Artists in Philadelphia have collected more than 30,000 knots representing life's daily struggles for an exhibit honoring the pope.

The knots will be housed in a grotto next to the city's Roman Catholic cathedral. Pope Francis will celebrate Mass at the basilica on Sept. 26 during his two-day visit.

The installation is inspired by one of the pontiff's favorite paintings, "Mary, Undoer of Knots." It shows Mary untangling a long ribbon — a symbol for smoothing life's difficulties.

At a recent public event, people wrote their burdens on strips of cloth and then knotted them. Challenges ranged from addictions to student loans to health problems.

Participants also were invited to untie someone else's knot — to share that person's hardship.

Organizers expect the grotto to open Sept. 3.