Alginate as a chondrocyte-delivery substance in combination with a non-woven scaffold for cartilage tissue engineering

Abstract

For tissue engineering of cartilage, chondrocytes can be seeded in a scaffold and stimulated to produce a cartilage-like matrix. In the present study, we investigated the effect of alginate as a chondrocyte-delivery substance for the construction of cartilage grafts. E210 (a non-woven fleece of polyglactin) was used as a scaffold.

When ‘bare’ E210 (without alginate and without chondrocytes) was implanted subcutaneously in nude mice for 8 weeks, the explanted tissue consisted of fat and fibrous tissue only. When E210 with alginate but without chondrocytes was implanted in nude mice, small areas of newly formed cartilage were found. Alginate seems to stimulate chondrogenesis of ingrowing cells. When chondrocytes were seeded in E210, large amounts of cartilage were found, independent of the use of alginate. This was expressed by a high concentration of glycosaminoglycans (30 μg/mg w.w.) and the presence of collagen type II (1.5 μg/mg w.w.). Macroscopically the grafts of E210 without alginate were shrunk and warped, whereas the grafts with alginate had kept their original shape during the 8 weeks of implantation. The use of alginate did not lead to inflammatory reactions nor increased capsule formation.

In conclusion, the use of alginate to seed chondrocytes in E210 does not influence the amount of cartilage matrix proteins produced per tissue wet weight. However, it provides retention of the graft shape.

Introduction

Hyaline cartilage defects still pose a major problem to orthopaedic and facial reconstructive surgeons, since these defects do not heal spontaneously with hyaline cartilage. The use of tissue-engineering techniques could be an appropriate way to generate hyaline cartilage grafts for the treatment of cartilage defects in the future. These techniques combine isolated cells with biodegradable scaffolds in order to stimulate production of new cartilage tissue with the typical characteristics of native hyaline cartilage. Autologous cells are generally preferred to avoid risks of immunological rejection and transmission of infectious diseases.

The ideal biodegradable scaffold should provide a preformed three-dimensional shape and initial mechanical strength. In addition it should make uniform cell spreading possible, stimulate the chondrogenic phenotype of the transplanted chondrocytes and prevent cells from floating out of the defect. Combinations of polylactic and polyglycolic acid are frequently used as cell carrier [1], [2], [3]. In previous studies, we obtained promising results using Ethisorb 210, a non-woven fleece composed of a polyglycolic–polylactic-copolymer punctually glued with polydioxanon. (Ethicon, Norderstedt, Germany) [4], [5], [6].

Although isolated chondrocytes can be seeded directly into the scaffold, one could also use a carrier gel for cell-seeding. Nowadays, alginate is frequently applied as cell-carrying gel, both in vitro and in vivo [6], [7], [8], [9], [10], [11], [12]. The use of alginate may facilitate a uniform distribution of chondrocytes in the relatively wide pores of the scaffold and prevent cells from floating out. Moreover, in vitro experiments showed that alginate can stimulate expression of the chondrogenic phenotype [13]. Whereas alginate has been used in humans for transplantation of pancreatic-islets cells without negative effects [14], alginate or its degradation products could possibly influence chondrocyte matrix neosynthesis.

In this study, we investigated the effect of the use of alginate as a chondrocyte-delivery substance for the construction of a cartilage graft. E210 was used as a scaffold and implanted in athymic mice, with and without alginate and with and without differentiated bovine articular chondrocytes.