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Polylactide nanofibers in skin tissue engineering

Bacakova M., Varga M., Riedel T., Stranska D., Bacakova L.

Engineering of Biomaterials

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2012

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Vol. 15, no. 116-117 spec. iss.

127--128

EN

Various artificial or natural biomaterials can be used for constructing a scaffold suitable for treating skin injuries. Artificial skin replacements are made from polyhema, polybutylene terephthalate, nylon, polylactic acid and polyglycolic acid or their copolymers. The most widely applied natural biomaterials are collagen, chitin, hyaluronic acid and chondroitin sulfate [1]. In recent tissue engineering, nanofibrous scaffolds have been very attractive because they better simulate the architecture of natural extracellular matrix. In skin tissue engineering, nanofibrous membranes can be used for constructing a bilayer of fibroblasts and keratinocytes [2]. These membranes will separate the two cell types, ensuring their physical and humoral communication; thus the layer of fibroblasts will serve as a feeder for keratinocytes. For our study, we chose nanofibers made of polylactide (PLA), prepared in external collaboration with Elmarco Ltd. (Liberec, Czech Republic). The main advantage of PLA is its biodegradability; it is slowly resorbed in the organism, and is finally replaced by regenerate tissue. The adhesion and growth of cells on the scaffolds can be improved by further modifications, e.g. plasma treatment or coating the scaffold fibers with biomolecules that are normally present in the natural skin (collagen, hyaluronic acid), or that occur during wound healing (fibrin). Modification by plasma leads to changes in the physical and chemical properties of the material surface (i.e., surface wettability, morphology, electric conductivity, roughness, morphology, mechanical properties) [3]. In our experiment we evaluated the interaction of human HaCaT keratinocytes with PLA nanofibrous meshes that were modified by plasma irradiation or by coating with collagen, fibrin and hyaluronan of low (70-120 KDa) or high (1000-1250 KDa) molecular weight. For plasma irradiation, PLA nanofibers were exposed to O2, CH4 or Ar plasma for different times, with various ranges of power. For more detailed studies, O2 plasma was chosen, because this type of plasma best supported the adhesion and growth of cells. PLA nanofibrous meshes were prepared with different densities of the fibres (5 g/m2, 9 g/m2, 16 g/m2, 30 g/m2). The potential damage to the fibres after plasma modification was observed using scanning electron microscopy (SEM). The cell adhesion, growth and metabolic activity were evaluated by the number of cells, their morphology, the amount of cellular DNA (PicoGreen ds DNA assay kit, Invitrogen®) and the XTT test (Roche) on days 1, 3 and 7 after seeding. The results indicated that polylactide nanofibrous scaffolds promote adhesion and growth of HaCaT keratinocytes. Modification in plasma further improved the proliferation of cells on PLA nanofibers. The cells proliferated better on PLA meshes with lower densities of the fibers (5 g/m2, 9g/m2). SEM showed that damage to the fibers increased with the length of the period of plasma treatment. The collagen deposited on the fibers changed the morphology of the cells. The cells on the control unmodified fibers adhered in clusters, but on the collagen-coated fibers they were spread homogeneously. We can conclude that polylactide nanofibrous membranes are a promising material for the construction of temporary carriers for skin cells, particularly after they have been physically or biologically modified.

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Combined Hybrid ARQ and Link Adaptation for Coded Cooperation in Block-Fading Channels

Varga M., Badiu M. A., Bota V.

Advances in Electronics and Telecommunications

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2011

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Vol. 2, no. 4

47--53

EN

Cooperative hybrid ARQ (HARQ) protocols have been widely studied in recent years and they were shown to provide higher efficiency than cooperative protocols. This paper proposes a joint design within which the HARQ protocol collaborates with the link adaptation functionality and the cooperative transmission scheme in order to adapt the behavior of the HARQ protocol to the QoS requirements of the supported services. As performance metrics of the HARQ protocol, we use the expected number of retransmissions and the expected spectral efficiency. The paper also studies the influence of the protocol parameters upon the performance provided.

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Welding plugs on gas pipes at accelerated heat offtake under laboratory condition

Pallo P., Mician M., Varga M.

International Journal of Applied Mechanics and Engineering

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2010

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Vol. 15, no 2

545-550

EN

This article deals with the design of a constructional solution for measuring thermal cycles at accelerated heat offtake from the weld area. The designed model gives appropriate conditions for real weld evaluation on gas pipes. It enables evaluation of the welds not only by non-destructive test methods, but for example also by microscopic, macroscopic and others destructive test methods.