The development of the collagen fibre network in tissue-engineered cartilage constructs in vivo. Engineered cartilage reorganises fibre network.

For long term durability of tissue-engineered cartilage implanted in vivo, the development of the collagen fibre network orientation is essential as well as the distribution of collagen, since expanded chondrocytes are known to synthesise collagen type I. Typically, these properties differ strongly between native and tissue-engineered cartilage. Nonetheless, the clinical results of a pilot study with implanted tissue-engineered cartilage in pigs were surprisingly good. The purpose of this study was therefore to analyse if the structure and composition of the artificial cartilage tissue changes in the first 52 weeks after implantation. Thus, collagen network orientation and collagen type distribution in tissue-engineered cartilage-carrier-constructs implanted in the knee joints of Göttinger minipigs for 2, 26 or 52 weeks have been further investigated by processing digitised microscopy images of histological sections. The comparison to native cartilage demonstrated that fibre orientation over the cartilage depth has a clear tendency towards native cartilage with increasing time of implantation. After 2 weeks, the collagen fibres of the superficial zone were oriented parallel to the articular surface with little anisotropy present in the middle and deep zones. Overall, fibre orientation and collagen distribution within the implants were less homogenous than in native cartilage tissue. Despite a relatively low number of specimens, the consistent observation of a continuous approximation to native tissue is very promising and suggests that it may not be necessary to engineer the perfect tissue for implantation but rather to provide an intermediate solution to help the body to heal itself.

Technical strategies to improve tissue engineering of cartilage-carrier-constructs.

Technical aspects play an important role in tissue engineering. Especially an improved design of bioreactors is crucial for cultivation of artificial three-dimensional tissues in vitro. Here formation of cartilage-carrier-constructs is used to demonstrate that the quality of the tissue can be significantly improved by using optimized culture conditions (oxygen concentration, growth factor combination) as well as special bioreactor techniques to induce fluid-dynamic, hydrostatic or mechanical load during generation of cartilage.

The effect of light and temperature on the growth of two subtropical and two temperate grass species.

The effect of light intensity and temperature on the growth of young plants of two temperate (Lolium perenne, Festuca arundinacea) and two subtropical (Lolium rigidum, Bromus unioloides) grass species was studied in the northern part of the GDR under open-air conditions. It was found that the subtropical species reacted highly sensitive to changes in the two environmental factors and showed absolutely higher growth performance during the summer as compared with the temperate species. The multiple regression analysis showed positive correlations between the relative growth rate (RGR) and the net assimilation rate (NAR) on the one hand and temperature and light intensity on the other hand. For most regression functions the range of variation was found to be between 63.5 and 91.3 per cent. No clear proof could be found of the dependence of the leaf area ratio (LAR) on light and temperature. The results are discussed and compared with similar investigations.