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Axial vascularization of tissue constructs is essential to maintain an adequate blood supply for a stable regeneration of a clinically relevant tissue size. The versatility of the arterio-venous loop (AVL) has been previously shown in various small and large animal models as well as in clinical reports for bone regeneration. We have previously demonstrated the capability of the AVL to induce axial vascularization and to support the nourishment of tissue constructs in small animal models after applying high doses of ionizing radiation comparable to those applied for adjuvant radiotherapy after head and neck cancer. We hypothesize that this robust ability to induce regeneration after irradiation could be related to a state of hypoxia inside the constructs that triggers the HIF1 (hypoxia induced factor 1) - SDF1 (stromal derived factor 1) axis leading to chemotaxis of progenitor cells and induction of tissue regeneration and vascularization. We analyzed the expression of HIF1 and SDF1 via immunofluorescence in axially vascularized bone tissue engineering constructs in Lewis rats 2 and 5 weeks after local irradiation with 9Gy or 15Gy. We also analyzed the expression of various genes for osteogenic differentiation (collagen 1, RUNX, alkaline phosphatase and osteonectin) via real time PCR analysis. The expression of HIF1 and SDF1 was enhanced two weeks after irradiation with 15Gy in comparison to non-irradiated constructs. The expression of osteogenic markers was enhanced at the 5-weeks time point with significant results regarding collagen, alkaline phosphatase and osteonectin. These results indicate that the hypoxia within the AVL constructs together with an enhanced SDF1 expression probably play a role in promoting tissue differentiation. The process of tissue generation triggered by hypoxia in the vicinity of a definite vascular axis with enhanced tissue differentiation over time resembles hereby the well-known concept of organogenesis in fetal life. [ABSTRACT FROM AUTHOR]

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Background: The utilization of an arteriovenous loop is an underreported technique that affords the creation of reliable vascular options. Understanding the efficacy and impacting variables of microvascular reconstruction with an arteriovenous loop can be critical to its use. Methods: Multi‐institutional study of 36 patients who underwent vein grafting or AV loop with free tissue transfer. Results: 58.3% of patients received prior radiation and 38.9% prior flap reconstruction. Flap success for vein grafting was 76% and AV loop was 100% (p = 0.16). Success for the radiated cohort was 90.5% and non‐radiated 80% (p = 0.63). Flap success for the radiated, vein grafted patient was 83.3% and 100% flap success rate for radiated, AV loop patient (p = 0.49). Overall flap survival was 83.3% versus 97% overall success rate in the United States. Conclusion: The AV loop is a viable modality for vessel‐depleted free tissue reconstruction. Radiation and previous surgery do not significantly impact flap success rates. [ABSTRACT FROM AUTHOR]

In this study, we aimed to evaluate the human placenta as a source of blood vessels that can be harvested for vascular graft fabrication in the submillimeter range. Our approach included graft modification to prevent thrombotic events. Submillimeter arterial grafts harvested from the human placenta were decellularized and chemically crosslinked to heparin. Graft performance was evaluated using a microsurgical arteriovenous loop (AVL) model in Lewis rats. Specimens were evaluated through hematoxylin-eosin and CD31 staining of histological sections to analyze host cell immigration and vascular remodeling. Graft patency was determined 3 weeks after implantation using a vascular patency test, histology, and micro-computed tomography. A total of 14 human placenta submillimeter vessel grafts were successfully decellularized and implanted into AVLs in rats. An appropriate inner diameter to graft length ratio of 0.81 ± 0.16 mm to 7.72 ± 3.20 mm was achieved in all animals. Grafts were left in situ for a mean of 24 ± 4 days. Decellularized human placental grafts had an overall patency rate of 71% and elicited no apparent immunological responses. Histological staining revealed host cell immigration into the graft and re-endothelialization of the vessel luminal surface. This study demonstrates that decellularized vascular grafts from the human placenta have the potential to serve as super-microsurgical vascular replacements. [ABSTRACT FROM AUTHOR]

Microvascular reconstruction frequently requires anastomosis outside of the zone of injury for successful reconstruction. Multiple options exist for pedicle lengthening including vein grafts, arteriovenous loops, and arteriovenous bundle interposition grafts. The authors performed a systematic review of arteriovenous bundle interposition grafts to elucidate indications and outcomes of arteriovenous grafts in microvascular reconstruction. A systematic review of the literature was performed using targeted keywords. Data extraction was performed by two independent authors, and descriptive statistics were used to analyze pooled data. Forty-four patients underwent pedicle lengthening with an arteriovenous graft from the descending branch of the lateral circumflex femoral artery. Most common indications for flap reconstruction were malignancy (n = 12), trauma (n = 7), and diabetic ulceration (n = 4). The most commonly used free flap was the anterolateral thigh flap (n = 18). There were five complications, with one resulting in flap loss. Arteriovenous bundle interposition grafts are a viable option for pedicle lengthening when free flap distant anastomosis is required. The descending branch of the lateral circumflex femoral artery may be used for a variety of defects and can be used in conjunction with fasciocutaneous, osteocutaneous, muscle, and chimeric free flaps.

Due to the limitations of current in vivo experimental designs, our comprehensive knowledge of vascular development and its implications for the development of large-scale engineered tissue constructs is very limited. Therefore, the purpose of this study was to develop unique in vivo imaging chambers that allow the live visualization of cellular processes in the arteriovenous (AV) loop model in rats. We have developed two different types of chambers. Chamber A is installed in the skin using the purse sting fixing method, while chamber B is installed subcutaneously under the skin. Both chambers are filled with modified gelatin hydrogel as a matrix. Intravital microscopy (IVM) was performed after the injection of fluorescein isothiocyanate (FITC)-labeled dextran and rhodamine 6G dye. The AV loop was functional for two weeks in chamber A and allowed visualization of the leukocyte trafficking. In chamber B, microvascular development in the AV loop could be examined for 21 days. Quantification of the microvascular outgrowth was performed using Fiji-ImageJ. Overall, by combining these two IVM chambers, we can comprehensively understand vascular development in the AV loop tissue engineering model¯. [ABSTRACT FROM AUTHOR]

Rationale: Elevated shear stress (ESS) induces vascular remodeling in veins exposed to arterial blood flow, which can lead to arteriovenous (AV) fistula failure. The molecular mechanisms driving remodeling have not been comprehensively examined with a single-cell resolution before. Objective: Using an in vivo animal mode, single-cell RNA sequencing, and histopathology, we precisely manipulate blood flow to comprehensively characterize all cell subpopulations important during vascular remodeling. Methods: AV loops were created in saphenous vessels of rats using a contralateral saphenous vein interposition graft to promote ESS. Saphenous veins with no elevated shear stress (NSS) were anastomosed as controls. Findings: ESS promoted transcriptional homogeneity, and NSS promoted considerable heterogeneity. Specifically, ESS endothelial cells (ECs) showed a more homogeneous transcriptional response promoting angiogenesis and upregulating endothelial-to-mesenchymal transition inhibiting genes ( Klf2 ). NSS ECs upregulated antiproliferation genes such as Cav1 , Cst3 , and Btg1 . In macrophages, ESS promoted a large homogeneous subpopulation, creating a mechanically activated, proinflammatory and thus proangiogenic myeloid phenotype, whereas NSS myeloid cells expressed the anti-inflammatory and antiangiogenetic marker Mrc1 . Conclusion: ESS activates unified gene expression profiles to induce adaption of the vessel wall to hemodynamic alterations. Targeted depletion of the identified cellular subpopulations may lead to novel therapies to prevent excessive venous remodeling, intimal hyperplasia, and AV fistula failure.

The arteriovenous (AV) loop model is a key technique to solve one of the major problems of tissue engineering—providing adequate vascular support for a tissue construct of significant size. However, the molecular and cellular mechanisms of vascularization and factors influencing the generation of new tissue in the AV loop are still poorly understood. We previously established a novel intravital microscopy approach to study these events. In this study, we implanted our observation chamber filled with two types of hydrogels such as fibrin and methacrylate gelatin (GelMA) and performed intravital microscopy (IVM) on days 7, 14, and 21. Initial microvessel formation was observed in GelMA on day 14, while the vessel network showed clear indicators of network rearrangement and maturation on day 21. No visible microvessels were observed in fibrin. The chambers were explanted on day 21. Histological examination revealed higher numbers of microvessels in GelMA compared to fibrin, while the AV loop was thrombosed in all fibrin constructs, possibly due to matrix degradation. GelMA proved to be an ideal matrix for IVM studies in the AV loop model due to its slow degradation and transparency. This IVM model can be employed as a novel tool for live and thus faster comprehension of crucial events in the tissue regeneration process, which can improve tissue engineering application. [ABSTRACT FROM AUTHOR]

Animal models are important tools to investigate the pathogenesis and develop treatment strategies for breast cancer in humans. In this study, we developed a new three-dimensional in vivo arteriovenous loop model of human breast cancer with the aid of biodegradable materials, including fibrin, alginate, and polycaprolactone. We examined the in vivo effects of various matrices on the growth of breast cancer cells by imaging and immunohistochemistry evaluation. Our findings clearly demonstrate that vascularized breast cancer microtissues could be engineered and recapitulate the in vivo situation and tumor-stromal interaction within an isolated environment in an in vivo organism. Alginate–fibrin hybrid matrices were considered as a highly powerful material for breast tumor engineering based on its stability and biocompatibility. We propose that the novel tumor model may not only serve as an invaluable platform for analyzing and understanding the molecular mechanisms and pattern of oncologic diseases, but also be tailored for individual therapy via transplantation of breast cancer patient-derived tumors. [ABSTRACT FROM AUTHOR]

Microvascular reconstruction frequently requires anastomosis outside of the zone of injury for successful reconstruction. Multiple options exist for pedicle lengthening including vein grafts, arteriovenous loops, and arteriovenous bundle interposition grafts. The authors performed a systematic review of arteriovenous bundle interposition grafts to elucidate indications and outcomes of arteriovenous grafts in microvascular reconstruction. A systematic review of the literature was performed using targeted keywords. Data extraction was performed by two independent authors, and descriptive statistics were used to analyze pooled data. Forty-four patients underwent pedicle lengthening with an arteriovenous graft from the descending branch of the lateral circumflex femoral artery. Most common indications for flap reconstruction were malignancy (n=12), trauma (n=7), and diabetic ulceration (n=4). The most commonly used free flap was the anterolateral thigh flap (n=18). There were five complications, with one resulting in flap loss. Arteriovenous bundle interposition grafts are a viable option for pedicle lengthening when free flap distant anastomosis is required. The descending branch of the lateral circumflex femoral artery may be used for a variety of defects and can be used in conjunction with fasciocutaneous, osteocutaneous, muscle, and chimeric free flaps. [ABSTRACT FROM AUTHOR]

Massive segmental bone defects (SBD) are mostly treated by removing the fibula and transplanting it complete with blood supply. While revolutionary 50 years ago, this remains the standard treatment. This review considers different strategies to repair SBD and emerging potential replacements for this highly invasive procedure. Prior to the technical breakthrough of microsurgery, researchers in the 1960s and 1970s had begun to make considerable progress in developing non autologous routes to repairing SBD. While the breaktthrough of vascularised bone transplantation solved the immediate problem of a lack of reliable repair strategies, much of their prior work is still relevant today. We challenge the assumption that mimicry is necessary or likely to be successful and instead point to the utility of quite crude (from a materials technology perspective), approaches. Together there are quite compelling indications that the body can regenerate entire bone segments with few or no exogenous factors. This is important, as there is a limit to how expensive a bone repair can be and still be widely available to all patients since cost restraints within healthcare systems are not likely to diminish in the near future. This review is significant because it is a multidisciplinary view of several surgeons and scientists as to what is driving improvement in segmental bone defect repair, why many approaches to date have not succeeded and why some quite basic approaches can be as effective as they are. While there are many reviews of the literature of grafting and bone repair the relative lack of substantial improvement and slow rate of progress in clinical translation is often overlooked and we seek to challenge the reader to consider the issue more broadly. [Display omitted] [ABSTRACT FROM AUTHOR]

The arteriovenous loop (AVL) model allows the in vivo engineering of axially vascularized flaps, the so-called AVL flaps. Although AVL flaps can be transplanted microsurgically to cover tissue defects, they lack an epithelial layer on the surface. Therefore, the objective of this study was to engineer axially vascularized AVL flaps with an accompanying epithelial layer for local defect reconstruction. In this study, AVLs were established in 20 male Lewis rats. Minimally invasive injection of keratinocytes onto the surface of the AVL flaps was performed on postoperative day (POD) 21. AVL flaps were explanted from 12 rats on POD 24 or POD 30, then the epithelium formed by the keratinocytes on the surface of the flaps was evaluated using immunofluorescence staining. In six other rats, the AVL flap was locally transposed to cover a critical defect in the rats' leg on POD 30 and explanted for analysis on POD 40. In two control rats, sodium chloride was applied instead of keratinocytes. These control flaps were also transplanted on POD 30 and explanted on POD 40. Our results revealed that 3 days after keratinocyte application, a loose single-layered epithelium was observed histologically on the AVL flaps surface, whereas after 9 days, a multilayered and structured epithelium had grown. The epithelium on the transplanted AVL flaps showed its physiological differentiation when being exposed to an air-liquid interface. Histologically, a layered epithelium identical to the rats' regular skin was formed. In the sodium chloride control group, no epithelium had been grown. This study clearly demonstrates that axially vascularized AVL flaps can be processed in the subcutaneous chamber by minimally invasive injection of keratinocytes. Thus, AVL flaps with an intact epithelial layer were engineered and could be successfully transplanted for local defect coverage in a small animal model.

Mechanically processed stromal vascular fraction (mSVF) is a promising source for regenerative purposes. To study the in vivo fate of the mSVF, we herein used a vascularized tissue engineering chamber that insulates the target mSVF from the surrounding environment. In contrast to previous models, we propose an arteriovenous (AV) shunt between saphenous vessels in rats without a venous graft. Mechanical SVF was processed from the fat pads of male Sprague Dawley rats, mixed with a fibrin hydrogel and implanted into an inguinal tissue engineering chamber. An arteriovenous shunt was established between saphenous artery and vein. On the contralateral side, an mSVF-fibrin hydrogel mix without vascular axis served as a non-vascularized control. After two and six weeks, rats were sacrificed for further analysis. Mechanical SVF showed significant numbers of mesenchymal stromal cells. Vascularized mSVF explants gained weight over time. Perilipin and CD31 expression were significantly higher in the mSVF explants after six weeks while no difference in DAPI positive cells, collagen deposition and FABP4 expression was observed. Morphologically, no differentiated adipocytes but a dense cell-rich tissue with perilipin-positive cells was found after six weeks. The phosphorylation of ERK1/2 was significantly enhanced after six weeks while Akt activation remained unaltered. Finally, mSVF explants stably expressed and released VEGF, bFGF and TGFb. Vascularized mSVF is able to proliferate and express adipocyte-specific markers. The AV shunt model is a valuable refinement of currently existing AV loop models in the rat which contributes to the fundamental 3R principles of animal research.

Free flaps in combination with arterial reconstruction by means of arteriovenous loops or bypass have, meanwhile, been established as a therapeutic option in defect reconstruction for areas without recipient vessels. Our aim was to analyse the long‐term performance, flap autonomy, and the flap perfusion. Patients receiving this combined reconstruction at a single‐centre institution were included. During follow‐up examination, the patency of arterial reconstruction was investigated by duplex ultrasound. Flap micro‐circulation was assessed by laser Doppler flowmetry and white light tissue spectrometry (O2C) as well as by indocyanine green fluorescence angiography. Twenty‐three patients could be clinically followed up. Duplex ultrasound showed, in four cases, arterial pedicle occlusion in spite of vital flap. Comparison of the O2C perfusion parameters between flaps with occluded pedicles and those with intact inflow showed no significant difference (parameters sO2: P =.82; Flow: P =.31). Similar results were obtained by fluorescence angiography; no significant difference could be detected between both groups (parameters Ingress P =.13; Ingressrate P =.54). Combined vascular reconstruction with free tissue transfer is associated with a good long‐term outcome and wound closure. Even after flap transplantation to areas with critical tissue perfusion, the flap can develop autonomy and thus survive after pedicle occlusion. [ABSTRACT FROM AUTHOR]

Loss of penis due to injury or disease is physically and psychologically devastating to any male. While the technique of penile reconstruction continues to evolve in conjunction with the evolution of flaps in reconstructive surgery, the free tissue transfer using radial artery forearm flap (RAFF) in a single stage is recognized as the most preferred method at present. However, to avoid the complications often seen in such single-stage method, we used a novel two-stage technique for total penile reconstruction in two cases after penile loss. We prefabricated the neophallus in the forearm and constructed saphenofemoral arteriovenous loop in the groin in the first stage to allow all the suture lines to heal and provide for easy and reliable recipient vessels. The neophallus was transferred after 4 weeks and vessel anastomoses done conveniently in the groin with adequate sized vessels with robust inflow. Both the patients recovered well without any need for urinary diversion and quickly attained the ability to pass urine in standing position. We offer that the two-stage method of penile reconstruction using free RAFF is reliable, easy to perform and can avoid many of the complications seen with single-stage reconstruction.

Objective: To evaluate the safety and efficacy of transcatheter closure for Perimembranous Vetrntricularseptal defect (pm VSD) without arteriovenous (AV) loop. The most common congenital heart defect is PMVSD. Transcatheter closure of PMVSD without AV loop is a recently described technique with limited results for follow-up. Study Design: Retrospective analytical study. Place and Duration of Study: Paediatric Cardiology, Armed Forces Institute of Cardiology and National Institute of Heart Diseases, Rawalpindi Pakistan, from Jan 2015 to Oct 2018. Method and Methods: Total of 30 patients with PMVSD were enrolled in this retrospective analytical study and treated percutaneously with VSD occluders. Results: All patients were followed up to date. According to colour Doppler transthoracic echocardiography the mean ± SD end-diastolic PMVSD size was 4.87 ± 1.32mm. Placement of the device was successful in all patients (100%) and the mean ± SD device size 7 ± 1.58mm. During follow-up, No major adverse events were reported. Conclusions: In experienced hands, transcatheter PMVSD closure without AV loop can be performed safely and successfully with low morbidity and mortality. Short-term results are favorable, and the transcatheter approach provides a less-invasive alternative that may become the first choice in selected pmVSD patients. [ABSTRACT FROM AUTHOR]

Background and objectives: Complex limb traumas are commonly treated with microsurgical reconstruction and free flaps. However, complications are frequent in patients affected by a previous trauma or comorbidity, atheromasia and a single valid vessel. Free flap reconstruction is indeed a challenging procedure in complex injuries, which may increase the risk of limb ischemia. The Arteriovenous loop (AVL) technique may be considered an efficient alternative treatment. We herein report our procedure and previous research regarding the AVL method using a two-step reconstruction in cases of complex high-energy limb injuries. Materials and Methods: In this single center retrospective cohort study, all the patients from 2014 to 2018 who underwent to AVL reconstruction were assessed. A total of six patients were included in the study for traumatic limb trauma. The two-stage technique was performed each time. The age and sex of patient, the time between stage one and two, the length of AVL loop and rate of free flap success were evaluated. Results: A total of seven AVL reconstructions were performed. The mean age of patients was 36 years old. Eight free flaps were performed; six free flaps were transferred to the vascular loops. The average time between stage one and two was 13 days. The mean length of the pedicle was 25 cm for the upper limb and 33.7 cm for the lower limb. All the free flaps successfully take root. In one case, a surgical revision was required the second day post-operatory due to venous congestion. Conclusions: AVL is a useful and safe technique in microsurgical reconstruction which will prevent vascular complications. Our investigations suggest the efficacy and feasibility of a two-step intervention in acute post-traumatic events. A single-step procedure should be preferred in chronic situation and oncologic reconstruction.

Major defects of the facial structures cause severe functional and esthetic impairment. Difficulty in head and neck reconstruction lies in cases of secondary, tertiary, or further reconstruction. This is not a rare situation for patients who had cancer of the upper airways, since the rate of recurrence, second location, or osteoradionecrosis is high. Multiple surgeries and radiation therapy cause significant fibrosis and scar tissues, making any further reconstruction a major challenge for the surgeon when operating patients with vessel- depleted neck. We report our experience with a clinical case of a patient to whom we performed a double free flap reconstruction anastomosed on a vascular loop in a context of vascular cervical desert. In our case, the use of an arteriovenous loop proved to be a reliable approach for a vessel-depleted free tissue reconstruction. This technique has received insufficient attention, yet it provides a means to establish dependable vascular alternatives., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Masson SAS. All rights reserved.)

Background  Regenerative medicine is still deficient in the reconstruction after cancer due to impaired vascularization after radiotherapy and due to the need to substitute larger defects after tumor excision. Aiming at introducing regenerative medicine for reconstruction after cancer, we tested an axially vascularized bone construct in an experimental setting that mimics the clinical situation after tumor resection and adjuvant radiotherapy. Methods  Twenty bone constructs were axially vascularized using microsurgically created arteriovenous loops and were implanted subcutaneously in Lewis rats. After 2 weeks, the animals were randomly allocated either to receive a clinically relevant single dose of external beam irradiation or not (n  = 10 for each group). The animals were sacrificed either after 1 week or 10 weeks after irradiation (n  = 5 for each time point). The constructs were tested for vascularization, tissue growth, cellular proliferation, cellular apoptosis, and osteogenic differentiation via histomorphometric, immunohistochemical, and polymerase chain reaction (PCR) analysis. One construct per group was subjected at 10 weeks to qualitative micro-computed tomography (CT) imaging. Results  Tissue generation and cellular proliferation were significantly reduced at 1 week after irradiation, but no longer significantly different after 10 weeks. No significant differences in vascularization were detected at any time point. Apoptosis did not show any statistically significant differences between both groups at both time points. At the late time point, mature bone was considerably more in the irradiated group, but the results were not statistically significant. PCR analysis showed a significantly enhanced expression of osteocalcin in the irradiated group at 1 week. Micro-CT imaging showed that both constructs were adequately vascularized with no evident morphologic differences regarding vascular density or vascular distribution. Conclusions  Axially vascularized bone constructs can withstand clinically relevant doses of irradiation and retain their angiogenic and osteogenic potential in the long term. Irradiation led to a delayed tissue generation with a comparatively enhanced osteogenic differentiation within the constructs. [ABSTRACT FROM AUTHOR]

Background: Most of the current treatment options for large-scale tissue defects represent a serious burden for the patients, are often not satisfying, and can be associated with significant side effects. Although major achievements have already been made in the field of tissue engineering, the clinical translation in case of extensive tissue defects is only in its early stages. The main challenge and reason for the failure of most tissue engineering approaches is the missing vascularization within large-scale transplants. Summary: The arteriovenous (AV) loop model is an in vivo tissue engineering strategy for generating axially vascularized tissues using the own body as a bioreactor. A superficial artery and vein are anastomosed to create an AV loop. This AV loop is placed into an implantation chamber for prevascularization of the chamber inside, e.g., a scaffold, cells, and growth factors. Subsequently, the generated tissue can be transplanted with its vascular axis into the defect site and anastomosed to the local vasculature. Since the blood supply of the growing tissue is based on the AV loop, it will be immediately perfused with blood in the recipient site leading to optimal healing conditions even in the case of poorly vascularized defects. Using this tissue engineering approach, a multitude of different axially vascularized tissues could be generated, such as bone, skeletal or heart muscle, or lymphatic tissues. Upscaling from the small animal AV loop model into a preclinical large animal model could pave the way for the first successful attempt in clinical application. Key Messages: The AV loop model is a powerful tool for the generation of different axially vascularized replacement tissues. Due to minimal donor site morbidity and the possibility to generate patient-specific tissues variable in type and size, this in vivo tissue engineering approach can be considered as a promising alternative therapy to current treatment options of large-scale defects. [ABSTRACT FROM AUTHOR]

Summary Defect reconstruction of the trunk can be performed using microsurgical free flap transplantation. In cases of missing or inappropriate recipient vessels, microsurgical defect reconstruction of the trunk can be achieved by combining free flaps with arteriovenous loops. Here we present our 5-year experience of trunk reconstruction using AV loops and free flaps in a retrospective evaluation. We analyzed 32 cases of trunk reconstruction using a combined approach of free flap transplantation and arteriovenous loops between 2011 and 2016 regarding postoperative complications and perioperative course. Twenty-one patients suffered from sternal defects, 4 from presacral defects, 3 patients presented with lateral chest wall defects, 2 patients suffered from lumbosacral defects, 1 patient had a gluteal defect and 1 patient a defect at the clavicle. In all cases, free flap transplantation and arteriovenous loop creation were performed in a two-stage procedure. There were 8 thromboses of the arteriovenous loops with 4 flap failures. Only 1 flap loss was located in the sternal region, whereas one presacral flap and both lumbosacral flaps were lost. Reconstruction of large soft tissue defects of the trunk by a combined approach with an arteriovenous loop creation and consecutive free flap transplantation represents a reliable procedure in ventral and posterior cranial localization, whereas in the caudal posterior region, AV loop thrombosis can occur. Therefore, to minimize flap loss, a two-stage procedure should be performed. [ABSTRACT FROM AUTHOR]

Objetivos: se describe la experiencia del cierre endovascular de comunicación interventricular realizada durante tres años en diferentes centros de cardiología intervencionista, y se destaca el resultado en un grupo de pacientes seleccionados en quienes dicho procedimiento se efectuó mediante el uso de un dispositivo de última generación diseñado para el cierre de ductus arterioso. Pacientes: entre junio de 2006 hasta octubre de 2009 se sometió un total de 34 pacientes a la técnica de oclusión de comunicación interventricular por vía endovascular. La indicación del procedimiento incluyó sobrecarga de volumen, sobrecarga de presión y volumen, falla cardiaca crónica, prolapso de válvula aórtica con insuficiencia y lesión traumática. La edad promedio fue de 12,9 años y el peso fue de 36 kilos. Se evidenció un predominio del sexo masculino (53%). El promedio de cálculo de flujos demostró Qp/Qs de 1,71 a 1 y el de resistencias vasculares pulmonares fue 1,18 U Wood/m2. Materiales y Métodos: el dispositivo PM VSD Occluder se implantó con la técnica clásica (62,5%) mientras que el dispositivo Duct Occluder II (28,1%) se utilizó con la técnica simplificada propuesta. Se usó anestesia general en 98% de los casos, 60% fueron guiados con fluoroscopia y ecocardiografía transesofágica y 40% con transtorácica. Resultados: el tamaño del defecto varió entre 4 y 12 mm. El 91% de los pacientes tenía un defecto septal aislado. La mediana del tiempo quirúrgico se cuantificó en 56 minutos, siendo mayor en el grupo en el cual se utilizó la técnica clásica (85 min) en comparación con aquel grupo en el que se empleó la técnica simplificada con un promedio de 36 minutos. El promedio de estancia hospitalaria se estimó en 36 horas. Seguimiento: se documentó el cierre completo en 100% a los 30 días. Hubo tres eventos adversos por complicaciones menores relacionadas con disturbios transitorios en el ritmo. Siete pacientes (21,9%) acusaron aparición o acentuación de episodios de cefalea vascular migrañosa. Hubo una complicación mayor dada por bloqueo atrioventricular completo y embolización del dispositivo. Conclusiones: el cierre endovascular de la comunicación interventricular es un procedimiento factible en nuestro medio, con el cual se alcanza un éxito cercano al 100%. El dispositivo para cierre de ductus de última generación puede implantarse con modificaciones en la técnica que aminora los tiempos de operatividad (hasta 60%), anestesia, utilización de medio de contraste y estancia hospitalaria. Por otra parte, su perfil hace posible el uso de sistemas de entregas 4 French que posibilitaría la inclusión de lactantes menores.Objectives: we describe the experience of the endovascular closure of interventricular communication performed for three years in different centers of interventional cardiology and highlight its result in a group of selected patients in whom such procedure was made by the use of a last generation device designed for the closure of ductus arteriosus. Methodology: between June 2006 and October 2009, a total of 34 patients underwent endovascular occlusion for interventricular septal defect. Indication of this procedure included volume overload, pressure and volume overload, chronic congestive heart failure, aortic valve prolapse with insufficiency and traumatic injury. Mean age was 12,9 years old and mean weight was 36 kg. A prevalence in male gender (53%) was evidenced. Main blood flow calculation showed Qp / Qs of 1.71 to 1 and the pulmonary vascular resistance was 1.18 U Wood/m2. Materials and methods: PM VSD occluder device was implanted with the classic technique (62,5%) while the Duct Occluder II (28,1%) was used with the proposed simplified technique. General anesthesia was used in 98% cases; 60% were guided by fluoroscopy and transesophageal echocardiography and 40% with transthoracic echocardiography. Results: size of the defect varied from 4 to 12 mm. 91% of patients had an isolated septal defect. Mean surgical time was 56 min, being longer in the group in which the classic technique was used (85 min) compared with the group in which the technique used was the simplified one, with a mean duration of 36 min. Mean hospital stay was estimated in 36 hours. Follow up: complete closure was documented in 100% of patients at 30 days. There were three adverse events due to minor complications related to transient rhythm disturbances. A total of seven patients (21.9%) complained onset or exacerbation of vascular migraine headache episodes. There was one major complication due to complete atrioventricular block and embolization of the device. Conclusions: endovascular closure of interventricular septal defect is a feasible procedure in our country achieving a success closure in 100% of the patients. The latest generation device for closure of the ductus may be implanted with modifications in the technique that reduce surgical time (up to 60%), anesthesia, use of contrast media and hospital stay. Moreover, its profile makes possible the use of 4 French delivery systems that would make possible the inclusion of younger infants.

The survival of engineered tissue constructs during the initial phase after their implantation depends on the rapid development of an adequate vascularization. This, in turn, is a major prerequisite for the constructs' long-term function. ‘Prevascularization’ has emerged as a promising concept in tissue engineering, aiming at the generation of a preformed microvasculature in tissue constructs prior to their implantation. This should shorten the time period during which the constructs are avascular and suffer hypoxic conditions. Herein, we provide an overview of current strategies for the generation of preformed microvascular networks within tissue constructs. In vitro approaches use cell seeding, spheroid formation or cell sheet technologies. In situ approaches use the body as a natural bioreactor to induce vascularization by angiogenic ingrowth or flap and arteriovenous (AV)-loop techniques. In future, these strategies may be supplemented by the transplantation of adipose tissue-derived microvascular fragments or the in vitro generation of highly organized microvascular networks by means of sophisticated microscale technologies and microfluidic systems. The further advancement of these prevascularization concepts and their adaptation to individual therapeutic interventions will markedly contribute to a broad implementation of tissue engineering applications into clinical practice. [ABSTRACT FROM AUTHOR]

Background The Arterovenous Loop (AV Loop) model is a vascularization model in tissue engineering research, which is capable of generating a three dimensional in vivo unit with cells as well as the supporting vessels within an isolation chmaber. In our previous studies the AV loop in the isolation chamber was discovered to undergo hypoxia, characterized by Hypoxia Inducible Factor (HIF) up-regulation. The vascularization followed the increase of HIF-1α temporally, while it was spatially positively correlated with the HIF-1α level, as well. This study aims to prove that HIF-1a up-regulation is the stimulus for vascularization in the AV loop model. Method The AV loop model in rats was created by interposing a femoral vein graft into the distal ends of the contralateral femoral artery and vein, and the loop was embeded in fibrin matrix and fixed in isolation chamber. PHD (prolyl hydroxylases) inhibitor DMOG (Dimethyloxallyl Glycine) was applied systemically in the rats in 40mg/KG at day 0 and day 3 (DMOG-1), or in 15mg/KG at day 8, day10 and day12 (DMOG-2). Two weeks later the specimens were explanted and underwent morphological and molecular evaluations. Results Compared to the control group, in the DMOG-2 group the HIF-1α positive rate was siginicantly raised as shown in immunohistochemistry staining, accompanied with a smaller cross section area and greater vessel density, and a HIF-11α accumulation in the kidney. The mRNA of HIF-11α and its angiogenic target gene all increased in different extends. Ki67 IHC demostrate more positive cells. There were no significant change in the DMOG-1 group. Conclusion By applying DMOG systemically, HIF-11α was up-regulated at the protein level and at the mRNA level, acompanied with angiogenic target gene up-regulateion, and the vascularization was promoted correspondingly. DMOG given at lower dosage constantly after one week tends to have better effect than the group given at larger dosage in the early stage in this model, and promotes cell proliferation, as evidenced by Ki67 IHC. Thus, this study proves that HIF-1a up-regulation is the stimulus for vascularization in the AV loop model and that the process of the vessel outgrowth can be controlled in the AV Loop model utilizing this mechanism. [ABSTRACT FROM AUTHOR]

Objective: Reconstruction of large and complex bone segments is a challenging problem facing maxillofacial surgery. The majority of current regenerative approaches rely on extrinsic vascularization, which is deficient after cancer ablation and irradiation. The aim of the study was to investigate the efficacy of intrinsic axial vascularization of synthetic bone scaffolds in the management of critical-size mandibular defects. Materials and methods: Scaffold-guided mandibular regeneration in two groups of adult male goats was compared. Only the scaffolds of the second group were axially vascularized via in situ embedding of an arteriovenous loop through microsurgical anastomosis of facial vessels. After 6 months of follow up, both groups were compared through radiological, biomechanical, histological and histomorphometric analysis. Results: The axially vascularized constructs have showed significantly more central vascularization ( p = 0.021) and markedly enhanced central bone formation ( p = 0.08). The biomechanical characteristics were enhanced, but the difference between both groups was not statistically significant ( p = 0.98). Conclusions: Axially vascularized synthetic mandibular grafts show better vascularization at their central regions, permitting more efficient bone regeneration. Clinical relevance: The encouraging results of the proposed technique could be of benefit in optimizing the reconstruction of large critical-size bone defects. [ABSTRACT FROM AUTHOR]

Tissue Engineering (TE) and Regenerative Medicine (RM) have gained much popularity because of the tremendous prospects for the care of patients with tissue and organ defects. To overcome the common problem of donor-site morbidity of standard autologous bone grafts, we successfully combined tissue engineering techniques for the first time with the arteriovenous loop model to generate vascularized large bone grafts. We present two cases of large bone defects after debridement of an osteomyelitis. One of the defects was localized in the radius and one in the tibia. For osseus reconstruction, arteriovenous loops were created as vascular axis, which were placed in the bony defects. In case 1, the bone generation was achieved using cancellous bone from the iliac crest and fibrin glue and in case 2 using a clinically approved β-tricalciumphosphate/hydroxyapatite (HA), fibrin glue and directly auto-transplanted bone marrow aspirate from the iliac crest. The following post-operative courses were uneventful. The final examinations took place after 36 and 72 months after the initial operations. Computer tomogrphy (CT), membrane resonance imaging (MRI) and doppler ultrasound revealed patent arterio-venous (AV) loops in the bone grafts as well as completely healed bone defects. The patients were pain-free with normal ranges of motion. This is the first study demonstrating successfully axially vascularized in situ tissue engineered bone generation in large bone defects in a clinical scenario using the arteriovenous loop model without creation of a significant donor-site defect utilizing TE and RM techniques in human patients with long-term stability. [ABSTRACT FROM AUTHOR]

Thoracoabdominal defects usually result from trauma, tumour resection, infection or they may be congenital. Reconstruction of these defects is absolutely necessary, for function preservation, especially in cases of full-thickness and complex defects. Use of flaps or combination of flaps and alloplastic materials is usually the key to a successful reconstruction. Several different methods for the reconstruction of thoracoabdominal defects have been described with very good to excellent results. We present the case of a 69-year-old patient who presented to our unit with a rapidly growing mass on the right lateral thoracoabdominal wall. After full-thickness tumour resection, the defect was reconstructed by using a free anterolateral thigh flap along with the central part of the vastus lateralis muscle and a larger surrounding part of the fascia lata. The ipsilateral greater saphenous vein was dissected to mid-calf, reversed and anastomosed to the femoral artery in an end to side fashion thus creating an arteriovenous loop which was later divided in the middle, for anastomoses with flap's vessels. Flap survived in its entity without any complication from the donor or the recipient site. The patient had an uneventful recovery and left the hospital 7 days later. No abdominal wall herniation was noted on 3 months of follow-up. Single-stage reconstruction of complex lateral thoracoabdominal defect by using free anterolateral thigh together with a part of the fascia lata and an arteriovenous loop might be a reliable solution in cases where proper vessels are not available for anastomosis or other options are not feasible. Level of Evidence: Level V, therapeutic study. [ABSTRACT FROM AUTHOR]

Résumé: La réussite du transfert des lambeaux libres dépend de la qualité des micro-anastomoses mais aussi de celle des vaisseaux receveurs (VR). Dans certaines situations, les VR voisins de la perte de substance sont inutilisables, soient qu’ils aient été détruits, soient altérés. Un allongement du pédicule du lambeau est alors nécessaire, soit de l’artère, soit de la veine ou des deux. Cet allongement peut s’effectuer de deux manières : par interposition de greffons veineux (GV) ou par réalisation d’une boucle vasculaire (BV). La BV trouve sa principale indication dans le cas où artère et veine nécessitent un allongement. Deux types principaux de BV sont utilisées : celles avec GV et celles « in situ ». Les BV vasculaires peuvent être réalisées en un ou deux temps. Chaque technique présente des avantages et des inconvénients. La technique de BV est indiquée en cas de VR inutilisables : artère et/ou veine. Aucun consensus fort sur les avantages des BV en un ou deux temps ne ressort, même si la littérature tend à montrer une supériorité des BV en un temps. La technique de la BV apparaît plus avantageuse que la technique des GV interposés, même si le taux de succès est moins important qu’avec les lambeaux libres anastomosés directement. D’autres études sont nécessaires afin de répondre à toutes ces questions controversées. [ABSTRACT FROM AUTHOR]

Objective: Free tissue transfer is widely used for head and neck reconstruction. In certain circumstances, vein grafting is required to elongate free flap pedicles to connect them to appropriate recipient vessels. Because of controversy regarding the use of interposition vein grafts in free tissue reconstruction, this paper reports vein graft indications, techniques, safety, and outcomes for head and neck microvascular surgery., Methods: Twenty-six patients (23 men and 3 women) who underwent interposition vein grafting concurrent with free tissue transfer were included in this study. The most common reason for head and neck reconstruction with vein graft was tumor recurrence, followed by flap salvage. The interposition vein grafts were applied in two manners as temporary arteriovenous (A-V) loop and conduit to extend the length of the free flap for venous drainage., Results: The most common reconstructions were anterolateral thigh flaps (15 cases), followed by vastus lateralis myocutaneous (3 cases) and radial forearm (2 cases) flaps. The common recipient vessels were superior thyroid artery, superficial temporal artery and external jugular vein. The free flap loss rate was 7.7% with vein grafts and 4.9 without vein grafts (p = 0.380). The free flap complication rate was 50.0% and 16.8% in patients with and without vein grafts, respectively (p < 0.001). Radiation therapy, chemotherapy, prior neck dissection, and prior free flap transfer were more common in the vein graft group (all p < 0.001). The hospital stay was significantly longer for the vein graft group than for the non-vein graft group (29.5 vs. 19.0 days; p = 0.001)., Conclusion: Overall free flap survival rates of 92.3% and 95.1% in the vein and non-vein graft groups, respectively - indicating the reliability of the vein grafts in challenging head and neck reconstructions, particularly in salvage cases and patients with multiple reconstructions., Level of Evidence: Level 3., (Copyright © 2021 Associação Brasileira de Otorrinolaringologia e Cirurgia Cérvico-Facial. Published by Elsevier Editora Ltda. All rights reserved.)

Abstract: The most important problem for the survival of thick 3-dimensional tissues is the lack of vascularization in the context of bone tissue engineering. In this study, a modified arteriovenous loop (AVL) was developed to prefabricate an axial vascularized tissue engineering coral bone in rabbit, with comparison of the arteriovenous bundle (AVB) model. An arteriovenous fistula between rabbit femoral artery and vein was anastomosed to form an AVL. It was placed in a circular side groove of the coral block. The complex was wrapped with an expanded-polytetrafluoroethylene membrane and implanted beneath inguinal skin. After 2, 4, 6 and 8weeks, the degree of vascularization was evaluated by India ink perfusion, histological examination, vascular casts, and scanning electron microscopy images of vascular endangium. Newly formed fibrous tissues and vasculature extended over the surfaces and invaded the interspaces of entire coral block. The new blood vessels robustly sprouted from the AVL. Those invaginated cavities in the vascular endangium from scanning electron microscopy indicated vessel''s sprouted pores. Above indexes in AVL model are all superior to that in AVB model, indicating that the modified AVL model could more effectively develop vascularization in larger tissue engineering bone. [Copyright &y& Elsevier]

The aim of this in vivo study was to gather quantitative information on the three-dimensional morphology of a new vascular network under the influence of angioactive growth factors. For this purpose, the arteriovenous loop model was used in 10 Lewis rats to generate a bioartificial vascular assembly by means of vascular induction. In this model, an isolated organoid is created in the medial thigh of the animal by methods of tissue engineering. A fibrin gel containing vascular endothelial growth factor (VEGF165) and basic fibroblastic growth factor (bFGF) was used as a matrix in the effect group (GF+). Fibrin matrices devoid of growth factors were used as controls (GF−). A microvascular replica of the organoid was created by means of corrosion casting and the network was investigated on stereo-paired images obtained by scanning electron microscopy. Vectors of intercapillary and interbranching distances as well as the diameter of the pores in the intussusceptive events diameter and the ratio of sprouting versus intussusceptive angiogenic events were compared in the two groups. The results were highly significant. In the GF+ group there were more profound three-dimensional morphological traits of angiogenesis, whereas advanced neovascularisation in the phase of remodelling was demonstrated by a higher incidence of intussusception, compared to control. These results illustrate the importance of morphological studies with focus on the generation of three-dimensional vascular networks. [ABSTRACT FROM AUTHOR]

In later stages of vasculoangiogenesis a vascular network is going through a metamorphosis for optimal perfusion and economy of energy. In this study we make a quantitative approach to phenomena of remodelling in a bioartificial neovascular network and suggest variance of calibre as a parameter of neovascular maturation. For this study, 18 male Lewis rats were subjected to the AV loop operation in combination with a hard porous biogenic matrix and an isolation chamber. The animals were allocated into three groups for different explantation intervals set to 2, 4 and 8 weeks, respectively. Collective attributes like vascular density, percent fractional area and variance of calibre were evaluated for a predefined region of interest (ROI). Late morphogenesis was evaluated by means of scanning electron microscopy. After the fourth week the absolute number of vessels within the ROI decreased ( P < 0.03) whereas, on the contrary, the fractional area of all segments increased ( P < 0.02). The variance in calibre was significantly increased in the 8-week group ( P < 0.05). Lymphatic growth after week 4, early pericyte migration as well as intussusceptive angiogenesis were identified immunohistologically. Phenomena of remodelling were evaluated quantitatively in a neovascular network and variance could be proposed as a parameter of net vascular maturation. [ABSTRACT FROM AUTHOR]

Mechanically processed stromal vascular fraction (mSVF) is a promising source for regenerative purposes. To study the in vivo fate of the mSVF, we herein used a vascularized tissue engineering chamber that insulates the target mSVF from the surrounding environment. In contrast to previous models, we propose an arteriovenous (AV) shunt between saphenous vessels in rats without a venous graft. Mechanical SVF was processed from the fat pads of male Sprague Dawley rats, mixed with a fibrin hydrogel and implanted into an inguinal tissue engineering chamber. An arteriovenous shunt was established between saphenous artery and vein. On the contralateral side, an mSVF-fibrin hydrogel mix without vascular axis served as a non-vascularized control. After two and six weeks, rats were sacrificed for further analysis. Mechanical SVF showed significant numbers of mesenchymal stromal cells. Vascularized mSVF explants gained weight over time. Perilipin and CD31 expression were significantly higher in the mSVF explants after six weeks while no difference in DAPI positive cells, collagen deposition and FABP4 expression was observed. Morphologically, no differentiated adipocytes but a dense cell-rich tissue with perilipin-positive cells was found after six weeks. The phosphorylation of ERK1/2 was significantly enhanced after six weeks while Akt activation remained unaltered. Finally, mSVF explants stably expressed and released VEGF, bFGF and TGFb. Vascularized mSVF is able to proliferate and express adipocyte-specific markers. The AV shunt model is a valuable refinement of currently existing AV loop models in the rat which contributes to the fundamental 3R principles of animal research. [ABSTRACT FROM AUTHOR]

Abstract: The arteriovenous loop (AV loop) model is gaining importance as a means of initiating and sustaining perfusion in tissue engineering constructs in vivo. This study represents an attempt to dissect the morphology of early arterialization and angiogenesis in the AV loop in a fibrin matrix with special focus on the interpositional venous graft (IVG) segment. An AV loop was constructed in 30 rats using the femoral vessels and an IVG. The AV loop was encased in an isolation chamber filled with a fibrin matrix. Evaluation methods included scanning electron microscopy (SEM) of corrosion casts, immune histology and micro magnetic resonance angiography (MRA). Direct luminal neovascular sprouting was evident between day 10 and day 14 from the vein and the IVG but not from the arterial segment. Arterialization of the IVG manifested itself on the corrosion casts as a gradual reduction in luminal caliber with onset after day 7. Microdissection of the microvascular replicas could demonstrate for the first time the presence of direct luminal sprouts from the IVG. MRA was used to display the shunt pattern of perfusion in the patent AV loop. From the three segments of the vascular axis in the AV loop the IVG is the most versatile for applications in the clinical as well as the experimental setting. Kinetics of angiogenesis warrant further investigation in the IVG. [Copyright &y& Elsevier]

In tissue engineering cell cultures play a crucial role besides the matrix materials for the end of substituting lost tissue functions. The cell itself is situated at the cross-roads leading to different orders of scale, from molecule to organism and different levels of function, from biochemistry to macrophysiology. Extensive in vitro investigations have dissected a vast amount of cellular phenomena and the role of a number of bioactive substances has been elucidated in the past. Further, recombinant DNA technologies allow modulation of the expression profiles of virtually all kinds of cells. However, issues of vascularization in vivo limit transferability of these observations and restrict upscaling into clinical applications. Novel in vivo models of vascularization have evolved inspired from reconstructive microsurgical concepts and they encompass axial neovascularization by means of vascular induction. This work represents a brief description of latest developments and potential applications of neovascularization and angiogenesis in tissue engineering. [ABSTRACT FROM AUTHOR]

Abstract: Free tissue transfer has revolutionised reconstruction of the head and neck and there are currently few local factors that preclude its use. These include a lack of suitable recipient vessels in the area for microvascular anastomosis. We describe the use of a Corlett loop in which a temporary arteriovenous fistula (AVF) is created with a transposed cephalic vein to enable reconstruction of a mandibular defect with a fibular free flap. [Copyright &y& Elsevier]

Due to its low immunogenic potential and the possibility to fine-tune their properties, materials made of recombinant engineered spider silks are promising candidates for tissue engineering applications. However, vascularization of silk-based scaffolds is one critical step for the generation of bioartificial tissues and consequently for clinical application. To circumvent insufficient vascularization, the surgically induced angiogenesis by means of arteriovenous loops (AVL) represents a highly effective methodology. Here, previously established hydrogels consisting of nano-fibrillary recombinant eADF4(C16) were transferred into Teflon isolation chambers and vascularized in the rat AVL model over 4 weeks. To improve vascularization, also RGD-tagged eADF4(C16) hydrogels were implanted in the AVL model over 2 and 4 weeks. Thereafter, the specimen were explanted and analyzed using histology and microcomputed tomography. We were able to confirm biocompatibility and tissue formation over time. Functionalizing eADF4(C16) with RGD-motifs improved hydrogel stability and enhanced vascularization even outperforming other hydrogels, such as fibrin. This study demonstrates that the scaffold ultrastructure as well as biofunctionalization with RGD-motifs are powerful tools to optimize silk-based biomaterials for tissue engineering applications., (Creative Commons Attribution license.)

Introduction  Wound dehiscence is the most common complication after spinal fusion procedures, resulting in an increase in mortality rate and hospital length of stay. Reconstruction of these wounds presents a challenge, as the spine is dependent on these implants for stability and must be maintained throughout the wound dehiscence treatment protocol. We describe a method for extending the thoracodorsal pedicle with an arteriovenous loop to permit an increased excursion of the latissimus dorsi muscle in patients with exposed implants and present the results of this procedure. Materials and Methods  A retrospective review of patients treated with a latissimus free flap with saphenous vein pedicle extension for posterior spinal wounds from 2010 to 2020 were reviewed. Patient charts were reviewed for demographic information including comorbidities, previous spine operations, wound size and location, and postoperative complications including total flap loss, flap dehiscence, and need for secondary surgery. Results  Six patients were identified who underwent a total of eight extended pedicle free flaps. Mean age was 64.8 years with a mean follow-up of 12.3 months (range, 6-20 months). Four wounds were in the cervicothoracic region with two wounds in the cervical region. Mean number of previous spine surgeries was 3.5 (range, 2-4). Mean wound size was 189 cm 2 with a mean vein graft length of 28 cm. Wound coverage was successful in five of six patients. Major complications occurred in five of six patients. Total flap loss occurred in two patients (33%) and both underwent a second extended latissimus flap from the contralateral side. Three patients developed postoperative flap dehiscence which resolved with regular dressing changes. Conclusion  Extended pedicle latissimus flaps are an effective treatment for posterior spine wounds but are associated with a high complication rate, secondary to medically complex patients with multiple prior surgeries. Careful patient selection is critical for success., Competing Interests: Conflict of Interest None declared., (Society of Indian Hand Surgery & Microsurgeons. All rights reserved.)

Objective: To develop a novel approach for tissue engineering of soft-tissue flaps suitable for free microsurgical transfer, using an injectable nanofiber hydrogel composite (NHC) vascularized by an arteriovenous (AV) loop. Approach: A rat AV loop model was used for tissue engineering of vascularized soft-tissue flaps. NHC or collagen-elastin (CE) scaffolds were implanted into isolation chambers together with an AV loop and explanted after 15 days. Saphenous veins were implanted into the scaffolds as controls. Neoangiogenesis, ultrastructure, and protein expression of SYNJ2BP, EPHA2, and FOXC1 were analyzed by immunohistochemistry and compared between the groups. Rheological properties were compared between the two scaffolds and native human adipose tissue. Results: A functional neovascularization was evident in NHC flaps with its amount being comparable with CE flaps. Scanning electron microscopy revealed a strong mononuclear cell infiltration along the nanofibers in NHC flaps and a trend toward higher fiber alignment compared with CE flaps. SYNJ2BP and EPHA2 expression in endothelial cells (ECs) was lower in NHC flaps compared with CE flaps, whereas FOXC1 expression was increased in NHC flaps. Compared with the stiffer CE flaps, the NHC flaps showed similar rheological properties to native human adipose tissue. Innovation: This is the first study to demonstrate the feasibility of tissue engineering of soft-tissue flaps with similar rheological properties as human fat, suitable for microsurgical transfer using an injectable nanofiber hydrogel composite. Conclusions: The injectable NHC scaffold is suitable for tissue engineering of axially vascularized soft-tissue flaps with a solid neovascularization, strong cellular infiltration, and biomechanical properties similar to human fat. Our data indicate that SYNJ2BP, EPHA2, and FOXC1 are involved in AV loop-associated angiogenesis and that the scaffold material has an impact on protein expression in ECs., Competing Interests: S.K.R., J.M.S., and H.Q.M. are inventors on intellectual property covering the technology that has been filed by Johns Hopkins and have equity positions in LifeSprout, a privately held company that is seeking to bring these advances into clinical development. The content of this article was written by the authors listed. No ghostwriters were used to write this article., (Copyright 2020, Copyright © 2020 by Mary Ann Liebert, Inc., publishers.)