$string ='This is my body of text, you should all check out this item {item(7)} or even this item {item(21)} they are great...';


if(preg_match_all('#{item((?:.*?))}#is', $string, $output, PREG_PATTERN_ORDER))
$matches = $output[0];
foreach($matches as $match){
    item_widget(preg_replace("/[^0-9]/", '', $match));
}