Green Templating of Ultraporous Cross-Linked Cellulose Nanocrystal Microparticles

Cellulose nanocrystals (CNCs) are rigid rodlike nanoparticles that are derived from natural cellulose. Their high surface area, mechanical strength, and noncytotoxicity have elicited interest in their use for various applications, including composite and construction materials, cosmetic, food, and biomedical products. However, few methods exist to control the morphology and dimensions of assembled CNC structures in the micrometer range. Here, we use water-in-oil droplet microfluidics to template uniform spherical CNC droplets in a nontoxic and sustainable manner. Subsequent evaporation of the water within the droplets promotes the chemical cross-linking of surface-modified CNCs, resulting in ultraporous and flexible micrometer-sized particles. Changing the size of the microfluidic channel or the concentration of the CNC suspension results in microparticles with tunable sizes. The microparticles swell in polar solvents, with larger swelling observed for microparticles fabricated from less-concentrated CNC suspensions. While swelling is pH-independent, it is impacted by ionic strength for microparticles with low cross-link densities. Scanning electron microscopy reveals that the microparticles have macropores and mesopores, supporting a large specific surface area. These porous microparticles have potential for a range of applications, such as drug delivery or sorption agents, or as biodegradable beads for use in cosmetic and food applications.