[Tissue engineering of cartilage replacement material - mechanical stimulation in the in-vitro cultivation of human...

The treatment of cartilage defects remains a major problem in orthopaedics. With regard to cartilage tissue engineering, the reimplantation of pre-cultivated chondrocytes in the form of a chondrocyte graft is a promising alternative to conventional methods. Clinical practice requires this MACT procedure (matrix-associated autologous chondrocyte transplantation) to produce a biocompatible replacement tissue with adequate mechanical properties. Mechanical stimulation has the capacity to improve the quality of these cell-seeded biomaterials. By altering chondrocytes' cellular activities, the biological and biomechanical properties of cartilage replacement tissue can be modulated. Different systems are used for this purpose, e.g. shear, perfusion, hydrostatic pressure or compression. The mechanisms, biological effects, chances and problems of the techniques are presented and assessed. Among the stimulating techniques considered are systems that apply indirect and direct shear forces such as spinner flasks, rotating-wall bioreactors, direct tissue shear and perfusion culture systems. The application of hydrostatic pressure or compression may be brought about by either static or dynamic loading systems. Compressive loading is considered in the light of both its short- and long-term effects; additionally two exemplified systems are discussed in detail. However, despite promising approaches and seemingly favourable tissue characteristics, the in vitro culturing of functional cartilage replacement tissue with cartilage-like mechanical and biological characteristics still remains elusive. Furthermore, controlling, monitoring and regulating culturing conditions are general biotechnological requirements of a standardised in vitro cultivation. Among these, different aspects such as aseptic operation, media supplementation, nutrient and gas exchange, temperature and humidity control are considered.