Abstract: A system for manufacturing a gradient material structure comprises a proportioner feedblock section and a mixer feedblock section. The proportioner feedblock section has a first flow inlet for receiving a first polymer material in melted form, a second flow inlet for receiving a second polymer material in melted form, and one or more proportioner channels. Each mixer channel may 2024/159199 be configured to simultaneously receive from the corresponding proportioner channel the first polymer material at a first volume flow rate and the second polymer material at a second volume flow rate. Bic ratio between the first and second volume flow rates may be defined by a polymer transfer ratio for the respective mixer channel. The polymer transfer ratios may differ between two or more of the mixer channels. Each proportioner channel may be housed within a respective insert cassette removably mounted within the remainder of the proportioner feedblock section.