A method of joining and/or scaling tissues in a surgical procedure or medical treatment, comprising the steps of: (1) applying a matrix protein, a photoactivatable metal-ligand complex and an electron acceptor to a tissue portion; (2) irradiating said tissue portion to photactivate the photoactivatable metal-ligand complex: thereby initiating a cross-linking reaction of the matrix protein to seal said tissue portion or join said tissue portion to an adjacent tissue portion.