Mechanical fabrication and evaluation of bioresorbable barbed sutures with different barb geometries

Bioresorbable polymeric sutures are gaining interest from surgeons and patients as they reduce surgical stress and trauma. This study involves two bioresorbable polymers, namely, catgut and poly(4-hyrdorxybutyrate) (P4HB) that are used widely in cosmetic procedures. P4HB barbed sutures are favorably used in rhytidectomy (micro-facelifts) procedures while catgut sutures are widely used for external wound closure after surgical interventions. This study involves the mechanical fabrication of catgut and P4HB barbed sutures and compares their mechanical and anchoring properties. Barbed sutures were fabricated with two different barb geometries namely, straight and curved barbs. The mechanical properties were evaluated via tensile testing, and the anchoring performance was studied by means of a suture-tissue pull-out protocol using porcine dermis tissue which was harvested from the medial dorsal site. The fabricated barbed sutures of both materials showed a similar trend compared to non-barbed sutures of decreases in failure stress, strain at failure, and work to rupture or toughness which was reduced by about 70%. At the same time there was a 15% increase in the initial modulus or stiffness of the barbed sutures. The pull-out force for the barbed sutures with straight barbs was similar for both P4HB (5.04 ± 0.8 N) and catgut (4.47 ± 3.8 N), and as expected, were higher than that of non-barbed sutures of the same size. It was also observed that barbed sutures with curved barbs also required a higher pull-out force than those sutures with straight barbs. It was concluded that by barbing sutures with different barb shapes and geometries, a range of barbed suture products could be fabricated, each meeting the closure requirements for different types of tissue and therefore being suitable for different surgical procedures.


Introduction
Surgical procedures involving an incision require wound closure devices to close the incision, approximate the tissue so as to prevent infection and dehiscence, and promote wound healing [1][2][3].Surgical sutures are the most common and major type of wound closure device that is used clinically.These surgical sutures can be made from both resorbable and non-resorbable polymeric materials that are used based on their clinical and surgical requirements.Suturing and closing of bodily tissues are a time-consuming and stressful process in the operating room.But it is equally important, as with any implantable medical device, that the sutures be inserted in the adjoining tissue meticulously and with precision.Because if there are openings, nonuniformities or discontinuities in the stitching pattern, the risk of wound rupture and dehiscence increases significantly.Unfortunately, when this happens there is a need to repeat the surgical procedure, increasing morbidity to the patient.So in order to reduce the risk for both the surgeon and the patient, this barbed suture design with a plurality of projections along the surface make the operative procedures both more effective, secure and time efficient [4,5].
In this study, the design and development of barbed sutures was investigated in order to overcome the problems associated with conventional sutures: both smooth monofilaments and multifilament braided sutures.Along with eliminating the problems associated with knotted wound closure devices, these barbed sutures also reduce postoperative wound closure complications which have been reported in a number of cases [6,7].These barbed sutures are known as self-anchoring or knotless sutures are secured by barbs/ projections on the suture monofilament rather than knots.Barbed sutures are composed of a helical array of projections (figure 1) which are cut around the periphery of the monofilament suture.Furthermore, since barbed sutures have barbs all along the suture line, the retention forces are distributed along the length of the wound, rather than being concentrated at the knot.These barbed sutures stabilizes the wound by providing greater tension where the wound needs it (i.e. in the middle) because there is no suture slippage as occurring in the smooth monofilaments, and facilitates wound healing [8][9][10].
Barbed sutures can have barbs pointing either in one direction, that is a unidirectional barbed suture, or in two directions, which is a bidirectional barbed suture.In the former case, the barbed suture has a needle at one end and a loop at the other in order to anchor the suture during the surgical procedure.In the latter case, the barb direction changes at the center of the suture and the suture has needles at both ends.As a result the closure stitching protocol involves starting at the middle of the wound and proceeding to the ends with the two needles [10][11][12].After years of investigating the design, barbed sutures were commercially available once the company, Quill Medical LLC, was established in 1999 following the publication of patents by Dr Gregory L. Ruff in the years of 1994 and 2001 [7,13].
While non-resorbable synthetic filaments have higher mechanical strength than resorbable sutures, their main disadvantage is related to their in vivo biocompatibility and biodegradability.Early studies on barbed sutures were focused on their mechanical properties and anchoring performance of synthetic non-resorbable sutures.During the early 2000's, there were a number of studies evaluating the mechanical and anchoring properties of bi-directional barbed sutures.In 2003, a study focused on evaluating the performance of polydioxanone (PDO) sutures in terms of the barb geometry and their anchoring performance in different surrounding tissues.In this study, the researchers concluded that optimization of the barb geometry is essential in order to approximate wounds efficiently and securely [2].
Following this publication, there were a number of studies which evaluated the design and performance of bi-directional barbed sutures fabricated from different synthetic materials, namely, nylon [14], polypropylene (PP) [14][15][16], and polyvinylidene fluoride (PVDF) [16].Huang's study compared the anchoring properties of PVDF with PP sutures in a tendon repair procedure.In their study they concluded that PVDF bi-directional barbed sutures can be used as an alternative to PP barbed sutures as they showed superior mechanical performance in a tendon repair protocol [16].In Ingle et al's study he changed the barb parameters, such as the shape, size and frequency, through his innovative mechanical fabrication technique, and he determined how varying the barb geometry would impact its mechanical performance.Ingle also attempted to map the barb geometry with the type of surgery by comparing the suture-tissue pull out test on skin and tendon tissues [15,17].After the Food and Drug Administration (FDA) approved that poly(4hydroxybutyrate) (P4HB) could be used as a suture material in 2007 there has been increased interest in barbing these sutures as they have both superior mechanical characteristics and in vivo biocompatibility.As a result, Cong et al fabricated P4HB barbed sutures and compared their mechanical and anchoring properties with PDO barbed sutures in order to demonstrate their clinical superiority [4].
The present study focuses on the mechanical fabrication of barbed sutures from resorbable polymers such as catgut [18,19] and P4HB sutures [20,21].Two different barb geometries were fabricated and their mechanical properties and anchoring performance were measured using an in vitro test protocol [22].As previously concluded by Ingle et al, different barb geometries are required in order to close different types of wounds with various tissue compositions.The novelty of the work is that this is the first study which describes the fabrication of catgut barbed sutures and their property characterizations in terms of their mechanical, anchoring and degradation properties.And this is the first study which evaluated the mechanical and anchoring properties of barbed sutures with barbs fabricated at two different barb cut angles to create a curved barb geometry.

Materials used
The materials used in this study were bioresorbable polymeric monofilaments made from P4HB, catgut, and expanded polytetrafluoroethylene (ePTFE).Catgut monofilaments, size 0 (0.400 mm-0.499mm) and size 2-0 (0.399 mm-0.400mm) (Ethicon Inc., Somerville, NJ) have been used for surgical closures since the origins of medicine back in 300 BC   [18,23].On the other hand, size 2-0 (0.300 mm-0.339mm) P4HB monofilaments (B.Braun Medical Inc., Barcelona, Spain) are a relatively new material that was approved by the US FDA in the year 2007 for use as a resorbable suture [20,21], and ePTFE monofilaments with a diameter ranging between 0.450 mm-0.500mm (Zeus Scientific Inc., Orangeburg, SC) have only been available commercially within the last 40 years.

Barbed suture fabrication 2.2.1. Mechanical barbing instrument
The surgical sutures were cut into 12.7 cm lengths for tensile testing and 5 cm lengths for suture-tissue pull-out tests.Bi-directional barbs were cut on P4HB size 2-0, catgut size 0 and size 2-0 monofilaments using the mechanical barbing instrument (figure 2) donated by the former Quill Medical Company [24].
The complete fabrication of a bi-directional barbed suture using the manual barbing instrument involves three barbing operations that are staggered around the suture diameter to create a helix.The barbed sutures were fabricated in sections and so different cutting templates were used which were fabricated at certain offset distances in order to create a helical array of barbs around the suture.This is not shown in the figure [4,16,25].
The monofilaments were held in place using two suture retention clamps at either end of the instrument.These clamps held the suture in place while barbing.One complete barbing operation involves the following steps: (1) the tamp plate was positioned face down on the instrument and the tightening screws were used to secure the suture in place within the V-shaped groove.( 2 7) The third and fourth barb series were cut in a similar manner to the first template.( 8) So, for the next series of barbing operations, the knife positioning templates I and II with the same dot numbers were used for the next four sets of barbed sections.( 9) After each barbing operation, the suture retention clamps were rotated by 120 • , and the above-mentioned process was repeated with the next pair of positioning templates.It was important to make sure that the dot numbers on the retention clamps and the knife positioning templates were the same.
The shape and geometry of the barb are crucial characteristics when fabricating barbed sutures.When considering a straight barb, the two main parameters are the cut angle and cut depth as shown in figure 3.There is a need to alter these parameters in order to optimize the anchoring capability with respect to the surrounding tissue.In previous research, different surgical procedures evaluated barbed sutures in closing different types of wounds with different tissues.For example, in the study by Ingle et al, it was reported that barbed sutures used for tendon repair require barbs with a lower cut angle and higher cut depth, while in the case of skin tissues the sutures needed to have barbs with a higher cut angle and higher cut depth [15,17].

Barb geometry
In this study, barbed sutures were fabricated with both straight and curved barb geometries using the mechanical barbing instrument shown in figure 2. The frequency, angle and depth of the barbs (figure 3) were fixed and determined by the blade assembly.The blade assembly consisted of nine blades within a 4 cm distance arranged in series and held in a common base.For the bidirectional sutures, the barbed sections were 7 cm in length at both ends with a 2 cm gap in the middle.The straight barbs were cut with the following parameters: the cut depth was fixed at 20% of the suture diameter and the cut angle was fixed at ±165 • .Barbed sutures with curved barbs were fabricated using the same mechanical barbing instrument and blade assembly at the angle of 165 • and the same 20% of the suture diameter.After for producing the straight barbs, a second linear cut at 180 • (parallel to the suture axis) was made to increase the barb length and thereby develop a curved barb shape.In figure 3, we can observe the difference in the barb cut angles in order to fabricate the straight and curved barb geometries.After fabrication, the sutures were swaged with taper-pointed needles, which are commonly used for wound closure.The needles were sized for the corresponding suture sizes: size 22 for size 2-0 suture and size 24 for size 0 suture.

Optical microscopy
The fabricated barbed sutures were viewed under a Nikon Labophot-2 light optical macroscope (Nikon Corp, Tokyo, Japan) at 0.5× magnification.This provided a low power image of the variation in barb shape and geometry for the samples fabricated using the stationary blade assembly.

Suture tensile test
The tensile properties of the mechanically barbed and non-barbed sutures were measured and compared against commercially available barbed sutures on an MTS Q-test/ 5 mechanical tester (MTS Systems, Eden Prairie, MN, USA) with a 250N load cell following ASTM D2256/ D2256M-2021 'Standard test method for Tensile Properties of Yarns by the Single-Strand Method' .Sutures were mounted between the flat capstan clamps at a pressure of 60 psi with a set gauge length of 5 inches (12.7 cm) and a crosshead speed of 150 mm min −1 .The mechanical properties of failure stress and strain were measured and recorded at the break.The initial tensile modulus, which measures the resistance to stretching, was determined from the slope of the recorded stress-strain curve, and the work to rupture or toughness was determined as the area under the load-displacement curve.Stiffness measures how sutures resist deformation when a tensile load is applied, and toughness measures how sutures absorb energy and undergo plastic deformation until they break at the failure point.

In-vitro hydrolytic degradation test
The resistance to hydrolytic degradation was evaluated for catgut and P4HB sutures with the view to determine whether or not the barbs fabricated mechanically degraded earlier than the non-barbed suture monofilaments.The suture materials of catgut [18,26,27] and P4HB [4,21] undergo degradation through hydrolytic degradation.An in vitro hydrolytic degradation protocol was studied in order to determine the degradation profiles of both P4HB and catgut monofilaments.
The non-barbed and barbed suture monofilaments were incubated at 37 • C in 5 ml of phosphate buffer solution (pH = 7.4) for up to six weeks for P4HB sutures and up to 10 d for catgut sutures.The degradation solution was renewed at every time point of 0, 1, 2, 3, 4, 5 and 6 weeks for P4HB and at 0, 2, 4, 6, 8, and 10 d for catgut sutures.At each time point, the tensile characteristics, mainly the ultimate tensile force (N) of fabricated barbed sutures were measured and compared against their respective nonbarbed counterparts.

Suture-tissue pull out test
In order to mimic the in vivo anchoring performance of barbed sutures with their surrounding tissue, porcine dermis was used in an in vitro protocol to evaluate the suture-tissue pull out strength [22].Figure 4 illustrates the suture-tissue pull out test protocol together with how sutures were inserted into the thickness of the dermis.
The samples of dermis tissue were kept in phosphate buffered solution (PBS) as soon as they were harvested from the mid-dorsal portion of the pig at the College of Veterinary Medicine, North Carolina State University.3/8 taper point needles were swaged for both bi-directional barbed and nonbarbed sutures.The suture bite length (Ds) was calculated to be 0.804 mm for a size 2-0 suture and 0.941 mm for a size 0 suture with a 3/8 taper point needle.The anchoring properties of the mechanically barbed and non-barbed sutures were measured and compared against commercially available barbed sutures on an MTS Q-test/ 5 mechanical tester (MTS Systems, Eden Prairie, MN, USA) with a modification to the clamps on the test instrument.Anchoring properties of maximum pull-out load and elongation were evaluated using the ASTM D3822/ D3822M-2020 'Standard Test Method for Tensile Properties of Single Textile Fibers' .One suture end was attached to the top clamp while the porcine dermis was held by the bottom clamp with sandpaper lining the clamp surfaces so as to avoid slippage of the dermis at a pressure of 50 psi.The standard uniaxial tensile test was performed with a gauge length of 2 inches (7.62 cm) and a crosshead speed of 150 mm min −1 .The maximum pull-out load at failure was considered a direct measurement of suture engagement with the surrounding tissue.

Statistical analysis
Barb geometry, mechanical properties and anchoring performance results were compared between the barbed and non-barbed suture control for each of the respective materials: P4HB, catgut and ePTFE.The data were also compared against the commercially available PP Quill TM barbed 2-0 sutures.Each group had four specimens on which to perform the statistical analysis.The statistical analysis was performed using a one-way ANOVA with Tukey's adjustments with a p-level of 0.05 using Origin software (Origin Lab, Northampton, Massachusetts, USA).The average data is reported as mean ± standard deviation.

Optical microscopy-barb geometry
Barbed sutures were fabricated with two different barb geometries, namely, straight and curved, that were observed under low power optical microscopy (figure 5).From these optical micrographs, it can be observed that it is possible to fabricate curved barbs using the mechanical barbing instrument and blade assembly described above.

Suture tensile test and degradation results
The tensile results of the mechanically barbed and non-barbed sutures were measured and compared against the commercially barbed PP sutures (figure 6, table 1).The ultimate tensile force (figure 6(A)) was significantly reduced after barbing irrespective of the polymer material.From the values listed in table 1, it can be seen that there was a 74.5% loss for the size 0 catgut straight barbed suture (p < .001); a 77.5% loss for the size 2-0 catgut straight barbed suture (p < .001); a 87.5% loss for the P4HB size 2-0 straight barbed suture (p < .001),and a 51.9% loss for the ePTFE straight barbed suture (p < .001).All the barbed sutures were compared to their respective non-barbed controls.The elongation at break (figure 6(B)) was significantly reduced after barbing irrespective of the polymer material and the percent change followed a similar trend to the decrease observed in the failure stress results.The toughness or work to rupture (figure 6(D)) was significantly reduced after barbing irrespective of the polymer material and the percent change followed a similar trend to the decrease observed in the failure stress results.All the barbed sutures were compared to their respective non-barbed controls.
The stiffness or initial tensile modulus of the sutures showed an increase after barbing compared to their non-barbed controls.From the values listed in table 1, it can be seen that there was a 18.7% increase in the size 0 catgut straight barbed suture (p < .001); a 6.8% increase for the size 2-0 catgut straight barbed suture (p < .001); a 99.1% increase for P4HB size 2-0 straight barbed suture (p < .001),The filaments were hydrolytically degraded in PBS solution through an in vitro hydrolytic degradation protocol.The time points were chosen based on the literature with regards to P4HB and catgut sutures.The tensile property of ultimate tensile force was measured at each of the time point for both the sutures in order to determine whether barbing did alter the degradation profile or not.From the plot for the variation in tensile force of P4HB sutures (figure 6(E)), it can be observed that there was not any significant variation due to mechanical barbing.From the plot for variation in tensile force of catgut sutures (figure 6(F)), it was seen that even though there was variation in the results, the profile remained almost similar after mechanical barbing was performed.

Suture-tissue pull out test
The anchoring performance results for the mechanically barbed sutures were compared against their non-barbed controls (figure 7, table 1).Invariably the barbed sutures with their higher maximum pull-out load (figure 7(A)), showed superior anchoring performance because the barbs engaged with the surrounding tissue.From the values listed in table 1, it can be seen that there was a 66.8% increase for the size 0 catgut straight barbed suture (p < .001); a 76.9% increase for the size 2-0 catgut straight barbed suture (p < .001),and a 496% increase for the P4HB size 2-0 straight barbed suture (p < .001)compared to their respective non-barbed controls.The results for the elongation at maximum pull-out load (figure 7(B)) showed similar increases as observed in the maximum pull-out load data for the two sizes of catgut sutures (table 1).

Discussion
Barbed sutures have been available for surgeons to use in different surgical procedures since they were approved by the United States FDA in 2004.Catgut sutures have been used for centuries, especially for wound closure.In fact they date back to the Egyptian era around 300 BC [18,23].On the other hand, P4HB was approved by the FDA in the year 2007 for use in resorbable implantable medical devices.In the current study, we successfully fabricated barbed sutures using the mechanical barbing instrument and blade assembly described above.Despite the difficulty of altering the barb shape using the mechanical fabrication approach, curved barbs were successfully created with two different rotational angles (figure 5).The images D, E, I and J in figure 5 illustrate how curved barbs were fabricated with one and two rotational angles.Since they were fabricated manually, it was difficult to maintain a consistent cut depth for all the barbed samples.As a result, it was impossible to fabricate curved barbs with three rotational angles because they broke and failed.
The present study has demonstrated that it is possible to fabricate catgut and P4HB barbed sutures using a mechanical barbing approach, and the tensile properties and anchoring performance were evaluated using a tensile test and a suture-tissue pull-out protocol.From the evaluation of the tensile properties, it was observed that barbing caused a significant 75%-80% reduction in ultimate tensile force (N) (figure 6(A)).In comparison, the loss in the effective cross-sectional area of the monofilament suture due to barbing was calculated to be about 42.5%.This significant difference in the amount of decrease points to the fact that the cross-sectional structure of the monofilament is not homogeneous and indicates the likelihood of a skin/core structure with a stronger, more oriented, crystalline and denser outer skin compared to the central core [17].
The decrease in ultimate tensile force due to barbing was seen irrespective of the type of suture material.From the elongation at break results (figure 6(B)), it was observed that the catgut barbed sutures of both geometries had a higher reduction due to barbing compared to the P4HB and ePTFE sutures.From the work to rupture results (figure 6(D)), the toughness of the sutures was reduced significantly by at least 80% as a result of barbing, which is also attributed to the loss in cross-sectional area of the barbed sutures.The results for stiffness (figure 6(C)) showed an increase in the initial tensile modulus as a result of barbing.For example, the stiffness of catgut sutures are postulated to marginally increase due to the effect of the plasticizer components in the alcoholic sterilizing solution that is used to maintain the catgut filaments at an alkaline pH [19,28].Whereas in the case of P4HB, the increase ranged from about 70%-100%, which is equivalent to the inherent loss in elongation at break caused by barbing.
After tensile testing, the suture specimen fragments in the failure zone were viewed visually to identify any changes that occurred to the monofilaments during the tensile test.Observations were made for both barbed and non-barbed sutures in order  to determine if the barbing procedure modified the suture structure and promoted failure.In the case of the two sizes of catgut sutures, there were longitudinal striations and splits at the ends of the failed fragments.This indicated that the different strands of catgut tissue were twisted in a helical fashion during manufacture.In the case of the P4HB sutures, the monofilaments, which were straight before testing, exhibited a coiled or spring-like appearance after testing.And with respect to the ePTFE sutures, the failed filaments fragments appeared to have increased extensibility and a more open microporous structure caused by the additional drawing process during tensile testing.For the PP sutures, the filaments failed with a similar morphology to P4HB with the failed filament fragments exhibiting a coiled or spring-like appearance after testing.
In vitro hydrolytic degradation of P4HB and catgut sutures was done in phosphate buffer solution in order to mimic in vivo hydrolytic conditions.From previous literature studies it was seen that the degradation period for P4HB sutures is 6-10 weeks [4,29] and the degradation period of plain catgut sutures is 6-15 d [19,30].The degradation profiles of catgut and P4HB sutures (figures 6(E) and (F)) were observed to be similar to those mentioned previously in the literature.From the plots it was observed that the degradation profiles of barbed sutures were similar to those of non-barbed smooth monofilament sutures concluding that mechanical barbing did not affect the degradation rate or profile of the sutures.The variation observed for catgut sutures is attributed to the plasticizing effect occurring in the filaments as they are usually stored in a hydrating solution to retain their properties [19,28,30].
The barbed sutures provided effective anchoring within the porcine dermis whereas the nonbarbed sutures tended to slip out of the surrounding tissue and exit the tissue at a lower pull-out load.Having measured the anchoring performance for both straight and curved barbed sutures, it was observed that the sutures with curved barbs did exhibit marginally superior anchoring as demonstrated through the in vitro suture-tissue pull out test protocol (figure 4).The anchoring observations were undertaken to understand how the barbs engaged with the surrounding tissue.In the case of the catgut sutures, the monofilaments appeared compatible with the porcine dermis and failed within the dermal tissue layer.For the P4HB sutures, the barbed monofilaments failed close to the tissue surface.Whereas for the commercial PP barbed sutures, they failed at a point before the suture exited the dermal tissue layer.In fact, it was observed that the PP size 2-0 barbed sutures had superior anchoring compared to the P4HB and catgut barbed sutures, since they had a higher bending resistance, and the P4HB barbed sutures failed when the barbs peeled off from the surface of the monofilament.It was difficult to swage needles onto the ePTFE sutures as it required an additional heat stabilizing process to harden the ends for swaging.Due to this reason, no anchoring properties were measured on the ePTFE sutures.
Two different barb geometries were fabricated, and their mechanical and anchoring performances were evaluated in porcine dermis.In a previous research study conducted by Ingle et al, it was determined that the barbs with higher cut angle and cut depth had the greatest anchoring in skin or dermal tissue [17].With regards to this viewpoint, in this study two different barb geometries were fabricated mechanically, and their mechanical and anchoring performances were evaluated.From the anchoring results, it was observed that curved barbed sutures showed significantly better anchoring performance in dermal tissue compared to straight barbed sutures.

Conclusions
In conclusion, this study showed that different barb geometries could be fabricated using the mechanical barbing procedure by fabricating barbs with more than one cut angle.But it was observed that there was difficulty in maintaining a consistent cut depth through the fabrication procedure done on both P4HB and catgut monofilament sutures.As discussed earlier, even though the barbed sutures showed significant loss in their mechanical properties, the fabricated barbed sutures showed higher anchoring as the barbs engage with the surrounding tissues.From the results it was also observed that the curved barbed sutures showed marginal higher anchoring compared to straight barbs in porcine dermal tissue.The resorbable barbed sutures are advantageous over non-resorbable barbed sutures as the barbs would be buried under the dermal layers and hence need not be removed.For the future direction of research, we propose selecting an alternative fabrication technique like a laser ablation technique which is capable of fabricating more precise and accurate barbs with a range of different barb geometries.
findings of this study are available upon reasonable request from the authors.
) After securing the suture, a knife positioning template I (with one dot) was placed on the base.(3) The blade assembly with the knives was used to cut the first series of barbs.(4) The instrument was rotated by 180 • to cut the first series of barbs on the opposite side.(5) The instrument was rotated back by 180 • to its original position.(6) Knife positioning template I was replaced by knife positioning template II (with two dots) on the base.(

Figure 3 .
Figure 3. Illustration representing the important parameters of a single barb-parameters of a straight barb (left) and parameters of a curved barb (right).

Figure 4 .
Figure 4. (A) Schematic diagram of the suture/ tissue pull-out test protocol; (B) P4HB 2-0 bidirectional barbed suture; (C) catgut 2-0 bi-directional barbed suture sewn through the thickness of the porcine dermis; (D) and (E) anchoring samples (prepared as shown in (B) and (C)) are mounted on MTS Q-test tensile tester for anchoring performance evaluation.

Figure 6 .
Figure 6.Tensile properties of the mechanically barbed and non-barbed monofilament sutures: (A) ultimate tensile force (N), (B) elongation at break (%), (C) Initial modulus, and (D) work to rupture (J).All the sutures were compared with size 2/0 Quill polypropylene (PP) barbed sutures; In vitro hydrolytic degradation results for ultimate tensile force (N): (E) variation in ultimate tensile force (N) of P4HB barbed sutures and (F) variation in ultimate tensile force (N) of Catgut barbed sutures.

Figure 7 .
Figure 7. Anchoring performance for both the mechanically barbed and non-barbed monofilament sutures.(A) Maximum pull-out load of sutures in porcine dermis and (B) elongation at maximum pull-out load of sutures in porcine dermis.All samples were compared with the barbed size 2-0 Quill polypropylene suture.

Table 1 .
Results of suture tensile tests and suture-tissue pull out tests (mean ± SD), n = 4 per suture material/ type/ size.