A fibrin sealant comprises a mixture of first microparticles that comprise fibrinogen, second microparticles that comprise thrombin, and additive material. The additive material may be particulate, and may be, for instance, a biocompatible, water-absorbent, material, a biocompatible, water-swellable material, a biocompatible, water-insoluble material, a polysaccharide or silica.
