N.F.L. stars and other investors in Vicis, the heralded Seattle-based helmet maker, were officially informed that the company was running out of cash, the New York Times reported. “Our employees are currently furloughed and we need to raise capital in order to continue operating, or we may have no other option but to wind down all operations,” wrote Ralph Greene Jr., who took over as the new chief executive just days before, in a letter. The plea for millions of dollars to cover basic expenses represents a startling fall for a company that has won plaudits for its high-tech helmets and raised more than $90 million from venture capital and some of the N.F.L.’s highest-profile players. The company, with a board that includes highly respected doctors, business leaders and military advisers, also secured $1.1 million in grants from the N.F.L., though the league does not have an ownership stake. The financial crisis at Vicis highlights one of the biggest challenges in football’s fight to make the game safer. Most brain scientists dismiss the idea that a new helmet can significantly reduce the risk of traumatic brain injuries and long-term brain damage. Wilson, Kansas City Chiefs quarterback Patrick Mahomes and dozens of other players wear a Vicis helmet each Sunday. Shock absorbers inside the helmet have been shown to reduce the impact of direct hits and limit the rotational energy the head absorbs. So far, that has not been enough for Vicis to succeed. Youth and high school football participation is falling, and the helmet business is dominated by Riddell and a handful of companies that are weighed down by insurance costs. Still, Vicis and other companies continue to try to develop better helmets for athletes and other commercial and military uses.