Introduction: Recipient site preparation using external volume expansion (EVE) increases graft survival in large-volume fat grafting. To improve patient compliance with using the device, we tested a new cyclic high negative-pressure (CHNP) mode that involves 1 h/day at -55 mm Hg, cycled between 1-second negative-pressure activation, followed by a 2-second deactivation period in an animal model. Material and Method: A miniaturized EVE device was applied to 30 8-week-old male Sprague-Dawley rats. The rats were assigned to 3 groups (no pressure for the control group, conventional -25 mm Hg for 8 h/day for conventional EVE, and CHNP mode for the CHNP group). After 28 days, micro-computed tomography was performed and skin biopsy specimens were obtained. Results: The CHNP group showed a 6.6-fold increase and the conventional EVE group showed a 4.4-fold increase in volume compared to the control group. Hematoxylin and eosin staining showed a similar increase in subcutaneous tissue thickness in both EVE groups, compared to the control group. Masson\'s trichome and proliferating cell nuclear antigen staining showed significantly higher collagen deposition and subdermal adipocytes in EVE groups. Immunohistochemistry against platelet endothelial cell adhesion molecule 1 showed 2.5- and 2.7-times higher vessel density in the conventional and CHNP EVE groups, respectively. There was no statistically significant difference in subcutaneous tissue thickness, collagen deposition, subdermal adipocyte proliferation, and vessel density between the 2 EVE groups. Conclusion: CHNP produced comparable results in recipient site preparation (subcutaneous tissue thickening and angiogenesis) compared to the conventional protocol, while markedly reducing the daily wear-time from 8 hours to 1 hour. Although further clinical data must be acquired, our new pressure setting seems promising and provides a more patient-friendly pre-expansion environment.
Introduction: La préparation du site receveur utilisant l’expansion de volume externe (EVE) augmente la survie d’une greffe dans une greffe de tissu adipeux de grand volume. Pour améliorer l’observance de l’utilisation du dispositif par le patient, nous avons testé un nouveau mode cyclique à forte pression négative (CHNP) qui implique 1 heure par jour à −55 mm Hg, dans un cycle entre une activation de pression négative 1-s suivie d’une période de désactivation de 2-s dans un modèle animal. Matériel et Méthode: Un dispositif EVE miniaturisé a été appliqué à 30 rats mâles Sprague-Dawley âgés de 8 semaines. Les rats ont été répartis en trois groupes (pas de pression dans le groupe témoin, pression conventionnelle de −25 mm Hg pendant 8 h/jour pour l’EVE conventionnelle et forte pression cyclique négative pour le groupe CHNP). Après 28 jours, une micro-tomodensitométrie (TDM) a été réalisée et des échantillons de biopsie de peau ont été prélevés. Résultats: Le groupe CHNP avait une augmentation de 6,6 fois, et le groupe d\'EVE conventionnelle présentait une augmentation de 4,4 fois le volume comparativement au groupe contrôle. La coloration à l’hématoxyline-éosine a mis en évidence une augmentation similaire de l’épaisseur du tissu sous-cutané dans les 2 groupes EVE, par rapport au groupe contrôle. Le trichrome de Masson et la coloration pour l’antigène nucléaire de prolifération cellulaire (PCNA) ont montré un dépôt de collagène significativement plus important et des adipocytes sous-dermiques plus nombreux dans les groupes EVE. L’immunohistochimie contre les molécules d’adhésion-1 des cellules endothéliales d’origine plaquettaire a montré une densité vasculaire plus élevée de 2,5 fois et 2,7 fois dans, respectivement, les groupes EVE conventionnelle et EVE CHNP. Il n’y a pas eu de différence statistiquement significative concernant l’épaisseur du tissu sous-cutané, le dépôt de collagène, la prolifération des adipocytes sous-dermiques et la densité des vaisseaux sanguins entre les deux groupes EVE. Conclusion: La forte pression négative cyclique a obtenu des résultats comparables pour la préparation d’un site receveur (épaississement du tissu sous-cutané et angiogenèse) comparativement au protocole conventionnel, tout en ayant une durée de port quotidien nettement réduite de 8 heures à 1 heure. Des données cliniques supplémentaires doivent être obtenues, mais notre nouveau cadre de pression semble prometteur et offre un environnement préexpansion plus agréable pour le patient.

OBJECTIVE: Fat grafting has been widely used for soft-tissue augmentation. External volume expansion (EVE) is a favorable tool for improvement in the rate of fat graft retention. However, few studies have focused on the most appropriate time for its implementation. In this study, BALB/c nude mice were used to investigate the effective time for the implementation of external volume expansion to improve the rate of fat retention.
METHODS: Sixteen mice were divided into four groups, and EVE was performed at different time points before or both before and after fat grafting. Fat tissue from a human donor was injected into the mice following EVE. Visual assessment, micro-computed tomography analysis, and histopathological evaluation were used to assess fat retention.
RESULTS: After 10 weeks, the group that underwent EVE 5 days before fat grafting demonstrated a significantly higher preserved fat volume, as determined by micro-computed tomography (p<0.05). Moreover, the group that received additional EVE after fat grafting exhibited a higher retention rate compared to the groups receiving EVE only before grafting (p<0.05). Histopathological analysis indicated that swelling, edema, and inflammation were more pronounced in the group with EVE immediately before grafting, while angiogenesis and lipogenesis were more active in the group with additional EVE after grafting.
CONCLUSIONS: EVE is a safe and effective approach for improving the rate of fat graft retentions. Furthermore, the timing of external tissue expansion plays a crucial role in fat retention. Based on our animal study, performing EVE immediately before and after fat grafting may be an effective strategy for enhancing the rate of fat graft retentions.

External volume expansion (EVE) has been shown to improve fat graft survival. In this study, we investigated the xenogenic implantation of human allograft adipose matrix (AAM) in non-immunocompromised mice in combination with pre- and post-conditioning with EVE to assess long-term adipose tissue survival. Sixty-eight recipient sites in thirty-four eight-week-old wild type (C57BL/6J) mice were separated into four groups. Thirty-four sites received no conditioning and either a subcutaneous injection of 300 μl saline (n= 17; PBS group) or AAM (n= 17; AAM group). Thirty-four sites received pre-conditioning with EVE (Day -7-3 pre-grafting) and 300 μl of AAM. Seventeen of these sites received immediate post-conditioning (Day 1-5 post-grafting) and 17 delayed post-conditioning (Day 28-32 post-grafting). Tissue was harvested at week 12 for analysis. At 12 weeks, immediate and delayed post-conditioning enabled higher volume retention (p= 0.02 andp< 0.0001, respectively). Adipose Stem Cells were greater in the AAM+Del-EVE group compared to the AAM (p= 0.01). Microvessel density was lower in the AAM group compared to the AAM+Imm-EVE (p= 0.04) and AAM+Del-EVE group (p= 0.02). Macrophage infiltration was lower in the AAM+Imm-EVE (p= 0.002) and AAM+Del-EVE (p= 0.003) groups compared to the AAM group. PCR analysis and Western blotting identified a significantly higher expression of PPAR-γ, LPL and VEGF with delayed-conditioning. Pre- and post-conditioning, particularly delayed-post-conditioning, of the recipient site optimized the microenvironment allowing significant adipogenesis and survival of neo-adipose tissue through robust angiogenesis. This study supports that xenogenic transplantation of adipose matrix allows adipose tissue formation and survival with EVE as an adjuvant.

We hypothesized that use of a composite three-dimensionally (3D) printed scaffold with electrospun nanofibers in conjunction with recipient-site preconditioning with an external volume expansion (EVE) device would enable successful dermal tissue regeneration of a synthetic polymer scaffold. Cell viability, cell infiltration, extracellular matrix deposition, scaffold contraction, and mRNA expression by dermal fibroblasts cultured on three different scaffolds, namely, 3D-printed scaffold with a collagen coating, 3D-printed scaffold with an electrospun polycaprolactone nanofiber and collagen coating, and 3D-printed scaffold with an electrospun polycaprolactone/collagen nanofiber, were measured. Before scaffold implantation, rats were treated for 2 h with an EVE device to evaluate the effect of this device on the recipient site. Cell proliferation rates were significantly higher on the 3D-printed scaffold with electrospun polycaprolactone nanofiber and collagen coating than on the other scaffolds. In cell invasion studies, the 3D-printed scaffold with electrospun polycaprolactone nanofiber and collagen coating showed better cell integration than the other scaffolds. Under stereomicroscopy, fibroblasts adhered tightly to the electrospun area, and the fibroblasts effectively produced both collagen and elastin. Rat skin treated with an EVE device exhibited increased HIF-1α protein expression and capillary neoformation compared with control skin. Invasion of CD8+ cytotoxic lymphocytes surrounding the scaffold decreased when the recipient site was preconditioned with the EVE device. The composite 3D printed scaffold with electrospun nanofibers provided a favorable environment for proliferation, migration, and extracellular matrix synthesis by fibroblasts. Recipient-site preconditioning with an EVE device allowed for scaffold incorporation with less inflammation due to improved angiogenesis.

UNASSIGNED: To review the application progress, mechanism, application points, limitations, and oncological safety of external volume expansion (EVE) assisted autologous fat grafting for breast reconstruction and provide a reference for optimizing the design of EVE.
UNASSIGNED: Based on the latest relevant articles, the basic experiments and clinical applications of EVE were summarized.
UNASSIGNED: EVE can reduce interstitial fluid pressure, increase blood supply, and promote adipogenic differentiation, thereby benefiting the survival of transplanted fat. EVE assisted autologous fat grafting in clinical practice can improve the retention rate of breast volume and the outcome of breast reconstruction, meanwhile it doesn\'t increase the risk of local recurrence. But there is no standard parameters for application, and there are many complications and limitations.
UNASSIGNED: EVE improves the survival of transplanted fat, but its complications and poor compliance are obvious, so it is urgent to further investigate customized products for breast reconstruction after breast cancer and establish relevant application guidelines.
UNASSIGNED: 总结体外扩张器（external volume expansion，EVE）辅助自体脂肪移植乳房再造的应用进展、作用机制、应用要点、局限性及肿瘤安全性，为优化EVE设计提供参考。.
UNASSIGNED: 结合近年相关文献，就EVE相关基础实验、临床应用做一综述。.
UNASSIGNED: EVE可降低组织间隙压、增加血供、促进脂肪细胞新生，从而有利于移植脂肪存活。临床应用EVE辅助自体脂肪移植可增加脂肪体积留存率，提升乳房重建效果，且不会增加乳腺癌患者局部复发率。但应用参数暂无标准，且应用并发症、局限性多。.
UNASSIGNED: EVE可促进移植脂肪存活，但存在并发症多、依从性差等缺点，亟需进一步研究开发乳腺癌术后乳房再造的专用产品并建立相关应用指南。.

The autologous fat grafting is commonly used for reconstructive or aesthetic purposes. However, due to the huge variation in methods, its retention rate varies a lot. External volume expansion (EVE) has been used to treat recipient sites of fat grafting. Concerns have been raised regarding its efficacy and safety.
We have searched PubMed, EMBASE, and the Cochrane Library for studies on EVE-assisted fat grafting published from 2000 to 2020. A meta-analysis was conducted to pool the retention rate. The incidence of complications was assessed for reconstructive or aesthetic purposes.
The 11 included studies involved 1152 patients with operations on 1794 breasts. Four studies were included in the meta-analysis. The pooled retention rate was 65% [95%CI 49, 79]. Eight studies reported the complications. The total complication incidence was 34%, which is 35% for the aesthetic group and 33% for the reconstructive group. The complication rate was not obviously different between the two groups.
The study shows that the EVE-assisted fat grafting has better retention rate than traditional fat grafting. However, the data showed that the complication rate was much higher in the EVE-assisted group.

The reconstruction of large-volume soft tissue defects is a major problem in plastic surgery. Many plastic surgeons have focused on external volume expansion (EVE) because of its capacity to promote regeneration of soft tissues, including breast, subcutaneous fat, and skin. EVE is a minimally invasive and less costly tissue engineering approach that has shown great clinical potential. However, many challenges still need to be addressed before such technology can become a common clinical practice. Basic in vivo and in vitro studies have been performed to determine the possible mechanisms by which EVE promotes tissue regeneration and to design optimized animal models. EVE application was found to facilitate cell proliferation and migration, enhance adipogenesis, improve angiogenesis, and provide available space for soft tissue growth. Understanding the mechanical and chemical signals associated with EVE during tissue regeneration may enable the clinical adaptation of this technology. This article reviews the clinical application of EVE techniques, describes preclinical animal models, and evaluates the possible mechanisms by which EVE induces tissue regeneration. Impact statement The reconstruction of large-volume soft tissue defects is a major problem in plastic surgery. External volume expansion (EVE) is a minimally invasive and less costly tissue engineering approach that has shown promise in clinical applications. This article reviews the clinical application of EVE techniques, describes preclinical animal models, and evaluates the possible mechanisms by which EVE induces tissue regeneration.

Background: There is a clinical need for the use of engineered adipose tissue in place of surgical reconstruction. We previously found that the external volume expansion (EVE) device increased special cell clusters in well-vascularized connective stroma during adipose regeneration. However, the origin of these cell clusters and their role in adipose tissue regeneration remain unknown. Aim: In the present study, we evaluated EVE in the construction of expanded prefabricated adipose tissue (EPAT) in a rat model. Methods: Rats were randomized into an EVE suction group and a control group, with 24 rats in each group. The structure and origin of the special cell clusters were determined by hematoxylin and eosin staining, and immunohistochemistry; their role in adipose tissue regeneration was investigated by immunohistochemistry and Western blot analyses. Results: Special cell clusters began to increase at week 1 with a peak at week 4, and then receded from weeks 8 to 12. Clusters were identified as glandular epithelial cells as determined by their gland-like structure and expression of specific markers. The cell clusters induced significant infiltration of macrophage antigen-2 (Mac-2) positive macrophages by secreting monocyte chemoattractant protein-1 (MCP-1) at the early stage of suction. Subsequently, these infiltrated macrophages expressed massive vascular endothelial growth factor (VEGF) to promoted angiogenesis. Conclusion: EVE generated glandular epithelial cell clusters, which recruited macrophages to promote angiogenesis and subsequent adipose tissue regeneration. These findings shed light on the mechanisms underlying the effects of EVE devices on adipose tissue regeneration.

In reconstructive surgery, tissues are routinely transferred to repair a defect caused by trauma, cancer, chronic diseases, or congenital malformations; surgical transfer intrinsically impairs metabolic supply to tissues placing a risk of ischemia-related complications such as necrosis, impaired healing, or infection. Pre-surgical induction of angiogenesis in tissues (preconditioning) can limit postsurgical ischemic complications and improve outcomes, but very few preconditioning strategies have successfully been translated to clinical practice due to the invasiveness of most proposed approaches, their suboptimal effects, and their challenging regulatory approval. We optimized a method that adopts noninvasive external suction to precondition tissues through the induction of hypoxia-mediated angiogenesis. Using a sequential approach in a rodent model, we determined the parameters of application (frequency, suction levels, duration, and interfaces) that fine-tune the balance of enhanced angiogenesis, attenuation of hypoxic tissue damage, and length of treatment. The optimized repeated short-intermittent applications of intermediate suction induced a 1.7-fold increase in tissue vascular density after only 5 days of treatment (p < 0.05); foam interfaces showed the same effectiveness and caused less complications. In a second separate experiment, our model showed that the optimized technique significantly improves survival of transferred tissues. Here we demonstrate that noninvasive external suction can successfully, safely, and promptly enhance vascularity of soft tissues: these translational principles can help design effective preconditioning strategies, transform best clinical practice in surgery, and improve patient outcomes.

To allow for a better implementation of external volume expansion to clinical applications for soft tissue regeneration, it is necessary to comprehensively understand the underlying mechanisms. As human adipose-derived stem cells (hASCs) play a crucial role in soft tissue enlargement, we investigated the impact of cyclic stretch on gene expression, proliferation rate and adipogenic differentiation of these cells. After cyclic stretching, RNA was extracted and subjected to DNA microarray analysis and reverse transcription-quantitative polymerase chain reaction (RT-qPCR). Also, the expression of FABP4 mRNA was analysed by RT-qPCR to test whether mechanical stretch affected adipogenic differentiation of hASCs. The proliferation rate was assessed using the alamarBlue assay and Ki-67 staining. A cell cycle analysis was performed with flow cytometry and Western blot. We found that cyclic stretch significantly induced the expression of CYP1B1 mRNA. Furthermore, the adipogenic differentiation of hASCs was impaired, as was the proliferation. This was partly due to a decrease in extracellular signal-regulated kinase (ERK) 1/2 and histone H3 phosphorylation, suggesting a growth arrest in the G2 /M phase of the cell cycle. Enrichment analyses demonstrated that stretch-regulated genes were over-represented in pathways and biological processes involved in extracellular matrix organization, vascular remodelling and responses to cell stress. Taken together, mechanical stress impaired both proliferation and adipogenic differentiation, but led to a tissue-remodelling phenotype of hASCs. These data suggest that extracellular matrix remodelling and neoangiogenesis may play a more important role in external volume expansion than proliferation and adipogenesis of hASCs. Copyright © 2017 John Wiley & Sons, Ltd.