Juventus have announced the re-signing of Italy defender Leonardo Bonucci from AC Milan just 12 months after his departure.
Bonucci, capped 80 times by Italy, spent seven years at Juventus, where he won six Serie A titles and reached two Champions League finals, before leaving for San Siro last summer.
Milan will reportedly pay an initial £16m as part of a season-long loan deal for Higuain, with the option of making the move permanent for an additional £32m at the end of the season.
Caldara, meanwhile, spent just one month at Juventus following his move from Atalanta and has been used as a makeweight in the deal to bring back Bonucci.
"After spending seven wonderful years in black and white, Leonardo Bonucci has returned to the club following a season at AC Milan," Juve said in a statement. "Both Juventus and Bonucci are ready to start winning things again together."
Milan's acquisitions, meanwhile, were described as follows: "Gonzalo and Mattia are two important pieces of the new era of the club."
Juve won the Serie A championship last term, while Milan finished sixth in the standings.