Abstract:To repair articular cartilage defects in osteoarthritic patients with three-dimensional tissue engineered chondrocyte grafts, requires the formation of new cartilage with sufficient mechanical properties. The premise is that mechanical stimulation during the culturing process is necessary to reach this aim. Therefore, mechanical stimulation systems have been integrated in aseptic bioreactors for in vitro cultivation of tissue engineered cartilage. These vary from simple unconfined compression systems to advanced bioreactors in which deformation and loading are fully controlled. Fluid handling in these devices is another decisive parameter for the success of cartilage tissue engineering.Over the last decades bioreactor developments have resulted in the filing of many patents. The aim of this paper is to review these patents, categorize them according to their possibilities for mechanical stimulation and fluid handling systems and finally to discuss them in the context of the demands of a functional tissue engineered cartilage from a mechanical perspective.
Most current cartilage testing devices require the preparation of excised samples and therefore do not allow intra-operative application for diagnostic purposes. The gold standard during open or arthroscopic surgery is still the subjective perception of manual palpation. This work presents a new diagnostic method of ultrasound palpation (USP) to acquire applied stress and strain data during manual palpation of articular cartilage. With the proposed method, we obtain cartilage thickness and stiffness. Moreover, repeated palpations allow the quantification of relaxation effects. USP measurements on elastomer phantoms demonstrated very good repeatability for both, stage-guided (97.2%) and handheld (96.0%) applications. The USP measurements were compared with conventional indentation experiments and revealed very good agreement on elastomer phantoms ([Formula: see text]) and good agreement on porcine cartilage samples ([Formula: see text]). Artificially degenerated cartilage samples showed reduced stiffness, weak capacity to relax after palpation and an increase of stiffness of approximately 50% with each single palpation. Intact cartilage was measured by USP directly at the patella (in situ) and after excision and removal of the subchondral bone (ex situ), leading to stiffness values of [Formula: see text] and [Formula: see text] ([Formula: see text]), respectively. The results demonstrate the potential of the USP system for cartilage testing, its sensitivity to degenerative changes and as a method for quantifying relaxation processes by means of repeated palpations. Furthermore, the differences in the results of in-situ and ex-situ measurements are of general interest, since such comparison has not been reported previously. We point out the limited comparability of ex-situ cartilage with its in-situ biomechanical behavior.
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