The investigators designed this prospective, randomized control study to confirm the efficacy and safety of methylene blue - mediated photodynamic therapy for diabetic lower limb ulcer and to explore its mechanism.

OBJECTIVE- Infection is associated with poor healing of diabetic lower limb ulcer. Diabetic lower limb ulcer are often lower extremity vascular stenosis or occlusion, poor blood supply, making local ulcer local antibacterial drugs difficult to effectively reach and distribution, resulting in systemic antibacterial efficacy is limited, and easy to induce bacterial resistance at the same time . In recent years, the incidence of clinical multidrug-resistant bacteria increased, increasing the difficulty and cost of treatment.

The current study attempts to identify whether the photodynamic therapy (PDT) would kill the surface of ulcer bacteria and promote ulcer healing, and explore the mechanism of methylene blue-mediated photodynamic therapy for diabetic lower limb ulcer RESEARCH DESIGN AND METHODS-This study evaluated six clinical indicators： diabetic foot ulcer area reduction rate, inflammation control rate, Local bacterial load, the dose and use time of antibiotics, adverse reaction rate, bacterial biofilm,local neutrophil extracellular traps. The efficacy and safety of PDT could be confirmed if the clinical indicators of PDT group is better than the control group. In this study, three methods were used to investigate the mechanism of -methylene blue mediated photodynamic therapy for diabetic lower limb ulcer: a comparison of the bacterial load, bacterial biofilm,local neutrophil extracellular traps of the ulcer immediately pre-treatment and immediately,1-week ,2 week,1 momth post-treatment ; EXPECTED RESULTS-The investigators will expect that methylene blue-mediated photodynamic therapy could kill bacteria on the surface of diabetic lower limb ulcer and accelerate wound healing.

Inclusion Criteria:

• 1. Understand the whole test process, voluntary and signed informed consent form.
• 2. Men and women aged 18 to 80 years old.
• 3. Diagnosed with diabetic lower limb ulcer.
• 4. Ulcer duration> 1 month of wagner grade Ⅱ, Ⅲ subjects.
• 5. An ulcer area ≤100 cm² or of linear dimension ≤ 10 cm.

Exclusion Criteria:

• 1. Diagnosis of systemic infection or any concomitant infection that would require treatment with an additional antimicrobial agent.
• 2. Pregnant or lactating women.
• 3. Wagner grade Ⅰ, Ⅳ, Ⅴ subjects.
• 4. Patients with a peripheral vascular disease require immediate revascularization, and/or an ankle brachial systolic blood pressure (SBP) index<0.5 in the infected limb.
• 5. Patients with inappropriate health to participate as determined by the principal investigators.
• 6. Patients in the hepatitis A, hepatitis B, AIDS, tuberculosis and other infectious diseases of the active period.