Filed Pursuant to Rule 424(b)(7)
Registration No. 333-139056

Prospectus Supplement No. 2
(To Prospectus dated February 13, 2007)

2,659,241 Shares of Common Stock

     This prospectus supplement relates to the resale from time to time by selling stockholders of 2,659,241 shares of our common stock.

     This prospectus supplement, which supplements the prospectus dated February 13, 2007, contains information about certain selling stockholders.

NEITHER THE SECURITIES AND EXCHANGE COMMISSION NOR ANY STATE SECURITIES COMMISSION HAS APPROVED OR DISAPPROVED OF THESE SECURITIES OR PASSED UPON THE ADEQUACY OR ACCURACY OF THIS PROSPECTUS. ANY REPRESENTATION TO THE CONTRARY IS A CRIMINAL OFFENSE.

January 20, 2010

SELLING STOCKHOLDERS

     The shares of common stock being offered by the selling stockholders are those previously issued to the selling stockholders and those issuable to the selling stockholders upon exercise of the warrants. We are registering the shares of common stock in order to permit the selling stockholders to offer the shares for resale from time to time. Except for the ownership of the shares of common stock and the warrants, and except for Mr. Lufkin who serves on our Board of Directors, the selling stockholders have not had any material relationship with us within the past three years.

     The table below lists the selling stockholders and other information regarding the beneficial ownership of the shares of common stock by each of the selling stockholders. We prepared the table below based on the information supplied to us by the selling stockholders named in the table. The selling stockholders may, however, have sold, transferred or otherwise disposed of all or a portion of their securities since the date on which they provided such information. The second column lists the number of shares of common stock beneficially owned by each selling shareholder, based on its ownership of the shares of common stock and the warrants, as of November 29, 2006, assuming exercise of the warrants held by the selling stockholders on that date, without regard to any limitations on exercise.

     The third column lists the shares of common stock being offered by this prospectus by the selling stockholders.

     In accordance with the terms of registration rights agreement with the holders of the shares of common stock and the warrants, this prospectus generally covers the resale of that number of shares of common stock equal to the number of shares of common stock issued and the shares of common stock issuable upon exercise of the related warrants, determined as if the outstanding warrants were exercised, as applicable, in full, in each case, as of the trading day immediately preceding the date this registration statement was initially filed with the SEC. The fifth and sixth columns assume the sale of all of the shares offered by the selling stockholders pursuant to this prospectus.

     Under the terms of the warrants, a selling shareholder may not exercise the warrants, to the extent such exercise would cause such selling shareholder, together with its affiliates, to beneficially own a number of shares of common stock which would exceed 4.99% of our then outstanding shares of common stock following such exercise, excluding for purposes of such determination shares of common stock issuable upon exercise of the warrants which have not been exercised. The number of

shares in the fourth column does not reflect this limitation. The selling stockholders may sell all, some or none of their shares in this offering. See “Plan of Distribution.”

														Maximum Number of
														Common Shares
										Maximum Number of				Underlying the
						Number of Shares				Common Shares to be				Warrants to be Sold				Number of Shares				Percentage of Class
						Owned Prior to				Sold Pursuant to				Pursuant to				Owned After				Owned After
				Name of Selling Stockholder		Offering1				this Prospectus				this Prospectus				Offering				Offering
	(1	)		Dan W. Lufkin2			490,418				70,175				10,526				490,418				4.5	%
	(2	)		Lake Union Capital Fund, LP3			0				100,000				15,000				0			—
	(3	)		Wasatch Ultra Growth Fund4			0				103,400				0				0			—
	(4	)		Wasatch Micro Cap Value Fund4			0				35,300				0				0			—
	(5	)		Variable Insurance Products Fund IV: Health Care Portfolio5			0				50,420				7,563				0			—
	(6	)		Fidelity Select Portfolios: Medical Equipment and Systems5			0				602,089				90,313				0			—
	(7	)		Fidelity Advisor Series VII: Fidelity Advisor Health Care Fund5			0				400,123				60,018				0			—
	(8	)		Eric S. Dobkin			358,538				87,719				13,158				358,538				3.3	%
	(9	)		Phronesis Partners, LP6			100,000				600,000				90,000				100,000				*
	(10	)		John Hancock Trust Emerging Growth Trust7			0				5,736				0				0			—
	(11	)		John Hancock Health Sciences Fund7			250,000				43,860				0				250,000				2.3	%
	(12	)		John Hancock Small Cap Equity Fund7			0				177,590				0				0			—
	(13	)		John Hancock Funds II Emerging Growth Fund7			0				35,972				0				0			—
	(14	)		Warrant Strategies Fund LLC8			0				0				27,384				0			—
	(15	)		Manchester Explorer Fund L.P.9			0				0				6,256				0			—
	(16	)		OTA LLC10			352,989				0				26,639				352,989				1.6	%