Its based on technology, market and percieved value to buyer.
Titan Technology - Innovative and nothing like it in the current market
Robotics Market growth - Over $20B in 4 years
Perceived Value - Does JnJ, Medtronic (insert any big company) want to get into Robotics and own the hospital OR.
And no, TRXC patents aren't worth a Billion dollars b/c its crap b/c if it is so good and so close to market, it should have been purchased by now. When Titan gets as close to market as TRXC is right now, Titan will be purchased.