No abstract

Cryogenic 3D printing, or freeze 3D printing, is an additive manufacturing process that prints an object at “low” temperature atmosphere. It uses a temperature lower than the melting point of the printing material (commonly a water‐based suspension or slurry) to solidify the layered part. Cryogenic 3D printing compasses several different processes including ice 3D printing, freeze from extrusion, freeze nano‐printing (FNP), etc. However, no systematic survey of these technologies is present. In the current review, various 3D printing technologies that use low temperature to solidify the layer are reviewed. The technical aspects such as path planning, heat transfer, and diffusion in multi‐material are investigated. The applications of cryogenic 3D printing are presented including the investment casting, ice sculpture, and microfluidic channel from original ice 3D printing, and functional porous materials from the emerging FNP and low‐temperature deposition. Overall, this article gives a summary of cryogenic 3D printing technologies, including a survey on its technical aspects and potential applications for future research and development.

The problems of step effects, supporting material waste, and conflict between flexibility and toughness for 3D printed intestinal fistula stents are not yet resolved. Herein, the fabrication of a support‐free segmental stent with two types of thermoplastic polyurethane (TPU) using a homemade multi‐axis and multi‐material conformal printer guided with advanced whole model path planning is demonstrated. One type of TPU segment is soft to increase elasticity, and the other is used to achieve toughness. Owing to advancements in stent design and printing, the obtained stents present three unprecedented properties compared to previous three‐axis printed stents: i) Overcoming step effects; ii) Presenting comparable axial flexibility to a stent made of a single soft TPU 87A material, thus increasing the feasibility of implantation; and iii) Showing equivalent radial toughness to a stent made of a single hard TPU 95A material. Hence, the stent can resist the intestinal contractive force and maintain intestinal continuity and patency. Through implanting such stents to the rabbit intestinal fistula models, therapeutic mechanisms of reducing fistula output and improving nutritional states and intestinal flora abundance are revealed. Overall, this study develops a creative and versatile method to improve the poor quality and mechanical properties of medical stents.