$re = '/,[^,]*,/';
$str = 'Model1,Model2,Model3,Model4,Model5,Model6,Model7,Model8,Model9,Model10';
$subst = "$0\n";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php