide radical gas

Nanoporous polymer microspheres fabricated from biodegradable and biocompatible polymers such as poly (L-lactic acid) (PLLA) are excellent candidates for bone tissue engineering due to their high surface area and porosity. However, nanoporous surfaces often exhibit high hydrophobicity, and the lack of functional groups on PLLA limits their ability to support the efficient biomineralization process required for bone tissue engineering. In this study, we report a mild and non-destructive surface oxidation method to functionalize the surface of nanoporous PLLA microspheres using light-activated chlorine dioxide (ClO₂ • ) radical gas. This gas-phase surface oxidation approach introduces polar functional groups onto the microsphere surface while preserving its nanoporous morphology. The oxidation process was optimized via X-ray photoelectron spectroscopy (XPS) and toluidine blue (TBO) dye adsorption studies. Scanning electron microscopy (SEM) and nitrogen adsorption-desorption isotherm measurements confirmed that the nanoporous structure remained largely intact post-oxidation. Importantly, the oxidized microspheres were successfully functionalized with carboxyl and hydroxyl groups and exhibited improved hydroxyapatite deposition upon immersion in modified simulated body fluid (mSBF). This work demonstrates a facile, non-destructive strategy for surface functionalization of nanoporous PLLA microspheres without sacrificing their nanoporous architecture, representing a crucial step towards developing nanoporous biomineralization scaffolds for future bone tissue engineering applications.