A 35-year-old man undergoes elective abdominal surgery for peptic ulcer disease. His wound heals uneventfully over 2 weeks with good epithelialization and collagen deposition. A 42-year-old diabetic woman with chronic kidney disease undergoes the same procedure but develops delayed wound healing with poor tensile strength at 3 weeks. Which of the following best distinguishes the impaired healing in the diabetic patient from normal healing?