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Marketa Bacakova,*,1 Julia Pajorova,*,1,2 Antonin Broz,1 Daniel Hadraba,1,3 Frantisek Lopot,3 Anna Zavadakova,4 Lucie Vistejnova,4 Milan Beno,5 Ivan Kostic,6 Vera Jencova,7 Lucie Bacakova11Department of Biomaterials and Tissue Engineering, Institute of Physiology of the Czech Academy of Sciences, Prague, Czech Republic; 22nd Faculty of Medicine, Charles University, Prague, Czech Republic; 3Department of Anatomy and Biomechanics, Faculty of Physical Education and Sport, Charles University, Prague, Czech Republic; 4Biomedical Center, Medical Faculty in Pilsen, Charles University, Pilsen, Czech Republic; 5Institute of Experimental Endocrinology, Biomedical Research Center of the Slovak Academy of Sciences, Bratislava, Slovak Republic; 6Institute of Informatics, Slovak Academy of Sciences, Bratislava, Slovak Republic; 7Department of Chemistry, Technical University of Liberec, Liberec, Czech Republic*These authors contributed equally to this workBackground: Repairs to deep skin wounds continue to be a difficult issue in clinical practice. A promising approach is to fabricate full-thickness skin substitutes with functions closely similar to those of the natural tissue. For many years, a three-dimensional (3D) collagen hydrogel has been considered to provide a physiological 3D environment for co-cultivation of skin fibroblasts and keratinocytes. This collagen hydrogel is frequently used for fabricating tissue-engineered skin analogues with fibroblasts embedded inside the hydrogel and keratinocytes cultivated on its surface. Despite its unique biological properties, the collagen hydrogel has insufficient stiffness, with a tendency to collapse under the traction forces generated by the embedded cells.Methods: The aim of our study was to develop a two-layer skin construct consisting of a collagen hydrogel reinforced by a nanofibrous poly-L-lactide (PLLA) membrane pre-seeded with fibroblasts. The attractiveness of the membrane for dermal fibroblasts was enhanced by coating it with a thin nanofibrous fibrin mesh.Results: The fibrin mesh promoted the adhesion, proliferation and migration of the fibroblasts upwards into the collagen hydrogel. Moreover, the fibroblasts spontaneously migrating into the collagen hydrogel showed a lower tendency to contract and shrink the hydrogel by their traction forces. The surface of the collagen was seeded with human dermal keratinocytes. The keratinocytes were able to form a basal layer of highly mitotically-active cells, and a suprabasal layer.Conclusion: The two-layer skin construct based on collagen hydrogel with spontaneously immigrated fibroblasts and reinforced by a fibrin-coated nanofibrous membrane seems to be promising for the construction of full-thickness skin substitute.Keywords: full-thickness skin substitutes, collagen hydrogel, fibroblast and keratinocyte co-cultivation, fibrin, nanostructure

Julia Pajorova,1 Marketa Bacakova,1 Jana Musilkova,1 Antonin Broz,1 Daniel Hadraba,1,2 Frantisek Lopot,2 Lucie Bacakova1 1Department of Biomaterials and Tissue Engineering, Institute of Physiology of the Czech Academy of Sciences, Prague, Czech Republic; 2Department of Anatomy and Biomechanics, Faculty of Physical Education and Sport, Charles University, Prague, Czech Republic Background: Our study focuses on the fabrication of appropriate scaffolds for skin wound healing. This research brings valuable insights into the molecular mechanisms of adhesion, proliferation, and control of cell behavior through the extracellular matrix represented by synthetic biodegradable nanofibrous membranes coated by biomolecules. Methods: Nanofibrous polylactic acid (PLA) membranes were prepared by a needle-less electrospinning technology. These membranes were coated with fibrin according to two preparation protocols, and additionally they were coated with fibronectin in order to increase the cell affinity for colonizing the PLA membranes. The adhesion, growth, and extracellular matrix protein production of neonatal human dermal fibroblasts were evaluated on the nanofibrous membranes. Results: Our results showed that fibrin-coated membranes improved the adhesion and proliferation of human dermal fibroblasts. The morphology of the fibrin nanocoating seems to be crucial for the adhesion of fibroblasts, and consequently for their phenotypic maturation. Fibrin either covered the individual fibers in the membrane (F1 nanocoating), or covered the individual fibers and also formed a fine homogeneous nanofibrous mesh on the surface of the membrane (F2 nanocoating), depending on the mode of fibrin preparation. The fibroblasts on the membranes with the F1 nanocoating remained in their typical spindle-like shape. However, the cells on the F2 nanocoating were spread mostly in a polygon-like shape, and their proliferation was significantly higher. Fibronectin formed an additional mesh attached to the surface of the fibrin mesh, and further enhanced the cell adhesion and growth. The relative gene expression and protein production of collagen I and fibronectin were higher on the F2 nanocoating than on the F1 nanocoating. Conclusion: A PLA membrane coated with a homogeneous fibrin mesh seems to be promising for the construction of temporary full-thickness skin tissue substitutes. Keywords: nanofibers, fibrin, nanocoating, dermal fibroblasts, extracellular matrix synthesis, skin substitute, polylactic acid

Marketa Bacakova,1,2 Julia Pajorova,1,2 Denisa Stranska,3 Daniel Hadraba,1,4 Frantisek Lopot,4 Tomas Riedel,5 Eduard Brynda,5 Margit Zaloudkova,6 Lucie Bacakova1 1Department of Biomaterials and Tissue Engineering, Institute of Physiology, Czech Academy of Sciences, 2Second Faculty of Medicine, Charles University, Prague, 3InStar Technologies, Liberec, 4Department of Anatomy and Biomechanics, Faculty of Physical Education and Sport, Charles University, 5Department of Chemistry and Physics of Surfaces and Biointerfaces, Institute of Macromolecular Chemistry, 6Department of Composites and Carbon Materials, Institute of Rock Structure and Mechanics, Czech Academy of Sciences, Prague, Czech Republic Abstract: Protein-coated resorbable synthetic polymeric nanofibrous membranes are promising for the fabrication of advanced skin substitutes. We fabricated electrospun polylactic acid and poly(lactide-co-glycolic acid) nanofibrous membranes and coated them with fibrin or collagen I. Fibronectin was attached to a fibrin or collagen nanocoating, in order further to enhance the cell adhesion and spreading. Fibrin regularly formed a coating around individual nanofibers in the membranes, and also formed a thin noncontinuous nanofibrous mesh on top of the membranes. Collagen also coated most of the fibers of the membrane and randomly created a soft gel on the membrane surface. Fibronectin predominantly adsorbed onto a thin fibrin mesh or a collagen gel, and formed a thin nanofibrous structure. Fibrin nanocoating greatly improved the attachment, spreading, and proliferation of human dermal fibroblasts, whereas collagen nanocoating had a positive influence on the behavior of human HaCaT keratinocytes. In addition, fibrin stimulated the fibroblasts to synthesize fibronectin and to deposit it as an extracellular matrix. Fibrin coating also showed a tendency to improve the ultimate tensile strength of the nanofibrous membranes. Fibronectin attached to fibrin or to a collagen coating further enhanced the adhesion, spreading, and proliferation of both cell types. Keywords: skin-tissue engineering, nanocoating, nanofibers, skin cells, fibrin, collagen

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This article reviews vascular access (VA) assessment methods and procedures. It gives an overview of the existing methods for bed-side VA assessment by means of pressures, recirculation and access flow measurement. Pros and cons of the methods are discussed and additional benefits of a combined recirculation and access flow measurement are explained. Present vascular access care guidelines are discussed, namely the K/DOQI and EVAS documents. Practical setup of a vascular access monitoring and surveillance system is illustrated with data from the authors' own unit where such a system has been in use since 1999. The issue of adequate target setting is analysed in view of published works on clinical impact of access surveillance system introduction (timely detection of access stenosis and access patency). Critical re-evaluation is needed especially in current QVA threshold and intervention timing. [ABSTRACT FROM AUTHOR]