Controlling the Interfaces of Supramolecular Hydrogels for Tissue Culture Application

The research work undertaken focused on the preparation and characterization of novel low molecular weight (LMW) hydrogels as functional biomaterials for tissue culture applications. To achieve this objective, new LMW compounds (as potential hydrogelators) were synthesized bearing a galactosamine or glucosamine moiety. The incorporation of carbohydrates was anticipated to confer molecular recognition of certain biomolecules upon the formed supramolecular gels and therefore act as potential anchor sites for cell-binding. The synthesis was based on short synthetic routes and low-cost starting materials were used as supplied. The target compounds were not confined only to those containing carbohydrates. A cinnamoyl-protected diphenylalanine hydrogelator was prepared and the properties of its corresponding hydrogel were investigated. Understanding the self-assembly mechanisms of supramolecular hydrogels is fundamental for the preparation and application of these novel materials. Therefore, a variety of techniques were employed for assessing and characterisation of gelation and to determine the configurational alignment of the formed fibres within the three-dimensional network of the gels. Specifically, the preparation and handling of hydrogels were optimized leading to robust gelation protocols. TEM and SEM microscopy revealed the size, shape and perplexing patterns of the fibres. XRD measurements verified polymorphism whereas rheology studies confirmed the viscoelastic properties of the gels. Non-covalent intermolecular interactions are the driving forces of the molecular packing, leading to higher order architectures. The combined spectroscopic analysis of the prepared hydrogels (by NMR, IR, UV-vis, CD) was advantageous to explore the nature of such interactions and allow the identification of key functional groups which actively participated in the self-assembly process. As a result of the CD work undertaken, utilisation of a synchrotron facility led to the establishment of a protocol for the evaluation of LMW hydrogels by SRCD spectroscopy, which was recently published. Finally, a preliminary biocompatibility study was undertaken to assess the toxicity of the hydrogels upon brain cancer cells. This project therefore required an interdisciplinary approach which involved the synthesis of a number of LMW compounds where some were found to be hydrogelators. This led to the preparation of their corresponding hydrogels and the study of their microscopic/macroscopic properties for the development of novel biocompatible materials suitable for tissue culture applications

Synthesis of inositol phosphate-based competitive antagonists of inositol 1,4,5-trisphosphate receptors.

Inositol 1,4,5-trisphosphate receptors (IP3Rs) are intracellular Ca(2+) channels that are widely expressed in animal cells, where they mediate the release of Ca(2+) from intracellular stores evoked by extracellular stimuli. A diverse array of synthetic agonists of IP3Rs has defined structure-activity relationships, but existing antagonists have severe limitations. We combined analyses of Ca(2+) release with equilibrium competition binding to IP3R to show that (1,3,4,6)IP4 is a full agonist of IP3R1 with lower affinity than (1,4,5)IP3. Systematic manipulation of this meso-compound via a versatile synthetic scheme provided a family of dimeric analogs of 2-O-butyryl-(1,3,4,6)IP4 and (1,3,4,5,6)IP5 that compete with (1,4,5)IP3 for binding to IP3R without evoking Ca(2+) release. These novel analogs are the first inositol phosphate-based competitive antagonists of IP3Rs with affinities comparable to that of the only commonly used competitive antagonist, heparin, the utility of which is limited by off-target effects.Supported by a Senior Investigator Award from the Wellcome Trust 101844 (to C.W.T.), Biotechnology and Biological Sciences Research Council UK and the German Academic Exchange Service (to V.K.). A.E.K. thanks the Research Committee of AUTh for financial support. C.W.T. and V.K. thank Dr S. B. Shears (N.I.E.H.S, U.S.A.) for his helpful advice.This is the final version of the article. It first appeared from the Royal Chemistry Society via http://dx.doi.org/10.1039/C5OB02623

Solvent-induced transient self-assembly of peptide gels: gelator-solvent reactions and material properties correlation

Herein, we introduce a new methodology for designing transient organogels that offers tunability of the mechanical properties simply by matching the precursor’s protective groups to that of the solvent. We developed solvent-induced transient materials in which the solvent chemically participates in a set of reactions and actively supports the assembly event. The activation of a single precursor by an acid (accelerator) yields the formation of two distinct gelators and induces gelation. The interconversion cycle is supplied by the secondary solvent (originating from the hydrolysis of the primary solvent by the accelerator), which then progressively solubilizes the gel network. We show that this gelation method offers a direct correlation between the mechanical and transient properties by modifying the chemical structure of the precursors and the presence of accelerator in the system. Such a method paves the way for designing self-abolishing and mechanically tunable materials for targeted purposes. The biocompatibility and versatility of amino acid-based gelators can offer a wide range of biomaterials for applications requiring a controllable and definite lifetime, such as drug delivery platforms exhibiting a burst release or self-abolishing cell culture substrate

Diversity at the nanoscale : laser-oxidation of single-layer graphene affects Fmoc-phenylalanine surface-mediated self-assembly

We report the effects of a laser-oxidized single layer graphene (SLG) surface on the self-assembly of amphiphilic gelator N-fluorenylmethoxycarbonyl-L-phenylalanine (Fmoc-Phe) towards an gel–SLG interface. Laser oxidation modulates the levels of hydrophobicity/hydrophilicity on the SLG surface. Atomic force, scanning electron, helium ion and scattering scanning nearfield optical microscopies (AFM, SEM, HIM, s-SNOM) were employed to assess the effects of surface properties on the secondary and tertiary organization of the formed Fmoc-Phe fibres at the SLG–gel interface. S-SNOM shows sheet-like secondary structures on both hydrophobic/hydrophilic areas of SLG and helical or disordered structures mainly on the hydrophilic oxidized surface. The gel network heterogeneity on pristine graphene was observed at the scale of single fibres by s-SNOM, demonstrating its power as a unique tool to study supramolecular assemblies and interfaces at nanoscale. Our findings underline the sensitivity of assembled structures to surface properties, while our characterization approach is a step forward in assessing surface–gel interfaces for the development of bionic devices.peerReviewe

Triggering a transient organo-gelation system in a chemically active solvent

A transient organo-gelation system with spatiotemporal dynamic properties is described. Here, the solvent actively controls a complex set of equilibria that underpin the dynamic assembly event. The observed metastability is due to the in situ formation of a secondary solvent, acting as an antagonist against the primary solvent of the organogel.peerReviewe

Tuning protein adsorption on graphene surfaces via laser-induced oxidation

An approach for controlled protein immobilization on laser-induced two-photon (2P) oxidation patterned graphene oxide (GO) surfaces is described. Selected proteins, horseradish peroxidase (HRP) and biotinylated bovine serum albumin (b-BSA) were successfully immobilized on oxidized graphene surfaces, via non-covalent interactions, by immersion of graphene-coated microchips in the protein solution. The effects of laser pulse energy, irradiation time, protein concentration and duration of incubation on the topography of immobilized proteins and consequent defects upon the lattice of graphene were systemically studied by atomic force microscopy (AFM) and Raman spectroscopy. AFM and fluorescence microscopy confirmed the selective aggregation of protein molecules towards the irradiated areas. In addition, the attachment of b-BSA was detected by a reaction with fluorescently labelled avidin-fluorescein isothiocyanate (Av-FITC). In contrast to chemically oxidized graphene, laser-induced oxidation introduces the capability for localization on oxidized areas and tunability of the levels of oxidation, resulting in controlled guidance of proteins by light over graphene surfaces and progressing towards graphene microchips suitable for biomedical applications.peerReviewe