Это просто как ...
Контроллер:
function foo()
{
if( ! empty($_POST))
{
$hello = serialize($_POST['hello']);
// You can do your database abstraction here, but is better to have these in your model
// Btw, by using CI AR, all values are escaped automatically producing safer queries.
$this->db->insert('some_table', array('hello' => $hello));
}
else
{
// do something
}
}