Mechanical loading of cartilage

Gabriela Mielke, Elisa Hoenig, Helge Paetzold

Abb.1: Construct of cultured cartilage on a ceramic carrier	Abb.2: Bioreactor for the mechanical loading of cartilage constructs	Abb.3: SEM image of collagen fibers in native pig cartilage

Cartilage tissue is not simply a cluster of cartilage cells (chondrocytes), but contains of well-defined extracellular structures, called the extracellular matrix (ECM).  In hyaline joint cartilage, the ECM is mostly made from collagen type II which, combined with the proteoglycan aggrecan, defines the compressive-elastic properties of the cartilage. In vivo, those properties depend upon mechanical stimuli. For a healthy person, the joint cartilage is compressed and decompressed thousands of times each day. These load cycles are essential to prevent cartilage degeneration.
Adult cartilage is characterized by its limited capability to regenerate. Damages caused by mechanical traumata or diseases will aggravate continuously causing severe pain for the patient. Available surgical treatments to restore the biological and mechanical capacities of the cartilage tissue are still not fully satisfactory. When joint cartilage fails, today’s gold standard still is to replace the affected joint with an endoprosthesis.

Abb.4: Histological staining of GAG in cultured cartilage	Abb.5: Cultured cartilage	Abb.6: Immunofluorescence of collagen in native pig cartilage

A newer and less invasive approach is the tissue engineering (TE), where functional tissue for future implantation at damaged areas is grown in vitro. At our institute, tissue engineering of porcine joint cartilage is one field of research. Cooperation partners are the Institute of Bioprocess and Biosystems Engineering at TUHH and the Department of Biomechanics at UKE. An innovative bioreactor, reproducing the physiological movement of the knee joint, has been built and brought into service. With this reactor, various loading situations including compression, shear and the characteristic roll-glide-movement of the knee joint can be applied to the tissue while it is cultivated.
Aim of the project is to analyze the influence of different load collectives upon the mechanical, biochemical and structural properties of the TE-cartilage and to thereby derive the optimal conditioning parameters to increase the overall quality of TE-cartilage tissue.

Publications:

Hoenig, E., Leicht, U., Winkler, T., Mielke, G., Beck, K., Peters, F., Schilling, A.F., Morlock, M.M. Mechanical Properties of Native and Tissue-Engineered Cartilage depend on Carrier Permeability: A Bioreactor Study Tissue Eng Part A. 2013 Volume 19: Issue 13-14, 2013.

Paetzold, H., Goepfert, C., Huber, G., Hoenig, E., Pörtner, R., Schilling, A.F., Meenen, N.M., Morlock, M.M. The development of the collagen fibre network in tissue-engineered cartilage constructs in vivo. Engineered cartilage reorganises fibre network  Eur Cell Mater. 2012 Apr 5;23: 209-21, 2012

Hoenig, E., Winkler, T., Goepfert, C., Mielke, G., Paetzold, H., Schuettler, D., Machens, H.G., Morlock, M.M., Schilling, A.F. High amplitude direct compressive strain enhances mechanical properties of scaffold-free tissue-engineered cartilage Tissue Eng Part A. 2011 May; 17(9-10): 1401-11, Epub 2011 Feb 27, 2011.

Pörtner, R., Goepfert, C., Wiegandt, K., Janssen, R., Ilinich, E., Paetzold, H., Eisenbarth, E., Morlock, M. Technical Strategies to Improve Tissue Engineering of Cartilage-Carrier-Constructs Adv Biochem Eng Biotechnol. 2009;112:145-81.