Bioreactor based engineering of large-scale human cartilage grafts for joint resurfacing Rosaria Santoro a , Andy L. Olivares b , Gerben Brans c , Dieter Wirz d , Cristina Longinotti e , Damien Lacroix b , Ivan Martin a, * , David Wendt a a Departments of Surgery and of Biomedicine, University Hospital Basel, Hebelstrasse 20, 4031 Basel, Switzerland b Institute for Bioengineering of Catalonia, Spain c Applikon Biotechnology BV, The Netherlands d Laboratory of Biomechanics & Biocalorimetry, University of Basel, Switzerland e Fidia Advanced Biopolymers srl, Italy article info Article history: Received 30 July 2010 Accepted 4 August 2010 Available online 25 August 2010 Keywords: Bioreactor Cartilage repair Computational fluid dynamics Scale-up Regenerative medicine Tissue engineering abstract Apart from partial or total joint replacement, no surgical procedure is currently available to treat large and deep cartilage defects associated with advanced diseases such as osteoarthritis. In this work, we developed a perfusion bioreactor system to engineer human cartilage grafts in a size with clinical relevance for unicompartmental resurfacing of human knee joints (50 mm diameter  3 mm thick). Computational fluid dynamics models were developed to optimize the flow profile when designing the perfusion chamber. Using the developed system, human chondrocytes could be seeded throughout large 50 mm diameter scaffolds with a uniform distribution. Following two weeks culture, tissues grown in the bioreactor were viable and homogeneously cartilaginous, with biomechanical properties approaching those of native cartilage. In contrast, tissues generated by conventional manual production procedures were highly inhomogeneous and contained large necrotic regions. The unprecedented engineering of human cartilage tissues in this large-scale opens the practical perspective of grafting functional biological substitutes for the clinical treatment for extensive cartilage defects, possibly in combination with surgical or pharmacological therapies to support durability of the implant. Ongoing efforts are aimed at inte- grating the up-scaled bioreactor based processes within a fully automated and closed manufacturing system for safe, standardized, and GMP compliant production of large-scale cartilage grafts. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction While Carticel Ò and Hyalograft-C Ò have been well established in the clinic for the treatment of traumatic focal cartilage defects [1e3], no tissue engineered product is currently available to treat large defects or those associated with advanced diseases such as osteoar- thritis. Beyond the biological challenges that must be addressed to treat such joint disorders, it remains a significant engineering chal- lenge to generate up-scaled cartilage grafts with dimensions that would be sufficient for the repair of large, advanced, and deep defects. We previously developed a perfusion bioreactor for seeding and culturing cell-scaffold constructs with a clinically relevant thick- ness (z4 mm) and demonstrated that highly viable and homoge- neous tissues could be generated [4]. However, the diameter of the engineered tissues, representative of constructs typically described in the literature for research purposes (i.e., z8 mm diameter), would not be applicable for the treatment of large defects unless multiple plugs were generated and implanted in a surgical proce- dure resembling mosaicplasty. Therefore, in this work, we scaled- up our perfusion bioreactor system to engineer large-sized human cartilage grafts, in dimensions that would be sufficient for uni- compartmental resurfacing of a human knee joint (50 mm diam- eter  3 mm thick). Computational fluid dynamics (CFD) models were developed to assist in the design of a bioreactor that could generate a uniform velocity profile over the surface of the large- diameter scaffold. Experimental validations demonstrated that the developed bioreactor system seeded cells uniformly throughout the large-scale scaffold, and following prolonged culture, supported the generation of viable, homogeneous, and cartilaginous tissue constructs with biomechanical properties approaching those of native cartilage. In contrast, constructs generated by conventional manual production procedures were highly inhomogeneous con- taining a significant non-viable and void region, highlighting the necessity of a perfusion bioreactor based approach for engineering large-scale cartilage grafts. * Corresponding author. Tel.: þ41 61 265 2384; fax: þ41 61 265 3990. E-mail address: imartin@uhbs.ch (I. Martin). Contents lists available at ScienceDirect Biomaterials journal homepage: www.elsevier.com/locate/biomaterials 0142-9612/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.biomaterials.2010.08.009 Biomaterials 31 (2010) 8946e8952