Electrospun piezoelectric nanofibers from polyvinylidene fluoride (PVDF) have been widely used in many applications. In PVDF-based polymers, the molecular weight (Mw) plays an important role in determining both crystallization and polarization responses. In the past, polyvinylidene fluoride trifluoroethylene [P(VDF-TrFE)] electrospun nanofibers were produced strictly from high molecular weight polymers (Mw > 200 kDa). Here, we study the electrospun P(VDF-TrFE) nanofibers from comparatively lower Mw polymers (Mw ∼ 100 kDa). We demonstrated a highly electroactive phase in electrospun P(VDF-TrFE) nanofibers without post treatments. During electrospinning, shorter P(VDF-TrFE) polymer chains exhibited higher mobility, which facilitate the formation of all-trans ferroelectric crystals with high crystallinity. By optimizing the mean size of electrospun nanofiber through tailoring the solution concentration and other controlling parameters, P(VDF-TrFE) nanofibers achieved the crystallinity as high as 67% and all-trans conformation reached 79%. The results pave a way for improving the electroactive performance in ferroelectric polymer electrospun nanofibers.

The ability of shape memory polymeric materials to repair physical damage and restore original functionality is of great significance in self-healing technologies, offering a broad application. In this study, we present a novel approach: electrospun shape memory-assisted self-healing (SMASH) polymer blends, which build upon prior research utilizing latent crosslinkable polyurethane (x-PU). By homogeneously blending x-PU with linear polyurethane (l-PU) and electrospinning the solution, we produced a family of blends with varying compositions. These blends were characterized through thermal, mechanical, and microstructural analyses, and their self-healing capabilities were evaluated using a series of damage types. Among the compositions, the 80:20 (w/w x-PU:l-PU) blend demonstrated superior healing performance, achieving an average healing efficiency (eta) of 92.2% for puncture damage. The introduction of structural anisotropy during electrospinning further enhanced the healing efficiency, particularly for fibers oriented perpendicular to the damage direction. These findings underscore the importance of compositional tuning and structural optimization in enhancing SMASH performance. This work highlights a scalable and versatile platform for self-healing materials, with promising implications for extending the lifespan and functionality of polymeric systems in practical applications.

The decentralized production associated with material extrusion additive manufacture (MEX) has been proposed as an ideal path to increase the circularity of plastics through direct recycling. Although multiple studies have reported on the 3D printing of various recycled plastics, variability in recycled materials, in particular post-consumer waste, challenges the direct extension of these results into production through MEX. Here, we demonstrate filament fabrication and printing of post-consumer polypropylene (PP), where the PP is sourced from clear, cold drink cups from three large international food service and beverage retail chains to provide well defined plastic waste that is perfectly sorted for recycling. These sources for the recycled PP were selected due to their ready availability to enable the results to be directly applied for hobbyist printing, blow molded products to provide good mechanical performance, and the clarity of the PP which suggests formulation design to minimize the PP crystal size. Despite the similarities in the end use product and their physical appearance, the source for the PP impacted the mechanical properties and the visual appearance of the printed objects. These differences can be directly traced to the rheological properties and oxidative stability of the PP at conditions relevant with the print process. These results clearly illustrate differences in initial formulation design and branding details, even when the product is for the same application, impacts the performance of recycled plastics in AM. The high viscosity associated with the PP from blow molding leads to requirements for higher extrusion temperatures for printing. The combination of high temperature and shear during extrusion process of 3D printing degrades the recycled PP. For circularity with MEX with recycled PP, one needs to consider the evolution in the properties of the polymer. Rheological details of recycled plastics are critical to selection of processing conditions and performance of MEX parts. Reporting of rheological data of recycled plastics and after printing is critical to enable translation towards circular 3D printing of recycled plastics.

Triple-shape-memory polymers (triple-SMPs) are a class of polymers capable of fixing two temporary shapes and recovering sequentially from the first temporary shape to the second temporary shape and, last, to the permanent shape. To accomplish a sequential shape change, a triple-SMP must have two separate shape-fixing mechanisms triggerable by distinct stimuli. Despite the biomedical potential of triple-SMPs, a triple-SMP that with cells present can undergo two different shape changes via two distinct cytocompatible triggers has not previously been demonstrated. Here, we report the design and characterization of a cytocompatible triple-SMP material that responds separately to thermal and light triggers to undergo two distinct shape changes under cytocompatible conditions. Tandem triggering was achieved via a photothermally triggered component, comprising poly(ε-caprolactone) (PCL) fibers with graphene oxide (GO) particles physically attached, embedded in a thermally triggered component, comprising a tert-butyl acrylate-butyl acrylate (tBA-BA) matrix. The material was characterized in terms of thermal properties, surface morphology, shape-memory performance, and cytocompatibility during shape change. Collectively, the results demonstrate cytocompatible triple-shape behavior with a relatively larger thermal shape change (an average of 20.4 ± 4.2% strain recovered for all PCL-containing groups) followed by a smaller photothermal shape change (an average of 3.5 ± 0.8% strain recovered for all PCL-GO-containing groups; samples without GO showed no recovery) with greater than 95% cell viability on the triple-SMP materials, establishing the feasibility of triple-shape memory to be incorporated into biomedical devices and strategies.

Recent decades have seen substantial interest in the development and application of biocompatible shape memory polymers (SMPs), a class of "smart materials" that can respond to external stimuli. Although many studies have used SMP platforms triggered by thermal or photothermal events to study cell mechanobiology, SMPs triggered by cell activity have not yet been demonstrated. In a previous work, we developed an SMP that can respond directly to enzymatic activity. Here, our goal was to build on that work by demonstrating enzymatic triggering of an SMP in response to the presence of enzyme-secreting human cells. To achieve this phenomenon, poly(ε-caprolactone) (PCL) and Pellethane were dual electrospun to form a fiber mat, where PCL acted as a shape-fixing component that is labile to lipase, an enzyme secreted by multiple cell types including HepG2 (human hepatic cancer) cells, and Pellethane acted as a shape memory component that is enzymatically stable. Cell-responsive shape memory performance and cytocompatibility were quantitatively and qualitatively analyzed by thermal analysis (thermal gravimetric analysis and differential scanning calorimetry), surface morphology analysis (scanning electron microscopy), and by incubation with HepG2 cells in the presence or absence of heparin (an anticoagulant drug present in the human liver that increases the secretion of hepatic lipase). The results characterize the shape-memory functionality of the material and demonstrate successful cell-responsive shape recovery with greater than 90% cell viability. Collectively, the results provide the first demonstration of a cytocompatible SMP responding to a trigger that is cellular in origin.

Focal adhesion complexes function as the mediators of cell-extracellular matrix interactions to sense and transmit the extracellular signals. Previous studies have demonstrated that cardiomyocyte focal adhesions can be modulated by surface topographic features. However, the response of focal adhesions to dynamic surface topographic changes remains underexplored. To study this dynamic responsiveness of focal adhesions, we utilized a shape memory polymer-based substrate that can produce a flat-to-wrinkle surface transition triggered by an increase of temperature. Using this dynamic culture system, we analyzed three proteins (paxillin, vinculin and zyxin) from different layers of the focal adhesion complex in response to dynamic extracellular topographic change. Hence, we quantified the dynamic profile of cardiomyocyte focal adhesion in a time-dependent manner, which provides new understanding of dynamic cardiac mechanobiology.

Cardiomyocyte (CM) alignment with striated myofibril organization is developed during early cardiac organogenesis. Previous work has successfully achieved in vitro CM alignment using a variety of biomaterial scaffolds and substrates with static topographic features. However, the cellular processes that occur during the response of CMs to dynamic surface topographic changes, which may provide a model of in vivo developmental progress of CM alignment within embryonic myocardium, remains poorly understood. To gain insights into these cellular processes involved in the response of CMs to dynamic topographic changes, we developed a dynamic topographic substrate that employs a shape memory polymer coated with polyelectrolyte multilayers to produce a flat-to-wrinkle surface transition when triggered by a change in incubation temperature. Using this system, we investigated cellular morphological alignment and intracellular myofibril reorganization in response to the dynamic wrinkle formation. Hence, we identified the progressive cellular processes of human-induced pluripotent stem cell-CMs in a time-dependent manner, which could provide a foundation for a mechanistic model of cardiac myofibril reorganization in response to extracellular microenvironment changes.

Freeze-thaw poly(vinyl alcohol) hydrogels (PVAH) offer great potential for several biomedical applications due to their biomimetic mechanical properties and biocompatibility. Despite these advantages, the use of PVA-H for load bearing applications has been limited due to poor performance in boundary lubrication compared to natural tissue such as articular cartilage. Recently, zwitterionic polymer brushes have been shown to act as effective boundary lubricants on rigid substrates; however, to the best of our knowledge, the synergistic effects of zwitterionic brushes coupled with the biomimetic fluid load support exhibited by hydrogels have not been reported. We report here on our investigation involving the synthesis and characterization of two unique types of polymer brush functionalized PVA hydrogels. The zwitterionic polymers that were compared contained either [2-(methacryloyloxy)ethyl]dimethyl-3-sulfopropylammonium hydroxide, PMEDSAH, or 2-methacryloyloxyethylphosphorylcholine, PMPC, repeating units. Both hydrogels coated with zwitterionic polymers were found to be cytocompatible. We report further on micrometer-scale surface properties via water contact angle goniometry, surface roughness measurements, and scanning electron microscopy. Finally, the impact of brush functionalization on the mechanics of the tribologically enhanced gels is reported with comparison to natural articular cartilage within the context of Hertzian contact theory.

Dynamic covalent exchange (DCE) of anhydride moieties is examined in both model compounds and network polymers.

Despite decades of biomimetic materials development, the tribological properties of articular cartilage remain unrivalled. This manuscript presents the design and material properties of a polymer blend composed of poly (vinyl alcohol) (PVA) and a zwitterionic polysulfobetaine (PMEDSAH) prepared into hydrogel form using a cyclic freeze-thaw method. The PVA hydrogel matrix provides mechanical strength while the zwitterionic polymer, PMEDSAH, is intended to act as a boundary lubricant. The formation of PVA-PMEDAH hydrogel blends was found to result in unique biomimetic system where the boundary lubricant elutes from the bulk material to the surface in response to applied pressure. This behavior is attributed to the high-water content of the PVA hydrogel matrix and the solubility of PMEDSAH in aqueous solution. In addition to characterizing the effects of boundary lubricant molecular weight on the diffusive properties of the hydrogel blend, we report the coefficient of friction, μ, versus sliding speed for the hydrogel/glass interface. Consistent with our prior findings, PMEDSAH was found to engender lubricious behavior and the dependence of μ on sliding velocity indicated a repulsive interaction with glass rather than an attractive one. This result agrees with the hydration lubrication hypothesis. Contact mechanics analyzed within the context of Hertzian biphasic theory were also investigated, revealing that the introduction of PMEDSAH enhances the hydrogel's ability to provide interstitial fluid load support.

Cytocompatible shape memory polymers activated by thermal or photothermal triggers have been developed and established as powerful "smart material" platforms for both basic and translational research. Shape memory polymers (SMPs) that could be triggered directly by biological activity have not, in contrast, been reported. The goal of this study was to develop an SMP that responds directly to enzymatic activity and can do so under isothermal cell culture conditions. To achieve this goal, we designed an SMP with a shape fixing component, poly(ε-caprolactone) (PCL), that is vulnerable to enzymatic degradation and a shape memory component, Pellethane, that is enzymatically stable - as the shape fixing component undergoes enzymatically-catalyzed degradation, the SMP returns to its original, programmed shape. We quantitatively and qualitatively analyzed material properties, shape memory performance, and cytocompatibility of the enzymatically-catalyzed shape memory response. The results demonstrate enzymatic recovery, as contraction of tensile specimens, using bulk enzymatic degradation experiments and show that shape recovery is achieved by degradation of the PCL shape-fixing phase. The results further showed that both the materials and the process of enzymatic shape recovery are cytocompatible. Thus, the SMP design reported here represents both an enzyme responsive material capable of applying a programmed shape change or direct mechanical force and an SMP that could respond directly to biological activity. STATEMENT OF SIGNIFICANCE: Cytocompatible shape memory polymers activated by thermal or photothermal triggers have become powerful "smart material" platforms for basic and translational research. Shape memory polymers that could be triggered directly by biological activity have not, in contrast, been reported. Here we report an enzymatically triggered shape memory polymer that changes its shape isothermally in response to enzymatic activity. We successfully demonstrate enzymatic recovery using bulk enzymatic degradation experiments and show that shape recovery is achieved by degradation of the shape-fixing phase. We further show that both the materials and the process of enzymatic shape recovery are cytocompatible. This new shape memory polymer design can be anticipated to enable new applications in basic and applied materials science as a stimulus responsive material.

We investigate wrinkling patterns in a tri-layer torus consisting of an expanding thin outer layer, an intermediate soft layer and an inner core with a tunable shear modulus, inspired by pattern formation in developmental biology, such as follicle pattern formation during the development of chicken embryos. We show from large-scale finite element simulations that hexagonal wrinkling patterns form for stiff cores whereas stripe wrinkling patterns develop for soft cores. Hexagons and stripes co-exist to form hybrid patterns for cores with intermediate stiffness. The governing mechanism for the pattern transition is that the stiffness of the inner core controls the degree to which the major radius of the torus expands - this has a greater effect on deformation in the long direction as compared to the short direction of the torus. This anisotropic deformation alters stress states in the outer layer which change from biaxial (preferred hexagons) to uniaxial (preferred stripes) compression as the core stiffness is reduced. As the outer layer continues to expand, stripe and hexagon patterns will evolve into zigzags and segmented labyrinths, respectively. Stripe wrinkles are observed to initiate at the inner surface of the torus while hexagon wrinkles start from the outer surface as a result of curvature-dependent stresses in the torus. We further discuss the effects of elasticities and geometries of the torus on the wrinkling patterns.

Seeking a latent-crosslinkable, mechanically flexible, fully thermoplastic shape memory polymer, we have developed a simple but effective macromolecular design that includes pendent crosslinking sites via the chain extender of a polyurethane architecture bearing semicrystalline poly(ε-caprolactone) (PCL) soft segments. This new composition was used to prepare fibrous mats by electrospinning and films by solvent casting, each containing thermal initiators for chemical crosslinking. The one-step synthesis strategy proved successful, and the crosslinking sites within PCL segments resulted in two-way (reversible) shape memory: repeatable elongation (cooling) and contraction (heating) under constant tensile stress. Being fully characterized, the crosslinked fiber mats revealed promising one-way and two-way (reversible) shape memory phenomena, with lower storage moduli though, compared to uncrosslinked films. We observed for both fibrous mats and films that increasing the applied tensile stress led to greater crystallization-induced elongation upon cooling as well as smaller strain hysteresis, particularly for covalently crosslinked samples. Relevant to medical applications, the materials were observed to feature unique, two-stage enzymatic degradation that was sensitive to differences in crystallinity and microstructure among samples.

We report the design and characterization of a multiphase quadruple shape memory composite capable of switching between 4 programmed shapes, three temporary and one permanent. Our approach combined two previously reported fabrication methods by embedding an electrospun mat of PCL in a miscible blend of epoxy monomers and PMMA as a composite matrix. As epoxy polymerization occurred the matrix underwent phase separation between the epoxy and PMMA materials. This created a multiphase composite with PCL fibers and a two-phase matrix composed of phase-separated epoxy and PMMA. The resulting composite demonstrated three separate thermal transitions and amenability to mechanical programming of three separate temporary shapes in addition to one final, equilibrium shape. In addition, quadruple surface shape memory abilities are successfully demonstrated. The versatility of this approach offers a large degree of design flexibility for multi-shape memory materials.

There exists a need for reversible actuation involving two-way shape memory polymers that can respond to changes in ambient temperature in the 20 degrees C-40 degrees C range, especially for soft actuators in applications requiring near-room-temperature environmental responsiveness. Herein, we report on the fabrication and analysis of a family of soft, semicrystalline copolymers based upon cis-cyclooctene and various melting point reducing comonomers via ring-opening metathesis polymerization (ROMP). Reversible actuation behavior of such copolymers was tuned by varying not only the species and the incorporation level of a second comonomer but also the concentration of an incorporated thermal initiator for crosslinking. Results revealed that actuation was tuned to occur best and near room temperature for a copolymer consisted of 97 mol% cis-cyclooctene and 3 mol% 1,5-cyclooctadiene and 0.50 wt% dicumyl peroxide initiator. Also, all crosslinked copolymers feature actuation magnitude greater than 50% and recovery magnitude greater than 94% at a single stress of 0.8 MPa, while thermal strain hysteresis was 17.5 degrees C in breadth, on average.

Triggering shape-memory functionality under clinical hyperthermia temperatures could enable the control and actuation of shape-memory systems in clinical practice. For this purpose, we developed light-inducible shape-memory microparticles composed of a poly(d,l-lactic acid) (PDLLA) matrix encapsulating gold nanoparticles (Au@PDLLA hybrid microparticles). This shape-memory polymeric system for the first time demonstrates the capability of maintaining an anisotropic shape at body temperature with triggered shape-memory effect back to a spherical shape at a narrow temperature range above body temperature with a proper shape recovery speed (37 < T < 45 °C). We applied a modified film-stretching processing method with carefully controlled stretching temperature to enable shape memory and anisotropy in these micron-sized particles. Accordingly, we achieved purely entanglement-based shape-memory response without chemical cross-links in the miniaturized shape-memory system. Furthermore, these shape-memory microparticles exhibited light-induced spatiotemporal control of their shape recovery using a laser to trigger the photothermal heating of doped gold nanoparticles. This shape-memory system is composed of biocompatible components and exhibits spatiotemporal controllability of its properties, demonstrating a potential for various biomedical applications, such as tuning macrophage phagocytosis as demonstrated in this study.

Shape-memory elastomers based on a commercial rubber cross-linked by both ionic and covalent bonds have been developed. The elastomeric matrix was a carboxylated nitrile rubber (XNBR) vulcanized with magnesium oxide (MgO) providing ionic interactions that form hierarchical structures. The so-named ionic transition is used as the unique thermal transition responsible for the shape-memory effect (SME) in these elastomers. These ionic interactions fix the temporary shape due to their behavior as dynamic cross-links with temperature changes. Covalent cross-links were incorporated with the addition of different proportions of dicumyl peroxide (DCP) to the ionic elastomer to establish and recover the permanent shape. In this article, the SME was modulated by modifying the degree of covalent cross-linking, while keeping the ionic contribution constant. In addition, different programming parameters, such as deformation temperature, heating/cooling rate, loading/unloading rate and percentage of tensile strain, were evaluated for their effects on shape-memory behavior.