Filtrar consulta MYSQL com opções de formulário

$n_req = 0;
$_POST['usuario'] = 'test';
$_POST['resumo'] = 'test2';
$_POST['status'] = 'test3';
if (!empty($_POST['usuario'])) {
$req_usuario = $_POST['usuario'];
$where[] = " usuario = ? ";
$params[] = $req_usuario;
$n_req++;
}
if (!empty($_POST['resumo'])) {
$req_resumo = $_POST['resumo'];
$where[] = " resumo = ? ";
$params[] = $req_resumo;
$n_req++;
}
if (!empty($_POST['status'])) {
    $req_status = $_POST['status'];
$where[] = " status = ? ";
$params[] = $req_status;
$n_req++;
}
$sql_where = !empty($where) ? ' where ' . implode(' and ', $where) : '';
echo $sql_where;
$tot = mysqli_prepare($con, "SELECT * FROM solicitacoes $sql_where");
if(!empty($params)) {
//foreach($params as $param) {
//  mysqli_stmt_bind_param($tot, "s", $param);
    //echo $param;
//}
$params = array_merge(array($tot),
                  array(str_repeat('s', count($params))), 
                  array_values($params));
print_r($params);
call_user_func_array('mysqli_stmt_bind_param', $params);
// adapated from https://stackoverflow.com/questions/793471/use-one-bind-param-with-variable-number-of-input-vars and http://www.pontikis.net/blog/dynamically-bind_param-array-mysqli may need to be altered
}
echo "SELECT * FROM solicitacoes $sql_where";
mysqli_execute($tot);