[Performance of PHMB-surface mesoporous silica composite material and its effect on infected full-thickness skin...

Objective: To investigate the performance of polyhexamethylene biguanide hydrochloride (PHMB)-surface mesoporous silica composite material (hereinafter referred to as the composite material) and its effect on infected full-thickness skin defect wounds in rats. Methods: This study was an experimental study including group design, factorial design, and repeated measures design. The composite material with a 1:1 mass ratio of PHMB to surface mesoporous silica and good biocompatibility was prepared by rotary evaporation method. The in vitro release of PHMB from the composite material was detected by continuous quantitative measurement. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of PHMB and the composite material against Staphylococcus aureus ATCC 6538 and Escherichia coli ATCC 35150 were detected by broth microdilution method. The continuous bactericidal duration of PHMB and the composite material against the above-mentioned two types of bacteria was detected by continuous bacterial addition assay. The resistance of the above-mentioned two types of bacteria to PHMB and the composite material was detected by sub-lethal concentration induction assay. The sample size for the above experiments was 3. Forty-five female Sprague-Dawley rats aged 10-12 weeks were divided into routine dressing change group, PHMB group, and composite material group by random number table method, with 15 rats in each group. After preparing infected full-thickness skin defect wounds on the back of all rats, the wounds of rats in routine dressing change group, PHMB group, and composite material group were rinsed and dressed with normal saline, PHMB solution and composite material dispersion with a final PHMB mass fraction of 0.100%, respectively. The wound healing rates were calculated, the wound infection status was observed, and the wound tissue bacterial load was detected by the plate counting method at post injury day (PID) 6, 12, and 18, respectively. Results: The composite material could continuously release PHMB for >144 h. For both Staphylococcus aureus and Escherichia coli, the MICs of the composite material were lower than those of PHMB, but the MBCs of both materials against two bacteria were identical. The continuous bactericidal duration of PHMB against Staphylococcus aureus and Escherichia coli was both 3 d, and the continuous bactericidal duration of the composite material against Staphylococcus aureus and Escherichia coli was both 6 d. Staphylococcus aureus and Escherichia coli exhibited resistance to composite materials significantly later than to PHMB. The wound healing rates of rats in composite material group at PID 6, 12, and 18 were significantly higher than those in routine dressing change group and PHMB group (P<0.05). At PID 6, 12, and 18, no infection occurred in the wounds of rats in composite material group, whereas all wounds of rats in routine dressing change group continuously showed infection, and some wounds of rats in PHMB group still continuously showed infection. The wound tissue bacterial loads of rats in composite material group at PID 6, 12, and 18 were (4.6±3.1), (3.4±3.4), and (1.6±1.5) colony-forming unit (CFU)/g, respectively, which were all significantly lower than those in routine dressing change group ((1 876.0±241.5), (1 076.0±151.1), and (1 184.0±156.6) CFU/g) and PHMB group ((824.0±277.6), (800.0±231.0), and (832.0±350.9) CFU/g, P<0.05). The wound tissue bacterial loads of rats in PHMB group at PID 6 and 12 were both significantly lower than those in routine dressing change group (P<0.05). Conclusions: The composite material can enhance and sustain the release of PHMB, thereby delaying the development of bacterial resistance, reducing the bacterial load in wound tissue, and facilitating the healing of infected full-thickness skin defect wounds in rats.