The present invention relates to compounds of formula :wherein R1, R2, R2\u2032, L, Het, p and p\u2032 are as defined herein, compositions containing them, and their use as medicinal products. The printing apparatus includes a printing roll having target pattern forming material spread thereon, a printing substrate have at least one pair of adjacent printing plate patterns and at least one barrier rib pattern therebetween, and a target substrate. Such a system does not require a second source of irrigation fluid, minimizes pressure surges into the irrigation fluid line and does not affect the fluidic performance of the aspiration system.