A functional blood vessel network is a prerequisite for the survival and growth of almost all tissues and organs in the human body. Moreover, in pathological situations such as cancer, vascularization plays a leading role in disease progression. Consequently, there is a strong need for a standardized and well-characterized in vivo model in order to elucidate the mechanisms of neovascularization and develop different vascularization approaches for tissue engineering and regenerative medicine. We describe a microsurgical approach for a small animal model for induction of a vascular axis consisting of a vein and artery that are anastomosed to an arteriovenous (AV) loop. The AV loop is transferred to an enclosed implantation chamber to create an isolated microenvironment in vivo, which is connected to the living organism only by means of the vascular axis. Using 3D imaging (MRI, micro-CT) and immunohistology, the growing vasculature can be visualized over time. By implanting different cells, growth factors and matrices, their function in blood vessel network formation can be analyzed without any disturbing influences from the surroundings in a well controllable environment. In addition to angiogenesis and antiangiogenesis studies, the AV loop model is also perfectly suited for engineering vascularized tissues. After a certain prevascularization time, the generated tissues can be transplanted into the defect site and microsurgically connected to the local vessels, thereby ensuring immediate blood supply and integration of the engineered tissue. By varying the matrices, cells, growth factors and chamber architecture, it is possible to generate various tissues, which can then be tailored to the individual patient's needs.

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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.

Adequate vascularization is pivotal for tumor progression and metastasis. Tumor angiogenesis is based on a sequence of interactions between the tumor and surrounding cells and the extracellular matrix. It is widely known that a tumor can influence and control its surroundings to create favorable conditions for further growth. To investigate the influence of various tumor types on endothelial cells (ECs), an in vitro rat cell model was used and rat liver EC52 cells were co-cultured with conditioned medium derived from breast cancer MCR86, osteosarcoma ROS-1, colon cancer CC531 and rhabdomyosarcoma R1H cell lines. In a distinct tumor-type-dependent manner, the EC52 cells exhibited changes in their function and gene expression. In all functional cell culture assays (proliferation, migration, transmigration, invasion and tube formation) the breast cancer cells exerted a significant effect on the angiogenic abilities of the ECs. When comparing the various tumor cell types, only the breast and colon cancer cells led to a significant stimulation of the EC migration and invasion. Proliferation, migration, invasion and tube formation were not or only hardly influenced by the osteosarcoma or rhabdomyosarcoma cells. Similarly, the breast and colon cancer cells exhibited the strongest influence on the upregulation of EC angiogenic genes, including the ones encoding vascular endothelial growth factor A, platelet and endothelial cell adhesion molecule 1, fibroblast growth factor 2, Von Willebrand factor, C-X-C motif chemokine ligand 12 and tyrosine kinase with immunoglobulin-like and EGF-like domains 1. Therefore, it is hypothesized that tumor cells enhance the angiogenic properties of ECs, including proliferation, migration, invasion and tube formation in a tumor-type-dependent manner. This is likely based on the upregulation of pro-angiogenic genes in ECs induced by varying cytokine secretion signatures of tumor cells.

A functional blood vessel network is a prerequisite for the survival and growth of almost all tissues and organs in the human body. Moreover, in pathological situations such as cancer, vascularization plays a leading role in disease progression. Consequently, there is a strong need for a standardized and well-characterized in vivo model in order to elucidate the mechanisms of neovascularization and develop different vascularization approaches for tissue engineering and regenerative medicine.We describe a microsurgical approach for a small animal model for induction of a vascular axis consisting of a vein and artery that are anastomosed to an arteriovenous (AV) loop. The AV loop is transferred to an enclosed implantation chamber to create an isolated microenvironment in vivo, which is connected to the living organism only by means of the vascular axis. Using 3D imaging (MRI, micro-CT) and immunohistology, the growing vasculature can be visualized over time. By implanting different cells, growth factors and matrices, their function in blood vessel network formation can be analyzed without any disturbing influences from the surroundings in a well controllable environment.In addition to angiogenesis and antiangiogenesis studies, the AV loop model is also perfectly suited for engineering vascularized tissues. After a certain prevascularization time, the generated tissues can be transplanted into the defect site and microsurgically connected to the local vessels, thereby ensuring immediate blood supply and integration of the engineered tissue. By varying the matrices, cells, growth factors and chamber architecture, it is possible to generate various tissues, which can then be tailored to the individual patient's needs.