The University of Minnesota has held onto its eighth-place research ranking.

Research spending of $847 million in 2011 put the university eighth among public universities, according to the National Science Foundation. In his final briefing to the Board of Regents before retiring, Tim Mulcahy, the U's vice president for research, also reported higher-than-average growth in such spending since 2005, when he started.

But Mulcahy, who is given much of the credit for retooling the U's research and technology transfer, warned of challenges that await his successor, Brian Herman, who will join the U in January from the University of Texas. Among them: increased competition for fewer federal research dollars.

"I do not believe, in the face of the national research landscape, that the growth rate we've experienced over the last five or six years is sustainable," Mulcahy said. "I think we'll have to work hard to maintain our position and even harder to improve it."

In fiscal year 2012, U faculty nabbed $749.1 million in grants, Mulcahy reported -- a drop due to an expected loss of federal stimulus money. If those funds are subtracted from the totals, he said, $749.1 million is 7.4 percent more than awarded in fiscal year 2011.

Seven years back, Mulcahy gave his first report to the board. It was bleak.

The U was one of just three schools among the top 100 U.S. research universities that spent less federal money on science and engineering research in 2003 than the year before -- a distinction that pushed the university down in the rankings.

On Friday, the regents learned that since 2005, the university's research expenditures grew 59 percent, compared with a 45 percent average among the top 20 universities. The U's growth over that time ranks fourth among public universities, Mulcahy said.

Those gains "occurred in a tenaciously competitive environment in the midst of an economic downturn of historic magnitude," U President Eric Kaler said.

Revenues from technology commercialization have dropped in recent years due to expiring patents on Ziagen, the blockbuster anti-AIDS drug that brings in the vast majority of its licensing income.

Overseas patents on the drug, licensed to GlaxoSmithKline, have expired and in the United States, they'll end next year. The university had expected diminished return on the drug in 2012. But because of a boost in sales, the university earned $35 million, bringing total revenues to $45.7 million.

Mulcahy has kept a close eye on income beyond Ziagen, what he calls the "steady-state royalty stream." That has risen from $8.5 million in 2007 to $10.7 million in 2012.

Other measures have improved, too. More patents, more disclosures, more transfer agreements. The university launched 12 start-ups in fiscal year 2012, compared to just one in 2005.

Mulcahy got choked up while talking about the faculty and staff members who helped him hit those high-water marks.

"This is their legacy," he said, "and they rightly deserve the credit."

Jenna Ross • 612-673-7168 Twitter: @ByJenna