Dynamic global variable in Codeigniter Controller

I'm trying to put a dynamic title on my website so here it is.

class Survey extends MY_Controller {

   public $my_title;

   public function __construct(){
     parent::__construct();
     $this->load->model('Survey_model');
     $this->my_title = ""; //setting to blank
   }

   public function survey_form(){
     $this->data['title']    = $this->my_title; //display the title
     $this->middle       = 'Survey_view';
     $this->layout();
   }

   public function validate_stub($survey_code){
     $data          = $this->Survey_model->get_questions($survey_code);
     $this->my_title    = $this->Survey_model->get_quest_title($survey_code); //getting from database title 

     $this->session->set_userdata('stub_data', $data);
     redirect('Survey/survey_form');
   }
}

The first to trigger is the validate_stub function then i would like to pass the return of get_quest_title to global variable $my_title then pass it to the survey_form function. In this case $this->my_title is blank, how can i pass the title from db then put into the global variable then pass to the view. Thanks