Cambridge, MA-based health sensor developers MC10 announced an additional $8 million in its third-round funding, led by two new undisclosed strategic investors. The new investment brings the round total to $18 million and the company's total funding to $40.7 million, including investors like Aberdare Ventures, North Bridge Venture Partners, and Windham Venture Partners.

When the company raised the first $10 million of this round, it announced that Medtronic was a strategic investor, but kept a second such investor secret, describing it as a “consumer health company” that is a “clear leader” in its field.

"With the close of this financing, MC10 is fortunate to have strategic investors behind each of our three main business thrusts: consumer, digital health, and medical devices," said David Icke, CEO of MC10, in a statement this week. "Moreover, we've added partners who will help us scale globally."

Assuming Medtronic is the medical device company Icke is referring to, the consumer health company is most likely Reebok -- although we're only speculating -- which has already partnered with MC10 to develop the CheckLight, a sensor-laden mesh skull cap for athletes. The identity of MC10's digital health partner is less clear, but the company says it will disclose the other partners as it announces product and business collaborations.

MC10 emerged as a sports sensor company, with the CheckLight mesh cap designed to provide realtime feedback about athlete head injuries. Lately, though, the company has branched out to develop a number of different wearable sensors, all predicated on the idea of "stretchable" or flexible electronics. The company's website lists a band-aid like patch that measures hydration in near realtime, a wristband that tracks heart rate and activity, and a skin patch that alerts the wearer's smartphone when it's time to reapply sunscreen.

On the medical side, the company is developing a skin patch thermometer for remotely monitoring a baby's temperature as well as stretchable sensors for internal use in catheters and surgical implantation for post-surgical monitoring. Finally, the company has teamed up with the US Army to develop flexible solar panels.

None of these devices is available for purchase yet, although the CheckLight is slated for a June 2013 release. Last December, Icke told the Wall Street Journal the company's various skin sensors were 12 to 18 months away from market.