The influence of porosity on the integration histology of two polypropylene meshes for the treatment of abdominal wall defects in dogs

Spider-Silk-like Fiber Mat-Covered Polypropylene Warp-Knitted Hernia Mesh for Inhibition of Fibrosis under Dynamic Environment

Hernia surgery is a widely performed procedure, and the use of a polypropylene mesh is considered the standard approach. However, the mesh often leads to complications, including the development of scar tissue that wraps around the mesh and causes it to shrink. Consequently, there is a need to investigate the relationship between the mesh and scar formation as well as to develop a hernia mesh that can prevent fibrosis. In this study, three different commercial polypropylene hernia meshes were examined to explore the connection between the fabric structure and mechanical properties. In vitro dynamic culture was used to investigate the mechanism by which the mechanical properties of the mesh in a dynamic environment affect cell differentiation. Additionally, electrospinning was employed to create polycaprolactone spider-silk-like fiber mats to achieve mechanical energy dissipation in dynamic conditions. These fiber mats were then combined with the preferred hernia mesh. The results demonstrated that the composite mesh could reduce the activation of fibroblast mechanical signaling pathways and inhibit its differentiation into myofibroblasts in dynamic environments.

A soft elastomer alternative to polypropylene for pelvic organ prolapse repair: a preliminary study

INTRODUCTION AND HYPOTHESIS

We compared the impact of a mesh manufactured from the soft elastomer polydimethylsiloxane (PDMS) to that of a widely used lightweight polypropylene (PP) mesh. To achieve a similar overall device stiffness between meshes, the PDMS mesh was made with more material and therefore was heavier and less porous. We hypothesized that the soft polymer PDMS mesh, despite having more material, would have a similar impact on the vagina as the PP mesh.

METHODS

PDMS and PP meshes were implanted onto the vaginas of 20 rabbits via colpopexy. Ten rabbits served as sham. At 12 weeks, mesh-vagina complexes were explanted and assessed for contractile function, histomorphology, total collagen, and glycosaminoglycan content. Outcome measures were compared using one-way ANOVA and Kruskal-Wallis testing with appropriate post-hoc testing.

RESULTS

Relative to sham, vaginal contractility was reduced following the implantation of PP (p = 0.035) but not the softer PDMS (p = 0.495). PP had an overall greater negative impact on total collagen and glycosaminoglycan content, decreasing by 53% (p < 0.001) and 54% (p < 0.001) compared to reductions of 35% (p = 0.004 and p < 0.001) with PDMS. However, there were no significant differences in the contractility, collagen fiber thickness, total collagen, and glycosaminoglycan content between the two meshes.

CONCLUSIONS

Despite having a substantially higher weight, PDMS had a similar impact on the vagina compared to a low-weight PP mesh, implicating soft polymers as potential alternatives to PP. The notion that heavyweight meshes are associated with a worse host response is not applicable when comparing across materials.

Effect of Hernia Mesh Weights on Postoperative Patient-Related and Clinical Outcomes After Open Ventral Hernia Repair: A Randomized Clinical Trial

Importance

Although multiple versions of polypropylene mesh devices are currently available on the market for hernia repair, few comparisons exist to guide surgeons as to which device may be preferable for certain indications. Mesh density is believed to impact patient outcomes, including rates of chronic pain and perception of mesh in the abdominal wall.

Objective

To examine whether medium-weight polypropylene is associated with less pain at 1 year compared with heavy-weight mesh.

Design, Setting, and Participants

This multicenter randomized clinical trial was performed from March 14, 2017, to April 17, 2019, with 1-year follow-up. Patients undergoing clean, open ventral hernia repairs with a width 20 cm or less were studied. Patients were blinded to the intervention.

Interventions

Patients were randomized to receive medium-weight or heavy-weight polypropylene mesh during open ventral hernia repair.

Main Outcomes and Measures

The primary outcome was pain measured with the National Institutes of Health (NIH) Patient-Reported Outcomes Measurement Information System (PROMIS) Pain Intensity Short Form 3a. Secondary outcomes included quality of life and pain measured at 30 days, quality of life measured at 1 year, 30-day postoperative morbidity, and 1-year hernia recurrence.

Results

A total of 350 patients participated in the study, with 173 randomized to receive heavy-weight polypropylene mesh (84 [48.6%] female; mean [SD] age, 59.2 [11.4] years) and 177 randomized to receive medium-weight polypropylene mesh (91 [51.4%] female; mean [SD] age, 59.3 [11.4] years). No significant differences were found in demographic characteristics (mean [SD] body mass index of 32.0 [5.4] in both groups [calculated as weight in kilograms divided by height in meters squared] and American Society of Anesthesiologists classes of 2-4 in both groups), comorbidities (122 [70.5%] vs 93 [52.5%] with hypertension, 44 [25.4%] vs 43 [24.3%] with diabetes, 17 [9.8%] vs 12 [6.8%] with chronic obstructive pulmonary disease), or operative characteristics (modified hernia grade of 2 in 130 [75.1] vs 140 [79.1] in the heavy-weight vs medium-weight mesh groups). Pain scores for patients in the heavy-weight vs medium-weight mesh groups at 30 days (46.3 vs 46.3, P = .89) and 1 year (30.7 vs 30.7, P = .59) were identical. No significant differences in quality of life (median [interquartile range] hernia-specific quality of life score at 1 year of 90.0 [67.9-96.7] vs 86.7 [65.0-93.3]; median [interquartile range] hernia-specific quality of life score at 30 days, 45.0 [24.6-73.8] vs 43.3 [28.3-65.0]) were found for the heavy-weight mesh vs medium-weight mesh groups. Composite 1-year recurrence rates for patients in the heavy-weight vs medium-weight polypropylene groups were similar (8% vs 7%, P = .79).

Conclusions and Relevance

Medium-weight polypropylene did not demonstrate any patient-perceived or clinical benefit over heavy-weight polypropylene after open retromuscular ventral hernia repair. Long-term follow-up of these comparable groups will elucidate any potential differences in durability that have yet to be identified.

Trial Registration

ClinicalTrials.gov Identifier: NCT03082391.

Effect of pore size and spacing on neovascularization of a biodegradble shape memory polymer perivascular wrap

Neointimal hyperplasia (NH) is a main source of failures in arteriovenous fistulas and vascular grafts. Several studies have demonstrated the promise of perivascular wraps to reduce NH via promotion of adventitial neovascularization and providing mechanical support. Limited clinical success thus far may be due to inappropriate material selection (e.g., nondegradable, too stiff) and geometric design (e.g., pore size and spacing, diameter). The influence of pore size and spacing on implant neovascularization is investigated here for a new biodegradable, thermoresponsive shape memory polymer (SMP) perivascular wrap. Following an initial pilot, 21 mice were each implanted with six scaffolds: four candidate SMP macroporous designs (a-d), a nonporous SMP control (e), and microporous GORETEX (f). Mice were sacrificed after 4 (N = 5), 14 (N = 8), and 28 (N = 8) days. There was a statistically significant increase in neovascularization score between all macroporous groups compared to nonporous SMP (p < .023) and microporous GORETEX (p < .007) controls at Day 28. Wider-spaced, smaller-sized pore designs (223 μm-spaced, 640 μm-diameter Design c) induced the most robust angiogenic response, with greater microvessel number (p < .0114) and area (p < .0055) than nonporous SMPs and GORETEX at Day 28. This design also produced significantly greater microvessel density than nonporous SMPs (p = 0.0028) and a smaller-spaced, larger-sized pore (155 μm-spaced, 1,180 μm-sized Design b) design (p = .0013). Strong neovascularization is expected to reduce NH, motivating further investigation of this SMP wrap with controlled pore spacing and size in more advanced arteriovenous models.

Closing Contaminated Fascial Defects With Synthetic Mesh and a Vacuum-Assisted Closure Device

BACKGROUND

The use of synthetic mesh is considered too high risk, and therefore, not an option when closing a contaminated abdominal fascial defect. This study evaluated the clinical outcomes when using synthetic mesh combined with vacuum-assisted closure (VAC) dressing to close these facial defects.

MATERIALS AND METHODS

From 2010 to 2016, a retrospective review was performed, including 34 patients in a single rural trauma center who underwent a damage control laparotomy in the presence of a contaminated or infected field. Definitive abdominal closure with a bridging polypropylene mesh along with the application of a VAC dressing was done in all cases. Data collection included baseline demographics, operative indication, postoperative complications, mortality and length of follow up.

RESULTS

Median age of the patients was 67 y (IQR 40-87 y), with 22 (65%) being male at the time of operation. The median duration of clinical follow-up was 15.15 mo. The observed complications included three fistulas, two hernias, nine draining sinus tracts, and three mesh explanations with an overall complication rate of 41.1%. Although the absolute observed fistula rate was 8.8% (3 cases), the adjusted mesh-related fistulas formation rate after chart review was 0.0%. No mortalities were attributed directly to mesh-related complication.

CONCLUSIONS

This study found no mesh-related fistulas when using a synthetic mesh along with a VAC dressing for abdominal closure in a contaminated field. These results may provide a platform for further study regarding the safety of this technique.

Deformation of Transvaginal Mesh in Response to Multiaxial Loading

Synthetic mesh for pelvic organ prolapse (POP) repair is associated with high complication rates. While current devices incorporate large pores (>1 mm), recent studies have shown that uniaxial loading of mesh reduces pore size, raising the risk for complications. However, it is difficult to translate uniaxial results to transvaginal meshes, as in vivo loading is multidirectional. Thus, the aim of this study was to (1) experimentally characterize deformation of pore diameters in a transvaginal mesh in response to clinically relevant multidirectional loading and (2) develop a computational model to simulate mesh behavior in response to in vivo loading conditions. Tension (2.5 N) was applied to each of mesh arm to simulate surgical implantation. Two loading conditions were assessed where the angle of the applied tension was altered and image analysis was used to quantify changes in pore dimensions. A computational model was developed and used to simulate pore behavior in response to these same loading conditions and the results were compared to experimental findings. For both conditions, between 26.4% and 56.6% of all pores were found to have diameters <1 mm. Significant reductions in pore diameter were noted in the inferior arms and between the two superior arms. The computational model identified the same regions, though the model generally underestimated pore deformation. This study demonstrates that multiaxial loading applied clinically has the potential to locally reduce porosity in transvaginal mesh, increasing the risk for complications. Computational simulations show potential of predicting this behavior for more complex loading conditions.

Preventing Mesh Pore Collapse by Designing Mesh Pores With Auxetic Geometries: A Comprehensive Evaluation Via Computational Modeling

Pelvic organ prolapse (POP) meshes are exposed to predominately tensile loading conditions in vivo that can lead to pore collapse by 70-90%, decreasing overall porosity and providing a plausible mechanism for the contraction/shrinkage of mesh observed following implantation. To prevent pore collapse, we proposed to design synthetic meshes with a macrostructure that results in auxetic behavior, the pores expand laterally, instead of contracting when loaded. Such behavior can be achieved with a range of auxetic structures/geometries. This study utilized finite element analysis (FEA) to assess the behavior of mesh models with eight auxetic pore geometries subjected to uniaxial loading to evaluate their potential to allow for pore expansion while simultaneously providing resistance to tensile loading. Overall, substituting auxetic geometries for standard pore geometries yielded more pore expansion, but often at the expense of increased model elongation, with two of the eight auxetics not able to maintain pore expansion at higher levels of tension. Meshes with stable pore geometries that remain open with loading will afford the ingrowth of host tissue into the pores and improved integration of the mesh. Given the demonstrated ability of auxetic geometries to allow for pore size maintenance (and pore expansion), auxetically designed meshes have the potential to significantly impact surgical outcomes and decrease the likelihood of major mesh-related complications.

New surgical meshes with patterned nanofiber mats

Abdominal wall hernia repair is one of the most common general surgeries nowadays. Surgical meshes used in hernia repair indeed improved the outcomes, but complications like chronic pain or hernia recurrence partly caused by mechanical mismatch cannot be ignored. This work designed six warp-knitted polypropylene (PP) meshes and found the properties of surgical meshes could be improved to better mimic the performances of human abdominal wall by designing meshes with appropriate textile structures. Poly-caprolactone was electrospun onto newly designed PP meshes and formed a thin layer of patterned nanofiber mat. The pattern of nanofiber mats was affected by the structure of meshes. Diverse nanofiber morphology (straight aligned, straight random or spiral random pattern) and fiber diameters (50–70 nm ultra-thin nanofibers or from 330 nm to 700 nm nanofibers) were observed in different regions of a single patterned nanofiber scaffold. The addition of electrospinning nanofibers enhanced cell adherence and proliferation as compared with naked PP meshes. Cell actin filaments spread along the nanofibers and formed a morphology exactly similar with the patterned mats on day 7. Furthermore, cells on thin and aligned patterned nanofibers showed much more elongation and better orientation than that of the spiral random fibers, suggesting that cell morphology can be altered by changing the patterns of scaffolds. This study helps us in further understanding the properties of hernia repair meshes with their textile structures and the biological interactions of cells with different substrates in order to develop new biomedical scaffolds with desired properties.

Newly designed warp-knitted meshes with different textile parameters and the interactions between cell and patterned nanofiber mats and different meshes.

Surgery for Apical Vaginal Prolapse after Hysterectomy: Transvaginal Mesh-Based Repair

Several transvaginal mesh products have been marketed to address vaginal vault prolapse. Although data are limited, prolapse recurrence rates and subjective outcome measures seem to be equivalent for vaginal mesh compared with native tissue apical prolapse repair, and the different vaginal meshes have not proven superior to one another. Given the known unique complications specific to vaginal mesh with equivalent outcomes for the apical vaginal prolapse, it is reasonable to reserve mesh use for specific high-risk cases, such as patients with large apical prolapse recurrence after native tissue repair who are not candidates for sacrocolpopexy.

Using poly(l-lactic acid) and poly(ɛ-caprolactone) blends to fabricate self-expanding, watertight and biodegradable surgical patches for potential fetoscopic myelomeningocele repair

Our study focuses on the development and characterization of a self-expanding, watertight and biodegradable patch for fetoscopic myelomeningocele (MMC) prenatal repair. We fabricated poly(l-lactic acid) (PLA) and poly(ɛ-caprolactone) (PCL) blend films by solution casting. Formulation c with average glass transition temperature of 37.6 ± 1.2°C was chosen for temporospatial recovery. Favorable results from surface studies reflected homogeneous dispersion of polymers in the blend. The cytotoxicity was studied in human foreskin fibroblasts. The blend film was cytocompatible, evidenced by matching percentage of live cells in exposed and control solutions. Subsequently, liquid water permeability experiments confirmed watertight nature of films. Finally, in vitro degradation was investigated in phosphate buffered saline (PBS) and amniotic fluid (AF) separately for 16 weeks. Similar weight loss (n = 6, p = 0.912) and significantly different (n = 3, p = 0.025) surface roughness was observed in PBS and AF, respectively, at 16 weeks. Functional group analysis displayed increasing carbonyl and hydroxyl bonds in PBS and AF, respectively, over time, indicating progression of hydrolytic degradation. Favorable characterization results provide strong evidence to employ PLA-PCL blend films as surgical patches in fetoscopic MMC repair. Designed patch serves as standalone system to successfully tackle impending hurdles of MMC repair and proves to be a superior alternative compared to existing patches. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 107B: 295-305, 2019.

Comparison of partially-absorbable lightweight mesh with heavyweight mesh for inguinal hernia repair: multicenter randomized study

Purpose

Prosthetic mesh is widely used for inguinal hernia repair; however, pain and stiffness can develop. This study was a prospective, multicenter, single-blind, randomized trial to assess postoperative pain and quality of life according to mesh type after inguinal hernia repair.

Methods

Forty-seven patients who underwent Lichtenstein repair for unilateral inguinal hernia with prosthetic mesh were enrolled and randomly allocated to the partially-absorbable lightweight mesh (LW group, n = 24) or heavyweight mesh group (HW group, n = 23). Data were collected using a visual analogue scale (VAS), Carolinas Comfort Scale (CCS), and Activities Assessment Scale (AAS) at screening and postoperative day 1, 7, 90, and 120; foreign body sensation, sense of stiffness, and sense of pull during activity were also evaluated.

Results

There were no significant differences in patients' demographics and clinical characteristics between groups. The VAS at day 90 was significantly lower in the LW group (0.46 ± 0.78 vs. 0.96 ± 0.82, P = 0.027). The CCS and AAS were significantly lower in the LW group at day 1 (51.33 ± 20.29 vs. 64.65 ± 22.64, P = 0.047 and 39.83 ± 9.88 vs. 46.43 ± 7.82, P = 0.015, respectively). Foreign body sensation was significantly lower in the LW group at day 120 (4.2% vs. 30.4 %, P = 0.023), as was sense of stiffness (P = 0.023). The sense of pull during activity was lower in the LW group at day 90 and 120 (P = 0.012 and P = 0.022, respectively). There was no recurrence or serious complication during follow-up.

Conclusion

Partially-absorbable lightweight prosthetic mesh can be used for inguinal hernia repair safely and improve functional outcomes and quality of life after surgery.

Use of a Rat Model to Study Ventral Abdominal Hernia Repair

Ventral abdominal hernia is a relatively common clinical condition that sometimes requires herniorraphy (surgical repair). The repair of ventral abdominal hernia typically requires implantation of a material to serve as a mechanical bridge across the defect in the abdominal wall. Biomaterials, such as porcine small intestinal submucosa (SIS), also serve as a lattice for cell growth into the implant and can naturally incorporate into the host tissue. Development of such repair materials benefits from use of animal models in which experimental abdominal wall defects are easily created and are amenable to repair in a reproducible fashion. The method offered here describes surgical creation and repair of ventral abdominal hernia in a rat model. When SIS is used to repair an experimental ventral abdominal hernia in this model, it is rapidly incorporated into host tissue within 28 days of implantation. Histologically, incorporation of their implanted material into host tissue is characterized by a robust fibrovascular response. Future refinements and applications of the rat abdominal hernia model may likely involve diabetic and/or obese animals as a means to more closely mimic common co-morbidities of man.

Biomimetic implants for pelvic floor repair

BACKGROUND

Polypropylene implants are used for the reconstructive surgery of urogynaecological disorders like pelvic organ prolapse, but severe complications associated with their use have been reported. There is evidence that surface properties and a difference in mechanical stiffness between the implant and the host tissue contribute to these adverse events. Electrospinning is an innovative engineering alternative that provides a biomimetic microstructure for implants, resulting in a different mechano-biological performance.

AIM

The main objective of this review is to inform about the potential of electrospun matrices as an alternative modality for pelvic floor repair.

METHODS

Publications with the following studies of electrospun matrices were reviewed: (i) the technique; (ii) in vitro use for soft tissue engineering; (iii) in vivo use for reconstruction of soft tissues in animals; and (iv) clinical use in humans.

RESULTS

Electrospun matrices provide a synthetic mimic of natural extracellular matrix (ECM), favoring cellular attachment, proliferation and matrix deposition, through which a proper, low-inflammatory tissue-implant interaction can be established. Electrospun sheets can also be created with sufficient mechanical strength and stiffness for usage in prolapse surgery.

CONCLUSION

Electrospun matrices mimic the structural topography of the extracellular matrix and can be functionalized for better biological performance. As such, they have great potential for the next generation of urogynecological implants. However, their long-term safety and efficacy must still be established in vivo.

Biomaterial-Based Approaches to Address Vein Graft and Hemodialysis Access Failures

Veins used as grafts in heart bypass or as access points in hemodialysis exhibit high failure rates, thereby causing significant morbidity and mortality for patients. Interventional or revisional surgeries required to correct these failures have been met with limited success and exorbitant costs, particularly for the US Centers for Medicare & Medicaid Services. Vein stenosis or occlusion leading to failure is primarily the result of neointimal hyperplasia. Systemic therapies have achieved little long-term success, indicating the need for more localized, sustained, biomaterial-based solutions. Numerous studies have demonstrated the ability of external stents to reduce neointimal hyperplasia. However, successful results from animal models have failed to translate to the clinic thus far, and no external stent is currently approved for use in the US to prevent vein graft or hemodialysis access failures. This review discusses current progress in the field, design considerations, and future perspectives for biomaterial-based external stents. More comparative studies iteratively modulating biomaterial and biomaterial-drug approaches are critical in addressing mechanistic knowledge gaps associated with external stent application to the arteriovenous environment. Addressing these gaps will ultimately lead to more viable solutions that prevent vein graft and hemodialysis access failures.

Textile properties of synthetic prolapse mesh in response to uniaxial loading

BACKGROUND

Although synthetic mesh is associated with superior anatomic outcomes for the repair of pelvic organ prolapse, the benefits of mesh have been questioned because of the relatively high complication rates. To date, the mechanisms that result in such complications are poorly understood, yet the textile characteristics of mesh products are believed to play an important role. Interestingly, the pore diameter of synthetic mesh has been shown to impact the host response after hernia repair greatly, and such findings have served as design criteria for prolapse meshes, with larger pores viewed as more favorable. Although pore size and porosity are well-characterized before implantation, the changes in these textile properties after implantation are unclear; the application of mechanical forces has the potential to greatly alter pore geometries in vivo. Understanding the impact of mechanical loading on the textile properties of mesh is essential for the development of more effective devices for prolapse repair.

OBJECTIVE

The objective of this study was to determine the effect of tensile loading and pore orientation on mesh porosity and pore dimensions.

STUDY DESIGN

In this study, the porosity and pore diameter of 4 currently available prolapse meshes were examined in response to uniaxial tensile loads of 0.1, 5, and 10 N while mimicking clinical loading conditions. The textile properties were compared with those observed for the unloaded mesh. Meshes included Gynemesh PS (Ethicon, Somerville, NJ), UltraPro (Artisyn; Ethicon), Restorelle (Coloplast, Minneapolis, MN), and Alyte Y-mesh (Bard, Covington, GA). In addition to the various pore geometries, 3 orientations of Restorelle (0-, 5-, 45-degree offset) and 2 orientations of UltraPro (0-, 90-degree offset) were examined.

RESULTS

In response to uniaxial loading, both porosity and pore diameter dramatically decreased for most mesh products. The application of 5 N led to reductions in porosity for nearly all groups, with values decreasing by as much as 87% (P < .05). On loading to 10 N of force, nearly all mesh products that were tested were found to have porosities that approached 0% and 0 pores with diameters >1 mm.

CONCLUSION

In this study, it was shown that the pore size of current prolapse meshes dramatically decreases in response to mechanical loading. These findings suggest that prolapse meshes, which are more likely to experience tensile forces in vivo relative to hernia repair meshes, have pores that are unfavorable for tissue integration after surgical tensioning and/or loading in urogynecologic surgeries. Such decreases in pore geometry support the hypothesis that regional increases in the concentration of mesh leads to an enhanced local foreign body response. Although pore deformation in transvaginal meshes requires further characterization, the findings presented here provide a mechanical understanding that can be used to recognize potential areas of concern for complex mesh geometries. Understanding mesh mechanics in response to surgical and in vivo loading conditions may provide improved design criteria for mesh and a refinement of surgical techniques, ultimately leading to better patient outcomes.

Mesh implants: An overview of crucial mesh parameters

Hernia repair is one of the most frequently performed surgical interventions that use mesh implants. This article evaluates crucial mesh parameters to facilitate selection of the most appropriate mesh implant, considering raw materials, mesh composition, structure parameters and mechanical parameters. A literature review was performed using the PubMed database. The most important mesh parameters in the selection of a mesh implant are the raw material, structural parameters and mechanical parameters, which should match the physiological conditions. The structural parameters, especially the porosity, are the most important predictors of the biocompatibility performance of synthetic meshes. Meshes with large pores exhibit less inflammatory infiltrate, connective tissue and scar bridging, which allows increased soft tissue ingrowth. The raw material and combination of raw materials of the used mesh, including potential coatings and textile design, strongly impact the inflammatory reaction to the mesh. Synthetic meshes made from innovative polymers combined with surface coating have been demonstrated to exhibit advantageous behavior in specialized fields. Monofilament, large-pore synthetic meshes exhibit advantages. The value of mesh classification based on mesh weight seems to be overestimated. Mechanical properties of meshes, such as anisotropy/isotropy, elasticity and tensile strength, are crucial parameters for predicting mesh performance after implantation.

The long-term behavior of lightweight and heavyweight meshes used to repair abdominal wall defects is determined by the host tissue repair process provoked by the mesh

BACKGROUND

Although heavyweight (HW) or lightweight (LW) polypropylene (PP) meshes are widely used for hernia repair, other alternatives have recently appeared. They have the same large-pore structure yet are composed of polytetrafluoroethylene (PTFE). This study compares the long-term (3 and 6 months) behavior of meshes of different pore size (HW compared with LW) and composition (PP compared with PTFE).

METHODS

Partial defects were created in the lateral wall of the abdomen in New Zealand White rabbits and then repaired by the use of a HW or LW PP mesh or a new monofilament, large-pore PTFE mesh (Infinit). At 90 and 180 days after implantation, tissue incorporation, gene and protein expression of neocollagens (reverse transcription-polymerase chain reaction/immunofluorescence), macrophage response (immunohistochemistry), and biomechanical strength were determined. Shrinkage was measured at 90 days.

RESULTS

All three meshes induced good host tissue ingrowth, yet the macrophage response was significantly greater in the PTFE implants (P < .05). Collagen 1/3 mRNA levels failed to vary at 90 days yet in the longer term, the LW meshes showed the reduced genetic expression of both collagens (P < .05) accompanied by increased neocollagen deposition, indicating more efficient mRNA translation. After 90-180 days of implant, tensile strengths and elastic modulus values were similar for all 3 implants (P > .05).

CONCLUSION

Host collagen deposition is mesh pore size dependent whereas the macrophage response induced is composition dependent with a greater response shown by PTFE. In the long term, macroporous meshes show comparable biomechanical behavior regardless of their pore size or composition.

Polypropylene mesh and the host response

The use of polypropylene (PP) mesh for pelvic floor repair has been increasing dramatically over the past decade; however, tissue response in humans has not been extensively studied. This review discusses PP mesh and postimplantation host tissue response. Emphasis is placed on studies investigating the relationship between individual mesh properties and specific responses. There is an immediate inflammatory response after PP mesh implantation that lays the framework for tissue ingrowth and subsequent mesh integration. This response varies based on physical properties of individual mesh, such as pore size, weight, coatings, bacterial colonization, and biofilm production.

Mechanical properties and tissue reinforcement of polypropylene grafts used for pelvic floor repair--an experimental study

PURPOSE

Although grafts can be made from the same materials, the final weave of the product may play a role in the ultimate outcomes or complications. The aim of this experimental study is to evaluate and compare the mechanical properties of the meshes and their influence on biological characteristics as well.

METHODS

Full-thickness abdominal wall defect with respect to the peritoneum was primary repaired in 144 male Wister rats using the overlay technique. Monofilament, multifilament and coated polypropylene grafts were used for the repairs. Graft shrinkage, thickness and tensile strength of the explants were analysed after 3 and 6 weeks.

RESULTS

Monofilament grafts showed the highest shrinkage level of 11.97-18% during the investigated period. The thickness of monofilament explants increased gradually, with a maximum of 25.35% after 6 weeks. Multifilament and collagen explants did swell more rapidly in the third week, decreasing thereafter to 19.63-23.04% above the pre-implantation values after 6 weeks. The tensile strength showed a gradual increase over the course of the experiment in all groups.

CONCLUSION

After graft stabilisation, all samples had similar strength, regardless of the significant differences in the pre-implantation values of graft strength.

Prolene mesh mentoplasty

Augmentation mentoplasty is a cosmetic surgical procedure to correct chin retrusion or microgenia which usually requires placement of an alloplastic material over the pogonion, and which results in increased chin projection and a more aesthetically balanced facial profile. Polypropylene mesh is easy to purchase, widely available in a general hospital and most commonly used by general surgeons. In this series of 192 patients, we wanted to demonstrate our simple mentoplasty technique using prolene mesh that can easily be combined with a rhinoplasty procedure, with possible causes of infection and the rationale for using prolene mesh in such procedures.

Effect of biomaterial design criteria on the performance of surgical meshes for abdominal hernia repair: a pre-clinical evaluation in a chronic rat model

Despite the recognized advantage of surgical meshes in abdominal hernia repair, reports of long term complications after implantation are increasing. 25 chronic hernia rats underwent incisional repair (n = 5/mesh group) with compressed poly(tetra-fluoro-ethylene) (cPTFE), expanded poly(tetra-fluoro-ethylene) (ePTFE), polypropylene (PP), poly(ethylene-terephtalate) + collagen (PET + C), and porcine intestinal submucosa (SIS). At 30 days, the extent and strength of intra-abdominal adhesions was evaluated, along with tissue-mesh integration, material shrinkage, and inflammatory response. The extent and tenacity of adhesions were reduced in PET + C and SIS, while tissue contraction was largely reduced in the presence of cPTFE. The tissue integration was not affected by composition or material construction. The host tissue response was elevated and arrested in a chronic imflammatory phase in the presence of PET + C and SIS, and resolved in the case of cPTFE. The different composition and material construction did not affect significantly the overall performance of the evaluated surgical meshes, apart from PP.

Retraction and fibroplasia in a polypropylene prosthesis: experimental study in rats

BACKGROUND

The treatment of hernia, independent of anatomical site and technique utilized, generally involves using prostheses, which may cause complications, despite their unarguable advantage in allowing safe reinforcement. An example of this is possible retraction, which causes discomfort and hernia recurrence. Polypropylene is still the most often used biomaterial of the great number available. The purpose of this study is to evaluate the amount of retraction of the polypropylene mesh, as well as the histological reactions that accompany this phenomenon.

METHODS

Polypropylene meshes (Marlex) were inserted in an anterior position to the whole abdominal aponeurosis of 25 Wistar rats (Rattus norvegicus albinus). The animals were divided into groups and another intervention was performed 7, 28, and 90 days later to measure the dimensions of the prostheses and to calculate the final area. Histological analysis was performed with hematoxylin-eosin to evaluate neutrophils, macrophages, giant cells, and lymphocytes surrounding the mesh threads in ten random fields of each slide.

RESULTS

Seven days after the mesh was inserted, the mean rate of retraction was 1.75% (P = 0.64); at 28 days, it was 3.75% (P = 0.02); and at 90 days, it was 2.5% (P = 0.01). As to the histological analysis, there was a total decline of neutrophils and a progressive increase of macrophages, giant cells, and lymphocytes proportional to the post-implant time of the mesh (P < 0.05).

CONCLUSION

There was a statistically significant retraction of 3.75% at 28 days and 2.5% at 90 days after the prosthesis was inserted. There is a well-established sequence of cellular events which aim at synthesizing new connective tissue to reinforce the mesh.

Different tissue reaction of oesophagus and diaphragm after mesh hiatoplasty. Results of an animal study

BACKGROUND

Laparoscopic mesh-reinforcement of the hiatal region in the treatment of gastroesophageal reflux disease (GERD) and paraesophageal hernia (PEH) reduces the risk of recurrence. However, there are still controversies about the technique of mesh placement, shape, structure and material. We therefore compared tissue integration and scar formation after implantation of two different polypropylene-meshes in a rabbit model.

METHODS

A total of 20 female chinchilla rabbits were included in this study. Two different meshes (Polypropylene PP, Polyglecaprone 25 Composite PP-PG) were implanted on the abdominal diaphragm around the oesophagus. After 3 months the implanted meshes were excised en-bloc. Histological and morphological analyses were carried out accordingly proliferation rate, apoptosis and collagen type I/III ratio.

RESULTS

Regarding proliferation rate of oesophagus PP (9.31 +/- 3.4%) and PP-PG (13.26 +/- 2.54%) differ in a significant (p = 0.0097) way. In the diaphragm we found a significant (p = 0.00066) difference between PP (9.43 +/- 1.45%) and PP-PG (18.73 +/- 5.92%) respectively. Comparing oesophagus and diaphragm we could prove a significant difference within PP-PG-group (p = 0.0195). Within PP-group the difference reached no statistical significance (p = 0.88). We found analogous results regarding apoptosis.Furthermore, there is a significant (p = 0.00013) difference of collagen type I/III ratio in PP-PG (12.28 +/- 0.8) compared to PP (8.44 +/- 1,63) in case of oesophageal tissue. Concerning diaphragm we found a significant difference (p = 0.000099) between PP-PG (8.85 +/- 0.81) and PP (6.32 +/- 1.07) as well.

CONCLUSION

The histologic and morphologic characteristics after prosthetic enforcement of the hiatus in this animal model show a more distinct tissue integration using PP-PG compared to PP. Additionally, different wound healing and remodelling capability influence tissue integration of the mesh in diaphragm and oesophagus.

Mesh repair of common abdominal hernias: a review on experimental and clinical studies

Results on hernia surgery from numerous centers confirm that tensionless repair with various meshes reduces the complication rates and the frequency of recurrences. Some evidence on incisional hernias suggests, however, that the use of mesh seems to transfer the onset of recurrences by several years. Persistent pain and other discomfort is also an unpleasant complication of otherwise successful surgery in a number of patients. Thus, improved, slowly degrading, mesh materials, with strong connective tissue-inducing action, might be more optimal for hernia surgery. Accumulating evidence also suggests that recurrent hernias appear in patients having inherited weakness of connective tissues. Numerous tissue specific collagens, in addition to the classical fibrillar I-III collagens and numerous substrate specific matrix proteinases, have recently been described in biochemical literature, and their roles as possible causes of tissue weakness are discussed.