Has anyone worked on higher dimensional strings?

[vibe3]

Possibly naive question. Wikipedia describes string theory as follows:

String theory is a theoretical framework in which the point-like particles of particle physics are replaced by one-dimensional objects called strings.

The obvious next step (since string theory hasn't succeeded in describing our universe) would be to define elementary particles as 2D surfaces or 3D volumes or 4D space-time volumes, which may have vibrational modes similar to the 1D strings. Is anyone working on such a theory? Has any progress been made? What is the name of such a theory if it exists?

 

[mitchell porter]

They are called branes (short for membranes) and they are already part of string theory.