methods and artificial matrices for the growth and implantation of urological structures and surfaces are disclosed in which urothelial cells are grown in culture on biodegradable , biocompatible , fibrous matrices formed of polymers , such as polyglycolic acid , polylactic acid , or other polymers which degrade over time . the cells can be cultured in vitro until an adequate cell volume and density has developed for the cells to survive and proliferate in vivo . alternatively , when adequate cell numbers for implantation are available , the cells can be attached to the matrix and implanted directly , without proliferation in vitro . the implants approximate the desired urological structure to be replaced or repaired , such as the kidney , urether , bladder , urethra , and the like . implantation is followed by remodeling through cell growth and proliferation in vivo . in another aspect of the invention , techniques are disclosed for selectively extracting or harvesting urothelial cells either from excised urological tissue in vitro or from intact urological tissue in vivo by treating the tissue with a digestive enzyme , such as collagenase .