The Arteriovenous (AV) Loop in a Small Animal Model to Study Angiogenesis and Vascularized Tissue Engineering

Abstract

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.

When free flaps are not the first choice: is the distally based peroneus brevis still an option for foot and ankle reconstruction in the era of microsurgery?

“…Methods of tissue engineering and regenerative medicine [37][38][39][40][41][42][43][44][45][46][47][48][49][50][51] to circumvent the use of autologous tissue and their inherent donor site morbidity seem promising but are not clinically available for these problems yet. Although a considerable number of local or free flaps has been successfully described to surgically reconstruct these defects [7,[52][53][54][55][56][57][58] each individual case needs the optimal indication for the most suitable flap procedure.…”

Oxygen and nutrient delivery in tissue engineering: Approaches to graft vascularization

“…An often mentioned disadvantage of this technique is the multiple surgeries required, as well as the possible necessity of reseeding prior to the final implantation due to tissue necrosis caused by nutrient and oxygen deprivation at the initial implantation site (Laschke et al, 2009). Nevertheless, these in vivo vascularization approaches are promising as there have already been examples of successful clinical application, such as augmenting the angiogenic response, implantation of a pre-existing artery into the tissue graft prior to graft implantation (Koepple, Kneser, & Schmidt, 2017), or prevascularization at a secondary site, for example, using the flap technique or the arteriovenous (AV) loop technique (Eweida et al, 2015;Kokemueller et al, 2010;Polykandriotis et al, 2007;Weigand et al, 2016).…”

“…This is due to the intrinsic properties of the prefabricated AV loop technique that does not require embedding of the tissue graft into the surrounding tissue. In contrast, the tissue construct is contained within a growth chamber that is placed around the AV loop, which is only connected to the host's vascular system (Eweida et al, 2015;Polykandriotis et al, 2007;Weigand et al, 2016). This growth chamber, usually made from polycarbonate, may be either empty or supplemented with ECM components.…”

Biofabrikation – neue Ansätze für den artifiziellen Gewebeersatz

“…Diese werden zur Ver vielfältigung meist im Labor kultiviert, um sie dann in den Emp fängerorganismus zu implantieren [6][7][8][9][10][11][12]. In vitro unter Laborbe dingungen und im Kleintiermodell [13] hat diese Methode teils erstaunliche Ergebnisse gezeigt [14][15][16]. U.a.…”