Coaxial 4D Printing of Vein-Inspired Thermoresponsive Channel Hydrogel Actuators

Although significant progress has been made in coaxial printing of vascularized tissue models, this technique has not yet been used to fabricate stimulus-responsive scaffolds capable of shape change over time. Here, a new method of direct ink printing (DIP) is proposed with a coaxial nozzle, coaxial 4D printing, enabling the manufacturing of thermoresponsive constructs embedded with a network of interconnected channels. In this approach, a poly(N-isopropylacrylamide) (PNIPAAm)-based thermoink is coaxially extruded into either core/sheath microfibers or microtubes. PNIPAAm renders a hydrogel temperature-sensitive and endows it with a shape-morphing property both at the micro- and macroscale. Specifically, the lumen diameter of the microtubes can be controlled by temperature by 30%. The macrostructural soft actuators can undergo programmed and reversible temperature-dependent shape changes due to the structural anisotropy of the hydrogel. The permeability tests demonstrate that the hydrogel can possess enough strength to maintain the hollow channels without breaking. In vitro tests confirm the biocompatibility of the material with EA.hy926 cells, paving the avenue for new perfusable soft robots, or active implants. Finally, microalgae Chlamydomonas reinhardtii is combined with the hydrogels to fabricate materials having functions of both living microorganisms and stimuli-responsive polymers toward creating engineered living materials (ELMs) with a vein-like geometry. Herein, a temperature-sensitive hydrogel with a network of permeable channels is fabricated by coaxial 4D printing. The thermoresponsivity of the hydrogel allows for temperature-dependent shape changes at both micro- and macro-scales. The macrostructure undergoes reversible shape transformation when transferred from cold to hot water and vice versa. At the microscale, the lumen diameter of the channels is controlled by temperature.image