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Open Access Highly Accessed Research article

A novel in vitro bovine cartilage punch model for assessing the regeneration of focal cartilage defects with biocompatible bacterial nanocellulose

David Pretzel14*, Stefanie Linss1, Hannes Ahrem26, Michaela Endres3, Christian Kaps3, Dieter Klemm5 and Raimund W Kinne1

Author affiliations

1 Experimental Rheumatology Unit, Department of Orthopedics, Jena University Hospital, Friedrich Schiller University Jena, Waldkrankenhaus "Rudolf-Elle" GmbH, Klosterlausnitzer Str. 81, D-07607 Eisenberg, Germany

2 Jenpolymer Materials Ltd. & Co. KG, Technologie- und Innovationspark Jena - TIP, Wildenbruchstraße 15, D-07745 Jena, Germany

3 TransTissueTechnologies GmbH, Charitéplatz 1/Virchowweg 11, D-10117 Berlin, Germany

4 Institute of Macromolecular and Organic Chemistry, Friedrich Schiller University Jena, Lessingstr. 8, D-07743 Jena, Germany

5 Transfer Group Polymet e.V., Wildenbruchstr. 15, D-07745 Jena, Germany

6 Institute of Pharmacy, Department of Pharmaceutical Technology, Friedrich Schiller University Jena, Otto-Schott-Straße 41, D-07745 Jena, Germany

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Citation and License

Arthritis Research & Therapy 2013, 15:R59  doi:10.1186/ar4231

Published: 14 May 2013

Abstract

Introduction

Current therapies for articular cartilage defects fail to achieve qualitatively sufficient tissue regeneration, possibly because of a mismatch between the speed of cartilage rebuilding and the resorption of degradable implant polymers. The present study focused on the self-healing capacity of resident cartilage cells in conjunction with cell-free and biocompatible (but non-resorbable) bacterial nanocellulose (BNC). This was tested in a novel in vitro bovine cartilage punch model.

Methods

Standardized bovine cartilage discs with a central defect filled with BNC were cultured for up to eight weeks with/without stimulation with transforming growth factor-β1 (TGF-β1. Cartilage formation and integrity were analyzed by histology, immunohistochemistry and electron microscopy. Content, release and neosynthesis of the matrix molecules proteoglycan/aggrecan, collagen II and collagen I were also quantified. Finally, gene expression of these molecules was profiled in resident chondrocytes and chondrocytes migrated onto the cartilage surface or the implant material.

Results

Non-stimulated and especially TGF-β1-stimulated cartilage discs displayed a preserved structural and functional integrity of the chondrocytes and surrounding matrix, remained vital in long-term culture (eight weeks) without signs of degeneration and showed substantial synthesis of cartilage-specific molecules at the protein and mRNA level. Whereas mobilization of chondrocytes from the matrix onto the surface of cartilage and implant was pivotal for successful seeding of cell-free BNC, chondrocytes did not immigrate into the central BNC area, possibly due to the relatively small diameter of its pores (2 to 5 μm). Chondrocytes on the BNC surface showed signs of successful redifferentiation over time, including increase of aggrecan/collagen type II mRNA, decrease of collagen type I mRNA and initial deposition of proteoglycan and collagen type II in long-term high-density pellet cultures. Although TGF-β1 stimulation showed protective effects on matrix integrity, effects on other parameters were limited.

Conclusions

The present bovine cartilage punch model represents a robust, reproducible and highly suitable tool for the long-term culture of cartilage, maintaining matrix integrity and homoeostasis. As an alternative to animal studies, this model may closely reflect early stages of cartilage regeneration, allowing the evaluation of promising biomaterials with/without chondrogenic factors.