"constant interplay" is a correct and usable phrase in written English.
You can use it when referring to two or more entities that interact with one another in a dynamic, ongoing way. For example, "The constant interplay between cultures in this city makes it truly unique and remarkable."
There was constant interplay in his thinking, praying and preaching between global and local.
There is tremendous drive here in the constant interplay between the two male soloists and the quartet.
But risk is a murky concept, Dr. Slovic and others said, and risk perception reveals a constant interplay between reason and emotions.
The impact of the show is indicative of the constant interplay between advertising and popular culture, which is intensified because of its setting.
In Ellison's view, America is not made up of separate, free-floating cultures but, rather, of a constant interplay and exchange.
There is a constant interplay between the permanence and grandeur of monumental Paris and the serendipity and surprise of intimate Paris.
The world Wright gives his players is one defined by a constant flickering interplay between progress and equilibrium, a gentle utopia of possibility.
This deliberate, dense layering of paint makes it hard for the viewer to tell what is figure and what is ground, and the constant, jockeying interplay between the two gives Ms. Passlof's work much of its dynamism.
Now that Television's first albums have been reissued, this live set reveals what was missing: the constant, peripatetic interplay of Mr. Verlaine and Richard Lloyd on guitar and the dynamics of a rhythm section that brought jazz subtlety to basic, two-chord rock.
Instead there is a constant dynamic interplay between genome and environment".
By Mr. Wuorinen's standards it is an easygoing piece: each instrument line had a distinct character, and they were wound around each other in constant, hard-driven interplay.
