Early imaging of integration response to polypropylene mesh in abdominal wall by environmental scanning electron microscopy: comparison of two placement techniques and correlation with tensiometric studies

Different techniques for mesh application give the same abdominal muscle strength

PURPOSE

This study investigates abdominal muscle strength after surgery for giant hernia with the onlay, sublay or intraperitoneal (IPOM) method. Theoretically, placement of the mesh may result in different possibilities regarding function and postoperative physical activity related to abdominal muscle function.

METHOD

Twenty-four patients operated for large ventral hernias using the onlay, sublay or IPOM technique were evaluated 1 year following surgery for abdominal wall strength using Biodex system 4.

RESULTS

Despite the different surgical techniques used, no differences were observed in abdominal wall strength between the groups.

CONCLUSION

The postoperative strength of abdominal wall muscles is independent of the method used for reconstruction of large abdominal wall hernia, and the choice of surgical technique should be directed by anatomical circumstances.

Tensile strength and host response towards different polypropylene implant materials used for augmentation of fascial repair in a rat model

We compared inflammatory response, fibrosis and biomechanical properties of different polypropylene materials from one manufacturer (Tyco Healthcare) in a rat model for primary fascial repair. Full-thickness abdominal wall defects were primarily repaired using 'overlay' technique. Multifilament implants were Surgipro SPM and SPMW, the latter a wider-weave type of the former. Monofilament SPMM implants and polypropylene suture repair (Surgipro II) served as controls. Explants were evaluated macroscopically and changes in thickness, shrinkage and tensile strength were measured. Inflammatory and connective tissue response was assessed on haematoxylin-eosin and Movat stains. Immunohistochemistry was done to localise rat macrophages/monocytes. Multifilament materials induced a shorter acute inflammatory response and more pronounced chronic inflammatory reaction compared to monofilament implants. Macrophages could be found deep in interstices 7.5 by 12.5 microm. No difference in collagen deposition and neovascularisation was observed. At 90 days time point, explants reconstructed with tighter woven multifilament SPM were weaker than sutured or SPMM controls. Overall shrinkage of 10% was comparable for all groups.

Reformulación conceptual de la técnica de reparación doble: una solución sencilla para defectos muy complejos de la pared abdominal

INTRODUCTION

Repair of complex abdominal wall defects remains a challenge for the general surgeon. The aim of the present study was to validate the double mesh repair technique in complex hernias.

MATERIAL AND METHOD

We performed a prospective study of 15 patients with complex abdominal wall defects who underwent surgery in a university hospital. All patients were evaluated in a multidisciplinary unit. Indications consisted of incisional hernias with multiple recurrences (> 3 times), prior mesh complicated by fistula and chronic infection, giant diffuse lumbar hernia, and ventral hernia (associated with parastomal hernia or occurring after bariatric surgery with associated dermolipectomy). The surgical technique used was double intra-abdominal and supra-aponeurotic mesh repair without associated plasty techniques. Clinical, surgical and follow-up data were analyzed.

RESULTS

Nine defects were lateral, three were lumbar, one was parapubic, and two were located in the mid-line (one associated with giant parastomal hernia and one occurring after bariatric surgery). Eight showed significant tissue loss, five showed trophic skin lesions, and two showed chronic suppurative infection. The mean size of the defects was 17.5 cm. Seroma occurred in three patients and limited cutaneous necrosis occurred in one patient. The mean length of hospital stay was 4.3 days (range 2-7 days). No complications, recurrences or mortality were detected during follow-up.

CONCLUSION

Complex abdominal wall defects can be corrected through double repair using mesh only. This technique is simple to learn and perform and can be applied in many anatomical sites and types of defect, as well as in the presence of tissue destruction.

Improved surgical mesh integration into the rat abdominal wall with arginine administration

Prosthetic meshes are used as the standard of care in abdominal wall hernia repair. However, hernia recurrences and side effects remain unsolved problems. The demand by health care providers for increasingly efficient and cost-effective surgery encourages the development of newer strategies to improve devices and outcomes. Here, we evaluated whether l-arginine administration was able to ameliorate long-term polypropylene prostheses incorporation into the abdominal wall of Sprague-Dawley rats. Meshes were placed on-lay and continuous l-arginine was administered. In vivo biocompatibility was studied at 7, 25 and 30 days post-implantation. Effectively, l-arginine administration in combination with mesh triggered subtle changes in ECM composition that impinged on critical biochemical and structural features. Lastly, tensile strength augmented and stiffness decreased over the control condition. This could help to restructure the mechanical load transfer from the implant to the brittle surrounding tissues, i.e., impact load and fatigue load associated with mechanical tensions could be distributed between the mesh and the restored tissue in a more balanced manner, and ultimately help to reduce the incidence of loosening, recurrences, and local wound complications. Since the newly formed tissue is more mechanically stable, this approach could eventually be introduced to human hernia repair.

Comparison of host response to polypropylene and non-cross-linked porcine small intestine serosal-derived collagen implants in a rat model

OBJECTIVE

To compare the host response, architectural integration and tensile strength of polypropylene and porcine small intestine submucosa-derived implants in a rat model.

DESIGN

Experimental study.

SETTING

Center for Surgical Technologies, Faculty of Medicine, Katholieke Universiteit Leuven, Belgium.

SAMPLE

Forty-eight adult male Wistar rats weighing 220-250 g randomised to receive either implant.

METHODS

Full thickness abdominal wall defects were primarily repaired with polypropylene mesh (Marlex) (MX group) or porcine small intestine submucosa (Surgisis) (SIS group). Animals were sacrificed at 7, 14, 30 and 90 days after implantation.

MAIN OUTCOME MEASURES

The presence of herniation, infection and intra-peritoneal adhesions. Change in thickness and tensile strength of implant. Histopathological and immunohistochemical appearances of inflammatory response and collagen deposition.

RESULTS

Implants from the SIS group showed a short term increase in thickness in the first 14 days. Formation of adhesions was significantly more intense in the MX group at 30 days, and more extensive in the SIS group at 90 days. Tensile strength increased over time in both groups but was significantly lower in the SIS group than the MX group at 30 days. Implants in the MX group showed a more pronounced inflammatory response and more pronounced new vessel formation than the SIS group. Collagen formation was initially more fibrous and better organised in the MX group but became greater in the SIS group at 90 days.

CONCLUSIONS

Biologically derived implant material induced a less pronounced inflammatory response and differences in collagen deposition. At 30 days tensile strength was weaker in the biological implant group but was equivalent by 90 days. These differences may have implications for the in vivo performance of the materials.

Relationship between tissue ingrowth and mesh contraction

Contraction is a well-documented phenomenon occurring within two months of mesh implantation. Its etiology is unknown, but it is suggested to occur as a result of inadequate tissue ingrowth into the mesh and has been associated with hernia recurrence. In continuation of our previous studies, we compared tissue ingrowth characteristics of large patches of polyester (PE) and heavyweight polypropylene (PP) and their effect on mesh contraction. The materials used were eight PE and eight PP meshes measuring 10 x 10 cm2. After random assignment to the implantation sites, the meshes were fixed to the abdominal wall fascia of swine using interrupted polypropylene sutures. A necropsy was performed three months after surgery for evaluation of mesh contraction/shrinkage. Using a tensiometer, tissue ingrowth was assessed by measuring the force necessary to detach the mesh from the fascia. Histologic analysis included inflammatory and fibroblastic reactions, scored on a 0-4 point scale. One swine developed a severe wound infection that involved two PP meshes and was therefore excluded from the study. The mean area covered by the PE meshes (87 +/- 7 cm2) was significantly larger than the area covered by the PP meshes (67 +/- 14 cm2) (p = 0.006). Tissue ingrowth force of the PE meshes (194 +/- 37 N) had a trend toward being higher than that of the PP meshes (159 +/- 43 N), although it did not reach statistical significance. There was no difference in histologic inflammatory and fibroblastic reactions between mesh types. There was a significant correlation between tissue ingrowth force and mesh size (p = 0.03, 95% CI: 0.05-0.84). Our results confirm those from previous studies in that mesh materials undergo significant contraction after suture fixation to the fascia. PE resulted in less contraction than polypropylene. A strong integration of the mesh into the tissue helps prevent this phenomenon, which is evidenced by a significant correlation between tissue ingrowth force and mesh size.

Improved surgical outcome by modification of porcine dermal collagen implant in abdominal wall reconstruction in rats

AIM

We earlier showed in rats that fascial repair with Pelvicol, a porcine dermal collagen implant, was associated with a lesser inflammatory response but lower tensile strength in the early postoperative period as compared to Prolene. Herein we wanted to evaluate whether creation of pores in Pelvicol, facilitating ingrowth of fibrous tissue and vessels, would result in a higher tensile strength at d30 without compromising longer term results.

METHODS

First tensile strength of Pelvicol modified with different pore sizes was evaluated ex vivo. In a second step, Pelvicol implants with pores were used to cover full-thickness abdominal wall defects in 36 rats. Implants were either Pelvicol (non-porous) or with pores of Phi : 0.7, 1.2, or 2.0 mm (n=6 each). Animals were sacrificed on d30 and 90 to evaluate the presence of herniation, infection, adhesions, change in thickness and tensile strength. Histopathology was performed to assess inflammatory response and collagen deposition. Data were compared to available data on Prolene implanted animals at same time points.

RESULTS

Pelvicol with pore diameter of 2.5 mm was significantly weaker ex vivo. Animals repaired with non-porous material did develop seroma (2/6) or clinical infection (1/6) whereas none in the other groups did. There was a trend for increasing tensile strength at 30 d with increasing pore diameter, being significant in the 2.0-mm pore size group. This difference disappeared by 90 d, where all materials were equally strong as Prolene. The foreign body reaction was less intense in a pore-size dependent manner, with more abundant neo-vascularization and collagen deposition passing through the pores.

CONCLUSION

Creation of pores in Pelvicol promotes neo-vascularization, collagen deposition, and fibrous tissue ingrowth, and at pore size 2.0 mm tensile strength was increased at d30 whereafter all materials had comparable strength.

Applications of environmental scanning electron microscopy (ESEM) in biomaterials field

Various tasks were undertaken in our laboratory where environmental scanning electron microscopy (ESEM) has been of particular interest within the biomaterials field. The possibility of observing wet samples, as well as the fact that sample preparation is minimal, has improved shorter time scales and lower costs in microscopy. Minimal preparation has also reduced the possibility of introducing artifacts. Examples like cell cultures used for pit resorption assays, calcium phosphate deposition processes, and dissolution of phosphate glasses used as biomaterials are presented. Finally, a servohydraulic testing machine designed for mechanical testing in situ in ESEM has allowed the study of shape memory alloys for orthodontic applications or the behavior of different adhesives used in odontology.