Development and validation of a three-dimensional electro-chemo-mechanical model for the discription of the urinary bladder

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The urinary bladder is a central organ of vertebrates and imposes, based on its extreme deformation (volume changes up to several 100%), special requirements on the entire bladder tissue and especially on the active smooth muscle tissue. Although there are many dysfunctions combined with tissue changes, mechanical analyses are rare. Consequently, the main aim of this project is the development and validation of an electro-chemo-mechanical model based on experimental investigations on the swine urinary bladder.For the development and validation of the model, four steps are scheduled. Thereby, experiments on domestic pigs will be performed, as structure and contraction behaviour are similar to those of humans. Basic requirement for the model generation is the development of the used techniques (I). These are the registration of the three-dimensional deformation as well as of the activation potential propagation at the bladder's surface. Based on an optical measurement technique, developed by the applicants for the recording of skeletal muscles deformation, in this project a procedure will be established to measure the bladder geometry in physiological saline solution. Further, surface electrodes for the measurement of the propagation of the action potential at the bladder's surface will be developed. The first experimental step includes analyses of tissue strips (II). In order to capture local differences of the bladder's structure, preparations will be dissected at defined positions of the bladder wall. Thus, the layer specific architecture as well as its active and passive characteristics can be determined. These data are used for an interim validation and the parameter identification of the electro-chemo-mechanical model. Based on active and passive analyses on the whole bladder (III) its capacity, the pressure-volume dependence, the three-dimensional deformation and the propagation of the action potential at the bladder's surface will be determined. In a final step these additional data of the whole bladder are used to validate the whole model (IV).The model developed in this project can be seen to be a compensational method for animal models and, based on the similarity between human and porcine bladders, for human studies. Thus, it can contribute in future to a reduction of animal experiments and can help to have a more comprehensive understanding of bladder functions. Prospective developments of the model could deal with the prediction of different functional impacts of tissue changes (i.e. cicatrisation of the muscle layer due to interstitial cystitis). Therefore, morphological and mechanical changes of the sickened tissue will be determined experimentally and implemented and converted into the model.