Nanotech investment company Arrowhead Research Corp. said Tuesday that it sold approximately $4.4 million worth of securities to fund operations, research and development. Most of the buyers were long-standing Arrowhead shareholders or company officers.

Pasadena-based Arrowhead sold 2.5 million units, consisting of common stock and common stock purchase warrants, in a registered direct offering to investors. Some of Arrowhead’s senior management participated in the offering, including Chief Executive Chris Anzalone who invested more than $300,000. Net proceeds were not given.

“We thought it prudent to increase our liquidity during this time of general market uncertainty,” said Anzalone in a statement. “However, we are also sensitive to dilution of our shareholders, so we were careful with the amount of capital raised.”

Arrowhead has four subsidiaries that commercialize nanotech products and applications, plus investments in two minority-owned subsidiaries. The company concentrates in the life sciences, electronics and energy sectors, and earlier this month reported a narrower second-quarter net loss of $7.5 million, compared to $12.5 million for the same period a year ago.

Arrowhead said it may sell up to an additional 3.1 million units in follow-on offerings at $1.80 per unit, or $1.83 per unit if purchased by a director or officer. Any offerings are expected to remain open until Sept. 15, the company said.

Arrowhead shares rose 9 cents, or 5.5 percent, to $1.72 in morning trading on the Nasdaq.