Seidenberg, a member of the German Olympic team at the 2010 Vancouver Games, has 23 points in 62 games for the Panthers.
Seidenberg, 28, leads the NHL in blocked shots with 179. He was on the Olympic team with new Bruins teammate Marco Sturm, and the two have played together in four international tournaments (2001 and 2008 world championships, and 2002 and 2010 Olympics Games).
"He's a good guy and he's a big, strong guy too," Sturm said. "So I think he's going to help us on the power play, too. He has a pretty good shot, a heavy shot and he blocks a lot of shots, too. He's just a solid defenseman."
In addition, the Panthers get a 2010 second-round pick from the Bruins.
Bartkowski, a sophomore at Ohio State, was drafted by the Panthers in the seventh-round of the 2008 draft.
The Bruins are 16th in the league on the power play and have struggled offensively all year. Earlier in the day, they traded defenseman Derek Morris to Phoenix.
Seidenberg will an unrestricted free agent in July.
"From what I know of him, he's one of those guys that plays hard," Bruins coach Claude Julien said after practice Wednesday. "He comes up big and I thought last year with Carolina, he was a pretty good defenseman. He didn't back down from anything and he's a guy that we look forward to having him in our lineup."
Scott Burnside covers the NHL for ESPN.com. ESPNBoston.com's Matt Kalman contributed to this report.