My lab performs three-dimensional culture of neuronal cell lines using 50% Matrigel. Usually, the 50% concentration of Matrigel is used as a condition that promotes efficient neurite outgrowth. For immunostaining, we fixed the cells in Matrigel in two different conditions; 4% PFA (approx 4 degrees in Cercius) or 3.7% formaldehyde (at room temperature), however, the Matrigel became a solution following fixation. I suppose that laminin depolymerization occurred. Although the Matrigel looked like a gel-like appearance during fixation, the following replacement with permeabilizing solution quickly lead the Matrigel to a solution and further operation was impossible. Do anyone know how to fix the Matrigel (ideally 50% concentration) for immunostaining? I found that Corning customer service recommends to use 0.1-1% glutaraldehyde (particularly 1%) in addition to 2% PFA. However, I am wondering that a high concentration (e.g. 1%) glutaraldehyde easily lead to over cross-linking and a lower accessibility of antibodies to an antigen. Thank you for your help in advance.