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Spatial control of material properties is highly desirable in additive manufacturing of functional structures with complex geometries. Whereas most previous efforts focused on developing new printing or material systems, we propose a new voxel design strategy of constructing digital materials to provide the additively manufactured polymeric structures with spatially customized thermomechanical properties. In our approach, a matrix-inclusion composite layout is adopted in the linearly patterned voxels that perform as building blocks to construct bulk material. Through rational design of voxel size and inclusion content, the printed polymeric digital material displays a tunable storage modulus up to three orders of magnitude and glass transition temperature ranging from 0 °C to 60 °C. By taking advantage of the design freedom, we demonstrate a sequential folding structure with spatially tunable actuation speed, and multi-stable configurations that trap elastic energy in deterministic collapse sequences. Overall, our approach provides an effective and convenient way of spatially customizing material properties for additive manufacturing and offers instructive inspirations to the realm of digital fabrication.

Bioactive synthetic scaffolds with 3D porous structure are the most attractive materials among various guided bone regeneration membranes. However, its osteogenic potential is still insufficient. This study was aimed to develop a Calcium surface-anchored Collagen I-PLGA/PCL scaffolds (PP/COL I-pDA-Ca) with enhanced osteogenicity. PP/COL I-pDA-Ca was electrospun from a collagen I-blended PLGA/PCL matrix and then modified by the chelation of Ca-ions via mussel-inspired polydopamine coating. PLGA/PCL, PLGA/PCL-polydopamine, PLGA/PCL-pDA chelated by Ca-ions were used as controls. Osteogenic effects of the scaffolds were examined using MC3T3-E1 cell culture. PP/COL I-pDA-Ca maintained 3D porous architecture with interconnected pores formed by randomly-oriented filamentous fibers and MC3T3-E1 cells cultured on it for 12 h or 24 h were more stretched and spread than those on the controls. PP/COL I-pDA-Ca significantly upregulated α10, α11 and β1 integrin expression after 48 h culture. ALP activity, OCN, OSX, BMP2 and RUNX2 expression of MC3T3-E1 cells cultured on PP/COL I-pDA-Ca scaffolds for 7 and 14 days were substantially enhanced when compared to controls (p

Shape-shifting structures have gained growing interest recently and found wide applications in areas such as soft robotics, biomedical devices and self-folding origami, attributed to their ability to construct complicated shapes directly from simple structures. However, an efficient method to design and fabricate programmable 3D shape-shifting structures from 2D polymer films still lacks. In this work, we design programmable shape-shifting 3D structures via the release of internal gradient stress using the frontal photopolymerization (FPP) method. First, the relation between the non-uniformly distributed material and loading parameters, and the geometric and fabrication parameters are established theoretically. The finite element (FE) model is then developed based on the theoretically obtained material and loading parameters. Next, the elastic instability in the shape-shifting behaviors of a cured film is captured through an elastic energy minimization. Furthermore, by using grayscale light patterns, it is shown that we can selectively manipulate the geometric and fabrication parameters to improve the design freedom of various complex 3D structures.

Three-dimensional (3D) printing has offered considerable convenience in fabricating functional structures constructed with shape memory polymers (SMPs). Conventionally, to meet the specific requirements for given applications, the shape memory property of a SMP is regulated by tailoring its molecular structure from the perspective of polymer chemistry. By virtue of the recent advances in multi-material 3D printing technology, new opportunities have emerged to customize the shape memory property from the perspective of composite material design. In this work, we propose a novel layout design strategy to 3D print multi-material composites incorporating heat-responsive SMP and flexible elastomer. Under a given volume ratio of SMP and elastomer, distinct shape memory performances are obtained for different material layouts. The underlying mechanisms are theoretically investigated based on the mechanics of composite materials and finite element (FE) simulations are conducted to provide quantitative predictions for the experimental results. As a demonstration, composites of different material layouts are used as building blocks to fabricate bilayer laminates where the incompatibility of shape fixity are pre-embedded to trigger the programmed active bending.