How to implement less cycle for mixins sprite?

In the layout there is a block with brands, pictures brands in the sprite. Generator sprites generate mixins for less, not to write for each style, trying to make through the cycle in less code like this:

@amount: 9;

.myLoop (@index) when (@index < @amount) {
 .brands__item@{index} { // here the name of the selector is generated correctly
.sprite();
 .sprite-brand-@{index}; //and here, swears unrecognized input
}
 .myLoop(@index + 1);
}

.myLoop (1);

Apparently, does not work the interpolation of the variable. Can't figure out how to fix it? Can braces what to add?