Large Biaxial Recovered Strains in Self‐Shrinking 3D Shape‐Memory Polymer Parts Programmed via Printing with Application to Improve Cell Seeding

Abstract

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...

Tuning the Topography of Dynamic 3D Scaffolds through Functional Protein Wrinkled Coatings

“…In terms of the effect of print temperature, an increase in nozzle temperature resulted in a decrease in the magnitude of shape change observed upon triggering (Figure 2B). This finding is consistent with previous studies demonstrating the effect of PvP in 3D architectures [19].…”

“…To develop a simple experimental method that can create tunable surface wrinkles on arbitrarily complex 3D structures, our strategy was to combine a recently developed 4D printing technique, known as programming via printing (PvP), with a simple dip-coating technique that applies a silk fibroin (SF) biopolymer thin film and thereby enables fabrication of complex structures that, when triggered to undergo shape recovery, form wrinkles upon all surfaces of the structure. The PvP 4D printing technique uses fused filament fabrication (FFF) to 3D-print a shape memory polymer (SMP) [ 19 ]. SMPs are a class of smart polymeric materials that can undergo a change from a fixed, temporary shape to a final, permanent shape upon exposure to an external stimulus (e.g., heat, light, pH variation) [ 20 ].…”

“…PvP draws (stretches) an SMP filament as it is deposited during FFF to program tensile strains in the printed SMP structure in a fiber-by-fiber fashion, ultimately enabling fabrication and strain programming simultaneously in a single 3D printing process [ 19 ]. This approach eliminates the traditional need for a separate programming step following fabrication, and the SMP substrate can immediately undergo shape transformation following printing once exposed to an external stimulus (e.g., heat) [ 19 ]. Thus, with PvP, we can enable fabrication of intricate, SMP scaffolds that can undergo heat-inducted contraction to revert to their permanent shape.…”

“…Strain programming in PvP is controlled via various printing parameters, with nozzle temperature serving as a key parameter [ 19 ]. To characterize the influence of nozzle temperature on strain recovery and, therefore, wrinkle formation of scaffolds fabricated via PvP, 3D scaffolds (n = 6 per nozzle temperature) were printed at three nozzle temperatures (200, 210, and 220 °C).…”

“…Cytocompatibility of the engineered silk wrinkled structures was evaluated using C3H/10T1/2 mouse embryonic fibroblasts (ATCC, Manassas, VA, USA), a cell line we have frequently used in the development and application of cytocompatible SMPs [ 19 , 33 , 34 , 35 ]. Prior to conducting the experiment, the following samples were prepared: unstrained SMP scaffolds not coated with silk; unstrained SF-SMP scaffolds; and strained SF-SMP scaffolds dip-coated in SF solution and post-treated in methanol (as previously described for the silk coating process).…”