Direct-write microfabrication of biodegradable polymer nanocomposites 3D scaffolds

Poly(lactic acid) (PLA) is a biodegradable and biocompatible thermoplastic derived from renewable plant sources such as starch and sugar. The direct-writing of ink offers the ability to rapidly and precisely fabricate functional materials in various complex 3D structures from a broad array of materials. In this work, we developed a PLA nanocomposite solution used as an ink to fabricate 3D periodic micro scaffolds by direct-write assembly. In this process, the polymer and the nanofillers (i.e., nanoclay) were well distributed in a volatile solvent to form a viscous solution. This polymer solution was then loaded into a syringe and extruded through a micro nozzle during the robotic deposition. Due to the rapid solvent evaporation, the filament behavior changed from fluid-like to solid-like right after its extrusion out of nozzle to facilitate the shape retention of the deposited features. The solvent played two important roles during the process: 1) dissolving the polymer within a moderate weight concentrations (20 ∼ 30 wt.%), and 2) possessing a high volatility due to its relatively low boiling point for rapid filament solidification post extrusion. The inks were prepared by dissolving PLA/nanoclay composites with various nanoclay loadings (0, 1, 2, 5, 10 wt.%) in dichloromethane (boiling point: 39.6 °C) solvent using solution process. Then the PLA nanocomposite solutions were used to build 2D planar filaments on a substrate, 3D scaffolds and spirals for various filament diameters (40 ∼ 250 μm). The fabrication parameters for the ink micro-extrusion process such as the applied pressure, the nozzle and filament diameter, the robot velocity and the ink apparent viscosity were investigated by capillary flow analysis. The morphology of extruded filaments was characterized by SEM and the results showed that the filament surface became rougher with increasing nanoclay loadings. Dynamic mechanical analysis (DMA) using a film tension clamp was performed for the nanocomposite filaments featuring different nanoclay contents, applied pressures and nozzle diameters.