This article was originally published in the Medical Device User Facility Bulletin, Issue No. 38, Spring 2002
EFFECTS OF REPEATED ETHYLENE OXIDE STERILIZATION ON SYNTHETIC ABSORBABLE SUTURES*
By Terry O. Woods, Ph.D., Stanley A. Brown, D.Eng., Katharine Merritt, Ph.D.,
|Editor's note: Although the August 14, 2000 Enforcement Priorities Guidance  exempts "open-but-unused" single-use devices (SUDs), the effects of resterilizing SUDs raise serious concerns.|
Scientists in the Food and Drug Administration's laboratory conducted a study to determine the effect of repeated ethylene oxide (EO) sterilization on sutures that had been opened-but-not-used. Four types of commonly used synthetic absorbable sutures were subjected to 1 and 2 EO resterilization cycles. Knot tensile strength was determined for new sutures and for sutures that had been subjected to 1 and 2 EO resterilization cycles. As has been found with other types of single-use devices, no general conclusions can be made for absorbable sutures. The strengths of different types of sutures increased, decreased, or stayed the same after repeated sterilization. In addition, the inner packages of some sutures were not intact after resterilizing, possibly exposing the sutures to increased humidity. This humidity can produce degradation leading to loss of strength immediately after exposure, after additional shelf aging, and after clinical use.
Many absorbable sutures are provided with two layers of packaging: an outer layer that maintains sterility and an inner layer that provides a moisture barrier. Sutures with opened outer packages and intact inner packages, often referred to as opened-but-unused devices , are commonly resterilized for reuse although labeled for single use only. Mechanical properties of the polymers used in many sutures can be affected by sterilization methods.
To investigate the possible effects of resterilizing on these single-use devices (SUD), we examined the effect of repeated ethylene oxide (EO) sterilizations on the knot tensile strength of four types of synthetic absorbable sutures. Ethylene oxide sterilization of the sutures was done by the staff at the Materials Management Center at the National Institutes of Health Clinical Center in Bethesda, Maryland.
The following table summarizes the four types** of size 1 synthetic absorbable sutures that were examined.
|Dexon II||coated, braided||polyglycolic acid|
|Vicryl||coated, braided||copolymers of glycolide and lactide|
|Polysorb||coated, braided||copolymers of glycolide and lactide|
The sutures were sterilized 1 or 2 times with EO (90:10 sterilant mixture with 90% hydrochlorofluorocarbons and 10% EO 75-21-8) for 130 minutes at 54º - 56º C and 50% - 65% relative humidity, followed by a 12 hour aeration period. Before each EO cycle, the outer packages were removed and the inner packages were placed into new outer packages to simulate handling of opened-but-not used sutures. All packages were carefully handled to avoid mechanically altering or damaging them.
Mean knot tensile strength was determined for the new samples sutures and after 1 or 2 EO resterilization cycles. Suture strength and knotting of the test strand was determined according to United States Pharmacopeial (USP) <881>.  All new samples met the USP limit on average knot pull strength given in the USP official monograph on absorbable surgical suture. 
After resterilization using EO, the out-of-package mean knot tensile strength for different types of synthetic absorbable sutures showed a range of responses: increasing, decreasing, or staying the same for different suture types (Figure 1). However, all tested sutures, regardless of EO exposure, met USP limits on average knot pull strength.
Figure 1. Mean knot tensile strength for four types of synthetic absorbable sutures new and after resterilization by EO once or twice. USP limit is 5.08 kgf for size 1 synthetic absorbable sutures
The two-tailed Student's t-test was used for statistical analyses. The test showed no difference in the strength of Dexon II and Vicryl initially and after 1 and 2 EO resterilization cycles. The strength of the Polysorb sutures was not affected after 1 EO cycle but decreased significantly after 2 EO cycles. The PDS II sutures showed a significant increase in strength after 1 EO cycle and an additional increase in strength after 2 EO cycles that was not statistically significant when compared to the 1 EO cycle.
The EO process had readily apparent effects on the suture inner packages.
- Visual observation revealed that some inner packages were not intact after resterlizing (Figure 2).
Figure 2: Resterilized suture inner package with ruptured seal.
- The seals on a number of the inner packages were breached, showing gaps in the seals that were easily visible without magnification.
- Some resterilized inner packages (after both 1 and 2 EO cycles) were visibly puffier than new packages and appeared to have been inflated. When the puffy inner packages were compressed with the fingers before opening, some deflated, indicating that the seal had broken.
- Most of the inner packages on the resterilized sutures contained wrinkles or creases that were not present on the new packages.
- Delamination was observed between the foil pack and an external polymer layer for a number of packages.
- Behavior of the adhesive seal on some of the resterilized packages (again after both 1 and 2 EO resterilization cycles) was different than that of new packages. When the resterilized packages were opened, some tore across the foil package, while all of the new packages separated at the adhesive seal.
Discussion and Conclusions
The testing highlighted a number of concerns related to resterlizing opened-but-unused sutures.
- Since the sterilization method and expiration date do not always appear on the inner package, a reprocessor may not have this information about an individual suture package. Even when the initial sterilization method is known, a reprocessor may not know the details of the sterilization protocol used on a given type of suture. In fact, for the suture types tested, package labeling indicated the method of sterilization for only one type and no details of the sterilization process were given.
- Seals on some inner packages were destroyed during resterilizing, exposing the absorbable sutures to humidity different than provided in the original packaging. The primary mechanism for degradation of the tested sutures is hydrolysis . Loss of seal integrity might not cause an initial strength loss, as was observed in two of the tested suture types. However, for all absorbable sutures with the inner seal destroyed during repackaging, exposure to increased humidity for an extended time will cause suture degradation. This leads to a loss of strength after shelf aging and a loss of strength and possible changes in the degradation behavior after clinical use. These changes in the suture material could result in wound dehiscence or other complications.
- The change in strength of these sutures implies potential changes in the in vivo degradation behavior of these polymers. Sutures that become stronger after resterilizing may degrade more slowly due to an increase in the crystalline fraction of the polymer. Sutures that become weaker could degrade faster. Further laboratory testing is needed to confirm or refute these concerns.
- For some types of sutures the original expiration date is not listed on the inner suture package. If the expiration date is related to the mechanical characteristics of the suture or to the package that insures its integrity rather than its sterility, the original date may be lost. If the expiration date is related to an assurance of sterility, then a new expiration date should be applied.
The most significant conclusion to be drawn from this study is the observation that, as is true for other types of devices , it is not possible to make general conclusions about the effects of resterilized on absorbable sutures. Suture strength was not affected for some sutures; others increased, and others decreased in strength with repeated EO sterilization cycles.
1. U.S. Food & Drug Administration, Center for Devices & Radiological Health, Office of Compliance. Guidance for Industry and for FDA staff: Enforcement Priorities for Single-Use Devices Reprocessed by Third Parties and Hospitals, August 14, 2000.
2. The United States Pharmacopeial Convention. USP 24-NF 19 Supplement 2. Rockville, MD: The United States Pharmacopeial Convention , July 1, 2000; 2903-4.
3. The United States Pharmacopeial Convention. USP 24-NF 19 Supplement 2. Rockville, MD: The United States Pharmacopeial Convention , July 1, 2000; 2859.
4. Middleton, J.C. and Tipton, A.J., Jr. Synthetic Biodegradable Polymers as Medical Devices. Medical Plastics and Biomaterials. 1998; Vol.5 No. 2. March-April:30-39.
5. Brown, S.A., Merritt, K., Woods, T.O., and Hitchins, V.M., "The Effects of Use and Simulated Reuse on PTCA Balloons and Catheters," Biomedical Instrumentation & Technology 2001;35:312-322.
Terry O. Woods, Ph.D., Stanley A. Brown, D.Eng., Katharine Merritt, Ph.D., Scott G. McNamee, Ph.D., and Victoria M. Hitchins, Ph.D. are scientists in CDRH's Office of Science and Technology.
**Polysorb, United States Surgical Corporation, Norwalk, CT; Dexon II, Davis+Geck, Division of American Cyanamid Company, Wayne, NJ; Vicryl, Ethicon, Inc., Johnson & Johnson, Somerville, NJ; and PDS II, Ethicon, Inc., Johnson & Johnson, Somerville, NJ. Representative products and manufacturers are named for identification only and the list does not imply endorsement by the U.S. Department of Health and Human Services.