Bilayered electrospun small-diameter vascular grafts with improved in vitro biological response

I. RIAL-HERMIDA; C. ALVAREZ-LORENZO; P.C. CARACCIOLO; A. CONCHEIRO; F. MONTINI BALLARIN; G.A. ABRAHAM

Otranto

Conferencia; 4 ° International Conference on Electrospinning, Electrospin 2016; 2016

Universita del Salento

The production of a small-diameter vascular graft (SDVG, < 6 mm) with an appropriate biomechanical response still presents a challenge. The development of an off-the-shelf conduit, without long in vitro culture periods, with proper biological and mechanical properties for coronary bypass surgery is the principal challenge of vascular tissue engineering current studies. The ideal SDVG must achieve numerous attributes: biocompatibility, no thrombogenicity, no toxicity, resistance to infection and neointimal hyperplasia, mechanical compliance, suturability, flexibility and elasticity without twisting collapse, capacity of locally therapeutic agents release, and potential tissue regeneration. In previous works, we developed a bilayered nanofibrous bioresorbable electrospun conduit from poly(L-lactic acid) (PLLA) and segmented poly(ester urethane) (PHD) blends, by mimicking the natural collagen-to-elastin ratio in the media and adventitia layers [1,2]. The biomimetic mechanical response was fully studied by uniaxial tension, suture, dynamical compliance, and burst pressure, displaying a behavior in the range of natural vessels. In vitro degradation studies suggested that degradation time would match the required for regeneration process.In this work, modification of inner surface SDVG was studied. Heparin and lyzosime immobilization was performed to introduce antithrombogenic properties and to reduce the risk of infection after implantation, respectively. Two strategies were explored. In the first one, PLLA carboxylic groups? density was increased through an alkaline treatment and then reaction with diaminoPEG (DAPEG) was performed. In the second one, PHD urethane groups were activated with sodium hypochlorite, and then reacted with allyl glycidyl ether. DAPEG modification was performed through the reaction of epoxy-capped oligomers with DAPEG amino terminal groups. Both strategies followed with heparin immobilization. Furthermore, lysozyme loading to obtain heparin-lysozyme electrostatic complex was also performed. Although the urethane route allowed higher heparin immobilization, both routes displayed good heparinization density. In vitro studies revealed a 90% reduction in platelet adhesion after heparin modification. Moreover, mesenchymal stem (MSC) cells proliferation was not reduced after modification, which indicates that immobilization did not induce cytotoxicity on MSC. Lysozyme activity was evaluated through m. lysodeikticus suspensions. Lysozyme remained active after immobilization and its activity showed a direct dependence with heparin content. Thus, the matrix obtained through urethane route displayed higher lysozyme activity. Finally, both strategies resulted adequate for heparin and lysozyme immobilization, being promising strategies for small diameter vascular graft modification.