Eric Miller — 2003-04 Fellow
Current tissue engineering therapies which deliver growth factors involve the use of degradable matrices or microcapsules that release signaling molecules into the interstitial space where they diffuse out to form liquid-phase concentration gradients. These gradients provide directional cues for cell proliferation, migration and differentiation. However, soluble gradients are transient and the only way to increase persistence is to deliver the growth factors in relatively large concentrations. One possible solution to address persistence and dosing issues is to immobilize the growth factors in gradient patterns within a delivery matrix, known as solid phase delivery. We have developed an ink jet printing process with the ability to create two-dimensional solid-phase gradient patterns of growth factors.
Since the main interest of our laboratory is bone, fibroblast growth factor-2 (FGF-2), a growth factor critical in bone regeneration, was selected as the model growth factor. Both uniform and gradient patterns of FGF-2 were printed onto fibrin-coated glass slides followed by seeding of the patterns with MG-63 human osteosarcoma cells in serum-free medium. The bio-ink used to create the patterns consisted of a mixture of FGF-2 and FGF-2 labeled with Cy3 dye to fluorescently image the printed patterns and to verify that the FGF-2 was immobilized on the fibrin. The surface concentration of FGF-2 was controlled by varying the number of overprints for each pattern. The cells proliferated in register with the patterns in a concentration dependent manner indicating that the printed FGF-2 was biologically active and remained bound to the fibrin long enough to elicit a biological response.
Our future work involves focusing on cell migration rather than proliferation by printing a gradient of immobilized FGF-2 and seeding the cells at the "starting line" to determine if they will migrate along a solid phase growth factor concentration gradient.