Chondrocyte aggregation on micrometric surface topography: a time-lapse study

Cellular aggregation or mesenchymal "condensation" is a prerequisite in the process of chondrogenesis. It has been observed that during in vitro engineering of cartilage, chondrocytes form aggregates in the initial cell seeding process of polymer scaffolds. However, the exact mechanism behind this aggregation has yet to be elucidated, although cell collision has been implicated. As all polymers have a surface topography, we hypothesized that topography may play a role in chondrocyte aggregation. 1(st) and 2(nd) passage chondrocytes were seeded on micrometric topography ranging from 0.75 to 8 microm in depth and 5 to 12.5 microm in width. Both 1(st) and 2(nd) passage cells formed aggregates as cells collided, and larger aggregates formed as aggregates collided with each other on the grooves. Furthermore, aggregates migrated parallel to the direction of the groove long axis. F-actin organization was altered only in the cellular layer in direct contact with the surface; stress fibers oriented in the direction of the groove long axis. Chondrocytes maintained type II collagen expression on all groove depths. This study shows that micrometric grooves could be an effective means for studying chondrocyte aggregation, and could additionally be utilized in the regeneration of cartilage.