Development and validation of a novel bioreactor system for load- and perfusion-controlled tissue engineering of chondrocyte-constructs

Osteoarthritis is a severe socio-economical disease,for which a suitable treatment modality does not exist.Tissue engineering of cartilage transplants is the most promisingmethod to treat focal cartilage defects. However,current culturing procedures do not yet meet the requirementsfor clinical implementation. This article presents anovel bioreactor device for the functional tissue engineeringof articular cartilage which enables cyclic mechanical loadingcombined with medium perfusion over long periods of time,under controlled cultivation and stimulation conditionswhilst ensuring system sterility. The closed bioreactor consistsof a small, perfused, autoclavable, twin chamber culturedevice with a contactless actuator for mechanical loading.Uni-axial loading is guided by externally applied magneticfields with real-time feedback-control from a platformload cell and an inductive proximity sensor. This precisemeasurement allows the development of the mechanicalproperties of the cultured tissue to be monitored in realtime.This is an essential step towards clinical implementation,as it allows accounting for differences in the cultureprocedure induced by patient-variability. This articledescribes, based on standard agarose hydrogels of 3 mmheight and 10 mm diameter, the technical concept, implementation,scalability, reproducibility, precision, andthe calibration procedures of the whole bioreactor instrument.Particular attention is given to the contactless loadingsystem by which chondrocyte scaffolds can be compressedat defined loading frequencies and magnitudes, whilstmaintaining an aseptic cultivation procedure. In a ¿¿proofof principle¿¿ experiment, chondrocyte seeded agarosegels were cultured for 21 days in the bioreactor system.Intermittent medium perfusion at a steady flow rate(0.5 mL/min) was applied. Sterility and cell viability (ds-DNA quantification and fluorometric live/dead staining)were preserved in the system. Flow induced shear stressstimulated sGAG (sulfated glycosaminoglycan) content(DMMB assay) after 21 days, which was confirmed byhistological staining of Alcian blue and by immunostainingof Aggrecan. Experimental data on mechanotransductionand long-term studies on the beneficial effects of combinedperfusion and different mechanical loading patterns onchondrocyte seeded scaffolds will be published separately