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This study investigated six-month outcomes of first models of ascending aortic replacement. The molds used to produce the Biotube were implanted subcutaneously in goats. After 2-3 months, the molds were explanted to obtain the Biotubes (inner diameter, 12 mm; wall thickness, 1.5 mm). Next, we performed ascending aortic replacement using the Biotube in five allogenic goats. At 6 months, the animals underwent computed tomography (CT) and histologic evaluation. As a comparison, we performed similar surgeries using glutaraldehyde-fixed autologous pericardial rolls or pig-derived heterogenous Biotubes. At 6 months, CT revealed no aneurysmalization of the Biotube or pseudoaneurysm formation. The histologic evaluation showed development of endothelial cells, smooth muscle cells, and elastic fibers along the Biotube. In the autologous pericardium group, there was no evidence of new cell development, but there was calcification. The histologic changes observed in the heterologous Biotube group were similar to those in the allogenic Biotube group. However, there was inflammatory cell infiltration in some heterologous Biotubes. Based on the above, we could successfully create the world's first Biotube-based ascending aortic replacement models. The present results indicate that the Biotube may serve as a scaffold for aortic tissue regeneration.

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Biotubes are autologous tubular tissues developed within a patient's body through in-body tissue architecture, and they demonstrate high potential for early clinical application as a vascular replacement. In this pilot study, we used large animals to perform implantation experiments in preparation for preclinical testing of Biotube. The biological response after Biotube implantation was histologically evaluated. The designed Biotubes (length: 50 cm, internal diameter: 4 mm, and wall thickness: 0.85 mm) were obtained by embedding molds on the backs of six goats for a predetermined period (1-5 months). The same goats underwent bypass surgery on the carotid arteries using Biotubes (average length: 12 cm). After implantation, echocardiography was used to periodically monitor patency and blood flow velocity. The maximum observation period was 6 months, and tissue analysis was conducted after graft removal, including the anastomosis. All molds generated Biotubes that exceeded the tensile strength of normal goat carotid arteries, and eight randomly selected Biotubes were implanted. Thrombotic occlusion occurred immediately postoperatively (1 tube) if anticoagulation was insufficient, and two tubes, with insufficient Biotube strength (<5 N), were ruptured within a week. Five tubes maintained patency for >2 months without aneurysm formation. The spots far from the anastomosis became stenosed within 3 months (3 tubes) when Biotubes had a wide intensity distribution, but the shape of the remaining two tubes remained unchanged for 6 months. The entire length of the bypass region was walled with an αSMA-positive cell layer, and an endothelial cell layer covered most of the lumen at 2 months. Complete endothelial laying of the luminal surface was obtained at 3 months after implantation, and a vascular wall structure similar to that of native blood vessels was formed, which was maintained even at 6 months. The stenosis was indicated to be caused by fibrin adhesion on the luminal surface, migration of repair macrophages, and granulation formation due to the overproliferation of αSMA-positive fibroblasts. We revealed the importance of Biotubes that are homogeneous, demonstrate a tensile strength > 5 N, and are implanted under appropriate antithrombotic conditions to achieve long-term patency of Biotube. Further, we clarified the Biotube regeneration process and the mechanism of stenosis. Finally, we obtained the necessary conditions for a confirmatory implant study planned shortly.

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Introduction: Ureteral injuries require surgical intervention as they lead to loss of renal function. The current reconstructive techniques for long ureteral defects are problematic. Consequently, this study aimed to reconstruct the ureter in a rat model using subcutaneously prepared autologous collagen tubes (Biotubes). Methods: The lower ureter of LEW/SsNSlc rats was ligated to dilate the ureter to make anastomosis easier, and reconstruction was performed six days later by anastomosing the dilated ureter and bladder with a Biotube that was prepared subcutaneously in syngeneic rats. Some rats underwent left nephrectomy and ureter reconstruction simultaneously as negative controls to evaluate the effects of urine flow on patency. The other rats were divided into three groups as follows: a group in which the ureter was reconstructed with the Biotube alone, a group in which cardiomyocyte sheets made from the neonatal hearts of syngeneic rats were wrapped around the Biotube, and a group in which an adipose-derived stem cell sheets made from the inguinal fat of adult syngeneic rats were wrapped. Contrast-enhanced computed tomography and pathological evaluations were performed two weeks after reconstruction. Result: In the Biotube alone group, all tubes were occluded and hydronephrosis developed, whereas the urothelium regenerated beyond the anastomosis when the left kidney was not removed, suggesting that urothelial epithelial spread occurred with urinary flow. The patency of the ureteral lumen was obtained in some rats in the cardiomyocyte sheet covered group, whereas stricture or obstruction of the reconstructed ureter was observed in all rats in the other groups. Pathological evaluation revealed a layered urothelial structure in the cardiomyocyte sheet covered group, although only a small amount of cardiomyocyte sheets remained. Conclusion: Urinary flow may support the epithelial spread of the urothelium into the reconstructed ureter. Neonatal rat cardiomyocyte sheets supported the patency of the regenerated ureter with a layered urothelium.

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Vascular regeneration and patency maintenance, without anticoagulant administration, represent key developmental trends to enhance small-diameter vascular grafts (SDVG) performance. In vivo engineered autologous biotubes have emerged as SDVG candidates with pro-regenerative properties. However, mechanical failure coupled with thrombus formation hinder translational prospects of biotubes as SDVGs. Previously fabricated poly(ε-caprolactone) skeleton-reinforced biotubes (PBs) circumvented mechanical issues and achieved vascular regeneration, but orally administered anticoagulants were required. Here, highly efficient and biocompatible functional modifications were introduced to living cells on PB lumens. The 1,2-dimyristoyl-sn-glycero-3-phosphoethanolamine-N-methoxy (DMPE)-PEG-conjugated anti-coagulant bivalirudin (DPB) and DMPE-PEG-conjugated endothelial progenitor cell (EPC)-binding TPS-peptide (DPT) modifications possessed functionality conducive to promoting vascular graft patency. Co-modification of DPB and DPT swiftly attained luminal saturation without influencing cell viability. DPB repellent of non-specific proteins, DPB inhibition of thrombus formation, and DPB protection against functional masking of DPT's EPC-capture by blood components, which promoted patency and rapid endothelialization in rat and canine artery implantation models without anticoagulant administration. This strategy offers a safe, facile, and fast technical approach to convey additional functionalization to living cells within tissue-engineered constructs.

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There are no small-diameter, long artificial vascular grafts for below-knee bypass surgery in chronic limb-threatening ischemia. We have developed tissue-engineered vascular grafts called "Biotubes®" using a completely autologous approach called in-body tissue architecture (iBTA). This study aimed at pre-implantation evaluation of Biotube and its in vivo preparation device, Biotube Maker, for use in below-knee bypass surgery. Forty nine makers were subcutaneously embedded into 17 goats for predetermined periods (1, 2, or 3 months). All makers produced Biotubes as designed without inflammation over all periods, with the exception of a few cases with minor defects (success rate: 94%). Small hole formation occurred in only a few cases. All Biotubes obtained had an inner diameter of 4 mm and a length of 51 to 52 cm with a wall thickness of 594 ± 97 µm. All Biotubes did not kink when completely bent under an internal pressure of 100 mmHg and did not leak without any deformation under a water pressure of 200 mmHg. Their burst strength was 2409 ± 473 mmHg, and suture retention strength was 1.75 ± 0.27 N, regardless of the embedding period, whereas tensile strength increased from 7.5 ± 1.3 N at 1 month to 9.7 ± 2.0 N at 3 months with the embedding period. The amount of water leakage from the needle holes prepared in the Biotube wall was approximately 1/7th of that in expanded polytetrafluoroethylene vascular grafts. The Biotubes could be easily connected to each other without cutting or anastomosis leaks. They could be stored for at least 1 year at room temperature. This study confirmed that even Biotubes formed 1 month after embedding of Biotube Makers had properties comparable to arteries.

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OBJECTIVE: There is a need for small diameter vascular substitutes in the absence of available autologous material. A small diameter, long tissue engineered vascular graft was developed using a completely autologous approach called "in body tissue architecture technology (iBTA)". The aim of this pilot study was to evaluate "Biotubes", iBTA induced autologous collagenous tubes, for their potential use as small diameter vascular bypass conduits. METHODS: Biotubes (internal diameter 4 mm, length 50 cm, wall thickness 0.85 mm) were prepared by subcutaneous embedding of plastic moulds (Biotube Maker) in three goats for approximately two months. Allogenic Biotubes (length 10 cm [n = 2], 15 cm [n = 2], 22 cm [n = 2]) were bypassed to both carotid arteries by end to side anastomosis with their ligation between the anastomoses in another three goats. Residual Biotubes were examined for their mechanical properties. After four weeks, the harvested Biotubes were evaluated histologically. RESULTS: All Biotubes had sufficient pressure resistance, approximately 3000 mmHg. Although wall thickening occurred at two proximal anastomosis sites, all six grafts were patent without luminal thrombus formation, stenosis, or aneurysm deformation throughout the implantation period. Endothelial cells covered both anastomosis sites almost completely, with partial covering in the central portion of the grafts. Furthermore, α smooth muscle actin positive cells infiltrated the middle layer along almost the entire graft length. CONCLUSION: This preliminary study showed that small diameter, long, tissue engineered Biotubes could function properly as arterial bypass conduits in a large animal for one month without any abnormal change in vascular shape. Thus, small diameter, long Biotubes are potentially viable conduits, which are biocompatible and labour non-intensive, and therefore, suitable for clinical practice. Additionally, Biotubes can start the regeneration process in a short period of time.

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Generally, the thickness of tubular tissues formed from silicone rods through encapsulation of the foreign-body reaction is less than approximately 0.2 mm. On the other hand, it is unclear how hollow cylindrical molds can provide thick tubular tissues, known as Biotubes, with a thickness exceeding 1 mm, during in-body tissue architecture (iBTA) using encapsulation. In this study, histological and structural analyses were performed to understand the reason for the formation of thick mold-based Biotubes. Molds were assembled with a gap between a silicone rod and a stainless-steel cylinder and were embedded into the dorsal subcutaneous pouches of beagles for 2 or 4 weeks. Thick Biotubes were obtained from the harvested mold. The histological analysis showed that the lumen side of the thick Biotubes consisted primarily of type I collagen fibers and α-smooth muscle actin-positive cells, similar to the original rod-based thin Biotubes formed only from silicone rods. Interestingly, the outer region of the thick Biotubes was an immature connective tissue consisting of type III collagen, including primitive somatic stem cells expressing CD90 and SSEA4. These stem cells may have contributed to the formation of the thick-walled Biotubes by differentiating into other cell types and through growth factor production. Because of the potential tissue-repair ability of these stem cells, iBTA could be useful for elucidating the regeneration process, remodeling the physiology/pathology of tissue defects/damage, and cell acquisition. This technology can provide autologous stem cells without in vitro cell culture. Moreover, thick-walled Biotubes may be useful as an alternative stem cell-containing material in regenerative medicine.

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PURPOSE: Tissue engineering of esophagus is required for management of long-gap esophageal atresia (LGEA). Collagenous connective tissue membranes fabricated by in-body tissue architecture (iBTA), called biosheets, can repair esophageal defects and generate tissues similar to native esophagus. However, iBTA requires second-stage surgery because of heterotopic preparation of biosheets. Our aim was to develop orthotopic iBTA for primary engineering of the esophagus by interposing a tubular mold to the esophageal defect. METHOD: The cervical esophagus of six rats was transected. An acrylic tube (internal diameter 2.6 mm, length 7.0 mm) was inserted and fixed between the ends of the upper and lower esophagus, and a 3 mm-long esophageal defect was created. Four weeks later, the rats were sacrificed for histological analysis. RESULTS: Postoperatively the rats could intake liquid food. After four weeks, the esophageal defects were filled with regenerated tissues. Histologically the new esophageal walls stained positive for collagen type I. The inner surfaces were covered with stratified squamous epithelium that expressed pan-cytokeratin. In only one of six rats, regeneration of muscular-like tissue was suggested by positive immunohistochemical staining for desmin. CONCLUSION: Orthotopic iBTA can regenerate a substitute esophagus with esophageal epithelium and collagenous wall. This technique may be a novel treatment for esophageal atresia with gaps of various lengths including LGEA.

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INTRODUCTION: The first choice of vascular access for hemodialysis is an autogenous arteriovenous fistula, because prosthetic arteriovenous grafts have a high probability of failure. In this study, Biotubes, in-body tissue architecture-induced autologous collagenous tubes, were evaluated for their potential use as vascular access grafts. Three animal implantation models were developed using beagle dogs, and the in vivo performance of Biotubes was observed after implantation in the acute phase as a pilot study. METHODS: Biotubes (internal diameter ca. 4.0 mm, length ca. 5.0 cm, and wall thickness ca. 0.7 mm) were prepared through subcutaneous embedding of specially designed molds in beagle dogs for 8 weeks. The Biotubes were then implanted between the common carotid artery and the jugular vein of beagles via three methods, including side-to-side (in) -end-to-end (out) as type 1 (n = 4), side-to-side (both) as type 2 (n = 4), and side-to-end (in) -end-to-side (out) as type 3 (n = 1 using a composite Biotube). RESULTS: Although two cases in type 1 and 2 resulted in Biotube deformation, all cases were patent for 4 weeks and maintained a continuous turbulent flow. At 4 weeks after implantation, percutaneous puncture could be performed repeatedly without aneurysm formation or hemorrhage. CONCLUSION: Within a short implantation period, with limited animal numbers, this proof-of-concept study showed that Biotubes may have a high potential for use in vascular access.

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This study presents the initial 3-year results of the first in-human study of internal shunt restoration using completely autologous vascular grafts, "Biotubes," based on in-body tissue architecture. Biotubes (diameter, 6 mm; length, 7 cm) were prepared as autologous collagenous tubular tissues with approximately 0.5 mm wall thickness by embedding molds (two per patient), assembled with a silicone rod and a stainless steel pipe with many slits, into the patients' abdominal subcutaneous tissue for 2 months. Two female patients with end-stage renal disease were undergoing hemodialysis with a high probability of failure due to repeated stenosis every few months at the venous outflow regions over 1.5 years. Biotubes formed in both patients and were bypassed over the venous stenosis region of the arteriovenous shunt. After bypass with Biotubes without living cells, palpable thrill and typical turbulent flow pattern were observed by pulsed-wave Doppler. Follow-up angiography showed no signs of dilation or stenosis after implantation, and puncture could be performed easily without graft damage. In both cases, stenosis of Biotubes occurred after 3-4 months. In the first case, percutaneous transluminal angioplasty was not required for over 2 years after implantation even after the development of Biotube stenosis. In the second case, stenosis at the proximal anastomotic site of the Biotube became prominent, and percutaneous transluminal angioplasty was needed 7 months after implantation and then repeated at up to 2 years. This was the first human study successfully supporting the concept of internal shunt restoration for hemodialysis using an autologous Biotube.

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INTRODUCTION: We devised a strategy for the fabrication of an 'anatomy-mimicking' cylinder-type engineered trachea combined with cartilage engineering. The engineered BIOTUBEs are used to support the architecture of the body tissue, for long-segment trachea (>5 cm) with carinal reconstruction. The aim of the present study was to fabricate an anatomy-mimicking cylinder-type regenerative airway, and investigate its applicability in a rabbit model. METHODS: Collagen sponge rings (diameter: 6 mm) were arranged on a silicon tube (diameter: 6 mm) at 2-mm intervals. Chondrocytes from the auricular cartilage were seeded onto collagen sponges immediately prior to implantation in an autologous manner. These constructs were embedded in dorsal subcutaneous pouches of rabbits. One month after implantation, the constructs were retrieved for histological examination. In addition, cervical tracheal sleeve resection was performed, and these engineered constructs were implanted into defective airways through end-to-end anastomosis. RESULTS: One month after implantation, the engineered constructs exhibited similar rigidity and flexibility to those observed with the native trachea. Through histological examination, the constructs showed an anatomy-mimicking tracheal architecture. In addition, the engineered constructs could be anastomosed to the native trachea without air leakage. CONCLUSION: The present study provides the possibility of generating anatomy-mimicking cylinder-type airways, termed BIO-AIR-TUBEs, that engineer cartilage in an in-vivo culture system. This approach involves the use of BIOTUBEs formed via in-body tissue architecture technology. Therefore, the BIO-AIR-TUBE may be useful as the basic architecture of artificial airways.

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In-body tissue architecture (iBTA), a cell-free, in vivo tissue engineering technology that can produce autologous implantable tissues of the desired shape by subcutaneously embedding specially designed molds, was used to develop long tubular collagenous tissues called Biotubes. Spiral molds for long Biotubes were assembled with an outer pipe-shaped spiral shell and an inner spiral mandrel, and embedded into subcutaneous pouches of beagle dogs or goats for 1 or 2 months. Tubular collagenous tissues were formed at the space between the shell and the mandrel of the mold. Depending on the spiral turn number in the mold, Biotubes of 25 cm or 50 cm (internal diameter 4 mm or 5 mm) were prepared with nearly homogeneous mechanical and histological properties over their entire length. Biotubes stored in 70% ethanol were allogenically implanted into beagle dogs or goats to evaluate their in vivo performance. The 25-cm Biotubes functioned as arterial grafts with no need for luminal modification or mechanical support, and demonstrated vascular reconstruction within 3 months after implantation into dogs. The 50-cm Biotubes functioned as arteriovenous shunt grafts in the neck region of goats without thrombus formation and vascular deformation for 1 month. Thus, the world's longest tissue-engineered vascular grafts with small diameter could be developed using iBTA.

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A type-C mold based on in-body tissue architecture was previously developed for preparing small-diameter biotube vascular grafts with a 2-mm diameter and approximately 1-mm wall thickness. In this study, the type-C mold was modified for preparing large-diameter biotubes with controlled wall thicknesses. Four types of molds were assembled by inserting silicone center rods (outer diameters 11, 13, 15, 17 mm) into stainless steel cages (inner diameter 19 mm) and surgically embedded in the abdominal subcutaneous pouches of Holstein cows. After 8-12 weeks, connective tissues occupied the rod-cage gap in the molds to form biotubes. The wall thickness of the biotubes obtained after removing the molds was approximately 1-3 mm, which corresponded to approximately 80% of each gap distance. The breaking strength almost linearly increased with the wall thickness of the biotubes. The strength of the biotubes with wall thickness over 1.5 mm was higher than that of beagle blood vessels. The thickest biotubes were as strong as bovine pericardium and can be used as an alternative trachea graft because of their adequate lumen-holding force.

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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.

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Biotubes, i.e., in vivo tissue-engineered connective tubular tissues, are known to be effective as vascular replacement grafts with a diameter greater than several millimeters. However, the performance of biotubes with smaller diameters is less clear. In this study, MicroBiotubes with diameters <1 mm were prepared, and their patency was evaluated noninvasively by optical coherence tomography (OCT) and magnetic resonance angiography (MRA). MicroBiotube molds, containing seven stainless wires (diameter 0.5 mm) covered with silicone tubes (outer diameter 0.6 mm) per mold, were embedded into the dorsal subcutaneous pouches of rats. After 2 months, the molds were harvested with the surrounding capsular tissues to obtain seven MicroBiotubes (internal diameter 0.59 ± 0.015 mm, burst pressure 4190 ± 1117 mmHg). Ten-mm-long MicroBiotubes were allogenically implanted into the femoral arteries of rats by end-to-end anastomosis. Cross-sectional OCT imaging demonstrated the patency of the MicroBiotubes immediately after implantation. In a 1-month follow-up MRA, high patency (83.3 %, n = 6) was observed without stenosis, aneurysmal dilation, or elongation. Native-like vascular structure was reconstructed with completely endothelialized luminal surfaces, mesh-like elastin fiber networks, regular circumferential orientation of collagen fibers, and α-SMA-positive cells. Although the long-term patency of MicroBiotubes still needs to be confirmed, they may be useful as an alternative ultra-small-caliber vascular substitute.

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Small-diameter biotube vascular grafts developed by in-body tissue architecture had high patency at implantation into rabbit carotid arteries or rat abdominal aortas. However, the thin walls (34 ± 14 µm) of the original biotubes made their implantation difficult into areas with low blood flow volumes or low blood pressure due to insufficient mechanical strength to maintain luminal shape. In this study, caged molds with several windows were designed to prepare more robust biotubes. The molds were assembled with silicone tubes (external diameter 2 mm) and cylindrical covers (outer diameter 7 mm) with 12 linear windows (1 × 9 mm). After the molds were embedded into beagle dorsal subcutaneous pouches for 4 weeks, type C (cage) biotubes were obtained by completely extracting the surrounding connective tissues from the molds and removing the molds. The biotube walls (778 ± 31 µm) were formed at the aperture (width 1 mm) between the silicone rods and the covers by connective cell migration through the windows of the covers. Excellent mechanical properties (external pressure resistance, approximately 4 times higher than beagle native femoral arteries; burst strength, approximately 2 times higher than original biotubes) were obtained. In the acute phase of implantation of the biotubes into beagle femoral arteries, perfect patency was obtained with little stenosis and no aneurysmal dilation. The type C biotubes may be useful for implantation into peripheral arteries or veins in addition to aortas.

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Completely autologous in vivo tissue-engineered connective tissue tubes (Biotubes) have promise as arterial vascular grafts in animal implantation studies. In this clinical study of patients undergoing peritoneal dialysis (PD) (n = 11; age: 39-83 years), we evaluated human Biotubes' (h-Biotubes) mechanical properties to determine whether Biotubes with feasibility as vascular grafts could be formed in human bodies. We extracted PD catheters, embedded for 4-47 months, and obtained tubular connective tissues as h-Biotubes (internal diameter: 5 mm) from around the catheter' silicone tubular parts. h-Biotubes were composed mainly of collagen with smooth luminal surfaces. The average wall thickness was 278 ± 178 µm. No relationship was founded between the tubes' mechanical properties and patients' ages or PD catheter embedding periods statistically. However, the elastic modulus (2459 ± 970 kPa) and tensile strength (623 ± 314 g) of h-Biotubes were more than twice as great as those from animal Biotubes, formed from the same PD catheters by embedding in the beagle subcutaneous pouches for 1 month, or beagle arteries. The burst strength (6338 ± 1106 mmHg) of h-Biotubes was almost the same as that of the beagle thoracic or abdominal aorta. h-Biotubes could be formed in humans over a 4-month embedding period, and they satisfied the mechanical requirements for application as vascular grafts. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 104B: 1431-1437, 2016.

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Biotubes, prepared using in-body tissue architecture (IBTA) technology, have adequate mechanical properties and excellent biocompatibility for vascular grafts. However, they have thin walls, lack vascular constructing cells, and are composed of subcutaneous connective tissues consisting mainly of collagen and fibroblasts. This study aimed to prepare Biotubes with a vascular-like structure including an endothelial cell lining and a smooth muscle cell by IBTA using adipose-derived vascular stromal cell (ADSCs)-exuding specially designed multiporous tubes (outer diameter 5 mm, length 24 mm, pore size 500 µm, pore number 180, cell number/tube >3.0 × 10(6)). ADSCs were separated from rat subcutaneous fat, suspended in a Matrigel™ solution at 4 °C, and then filled into the tubes. After the tubes were embedded into dorsal subcutaneous pouches of the same rats for 2 weeks, robust Biotubes with a wall thickness of >600 µm were formed surrounding the tubes. The luminal layer of the obtained Biotubes was dominated by the cells positive for an endothelial marker. Almost the entire intima, with a thickness of about 400 µm, was occupied with cells positive for a smooth muscle marker. Both cells were derived from ADSCs. Biotube walls were constructed by fusing ADSC-derived vascular constructing cells exuded from the tubes and fibroblasts and collagen from the surrounding connective tissue. A robust Biotubes with vascular cells component, were formed after only 2 weeks of subcutaneous incubation of ADSCs-exuding multiporous tubes.

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A novel eosin Y-releasing mold was designed to accelerate the fabrication of in vivo tissue engineered autologous vascular prosthetic tissues, called the "biotubes." The mold was prepared by addition of an aqueous solution of eosin Y (1∼6 w/v%) to the agar gel (0.3%), which was attached to the luminal surface of the microporous acrylate tube (diameter, 5 mm; length, 28 mm; pore size, 0.5 mmϕ). The eosin Y release period was controlled by the number of pores (3∼160). On embedding the molds into dorsal, subcutaneous pouches of rats for 1 week, completely encapsulated biotubes, mainly consisting of collagen, with thick walls (418.2 ± 173.4 µm) and robust mechanical properties (elastic modulus, 956.2 ± 196.5 kPa; burst pressure 5850 ± 2383 mmHg) were formed. These values were, respectively, more than 4.3, 3.8, and 5.6 times greater than the corresponding controls (acrylate rods). The high elastic modulus of the biotubes was obtained even with a small number of micropores (3), and a low concentration of eosin Y (1%) within a very short embedding period (5 days), irrespective of rat weights. This innovative method for rapid production of vascular grafts with thick walls and robust mechanical properties may be adaptable for the sub-emergency clinical use of biotubes in regenerative medicine.

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The aim of this study was to explore and evaluate biotubes consisting of autologous tissues. The biotubes were prepared by intra-abdominally embedding silicon rods as moulds. The specimens were analyzed by mechanical tests, histological observation and superficial study. The intra-abdominal implantation of the silicone tubes readily stimulated the development of the biotubes. The biotubes consisted of collagen-rich extracellular matrices. Myofibroblasts appeared as elongated cells with circumferential or longitudinal orientations. Subsequent to one month of embedding, the thickness of the tube wall was 70-250 µm. The burst strength was 1100±187 mmHg and the suturability was excellent. Biotubes that have the ability to be widely variable in their shapes are composed of autologous cells and glomerular extracellular matrices. Biotubes are ideal grafts for tissue engineering as they are able to avoid immunological rejection and are of sufficient mechanical strength.