Cyclo-(DfKRG) peptide grafting onto Ti-6Al-4V: physical characterization and interest towards human osteoprogenitor cells adhesion.

In the present paper, specific interest has been devoted to the design of new hybrid materials associating Ti-6Al-4V alloy and osteoprogenitor cells through the grafting of two RGD containing peptides displaying a different conformation (linear RGD and cyclo-DfKRG) onto titanium surface. Biomimetic modification was performed by means of a three-step reaction procedure: silanization with APTES, cross-linking with SMP and finally immobilization of peptides thanks to thiol bonding. The whole process was performed in anhydrous conditions to ensure homogeneous biomolecules layout as well as to guarantee a sufficient amount of biomolecules grafted onto surfaces. The efficiency of this new route for biomimetic modification of titanium surface was demonstrated by measuring the adhesion between 1 and 24 h of osteoprogenitor cells isolated from HBMSC. Benefits of the as-proposed method were related to the high concentration of peptides grafted onto the surface (around 20 pmol/mm(2)) as well as to the capacity of cyclo-DfKRG peptide to interact with integrin receptors. Moreover, High Resolution beta-imager (using [(35)S]-Cys) has exhibited the stability of peptides grafted onto the surface when treated in harsh conditions.

Design of new titanium alloys for orthopaedic applications.

Parallel to the biofunctionalisation of existing materials, innovation in biomaterials engineering has led to the specific design of titanium alloys for medical applications. Studies of the biological behaviour of metallic elements have shown that the composition and structure of the material should be carefully tailored to minimise adverse body reactions and to enhance implant longevity, respectively. Consequently, interest has focused on a new family of titanium alloys: Ti-6Mo-3Fe-5Ta, Ti-4Mo-2Fe-5Ta and Ti-6Mo-3Fe-5Zr-5Hf alloys. The non-toxicity of the specially designed titanium alloys compared with osteoblastic cells has been ascertained using MTT and RN tests. In addition, phase transformations upon thermal processing have been investigated, with comparison with a well-defined beta titanium alloy. Optimum thermal processing windows (above 550 degrees C) have been designed to generate a stable and nanostructured alpha phase from the isothermal omega phase that precipitates in a low temperature range (150-350 degrees C). The generation of such nanostructured microstructures should provide a promising opportunity to investigate tissue-biomaterial interactions at the scale of biomolecules such as proteins.

Development of "heparin-like" polymers using swift heavy ion and gamma radiation. I. Preparation and characterization of the materials.

The development of ideal antithrombogenic polymers, a major problem in biomaterials sciences, is a primary objective in the fields of cardiovascular prostheses, artificial hearts, and other devices. To decrease their thrombogenicity, which remains the major obstacle, we have developed polymeric materials endowed with a specific affinity for antithrombin III (ATIII) and thus able, like heparin, to catalyze the inhibition of thrombin by ATIII. Sulfonate and sulfonamide groups are introduced onto phenyl rings belonging to styrene residues, which are radiation grafted (using swift heavy ion and gamma radiation) onto poly(vinylidene difluoride) (PVDF) and also onto poly(vinylidene fluoride/hexafluoropropylene) [P(VDF-HFP)]. In contrast to gamma radiation, which leads to a homogeneous modification, the advantage of swift heavy ion grafting is that only small regions are modified; thus, the surface may present hydrophilic (corresponding to the modified areas) and hydrophobic microdomains (corresponding to the unmodified areas) of different sizes, depending on the absorbed dose and grafting yield. Surface topography and composition are characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Sulfur, sodium, fluorine, and carbon are determined by scanning electron microscopy combined with energy-dispersive X-ray analysis (SEM-EDXA). The amount of fluorine decreases as polystyrene (PS) is grafted, whatever the kind of radiation and polymer. When the polymers are functionalized, the amount of fluorine also decreases while sodium and sulfur appear. Functionalization seems to increase the roughness of the surface, and its area.

Development of RGD peptides grafted onto silica surfaces: XPS characterization and human endothelial cell interactions.

The attachment of human umbilical vein endothelial cells (HUVECs) on substrates that had been covalently grafted with the cell adhesion peptides Arg-Gly-Asp (RGD) was investigated. This approach was used to provide substrates that are adhesive to cells even in the absence of serum proteins and to cells that have had no prior treatment of the surface with proteins that promote cell adhesion. We wanted to improve control of cellular interactions with cell-adhesive materials by providing fixedly bound adhesion ligands. Silica was examined as a model surface. The peptides were grafted using three different steps: grafting of aminosilane molecules; reaction with a maleimide molecule; and immobilization of cell-binding peptides containing the RGD sequence. The RGD-grafted surface was characterized by X-ray photoelectron spectroscopy (XPS) and contact-angle measurements.

In vitro and in situ intercellular adhesion molecule-1 (ICAM-1) expression by endothelial cells lining a polyester fabric.

In order to improve long-term patency of vascular grafts, the promising concept of endothelial cell seeding is actually under investigation. Our laboratory tested a polyester coated with albumin and chitosan which permits a rapid colonization by human umbilical vein endothelial cells (HUVEC) and it seems relevant to test in vitro the expression of adhesive molecules expressed by cells with regard to the inflammatory process. We studied intercellular adhesion molecule-1 (ICAM-1) expression and focused our work on the determination of ICAM-1 sites expressed per adherent cell lining the biomaterial, thus in situ, in comparison to control HUVEC on plastic wells: the results obtained by binding experiments were correlated to flow cytometry analyses and showed that the polyester does not induce a proinflammatory state and that HUVEC covering the structure are able to respond to a stimulus.