For porosity you can go for water displacement method.

If you have only a small quantity and you would like to keep using the scaffold for tissue engineering you could compare the polymer density with the scaffold density to calculate porosity. This fast, inexpensive method has its limits on accuracy, though when I compared it with nCT scans I got comparable numbers.  With nCT (and thick enough fibers) you could also calculate surface area etc.

DOI: 10.1039/c3tb20995d