4D Fabrication of Two-Way Shape Memory Polymeric Composites by Electrospinning and Melt Electrowriting.

This work presents a new method for 4D fabrication of two-way shape memory materials that are capable of reversible shapeshifting right after manufacturing, upon application of proper heating and cooling cycles. The innovative solution presented here consists in the combination of highly stretched electrospun shape memory polymer (SMP) nanofibers with a melt electrowritten elastomer. More specifically, the stretched nanofibers are made of a biocompatible thermoplastic polyurethane (TPU) with crystallizable soft segments, undergoing melt-induced contraction and crystallization-induced elongation upon heating and cooling, respectively. Reversible actuation during crystallization becomes possible due to the elastic recovery of the elastomer component, obtained by melt electrowriting of a commercial TPU filament. Thanks to the design freedom offered by additive manufacturing, the elastomer structure also has the role of guiding the shape transformation. Electrospinning and melt electrowriting process parameters are set up so to obtain smart 4D objects capable of two-way shape memory effect (SME), and the possibility of reversible and repeatable actuation is demonstrated. The two components are then combined in different proportions with the aim of tailoring the two-way SME, taking into account the effect of design parameters such as the SMP content, the elastomer pattern, and the composite thickness.

4D Biofabrication of Mechanically Stable Tubular Constructs Using Shape Morphing Porous Bilayers for Vascularization Application.

This study reports the fabrication of highly porous electrospun self-folding bilayers, which fold into tubular structures with excellent mechanical stability, allowing them to be easily manipulated and handled. Two kinds of bilayers based on biocompatible and biodegradable soft (PCL, polycaprolactone) and hard (PHB, poly-hydroxybutyrate) thermoplastic polymers have been fabricated and compared. Multi-scroll structures with tunable diameter are obtained after the shape transformation of the bilayer in aqueous media, where PCL-based bilayer rolled longitudinally and PHB-based one rolled transversely with respect to the fiber direction. A combination of higher elastic modulus and transverse orientation of fibers with respect to rolling direction allowed precise temporal control of shape transformation of PHB-bilayer - stress produced by swollen methacrylated hyaluronic acid (HA-MA) do not relax with time and folding is not affected by the fact that bilayer is fixed in unfolded state in cell culture medium for more than 1 h. This property of PHB-bilayer allowed cell culturing without a negative effect on its shape transformation ability. Moreover, PHB-based tubular structure demonstrated superior mechanical stability compared to PCL-based ones and do not collapse during manipulations that happened to PCL-based one. Additionally, PHB/HA-MA bilayers showed superior biocompatibility, degradability, and long-term stability compared to PCL/HA-MA.

Smart Mechanically Tunable Surfaces with Shape Memory Behavior and Wetting-Programmable Topography.

This paper reports for the first time the fabrication and investigation of wetting properties of structured surfaces formed by lamellae with an exceptionally high aspect ratio of up to 57:1 and more. The lamellar surfaces were fabricated using a polymer with tunable mechanical properties and shape-memory behavior. It was found that wetting properties of such structured surfaces depend on temperature, and thermal treatment history-structured surfaces are wetted easier at elevated temperature or after cooling to room temperature when the polymer is soft because of the easier deformability of lamellae. The shape of lamellae deformed by droplets can be temporarily fixed at low temperature and remains fixed upon heating to room temperature. Heating above the transition temperature of the shape-memory polymer restores the original shape. The high aspect ratio allows tuning of geometry not only manually, as it is done in most works reported previously but can also be made by a liquid droplet and is controlled by temperature. This behavior opens new opportunities for the design of novel smart elements for microfluidic devices such as smart valves, whose state and behavior can be switched by thermal stimuli: valves that can or cannot be opened that are able to close or can be fixed in an open or closed states.

4D Biofabrication Using a Combination of 3D Printing and Melt-Electrowriting of Shape-Morphing Polymers.

We report the fabrication of scroll-like scaffolds with anisotropic topography using 4D printing based on a combination of 3D extrusion printing of methacrylated alginate, melt-electrowriting of polycaprolactone fibers, and shape-morphing of the fabricated object. A combination of 3D extrusion printing and melt-electrowriting allows programmed deposition of different materials and fabrication of structures with high resolution. Shape-morphing allows the transformation of a patterned surface of a printed structure in a pattern on inner surface of a folded object that is used to align cells. We demonstrate that the concentration of calcium ions, the environment media, and the geometrical shape of the scaffold influences shape-morphing that allows it to be efficiently programmed. Myoblasts cultured inside a scrolled bilayer scaffold demonstrate excellent viability and proliferation. Moreover, the patterned surface generated by PCL fibers allow a very high degree of orientation of cells, which cannot be achieved on the alginate layer without fibers.

Shape-Morphing Fibrous Hydrogel/Elastomer Bilayers Fabricated by a Combination of 3D Printing and Melt Electrowriting for Muscle Tissue Regeneration.

This paper reports an approach for the fabrication of shape-changing bilayered scaffolds, which allow the growth of aligned skeletal muscle cells, using a combination of 3D printing of hyaluronic acid hydrogel, melt electrowriting of thermoplastic polycaprolactone-polyurethane elastomer, and shape transformation. The combination of the selected materials and fabrication methods allows a number of important advantages such as biocompatibility, biodegradability, and suitable mechanical properties (elasticity and softness of the fibers) similar to those of important components of extracellular matrix (ECM), which allow proper cell alignment and shape transformation. Myoblasts demonstrate excellent viability on the surface of the shape-changing bilayer, where they occupy space between fibers and align along them, allowing efficient cell patterning inside folded structures. The bilayer scaffold is able to undergo a controlled shape transformation and form multilayer scroll-like structures with cells encapsulated inside. Overall, the importance of this approach is the fabrication of tubular constructs with a patterned interior that can support the proliferation and alignment of muscle cells for muscle tissue regeneration.

4D Biofabrication of fibrous artificial nerve graft for neuron regeneration.

In this paper, we describe the application of the 4D biofabrication approach for the fabrication of artificial nerve graft. Bilayer scaffolds consisting of uniaxially aligned polycaprolactone-poly(glycerol sebacate) (PCL-PGS) and randomly aligned methacrylated hyaluronic acid (HA-MA) fibers were fabricated using electrospinning and further used for the culture of PC-12 neuron cells. Tubular structures form instantly after immersion of fibrous bilayer in an aqueous buffer and the diameter of obtained tubes can be controlled by changing bilayer parameters such as the thickness of each layer, overall bilayer thickness, and medium counterion concentration. Designed scaffolds showed a self-folded scroll-like structure with high stability after four weeks of real-time degradation. The significance of this research is in the fabrication of tuneable tubular nerve guide conduits that can simplify the current existing clinical treatment of neural injuries.