Astrocyte infiltration into injectable collagen-based hydrogels containing FGF-2 to treat spinal cord injury

Astrocytes can play dual roles in the response to spinal cord injury (SCI) acting as both an inhibitory barrier and a trophic support for growth axons. Therefore, migration of these cells into the defect as opposed to forming a scar at the periphery, may promote axon regeneration through the lesion. However, infiltration requires the conformal filling of the cyst-like lesion, which often forms after SCI, with a biomaterial scaffold encouraging of astrocyte migration. For this application, we investigated injectable collagen-based hydrogels covalently cross-linked with genipin and incorporating fibroblast growth factor-2 (FGF-2) either freely or encapsulated within lipid microtubules (LMTs). An outgrowth assay was used to evaluate in vitro the number of primary rat astrocytes infiltrating into the collagen gels and the distance to which they infiltrated. The presence of FGF-2 within the encapsulating gel significantly increased the number of astrocytes within the gel, their penetration distance into the gel, and caused them to move out in a chain-like pattern, compared to control gels without FGF-2. Genipin cross-linking of the collagen gel decreased the number of infiltrating astrocytes, compared to the non-cross-linked control gel; however, incorporation of FGF-2-containing LMTs within genipin-cross-linked gels restored the astrocyte infiltration to levels approaching non-cross-linked gels incorporating FGF-2. Overall, injectable collagen-genipin hydrogels containing FGF-2-containing LMTs are a promising candidate for the treatment for SCI through the attraction of astrocytes into the graft.