Controlled growth factor delivery induces differential neurite outgrowth in three-dimensional cell cultures

Abstract Long-term, localized delivery of growth factors may help regenerate lost structure and function in diseased or traumatized tissues. In previous reports, we have described techniques for releasing precisely controlled quantities of mouse nerve growth factor (NGF) from a poly (ethylene-co-vinyl acetate) matrix. To further study the dynamics and bioactivity of NGF released from a polymer matrix, we cultured PC 12 cells within hydrated gels of type I collagen and embedded a polymer matrix containing NGF in one end of the gel. Spatial variations in neurite outgrowth and NGF concentration were determined for 2 weeks. For comparison, the rate of NGF release from the polymer matrix into buffered saline was also determined. NGF released from a biocompatible polymer matrix induced neurite outgrowth in cells cultured within a three-dimensional gel of collagen. NGF was transported through the collagen gel by diffusion through the gel and convection due to fluid movement into the overlying, well-mixed fluid layer. The extent of neurite outgrowth from the cell clumps at any position in the gel depended on both the time following polymer insertion and distance from the polymer. Neurite outgrowth was most dense within the 15-mm region nearest the polymer, although biologically active NGF did penetrate as far as 38 mm. These techniques may be useful in evaluating the role of controlled release polymers in growth factor delivery to tissues. In addition, this experimental system can be used to quantify the response of tissue-derived cells to well-defined gradients of biologically active factors.