Regeneration after trauma or injury is a fascinating and complex process. Some species are more capable of regenerating different body parts, tissues or organs while others possess only very limited regenerative abilities. Hydra for example, a freshwater polyp, can regenerate its entire body. Polyps are the early stage of what is commonly known as a jellyfish. After injuries, Hydra can rearrange its existing tissue which leads to a full regeneration of the lost parts.
We humans in contrast can only dream about regenerating whole body parts. Tissues or organs can to a certain extend be regenerated, but mammals and thus humans have bad regenerative capabilities compared to other animal groups. What is biologically possible and what can be supported by engineered materials is part of many research projects all over the world.