Drones are getting smarter at avoiding collisions but they can still happen, so that still poses a danger to humans and drones themselves. Tombo Propellers are biomimetic drone propellers inspired by the flexibility and resilience of dragonfly wings. As the researchers explain:
The results show that the maximum collision force generated by the proposed Tombo propeller is less than two-thirds that of a traditional rigid propeller
This video from HO lab shows these propellers in action. You can read the paper here.