neural network problem in modelling plant

I make a close loop control scheme in simulink and i use neural network to modelling plant in my case. I've trained and validated my NN using NNTOOL and i've found the best architechture. How to use my best architechture in my simulink? i've tried to call my file.mat in simulink use S-function toolbox, but it didn't work. Can you help me to solve it?