Wa `alaykum as-salamu wa rahmatullahi wa barakatuh.
In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
Brother, thank you for your good question. May Allah Almighty bless you with His favors and grace!
Men, of course, are not allowed to wear gold or natural silk. Moreover, imitating women is not allowed for men in dress, talk, etc., is not allowed too.
Answering your question, Dr. Wael Shehab, PhD in Islamic Studies from Al-Azhar University and currently the Imam of the Downtown Toronto Masjid in Canada, states:
Generally speaking, it is not permissible for men to wear chains as this is considered an imitation to women. In this context, the Prophet (peace and blessings of Allah be upon him) is reported to have said, “May Allah curse men who imitate women, and vice versa.“ (An-Nawawi, al-Majmu`, 4: 445)
However, a Shari`ah maxim says “necessities relax prohibitions”. So, if a man is required for health reasons to wear chains, he is then allowed to for such a necessity.
It is noteworthy that silver is not generally prohibited for men. For example, a man may wear a sliver ring.
Allah Almighty knows best.