Final answer:
Collagen synthesis is the substance that contributes to the strength of the healing wound site during the healing process.
Step-by-step explanation:
During the healing process of a wound, the strength of the healing wound site is developed based on collagen synthesis. Collagen is a protein that provides structural support to tissues, including the skin. When a wound occurs, fibroblasts in the surrounding connective tissues replace the collagen and extracellular material lost by the injury, contributing to the strength of the healing wound site.