To simplify the expression, we first need to combine like terms within each parentheses:

(6a + 1/a^2 - 6a + 6a - 1/a^2 + 6a) = (6a - 6a + 6a + 6a + 1/a^2 - 1/a^2) = 12a

Now the expression becomes:

(12a) * (a^4 - 35a^2 - 36) / (a^4 + 2a^2 + 1)

To further simplify, we factor the numerator and denominator:

Numerator: a^4 - 35a^2 - 36 = (a^2 + 4)(a^2 - 9) = (a^2 + 4)(a + 3)(a - 3)
Denominator: a^4 + 2a^2 + 1 = (a^2 + 1)^2 = (a + i)(a - i)(a + i)(a - i)

Now, our expression can be simplified as:

12a * (a^2 + 4)(a + 3)(a - 3) / ((a + i)(a - i)(a + i)(a - i))

This is the simplified form of the expression.