Mast Therapeutics, Inc. (MSTX)

[lux1]

per S4 10 Feb. 2017, pag.31 pdf:

As of February 2, 2017, Mast had an outstanding principal balance of $3.1 million under its debt facility with Hercules Capital, Inc. and Hercules
Technology III, L.P. (collectively referred to as Hercules) that is
secured by a lien covering substantially all of Mast’s assets, excluding intellectual property, but including proceeds from the sale, licensing or disposition of Mast’s intellectual property.
....
The loan would remain in place upon its existing terms, including the January 1, 2019 scheduled maturity date.

The terms are that they must be able to raise some cash 4-6 millions by April 30 and Savara must raise at least 20 mil by August 31, 2017

In other words Hercules controls Mast's assets until merger and, after the merger, they demand a minimal cash supply as guarantee to maintain the loan.

My free interpretation