Bioinspired Multi-Activities 4D Printing Objects: A New Approach Toward Complex Tissue Engineering.

4D printing is an innovative approach which might in a near future lead to the achievement of highly complex smart materials. The authors describe a new strategy for the achievement of 4D printed objects with multiple biological activities. These activities are generated through the entrapment, during 3D printing, of two distinct enzymes (alkaline phosphatase and thrombin). These two enzymes give then the ability to the 4D printed object to generate bioactivities useful for in vitro tissue engineering. Indeed, it is shown that the entrapped alkaline phosphatase enables the localized and pre-programmed calcification of some 3D object parts while the diffusion of thrombin from the object permits the formation of fibrin biofilm (including living cells) directly at the surface of 3D object. Both activities and enzyme behavior within the 4D printed hydrogel are characterized through enzymatic measurements, microscopy, magnetic resonance imaging (MRI), and cell seeding.