Hemostatic and Absorbent PolyHIPE-Kaolin Composites for 3D Printable Wound Dressing Materials.

A novel hemostatic and absorbent wound dressing material compatible with 3D printing is developed to address deficiencies in current wound dressing protocol. The design involves an open celled, microporous hydrogel foam via a high internal phase emulsion (HIPE) template with biocompatible components and tunable hemostatic character by kaolin loading, the viscosity and cure kinetics of which are tailored for 3D printing applications. The use of nontoxic mineral oil organic phase results in cytocompatability with human dermal fibroblasts. Kaolin distribution is shown by X-ray diffraction and elemental dispersive spectroscopy to be exfoliated and dispersed in the hydrogel dressing. In addition to demonstrating high fluid absorption and noncytotoxicity of relevant cell lines, the high internal phase emulsion polymers (polyHIPEs) also match the hemostatic performance of commercial wound dressing materials. Furthermore, the polyHIPEs display the requisite rheological properties for 3D printing that result in the fabrication of a prototype dressing with hierarchical porosity and a large number of controllable form factors.

Measuring RNA-Ligand Interactions with Microscale Thermophoresis.

In recent years, there has been dramatic growth in the study of RNA. RNA has gone from being known as an intermediate in the central dogma of molecular biology to a molecule with a large diversity of structure and function that is involved in all aspects of biology. As new functions are rapidly discovered, it has become clear that there is a need for RNA-targeting small molecule probes to investigate RNA biology and clarify the potential for therapeutics based on RNA-small molecule interactions. While a host of techniques exist to measure RNA-small molecule interactions, many of these have drawbacks that make them intractable for routine use and are often not broadly applicable. A newer technology called microscale thermophoresis (MST), which measures the directed migration of a molecule and/or molecule-ligand complex along a temperature gradient, can be used to measure binding affinities using very small amounts of sample. The high sensitivity of this technique enables measurement of affinity constants in the nanomolar and micromolar range. Here, we demonstrate how MST can be used to study a range of biologically relevant RNA interactions, including peptide-RNA interactions, RNA-small molecule interactions, and displacement of an RNA-bound peptide by a small molecule.

Solid-Phase Synthesis of Self-Assembling Multivalent π-Conjugated Peptides.

We present a completely solid-phase synthetic strategy to create three- and four-fold peptide-appended π-electron molecules, where the multivalent oligopeptide presentation is dictated by the symmetries of reactive handles placed on discotic π-conjugated cores. Carboxylic acid and anhydride groups were viable amidation and imidation partners, respectively, and oligomeric π-electron discotic cores were prepared through Pd-catalyzed cross-couplings. Due to intermolecular hydrogen bonding between the three or four peptide axes, these π-peptide hybrids self-assemble into robust one-dimensional nanostructures with high aspect ratios in aqueous solution. The preparation of these systems via solid-phase methods will be detailed along with their self-assembly properties, as revealed by steady-state spectroscopy and transmission electron microscopy and electrical characterization using field-effect transistor measurements.

Photoinduced Electron Transfer within Supramolecular Donor-Acceptor Peptide Nanostructures under Aqueous Conditions.

We report the synthesis, self-assembly, and electron transfer capabilities of peptide-based electron donor-acceptor molecules and supramolecular nanostructures. These modified peptides contain π-conjugated oligothiophene electron donor cores that are peripherally substituted with naphthalene diimide electron acceptors installed via imidation of site-specific lysine residues. These molecules self-assemble into one-dimensional nanostructures in aqueous media, as shown through steady-state absorption, photoluminescence, and circular dichroism spectra, as well as transmission electron microscopy. Excitation of the oligothiophene donor moieties results in electron transfer to the acceptor units, ultimately creating polar, charge-separated states that persist for over a nanosecond as observed with transient absorption spectroscopy. This study demonstrates how transient electric fields can be engineered into aqueous nanomaterials of biomedical relevance through external, temporally controlled photonic inputs.

Supramolecular polymorphism: tunable electronic interactions within π-conjugated peptide nanostructures dictated by primary amino acid sequence.

We present a systematic study of the photophysical properties of one-dimensional electronically delocalized nanostructures assembled from π-conjugated subunits embedded within oligopeptide backbones. The nature of the excited states within these nanostructures is studied as a function of primary amino acid sequence utilizing steady-state and time-resolved spectroscopies, and their atomistic structure is probed by molecular simulation. Variations introduced into the amino acid side chains at specific residue locations along the molecular peptide backbone lead to pronounced changes in the observed photophysical behavior of the fibrillar structures (spanning H-like excitonic coupling and disordered excimeric coupling) that arise from subtle changes in the π-stacking within them. These results indicate that residue modification-in terms of relative size, solvation properties, and with respect to the distance from the central π-electron core-enables the ability to tune chromophore packing and the resulting photophysics of supramolecular assemblies of π-conjugated bioelectronic materials in a rational and systematic manner.

Peptide-Based Supramolecular Semiconductor Nanomaterials via Pd-Catalyzed Solid-Phase "Dimerizations".

We report a streamlined method for the synthesis of peptides embedded with complex and easily variable π-conjugated oligomeric subunits from commercially available precursors. These modified peptides self-assemble under aqueous conditions to form one-dimensional nanomaterials containing networks of π-stacked conduits, despite the inclusion of π-conjugated oligomers with quadrupoles extended over larger areas. The procedure has circumvented solubility and other synthetic issues to allow for the facile formation of a diverse library of bioelectronic nanomaterials, including a complex sexithiophene-containing peptide whose nanostructures display gate-induced conductivity within field effect transistors.