สอบถามปัญหาการใช้งาน str_replace กับ real_escape_string

$mysqli =mysqli_connect('my_host', 'my_user', 'my_pass', 'my_db');
	if ($mysqli->connect_error) {
		die('Connect Error (' . $mysqli->connect_errno . ') '. $mysqli->connect_error);
	}
	$text = "!@#$%^&*()_+|}{?>'<script>alert('aaaaa');</script>";
	$aa = $mysqli->real_escape_string($text);
	echo $aa."<br>";
	$letters = array('<','>','*', '#','?','$','!','%','^','{','}','(',')','|');
	$bb = str_replace($letters,'',$aa);
	echo $bb;