Flow and magnetic field induced collagen alignment.

A straightforward technique to align thin collagen gels is presented. This technique requires only collagen solution, surface-modified magnetic beads, a small magnet, and an incubator. As such, this is the only collagen alignment technique that requires no specialized equipment. The collagen gels are imaged with confocal reflectance microscopy, and degree of alignment is quantitatively assessed using image analysis techniques that allow for identification of fiber position and angular distribution. A series of experiments shows that magnetic beads coated with streptavidin lead to the most highly aligned gels. Rheology and microscopy experiments suggest that alignment results from bead coupling to, and entrainment and entrapment in, collagen fibrils during their assembly into fibers that form a sample-spanning gel. The timescales of gelation and bead motion to the poles of the external magnet must be similar to effect good alignment over large areas with this technique. It is also demonstrated that alignment can be attained in both plain and cell-bearing gels that are several millimeters thick.