A tissue-adhesive formulation consists of a naturally occurring or synthetic polymerisable and/or cross-linkable material in particulate form, the polymerisable and/or cross-linkable material being in admixture with particulate material comprising tissue-reactive functional groups. The formulation may be used in the preparation of a tissue-adhesive sheet, by applying the formulation to at least one side of a core of a naturally occurring or synthetic polymeric material.