Neuralink faced many challenges in its bid to implant humans with brain chips. Here are the big takeaways so far.

• Elon Musk's firm Neuralink said it's successfully implanted a brain chip in its first human patient.
• The company has faced years of regulatory hurdles and controversy over animal testing.
• Here's a look back at the company's biggest milestones and challenges.

Elon Musk's futuristic company Neuralink has implanted a brain chip into its first human patient.