Patrick T. Mather

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 (η) 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.

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.

Dynamic covalent exchange (DCE) of anhydride moieties is examined in both model compounds and network polymers. In addition, the polyanhydrides are shown to be capable of self-healing and recycling. Specifically, thermodynamic and kinetic analysis of the exchange process in symmetric model compounds methacrylic anhydride and 4-pentenoic anhydride, which produce an asymmetric anhydride upon exchange, was undertaken using ¹³C NMR spectroscopy. The equilibrium constant (K_eq) was determined to be approximately 2–3, and the activation energy (E_a) for the production of the asymmetric anhydride was 178 kJ mol⁻¹. The rate of exchange was shown to be increased catalytically in the presence of carboxylic acid. Poly(thioether anhydrides) were made using 4-pentenoic anhydride and mixtures of dithiol (1,6-hexanedithiol) and tetrathiol (pentaerythritol tetrakis(3-mercaptopropionate)) via radical-mediated thiol–ene polymerizations, and network relaxation rates studied using dynamic mechanical analysis. The activation energy and stress relaxation times for various polymer compositions were correlated to crosslink density and polymer composition. It was determined that cross-link density of the polymer system does not significantly impact E_a; however, relaxation time (τ) nearly quadrupled from the least cross-linked system to the most cross-linked system. The network polymers exhibited self-healing and facile recycling behavior, which we attributed to the anhydride DCE process that occurs readily in these materials at elevated temperatures. Using the composition with the fastest relaxation, we observed complete visible recovery of damage (notch) within a 4 hours duration at 90 °C. Recycling under compression molding for 15 minutes using 76 MPa hydrostatic pressure at 90 °C was successful. Both healed and recycled samples were successful in recovering or surpassing their original mechanical properties.