9 research outputs found

    Microfabrication of Custom Collagen Structures Capable of Guiding Cell Morphology and Alignment

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    The patterning of biological components into structural analogues of native tissues to simulate an environment for directing cell growth is one important strategy in biomaterials fabrication. It is widely accepted that chemical, mechanical, and topological cues from the extracellular matrix (ECM) provide important signals for guiding cells to exhibit characteristic polarity, orientation, and morphology. To fully understand the delicate relationship between cell behavior and ECM features, biomaterials fabrication requires improved techniques for tailoring nano/microstructured patterns from relevant biological building blocks rather than using nonbiological materials. Here we reveal a unique approach for the nano/microfabrication of custom patterned biomaterials using collagen as the sole building material. With this new fabrication technique, we further revealed that custom collagen patterns could direct the orientation and morphology of fibroblast growth as a function of vertex density and pattern spacing. Our findings suggest that this technique may be readily adopted for the free form fabrication of custom cell scaffolds purely from natural biological molecules including collagen, among other relevant ECM components

    Controlling and Assessing the Surface Display of Cell-Binding Domains on Magnetite Conjugated Fluorescent Liposomes

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    Biological systems provide us with a diverse source of peptide-based ligands for cellular adhesion. Controlling and assessing the ligand surface density as well as tailoring the surface chemistry to have specific cellular adhesion properties are important in biomaterials design. In the following work, we provide a means for displaying peptide-based ligands on magnetic liposomes in which the surface density and chemistry may be controlled. Simultaneously, the conjugated vesicles provide a fluorescent signal for examining steric hindrance among surface ligands. In addition, the inherent magnetic and fluorescence features of this system revealed potential for magnet-based cell isolation and fluorescent labeling of adhered cells, respectively. Adhered cells were found to remain viable and proliferative, thereby allowing them to be used for subsequent evaluation. In a specific demonstration, we control the density of fibronectin-mimetic ligands on the polydiacetylene liposome surfaces. We find that steric limitation occurring at over 20% surface density result in decreased cell adhesion, in accord with related techniques. The magnetic-liposome system offers the means for not only separating cells adhered to the biomaterial, but also providing the ability to control and assess the biomaterial surface. This may prove particularly useful for examining combinations of peptide-based ligands or for evaluating the molecular-level ligand accessibility and its effect on cell attachment to a biomaterial surface

    Controlled Supramolecular Assembly of Helical Silica Nanotube–Graphene Hybrids for Chiral Transcription and Separation

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    Chiral templating and enantioselective separations are demonstrated on graphene surfaces as directed by encapsulated silica nanotubes. Electrostatic assembly of helical silica nanotubes within graphene sheets results in a hybrid material with the electrochemical properties of graphene and the capability for chiral recognition. Control of the silica nanotube helicity within the graphene hybrid provides a means for directed chiral templating of guest molecules on the outer graphene surface as revealed in the chiral transcription of <i>N</i><sup>1</sup>,<i>N</i><sup>3</sup>,<i>N</i><sup>5</sup>-tri(4-pyridinyl)cyclohexane-1,3,5-tricarboxamide as well as polyallylamine into supramolecular templated assemblies. Changing the helicity of the internal nanotube also provides control over enantiomer selectivity as demonstrated by the chiral separation of racemic mixtures of phenylalanine, tryptophan, and alanine derivatives

    Reinforcement of a Sugar-Based Bolaamphiphile/Functionalized Graphene Oxide Composite Gel: Rheological and Electrochemical Properties

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    A sugar-based bolaamphiphile/graphene oxide composite hydrogel has been prepared using simple mixing. Unlike the corresponding sugar-based native gel, the composite gel exhibits a fibrillar structure with a 10–20 nm fiber diameter. The composite gel forms an interdigitated bilayer structure incorporating intermolecular hydrogen-bonding interactions. The composite gel formation did not change the beneficial electrical properties of graphene offering the potential for integration of this new material into electronic systems. Interestingly, the mechanical and electrochemical properties of the composite gel are both dramatically enhanced when compared to the native gel, thereby reflecting that the functionalized graphene oxide layers are efficiently intercalated within the composite gel structure

    Chiral Arrangement of Achiral Au Nanoparticles by Supramolecular Assembly of Helical Nanofiber Templates

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    Chiral materials composed of organized nanoparticle superstructures have promising applications to photonics and sensing. Reliable customization of the chiroptical properties of these materials remains an important goal; hence, we report a customizable scheme making use of modular gelator components for controlling the helicity and formation of nanofibers over long length scales resulting in hydrogel templates. Controlled growth of gold nanoparticles at spatially arranged locations along the nanofiber is achieved by UV reduction of Au­(I) ions on the supramolecular templates. The resulting materials were found to have significant interparticle interactions and well-defined helicity to provide high quality, chiroptically active materials. With this novel approach, the tailored assembly of nanoparticle superstructures with predictable chiroptical properties can be realized in high yield, which we expect to allow rapid advancement of chiral nanomaterials research

    Luminescent Calix[4]arene-Based Metallogel Formed at Different Solvent Composition

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    We have synthesized a calix[4]­arene derivative (<b>1</b>) containing terpyridine and showed that gelation occurred in the presence of Pt<sup>2+</sup> in DMSO/H<sub>2</sub>O of varying compositions. Gelation was presumably mediated by the Pt–Pt and π–π stacking interactions. The scanning electron microscopy image of the xerogel showed a spherical structure with diameter of 1.8–2.1 μm. Interestingly, the metallogel showed strong luminescence enhancement, which was dependent on the DMSO/H<sub>2</sub>O ratio of the solvent. We examined the effects of concentration, temperature, and time resolution on the luminescence emission of both the gel <b>1</b>-Pt<sup>2+</sup> and the sol <b>1</b>-Pt<sup>2+</sup>. The luminescence lifetimes of the metallogel were particularly long, on the order of several microseconds. The luminescence lifetimes were also strongly dependent on the solvent composition. We also determined the thermodynamic parameters for the self-assembly of the gel by the Birks kinetic scheme. Furthermore, the rheological properties of the metallogels in the presence of more than 4.0 equiv of Pt<sup>2+</sup> were independent of the concentration of Pt<sup>2+</sup> applied

    Determining Chiral Configuration of Diamines via Contact Angle Measurements on Enantioselective Alanine-Appended Benzene-Tricarboxamide Gelators

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    Spectroscopic techniques exist that may discern between enantiomers and assess chiral purity. A nonspectroscopic approach that may be directly observed could provide numerous benefits. Using chiral alanine-appended benzene-tricarboxamide gelators, we reveal a methanol gel system that is capable of providing visual discrimination between enantiomers of various diamines. Specifically, gelation is induced by supramolecular nanofiber assembly resulting from interaction between a chiral gelator and a diamine of opposing chirality (i.e., a heterochiral system). Upon further implementing the chiral gelator in electrospun fibers as solid state films, we revealed enantioselective surface wetting properties that allowed for determining chirality through contact angle measurements. While these two approaches of observable gelation and surface wetting offer nonspectroscopic approaches, we also find that the supramolecular nanofiber assembly was able to enhance the induced circular dichroism signal resulting from addition of chiral diamines, allowing precise quantification of their enantiomeric purity

    Ultraviolet Patterned Calixarene-Derived Supramolecular Gels and Films with Spatially Resolved Mechanical and Fluorescent Properties

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    Supramolecular assemblies have in the past been considered mechanically weak and in most cases unable to withstand their own weight. Calixarene-derived networks can, however, provide robust supramolecular gels. Incorporating a photoreactive stilbene moiety, we show that the aggregation state of the material can be tuned by heating and UV exposure in order to control the mechanical as well as the fluorescent properties. Regulating the extent of heating to control the proportion of H-aggregates and J-aggregates and further cross-linking of H-aggregates by control over UV exposure allows for adjustable photopatterning of the fluorescence as well as the material stiffness in the range from ∼100 to 450 kPa. We expect this straightforward supramolecular system will be suitable for advanced prototyping in applications where modulus and shape are important design criteria

    Self-Assembled Tb<sup>3+</sup> Complex Probe for Quantitative Analysis of ATP during Its Enzymatic Hydrolysis via Time-Resolved Luminescence in Vitro and in Vivo

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    To more accurately assess the pathways of biological systems, a probe is needed that may respond selectively to adenosine triphosphate (ATP) for both in vitro and in vivo detection modes. We have developed a luminescence probe that can provide real-time information on the extent of ATP, ADP, and AMP by virtue of the luminescence and luminescence lifetime observed from a supramolecular polymer based on a <i>C</i><sub>3</sub> symmetrical terpyridine complex with Tb<sup>3+</sup> (<b>S1-Tb</b>). The probe shows remarkable selective luminescence enhancement in the presence of ATP compared to other phosphate-displaying nucleotides including adenosine diphosphate (ADP), adenosine monophosphate (AMP), guanosine triphosphate (GTP), thymidine triphosphate (TTP), H<sub>2</sub>PO<sub>4</sub><sup>–</sup> (Pi), and pyrophosphate (PPi). In addition, the time-resolved luminescence lifetime and luminescence spectrum of <b>S1-Tb</b> could facilitate the quantitative measurement of the exact amount of ATP and similarly ADP and AMP within living cells. The time-resolved luminescence lifetime of <b>S1-Tb</b> could also be used to quantitatively monitor the amount of ATP, ADP, and AMP in vitro following the enzymatic hydrolysis of ATP. The long luminescence lifetime, which was observed into the millisecond range, makes this <b>S1-Tb</b>-based probe particularly attractive for monitoring biological ATP levels in vivo, because any short lifetime background fluorescence arising from the complex molecular environment may be easily eliminated
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