Antithrombotic and hemocompatible properties of nanostructured coatings assembled from block copolymers.

We describe the antithrombotic properties of nanopatterned coatings created by self-assembly of poly(styrene-block-2-vinylpyridine) (PS-b-P2VP) with different molecular weights. By changing the assembly conditions, we obtained nanopatterns that differ by their morphology (size and shape of the nanopattern) and chemistry. The surface exposition of P2VP block allowed quaternization, i.e. introduction of positive surface charge and following electrostatic deposition of heparin. Proteins (albumin and fibrinogen) adsorption, platelet adhesion and activation, cytocompatibility, and reendothelization capacity of the coatings were assessed and discussed in a function of the nanopattern morphology and chemistry. We found that quaternization results in excellent antithrombotic and hemocompatible properties comparable to heparinization by hampering the fibrinogen adhesion and platelet activation. In the case of quaternization, this effect depends on the size of the polymer blocks, while all heparinized patterns had similar performance showing that heparin surface coverage of 40 % is enough to improve substantially the hemocompatibility.

Bactericidal nanopatterns generated by block copolymer self-assembly.

We describe the bactericidal capacity of nanopatterned surfaces created by self-assembly of block copolymers. Distinct nanotopographies were generated by spin-coating with polystyrene-block-poly(2-vinylpyridine) (PS-b-P2VP) followed by solvent vapor annealing. We demonstrate that the bactericidal efficiency of the developed coatings depends on the morphology and the chemistry of the surface: cylindrical nanotopographies presenting both blocks at the surface have stronger bactericidal effect on Escherichia coli than micellar patterns with only PS exposed at the surface. The identified mechanism of bacterial death is a mechanical stress exerted by the nanostructures on the cell-wall. Moreover, the developed nanopatterns are not cytotoxic, which makes them an excellent option for coating of implantable materials and devices. The proposed approach represents an efficient tool in the fight against bacteria, which acts via compromising the bacterial wall integrity. STATEMENT OF SIGNIFICANCE: Bacterial infections represent an important risk during biomaterial implantation in surgeries due to the increase of antibiotic resistance. Bactericidal surfaces are a promising solution to avoid the use of antibiotics, but most of those systems do not allow mammalian cell survival. Nanopatterned silicon surfaces have demonstrated to be simultaneously bactericidal and allow mammalian cell culture but are made by physical methods (e.g. plasma etching) applicable to few materials and small surfaces. In this article we show that block copolymer self-assembly can be used to develop surfaces that kill bacteria (E. coli) but do not harm mammalian cells. Block copolymer self-assembly has the advantage of being applicable to many different types of substrates and large surface areas.

Extracellular matrix-inspired assembly of glycosaminoglycan-collagen fibers.

We report on the fabrication of fibers exclusively from the extracellular matrix components by interfacial complexation without using any crosslinking agent. The obtained fibers may have different biomedical applications as they are flexible, and cells adhere and remodel them. Moreover, their stability and thickness can be finely tuned by the sulfation degree of the used glycosaminoglycans.

Organ-specific distribution and subcellular localisation of ascorbate peroxidase isoenzymes in potato (Solanum tuberosum L.) plants.

Ascorbate peroxidase (EC 1.11.1.11), a heme-containing homodimeric protein, is a hydrogen peroxide-scavenging enzyme, playing an important role in plants in order to protect them from oxidative stress, thus adverting cellular damage. Several ascorbate peroxidase isoenzymes have been reported but the understanding of their physiological role still depends on a better knowledge of their precise localisation within plant organs. Immunocytochemistry techniques were performed in order to elucidate the peroxisomal and cytosolic ascorbate peroxidase distribution within tissues of leaves and sprouts of potato plants. The peroxisomal isoenzyme was found to have a broad distribution in sprouts, but a differential one in leaves, being restricted to the spongy parenchyma. This differential expression may be associated to the mesophyll asymmetry and the diverse physiological processes that occur in it. The cytosolic isoenzyme was not detected in leaves under the used conditions, probably because it is present in low amounts in these tissues. The results obtained in sprouts were at least curious: cytosolic ascorbate was found to be adjacent to the amyloplasts. Given these results, it is possible to state that apart from their similarity, these two isoenzymes reside in different organelles and seem to take part in different physiological processes as suggested by their organ- and tissue-specific distribution.