This document summarizes research on using recycled poly lactic acid (PLA) polymer in 3D printing. It discusses how PLA can be recycled through a closed-loop process to produce 3D printing filament. Studies show that the mechanical and thermal properties of recycled PLA are similar to virgin PLA after one recycling cycle, but deteriorate with additional cycles. The document also examines combining recycled PLA with virgin PLA to improve properties. Adding 25% virgin PLA to recycled PLA maintained tensile strength after double recycling. Coating recycled PLA pellets with polydopamine also increased tensile strength of printed components, providing a potential method to enhance recycled plastics.