Hyperelastic model of a material which microstructure is formed by “balls and springs”

We develop a model of an incompressible material which microscopic structure is formed by flexible but incompressible balls connected mutually by linear springs. The model is motivated by the structure of smooth muscle tissues that exhibit perfect elastic (or visco-elastic) behavior in a large extent of deformations. Moreover, their bulk (macroscopic) stiffness may be very effectively controlled and changed from very low values to essentially higher ones by simply defined structural changes inside individual muscle cells. In the continuum limit, the “balls and springs” model gives a nontrivial, highly nonlinear hyperelastic material. The stored strain energy function has generally no analytical expression. However, we find an approximate analytic formula, that is suitable for describing certain mechanical effects coming from the special arrangement of smooth muscle cells.