Provided are compounds and methods useful for sealing air leaks in the thoracic cavity. Compounds and compositions of the invention comprise certain amphiphilic peptides, 8-200 amino acid residues long, that self-assemble spontaneously to form a gel in the presence of physiological pH and/or in the presence of a cation. In one embodiment, the peptide comprises a repeated sequence arginine-alanine-aspartic acid-alanine (RADA). Methods of the invention include a method of occluding a pulmonary air leak in a subject, comprising applying a compound of the invention to the site of a pulmonary air leak. The compounds and methods of the invention can be combined with other agents useful to treat cancer, inflammation, or infection.
