Mattaa, a 24-year-old, left-shot defenseman, should bolster the blue line for a Blackhawks team that ranked 30th in the league with 292 goals against last season.
The 6-foot-2 rearguard helped the Penguins capture back-to-back Stanley Cups in 2016 and 2017. He has three years remaining on his current contract and carries an annual cap hit of just over $4 million.
Kahun enjoyed a productive rookie campaign with the Blackhawks last season, contributing 13 goals and 37 points while playing in all 82 regular-season games.
The fifth-round pick helps a Penguins club that does not hold its own second-, third-, or fourth-round selections in this year's draft. The deal also freed up approximately $3.15 million in cap space for Pittsburgh, according to CapFriendly.