Porcupines do not grow bony spikes or have any kind of special substance that makes their pointers.
Their spikes are actually just hairs that contain extra keratin (keratin is also found in skin).
The quills don't shoot. The porcupine vibrates them as a warning. Then it charges and disconnects upon contact. All can be regrown.
Some of you might look at the image below and wonder why a snake would try to squash a porcupine.
Don't worry: the snake didn't crush a porcupine.