Cell behavior in QGel matrices is cell type-dependent. For example, cancer cells will keep a round shape and grow as spheroids, whereas fibroblastic cells will rather spread and adopt a spindle-like morphology. Regarding fibroblasts, in order to spread, proliferate and migrate in 3D within QGel matrices, they require 1) to adhere to the matrix via incorporated RGD peptide and 2) to degrade the matrix by expression and activation of MMPs. This is why degradable matrix with RGD (ref. 1001) is the suitable QGel matrix type for fibroblasts. The ability to degrade the matrix through MMP secretion and activation is an important aspect because if fibroblasts or the cells encapsulated in these QGel matrices cannot locally degrade the hydrogel network, they won't have enough space to spread/proliferate/migrate.

In fact, the pore size of QGel matrices is smaller than the size of a cell. This is also supported by the fact that in the non-degradable gels with RGD cells do not spread. This aspect is an important difference compared to collagen or basement membrane extract matrices, where cells can spread/proliferate/migrate even without the need of proteolytically degrading the gels. This is because of the presence of pores (this aspect is nicely described in Raeber G.P. et al., Biophysical Journal, 2005) as well as because of the ability of cells to mechanically remodel these matrices. In addition, in the case of open porous scaffolds (e.g. collagen sponges, alginate, polystyrene scaffolds), cells are often not encapsulated in the matrix but seeded on top and they migrate over time through the pores inside. Therefore, this also represents an important difference between porous scaffold and QGel matrices in terms of 3D culture methods.

Spreading, proliferation and migration in 3D, can also be influenced by the matrix stiffness. Despite the presence of RGD sites and of MMP sensitive sites, hydrogels with high stiffness (e.g. high G' moduli) do not allow or retard cell spreading and proliferation in 3D. This often means that the cell proteolytic machinery is not active enough to degrade the hydrogel network. The stiffer the QGel matrix, the higher the crosslink density and also the higher the concentration of MMP-substrates needed to be degraded to allow the cells to create enough space for spreading/proliferation/migration. We are currently working on protocols to lower stiffness of the current QGel matrix formulations. Indeed, certain cell types were shown to require softer matrices for enhanced activity and proliferation. Please contact us if you would like more information about it.

In the paper Bott K. et al, Biomaterials, 2010 you can find examples on how the different matrix characteristics (biological, biochemical and mechanical) are influencing independently spreading and proliferation of fibroblasts in biomimetic 3D gels similar to QGel MT 3D Matrix.