Hangartner spent four seasons with the Panthers from 2005-08, starting 27 games and playing in 54 before signing as a free agent with Buffalo in 2009.
Hangartner was cut Saturday by the Bills.
He'll have a chance to start at right guard along with five-year veteran Max Jean-Gilles, who was signed on Sunday. Jean-Gilles has started 25 games over the past three seasons with the Philadelphia Eagles.
Those moves help offset injuries to Geoff Schwartz, the starting right guard, and valuable reserve Garry Williams. Schwartz's season ended with a hip injury in training camp, while Williams broke his ankle in Thursday night's preseason finale against Pittsburgh.
Both players were at practice Monday, along with the team's five new waiver wire pickups: defensive tackle Marcus Harrison, cornerback Josh Thomas, safety Stevie Brown, wide receiver Seyi Ajirotutu and defensive end George Selvie.