Continuous Manufacture of Homogeneous and Graded Rods by Low-Temperature Extrusion

Overview

Freeze casting, the directional solidification of solutions and slurries, is a straightforward technique for the manufacture of porous materials. However, it has reached its limitations for the manufacture of long and slender components with its current mold-based approach. A process is needed with which slender materials and structures longer than 50 mm and 1-4 mm diameter can be made for applications such as peripheral nerve repair or ureteral stents. A low-temperature extrusion system has been developed for this purpose. Slender rods were extruded from chitosan solutions to demonstrate the principle of this continuous processing approach for the preparation of rods. The microstructural features achieved are currently unobtainable by other methods. Using our method, two types of samples with uniform dimensions have been created, either having homogeneous properties, or having carefully-controlled layered and graded properties, both through-thickness and along the length. Here, we present a manufacturing process and the principles of structure formation, as well as the results of the systematic structural and mechanical characterization of the resulting homogeneous and graded rods.