Objective
The process of wound healing is divided into three stages: inflammation, proliferation and maturation. Interleukins are cytokines that play a role in wound healing. Far infrared radiation (FIR), with wavelengths of 15-1000µm, has been shown to increase peripheral blood circulation, promote telangiectasia, and improve epithelial function. In this study, we measured inflammation-related interleukins in wound drainage fluid and investigated cytokine changes in tension linear suture wounds after FIR irradiation.

Material and Methods
Twenty-seven hospitalized participants enrolled in our study at a tertiary hospital in Kaohsiung with informed consent and were randomized into two groups. Both groups performed the same wound care procedures using biomycin ointment and dressings. The experimental group (n=17) received FIR (Firapy, TY-101F) wound irradiation for 40 minutes each time for 7 ± 3 times totally during hospitalization, and then received wound care. Control group (n=10), without FIR intervention. Wound drainage fluids were collected at three time points: before receipt, second day after receipt, and seventh day after the receipt. Four subsets of Interleukins: (IL-1β, IL-8, IL-10, and IL-17A) were under quantitative analysis by ELISA, and data were normalized with values of the first collections. SPSS was adopted for statistical analysis. We used student t-test and one-way ANOVA to analyze parametric data. Two-tailed P-value < 0.05 was considered as statistically significant.

Results
For between-group comparisons, there was no significant difference in interleukins. For within-group comparisons, IL-10 (1st versus 3rd) and IL-1β (1st versus 2nd; 1st versus 3rd) were significantly decreased in the control group. However, IL-8 was significantly increased in the experimental group (1st vs 3rd).

Discussion
FIR has biological benefits with both thermal and non-thermal effects. As we have known, FIR promotes wound healing by stimulating the secretion of transforming growth factor β1 (TGF-β1). Interleukins with number not more than 10 are cytokine prominent during wound healing. In this study, we investigate the interleukins in wound healing after FIR. The increase in IL-8 under FIR may imply that epithelialization and angiogenesis are more prominent at the wound site, thereby promoting wound healing. On the other hand, the downward trend in IL-10 and IL-1β in the control group compared to the experimental group may imply that the inflammatory effect subsided more significantly in the absence of FIR.

Conclusions
We found that IL-8 might be promoted under FIR. IL-1β and IL-10 were not descended as significantly as control group under FIR. Further discussion of molecular mechanism of FIR in the model of tension linear suture wounds after the thigh flap procedure is needed.

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