Polyelectrolyte Multilayer Films Containing Stiffness Gradients Or Matrix-Bound Growth Factor Gradients Influence Cell Behavior

Cellular fate in the native environment is determined by a number of cues (biochemical, mechanical, etc.) that are present in a gradient fashion. Towards developing materials that capture the native microenvironment, we engineered biomimetic films presenting a gradient in stiffness and of matrix-bound growth factors to investigate 1) the effect of film stiffness on cell adhesion and 2) the effect of matrix bound chemokines on cell migration and differentiation. Gradients were generated on polyelectrolyte multilayer (PEM) films composed of hyaluronan (HA) and poly(l-lysine) (PLL) using a microfluidic device. First, a gradient of water-soluble carbodiimide as cross-linking agent was used to generate the stiffness gradient, confirmed using atomic force microscopy. Pre-osteoblastic cells seeded on the stiffness gradients adhered better and spread more in regions of high stiffness; while in low stiffness regions they behave poorly with regards to adhesion and spreading. Subsequently, a matrix-bound gradient of the cytokine stromal derived factor 1 (SDF-1) was generated to investigate its effect on cellular migration. Time-lapse microscopy experiments showed that cellular velocities of C2C12 myoblasts decreased with decreasing SDF-1 concentration. Lastly, a matrix-bound gradient of the bone morphonogenic protein 2 (BMP-2) was generated to investigate muscle cell trans-differentiation in bone cells. C2C12 Cells responded by expressing SMAD and alkaline phosphatase in a spatially controlled manner. Moreover, on regions of low BMP-2 concentration, a dose dependent expression of myoblastic markers (troponin T) was observed. This technology allows for determining quickly and efficiently the optimal biochemical and physical cues necessary for specific cellular response, whilst furthering the knowledge of cell/material interactions in a mimetic niche.