90° Peel off Tests of Tissue Engineered Osteochondral Constructs: A New Method to Determine the Osteochondral Integration

One promising treatment of localized osteochondral defects in the knee joint may be the implantation of in vitro tissue-engineered osteochondral constructs. A crucial aspect of this kind of osteochondral construct is the bonding between the bone-scaffold and scaffold-based chondral layer. Here, a 90° peel off test is proposed as an appropriate method to measure the integration of cartilage to bone in osteochondral constructs for different primary methods of bonding the cartilage scaffold to the bone scaffold, with and without seeded chondroblasts. The method was developed and then tested on tissue-engineered constructs. The force/displacement data obtained allow determination of both the maximum force and the total energy required to separate the two layers. The tests showed good reproducibility and good discrimination between measurements as a function of seeding times. Average maximum peel-off forces varied between 10？mN for fibrin glue only to 575？mN for constructs with cells after four weeks of incubation. Linear regression of the area under the curve (AUC) as a function of maximum force shows a high correlation between the two parameters with R2？=？0.97. The main limitation of the test is that the data provide only a modest ability to decide how uniform the bond is over the area between the two layers. 1. Introduction In adolescents and young adults, osteochondritis dissecans is a severe but fortunately not too common problem in which cracks form in the articular cartilage and underlying bone. Both the poor self-healing capacity and progression of such chondral and osteochondral joint lesions to osteoarthritis and the limitations of current methods of treatment are still problems [1]. Quite often, if the replantation of the dissected osteochondral lesion is not possible, techniques like mosaicplasty are performed, even though these treatments are often not entirely effective and can entail complications with the donor site [2]. One of the promising treatments in the future may be the implantation of in vitro tissue-engineered osteochondral constructs [3]. The osseous layer of an osteochondral implant integrates well with the surrounding bone as Schaefer et al. [4] could demonstrate, with ready ingrowth of trabecular bone into the osseous layer of the graft. But the integration with the surrounding cartilage was poor. Therefore, an important aspect of the treatment of osteochondral joint lesions with osteochondral constructs will be the mechanical quality of the bond between the two layers as it is imperative that no separation occurs. For this