While this may not be the most solid of designs it is the best one i could come up with. And before anyone asks the metal of the blade would be protosteel while the rest will be whatever the Toa Akiru feel appropiate
Also here is a more detailed little bit explaining in depth the injection process. Though the best way to describe the process is like a snakes fang. The actual venom of the snake is not stored in the actual fang but a sac in the head that when the time comes the venom is transferred from said sac to the fang and out of it.
And here is the full sized version of the picture
Also as a update here are the mechanics of how to get the poison in
The Poison is held in a refillable canister that can be inserted into the handle. Essentially the half of the handle is unscrewable. You slide the refillable canister in then screw the bottom half back on and well yeah that is the jist of it. The real mechanics of the blade lies in the bottom half of the handle.
And feel free to give your opinion on this.. I am all ears
EDIT: I realized that if i switched the point of the blade to the top it would actually work better for if using the blade offensively it can slice at the target without getting caught on the end.