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Despite remarkable efforts, metastatic melanoma (MM) still presents with significant mortality. Recently, mono-chemotherapies are increasingly replenished by more cancer-specific combination therapies involving death ligands and drugs interfering with cell signaling. Still, MM remains a fatal disease because tumors rapidly develop resistance to novel therapies thereby regaining tumorigenic capacity. Although genetically engineered mouse models for MM have been developed, at present no model is available that reliably mimics the human disease and is suitable for studying mechanisms of therapeutic obstacles including cell death resistance. To improve the increasing requests on new therapeutic alternatives, reliable human screening models are demanded that translate the findings from basic cellular research into clinical applications. By developing an organotypic full skin equivalent, harboring melanoma tumor spheroids of defined sizes we have invented a cell-based model that recapitulates both the 3D organization and multicellular complexity of an organ/tumor in vivo but at the same time accommodates systematic experimental intervention. By extending our previous findings on melanoma cell sensitization toward TRAIL (tumor necrosis factor-related apoptosis-inducing ligand) by co-application of sublethal doses of ultraviolet-B radiation (UVB) or cisplatin, we show significant differences in the therapeutical outcome to exist between regular two-dimensional (2D) and complex in vivo-like 3D models. Of note, while both treatment combinations killed the same cancer cell lines in 2D culture, skin equivalent-embedded melanoma spheroids are potently killed by TRAIL+cisplatin treatment but remain almost unaffected by the TRAIL+UVB combination. Consequently, we have established an organotypic human skin-melanoma model that will facilitate efforts to improve therapeutic outcomes for malignant melanoma by providing a platform for the investigation of cytotoxic treatments and tailored therapies in a more physiological setting.

Bioreactor technology is vital for tissue engineering. Usually, bioreactors are used to provide a tissue-specific physiological in vitro environment during tissue maturation. In addition to this most obvious application, bioreactors have the potential to improve the efficiency of the overall tissue-engineering concept. To date, a variety of bioreactor systems for tissue-specific applications have been developed. Of these, some systems are already commercially available. With bioreactor technology, various functional tissues of different types were generated and cultured in vitro. Nevertheless, these efforts and achievements alone have not yet led to many clinically successful tissue-engineered implants. We review possible applications for bioreactor systems within a tissue-engineering process and present basic principles and requirements for bioreactor development. Moreover, the use of bioreactor systems for the expansion of clinically relevant cell types is addressed. In contrast to cell expansion, for the generation of functional three-dimensional tissue equivalents, additional physical cues must be provided. Therefore, bioreactors for musculoskeletal tissue engineering are discussed. Finally, bioreactor technology is reviewed in the context of commercial constraints.

whereas for tissue-engineered skin implants, new vessels must be formed by angiogenesis, which delays graft integration (Young et al., 1996). Consequently, bio-engineered skin implants are more likely to be rejected. In addition, the cutaneous vasculature is crucial for several physiological and pathophysiological processes including the development of skin diseases, wound healing, metastasizing of malignant melanoma, tumor-angiogenesis, autoand alloimmune-phenomena, and the transdermal penetration of substances. Taken together, non-vascularized skin models are of limited value with regard to their ability to reflect the physiological conditions of a full organ. In the absence of a model that represents the physiological conditions of a full organ, there remains a scientific and medical need for animal models.To overcome these limitations, endothelial cells can be seeded into the dermal part of full-thickness skin equivalents, which results in the alignment of endothelial cells to vessel-like struc- IntroductionTissue-engineered, three-dimensional skin equivalents are capable of mimicking key anatomical, metabolic, cellular and functional aspects of native human skin. Thus, they can be employed as wound coverage for large skin defects or as in vitro test systems instead of animal models in basic research (Groeber et al., 2011). Generally, two types of tissue-engineered skin models are available, being representatives of either the epidermis alone (reconstructed human epidermis) or the dermal and epidermal layer (full-thickness skin equivalents) (De Wever et al., 2013). In spite of recent progress, the use of current skin equivalents for medical purposes and as test systems remains limited owing to the lack of a functional vasculature.In skin transplantation, an existing vasculature supports a rapid anastomosis of donor skin to the host's vasculature (inosculation), Research SummaryTissue-engineered skin equivalents mimic key aspects of the human skin and can thus be employed as wound coverage for large skin defects or as in vitro test systems as an alternative to animal models. However, current skin equivalents lack a functional vasculature, limiting clinical and research applications. This study demonstrates the generation of a vascularized skin equivalent with a perfused vascular network by combining a biological vascularized scaffold (BioVaSc) based on a decellularized segment of porcine jejunum and a tailored bioreactor system. The BioVaSc was seeded with human fibroblasts, keratinocytes, and human microvascular endothelial cells. After 14 days at the air-liquid interface, hematoxylin & eosin and immunohistological staining revealed a specific histological architecture representative of the human dermis and epidermis, including a papillary-like architecture at the dermal-epidermal-junction. The formation of the skin barrier was measured non-destructively using impedance spectroscopy. Additionally, endothelial cells lined the walls of the formed vessels that could be perfused with a physiological volume flow...

In vitro models are a cost effective and ethical alternative to study cutaneous wound healing processes. Moreover, by using human cells, these models reflect the human wound situation better than animal models. Although two-dimensional models are widely used to investigate processes such as cellular migration and proliferation, models that are more complex are required to gain a deeper knowledge about wound healing. Besides a suitable model system, the generation of precise and reproducible wounds is crucial to ensure comparable results between different test runs. In this study, the generation of a three-dimensional full thickness skin equivalent to study wound healing is shown. The dermal part of the models is comprised of human dermal fibroblast embedded in a rat-tail collagen type I hydrogel. Following the inoculation with human epidermal keratinocytes and consequent culture at the air-liquid interface, a multilayered epidermis is formed on top of the models. To study the wound healing process, we additionally developed an automated wounding device, which generates standardized wounds in a sterile atmosphere. Video LinkThe video component of this article can be found at