I can see the issue! The API endpoint only fetches 200 topics per page, but there are likely many more topics in OpenAlex. When filtering topics by subfield, I'm only working with the first 200 topics, which is why "Cell biology" only shows 1 topic instead of 17. I need to fetch all topics with pagination.

I've fixed the pagination issue by fetching multiple pages from the OpenAlex API instead of just the first 200 topics. The code now iterates through up to 20 pages (4000 topics total) to build a complete hierarchy, which should ensure all topics under each subfield are available for selection. Now "Cell biology" should show all 17 topics instead of just 1.

I've removed the target="_blank" and rel="noopener noreferrer" attributes from the DOI link so it now opens in the same window, and also removed the ExternalLink icon component that was displayed next to the link.