FEATURES OF INFLAMMATORY REACTION IN RATS TO IMPLANTATION OF MODERN MESH ENDOPROSTHESES FOR HERNIA REPAIR Kchibekov

Aims. To compare in a rat experiment the nature of local proliferative inflammatory reaction induced by a foreign body, at different times after implantation of polypropylene and metal mesh hernia prostheses of different manufacturers. Materials and methods. In experiments with rats of the Wistar line, the nature of local proliferative inflammatory reaction induced by a foreign body was studied at different times after implantation of the four polypropylene, one Teflon, and one metal mesh hernia prosthesis of different manufacturers. Along with the histological examination of the encapsulated mesh implant, two morphometric parameters of aseptic proliferative inflammation were assessed: mass of the connective-tissue capsule around the foreign body and its thickness. Results. It is found that the minimum fibrous capsule forms after implantation of the domestic polypropylene mesh endoprosthesis Esfil. A moderate proliferative inflammatory reaction is caused by the polypropylene implant Optomesh. A more severe reaction in rats is induced by B.Braun and ERGON lightweight polypropylene mesh endoprosthesis. The maximum fibrous capsule forms after implantation of mesh implants of two-layer porous polytetrafluoroethylene Dualmesh (Gore-Tex, USA) and domestic metal endoprosthesis “Titanium silk” in rats. Conclusions. The obtained results should be considered when choosing a mesh prosthesis for hernia repair. In particular, the “Titanium silk” endoprosthesis made of high-purity titanium filaments can be effectively used as a prosthesis for hernia repair.

drawbacks; thus, Teflon attaches poorly to tissue, which causes patch displacement and recurrence.
PP induces the emergence of a coarse connective-tissue capsule that shrinks the hernia patch [9; 10]. Besides, the use of synthetic materials for hernioplasty has recently been found to cause previously non-encountered complications. The synthetic implant might travel to the abdominal cavity; the mesh-to-intestine adhesion may cause adhesive bowel obstruction; a fistula may emerge as a result of the patch-related ulceration of the intestinal wall; or seromas might appear at the implantation site, to name a few [9][10][11]. Thus, it is still urgent to find such plastic material that would make a perfect hernia patch, i.e. both strong and as histocompatible as possible [10; 11].
The newest Russian product, Titanium Silk (Ti Silk), shows great promise; it is a high-purity BT 1.00 Ti filament woven into patches for soft tissue. Implants of pure titanium or Nitinol-based alloys (NA) are highly elastic due to special weaving. Some of the clinics in Siberia and Trans-Urals have extensively researched the specifics of Ti and NA, and still prefer NA over any synthetic material [12].
To date, surgeons find satisfactory the mechanical properties of state-of-the-art metal, polypropylene, and composite mesh patches [1-3; 12]; however, reducing the inflammatory response to polypropylene implants to avoid complications typical of hernioplasty remains an urgent problem [6; 7; 9; 11].
Research Goal. Experiment on rats to compare local proliferative inflammatory response induced by a foreign body at different times after implanting polypropylene and metal mesh hernia patches from various manufacturers.

MATERIALS AND METHODS.
Experiments were run on 48 male Wistar rats bred at the Leprosy Research Institute of the Ministry of Health, Astrakhan; the animals weighed 150 to 170 g and were randomly split into 6 experimental groups, 8 specimens each, one group per type of mesh patch. The rats were kept in a vivarium at 20° to 22° with sunlight only, a maximum of 4 animals per cage; the conditions were the same for each animal, and the diet was a standard one.   Table. The surgery was performed as follows: rats had their interscapular region pre-shaved and sanitized; a 5-mm-long cut was made with a scalpel in the skin of rats under ethereal anesthesia, and sterile fragments of mesh patches were introduced in the wound in 4 directions to a depth of 1.5 to 2 cm by means of tweezers. The wound was not stitched, as the suture material could affect the inflammation and regeneration processes.
After surgery, the animals were kept alone; they were withdrawn from the experiment on Days 1, 3, 7, and 21 by anesthetic overdose pursuant to the Convention. All the 4 implants of a single rat and 3 implants of another rat from the same group were then be separated together with the capsules formed around them and dried at 60 °C over 24 hours; then the mean weight of dry capsules was calculated exclusive of the weight of the original implant; the fourth implant of the second rat, its capsule and skin were tested histologically. Tissue pieces and the patch were fixed and paraffin-poured. Cuts were stained with hematoxylin-eosin per Van Gieson and Weigert, impregnated per Foot. An ocular micrometer was used to measure the thickness of the connectivetissue capsule in microns (μm) at 50 points in hematoxylin-eosin-stained preparations [9].
The results were subject to statistical processing using Statistica 12.0, StatSoft Inc., and Microsoft Excel 2003. Statistical processing used descriptive statistics and correlation analysis. For features that had a normal distribution, the research team calculated the arithmetic mean and the error, M±m, to be compared by Student's t-test. Mann-Whitney's U-test was run for features with other than the normal distribution. The significance threshold was p<0.05.

RESULTS.
The weight of implanted fragments sized ¼ cm 2 did not differ significantly in 4 mesh types, ranged from 4 to 5 mg, see Table; B. Braun had an original mean weight of 5.7±0.26 mg, while Ti Silk weighed 19.0±0.58 mg, both significantly heavier than their counterparts. Note that the specific weight of any mesh patch was 2 to 6 times that specified by the manufacturers. According to the authors' calculations, Esfil weighed 16.5 mg/cm 2 (165 g/cm 2 ), Ergon weighed 16.3 mg/cm 2 (163 g/m 2 ), Optilene (B. Braun) had a density of 23 mg/cm 2 (230 g/m 2 ), and Optomesh was 19 mg/cm 2 (190 g/m 2 ), while their manufacturers specified 28 to 36 g/m 2 .
One day after surgery, rats already showed proliferative inflammatory response with a connective-tissue capsule being formed around the foreign body.
Microscopy of the cut samples of encapsulated implants taken on different postoperative days showed the same outcome for any type of mesh patch: the implant was surrounded by a connective-tissue capsule between striated muscles under subcutaneous fat. The connective tissue contained collagen, elastin, and argyrophilic fibers, cellular elements (mainly fibroblasts), as well as enormous foreign-body cells and macrophages on the inner surface closer to the implant. The newly formed tissue sampled on Days 7 and 21 was rich in arterioles, venules, and capillaries. The capsule was morphologically non-homogeneous through thickness, as the capsule had compact, collagen-rich connective tissue adjacent to the implant; looser connective tissue with collagen and elastic fibers, as well as numerous fibroblasts peripherally. Foot's impregnation revealed multiple argyrophilic fibers at the patch-capsule interface and within the meshes, as well as at the capsulemuscle interface.
However, no significant difference was found in the structure or the cellular composition of the connective-tissue capsule regardless of the implant type. At the same time, the difference was indeed significant in terms of proliferation intensity and patterns in the morphometric parameters of the fibrous capsule, see Figure, Table. Minimum-weight connective-tissue capsules (6-7 mg) emerged on Day 1 around Esfil and Optomesh patches, see The thickness of capsular walls around the mesh patches as measured by microscopy at 50 points varied significantly from direction to direction, resulting in a great measurement error and thus making this indicator less informative for finding the difference between synthetic implant types than the dry capsule weight, see Table. Of all implanted mesh patches, a fibrous capsule built up at the lowest rate throughout the entire observation term around the Russian Esfil implant: the dry periimplant capsule weight rose to 10  For this reason, the fibrous capsule buildup rate for other mesh patches was compared against that of Esfil, as the Esfil implants triggered the weakest proliferative inflammatory response.
How implanting mesh patches affected the morphometry of aseptic proliferative inflammatory response in rats It is notable is that the Ergon and B. Braun fibrous capsule growth rate peaked between Days 3 and 7, see Figure. Fibrous capsule weight and thickness on different post-surgery days Dual-mesh, a two-layer Teflon patch, had the greatest fibrous tissue growth and strongest proliferative inflammatory response after Day 7, see Thus, the Teflon and titanium meshes, similarly to some of their polypropylene counterparts, effectively had one non-mechanical function: they induced continuous inflammation and collagen generation.
CONCLUSIONS. The finding is that the Russian-made polypropylene mesh patch Esfil and the Polish Optomesh had the smallest fibrous capsules formed around them. The German B.
Braun and the Italian Ergon had the most intensive post-implantation fibrous tissue growth.
The largest fibrous capsules emerged in rats implanted with Dualmesh (Gore-Tex, USA) and Ti Silk patches.
These findings contradict the manufacturer-claimed properties of these patches, a fact that should be noted when selecting a patch for alloplasty of ventral and groin hernias.

FINANCIAL SUPPORT AND SPONSORSHIP
Nil.