Articular cartilage repair in rabbits by using suspensions of allogenic chondrocytes in alginate

Abstract

The feasibility of allogenic implants of chondrocytes in alginate gels was tested for the reconstruction in vivo of artificially full-thickness-damaged articular rabbit cartilage.The suspensions of chondrocytes in alginate were gelled by the addition of calcium chloride solution directly into the defects giving in situ a construct perfectly inserted and adherent to the subchondral bone and to the walls of intact cartilage. The tissue repair was controlled at 1, 2, 4 and 6 months after the implant by NMR microscopy, synchrotron radiation induced X-ray emission to map the sulfur of glycosaminoglycans and by histochemistry. Practically a complete repair of the defect was observed 4–6 months from the implant of the chondrocytes with the recovery of a normal tissue structure. Controls in which Ca-alginate alone was implanted developed only a fibrous cartilage.

Introduction

The ability of articular cartilage to repair after an injury is very limited. The limited healing potential of this tissue can potentially be ascribed to the low metabolic and biosinthetic activities of mature chondrocytes and, at least in part, to the lack of chondrogenic cells available for repair [1]. Numerous, different, strategies have been used to induce cartilage repair with the final goal to fill the defects with a repair tissue indistinguishable from the native cartilage. Periosteal and perichondral tissue grafting, subchondral drilling, osteochondral allografting and chondrogenic cell transplantation have been widely used in experimental animals and in man (see [1], [2] for review). The technical difficulties encountered with the different techniques have promoted an increasing interest in the trasplantation of chondrogenic cells. Both autologous and allogenic transplantations have been performed and cell suspensions have been used in some cases after an in vitro expansion or after the achievement of biocompatible constructs with natural and artificial matrices (see [1] for review). Fibrin, hyaluronate, collagen gels (see [3], [4], [5] for review) or artificial polymers as biodegradable polyesters [6] of α-hydroxyacids [7] have been shown to support tissue ingrowth and repair. Some years ago alginate, a family of Ca²⁺-gelling algal polysaccharides which are linear copolymers of 1-4 linked β-d-mannuronic acid and α-l-guluronic acid, has been tested and employed for suspension cultures of chondrocytes from growing and articular cartilages [8], [9]. Since 1995 Paige and coworkers [10] have been using slowly polymerizing calcium alginate gels to provide a three-dimensional scaffold for transplantation and engraftment of chondrocytes in plastic and reconstructive surgery. The same authors have also demonstrated that cartilage formation is dependent on the concentration of chondrocytes in the construct but not on that of alginate and calcium chloride used for the gel formation [11].

The aim of the present work was to establish the feasibility of allogenic implants of chondrocytes in alginate gels for the reconstruction in vivo of damaged articular cartilage. The novelty of the procedure is that the suspension of chondrocytes in alginate is gelled directly into the defects of articular cartilage by the addition of a calcium chloride solution giving a construct perfectly inserted into the defect and adherent to the subchondral bone and to the cartilaginous border. Having proved the optimal survival of the cells in the construct, the main uncertainty was represented by the mechanical resistance of the construct in order to guarantee the survival of cells until they produce a new normal matrix.