Long-term function of three-dimensional (3D) tissue constructs depends on adequate vascularization after implantation. Accordingly, research in tissue engineering has focused on the analysis of angiogenesis. For this purpose, 2 sophisticated in vivo models (the chorioallantoic membrane and the dorsal skinfold chamber) have recently been introduced in tissue engineering research, allowing a more detailed analysis of angiogenic dysfunction and engraftment failure. To achieve vascularization of tissue constructs, several approaches are currently under investigation. These include the modification of biomaterial properties of scaffolds and the stimulation of blood vessel development and maturation by different growth factors using slow-release devices through pre-encapsulated microspheres. Moreover, new microvascular networks in tissue substitutes can be engineered by using endothelial cells and stem cells or by creating arteriovenous shunt loops. Nonetheless, the currently used techniques are not sufficient to induce the rapid vascularization necessary for an adequate cellular oxygen supply. Thus, future directions of research should focus on the creation of microvascular networks within 3D tissue constructs in vitro before implantation or by co-stimulation of angiogenesis and parenchymal cell proliferation to engineer the vascularized tissue substitute in situ.

Long-term function of three-dimensional (3D) tissue constructs depends on adequate vascularization after implantation. Accordingly, research in tissue engineering has focused on the analysis of angiogenesis. For this purpose, 2 sophisticated in vivo models (the chorioallantoic membrane and the dorsal skinfold chamber) have recently been introduced in tissue engineering research, allowing a more detailed analysis of angiogenic dysfunction and engraftment failure. To achieve vascularization of tissue constructs, several approaches are currently under investigation. These include the modification of biomaterial properties of scaffolds and the stimulation of blood vessel development and maturation by different growth factors using slow-release devices through pre-encapsulated microspheres. Moreover, new microvascular networks in tissue substitutes can be engineered by using endothelial cells and stem cells or by creating arteriovenous shunt loops. Nonetheless, the currently used techniques are not sufficient to induce the rapid vascularization necessary for an adequate cellular oxygen supply. Thus, future directions of research should focus on the creation of microvascular networks within 3D tissue constructs in vitro before implantation or by co-stimulation of angiogenesis and parenchymal cell proliferation to engineer the vascularized tissue substitute in situ.

Bone represents a highly dynamic tissue whose development is strongly dependent on vasculogenic and angiogenic processes. Neovascularization also plays an important role in fracture healing and in tissue engineering applications aiming at restoring bone function. We have previously shown in a heterotopic subcutaneous implantation model of severe combined immunodeficiency (SCID) mice that implanted human umbilical vein endothelial cells (HUVECs) gave rise to the formation of a complex functional human neovasculature. In this study, we investigated the effect of HUVEC coimplantation on mesenchymal stem cell (MSC)-mediated bone regeneration in an orthotopic calvarial bone defect model in immunocompromised mice. For this purpose, human fibrin/Matrigel-immobilized HUVECs and MSCs were seeded alone or in combination into scaffolds consisting of decalcified processed bovine cancellous bone (Tutobone) and implanted into calvarial critical-sized defects. Our results show that implanted HUVECs formed complex three-dimensional networks of perfused human neovessels that were stabilized by recruiting perivascular cells. Neovessel formation was considerably higher in the coimplantation group, suggesting that implanted MSCs supported HUVEC-triggered neovascularization. In addition, implanted MSCs effectively supported bone formation in calvarial defects. However, the HUVEC-derived neovasculature did not improve MSC-triggered bone regeneration in this orthotopic critical-sized defect model.

No abstract

The findings demonstrate that long-term stable adipose tissue can be engineered in vivo by simple injection of human preadipocytes using fibrin as a carrier material. After further investigation, this approach may represent an alternative to the techniques currently used for soft tissue restoration.

Neovascularization of adipose tissue equivalents is a crucial step in successful adipose tissue engineering, since insufficient vascularization results in graft resorption in an in vivo situation. A possible cellular approach to overcome this limitation is the co-implantation of adipose-derived stem cells (ASCs) with endothelial cells to stimulate the formation of a vascular network. We investigated the potential of ASCs derived from human abdominal fat tissue co-cultured with endothelial progenitor cells (EPCs) from human peripheral blood to stimulate neovascularization of fibrin constructs on the chorioallantoic membrane (CAM) of fertilized chicken eggs, in direct comparison to human umbilical vein endothelial cells (HUVECs). After 9 days of incubation, cell-fibrin constructs were explanted and histologically evaluated with respect to ingrowth of avian blood vessels into the construct and formation of human blood vessels by co-implanted endothelial cells. When administered on the CAM, ASCs successfully guided host vasculature into the construct (angiogenesis) and guided formation of capillary-like structures by co-implanted human endothelial cells (vasculogenesis), with HUVECs being superior to EPCs, leading to a perfused avian and human capillary network within the fibrin construct. However, the results also showed that perfused human blood vessels were only observed near the CAM compared to unperfused capillary-like structures near the top of the construct, indicating that perfusion of the cell-fibrin construct takes longer than 9 days. In conclusion, as blood vessel formation is an essential step during adipogenic differentiation, the data support our hypothesis that cellular communication between transplanted ASCs and endothelial cells is beneficial for vasculogenesis. Copyright © 2013 John Wiley & Sons, Ltd.

The four previous articles in this series addressed the myths and facts surrounding lipoedema. We have shown that there is no scientific evidence at all for the key statements made about lipoedema – which are published time and time again. The main result of this “misunderstanding” of lipoedema is a therapeutic concept that misses the mark. The patient’s real problems are overlooked.The national and especially the international response to the series, which can be read in both German and English, has been immense and has exceeded all our expectations. The numerous reactions to our articles make it clear that in other countries, too, the fallacies regarding lipoedema have led to an increasing discrepancy between the experience of healthcare workers and the perspective of patients and self-help groups, based on misinformation mostly generated by the medical profession.Parts 1 to 4 in this series of articles on the myths surrounding lipoedema have made it clear that we have to radically change the view of lipoedema that has been held for decades. Changing our perspective means getting away from the idea of “oedema in lipoedema” – and hence away from the dogma that decongestion is absolutely necessary – and towards the actual problems faced by our patients with lipoedema. Such a paradigm shift in a disease that has been described in the same way for decades cannot be left to individuals but must be put on a much broader footing. For this reason, the lead author of this series of articles invited renowned lipoedema experts from various European countries to discussions on the subject. Experts from seven different countries took part in the two European Lipoedema Forums, with the goal of establishing a consensus. The consensus reflects the experts’ shared view on the disease, having scrutinized the available literature, and having taken into account the many years of clinical practice with this particular patient group. Appropriate to the clinical complexity of lipoedema, participants from different specialties provided an interdisciplinary approach. Nearly all of the participants in the European Lipoedema Forum had already published work on lipoedema, had been involved in drawing up their national lipoedema guidelines, or were on the executive board of their respective specialty society.In this fifth and final part of our series on lipoedema, we will summarise the relevant findings of this consensus, emphasising the treatment of lipoedema as we now recommend it. As the next step, the actual consensus paper “European Best Practice of Lipoedema” will be issued as an international publication.Instead of looking at the treatment of oedema, the consensus paper will focus on treatment of the soft tissue pain, as well as the psychological vulnerability of patients with lipoedema. The relationship between pain perception and the patient’s mental health is recognised and dealt with specifically. The consensus also addresses the problem of self-acceptance, and this plays a prominent role in the new therapeutic concept. The treatment of obesity provides a further pillar of treatment. Obesity is recognised as being the most common comorbid condition by far and an important trigger of lipoedema. Bariatric surgery should therefore also be considered for patients with lipoedema who are morbidly obese. The expert group upgraded the importance of compression therapy and appropriate physical activity, as the demonstrated anti-inflammatory effects directly improve the patients’ symptoms. Patients will be provided with tools for personalised self-management in order to sustain sucessful treatment. Should conservative therapy fail to improve the symptoms, liposuction may be considered in strictly defined circumstances.The change in the view of lipoedema that we describe here brings the patients’ actual symptoms to the forefront. This approach allows us to focus on more comprehensive treatment that is not only more effective but also more sustainable than focusing on the removal of non-existent oedema.

Neovascularization represents an important issue in tissue-engineering applications, since survival of implanted cells strongly relies on sufficient oxygen and nutrient supply. We have recently observed that human bone marrow-derived mesenchymal stem cells (MSCs) support neovessel formation originating from coimplanted endothelial cells (ECs) in vivo, suggesting that MSCs may function as perivascular cells by investing and stabilizing nascent EC-derived neovessels. In this study, we investigated EC-induced mural cell differentiation of MSCs in vitro. For this purpose, endothelial progenitor cells (EPCs) from two different origins, namely adult peripheral blood (pbEPCs) and neonatal cord blood (cbEPCs), or human umbilical vein endothelial cells (HUVECs), were cocultured with human MSCs to analyze the effect on MSC differentiation toward a smooth muscle cell (SMC)/pericyte phenotype. EPCs as well as HUVECs increased alpha-smooth muscle actin expression in MSCs upon cocultivation in a time-dependent manner. This effect was strongly dependent on direct cell-to-cell contact and extracellular signal-regulated kinase (ERK) signaling, but was not mediated by heterotypic gap junction communication. Beyond enhanced SMC marker gene expression in MSCs, EPCs also enhanced the functional characteristics of cocultured MSCs by increasing their ability to attach to EC tubes in vitro. In conclusion, our study has shown that EPCs from adult peripheral blood as well as from cord blood commit cocultivated MSCs toward an SMC/pericyte phenotype in a cell-contact- and ERK-dependent manner.