Micro/Nanoscale bonding and surface glass transition temperature of polymers under carbon dioxide

Studies of polymer thin films revealed that properties of polymers at the surface are different from those in the bulk. The most striking among these properties is the glass transition temperature, T _g. In this study, the surface T _g of poly(DL-lactide-co-glycolide) (PLGA) under carbon dioxide (CO ₂) was evaluated by embedding gold nanoparticles onto PLGA surfaces. The T _g profiles at the surface were determined by measuring the apparent height of embedded nanoparticles using atomic force microscopy (AFM). It was shown that CO ₂ could greatly depress the T _g near the surface. Using this idea, we demonstrated near room temperature bonding of polymers at a length scale as small as 3.9 μm. This CO ₂ bonding technique was successfully applied to seal polystyrene-based microfluidic chips and construct three-dimensional (3D) PLGA tissue scaffolds with well-defined structure.