RGD constructs with physical anchor groups as polymer co-electrospinnable cell adhesives

The tissue integration of synthetic polymers can be promoted by displaying RGD peptides at the biointerface with the objective of enhancing colonization of the material by endogenous cells. A firm but flexible attachment of the peptide to the polymer matrix, still allowing interaction with receptors, is therefore of interest. Here, the covalent coupling of flexible physical anchor groups, allowing for temporary immobilization on polymeric surfaces via hydrophobic or dipole–dipole interactions, to a RGD peptide was investigated. For this purpose, a stearate or an oligo(ethylene glycol) (OEG) was attached to GRGDS in 51–69% yield. The obtained RGD linker constructs were characterized by NMR, IR and MALDI-ToF mass spectrometry, revealing that the commercially available OEG and stearate linkers are in fact mixtures of similar compounds. The RGD linker constructs were co-electrospun with poly(p-dioxanone) (PPDO). After electrospinning, nitrogen could be detected on the surface of the PPDO fibers by X-ray photoelectron spectroscopy. The nitrogen content exceeded the calculated value for the homogeneous material mixture suggesting a pronounced presentation of the peptide on the fiber surface. Increasing amounts of RGD linker constructs in the electrospinning solution did not lead to a detection of an increased amount of peptide on the scaffold surface, suggesting inhomogeneous distribution of the peptide on the PPDO fiber surface. Human adipose-derived stem cells cultured on the patches showed similar viability as when cultured on PPDO containing pristine RGD. The fully characterized RGD linker constructs could serve as valuable tools for the further development of tissue-integrating polymeric scaffolds

Characterization of the paracrine effects of human skeletal myoblasts transplanted in infarcted myocardium

The discrepancy between the functional improvements yielded experimentally by skeletal myoblasts (SM) transplanted in infarcted myocardium and the paucity of their long-term engraftment has raised the hypothesis of cell-mediated paracrine mechanisms. Methods and results: We analyzed gene expression and growth factors released by undifferentiated human SM (CD56+), myotubes (SM cultured until confluence) and fibroblasts-like cells (CD56−). Gene expression revealed up-regulation of pro-angiogenic (PGF), antiapoptotics (BAG-1, BCL-2), heart development (TNNT2, TNNC1) and extracellular matrix remodelling (MMP-2, MMP-7) genes in SM. In line with the gene expression profile, the analysis of culture supernatants of SM by ELISA identified the release of growth factors involved in angiogenesis (VEGF, PIGF, angiogenin, angiopoietin, HGF and PDGF-BB) as well as proteases involved in matrix remodelling (MMP2, MMP9 and MMP10) and their inhibitors (TIMPs). Culture of smooth muscle cells (SMC), cardiomyocytes (HL-1) and human umbilical vein endothelial cells (HUVECs) with SM-released conditioned media demonstrated an increased proliferation of HUVEC, SMC and cardiomyocytes (pb0.05) and a decrease in apoptosis of cardiomyocytes (pb0.05). Analysis of nude rats transplanted with human SM demonstrated expression of human-specific MMP-2, TNNI3, CNN3, PGF, TNNT2, PAX7, TGF-β, and IGF-1 1 month after transplant. Conclusions: Our data support the paracrine hypothesis whereby myoblast-secreted factors may contribute to the beneficial effects of myogenic cell transplantation in infarcted myocardium. © 2008 European Society of Cardiology. Published by Elsevie

Fermi liquid theory of electronic topological transitions and screening anomalies in metals

General expressions for the contributions of the Van Hove singularity (VHS)in the electron density of states to the thermodynamic potential $\Omega are obtained in the framework of microscopic Fermi liquid theory. The renormalization of the singularities in$\Omega connected with the Lifshitz electronic topological transition (ETT) is found. Screening anomalies due to virtual transitions between VHS and the Fermi level are considered. It is shown that, in contrast with the one-particle picture of ETT, the singularities in $\Omega turns out to be two-sided for interacting electrons.Comment: 8 pages RevTeX, with minor corrections (Introduction and Conclusions are rewritten, new references are added), to appear in Physical review

The influence of electrospinning parameters on polydioxanone scaffold properties

Conduits currently used to reconstruct the right ventricular outflow tract (RVOT) have no growth potential and require reoperations, resulting in an increased level of morbidity and mortality. This work investigates the effect of electrospinning parameters on the mechanical properties and biocompatibility of bioresorbable tubular scaffolds, as part of a program to develop a tissue-engineered valved tube for RVOT replacement. Electrospinning was used to develop tubular scaffolds of polydioxanone, with the experimental parameters systematically varied. Three electrospinning parameters (volume of liquid, flow rate, and speed of mandrel rotation) were investigated, and their effects on the mechanical properties and cellular response of the scaffolds were analysed using scanning electron microscopy, X-ray diffraction, differential scanning calorimetry, gas chromatography, uniaxial tensile tests, cell viability and cytotoxicity assays. Mechanical properties were compared to those of the native RVOT reported in the literature. Increasing the mandrel rotation speed tended to increase fibre alignment slightly, and led to more profound rises in the stress at failure and Young's modulus. An increase in flow rate also increased the rigidity of the tubes. Cell viability and cytotoxicity assays showed all the tubes produced to have excellent biocompatibility. Through variation of the processing parameters, it is possible to tune mechanical properties of medical-grade polymer tubes over a wide range. By using a mandrel rotation speed of 50 rpm and a flow rate of 20 mL/h or higher we can prepare materials with Young's modulus, strain at failure, and tensile stress close to the native tissue. Electrospinning therefore offers great promise in the development of scaffolds to match the properties of the native RVOT, paving the way to a future bioresorbable device to replace the RVOT in children

Endogenous Wnt/β-Catenin Signaling Is Required for Cardiac Differentiation in Human Embryonic Stem Cells

Wnt/beta-catenin signaling is an important regulator of differentiation and morphogenesis that can also control stem cell fates. Our group has developed an efficient protocol to generate cardiomyocytes from human embryonic stem (ES) cells via induction with activin A and BMP4.We tested the hypothesis that Wnt/beta-catenin signals control both early mesoderm induction and later cardiac differentiation in this system. Addition of exogenous Wnt3a at the time of induction enhanced cardiac differentiation, while early inhibition of endogenous Wnt/beta-catenin signaling with Dkk1 inhibited cardiac differentiation, as indicated by quantitative RT-PCR analysis for beta-myosin heavy chain (beta-MHC), cardiac troponin T (cTnT), Nkx2.5, and flow cytometry analysis for sarcomeric myosin heavy chain (sMHC). Conversely, late antagonism of endogenously produced Wnts enhanced cardiogenesis, indicating a biphasic role for the pathway in human cardiac differentiation. Using quantitative RT-PCR, we show that canonical Wnt ligand expression is induced by activin A/BMP4 treatment, and the extent of early Wnt ligand expression can predict the subsequent efficiency of cardiogenesis. Measurement of Brachyury expression showed that addition of Wnt3a enhances mesoderm induction, whereas blockade of endogenously produced Wnts markedly inhibits mesoderm formation. Finally, we show that Wnt/beta-catenin signaling is required for Smad1 activation by BMP4.Our data indicate that induction of mesoderm and subsequent cardiac differentiation from human ES cells requires fine-tuned cross talk between activin A/BMP4 and Wnt/beta-catenin pathways. Controlling these pathways permits efficient generation of cardiomyocytes for basic studies or cardiac repair applications

Efficient Non-Viral Reprogramming of Myoblasts to Stemness with a Single Small Molecule to Generate Cardiac Progenitor Cells

The current protocols for generation of induced pluripotent stem (iPS) cells involve genome integrating viral vectors which may induce tumorgenesis. The aim of this study was to develop and optimize a non-viral method without genetic manipulation for reprogramming of skeletal myoblasts (SMs) using small molecules