The invention relates to a matrix in ball form comprising cross-linked fibrinogen, the matrix being free from fibrin, as well as to a method for preparing such a matrix, comprising the following steps: (a) providing an initial composition comprising fibrinogen and a platelet factor; (b) injecting said initial composition into an oil heated to a temperature of 50° C. to 80° C. so as to form an emulsion; (c) mixing the emulsion thus obtained at a temperature of 50° C. to 80° C. until a matrix in ball form is obtained; and (d) isolating the matrix thus obtained. The matrix is used as a cell carrier.