Brain tissue and neural graft reactivity to the implantation of in situ self-assembled collagen matrices

The extracellular matrices of living tissue provide scaffolding supports for cell migration and interaction during tissue remodelling and regeneration and therefore may also be relevant to processes of regeneration in the injured central nervous system. We implanted in artificially made cavities of the neostriatum or cortex of adult rats a fluid collagen gelling system into which fetal grafts from either the substantia nigra or cortex were introduced. The collagen polymerizes to form a fibrillar matrix (organogel) which restitutes a physical continuity to the neural tissue. The host tissue reaction consisted of the ingrowth of blood vessels, the migration of mesenchymatous cells, of reactive astrocytes and of microglia within the bioimplant which became the substrate of heterogeneous cell interactions. As a result, newly formed collagen and carbohydrate-rich materials were deposited upon the collagen matrix while the bioimplant underwent remodelling. After 2 months, the original matrix was replaced by a glial–mesenchymal matrix into which nerve fibers of the lesioned striatum regenerated. The neural transplants survived and differentiated according to the stability of collagen matrices. We conclude that a collagen gelling system can be used to introduce a scaffolding structure into open brain wounds, and suggest that instead of sealing off the lesion, the ensuing scarring process rather favors tissue repair by establishing a glial-mesenchymal matrix well-suited for inducing intrinsic and extrinsic (grafts) neural regeneration.