Magnetic-induced alignment of collagen fibrils in tissue equivalents

The use of reconstituted type I collagen gel as a scaffold for engineered soft tissues is a highly attractive prospect, given that collagen is the principal component of the extracellular matrix (ECM) in vivo, providing a mechanically suitable and information-rich scaffold for cell-ECM interactions. It has the advantage that cells can be directly entrapped within the comprising collagen fibrils as they grow into an entangled network from a cell containing solution of monomeric type I collagen. These tissue equivalents have the further advantage that the collagen fibrils can be aligned by applying a magnetic field during fibrillogenesis. Then, through a process termed "contact guidance," the cells align with the fibrils by directing their motility. Such alignment is characteristic of many tissues, and may provide microstructural and mechanical cues for regulation of cell phenotype and function, as well as influence the gross mechanical properties of the tissues. Recent research in our laboratory has used magnetic-induced alignment in the fabrication of tissue-equivalents, notably circumferential alignment in tubes, and longitudinal alignment in rods (patent pending). The former is aimed at reproducing the architecture of the arterial media; the latter is aimed at providing a bridge that promotes directed axonal growth between severed nerve ends. These tissue engineering applications exploit the finding of Torbet and Ronziere (1) in their cell-free studies that forming fibrils tend to align in the plane normal to the direction of the field (because of the negative diamagnetic anisotropy of collagen) and parallel to the mold surfaces (because of an uncharacterized interfacial effect).