Methods of generating thrombin and methods of applying a clotting tissue sealant to a site on a subject are provided. A blood component comprising platelets can be obtained from the subject. A hypotonic composition is contacted with a solid matrix to form a thrombin-containing liquid, where the hypotonic composition includes water, calcium, a blood component comprising platelets, and optionally a chelator. Calcium is present in the hypotonic composition in an amount greater than the amount of calcium that can be complexed by the chelator. Thrombin-containing liquid is then separated from the hypotonic composition and can be applied to the site on the subject to form a clot, for example, by combination with fibrinogen.