"string1", "string2"

$string = "
    iojefu { string1 }
    asdjhu { string2 }
";
preg_match_all('/{s*(?P<str>[^}]+?)s*}/', $string, $matches);
var_dump($matches['str']);
/*
array(2) {
  [0] => string(7) "string1"
  [1] => string(7) "string2"
}
*/

$matches = [];
preg_match_all('/{s*([^}s]*)s*}/', $string, $matches);

/[{]s*([^{}]+)s*[}]/

$array = preg_split('/.*?{|}|s/', $string, null, PREG_SPLIT_NO_EMPTY);