Unusual Two-Step Assembly of a Minimalistic Dipeptide-Based Functional Hypergelator

Self-assembled peptide hydrogels represent the realization of peptide nanotechnology into biomedical products. There is a continuous quest to identify the simplest building blocks and optimize their critical gelation concentration (CGC). Herein, a minimalistic, de novo dipeptide, Fmoc-Lys(Fmoc)-Asp, as an hydrogelator with the lowest CGC ever reported, almost fourfold lower as compared to that of a large hexadecapeptide previously described, is reported. The dipeptide self-assembles through an unusual and unprecedented two-step process as elucidated by solid-state NMR and molecular dynamics simulation. The hydrogel is cytocompatible and supports 2D/3D cell growth. Conductive composite gels composed of Fmoc-Lys(Fmoc)-Asp and a conductive polymer exhibit excellent DNA binding. Fmoc-Lys(Fmoc)-Asp exhibits the lowest CGC and highest mechanical properties when compared to a library of dipeptide analogues, thus validating the uniqueness of the molecular design which confers useful properties for various potential applications.     

Quasi‐One Dimensional in‐Plane Conductivity in Filamentary Films of PEDOT:PSS

The mechanism and magnitude of the in‐plane conductivity of poly(3,4‐ethy‐lenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) thin films is determined using temperature dependent conductivity measurements for various PEDOT:PSS weight ratios with and without a high boiling solvent (HBS). Without the HBS the in‐plane conductivity of PEDOT:PSS is lower and for all studied weight ratios well described by the relation $ \sigma = \sigma _0 {\rm exp}[- \left({{{{T_0}}\over{T}}} \right)^{0.5}] $ with T₀ a characteristic temperature. The exponent 0.5 indicates quasi‐one dimensional (quasi‐1D) variable range hopping (VRH). The conductivity prefactor σ₀ varies over three orders of magnitudes and follows a power law σ₀∝c^3.5_PEDOT with c_PEDOT the weight fraction of PEDOT in PEDOT:PSS. The field dependent conductivity is consistent with quasi‐1D VRH. Combined, these observations suggest that conductance takes place via a percolating network of quasi‐1D filaments. Using transmission electron microscopy (TEM) filamentary structures are observed in vitrified dispersions and dried films. For PEDOT:PSS films with HBS, the conductivity also exhibits quasi‐1D VRH behavior when the temperature is less than 200 K. The low characteristic temperature T₀ indicates that HBS‐treated films are close to the critical regime between a metal and an insulator. In this case, the conductivity prefactor scales linearly with c_PEDOT, indicating the conduction is no longer limited by a percolation of filaments. The lack of observable changes in TEM upon processing with the HBS suggests that the changes in conductivity are due to a smaller spread in the conductivities of individual filaments, or a higher probability for neighboring filaments to be connected rather than being caused by major morphological modification of the material.     

Phosphonate-anchored thin films on titanium and niobium oxide surfaces: Fabrication and characterization

Phosphonate-anchored thin films form on various metal oxide substrates. This paper compares structural details of these covalently anchored films on the oxidized surfaces of titanium, niobium and a Ti45Nb alloy. This is made possible by a sample configuration wherein the alkylphosphonates are coated onto a thin film of metal which is sputtered onto a double-side-polished silicon wafer and then oxidized. Samples are flat and reflective and are suitable for ellipsometry, wetting measurements, X-ray Photoelectron Spectroscopy, Atomic Force Microscopy, and Fourier Transform Infrared-Attenuated Total Reflectance Spectroscopy. Deposition from heated tetrahydrofuran produces ordered films with measurable differences among deposition protocols and among metal oxide substrates. These substrates enable identification of the mildest deposition procedures that still provide uniform, robust surface coatings.     

A Concept in Bactericidal Materials: The Entrapment of Chlorhexidine within Silver

A new concept in bactericidal agents is described: the entrapment of an organic biocidal agent within a bactericidal metal, which leads to synergism between the two components. Specifically this concept is demonstrated for the entrapment of chlorhexidine digluconate (CHD) within an aggregated silver matrix, a metal known for its own biocidal qualities, forming the CHD@silver composite. The bactericidal efficacy against E. coli is evaluated and compared with the separate components. While the bactericidal efficacy of the individual ingredients (CHD and metallic silver) is very low, CHD@silver exhibits a markedly enhanced efficacy. This enhanced bactericidal effect is partially attributed to the simultaneous release and presence of the active biocidal ingredients CHD and Ag⁺ in the solution. Detailed composite characterization is provided.     

Personalized Hydrogels for Engineering Diverse Fully Autologous Tissue Implants

Despite incremental improvements in the field of tissue engineering, no technology is currently available for producing completely autologous implants where both the cells and the scaffolding material are generated from the patient, and thus do not provoke an immune response that may lead to implant rejection. Here, a new approach is introduced to efficiently engineer any tissue type, which its differentiation cues are known, from one small tissue biopsy. Pieces of omental tissues are extracted from patients and, while the cells are reprogrammed to become induced pluripotent stem cells, the extracellular matrix is processed into an immunologically matching, thermoresponsive hydrogel. Efficient cell differentiation within a large 3D hydrogel is reported, and, as a proof of concept, the generation of functional cardiac, cortical, spinal cord, and adipogenic tissue implants is demonstrated. This versatile bioengineering approach may assist to regenerate any tissue and organ with a minimal risk for immune rejection.     

Surface modification of Ti45Nb alloy by immobilization of RGD peptide via self assembled monolayer

A new low modulus β Ti-Nb alloy with low elastic modulus and excellent corrosion resistance is currently under consideration as a surgical implant material. The usefulness of such materials can be dramatically enhanced if their surface structure and surface chemistry can be controlled. This control is achieved by attaching a self assembled monolayer (SAM) based on 11-chloroacetyl-1-undecylphosphonic acid, CAUDPA, to the surface and immobilization of a peptide to the monolayer. The SAM is characterized by Fourier Transform Infrared Spectroscopy (FTIR) and X-ray Photoelectron Spectroscopy (XPS) at two different takeoff angles. The CAUDPA molecules were covalently bonded on the substrate in a configuration in which the phosphonic group turns toward the Ti45Nb while the acetyl chloride end group tail turns to the topmost surface. In such configuration sequential in situ reaction is possible by exchange between the chloride and a biological molecule. Such biological molecule is the arginine-glycine-aspartic acid-cysteine, RGDC, small amino acid sequence present in many molecules of the extracellular matrix. Preliminary cell culture in-vitro result shows an improvement of the response of osteoblast cells to Ti45Nb after the peptide immobilization.