bench to bedside. As a class of smart functional materials, SMPs can "memorize" a permanent shape during fabrication, be programmed to hold a temporary shape, and then, upon application of a stimulus, [1][2][3] recover back to their permanent shape. Biomedical devices in which SMPs have been studied include self-tightening sutures, expanding synthetic bone grafts, and active cell culture substrates and scaffolds. [4][5][6][7][8][9][10][11][12] Traditionally, shape-memory programming of an SMP part, three-dimensional (3D) printed or otherwise, is an independent processing step that occurs following fabrication of the part. Such postfabrication programming requires controlled mechanically actuated deformation into the desired programmed temporary shape. [1,3] As a result, programming techniques currently in widespread use generally only produce simple, often uniaxial, strains in the part, which limits shape changes to rudimentary forms of expansion, shrinkage, folding, or twisting. [13][14][15] The complex and useful SMP part functions and geometries necessary for many prospective applications, including biomedical applications, will require correspondingly complex strain patterns within the part, such as biaxial, torsional, bending, or shear strains, strain gradients, or other spatially varying strains. These complex strain patterns are generally not feasible with current programming techniques, especially in the case of small or intricate part geometries. In fact, precise programming of complex strains remains beyond the current state of the art in shape-memory programming, and use of even relatively simple alternatives to uniaxial programming of 3D SMP parts, such as biaxial strain programming, has remained extremely limited due to the challenges involved in establishing the apparatuses necessary to perform the required mechanically actuated programming. For example, multiaxial programming of a 3D part requires a mechanism to grip the part and apply the desired distributed strains in multiple axes. As a result, to date only a few studies have successfully demonstrated multiaxial programming of 3D SMP parts, and these studies have been restricted exclusively to compressive programming, achieved using manual (literally finger and thumb) manipulation or specialized crimpers or clamps, [8,16] and so only expansile multiaxial recovery has been demonstrated. The lack of methods for Trapping of strain in layers deposited during extrusion-based (fused filament fabrication) 3D printing has previously been documented. If fiber-level strain trapping can be understood sufficiently and controlled, 3D shape-memory polymer parts could be simultaneously fabricated and programmed via printing (programming via printing; PvP), thereby achieving precisely controlled 3D-to-3D transformations of complex part geometries. Yet, because previous studies have only examined strain trapping in solid printed partssuch as layers or 3D objects with 100% infill-fundamental aspects of the PvP process and the potential for PvP to be applied to pr...
