Thermally-Conductive-Pin Patterned Substrate: Innovative Strategy for Controlled Formation of Tubular Pores in Biodegradable Polymer Membranes

The thermally-induced phase separation (TIPS) technique has been widely utilized for fabricating porous materials such as membranes and scaffolds. However, the precise positioning of pore formation is often challenging due to the uncontrolled temperature gradient within the materials during the TIPS process. Drawing inspiration from the coexistence of tubular pores with varying diameters in natural structures, a novel approach was devised to replicate this natural structure using a combination of biodegradable polymer (poly-L-lactic acid), a patterned cap-equipped mold, and a temperature-controllable one-directional-cooling apparatus. The pattern consisted of high-thermal-conductivity Ti alloy pins encased in low-thermal-conductivity polyethylene (PE). The differential thermal gradient between the pins and the PE portion of the cap facilitated the formation of tubular or flat-plate pores in the desired areas. Significantly, a porous structure featuring well-aligned flat-plate pores and a sandwich panel skeleton was successfully fabricated using a cosolvent system (benzene/dimethyl carbonate). It is anticipated that the innovative strategy incorporating the patterned cap, the one-directional-cooling apparatus, and the cosolvent system will introduce a novel and promising method for fabricating intricate porous structures extending beyond conventional polymer membranes and scaffolds.