Is it permissible to sell medical devices to an American company that has been acquired by an Israeli company, and is it permissible to maintain them and purchase their spare parts, knowing that there are other less efficient devices, and despite the doctors' insistence on this particular device even though they are aware of the Israeli acquisition?

The fact that the company is Israeli-American does not preclude the permissibility of acting as its agent in selling permissible goods. If the intention behind refusing the work is an economic boycott, then we refer to the considerations of benefit and harm. And whoever boycotts with the intention of supporting Islam and Muslims will be rewarded for his intention.