Problem with open several .dat files

I want to open several .dat files and I used the next command with uigetfile

filename = uigetfile({'*.*';'*.dat';'*.txt'}, 'Seleccionar archivos', 'MultiSelect', 'on');

The problem is that I can´t read the information of this files. I tried using -load-, but matlab said me that need an string arguments. I also tried to convert the cell array to number array, but matlab give only the names of my archives.

I need help to open de data of my files. Thanks