A 32-year-old man presents to the surgical outpatient clinic 10 days after undergoing an open appendicectomy. On examination, his surgical wound shows erythema, warmth, and purulent discharge. The wound edges are separated, and there is visible granulation tissue at the base. His haemoglobin is 9.2 g/dL, serum albumin 2.8 g/dL, and random blood glucose 280 mg/dL. He has a 5-year history of poorly controlled type 2 diabetes mellitus. Which of the following is the PRIMARY factor delaying his wound healing in the inflammatory phase?