Introduction: Surgical braided silk sutures have become one of excellent and widely used sutures in the world. However, silk sutures have the risk of bacteria bio-adherence because of protein nature and braided structure, which can increase the rate of surgical site infections (SSIs) on surgical incision. As a foreign body, antibacterial sutures may prevent the attachment and proliferation of bacteria, as well as reduce the probability of SSIs[1].
Materials and Methods: The silk sutures we fabricated were braided by multifilament yarns on normal circular braiding machine. Before braiding, all the yarns were coated with an antibacterial mixture system composed of levofloxacin hydrochloride, an artificial synthetic antibacterial drug, and polycaprolactone (PCL), the drug carrier. During the fabrication, three controllable variables were drug concentration (1500 µg/mL, 3000 µg/mL and 4500µg/mL), carrier concentration (5%, 7.5% and 10%, w/w) and molecular weight of PCL (80,000 and 180,000).
The antibacterial proterty and sustained efficacy assay were judged by zone of inhibition. Samples were challenged in vitro by Staphylococcus aureus (ATCC 25923) and Escherichia coli (ATCC 25922) with approximately 1 × 108 colony forming units/mL (CFU/mL) bacteria suspension. Then the dishes were cultivated at 37°C for 24h and zone of inhibition were measured. Samples were transferred daily onto new Petri dishes growing a similar number of bacteria until the sutures ceased antibacterial properties. TU-1901 UV-vis spectra photometer was used to test drug release amount at each procedural time point.
Results and Discussion: The results of the zone of inhibition assays are shown in Figure 1. Sutures with antibacterial treatment exhibited distinct zones of inhibition against both S. aureus and E. coli, no matter which parameters of antibacterial system were use. In contrast, the untreated sutures had no zones. Besides, with the increase of drug concentration and molecular weight of PCL, the antibacterial characteristics lasted varying from 2 to 5 days. However, the zones of inhibition with different carrier concentration indicated no siginificant difference, and the daily results were very similar.
Figure 1 Zone of inhibition assay with different (a) drug concentration; (b) carrier concentration; (c) molecular weight of PCL; and (d) diagram of zone of inhibition.
When considering drug concentration, the higher concentration meant prolong of antibacterial period. On the contrary, it related to a higher toxicological risk because of more drug surface accumulation and burst release. When considering PCL molecular weight, higher ones increased the viscosity of antibacterial system for a better sticking, meanwhile extended degradation period for slow drug release. Hence, the most superior parameters of antibacterial treatment were drug concentration as 3000 µg/mL, carrier concentration as 5% and 180,000 PCL molecular weight.
As presented in Figure 2, it was proved that the drug released continually from treated sutures up to 6 days, which was in keeping with wound healing rate.
Figure 2 Drug release curve of antibacterial treated suture with the most superior antibacterial treated parameters.
Conclusion: The silk braided sutures we fabricated provided sustained antibacterial efficacy against S. aureus and E. coli, which may effectively prevent the attachment and proliferation of bacteria during wound healing period.
111 project "Biomedical Textile Materials Science and Technology" (B07024)
References:
[1] David Leaper, Andrew J McBain, Axel Kramer, Ojan Assadian, Jose Luis Alfonso Sanchez, Jukka Lumio, and Martin Kiernan. Healthcare associated infection: novel strategies and antimicrobial implants to prevent surgical site infection. Ann R Coll Surg Engl, 2010, 92(6): 453–458.