Musk has said his brain implant company, Neuralink, will make the paralyzed walk, the blind see and eventually turn people into cyborgs. But the firm still struggles to secure clinical-trial approval for the relatively modest goal of helping disabled people type.

On at least four occasions since 2019, Elon Musk has predicted that his medical device company, Neuralink, would soon start human trials of a revolutionary brain implant to treat intractable conditions such as paralysis and blindness. Yet the company, founded in 2016, didn’t seek permission from the U.S. Food and Drug Administration (FDA) until early 2022 – and the agency rejected the application, seven current and former employees told Reuters.The rejection has not been previously reported. In explaining the decision to Neuralink, the agency outlined dozens of issues the company must address before human testing, a critical milestone on the path to final product approval, the staffers said. The agency’s major safety concerns involved the device’s lithium battery; the potential for the implant’s tiny wires to migrate to other areas of the brain; and questions over whether and how the device can be removed without damaging brain tissue, the employees said.

A year after the rejection, Neuralink is still working through the agency’s concerns. Three staffers said they were skeptical the company could quickly resolve the issues – despite Musk’s latest prediction at a Nov. 30 presentation that the company would secure FDA human-trial approval this spring.Neuralink has not disclosed details of its trial application, the FDA’s rejection or the extent of the agency’s concerns. As a private company, it is not required to disclose such regulatory interactions to investors. During the hours-long November presentation, Musk said the company had submitted “most of our paperwork” to the agency, without specifying any formal application, and Neuralink officials acknowledged the FDA had asked safety questions in what they characterized as an ongoing conversation. Musk and other Neuralink officials did not respond to requests for comment on the company’s device or its dealings with the FDA. The agency declined to comment on Neuralink, citing laws keeping commercial information private.

 The Neuralink sources declined to provide Reuters with the agency’s written rejection, a legally confidential document. The staffers, including four who had read the FDA document and others aware of the agency’s concerns, described the safety issues in interviews, speaking on condition of anonymity.Such FDA rejections do not mean a company will ultimately fail to gain the agency’s human-testing approval. But the agency’s pushback signals substantial concerns, according to more than a dozen experts in FDA device-approval processes.