The 27-year-old recorded two goals and seven points in 44 games this season with the Islanders.
"We weren't dissatisfied [with our depth] in any way," Blackhawks coach Joel Quenneville said. "We thought that if we could improve and deepen our lineup, that's what we'd look to do. Fortunately, we were able to do it.
"When we were looking at our team, we always felt that if we were going to add something somewhere, it would be in the middle. He can play offensive minutes, defensive minutes. He's got speed, which is what we look for. It's a good opportunity for everyone involved."
The Blackhawks did not hold a morning skate Friday but are expected to go with the following forward line combinations:
Brandon Pirri has been assigned to the AHL's Rockford IceHogs. Patrick Kane, who has returned home to Buffalo, N.Y., to attend his grandfather's funeral, will miss his first game of the season and only his third since late 2010.
On defense, Johnny Oduya is out, but he is day-to-day and he will be available to represent Sweden at the Olympics. With Mike Kostka subbing in at forward (Hossa) at Thursday's practice, it's expected Sheldon Brookbank will play in Oduya's place.
Indeed, some significant changes as the Blackhawks search for a third straight win.
"I think [Regin] will adapt quickly," Quenneville said. "It's a good chance for him to play with a couple nice players, and I'm looking forward to seeing how he does. The excitement of coming to a new team should help him get through the game. Just play and do what you do best. Without Kaner tonight, we might even try him out on the power play."