How to replace author's bio description links to rel="nofollow"?

Hi all,

I want to replace author’s bio description links to rel=”nofollow”? I’m using following code in function.php but not working:

add_filter ('get_the_author_meta', 'bio_nofollow_links', 10, 2);
 function bio_nofollow_links ($content, $user_id) {
	str_replace ('href','rel="nofollow" href', $content);
	return $content;
 }

If possible, how to disable save html content in contributor’s profile page “Bio: ” textbox?