Brain-injury device developer X2 Biosystems said it sold approximately $4.2 million worth of debt and securities under a previously filed $9 million offering.

The Seattle-based company is developing a cloud-based system to detect traumatic brain injuries in real time using wearable sensors and mobile devices. The system is being tested for use by the U.S. military and sports organizations.

The funding round, which dates back to April, involved 41 unnamed investors, according to a regulatory filing.

X2’s concussion detection device is a sensor about the size of a postage stamp worn by athletes that sends impact metrics to a web-based database. The data, supported by Windows Azure, can be sent to coaches and physicians real-time and can be managed with several analytical tools.

In August, X2 Biosystems appointed retired Army Maj. Gen. Stephen Layfield as president of its government & industrial division.