Spatial and temporal patterns of bone formation in ectopically pre-fabricated, autologous cell-based engineered bone flaps in rabbits.

Oliver Scheufler,Dirk J Schaefer,Alessandra Braccini,Gerhard Pierer,Claude Jaquiery,David J Wendt,Michael Heberer,Raffaele Galli,Ivan Martin,Jürg A Gasser

doi:10.1111/j.1582-4934.2008.00137.x

Oliver Scheufler, Dirk J Schaefer + Show 8 more

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https://doi.org/10.1111/j.1582-4934.2008.00137.x

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Abstract

Biological substitutes for autologous bone flaps could be generated by combining flap pre-fabrication and bone tissue engineering concepts. Here, we investigated the pattern of neotissue formation within large pre-fabricated engineered bone flaps in rabbits. Bone marrow stromal cells from 12 New Zealand White rabbits were expanded and uniformly seeded in porous hydroxyapatite scaffolds (tapered cylinders, 10–20 mm diameter, 30 mm height) using a perfusion bioreactor. Autologous cell-scaffold constructs were wrapped in a panniculus carnosus flap, covered by a semipermeable membrane and ectopically implanted. Histological analysis, substantiated by magnetic resonance imaging (MRI) and micro-computerized tomography scans, indicated three distinct zones: an outer one, including bone tissue; a middle zone, formed by fibrous connective tissue; and a central zone, essentially necrotic. The depths of connective tissue and of bone ingrowth were consistent at different construct diameters and significantly increased from respectively 3.1 ± 0.7 mm and 1.0 ± 0.4 mm at 8 weeks to 3.7± 0.6 mm and 1.4 ± 0.6 mm at 12 weeks. Bone formation was found at a maximum depth of 1.8 mm after 12 weeks. Our findings indicate the feasibility of ectopic pre-fabrication of large cell-based engineered bone flaps and prompt for the implementation of strategies to improve construct vascularization, in order to possibly accelerate bone formation towards the core of the grafts.

Highlights

Vascularization plays a crucial supportive role during bone growth and fracture healing [1]
In order to solve the size limitations in bone tissue engineering, one possible option is to combine it with the concept of flap prefabrication, namely a two-stage surgical procedure whereby a new blood supply is transferred into a volume of tissue by the introduction of a vascular carrier [19,20,21]
We first aimed at establishing a new model of ectopic prefabrication of autologous cell-based, large bone flaps in rabbits using porous ceramic scaffolds loaded with bone marrow stromal cells (BMSC) and wrapped by a panniculus carnosus flap as an external vascular carrier

Summary

Introduction

Vascularization plays a crucial supportive role during bone growth and fracture healing [1]. In order to solve the size limitations in bone tissue engineering, one possible option is to combine it with the concept of flap prefabrication, namely a two-stage surgical procedure whereby a new blood supply is transferred into a volume of tissue by the introduction of a vascular carrier [19,20,21]. The depths of vascularization and of bone tissue formation have not been assessed in any of these models, and no indication on size limits in the prefabrication of engineered bone flaps is available. We first aimed at establishing a new model of ectopic prefabrication of autologous cell-based, large bone flaps in rabbits using porous ceramic scaffolds loaded with BMSC and wrapped by a panniculus carnosus flap as an external vascular carrier. In order to exclude the possibility that such pattern was influenced by initially non-uniform cell distributions, we adapted and used a previously described direct perfusion bioreactor system for spatially homogenous cell seeding [26]

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