The mean (n = 3 donors) is plotted and the error bars represent SD.From the clinical or practical point of view, cell-based cartilage grafts do not only have to ensure formation of appropriate cartilage repair tissue but should also be easy in handling and allow for secure fixation of the graft in the defect. Therefore, the resorbable scaffold has to be initially stable. As shown here, the PGA scaffold shows a high tensile strength of 3.6 N/mm2 and stiffness slightly higher than articular cartilage. The mechanical characteristics of cell-based cartilage grafts cultured in vitro or matured in vivo are approximately an order of magnitude lower than native articular cartilage [46,47]. However, in clinical practice, the primary fixation of the scaffold by gluing, cartilage suture or trans-osseous fixation is of importance. If the fixation of the graft fails, the scaffolds get detached and result in PubMed ID:https://www.ncbi.nlm.nih.gov/pubmed/23410069 locking or catching of the knee and consequently in re-operations and a poor clinical outcome [12,48]. Since frictional forces are suggested to be the main reason for delamination or loosening of grafts [49], the tensile strength of the scaffolds may be more relevant for clinical applicability than the material’s elasticity or compressive strength. Therefore, measuring of the tensile strength is suggested to be of special importance for quality assurance of scaffold-based cartilage grafts. Polymerbased textile biomaterials like PGA or PLGA scaffolds as well as collagen-based scaffolds show sufficient (R)-3-Fluoropyrrolidine hydrochloride tensile strength with 10 to 40 N, as shown here and in a previous study [50], which withstand the forces that may occur directly after implantation of the graft and during rehabilitation with typical continuous passive motion (CPM) regime [50,51]. The PGA or PLGA scaffolds ensure initial mechanical stability for secure fixation of the PubMed ID:https://www.ncbi.nlm.nih.gov/pubmed/4155310 grafts and allow for an initiation of the chondrocytic redifferentiation process in vitro, while scaffold degradation and maturation of mechanical stable cartilaginous tissue occurs after transplantation in vivo [30,34]. This is in accordance with the formation and `mechanical’ development of cartilaginous tissue after transplantation of bovine articular chondrocytes embedded in PLGA-fibrin scaffolds, in a subcutaneous mouse model. Stiffness and tensile strength of the newly formed cartilage tissue increased between 6 and 12 weeks after transplantation of the chondrocyte PLGA-fibrin grafts. At 12 weeks, stiffness and strength of the generated tissue was comparable to native septal cartilage and showed 30-50 of the stiffness and strength found in native articular cartilage [46].Conclusion Our data found in the ovine model suggest that chondrocytes embedded in PGA-fibrin scaffolds re-differentiate in in vitro tissue culture without further stimuli like chondrogenic growth factors and that the cartilage markers type II collagen and aggrecan are relevant for testing of cell identity and potency for chondrocyte-based medicinal products. Characterization of the biomechanicalEndres et al. Journal of Orthopaedic Surgery and Research 2012, 7:37 http://www.josr-online.com/content/7/1/Page 13 ofproperties of the scaffold-assisted cartilage grafts should focus on measuring the tensile strength and, if applicable, the degradation kinetics of resorbable scaffolds.Competing interests ME, KN, UF and CK are employees of TransTissue Technologies GmbH. TransTiss.