Mechanically programmed shape change in laminated elastomeric composites.

Soft, anisotropic materials, such as myocardium in the heart and the extracellular matrix surrounding cells, are commonly found in nature. This anisotropy leads to specialized responses and is imperative to material functionality, yet few soft materials exhibiting similar anisotropy have been developed. Our group introduced an anisotropic shape memory elastomeric composite (A-SMEC) composed of non-woven, aligned polymer fibers embedded in an elastomeric matrix. The composite exhibited shape memory (SM) behavior with significant anisotropy in room-temperature shape fixing. Here, we exploit this anisotropy by bonding together laminates with oblique anisotropy such that tensile deformation at room temperature - mechanical programming - results in coiling. This response is a breakthrough in mechanical programming, since non-affine shape change is achieved by simply stretching the layered A-SMECs at room temperature. We will show that pitch and curvature of curled geometries depend on fiber orientations and the degree of strain programmed into the material. To validate experimental results, a model was developed that captures the viscoplastic response of A-SMECs. Theoretical results correlated well with experimental data, supporting our conclusions and ensuring attainability of predictable curling geometries. We envision these smart, soft, shape changing materials will have aerospace and medical applications.

Dual-Spun Shape Memory Elastomeric Composites.

Thermally responsive shape memory polymers (SMPs) are typically relatively stiff due to the need to vitrify the polymer chains to fix a temporary shape. A need exists for elastomeric SMPs with mechanical properties that more closely match those of human tissue. In this communication, we present a novel approach to fabricate a fully thermoplastic elastomeric SMP. Two polymers are simultaneously electrospun, or dual-spun, forming a composite fiber mat with a controllable composition. The two polymers were chosen such that one assists in "shape fixing" and the other in "shape recovery". We envision that the versatility and simplicity of this fabrication approach will allow for large scale production of shape memory elastomeric composites (SMECs) for a wide range of applications.