Finite interactive systems (FIS) are one of many equivalent presentations of regular 2-dimensional languages (2Reg). Known regular expressions for 2Reg (denoted 2RE) are based on intersection and renaming, giving little insight on the structure of regular languages. Recently, the authors have introduced a new type of regular expressions for 2-dimensional languages using arbitrary shapes and tiling operations parametrized by restrictions on the connection interfaces. Their result on the representation of FIS languages with this type of regular expressions (a Kleene theorem) is based on an unexpected connection between the shapes of scenarios in finite interactive systems and membrane systems. Compared with the usual P systems, these FIS-based membrane systems are more rigid (geometric) and they lack the dynamics; probably, the latter issue can be solved by adding a new dimension in the model, going to 3-dimensional shapes. The paper provides a detailed analysis of the FIS-based membrane systems.