A 38-year-old woman with poorly controlled diabetes mellitus (HbA1c 10.2%) undergoes open reduction and internal fixation of a femoral fracture. At 3 weeks postoperatively, the surgical wound shows delayed healing with minimal granulation tissue formation and poor epithelialization. The surgeon suspects impaired wound healing due to hyperglycemia and wants to assess the degree of collagen deposition and neovascularization in the wound. Which investigation best evaluates the histological status of wound healing at this stage?