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Yasuhide Nakayama - One of the best experts on this subject based on the ideXlab platform.

  • one year rat study of ibta induced microbiotube microvascular grafts with an ultra small diameter of 0 6 mm
    European Journal of Vascular and Endovascular Surgery, 2018
    Co-Authors: Daizo Ishii, Junichiro Enmi, Ryosuke Iwai, Kaoru Kurisu, Eisuke Tatsumi, Yasuhide Nakayama
    Abstract:

    Objective The world's smallest calibre “microbiotube” vascular graft was recently developed, with an inner diameter of 0.6 mm. It was formed using in-body tissue architecture (iBTA) and has a high degree of patency and capacity for regeneration in the acute phase, 1 month after implantation. This consecutive study investigated the compatibility and stability of microbiotubes in the chronic phase of implantation for 12 months for potential application in microsurgery. Methods This was an in vivo experimental study. The microbiotubes were prepared by embedding the mould subcutaneously in rats for 2 months. Allogenic microbiotubes (n = 16) were implanted into the bilateral femoral arteries (inner diameter 0.5 mm) of eight Wistar rats in an end to end anastomosis manner for 12 months. Follow up 7-Tesla magnetic resonance angiograms were performed every 3 months. Histological observation was performed 12 months after implantation. Results All patent grafts (n = 12, patency 75%) one month after implantation maintained their patency up to 12 months without any abnormal morphological changes or calcification. Histological observation at 12 months showed that layered α-smooth muscle actin positive cells with a monolayer luminal covering of endothelial cells had formed from the proximal to the distal anastomoses. A thin elastic fibre layer formed in the luminal area. After implantation, all components of the microbiotube were similar to those of a Native Artery. Conclusions This study suggests that microbiotubes have high compatibility, stability, and durability as replacement grafts over the short to mid-term period.

  • abstract 13054 perfect 1 year angiographic patency of in vivo tissue engineered vascular grafts with an ultra small diameter of 0 6 mm microbiotubes in a rat model
    Circulation, 2016
    Co-Authors: Daizo Ishii, Junichiro Enmi, Kaoru Kurisu, Hidehiro Iida, Yasuhide Nakayama
    Abstract:

    Background and Purpose: Biotubes are autologous tubular connective tissues formed by in-body tissue architecture technology, which is a novel and practical approach in regenerative medicine. We confirmed that Microbiotubes (MBs) with diameter of 0.6 mm had high performance potential as a reliable arterial graft in acute phase of implantation in a rat model. In this study, quality and patency of MBs in chronic phase were evaluated by histological or magnetic resonance angiographic (MRA) examinations, respectively. Method: The mold for multiple preparing of MBs was assembled by several stainless wires covered with silicone tubes. The molds were surgically embedded into the dorsal subcutaneous pouches of rats. After 2 months, the molds were harvested with surrounding tissues and MBs were obtained by removing the molds. MBs (length, 10 mm; internal diameter, 0.6 mm) were implanted in rat femoral arteries (diameter, ca. 0.5 mm) in allogenic manner by end-to-end anastomosis without use of any anticoagulant agents. Ten patent MBs after 1-month implantation were observed by follow-up 7- Tesla MRA until 1 year after implantation. Results: In all follow-up periods, all MBs were patent without any observable stenoses or dilatations and a difference of signal intensity between MBs and Native Artery was obscure (Fig. 1). Moreover, Native-like reconstructed structure of MBs’ wall was conserved histologically for 1 year. Conclusion: It was unprecedented result that there was no occluded case in chronic phase and MBs preserved high quality and patency for a long-term period. We are convinced that MBs could be useful grafts for ultramicrosurgery, such as a replantation of severed fingers or a reconstruction of lymphatic vesssels, in the not too distant future.

  • in vivo tissue engineered small caliber arterial graft prosthesis consisting of autologous tissue biotube
    Cell Transplantation, 2004
    Co-Authors: Yasuhide Nakayama, Hatsue Ishibashiueda, Keiichi Takamizawa
    Abstract:

    In this study, vascular-like tubular tissues called biotubes, consisting of autologous tissues, were prepared using in vivo tissue engineering. Their mechanical properties were evaluated for application as a small-caliber artificial vascular prosthesis. The biotubes were prepared by embedding six kinds of polymeric rods [poly(ethylene) (PE), poly(fluoroacetate) (PFA), poly(methyl methacrylate) (PMMA), segmented poly(urethane) (PU), poly(vinyl chloride) (PVC), and silicone (Si)] as a mold in six subcutaneous pouches in the dorsal skin of New Zealand White rabbits. For rods apart from PFA, biotubes were constructed after 1 month of implantation by encapsulation around the polymeric implants. The wall thickness of the biotubes ranged from about 50 to 200 microm depending on the implant material and were in the order PFA < PVC < PMMA < PU < PE. As for PE, PMMA, and PVC, the thickness increased after 3 months of implantation and ranged from 1.5-to 2-fold. None of the biotubes were ruptured when a hydrostatic pressure was gradually applied to their lumen up to 200 mmHg. The relationship between the intraluminal pressure and the external diameter, which was highly reproducible, showed a "J"-shaped curve similar to the Native Artery. The tissue mostly consisted of collagen-rich extracellular matrices and fibroblasts. Generally, the tissue was relatively firm and inelastic for Si and soft for PMMA. For PMMA, PE, and PVC the stiffness parameter (beta value; one of the indexes for compliance) of the biotubes obtained was similar to those of the human coronary, femoral, and carotid arteries, respectively. Biotubes, which possess the ability for wide adjustments in their matrices, mechanics, shape, and luminal surface design, can be applied for use as small-caliber blood vessels and are an ideal implant because they avoid immunological rejection.

Keiichi Takamizawa - One of the best experts on this subject based on the ideXlab platform.

  • mechanical responses of a compliant electrospun poly l lactide co e caprolactone small diameter vascular graft
    Biomaterials, 2006
    Co-Authors: Hiroyuki Inoguchi, Eiko Inoue, Il Keun Kwon, Keiichi Takamizawa, Takehisa Matsuda
    Abstract:

    Abstract To design a “mechano-active” small-diameter artificial vascular graft, a tubular scaffold made of elastomeric poly( l -lactide- co - e -caprolactone) fabrics at different wall thicknesses was fabricated using an electrospinning (ELSP) technique. The wall thickness of the fabricated tube (inner diameter; approximately 2.3–2.5 mm and wall thickness; 50–340 μm) increased proportionally with ELSP time. The wall thickness dependence of mechanical responses including intraluminal pressure-induced inflation was determined under static and dynamic flow conditions. From the compliance-related parameters (stiffness parameter and diameter compliance) measured under static condition, the smaller the wall thickness, the more compliant the tube. Under dynamic flow condition (1 Hz, maximal/minimal pressure of 90 mmHg/45 mmHg) produced by a custom-designed arterial circulatory system, strain, defined as the relative increase in diameter per pulse, increased with the decrease in wall thickness, which approached that of a Native Artery. Thus, a mechano-active scaffold that pulsates synchronously by responding to pulsatile flow was prepared using elastomeric PLCL as a base material and an ELSP technique.

  • in vivo tissue engineered small caliber arterial graft prosthesis consisting of autologous tissue biotube
    Cell Transplantation, 2004
    Co-Authors: Yasuhide Nakayama, Hatsue Ishibashiueda, Keiichi Takamizawa
    Abstract:

    In this study, vascular-like tubular tissues called biotubes, consisting of autologous tissues, were prepared using in vivo tissue engineering. Their mechanical properties were evaluated for application as a small-caliber artificial vascular prosthesis. The biotubes were prepared by embedding six kinds of polymeric rods [poly(ethylene) (PE), poly(fluoroacetate) (PFA), poly(methyl methacrylate) (PMMA), segmented poly(urethane) (PU), poly(vinyl chloride) (PVC), and silicone (Si)] as a mold in six subcutaneous pouches in the dorsal skin of New Zealand White rabbits. For rods apart from PFA, biotubes were constructed after 1 month of implantation by encapsulation around the polymeric implants. The wall thickness of the biotubes ranged from about 50 to 200 microm depending on the implant material and were in the order PFA < PVC < PMMA < PU < PE. As for PE, PMMA, and PVC, the thickness increased after 3 months of implantation and ranged from 1.5-to 2-fold. None of the biotubes were ruptured when a hydrostatic pressure was gradually applied to their lumen up to 200 mmHg. The relationship between the intraluminal pressure and the external diameter, which was highly reproducible, showed a "J"-shaped curve similar to the Native Artery. The tissue mostly consisted of collagen-rich extracellular matrices and fibroblasts. Generally, the tissue was relatively firm and inelastic for Si and soft for PMMA. For PMMA, PE, and PVC the stiffness parameter (beta value; one of the indexes for compliance) of the biotubes obtained was similar to those of the human coronary, femoral, and carotid arteries, respectively. Biotubes, which possess the ability for wide adjustments in their matrices, mechanics, shape, and luminal surface design, can be applied for use as small-caliber blood vessels and are an ideal implant because they avoid immunological rejection.

Gary L Bowlin - One of the best experts on this subject based on the ideXlab platform.

  • SBC2008-192895 MULTI-LAYERED POLYCAPROLACTONE -ELASTIN -COLLAGEN SMALL DIAMETER CONDUITS FOR VASCULAR TISSUE ENGINEERING
    2020
    Co-Authors: Michael J Mcclure, Scott A Sell, Gary L Bowlin
    Abstract:

    INTRODUCTION The architecture of the vascular wall is highly intricate and requires unique biomechanical properties in order to function properly. Native Artery is composed of a mix of collagens, elastin, endothelial cells (ECs), smooth muscle cells (SMC), fibroblasts, and proteoglycans arranged into three distinct layers: the intima, media, and adventitia. Throughout Artery, collagen and elastin play an important role, providing a mechanical backbone, preventing vessel rupture, and promoting recovery while undergoing pulsatile deformation

  • a three layered electrospun matrix to mimic Native arterial architecture using polycaprolactone elastin and collagen a preliminary study
    Acta Biomaterialia, 2010
    Co-Authors: Michael J Mcclure, David G Simpson, Scott A Sell, Beat H Walpoth, Gary L Bowlin
    Abstract:

    Throughout Native Artery, collagen, and elastin play an important role, providing a mechanical backbone, preventing vessel rupture, and promoting recovery under pulsatile deformations. The goal of this study was to mimic the structure of Native Artery by fabricating a multi-layered electrospun conduit composed of poly(caprolactone) (PCL) with the addition of elastin and collagen with blends of 45-45-10, 55-35-10, and 65-25-10 PCL-ELAS-COL to demonstrate mechanical properties indicative of Native arterial tissue, while remaining conducive to tissue regeneration. Whole grafts and individual layers were analyzed using uniaxial tensile testing, dynamic compliance, suture retention, and burst strength. Compliance results revealed that changes to the middle/medial layer changed overall graft behavior with whole graft compliance values ranging from 0.8 to 2.8%/100 mm Hg, while uniaxial results demonstrated an average modulus range of 2.0-11.8 MPa. Both modulus and compliance data displayed values within the range of Native Artery. Mathematical modeling was implemented to show how changes in layer stiffness affect the overall circumferential wall stress, and as a design aid to achieve the best mechanical combination of materials. Overall, the results indicated that a graft can be designed to mimic a tri-layered structure by altering layer properties.

  • a three layered electrospun matrix to mimic Native arterial architecture using polycaprolactone elastin and collagen a preliminary study
    ASME 2010 Summer Bioengineering Conference Parts A and B, 2010
    Co-Authors: Michael J Mcclure, David G Simpson, Scott A Sell, Beat H Walpoth, Gary L Bowlin
    Abstract:

    The architecture of the vascular wall is highly intricate and requires unique biomechanical properties in order to function properly. Native Artery is composed of a mix of collagens, elastin, endothelial cells (ECs), smooth muscle cells (SMC), fibroblasts, and proteoglycans arranged into three distinct layers: the intima, media, and adventitia. Throughout Artery, collagen and elastin play an important role, providing a mechanical backbone, preventing vessel rupture, and promoting recovery while undergoing pulsatile deformations [1]. The low-strain mechanical response of Artery to blood flow is dominated by the elastic behavior, of elastin, which prevents pulsatile energy from being dissipated as heat [2]. A higher amount of energy loss indicates a decrease in recoverability, which could lead to eventual disruption of blood flow. An effective way to quantify recoverability is through hysteresis and compliance measurement. The hypothesis of this study was that the fabrication of a multi-layered electrospun tissue engineering scaffold composed of polycaprolactone (PCL), elastin (ELAS), and collagen (COL) would demonstrate dynamic mechanical properties indicative of a highly elastic material, similar to the three distinct layers of Native arterial tissue, while remaining conducive to tissue regeneration. PCL was chosen, in this case, to provide mechanical integrity and elasticity, while elastin and collagen would provide further elasticity and bioactivity [3,4].Copyright © 2010 by ASME

  • electrospun polydioxanone elastin and collagen vascular scaffolds uniaxial cyclic distension
    Journal of Engineered Fibers and Fabrics, 2009
    Co-Authors: Michael J Mcclure, David G Simpson, Scott A Sell, Gary L Bowlin
    Abstract:

    The development of vascular grafts requires the matching of material and viscoelastic properties to those of Native Artery. The hypothesis of this study was to subject electrospun tissue engineering scaffolds composed of polydioxanone, elastin, and collagen to cyclic loading in order to quantify the hysteretic properties, uniaxial tensile mechanical properties of conditioned scaffolds, and stress relaxation properties over a period of 400 cycles when compared to ePTFE, one of the most popular vascular prosthetic materials, and decellularized pig Artery. In the electrospun graft, polydioxanone would provide a mechanical backbone, providing tensile support and preventing vessel rupture; while the elastin would provide elasticity and collagen would provide bioactivity (promote regeneration in vitro/in situ).

  • suture reinforced electrospun polydioxanone elastin small diameter tubes for use in vascular tissue engineering a feasibility study
    Acta Biomaterialia, 2008
    Co-Authors: Matthew J Smith, Michael J Mcclure, David G Simpson, Scott A Sell, Beat H Walpoth, Catherine P Barnes, Gary L Bowlin
    Abstract:

    This study characterizes the cross-linking of electrospun elastin and the mechanical properties of suture-reinforced 1.5mm internal diameter electrospun tubes composed of blended polydioxanone (PDO) and soluble elastin. Several tube configurations were tested to assess the effects of reinforcement on tube mechanical properties. Between the electrospun layers of each double-layered prosthetic, zero, one or two 6-0 sutures were wound, maintaining 1mm spacing with a pitch of 9 degrees . Single-layered tubes without suture were also examined. Samples were cross-linked and tested for compliance and burst strength. Compliance decreased significantly (p <0.05) and burst strength significantly increased (p <0.01) with reinforcement. Uncross-linked tubes were also tested to determine the effects of cross-linking. Results demonstrated that cross-linking significantly decreases burst strength (p <0.01), while decreases in compliance for cross-linked tubes were not significant. Cross-linked suture-reinforced PDO-elastin tubes had burst pressures more than 10 times greater than normal systolic pressures and exhibited a range of compliance values, including those matching Native Artery. These tubes display many characteristics of the "ideal" small-diameter graft, having mechanical properties that can be tailored to match those desired in vascular replacement applications.

Beat H Walpoth - One of the best experts on this subject based on the ideXlab platform.

  • a three layered electrospun matrix to mimic Native arterial architecture using polycaprolactone elastin and collagen a preliminary study
    Acta Biomaterialia, 2010
    Co-Authors: Michael J Mcclure, David G Simpson, Scott A Sell, Beat H Walpoth, Gary L Bowlin
    Abstract:

    Throughout Native Artery, collagen, and elastin play an important role, providing a mechanical backbone, preventing vessel rupture, and promoting recovery under pulsatile deformations. The goal of this study was to mimic the structure of Native Artery by fabricating a multi-layered electrospun conduit composed of poly(caprolactone) (PCL) with the addition of elastin and collagen with blends of 45-45-10, 55-35-10, and 65-25-10 PCL-ELAS-COL to demonstrate mechanical properties indicative of Native arterial tissue, while remaining conducive to tissue regeneration. Whole grafts and individual layers were analyzed using uniaxial tensile testing, dynamic compliance, suture retention, and burst strength. Compliance results revealed that changes to the middle/medial layer changed overall graft behavior with whole graft compliance values ranging from 0.8 to 2.8%/100 mm Hg, while uniaxial results demonstrated an average modulus range of 2.0-11.8 MPa. Both modulus and compliance data displayed values within the range of Native Artery. Mathematical modeling was implemented to show how changes in layer stiffness affect the overall circumferential wall stress, and as a design aid to achieve the best mechanical combination of materials. Overall, the results indicated that a graft can be designed to mimic a tri-layered structure by altering layer properties.

  • a three layered electrospun matrix to mimic Native arterial architecture using polycaprolactone elastin and collagen a preliminary study
    ASME 2010 Summer Bioengineering Conference Parts A and B, 2010
    Co-Authors: Michael J Mcclure, David G Simpson, Scott A Sell, Beat H Walpoth, Gary L Bowlin
    Abstract:

    The architecture of the vascular wall is highly intricate and requires unique biomechanical properties in order to function properly. Native Artery is composed of a mix of collagens, elastin, endothelial cells (ECs), smooth muscle cells (SMC), fibroblasts, and proteoglycans arranged into three distinct layers: the intima, media, and adventitia. Throughout Artery, collagen and elastin play an important role, providing a mechanical backbone, preventing vessel rupture, and promoting recovery while undergoing pulsatile deformations [1]. The low-strain mechanical response of Artery to blood flow is dominated by the elastic behavior, of elastin, which prevents pulsatile energy from being dissipated as heat [2]. A higher amount of energy loss indicates a decrease in recoverability, which could lead to eventual disruption of blood flow. An effective way to quantify recoverability is through hysteresis and compliance measurement. The hypothesis of this study was that the fabrication of a multi-layered electrospun tissue engineering scaffold composed of polycaprolactone (PCL), elastin (ELAS), and collagen (COL) would demonstrate dynamic mechanical properties indicative of a highly elastic material, similar to the three distinct layers of Native arterial tissue, while remaining conducive to tissue regeneration. PCL was chosen, in this case, to provide mechanical integrity and elasticity, while elastin and collagen would provide further elasticity and bioactivity [3,4].Copyright © 2010 by ASME

  • matching the diameter of eptfe bypass prosthesis with a Native Artery improves neoendothelialization
    European Surgical Research, 2008
    Co-Authors: Mustafa Cikirikcioglu, Erman Pektok, Y B Cikirikcioglu, Osorioda S Cruz, Jeanchristophe Tille, Afksendiyos Kalangos, Beat H Walpoth
    Abstract:

    Background and Aim: The undersizing of the bypass graft diameter compared to Native Artery changes blood flow characteristics and velocity which may affect conduit neo-endothelialization, intimal hyperplasia reaction and patency. The aim of this study was to evaluate conduit neoendothelialization, intimal hyperplasia reaction and patency results between undersized and matched ePTFE grafts. Material and Methods: In 16 male Sprague-Dawley rats, undersized (1-mm internal diameter) and matched (2-mm internal diameter) ePTFE grafts were anastomosed end-to-end in the infrarenal abdominal aorta. Blood flow volume per minute was measured and wall shear stress was calculated for each group. After 3 weeks of follow-up, angiography was performed via the left carotid Artery just before sacrifice. Conduit neoendothelialization and intimal hyperplasia reaction were measured by computer-assisted morphometry. Results: Wall shear stress was 8 times higher for the undersized group (840.56 vs. 105.07 mPa). Three weeks after implantation, conduit neoendothelialization was better in matched grafts compared to undersized grafts (441 vs. 574 µm, p = 0.008). Intimal hyperplasia reaction was similar for both groups (8.7 vs. 6.7 µm2/µm for undersized and matched grafts, respectively). Patency rate was 7/8 for undersized and 8/8 for matched ePTFE grafts. Conclusion: Although the graft patency and the intimal hyperplasia reaction were not different between the two groups after 3 weeks, matched grafts had a significantly better endothelialization compared to undersized grafts. This short-term beneficial effect may influence long-term patency results.

  • suture reinforced electrospun polydioxanone elastin small diameter tubes for use in vascular tissue engineering a feasibility study
    Acta Biomaterialia, 2008
    Co-Authors: Matthew J Smith, Michael J Mcclure, David G Simpson, Scott A Sell, Beat H Walpoth, Catherine P Barnes, Gary L Bowlin
    Abstract:

    This study characterizes the cross-linking of electrospun elastin and the mechanical properties of suture-reinforced 1.5mm internal diameter electrospun tubes composed of blended polydioxanone (PDO) and soluble elastin. Several tube configurations were tested to assess the effects of reinforcement on tube mechanical properties. Between the electrospun layers of each double-layered prosthetic, zero, one or two 6-0 sutures were wound, maintaining 1mm spacing with a pitch of 9 degrees . Single-layered tubes without suture were also examined. Samples were cross-linked and tested for compliance and burst strength. Compliance decreased significantly (p <0.05) and burst strength significantly increased (p <0.01) with reinforcement. Uncross-linked tubes were also tested to determine the effects of cross-linking. Results demonstrated that cross-linking significantly decreases burst strength (p <0.01), while decreases in compliance for cross-linked tubes were not significant. Cross-linked suture-reinforced PDO-elastin tubes had burst pressures more than 10 times greater than normal systolic pressures and exhibited a range of compliance values, including those matching Native Artery. These tubes display many characteristics of the "ideal" small-diameter graft, having mechanical properties that can be tailored to match those desired in vascular replacement applications.

Daizo Ishii - One of the best experts on this subject based on the ideXlab platform.

  • one year rat study of ibta induced microbiotube microvascular grafts with an ultra small diameter of 0 6 mm
    European Journal of Vascular and Endovascular Surgery, 2018
    Co-Authors: Daizo Ishii, Junichiro Enmi, Ryosuke Iwai, Kaoru Kurisu, Eisuke Tatsumi, Yasuhide Nakayama
    Abstract:

    Objective The world's smallest calibre “microbiotube” vascular graft was recently developed, with an inner diameter of 0.6 mm. It was formed using in-body tissue architecture (iBTA) and has a high degree of patency and capacity for regeneration in the acute phase, 1 month after implantation. This consecutive study investigated the compatibility and stability of microbiotubes in the chronic phase of implantation for 12 months for potential application in microsurgery. Methods This was an in vivo experimental study. The microbiotubes were prepared by embedding the mould subcutaneously in rats for 2 months. Allogenic microbiotubes (n = 16) were implanted into the bilateral femoral arteries (inner diameter 0.5 mm) of eight Wistar rats in an end to end anastomosis manner for 12 months. Follow up 7-Tesla magnetic resonance angiograms were performed every 3 months. Histological observation was performed 12 months after implantation. Results All patent grafts (n = 12, patency 75%) one month after implantation maintained their patency up to 12 months without any abnormal morphological changes or calcification. Histological observation at 12 months showed that layered α-smooth muscle actin positive cells with a monolayer luminal covering of endothelial cells had formed from the proximal to the distal anastomoses. A thin elastic fibre layer formed in the luminal area. After implantation, all components of the microbiotube were similar to those of a Native Artery. Conclusions This study suggests that microbiotubes have high compatibility, stability, and durability as replacement grafts over the short to mid-term period.

  • abstract 13054 perfect 1 year angiographic patency of in vivo tissue engineered vascular grafts with an ultra small diameter of 0 6 mm microbiotubes in a rat model
    Circulation, 2016
    Co-Authors: Daizo Ishii, Junichiro Enmi, Kaoru Kurisu, Hidehiro Iida, Yasuhide Nakayama
    Abstract:

    Background and Purpose: Biotubes are autologous tubular connective tissues formed by in-body tissue architecture technology, which is a novel and practical approach in regenerative medicine. We confirmed that Microbiotubes (MBs) with diameter of 0.6 mm had high performance potential as a reliable arterial graft in acute phase of implantation in a rat model. In this study, quality and patency of MBs in chronic phase were evaluated by histological or magnetic resonance angiographic (MRA) examinations, respectively. Method: The mold for multiple preparing of MBs was assembled by several stainless wires covered with silicone tubes. The molds were surgically embedded into the dorsal subcutaneous pouches of rats. After 2 months, the molds were harvested with surrounding tissues and MBs were obtained by removing the molds. MBs (length, 10 mm; internal diameter, 0.6 mm) were implanted in rat femoral arteries (diameter, ca. 0.5 mm) in allogenic manner by end-to-end anastomosis without use of any anticoagulant agents. Ten patent MBs after 1-month implantation were observed by follow-up 7- Tesla MRA until 1 year after implantation. Results: In all follow-up periods, all MBs were patent without any observable stenoses or dilatations and a difference of signal intensity between MBs and Native Artery was obscure (Fig. 1). Moreover, Native-like reconstructed structure of MBs’ wall was conserved histologically for 1 year. Conclusion: It was unprecedented result that there was no occluded case in chronic phase and MBs preserved high quality and patency for a long-term period. We are convinced that MBs could be useful grafts for ultramicrosurgery, such as a replantation of severed fingers or a reconstruction of lymphatic vesssels, in the not too distant future.