Axial vascularization of a large volume calcium phosphate ceramic bone substitute in the sheep AV loop model

Abstract

Vascularization still remains an obstacle to engineering of bone tissue with clinically relevant dimensions. Our aim was to induce axial vascularization in a large volume of a clinically approved biphasic calcium phosphate ceramic by transferring the arteriovenous (AV) loop approach to a large animal model. HA/β-TCP granula were mixed with fibrin gel for a total volume of 16 cm 3 , followed by incorporation into an isolation chamber together with an AV loop. The chambers were implanted into the groins of merino sheep and the development of vascularization was monitored by sequential non-invasive magnetic resonance imaging (MRI). The chambers were explanted after 6 and 12 weeks, the pedicle was perfused with contrast agent and specimens were subjected to micro-computed tomography (µ-CT) scan and histological analysis. Sequential MRI demonstrated a significantly increased perfusion in the HA/β-TCP matrices over time. Micro-CT scans and histology confirmed successful axial vascularization of HA/β-TCP constructs. This study demonstrates, for the first time, successful axial vascularization of a clinically approved bone substitute with a significant volume in a large animal model by means of a microsurgically created AV loop, thus paving the way for the first microsurgical transplantation of a tissue-engineered, axially vascularized bone with clinically relevant dimensions.

De novo Generation of an Axially Vascularized Processed Bovine Cancellous-Bone Substitute in the Sheep Arteriovenous-Loop Model

“…These promising results led to the development of a new large-animal model in order to pave the way towards clinical application: the sheep AV-loop model [6]. In contrast to previous studies, based on a granular, purely anorganic matrix [7], the aim of the present study was to employ a primarily stable biological hard matrix that should become axially vascularized in the sheep AV-loop model. By using clinically applicable imaging tools (MRI scans), the course of progressive vascularization was evaluated and followed by endpoint analysis including micro-CT scanning, histomorphometry and immunohistochemistry.…”

“…All operations were performed by the same microsurgeon on a total number of 13 female merino land sheep, each weighing 24–26 kg, as described previously [7]: briefly, an AV loop was generated by a microanastomosis between the greater saphenous artery and vein. The AV loop was placed within a custom-made sterile isolation chamber.…”

“…All experiments were approved by the Animal Care Committee of the University of Erlangen and the regional government. Housing, anesthesia and postoperative management were performed as described previously [7]. The sheep received orotracheal intubation with controlled intermittent positive-pressure ventilation.…”

Tissue Engineering of Skeletal Muscle

“…Thus, vascularization in general as well as number and pattern of vessel ingrowth of different matrices can be analyzed (Arkudas et al 2010, Polykandriotis et al 2009) and the vascularized matrix offers a platform for tissue engineering for skeletal (Messina et al 2005) or cardiac (Morritt et al 2007) muscle in vivo. The feasibility of the AV-loop model in large animals ) has been demonstrated recently and poses another step towards a more clinical setting (Beier et al 2010). Depending on the matrix architecture, a certain period of time is necessary for vascularization of the whole construct.…”

O desenho da alça vascular arteriovenosa não interfere na sua patência: estudo experimental na pata de coelho

“…Também animais maiores como as ovelhas podem ser usadas para simular situações mais próximas às humanas 72,73 .…”