Cuts heal when growth factors in the dermal layer of the skin signal cells in the epidermal layer to divide. This process takes time and coordination as shown in the figure below. In the past 10-20 years, researchers have conducted many in-vitro and animal studies that have showed promise using growth factors to facilitate healing in impaired wounds, bone regeneration, and nerve regeneration. Researchers hope that the application of growth factors may be used clinically to enhance the wound healing process. The cellular process that enables the cells to grow and develop into tissue is —