earlier tissue engineering

In earlier tissue engineering a basic 3D scaffold made using processed animal collagen to which cell cultures were added to build the structure. These scaffolds were, say, in the form of an ear, nose or even a urinary bladder. The cultures grew in this scaffold until they matured and yes, they are implantable - several patients have new bladders that were grown in a lab. This type of scaffold dissolved in time and is replaced by naturally growing collagen.

Why does the scaffold have to dissolved ? And why add cell cultures to the scaffold ?

Now they're working on literally 'printing' the structure one 2D layer at a time, including natural collagen tissue, until the full 3D structure is complete. If successful we're talking the ability to manufacture replacement organs or other parts.

What the differnce of using natural collagen and animal collagen ?