EFFECTS OF A RELATIVE TRIBOLOGICAL MOVEMENT ON THE EXPRESSION OF TRIBOLOGICAL FUNCTION OF REGENERATED CARTILAGE WITH BMSCS

Introduction It is essential to investigate the tribological maturation of tissue-engineered cartilage that is to be used in medical applications. The frictional performances of tissue engineered cartilage have been measured using flat counter surfaces such as stainless steel, glass or ceramics. However, the measured friction performances were significantly inferior to those of natural cartilage, likely because of cartilage adhesion to the counter surface. Tamura et al. reported that a poly (2- methacryloyloxyethyl phosphoryl-choline (MPC)) grafted surface shows low friction coefficient against cartilage without the adhesion to be equivalent to those for natural cartilage-on-cartilage friction. [1] On the other hand, Yamamoto et al. reported that applying a relative sliding movement had a potential to alter the expression of tribological function of regenerated cartilage of chondrocytes. [2] In this paper, the effects of the relative sliding movement on the expression of bone marrow stromal cells (BMSC)s were investigated using the poly(MPC) grafted surface as a counter surface. Material and methods BMSCs seeded onto fibroin sponge scaffolds were cultured by using the stirring chamber system (Figure 1), which can apply a relative tribological movement to the surface of the specimens. Three culture conditions were applied (dynamic in stirring chamber as frequency as 40 min [D1], as 40 sec [D2] and static in stirring chamber group [S]). The specimens were set into stirrer on a poly(MPC) grafted surface (MPC polymer coated surface, SANSYO). As a counter surface in friction tests, the poly(MPC) grafted surface was prepared by atom transfer radical polymerization, and the regenerated cartilage was prepared by seeding 5×10 5 cells (BMSCs from rat bone marrow) onto fibroin sponge scaffolds (8 mm diameter and 1 mm thickness) and by 14 days culture. Results and Discussion The friction coefficient in D1 group tended to be lower than that in S group. Similarly, D2 group tended to show lower value than S group (Figure 2). However, the value of D1 and D2 group was extraordinary high, compared to that of intact articular cartilage. The GAG amount of D1 and D2 group was significantly higher than that of S group. All of the groups showed Collagen type I and type II staining at the surface. S group showed wider staining region than D1 and D2 group. However there was no Alcian Blue staining (Figure 3). These results indicate that the stirring chamber system tended to improve the frictional performance of regenerated tissue. However this relative tribological movement has not a potential to induce effects on the differentiation of BMSCs to chondrocytes.