Tis was a no risk event. No blood would be transferred on a staple since they are solid and therfore would not hold on to blood in the unlikely circumstance that an HIV infected person sat on the staple before you. Further, even if an infected person sat on the staple before you, the virus would not survive to cause infection. HIV dies on exposure to the environment outside of the body. No one has ever been describe who has gotten HIV in the way that you were exposed. You will not be the first.
I hope this comment is helpful. There is nothing to worry about related to this exposure and no need for testing. EWH