A, Schematic drawing of 2 groups of sutures (orange and blue) suspended from the central peg and connected in tandem via c-clips to external masses. B, Actual setup before the submersion tank is filled with solution.
Failure load vs time data with overlaid best-fit statistical models for poliglecaprone 25 (A), polyglactin 910 (B), and chromic (C) sutures.
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Briddell JW, Riexinger LE, Graham J, Ebenstein DM. Comparison of Artificial Saliva vs Saline Solution on Rate of Suture Degradation in Oropharyngeal Surgery. JAMA Otolaryngol Head Neck Surg. 2018;144(9):824–830. doi:10.1001/jamaoto.2018.1441
Does artificial saliva change the degradation rate of absorbable sutures when compared with saline solution?
In this in vitro study of 3 representative suture types comparing the degradation of suture strength after immersion in a saliva or saline solution, salivary ions and enzymes were found to be associated with faster loss of suture strength, compared with saline. The rate of chromic suture degradation decreased by 13 days in saliva.
Surgeons working in the oropharyngeal environment, where sutures are exposed to saliva, should be aware of suture degradation rates (beyond the information provided by manufacturers) to be able to select sutures that degrade at an appropriate rate and thus aid healing.
Absorbable sutures are designed to degrade and lose strength over time. Manufacturers warn that exposure to various body fluids can change the estimated degradation rate of these sutures, but few studies have been conducted to quantify the degree of change associated with saliva.
To quantify the association of increased loss of strength of sutures over time after exposure to artificial saliva (hereinafter referred to as “saliva”).
Design, Setting, and Participants
This experimental in vitro study was conducted at Bucknell University (Lewisburg, Pennsylvania) from June 19, 2015, to July 4, 2015. No participants were involved. The loss of strength over time of sutures submerged in physiological saline and artificial saliva solutions was compared. Three types of absorbable sutures commonly used in oral surgery were tested: chromic, poliglecaprone 25, and polyglactin 910. Data analysis was conducted from July 15, 2016, to August 16, 2016.
Main Outcomes and Measures
The primary outcome measure was 50% strength reduction. To measure breaking strength, 6 knotted sutures of each type were pulled to failure at regular time intervals after immersion in either saline or synthetic saliva at 37°C. Regression analysis was used to interpret strength degradation profiles and to estimate the time to reach 50% of the original breaking strength.
Of the 3 suture types submerged in the 2 solutions, all 3 degraded to 50% strength faster (by 2 to 13 days) in saliva than in saline. The differences in the degradation profiles varied by suture type. Poliglecaprone 25 sutures demonstrated a sudden decrease in failure strength between day 5 and day 8 in both solutions, but the decrease was greater in saliva (–10.2 N; 95% CI, –15.5 to –4.9 N) than in saline (–6.1 N; 95% CI, –11.2 to –0.9 N). The polyglactin 910 and chromic sutures share a similar degradation profile when implanted in tissue, but saliva was associated with more degradation of chromic sutures. Differences in degradation rate were seen in polyglactin 910 sutures after day 6 (saline: –0.9 N/d; 95% CI, –1.0 to –0.7 vs saliva: –1.2 N/d; 95% CI, –1.4 to –1.1). After day 2, chromic sutures had a degradation rate of –0.3 N/d (95% CI, –0.5 to –0.2) in saline and –0.5 N/d (95% CI, –0.6 to –0.3) in saliva.
Conclusions and Relevance
Knowing the association of saliva with suture degradation rates of various suture types may enable oropharyngeal surgeons to select sutures that retain their strength and degrade at an appropriate rate to allow for the effective healing of the wound.
Closure of tissue defects in the oral cavity and oropharynx presents a unique problem to the surgeon. A watertight closure is sought to prevent migration of saliva into the soft tissues of the face and neck. If wound dehiscence occurs, patient discomfort may increase and wound healing may be impaired. If saliva escapes into the soft tissues, serious wound-healing problems, such as fistula formation and wound infection, can result. Because surgical sites within the oral cavity and oropharynx are often inaccessible to the surgeon for future suture removal, most surgeons use absorbable sutures for mucosal closure in the upper aerodigestive tract.
The ideal absorbable suture retains its strength long enough for the body tissues to heal and regain the necessary tensile strength and then dissolves rapidly when it is no longer needed to avoid inflammatory reactions.1,2 The 3 common absorbable sutures used in oral, pharyngeal, and laryngeal environments are chromic gut, a natural collagen-based monofilament fiber (Chromic Gut; Ethicon, Inc); poliglecaprone 25, a monofilament synthetic fiber (Monocryl; Ethicon, Inc); and polyglactin 910, a braided multifilament synthetic fiber (Vicryl; Ethicon, Inc).
When embedded in human tissues, synthetic sutures are broken down primarily by hydrolysis, whereas natural collagen-based sutures are broken down by proteolytic enzymes released by inflammatory cells during wound healing.3,4 Thus, both the chemistry and structure (eg, monofilament vs braided) of the suture affect the rate of degradation. With various rates of dissolution and strength loss, the type of suture must be carefully selected by the surgeon on the basis of the mechanical requirements of the suture, the rate of degradation and strength loss of the suture, and the anticipated rate of healing. This decision is particularly critical in high-tension closures or in patients with prolonged wound healing because of immunosuppression, diabetes, or radiation therapy.
When sutures are used on the mucosa of the upper aerodigestive tract, a portion of the suture is embedded in tissue and the remainder of the suture is exposed to air and saliva; thus, the rate of loss in strength can be affected by the environment of the suture. Saliva contains enzymes with proteolytic and antimicrobial capacities.5 The pH and ionic content of saliva differs from the content of interstitial fluid.5 Previous in vitro studies have quantified the association of various body fluids, including synovial fluid, urine, bile, and gastric content, with suture absorption and strength reduction.6-10 However, limited studies exist in the literature that quantify the association of saliva with strength degradation of suture materials, and these studies are highly varied in methods and conclusions.
The aim of this in vitro study was to better quantify the association of artificial saliva (hereinafter referred to as “saliva”) with the strength-reduction profile of sutures through direct comparison with a saline control. The inclusion of sutures that represent a range of materials and structures provides insight into the association of saliva with a broad range of absorbable sutures.
The protocol was reviewed by the Geisinger Medical Center Internal Review Board before the study was conducted. The study was deemed exempt given that no humans or animals were involved in testing. This study was conducted at Bucknell University (Lewisburg, Pennsylvania) from June 19, 2015, to July 4, 2015. Data analysis was conducted from July 15, 2016, to August 16, 2016.
The absorbable suture materials evaluated in this study were size 3-0 poliglecaprone 25, a copolymer of glycolide and ε-caprolactone (Monocryl); polyglactin 910, a copolymer of glycolide and lactide (coated Vicryl); and chromic suture (Chromic Gut). Ninety samples of each type of suture were prepared by tying lengths of each suture material around a frame to create consistent loops that were approximately 10 cm long. Standard instrument tie technique was used to tie each suture with 1 surgeon’s knot followed by 2 flat square knots. All knots were tied by one of us (J.W.B., an otolaryngologist).
Six knotted suture loop samples of each suture type were analyzed before their immersion in solution to provide baseline values to determine strength loss over time in each solution.11,12 After soaking each suture in deionized water, we determined the load at failure (ie, breaking force) by pulling each sample to failure using a universal testing machine (Instron 5965; Instron) at 20 cm/min.11
The remaining sutures were connected into groups of 6 in a series using c-clips so that one set could be easily removed and tested at each time point. Each group of sutures was woven between 6 nylon rods on a custom-built apparatus and was held in tension with a 100 g weight, such that each suture had an equal load (Figure 1A). A weight of 100 g was selected to provide a physiologically relevant load that maintained tension on the sutures in vitro to better simulate the in vivo suture conditions.12-14 Each apparatus was loaded with 7 groups of sutures of each type (Figure 1B) and then submerged in an aquarium containing either phosphate-buffered saline (median pH, 7.25) or artificial saliva (median pH, 6.24) maintained at 37°C using a water bath. A small pump moved air through a bubbling stone placed in each solution to provide mixing. A plastic cover was placed over the entire setup to help keep the temperature constant and reduce evaporation. Solutions were changed every 3 to 4 days.
The phosphate-buffered saline solution was prepared by adding 0.72 g of potassium phosphate (monobasic) and 3.975 g of sodium phosphate (dibasic) to 5 L of 0.9% sodium chloride physiological saline solution (McKesson Medi-Pak Performance USP Normal Saline; Moore Medical LLC). The artificial saliva solution was prepared, according to the recipe in Chou et al,15 by mixing 7 g of sodium chloride, 2.5 g of potassium chloride, 0.5 g of calcium chloride, 0.75 g of sodium phosphate (monobasic), 3.975 g of sodium phosphate (dibasic), 0.125 g of magnesium chloride, 0.45 g of urea, 1.0 g of glucose, 13.5 g of mucin type III (from porcine stomach), 0.04 g of acid phosphatase type II (from potato), 0.035 g of lysozyme (a bactericidal enzyme; human, combinant), and 500 kU of α-amylase (a digestive enzyme from bacillus licheniformis) into 5 L of deionized water. All chemicals were purchased (Sigma-Aldrich Corp).
Six samples of each suture type were removed from the immersion solutions for testing at regular time intervals (at day 2, and then every 3 days for poliglecaprone 25 sutures and every 4 days for polyglactin 910 and chromic sutures), as indicated in Table 1. The poliglecaprone 25 suture was tested more frequently because it was expected to degrade more rapidly than the other 2 materials. The sutures were placed in deionized water immediately after their removal from solution to prevent dehydration, and then they were tested for load at failure using the method described earlier. Most of the sutures failed immediately adjacent to the knots, as expected. However, by day 20, most of the poliglecaprone 25 sutures failed along the length, and 2 of the poliglecaprone 25 sutures broke during preparation for tensile testing.
For each material (poliglecaprone 25, polyglactin 910, and chromic), generalized linear regression was used to test for statistically significant differences in degradation rate between samples soaked in the 2 solutions (saline and artificial saliva). The dependent variable for regression was load at failure (N), and the primary independent variable was time (days). The models used a segmented or piecewise regression with 2 segments, on the basis of understanding of the chemical degradation process. For each material at day 0, the curves of failure load vs time for samples in both solutions were assumed to be identical; at a later time (or breakpoint), however, the curve for each solution was allowed to change both intercept and slope, representing a sudden reduction in strength and new degradation rate. Because samples were tested at discrete time points, a series of models were fit to the data from each material, varying when the breakpoint occurred, and the model with the smallest residual SE for analysis of each material was selected.
Wald unpaired, 2-sample t tests were performed to determine whether there was a statistically significant difference in final degradation rate (ie, slope) between saliva and saline. The models used load at failure as their dependent variable, but we also converted this variable to percent strength by dividing the failure load at each time point by the mean load at failure for that material at day 0. We constructed 95% CIs to estimate the time (in days) that each material would degrade to 50% of initial failure strength. All analysis was performed using the base and stats library packages of the R software, version 3.1.2 (R Foundation for Statistical Computing).16,17
Before immersion, poliglecaprone 25 sutures had the highest mean (SD) breaking force of 48.7 (9.6) N, whereas chromic sutures had the lowest mean (SD) breaking force of 30.8 (2.5) N (Table 1). Degradation was similar in both solutions at early time points, but degradation behavior differed statistically significantly at later time points between saliva and saline for all 3 suture types (Figure 2). Regression results for poliglecaprone 25 sutures (Figure 2A) suggest that between day 5 and day 8, a statistically significant decrease in failure strength occurred in saline (–6.1 N; 95% CI, –11.2 to –0.9 N) and a statistically significant decrease in failure strength occurred in saliva (–10.2 N; 95% CI, –15.5 to –4.9 N). However, no statistically significant difference was found in the final degradation rates between saline (–1.6 N/d; 95% CI, –2.0 to –1.1) and saliva (–1.4 N/d; 95% CI, –1.9 to –0.9). Regression results for polyglactin 910 sutures (Figure 2B) suggest that no statistically significant sudden decrease in failure strength occurred, but after day 6, the sutures showed considerably different degradation rates in saline (–0.9 N/d; 95% CI, –1.0 to –0.7) and in saliva (–1.2 N/d; 95% CI, –1.4 to –1.1). Similar to regression results for polyglactin 910 sutures, regression results for chromic sutures (Figure 2C) suggest that after day 2, the sutures showed a degradation rate of –0.3 N/d (95% CI, –0.5 to –0.2) in saline and –0.5 N/d (95% CI, –0.6 to –0.3) in saliva, with no statistically significant sudden decrease in failure strength. Our regression model is summarized in Table 2.
Before testing, we defined a 50% strength loss as the clinically pertinent end point. Only the poliglecaprone 25 sutures reached 50% strength in both saline and saliva within the time frame of the study. However, the statistical models can be used to extrapolate estimated times for each suture type to reach 50% strength in each solution. For the poliglecaprone 25 sutures, the estimated initial strength was 48.7 N based on the day 0, nonimmersed sample group, and the same models were used to estimate (with 95% CIs) the time required for the poliglecaprone 25 sutures to degrade to 25.4 N or 50% of initial strength. This 50% degradation time for the poliglecaprone 25 sutures was 9.6 days for saline (95% CI, 6.6-11.5) and 7.2 days for saliva (95% CI, 5.1-9.6). The estimated time required for the polyglactin 910 sutures to degrade to 50% of initial strength (22.9 N) was 32.3 days in saline (95% CI, 28.9-36.2) and 24.1 days in saliva (95% CI, 22.6-25.6). The estimated time required for the chromic sutures to degrade to 50% of initial strength (15.4 N) was 41.3 days in saline (95% CI, 34.4-52.1) and 28.3 days in saliva (95% CI, 25.0-32.4). Hence, all suture types were expected to reach 50% strength faster in saliva than in saline, but this was only statistically significant for polyglactin 910 and chromic sutures.
In this study, all 3 types of absorbable sutures lost strength at earlier time points in saliva than in saline, but the degradation profiles varied by suture type. The poliglecaprone 25 sutures in saliva showed a sudden drop in strength after day 5, with the sutures maintaining strength initially and then rapidly degrading. Chromic and polyglactin 910 sutures, in contrast, showed a higher degradation rate in saliva than in saline after day 2 or day 6 of immersion but no sudden drop in strength. In addition, sutures degraded to 50% strength faster in saliva compared with saline, although the magnitude of the differences varied by material.
Table 3 compares the time to reach 50% strength in saliva and saline reported in our study with the time reported in other in vitro studies18-20 and compares our findings with values reported by the manufacturer for time to reach 50% strength after suture implantation.3 The results in other studies vary widely, likely because of the differences in study conditions (eg, sutures immersed in small vials without tension) and immersion solution (eg, 1:1 serum to saliva ratio, varying saliva composition); this variation makes it difficult to interpret the results of different in vitro studies in relation to each other. The trends in our study are consistent with the results of Ferguson et al,18 the only other saliva study, to date, to include a saline control, but the 2 studies have a few important differences. In both studies, the time to reach 50% strength was substantially reduced in saliva compared with saline for all sutures tested, and the association of saliva with chromic sutures was more substantial than with polyglactin 910 sutures. The Ferguson et al18 study, however, did not define how the saliva was acquired, whereas to establish a controlled study, we carefully selected a synthetic saliva formulation that included the most relevant enzymes. In addition, the Ferguson et al18 study measured suture strength at only 1 time point after 14 days, at day 35, by which time strength had already degraded to less than 50%. Our study provides a more detailed degradation curve during this critical time by measuring strength at days 14, 18, 22, and 26, thereby presenting a more precise estimation of when suture degradation occurs.18 Specifically, in the study herein, saliva (compared with saline) reduced the number of days required to reach 50% strength by 2.4 days for poliglecaprone 25 sutures, 8.2 days for polyglactin 910 sutures, and 13 days for chromic sutures. If these accelerated degradation times translate to the in vivo environment, reaching 50% strength can be expected as early as 4.6 days for poliglecaprone 25 sutures, 12.8 days for polyglactin 910 sutures, and 8 days for chromic sutures when implanted in vivo (compared with the 7, 21, and 21 days reported by the manufacturer for internal implantation in the absence of saliva).3
When sutures are used in the oral cavity and pharynx, the body contributes to the degradation of the sutures. This explains some of the differences between our data in saline and those from the manufacturer and why chromic sutures (which are more affected by proteolytic enzymes and macrophages than polyglactin 910 sutures) degraded slightly slower in our study than expected. Although we do not know whether saliva would be directly additive to tissue-driven degradation, we still believe this study provides new, valuable insights into the potential correlation between saliva and the hastening of suture degradation.
We selected a degradation to 50% strength as our primary outcome measure to facilitate the comparison of our results with industry standards and other study findings. Surgeons want the suture to match or exceed the strength of the native tissue during healing; thus, from a clinical perspective, a comparison of absolute breaking forces may be of value. In a study of porcine oral mucosa, Goktas et al21 found that the tensile strength of mucosa varies throughout the oral cavity, but the highest breaking forces observed were in the range of 25 N and the lowest forces were around 7 N. The 50% breaking force of poliglecaprone 25 sutures was 25.4 N and of polyglactin 910 sutures was 22.9 N in our study, which match the highest forces seen in the Goktas et al study. This finding suggests that for poliglecaprone 25 and polyglactin 910 sutures, the 50% reduction in strength may be clinically relevant, especially if these sutures were used in regions where the mucosa is stronger. The initial breaking force for the chromic suture was 30.8 N, making the 50% breaking force 15.4 N. Thus, selecting 50% strength reduction as our primary outcome measure may be less clinically relevant for chromic sutures if they were used at sites where the mucosa is stronger, but this outcome measure may be reasonable if the sutures were used at sites that experience less force. If degradation to 25 N were our end point, instead of 50% loss of strength, our study would show that chromic sutures degraded to a strength of 25 N in saliva between day 10 and day 14 (Table 1 and Figure 2), whereas poliglecaprone 25 sutures reached this point between day 5 and day 8 and polyglactin 910 sutures between day 18 and day 22.
In addition, our strength reduction results can be compared with suture loss observations by in vivo studies involving size 3-0 chromic and polyglactin 910 sutures implanted in the oral mucosa,22-25 as sutures are expected to be dislodged soon after the sutures break in the dynamic oropharyngeal environment. Two studies showed that chromic sutures were lost between day 7 and day 11,22,25 a time frame that is closer to our extrapolated time to reach 50% strength (8 days) than to the manufacturer’s time after implantation (21 days). In most in vivo studies, however, polyglactin 910 sutures disappeared between 14 and 25 days,23-25 a time frame that is more consistent with the manufacturer’s 21 days than our extrapolated 12.8 days. However, disappearance of the polyglactin 910 suture may not correlate well with mechanical failure. Polyglactin 910 sutures may persist in vivo after breaking because of their braided structure that creates higher friction at the wound site or because not all filaments break simultaneously. No equivalent observational in vivo studies were found for size 3-0 poliglecaprone 25 sutures. However, the results of this present study provide quantitative evidence for the clinical observations by Huang et al1 of a 2-stage degradation profile for poliglecaprone 25 sutures implanted in the oral cavity during uvulopalatopharyngoplasty, given that only the poliglecaprone 25 suture type in our study showed a sudden drop in strength after day 5.
Clinically, these results provide new information on which surgeons can base their decisions when selecting sutures for use in the oropharyngeal environment. Healthy, well vascularized tissues under minimal tension are likely to heal in 5 to 10 days.2 However, procedures such as laryngectomies or cleft palate repairs place sutures under considerable mechanical stress, and patients with a history of radiation therapy or comorbidities such as diabetes or immunosuppression may also require prolonged healing times (lasting several weeks). This study demonstrated that both chromic and polyglactin 910 sutures retained their strength in saliva longer than poliglecaprone 25 sutures did. These results suggest that poliglecaprone 25 sutures may be most suitable for oropharyngeal wounds that are likely to heal in 5 days,1 polyglactin 910 sutures may be used for patients who require longer healing time, and chromic sutures may be useful in regions of lower tension and that are expected to heal within 1 week.
This study had several noteworthy limitations. First, although the components of saliva are well established, their concentration varies among individuals and changes over time within an individual. Our saliva formulation included many relevant enzymes, but this solution still did not include the other salts, proteins, and enzymes present in natural saliva in lower concentrations. Second, the study’s in vitro design allowed for regimented consistency in the testing environment, but comparing saliva and saline without the presence of enzymes, phagocytes, and neutrophils found during an inflammatory response represents a simplified situation. Third, we noted the differences in pH between the 2 solutions, as pH affects suture degradation. The saline solution maintained a relatively constant pH—between 7.05 and 7.40—throughout the study, with a median of 7.25. The saliva solution, however, although it had a pH of 7.25 when initially formulated, rapidly dropped in pH even with buffering, resulting in a median pH of 6.24 during the study but with some spikes as low as 4.03 and as high as 7.4. Studies of natural saliva reveal a pH range of 5.6 to 7.9,26,27 with acidic spikes below 5 during eating based on dietary intake,27 so the pH profile in our study was still representative of what could occur in the mouth.
Despite these limitations in saliva composition, this study serves as a valuable model for future in vitro studies that evaluate suture degradation in simulated body environments. The study offers a method for maintaining physiologically relevant knot tension during immersion in solution. Future studies could improve on the design of this study by using a physiologically relevant dynamic load, rather than a static load, on the submerged sutures; extending the length of time for polyglactin 910 and chromic sutures to allow full degradation; and increasing the number of sutures tested at each time point.
When interpreted in conjunction with past in vivo studies, the findings from this study appear to demonstrate that all types of sutures—natural or synthetic and monofilament or braided—undergo more rapid degradation in the presence of saliva. Polyglactin 910 and chromic sutures shared similar degradation curves when implanted in tissue, and both maintained strength longer than poliglecaprone 25 sutures did. However, our data revealed that saliva had a greater association with the degradation of chromic sutures compared with polyglactin 910 sutures. This information should be taken into consideration when selecting sutures for oropharyngeal procedures, to ensure that the suture will retain its strength and degrade at an appropriate rate to allow the effective healing of the wound.
Accepted for Publication: May 7, 2018.
Corresponding Author: Jenna W. Briddell, MD, Division of Otolaryngology—Head & Neck Surgery, Nemours/Alfred I. duPont Hospital for Children, 1600 Rockland Rd, Wilmington, DE 19803 (email@example.com).
Published Online: August 16, 2018. doi:10.1001/jamaoto.2018.1441
Author Contributions: Dr Briddell had full access to all of the data in the study and takes responsibility for the integrity and the accuracy of the data analysis.
Study concept and design: Briddell, Riexinger, Ebenstein.
Acquisition, analysis, or interpretation of data: Riexinger, Graham, Ebenstein.
Drafting of the manuscript: All authors.
Critical revision of the manuscript for important intellectual content: Riexinger, Graham, Ebenstein.
Statistical analysis: Graham.
Obtained funding: Briddell.
Administrative, technical, or material support: Briddell, Riexinger, Ebenstein.
Study supervision: Briddell, Ebenstein.
Conflict of Interest Disclosures: All authors have completed and submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest and none were reported.
Funding/Support: This study was supported by grant 128890 from the Bucknell-Geisinger Research Initiative and the Bucknell Program for Undergraduate Research.
Role of the Funder/Sponsor: The funding sources had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication.
Meeting Presentations: The results of this study were presented at the 2015 Biomedical Engineering Society Annual Meeting; October 7, 2015; Tampa, Florida; at the Society for Ear Nose and Throat Advancements in Children; December 5, 2015; San Antonio, Texas; 2016 Summer Biomechanics, Bioengineering and Biotransport Conference; June 30, 2016; National Harbor, Maryland; and 2016 Biomedical Engineering Society Annual Meeting; October 7, 2016; Minneapolis, Minnesota.
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