Keywords: Nanofibers; Hernia repair; Surgical mesh; Electrospinning; Tissue engineering
Biologic meshes are the most recent addition to the list of materials available for use in hernia repair. They are typically made of decellularized dermal matrix tissue derived from either human cadaveric or porcine sources [6]. These materials facilitate regenerative tissue formation and native collagen deposition prior to resorption and are often used in contaminated wound sites. Their mechanical properties, however, are not ideal for surgical mesh applications and it can be hard to predict how quickly the mesh will resorb in vivo leading to revision surgeries. Decellularized matrix materials also tend to undergo plastic deformation over time as a result of stress caused by intraabdominal pressure, which can lead to bulging of the abdominal wall and recurrent hernia. Biologic materials alone are therefore insufficient for bridging fascial defects [7].
Biologic meshes are the most recent addition to the list of materials available for use in hernia repair. They are typically made of decellularized dermal matrix tissue derived from either human cadaveric or porcine sources [6]. These materials facilitate regenerative tissue formation and native collagen deposition prior to resorption and are often used in contaminated wound sites. Their mechanical properties, however, are not ideal for surgical mesh applications and it can be hard to predict how quickly the mesh will resorb in vivo leading to revision surgeries. Decellularized matrix materials also tend to undergo plastic deformation over time as a result of stress caused by intraabdominal pressure, which can lead to bulging of the abdominal wall and recurrent hernia. Biologic materials alone are therefore insufficient for bridging fascial defects [7].
A typical electrospinning setup consists of a high voltage power source connected to the tip of a syringe with a metal needle. The syringe is filled with a viscous polymer solution and placed in a pump set to dispense the solution at a constant rate. As the solution flows from the tip of the syringe, it is charged by the high voltage power source, which exerts electrostatic forces on the solution at the tip of the needle, and causes it to form a Taylor cone. A jet of solution ejects from the Taylor cone and destabilizes in mid-air. As the solvent evaporates, solid nanofibers form and are deposited on to a grounded collector. The initial costs of equipment can be high, however the overall electrospinning process is quick and inexpensive.
Electrospun nanofiber scaffolds have the potential to provide a cheap hernia mesh with customized mechanical properties, degradation rates, drug release capabilities, and an excellent capacity to support native tissue regeneration, but there is a dearth of knowledge available on electrospun hernia meshes [13]. The goal of this study was to characterize the mechanical properties of a series of novel electrospun meshes made from the bioresorbable polymers: Polycaprolactone (PCL), Polydioxanone (PDO), Polylactide-Co-Glycolide (PLGA1090), Polylactide-Co- Glycolide (PLGA8218), and Poly-L-Lactide (PLLA), and the non-resorbable polymers Polyurethane (PU) and Polyethylene Terephthalate (PET) in order to select a suitable candidate for use in surgical mesh applications.
Mechanical tests were performed using a Universal Testing Machine (MTS Systems Corporation) fitted with a 50 lb. load cell and set to a displacement rate of 50 mm/min. Data was analyzed using Microsoft Excel and reported as mean ± standard deviation. The tests performed included Ball Burst Strength (BBS), Radial Stiffness (RS), Trouser Tear Strength (TTS), Suture Retention Strength (SRS), and Ultimate Tensile Strength (UTS). Mesh thickness was measured and reported, as well as Mesh Density. All tests were performed according to ASTM standards except suture retention strength, which followed ISO standards. Tests were performed using five samples of each mesh material.
Polymer |
Distance (cm) |
Flow Rate (ml/hr) |
Voltage (kV) |
Needle Gauge |
Needle Inner Ø (mm) |
PCL |
20 |
5 |
+12/-4 |
21 |
0.61 |
PDO |
20 |
5 |
+12/-5 |
21 |
0.61 |
PLGA1090 |
20 |
5 |
+14/-2 |
21 |
0.61 |
PLGA8218 |
20 |
5 |
+14/-3 |
21 |
0.61 |
PLLA |
20 |
5 |
+14/-3 |
21 |
0.61 |
PU |
20 |
5 |
+12/-3 |
21 |
0.61 |
PET |
20 |
5 |
+12/-3 |
21 |
0.61 |
Polymer |
Mesh Density (GSM) |
Fiber Diameter (µm) n=500 |
Tensile Strength (MPa) n=5 |
Tensile Strength (N/cm) n=5 |
% Elongation n=5 |
Elastic Modulus (MPa) n=5 |
Suture Retention Strength (N) n=5 |
Radial Stiffness (N) n=5 |
Ball Burst Strength (N/cm) n=5 |
Trouser Tear Strength (N) n=5 |
PCL |
157 ± 13 |
0.64 ± 0.32 |
2.00 ± 0.51 |
20.06 ± 5.13 |
327 ± 32 |
2.07 ± 0.57 |
19.8 ± 5.7 |
0.53 ± 0.08 |
50.60 ± 6.13 |
31.9 ± 9.3 |
PDO |
210 ± 18 |
0.86 ± 0.42 |
3.76 ± 0.49 |
37.74 ± 4.87 |
575 ± 128 |
6.7 ± 1.5 |
10.1 ± 2.5 |
0.57 ± 0.13 |
60.03 ± 8.21 |
12.3 ± 1.0 |
PLGA1090 |
263 ± 29 |
3.28 ± 0.57 |
6.47 ± 0.41 |
64.87 ± 1.82 |
399 ± 34 |
83.5 ± 8.6 |
13.2 ± 2.1 |
5.0 ± 1.2 |
79.98 ± 15.07 |
12.8 ± 0.6 |
PLGA8218 |
285 ± 18 |
1.28 ± 0.38 |
6.60 ± 1.40 |
65.7 ± 13.8 |
136 ± 12 |
103.3 ± 4.6 |
28.1 ± 2.7 |
4.0 ± 1.7 |
64.50 ± 17.98 |
23.9 ± 4.8 |
PLLA |
222 ± 20 |
1.48 ± 0.67 |
3.59 ± 0.25 |
35.85 ± 2.45 |
257 ± 74 |
49.5 ± 4.1 |
17.3 ± 4.3 |
2.53 ± 0.53 |
92.32 ± 25.38 |
25.9 ± 8.6 |
PU |
256 ± 44 |
0.89 ± 0.33 |
18.9 ± 5.9 |
189.6 ± 59.1 |
1107 ± 100 |
1.4 ± 0.5 |
17.5 ± 2.7 |
0.65 ± 0.45 |
91.32 ± 11.86 |
16.6 ± 9.0 |
PET |
194 ± 16 |
2.47 ± 0.69 |
4.02 ± 0.60 |
40.25 ± 5.94 |
434 ± 88 |
14.1 ± 2.7 |
12.6 ± 4.5 |
0.88 ± 0.16 |
29.23 ± 7.84 |
6.0 ± 0.6 |
Threshold |
n/a |
n/a |
n/a |
16 |
n/a |
n/a |
20 |
n/a |
50 |
20 |
MotifMESH |
n/a |
n/a |
70.23 |
105.3 |
n/a |
n/a |
27.7 |
2.8 |
43.56 |
15.1 |
* Material met or exceeded threshold value a Material met or exceeded MotifMESHTM
*Material met or exceeded threshold value a Material met or exceeded MotifMESHTM
In order to be considered sufficient for use in hernia repair applications, a mesh must have a minimum BBS of 50 N/cm, SRS
* Material met or exceeded threshold value a Material met or exceeded MotifMESHTM
* Material met or exceeded threshold value a Material met or exceeded MotifMESHTM
PCL, PLGA8218, and PLLA met or surpassed all of the mechanical test threshold values. PCL had the highest TTS, and was the only material of the three to surpass both the threshold value and the MotifMESHTM value. The BBS and UTS of PCL, however, were lower than those of PLLA and PLGA8218. PLGA8218 had the highest UTS of the three materials, and was the only material tested with a SRS comparable to that of MotifMESHTM. The BBS of PLGA8218, however, was significantly lower than that of PLLA, and the TTS of PLG8218 was the lowest of the three. PLLA mesh had the highest BBS, as well as the second highest TTS and UTS of the three. The only test in which PLLA was outperformed by both PCL and PLGA8218 was SRS; however the SRS of PLLA was not significantly different than the 20 N SRS threshold value. Furthermore, the SRS testing protocol tests the force necessary to pull out a single suture. Assuming multiple sutures will be used to fix the mesh in place in vivo, the actual SRS of the implanted mesh would be many times that of the test value. PLLA also performed well compared to MotifMESHTM. Although MotifMESHTM outperformed PLLA in UTS and SRS testing, PLLA surpassed MotifMESHTM in BBS as well as TTS. The RS of PLLA was also comparable to that of MotifMESHTM. Mesh stiffness is an important factor to consider because a mesh that is too stiff may restrict the patient’s range of motion in the abdominal region, causing discomfort, while a mesh that is too flexible may be difficult for surgeons to handle during the hernia repair procedure [1]. Although no universal radial stiffness standards or testing procedures have been established by the medical community at this time, the fact that the stiffness of PLLA is nearly equal to that of MotifMESHTM, a commercial surgical mesh approved by the FDA, is encouraging. Therefore, we believe the electrospun PLLA mesh is the most suitable material for use in hernia repair applications.
PLLA also offers several advantages from an in vivo degradation standpoint. PCL, PDO, PLGA1090, PLGA8218, and PLLA are all bioresorbable polymers, and therefore break down by natural processes in vivo. One advantage of resorbable meshes is a reduction of the long term foreign body response that often persists in patients with permanent mesh implants [16]. Due to chemical and structural differences, all of these polymers degrade at different rates. PDO and PLGA1090, for example, are completely resorbed in a matter of weeks post implantation. This short degradation profile does not give the hernia site adequate time to heal before the supporting mesh is gone, which may result in a high rate of recurrence in the years following a procedure [17]. PLLA, however, degrades over the course of 9-12 months. In some circumstances, this may provide enough time for native fascia to grow and remodel at the hernia site before the mechanical load is transferred from the mesh to the healed tissue. For example, a recent pilot study on the use of a resorbable mesh plug for inguinal hernia repair came to the conclusion that the plug was suitable for use in young and healthy patients with minor hernias [18].
While fully resorbable meshes may be useful in some circumstances, they will likely never be suitable for general use in hernia repairs. There is a growing body of evidence which suggests a genetic predisposition to hernia formation and recurrence in some patients [19,20]. A large portion of patients with recurrent hernias have a genomic profile displaying decreased expression of type I collagen and increased expression of type III collagen. This compromises the mechanical integrity of the patient’s connective tissue, and increases the likelihood of hernia formation and recurrence. In cases such as these, even if a resorbable mesh led to the complete regrowth and remodeling of healthy fascia, patients would still be prone to recurrences after the mesh was resorbed.
A composite mesh made up of an electrospun PLLA layer backed by a permanent mesh could be a solution to this issue. The electrospun PLLA mesh would adhere to the abdominal wall and promote tissue growth across the defect during the initial stages of wound healing. As the PLLA layer gradually degrades in the months following implantation, it would transfer the mechanical load onto the newly formed fascia and the permanent mesh layer. The permanent mesh would remain and play a permanent, supplemental role in order to prevent recurrences. Furthermore, this permanent mesh layer could have large pores and a low mesh density to reduce chronic foreign body reaction. This mesh could be produced by electrospinning a nanofiber layer directly on to a polypropylene sheet coated with a thin layer of resorbable adhesive to prevent delamination.
One study suggests that composite materials result in an acute inflammatory response as the resorbable polymer degrades, usually into acidic byproducts, and offer no benefits over simple permanent meshes [16]. The composites tested in this study were composed of a permanent mesh fixed to a resorbable film, and films may not offer any significant benefits to counteract the negative impact of local inflammation in response to their degradation. Furthermore, these films are often used as adhesion barrier layers and have no direct interaction with the hernia site [5]. Conversely, it has been demonstrated that resorbable nanofiber layers in direct contact with the hernia site promote collagen deposition and remodeling, and yield better mechanical properties at the wound interface compared to polypropylene mesh alone [21]. This suggests that if the adhesion barrier layer was made from nanofibers instead of a film, there would be a significantly lower inflammatory response.
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