From Deep Look:
The quills of North American porcupines have microscopic backward-facing barbs on the tips. Those barbs make the quills slide in easy but very difficult to remove.
Researchers at Harvard are looking to porcupine quills for inspiration in designing a new type of surgical staple that would also use tiny barbs to keep itself lodged into the patient's skin. This helps because traditional staples curve in under the skin to keep the staple in place. This creates more damage and can provide a place for bacteria to infect the wound.