A sharp drop in demand for temporary nurses sent Medical Staffing Network Holdings to bankruptcy court late Friday, when the Boca Raton-based company filed for Chapter 11 reorganization. The company is the largest provider of per diem health care staffing in the U.S. and among the largest providers of traveling nurses, but many hospitals have scaled back on temporary staff to cut costs. It has 101 branch locations, 915 corporate employees and about 19,000 field employees nationwide. Medical Staffing immediately signed a deal to sell its assets to MSN Acquisitions Co. a company formed by its first lien lenders. The $84.1 million proposed purchase price is the equivalent of the money Medical Staffing owes those creditors. The deal would essentially wipe out the company’s existing.