Aligned liquid crystal networks were synthesized by photopolymerization of liquid crystal monomers in the presence of magnetic fields. Grazing incident wide-angle X-ray scattering was used to characterize the degree of molecular alignment of mesogen chains and time-domain thermoreflectance was used to measure thermal conductivity. Liquid crystal networks with mesogenic units aligned perpendicular and parallel to the substrate exhibit thermal conductivity of 0.34 W m-1 K-1 and 0.22 W m-1 K-1, respectively. The thermal conductivity and orientational order of liquid crystal networks vary as a function of temperature. The thermal conductivity of liquid crystal networks can be manipulated by a magnetic field at above the glass transition temperature (65 °C) where the reduced viscosity enables molecular reorientation on the time scale of 10 min.
Abstract Amphiphilic in nature, lipids spontaneously self‐assemble into a range of nanostructures in the presence of water. Among lipid self‐assembled structures, liposomes and supported lipid bilayers have long held scientific interest for their main applications in drug delivery and plasma membrane models, respectively. In contrast, lipid‐based multilayered membranes on solid supports only recently begin drawing scientists' attention. Current studies show that the stacking of multiple bilayers on a solid support yields cooperative structural and dynamic behavior that enables new functionalities. Lipid films provide compartmentalization, templating, and enhanced release of molecules of interest. Importantly, supported lipid phases exhibit long‐range periodic nanoscale order and orientation that is tunable in response to a changing environment. Herein, the current understanding of lipid‐based film research is summarized focusing on how unique structural characteristics enable the emergence of new applications including label‐free biosensors, macroscale drug delivery, and substrate‐mediated gene delivery. The authors' recent contributions focusing on the structural characterization of lipid‐based films using small‐angle X‐ray scattering and atomic force microscopy are highlighted. In addition, new photothermally induced resonance and solid‐state nuclear magnetic resonance data are described, providing insights into drug partition in lipid‐based films as well as structure and dynamics at the molecular scale.
Extracellular vesicles have received a great interest as safe biocarriers in biomedical engineering. There is a need to develop more efficient delivery strategies to improve localized therapeutic efficacy and minimize off-target adverse effects. Here, exosome mimetics (EMs) are reported for bone targeting involving the introduction of hydroxyapatite-binding moieties through bioorthogonal functionalization. Bone-binding ability of the engineered EMs is verified with hydroxyapatite-coated scaffolds and an ex vivo bone-binding assay. The EM-bound construct provided a biocompatible substrate for cell adhesion, proliferation, and osteogenic differentiation. Particularly, the incorporation of Smoothened agonist (SAG) into EMs greatly increased the osteogenic capacity through the activation of hedgehog signaling. Furthermore, the scaffold integrated with EM/SAG significantly improved in vivo reossification. Lastly, biodistribution studies confirmed the accumulation of systemically administered EMs in bone tissue. This facile engineering strategy could be a versatile tool to promote bone regeneration, offering a promising nanomedicine approach to the sophisticated treatment of bone diseases.
Materials that can be switched between low and high thermal conductivity states would advance the control and conversion of thermal energy. Employing in situ time-domain thermoreflectance (TDTR) and in situ synchrotron X-ray scattering, we report a reversible, light-responsive azobenzene polymer that switches between high (0.35 W m-1 K-1) and low thermal conductivity (0.10 W m-1 K-1) states. This threefold change in the thermal conductivity is achieved by modulation of chain alignment resulted from the conformational transition between planar (trans) and nonplanar (cis) azobenzene groups under UV and green light illumination. This conformational transition leads to changes in the π-π stacking geometry and drives the crystal-to-liquid transition, which is fully reversible and occurs on a time scale of tens of seconds at room temperature. This result demonstrates an effective control of the thermophysical properties of polymers by modulating interchain π-π networks by light.
Although a demineralized bone matrix (DBM) is often used as an alternative to an autologous bone graft, its clinical application is still hampered by easy dispersion of DBM particles and insufficient osteoinductivity in the defect site. Herein, we designed a self-healing hydrogel for DBM that can rapidly restore its structural integrity after damage based on amino-rich black phosphorus (BP) nanosheets and aldehyde-functionalized hyaluronic acid (AHA). Given the increased expression of bone morphogenetic protein (BMP) antagonists by DBM stimulation, the osteogenic potency of DBM in the hydrogel carrier was further enhanced by abrogating the BMP antagonism. The BP/AHA hydrogel provided dynamic polymer-nanosheet networks that combine injectability, modability, and physical stability with high DBM loading, where the BP nanosheets served as osteogenic cross-linkers to promote biomineralization and deliver siRNA to suppress undesirable expression of BMP antagonist noggin by DBM. As a result, the BP/AHA hydrogel integrated with DBM and noggin-targeting siRNA synergistically promoted osteogenic differentiation of mesenchymal stem cells by enhancing BMP/Smad signaling. This work demonstrates a promising strategy to improve the efficacy of bone regeneration using bone graft.
The electro-optical performances of polymer dispersed liquid crystal (PDLC) were investigated in the presence of organically modified clays.With the addition and increasing amount of modified clay, driving voltage and memory effect, viz.transparent state of the film after the electricity is off simultaneously increased due most likely to the increased viscosity.Among the two types of modifier, 4-(4-aminophenyl) benzonitrile having greater chemical affinity with LC than hexylamine, gave finer dispersion of clay in liquid crystal, greater viscosity, larger driving voltage and response time, and greater memory effect.
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