The present invention relates to a method for preparing a neutralized matrix of non-antigenic collagenous material comprising the steps of: —a) preparing an acidic solution of non-antigenic collagenous material, —b) pouring the solution of a) into a mold in order to form a layer, —c) lyophilizing the layer of b) in order to obtain an acidic matrix of non-antigenic collagenous material, d) sterilizing the acidic matrix obtained in c) with ethylene oxide in order to obtain a neutralized matrix of non-antigenic collagenous material. The invention also relates to the matrices obtained and to surgical implants comprising such matrices.