The wound healing stages are
1. Hemeostasis and inflammation
2. Proliferation and repair
3. Remodeling
During stage 2 the actual repair process arises from actual follicles where stem cells are released to wounded areas where they start multiplying and creating new cells this happens around day 4 after dermarolling. Your bodies chemicals start creating blood vessels and collagen to supply nutrients and oxygen to the wound.
http://www.mate.tue.nl/mate/pdfs/4703.pdf
http://www.hindawi.com/journals/ecam/2011/438056/
When treated with herbal extract / amino acids, wounds were almost identical to normal tissue. Untreated or with placebos, tissue cells were less scattered like normal tissue and had thin and incomplete blood vessels. I believe mostly all hair loss is caused by bad circulation. Dermarolling fixes this.
the reason dermarolling works is because of the wounding and healing process. The body has a natural ability to heal itself if activated. Hardcore wounding heals in a completely different way, that's why your limbs don't grow back, because the matrix is not then anymore, your body starts developing bacteria due to lack of blood flow and the repair process is skipped.
when end working out its same as dermarolling and they get bigger because the repair process