After being physically assaulted by my brother, am I Islamically obligated to maintain contact with him or apologize for what I said to him in anger?
Bismihi ta'āla
Being violent to siblings is unacceptable, haram and very damaging for sibling relationships. Try to make mends with him, and apologise if you wronged him.
Hopefully, things will get back to normal between him and you, but he must know that what he did is wrong and must not be repeated.
And Allah knows best