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After the foundation of a trinational task force to develop quality criteria for a training and educational system in microsurgery at the annual conference of the German-speaking group for microsurgery of the nerves and vessels (DAM) in Erlangen 2009, at the 2010 conference in Basel, a modular educational system was approved and criteria for a basic course were discussed. Before the next annual conference in 2011 these aspects should be clarified and defined in a spring meet-ing.

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BACKGROUND/AIMS: The aim of this study was to generate an axially vascularized bone substitute. The arteriovenous (AV)-loop approach in a large-animal model was applied in order to induce axial vascularization in a clinically approved processed bovine cancellous bone (PBCB) matrix of significant volume with primary mechanical stability and to assess the course of increasing axial vascularization. METHODS: PBCB constructs were implanted into 13 merino sheep together with a microsurgically created AV loop in an isolation chamber. The vascularization process was monitored by sequential magnetic resonance imaging (MRI) scans. Explants were subjected to micro-computed tomography (micro-CT) analysis, histomorphometry and immunohistochemistry for CD31 and CD45. RESULTS: Increasing axial vascularization in PBCB constructs was quantified by histomorphometry and visualized by micro-CT scans. Intravital sequential MRI scans demonstrated a significant progressive increase in perfused volume within the matrices. Immunohistochemistry confirmed endothelial lining of newly formed vessels. CONCLUSION: This study demonstrates successful axial vascularization of a clinically approved, mechanically stable bone substitute with a significant volume by a microsurgical AV loop in a large-animal model. Thus microsurgical transplantation of a tissue-engineered, axially vascularized and mechanically stable bone substitute with clinically relevant dimensions may become clinically feasible in the future.

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The use of foetal liver cells (FLC) in the context of hepatic tissue engineering might permit efficient in vitro expansion and cryopreservation in a cell bank. A prerequisite for successful application of bioartificial liver tissue is sufficient initial vascularization. In this study, we evaluated the transplantation of fibrin gel-immobilized FLC in a vascularized arterio-veno-venous (AV)-loop model. FLC were isolated from embryonic/foetal (ED 16) rat livers and were enriched by using magnetic cell sorting (MACS). After cryopreservation, FLC were labelled by pkh-26. Cells were transplanted in a fibrin matrix into a subcutaneous chamber containing a microsurgically created AV-loop in the femoral region of the recipient rat. The chambers were explanted after 14 days. Subcutaneous implants without an AV-loop and cell-free implants served as controls. Fluorescence microscopy of the constructs was used to identify pkh-26(+)- donor cells. Characterization was performed by RT-PCR and immunhistology (IH) for CK-18 and CD31. Transplantation of FLC using the AV-loop permitted a neo-tissue formation in the fibrin matrix. A high-density vascularization was observed in the AV-loop constructs as shown by CD31 IH. Viable foetal donor cells were detected which expressed CK-18. FLC can be successfully used for heterotopic transplantation. Fibrin matrix permits rapid blood vessel ingrowth from the AV-loop and supports engraftment of FLC. It is therefore an appropriate environment for hepatocyte transplantation in combination with microsurgical vascularization strategies. Transplantation of fibrin gel-immobilized FLC may be a promising approach for the development of highly vascularized in vivo tissue-engineering-based liver support systems.

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Our aim was to quantitatively assess the angiogenetic effects of VEGF and bFGF immobilized in a fibrin-based drug delivery system in a suitable subcutaneous rat model. After evaluation of a suitable implantation technique (6 rats), four teflon isolation chambers containing fibrin gel matrices were implanted subcutaneously in an upside-down fashion on the back of 30 Lewis rats. The matrices consisted of 500 microl fibrin gel with two different fibrinogen concentrations (10 mg/ml or 40 mg/ml fibrinogen) and 2 I.U./ml thrombin and contained VEGF and bFGF in five different concentrations (0 to 250 ng/ml each). At 3, 7 and 14 days after implantation, matrices were explanted and subjected to histological and morphometrical analysis. At 1 week, the volume of the fibrin clots was significantly smaller in the 100 and 250 ng/ml VEGF and bFGF groups in comparison to lower concentrated growth factors. At 1 and 2 weeks, the use of growth factors in low concentrations (25 ng/ml VEGF and bFGF) significantly increased the amount of fibrovascular tissue, average fraction of blood vessels and number of blood vessels at the matrix-host interface in comparison to growth factor-free controls. Higher concentrations were neither associated with further increase of tissue formation nor with increased sprouting of blood vessels in this model. This study demonstrates that fibrin gel-immobilized angioinductive growth factors efficiently stimulate generation of fibrovascular tissue and sprouting of blood vessels in a newly developed subcutaneous upside-down isolation chamber model with an optimum between 25 and 100 ng/ml.

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Components of the activated complement cascade are considered to play a pivotal role in ischemia-reperfusion-induced organ injury. With the use of intravital epifluorescence microscopy, we investigated the effect of complement inhibition by the recombinant soluble complement receptor 1 (sCR1; TP10) on the effect of macromolecular microvascular permeability, functional capillary perfusion, and leukocyte endothelium interaction in postischemic pancreatitis. Anaesthetized Sprague-Dawley rats were subjected to 60 min of normothermic pancreatic ischemia induced by microclipping of the blood-supplying arteries of the organ. Rats who received sCR1 (15 mg/kg body wt iv; n = 7) during reperfusion showed a significant reduction of permeability (1.77 +/- 1.34 x 10(-8) cm/s; n = 7) of tetramethylrhodamine isothiocyanate-labeled albumin injected 90 min after the onset of reperfusion compared with vehicle-treated animals (6.95 +/- 1.56 x 10(-8) cm/s; n = 7). At 120 min after the onset of reperfusion, the length of red blood cell-perfused capillaries (functional capillary density) was significantly improved (from 279 +/- 15.7 to 330 +/- 3.7 cm(-1); n = 7) and the number of leukocytes adherent to postcapillary venules was significantly reduced (from 314 +/- 87 to 163 +/- 71 mm(-2); n = 7) by sCR1 compared with vehicle treatment. Complement inhibition by sCR1 effectively ameliorates pancreatic ischemia-reperfusion-induced microcirculatory disturbances and might be considered for treatment of postischemic pancreatitis.

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