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?
Tolerating the assault and harm from your relatives for the sake of Allah (SWT) is a type of Jihad in the way of Allah. The Holy Ahlul Bayt (AS) have tolerated great pain from some of their own relatives and taught Muslims how to deal with the relatives in all the circumstances. You should maintain good contact with your brother despite his assault on you and avoid any word or behavior which harms your relationship with him. You should also apologize for any wrong you said to him in anger.
Wassalam.