An in vivo biocompatibility study of surgical meshes made from bacterial cellulose modified with chitosan.

An in vivo biocompatibility study of surgical meshes made from bacterial

cellulose modi

fied with chitosan

Joanna Piasecka-Zelga

, Piotr Zelga

⁎

, Joanna Szulc

, Justyna Wietecha

, Danuta Ciecha

_ńska

a

Nofer Institute of Occupational Medicine, Research Laboratory for Medicine and Veterinary Products in the GMP Quality System,Św. Teresy od Dzieciątka Jezus 8, 91-348 Lodz, Poland

b_{Institute of Biopolymers and Chemical Fibres, Marii Skłodowskiej–Curie 19/27, 90-570 Łódź, Poland} c

Department of General and Colorectal Surgery, Medical University of Lodz, Pl. Hallera 1, 91-647 Lodz, Poland

a b s t r a c t

a r t i c l e i n f o

Article history: Received 6 January 2018

Received in revised form 12 May 2018 Accepted 17 May 2018

Available online 18 May 2018

Bacterial cellulose modified with chitosan (MBC) is an innovative biomaterial used in regenerative medicine which may potentially improve treatment outcomes mesh for hernia repair surgery by facilitating better absorp-tion in native tissue with less risk of mesh-related infecabsorp-tions. The aim of the present study was to evaluate the biocompatibility of mesh based on MBC, and determine whether immunological reactions occur due to hyper-sensitivity to the implants.

Fortyfive Imp:WIST rats were randomly assigned to be implanted with one of three mesh types: simple polypro-pylene mesh (n = 15), mesh modified by bacterial cellulose only (n = 15) and MBC mesh (n = 15) and evalu-ated after one and three months following intramuscular implantation. For MBC mesh, basic toxicological studies, i.e. Acute Dermal Irritation, Intradermal Reactivity and Acute Sensitization (GPMT), were also carried out on 9 Imp:BN albino rabbits and 15 Imp:D-H guinea pigs.

The lowest immune response and the highest degree offibroplasia were observed for MBC mesh both after one and three months after implantation. Toxicological studies classified the tested MBC mesh as a barely perceptible irritant with no signs of sensitization or allergic reactions observed during the studies.

Thefindings indicate that MBC mesh does not irritate, does not sensitize and does not cause hypersensitivity in the implant site, and therefore presents a low risk of provoking such reactions in humans.

© 2018 Elsevier B.V. All rights reserved.

Keywords: Bacterial cellulose Hernia repair Contact allergy Biocompatibility Histopathology In vivo 1. Introduction

Bacterial cellulose (BC) is a novel biomaterial possessing unique properties, including a high degree of crystallinity, water retention value, tensile strength, and moldability [1,2]. These remarkable physical properties result from its unique nanostructure, consisting of a three-dimensional network of linear b-1,4-glucan chains bonded together by hydrogen interactions, organized as twisting ribbons of microfibrillar bundles [3,4]. Such unique properties make BC an excellent biomaterial with many applications in the biomedicalfield [5,6].

BC has already proved itself as an essential component of modern medicine. Thefirst application of BC to be introduced was the wound healing system which exploits its elasticity, remarkable hydration level and significant mechanical strength [7–9]. Apart from being an ex-ceptional dressing material BC is also known to display good surgical ca-pabilities [5,10]. The value of bacterial cellulose in general surgery and regenerative medicine is enhanced by its susceptibility to vasculariza-tion, lack of swelling effect and prominent biocompatibility [11,12].

Later developments concerned the implementation of BC-coated polypropylene meshes. The purpose of the coating is to attenuate the host response to the prosthetic, yet still provide adequate strength for repair due to its biocompatibility. One of the requirements that Hutmacher has identified, aside from the need for it to have interconnecting pores of an appropriate scale to favour tissue integra-tion and the necessary vascularizaintegra-tion, as well as the appropriate sur-face chemistry to favour cellular attachment, is that tissue engineering scaffolds should undergo controlled biodegradation with regard to the surrounding tissue [13]. It was observed that the surface of native BC does not promote optimal cells adhesion [14]. Several studies have been carried out with the aim of modifying surface made of BC to opti-mize BC-cell interactions; one such approach, chitosan-modified bacte-rial cellulose, herein referred to as MBC (modified bacterial, or bacterial, cellulose) has shown greater biocompatibility by offering better cell ad-hesion, increased water holding capacity (WHC) and improved thermal stability compared to native BC structures [15–17]. Furthermore, Jaehwan et al. report that chitosan molecules can penetrate into BC, forming a three-dimensional multilayer structure scaffold, and that it demonstrates better biocompatibility than pure BC [18].

Appropriately for our present study, these attractive properties might enhance contemporary treatment of hernias [19].

⁎ Corresponding author at: Department of General and Colorectal Surgery, Medical University ofŁódź, Plac Hallera 1, 91-647 Lodz, Poland.

E-mail address:piotr.zelga@umed.lodz.pl(P. Zelga).

https://doi.org/10.1016/j.ijbiomac.2018.05.123

0141-8130/© 2018 Elsevier B.V. All rights reserved.

Contents lists available atScienceDirect

International Journal of Biological Macromolecules

Abdominal hernia (predominantly inguinal) is the most common type of hernia. It represents approximately two thirds of abdominal her-nias in adult and is much more common in men than in women [20]. Surgery remains the only option to treat hernia and relies on two groups of techniques: One closes the defect approximating the surrounding tis-sues with sutures (tension group), and the other uses a prosthetic ma-terial to close the hernia gap (tension-free group) [21]. Numerous repair techniques have been described to date; however, tension-free mesh repairs are widely used because of their low recurrence rates and better patient reported outcomes when compared to other methods [22]. Such advantages were confirmed in an EU trial list collab-oration in 2002 which analysed 58 randomised controlled [23]. Meshes have now virtually replaced suture repair in the developed world, with polypropylene mesh being the most frequently used. It is cheap, non-absorbable, and strong enough to avoid recurrence.

Using meshes with MBC for hernia repair could have many advan-tages arising from merging the favour of the newest polypropylene meshes with MBC enhanced biocompatibility [24]. Due to its remark-able biomimetic properties MBC may represent a significant improve-ment in hernia repair [25]. However, the foreign body reaction still presents a crucial and underestimated problem [19]. This is of such im-portance that surgeons should be aware of the full spectrum of physicomechanical properties of mesh materials, particularly the extent to which these properties can affect the body's response to the im-planted material [26]. BC materials have the potential to be effective, but their mode of action during repair and the effects they may cause need to be analysedfirst. The present study assesses the biocompatibil-ity of these meshes using reliable, microscopic, macroscopic and histo-pathological assessment of bioresorbable surgical meshes for hernia repair modified with bacterial cellulose and chitosan.

2. Materials and methods

The present study was conducted in accordance with the prior con-sent of the No. 9 Local Ethics Committee for animal experiments in Lodz, Poland; Resolution No. 57/LB 488/2009 on November 16, 2009. 2.1. Test material

Samples for the study were provided by the Institute of Biopolymers and Chemical Fibres, Lodz, Poland and obtained as follows [27]:

Culture media and conditions:

• Acetobacter xylinum strain (CCM 2360) - obtained from the Czech Collection of Microorganisms and stored in a liquid nutri-ent medium containing 3% yeast extract, 0.3% calcium carbon-ate, 3% ethanol.

• Medium of Hestrin and Schramm contained (%, w/v): glucose, 2.0; peptone, 0.5; yeast extract, 0.5; disodium phosphate, 0.27; citric acid, 0.115; 96% ethanol 20 cm3; this medium was modified by Chito Oligo-100 chitosan oligomers (Aminogen, Korea) - 60 g/1000 cm3_medium.

ChitoOligo-100 is a water-soluble oligomer ofβ-1,4-linkedD -glucos-amine, produced from crab chitosan by an enzymatic process using a chitosanase, developed by the Aminogen company (Korean Patent No. 0227040). Product characteristics: molec-ular weight N5 kDa, degree of acetylation 92%, molecular weight distribution of 1 to 1.5, an intrinsic viscosity of 0.020 to 0.250 g/D-sec, a moisture contentN 1%, and a inorganic content of 0 to 1%.

• Dallop M/MN synthetic surgical mesh (Tricomed S.A. Lodz, Poland). The mesh was made of polypropylene (PP) mono fil-ament using a knitting technique. Dimension - 6 × 11 cm. Be-fore biosynthesis, the PP mesh was sterilized in 70% ethanol.

It was characterized by a high macro-porosity and a low sur-face density. The physical-mechanical parameters of the mesh: surface density 53.1 ± 1.4 g/m2_{, puncture resistance}

1486 ± 77 N, suture pull out strength 33.8 ± 7.8 N, breaking force in the longitudinal direction 360 ± 25 N, breaking force in the transverse direction 82 ± 5 N.

• Before biosynthesis, the PP mesh was treated by UV-radiation. Lamp that generated UV emissions 366 nm was used. The UV intensity at the irradiation position was 640 W/cm2_{at a distance of 18 cm during 6 h.}

The biosynthesis was carried out for two days at 30 °C, with the use of the Acetobacter xylinum (CCM 2360) strain (Czech Collection of Mi-croorganisms) in Hestrin-Schramm (HS) culture medium containing 6 wt% of Chito Oligo-100 chitosan oligomers (Amicogen, Korea) and Dallop M/MN PP mesh in sterileflat-bottomed flasks. According to Ciechańska, 6 wt% is the highest concentration at which both a high yield of MBC biosynthesis and high susceptibility to enzymatic degrada-tion can be achieved [27]. PP mesh was placed at the bottom of the ves-sel and a liquid culture medium was added. The MBC modified meshes obtained after two days biosynthesis were washed with distilled water until complete removal of culture medium components (water conduc-tivity after washingb 20 μS). Next, the meshes were soaked in 1% NaOH and autoclaved at 121 °C for 15 min, before being washed with distilled water until neutral pH and conductivityb20 μS. In the last step the com-posite meshes were immersed for 24 h in 10% glycerol solution and dry-ing at 40 °C.

2.2. Evaluation of structure and properties of MBC modified meshes GPC analysis of the MBC layer was carried out according to Turbak [28,29] procedure using HP 1050 (Hewlett Packard, USA) apparatus equipped with a HP 1047A refractometric detector and a set of columns with a rigid hydrophilic packing material based on a polymeric gel. Sam-ples were prepared for the analysis according to the modi_{fied Ekmanis} method [30]. Morphological structure analysis of MBC and composite MBC/PP surgical mesh was performed by scanning electron microscopy (SEM) using a JSM-5500LV microscope (Jeol, Japan), equipped with a tungsten electron source. Test samples were coated with a layer of gold using a JFC 1200 sputter coater (Jeol, Japan). Sputter coating oper-ation was carried out under a vacuum of 0.003 Pa. Microscopic observa-tions were carried out.

Infrared spectrophotometric analysis of the MBC layer was made with the use of FTIR Unicam apparatus with WinFIRST software of Mattson Co, within a wave number range of 4000–650 cm−1_.

Mechanical properties of composite surgical meshes were evaluated according to the relevant standards: surface density - PN EN 12127:2000, puncture resistance - PN-EN ISO 12236:2007, suture pull out strength - ISO 7198:1998, breaking force, elongation at maximal force in the transverse and longitudinal directions - PN-EN ISO 13934-1:2002.

2.3. Animals

Han Wistar Imp:WIST rats (total number 45), outbred, healthy, both sexes, aged approximately two to three months, body mass about 300 g.

New Zealand albino rabbits Imp:BN (total number nine), outbred, healthy, both sexes, approximately three months old, body mass 240–350 g.

Dunkin-Hartley Imp:D-H guinea pigs (total number 15), outbred, healthy, both sexes, aged approximately two to three months, body mass 240–350 g.

All laboratory animals were provided by the Institute of Occupa-tional Medicine (own breeding). The animals were housed one ani-mal per cage at 19_{–21.5 °C, 55–60% relative humidity and 12 h:12 h} light/dark cycle. Animals had access to standard feed and water ad libitum.

2.4. Reagents

Sensitization study: Freund's adjuvant, sodium dodecyl sulfate and cottonseed oil were supplied by Sigma-Aldrich Corporation (Poznan, Poland) and saline solution (0.9% NaCl) was provided by Baxter Manufacturing Sp. z o.o. (Lublin, Poland).

Sensitization and irritation study: aqua pro injectione was provided by Baxter Manufacturing Sp. z o.o. (Lublin, Poland) and sterile gauze compress 17filiform was supplied by TZMO SA (Torun, Poland). Validation of skin sensitization: 85%α-hexyl cinnamaldehyde was supplied by Sigma-Aldrich Corporation (Poznan, Poland).

Implantation: ketamine 10% supplied by Biowet (Pulawy, Poland). Histopathology: paraffin, hematoxylin and eosin supplied by Mar-Four (Lodz, Poland), acidic fuchsin supplied by KrakChemia S.A. (Krakow, Poland) and picric acid supplied by CHMES (Poznan, Poland).

2.5. Implantation

The study was conducted on 45 male Wistar rats. For each analysed mesh, 15 Wistar rats were used. The animals were placed under deep anaesthesia (intramuscular, 10% ketamine, 40 mg/kg) before undergo-ing implantation of the tested meshes into the pocket of panniculus carnosus muscles along the dorsal midline, for a one-month period. The growth of the animals was monitored together and their behaviour observed.

For further research, a 2 cm × 2 cm block was resected from the point of entry of the implant (cervical-interscapular region) after one and three months. The sample covered the entire thickness of the back muscles and the implant itself. The process of the implantation is shown in Video 1.

2.6. Histopathological evaluation after implantation

The resected muscle sections were dehydrated in increasing concen-trations of alcohol and imbued with paraffin in an RVG/1 computer tis-sue processor. Microscopic samples of 4–6 μm thickness were prepared on HM 325 Rotary Microtome and stained with hematoxylin and eosin in the staining machine (Varistan Gemini). In addition, samples were stained in acidic fuchsin and picric acid in order to visualize collagen fibres.

The resected implants with the surrounding tissues were evaluated with regard to the following characteristics: extent of thefibrous cap-sule and the inflammation state; degree of degeneration determined by changes in the tissues; the number and position of inflammatory cells, particularly polymorphonuclear leukocytes, lymphocytes, plasma cells, eosinophils, macrophages and polymorphonuclear cells as a func-tion of their distance from the material/tissue contact.

2.7. Pathological examination

After collecting samples for histopathology, the autopsy evaluation of organs and the level of their blood supply were conducted. The next step was a macroscopic examination of the tissue surrounding the im-plants and organs of the chest and abdomen, including the stomach, liver and kidneys.

2.8. Acute Dermal Irritation

The study was conducted on six New Zealand albino rabbits. Polar and non-polar extracts were tested on three rabbits each: 60 cm2_of

the test material was cut into small pieces and immersed in 20 ml of cor-responding_{fluid (cottonseed oil or sodium chloride), to maintain a 3:1} extraction ratio. Extraction conditions were as follows: 70 ± 2 °C for 24 ± 2 h.

The day before the examination, the hair on the dorsal surface of the rabbit's body was carefully shaved. The shaved parts on the right side of the trunk (stratum corneum) were incised with a sterile scalpel so as not to cause any bleeding. Twofields in the upper part of the body were assigned for the test sample, and the twofields in the lower back for the control (Fig. 2).

Thefirst assessment of skin condition following the imposition of the polar and non-polar extracts and the non-polar and polar control so-lution was carried out 24 h from thefirst single exposure. Multiple ex-posures were carried out forfive days, 6 h per day. Every day, the dressings were removed after the six-hour exposure, and dermal re-sponses were assessed after 1 h.

2.9. Intradermal Reactivity Test

The study used three Imp:BN rabbits. Two extracts were prepared, according to the method used in the previous study: nonpolar in cotton-seed oil and polar in isotonic sodium chloride solution.

Intracutaneous injections with 0.2 ml of the extract obtained with polar or non-polar solvent were made atfive sites on lower and upper left side of each rabbit. Similarly, the right side was injected with polar or non-polar solvent control as shown inFig. 2. Observations were made immediately after injection, and then each day forfive days after the injections.

The skin irritation effect was evaluated on the basis of the classi-fication of the skin reaction. Skin reactions were assessed indepen-dently for erythema and edema, based on a 0–4 grading scale. For erythema, 0 means no erythema, 1 very slight/barely perceptible er-ythema, 2 well-defined erythema, 3 moderate to severe erythema, and 4 severe erythema to slight eschar formation (injuries in depth). For edema, 0 means no edema, 1 very slight/barely percepti-ble edema, 2 slight edema (edges of area well defined by rising), 3 moderate edema (raised approximately 1 mm), and 4 severe edema (raisedN1 mm and extending beyond the area of exposure). The Primary Irritation Score was calculated by summing the scores for erythema and edema at the test site, minus the sum of the ery-thema and edema at the control site for the whole analysed period, divided by the number of observations (i.e. 14). The Primary Irrita-tion Index (PII) was calculated as the arithmetical mean of the sum of the Primary Irritation Scores for all animals in the group (i.e. three). According to OECD test guideline number 404, absorbers with a PII of 0 can be classified as a non-irritant, 0.04 to 0.99 as a barely-perceptible irritant, 1.00 to 1.99 as a slight irritant, 2.00 to 2.99 as a mild irritant, 3.00 to 5.99 as a moderate irritant, and 6.00 to 8.00 as a severe irritant.

2.10. Guinea Pig Maximization Test (GPMT)

The maximization test was conducted according to Magnusson and Kligman [31,32]. The extract was prepared under the same conditions as in previous tests, with use of aqua pro injectione as extraction medium.

The study was performed as described inFig. 3. The results of the sensitization effect were evaluated after 48, 72 and 96 h following the occurrence of the sensitization reaction, according to the Magnusson-Kligman Classification.

3. Results

3.1. Completeness of biosynthesis

Culture medium was applied at 1.8 dm3_{/1 m}2_{of the mesh area,}

resulting in an even growth of MBC at the verge between gas phase and liquid medium phase across the whole surface of the mesh, and good adherence of the MBCfilm to the polypropylene carrier (Fig. 1A and B). Following the application of the CCM 2230 strain, biosynthesis was achieved in two days.

In the case of the composite MBC/PP surgical mesh only a cellulose layer was analysed by Fourier transform infrared spectroscopy (FTIR). A wide band at 3370 cm−1, attributed to the stretching vibration of the OH and/or NH group, another band at 2915 cm−1– typical C\\H vi-bration and 870 cm−1which correspond to saccharide structure could be observed in the FTIR spectrum (Fig. 4). These peaks are characteristic for both– cellulose and chitosan oligomers. Also detected was the pres-ence of the following bands characteristic of chitosan and chitosan olig-omers: 1650 cm−1, corresponding to the stretching vibration of the C_O bond in primary amides, and 1420 cm−1_{characterized stretching}

vibration of amino group in chitosan oligomers [33,34].

The weight-average molecular weight Mw of MBC modified with 6 wt% oligomers in the culture medium was 305,000 g/mol. For the cho-sen biosynthesis variant, the MBCfilm surface density was 3.0 g/m2_{. The}

PP substrate surface density was 53.1 ± 1.4 g/m2(31.5 wt%), whereas the surface density of the composite surgical mesh obtained in selected conditions was approximately 170 g/m2_{(including also water and}

glyc-erol - water for 10 wt% and glycglyc-erol for nearly 50 wt% of the total weight of the composite mesh), including 53 g/m2_{of PP mesh, about 15 g/m}2_of

MBC, and 17 g/m2_{of water, 85 g/m}2_{of glycerol.}

The single-sided modification of the knitting structure with a layer of bacterial cellulose containing N-glucosamine oligomers did not change the physico-mechanical properties of composite surgical meshes. The

mechanical parameters complied with the minimum requirements re-lated to the clinical area of application of hernia meshes.

The UV modi_{fication of the PP mesh did not change the mechanical} parameters of the mesh; the values after irradiation were at the same level as before the modification: puncture resistance - 1420 N, breaking force in the longitudinal direction - 360 N, breaking force in the transverse direction - 87 N. But this kind of treatment was critical for peel off strength of MBC layer. Irradiation affected the changes in the structure of the sur-face layer of the PP mesh, by creating macro-radicals that under the in flu-ence of atmospheric oxygen gives rise to peroxide, carboxylic, ketone and hydroxyl groups [35,36]. This increases the contact angle of the material, but does not affect its structure or strength parameters. MBC layers formed during biosynthesis on the pretreated meshes exhibited higher adhesion to the PP substrate. There were no significant changes in SEM analysis, but the increase in adhesion was observed. The peel off strength of MBC layer was 100% higher in the longitudinal and the transverse di-rection for pre-treated meshes than for non-pre-treated ones.

3.2. Histopathology

The resected implants with the surrounding tissues were evaluated to compile the results comparing the three meshes, shown inTable 1. All the implants were the MBC mesh group. Van Gieson staining re-vealed the weak presence of collagen in the analysed samples. In the PP mesh group, the capsule was sharply bordered from surrounding tis-sue (Fig. 5). The bag was formed by histiocytes,fibroblasts and the col-lagenfibres, which confirm the presence of the mesh implantation process. Only in the PP mesh group was the presence of foreign body giant cells observed, as well as general signs of local inflammation, but this process was of slight to moderate intensity. In the remaining two meshes, a slightly lower immune response and more signs offibroplasia were observed. However, all meshes demonstrated the presence of angioplasia. All changes associated with implantation in the analysed

meshes observed after one month were also found to be present after three months. Numerous fibroblasts surrounded the vascular-connective bands growing between the capsule and implant. The MBC implants introduced into the intramuscular area were surrounded with a connective capsule, which was well separated from the structure of skeletal muscle. No visible changes in the form of reactive in flamma-tory cells were observed in the muscle area. There were no apparent signs of muscle interstitialfibrosis. Selected images with descriptions are presented inFig. 5.

3.3. Pathological examination

After the histopathological assessment of the tissues surrounding the implants was completed, the internal organs were then examined. The sectional study confirmed that the structure of the internal organs was correct, and that the level of their blood supply was normal in all three analysed meshes. The macroscopic image of the upper gastroin-testinal system, and the small and large bowel was within normal limits in all groups.

Fig. 2. Location of skin application sites.

3.4. Irritation tests

This study did not only focus on the success of the mesh's incorpora-tion into the body and its effects on the tissues, organs and blood supply, but also on the potential outer effects that could be just as harmful or undesirable. Biocompatibility aims for complete function with limited irritation.

3.4.1. Acute Dermal Irritation

The irritation tests found that polar and nonpolar extracts have dif-fering irritation potentials at the dermal location. The polar extract caused erythema in one rabbit following application to the incised skin. This effect appeared on the second day of the multiple exposures and continued until the third day.

The nonpolar extract did not cause any visible changes in neither the incised nor the non-incised skin of the same rabbit. Thefive-day single and multiple exposures (nonpolar and polar extracts applied to both in-cised and not inin-cised skin) did not result in any noticeable changes in the appearance of the skin of thefive remaining rabbits. The Cumulative Irritation Index was 0.05. A more detailed summary of the results is shown inTable 2.

3.4.2. Intradermal Reactivity Test

Similar to in the Acute Dermal Irritation test, the results of the appli-cation of solvents with different polarities to the interdermal areas of rats differed, but again without statistical significance. The extract in so-dium chloride solution caused mild erythema after 24 h from injection in one of the three tested rabbits, which then disappeared after 48 h of observation. The polar extract caused no response in the other two

Fig. 4. Fourier transform infrared spectroscopy (FTIR) analysis of investigated samples.

Fig. 5. Histopathological examination of implanted polypropylene mesh (1), mesh covered with bacterial cellulose (2) and mesh covered with bacterial cellulose modified with chitosan (3).Subcutaneous tissue taken (1a) one month and (1b) three months after implantation; (2a) one month and (2b) three months after implantation; (3a) one month and (3b) three months after implantation. Pm - polypropylene mesh; C - capsule consisted offibroblasts and histiocytes; MC – bacterial cellulose layer. All specimens have been stained using hematoxylin and eosin staining.

rabbits, and the non-polar extract caused no response in any of the three tested rabbits.

The Primary Irritation Index was 0.01. A more specific summary of the results is shown inTable 3.

3.5. Guinea Pig Maximization Test (GPMT)

This sensitization test resulted in completely uniform results, as op-posed to the irritation tests. No allergic skin reaction according to the Magnusson and Kligman classification was observed at the site of expo-sure in any of the animals. For the control group offive guinea pigs, no perceptible changes were observed in the skin exposure site, neither for the tested extract nor for the vehicle (aqua pro injectione). More comprehensive results are presented inTable 4.

4. Discussion

Thefirst widely understood definition of biocompatibility states that “Biocompatibility refers to the ability of a material to perform with an appropriate host response in a specific situations” [37,38]. Only meshes modified by cellulose have been tested in both animal and human models [39]. These cellulose-based biomaterials were shown to provide significant reductions in the severity, incidence and width of postoper-ative adhesion formation in early studies led by Saravelos and Azziz [40,41]. The potential for bacterial cellulose modification with chitosan oligomers is enormous, bestowing the material with good mechanical properties, bacteriostatic activity and the ability to partially biodegrade

[4,27]. Moreover, as the MBC layer can be biosynthesized in as little as two days after the addition of the particular CCM strain, it would be fea-sible to design a manufacturing process [42–44]. All these features are very attractive concerning hernia repair and new, more effective mesh creation.

The biomodified mesh used in the present study was formed of PP mesh coated on one or both sides with MBC. Satisfactory adhesion be-tween MBC and PP mesh was obtained after irradiating the PP mesh with UV prior to MBC biosynthesis, resulting in greater adhesion be-tween the MBC layer and the PP mesh, while maintaining the strength parameters of the PP mesh. As shown inFig. 1, the MBC layer covers both the PP mesh surface and the spaces between the PPfilaments, with minor breaks where the PPfilaments interlace. Although this does not decrease the mechanical properties of the PP mesh, thus sus-taining the mesh function, the reduced exposure of the PP mesh fila-ments to surrounding tissue diminished thefibrotic response of the tissue, preventing painful adhesions, scar formation and tissue tension in that area [27]. Moreover, it was reported that the chitosan coating on polypropylene promotes myoblast early attachment overfibroblast attachment which is believed to generate significantly higher tetanic force of mesh [45]. Udpa et al. evaluated the in vitro and in vivo re-sponses of a chitosan coating on polypropylene mesh (Ch-PPM) in com-parison with commercially available meshes in a rat abdominal defect model. They observed that chitosan coating is associated with the resto-ration of functional skeletal muscle with histomorphologic characteris-tics that resemble native muscle and an early macrophage phenotypic response that has previously been shown to lead to more functional

Table 1

Comparative results of histopathological analysis of polypropylene mesh, mesh modified by bacterial cellulose only and mesh modified by bacterial cellulose and chitosan. Type of mesh Neovascularization Inflammatory response Fibroplasia Connective tissue (measured

thickness range) Visible signs of

inflammation

Granulocytes Histiocytes Foreign body giant cells After 1 month

Polypropylene mesh Present ++ + + + ++ Capsule sharply bordered from local tissue

Polypropylene with cellulose mesh Present + + ++ − ++/+++ Capsule separated from the local tissue with

Polypropylene with cellulose and chitosan mesh

Present − − +++ − +++ Capsule mildly separated from local tissue

After 3 months

Polypropylene mesh Present ++ + ++ −/+ ++ 40–100 μm thick connective capsule Polypropylene with cellulose mesh Present + −/+ +/++ − ++ 20–80 μm thick connective capsule Polypropylene with chitosan and

cellulose mesh

Present − −/+ ++ − +++ 25–50 μm thick connective capsule − absent; + slightly present; ++ moderately present; +++abundantly present.

Table 2

Irritation study results.

Extract type Rabbit code Days PIS PII CII

I II III IV V

Subsequent observations

1 2 3 4 5 6 7 8 9 10

S NS S NS S NS S NS S NS S NS S NS S NS S NS S N Nonpolar extract (in cottonseed oil) 96 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0.00

0.00 0.05 105 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0.00

116 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0.00 Polar extract (in sodium chloride) 120 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0.00

0.1 122 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0.00

60 0 0 0 0 0 1 0 1 0 1 0 1 0 0 0 0 0 0 0 0 0.4

S– test area with scaring, NS – test area with no scaring.

Primary Irritation Score (PIS) = sum of the scores for erythema and edema for particular rabbit in whole analysed period divided by number of observations e.g. 2 / 10 = 0.2. Primary Irritations Index (PII) = PISrabbit1 + PISrabbit2 + PISrabbit3 divided by number of tested animals e.g. (0.33 + 0.20 + 0.00) / 3 = 0.18.

outcomes. Udpa further concluded that the microarchitecture of the chi-tosan polypropylene offers a greater surface area for cell attachment and smaller pores for cell entrapment when compared to the reference mesh [45]. In addition, chitosan, when degraded by endogenous en-zymes e.g. lysozyme, released mono- and oligosaccharides, which stim-ulate angiogenesis and tissue regeneration [4,46].

The intramuscular implantation of bacterial cellulose mesh struc-tures modified with chitosan, performed on Imp: WIST rats and de-signed in our laboratory, revealed very promising results. The implants did not induce inflammation, with no giant cells detected,

and no connective tissue proliferation was observed in nearby muscle structures. Our results show successful BC implantation, similar to the 2001 study described that inserted BC tubes into carotid arteries [2]. These implants were evaluated after one month, as in the present study. The researchers found that tested implants were completely in-corporated in the body and there were no signs of rejection. The im-plants were surrounded by connective tissue, but this did not penetrate the test material. Another study by Helenius et al. from 2005 described the results of subcutaneous implantation of small bacte-rial cellulose pieces after one, four and 12 weeks. Again, the key obser-vation was that no signs of inflammation were revealed by macroscopic or histopathological analysis. Blood vessels were found to form around and within the implant, andfibroblasts were seen to be penetrating the porous material [47]. The present analyses performed in our laboratory as part of a basic toxicological study indicate no irrita-tion or allergic reacirrita-tions. It is impossible to compare thesefindings with those of other studies, as related studies assess bacterial cellulose and its modifications mainly by implantation in other types of experimental animal model. In addition, none of the previous studies provide results based on acknowledged acute irritation and sensitization tests and this is thefirst study to provide such evidence. All these features confirm that bacterial cellulose modi_{fied with chitosan has great potential and} should be further tested for potential future application in routine her-nia repair operations.

5. Conclusions

Surgical polypropylene meshes for hernia repair coated with bacte-rial cellulose and modified with chitosan evokes the lowest immune re-sponse to surrounding tissue after implantation, while effectively inducing the tissue remodelling. The tested material neither cause any allergic or significant intradermal reactions nor pathological changes in internal organs. The results can confirm that these surgical meshes show superior to common polypropylene meshes biological integration with surrounding tissues and should not pose a threat while being ap-plied into the human organism.

Supplementary data to this article can be found online athttps://doi.

org/10.1016/j.ijbiomac.2018.05.123.

Acknowledgements

We would like to offer our special thanks to The Institute of Biopoly-mers and Chemical Fibres, Lodz, for providing the material for research. The authors wish to thank Prof Jan Stetkiewicz for the help with patho-logical evaluation and assessment of tissues and assistance when pre-paring corresponding tables andfigures.

Table 3

Intradermal Reactivity Test results.

Extract type Rabbit code

Symptoms Time Together PII

Immediately after injection

After 24 h After 48 h After 72 h After 4 days After 5 days Nonpolar extract (in cottonseed

oil) 2 Erythema 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0.01 Edema 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3 Erythema 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Edema 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 5 Erythema 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Edema 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Polar extract (in sodium chloride) 2 Erythema 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

0 Edema 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3 Erythema 0 0 0 0 0 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3 Edema 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 5 Erythema 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Edema 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Primary Irritations Index (PII) = 1st equation− number of response points for each rabbit and extract individually, divided by number of observations (30). 2nd equation– added result for both extracts for each rabbit is then divided by 2 (two extracts).

3rd equation– added results from previous analysis is divided by three tested rabbits.

Table 4

Skin sensitization test results.

Guinea pig code Observation time (h) Microbial cellulose mesh extract Aqua pro injectione E O D E O D 239 48 0 0 0 0 0 0 72 0 0 0 0 0 0 96 0 0 0 0 0 0 208 48 0 0 0 0 0 0 72 0 0 0 0 0 0 96 0 0 0 0 0 0 241 48 0 0 0 0 0 0 72 0 0 0 0 0 0 96 0 0 0 0 0 0 206 48 0 0 0 0 0 0 72 0 0 0 0 0 0 96 0 0 0 0 0 0 216 48 0 0 0 0 0 0 72 0 0 0 0 0 0 96 0 0 0 0 0 0 600 48 0 0 0 0 0 0 72 0 0 0 0 0 0 96 0 0 0 0 0 0 3 48 0 0 0 0 0 0 72 0 0 0 0 0 0 96 0 0 0 0 0 0 43 48 0 0 0 0 0 0 72 0 0 0 0 0 0 96 0 0 0 0 0 0 23 48 0 0 0 0 0 0 72 0 0 0 0 0 0 96 0 0 0 0 0 0 50 48 0 0 0 0 0 0 72 0 0 0 0 0 0 96 0 0 0 0 0 0

Percentage of allergic reaction 0.00% E– erythema, O – edema, D - different.

This research did not receive any specific grant from funding agen-cies in the public, commercial, or not-for-profit sectors.

References

[1] S. Bielecki, A. Krystynowicz, M. Turkiewicz, H. Kalinowska, Bacterial cellulose. In A. Steinbuchel, R.H. Marchessault (Eds.), Biopolymers. Wiley-Vch Verlag GmbH & Co. KgaA, Weinheim, Germany. pp. 37–90 (n.d.).

[2] D. Klemm, D. Schumann, U. Udhardt, S. Marsch, Bacterial synthesized cellulose - ar-tificial blood vessels for microsurgery, Prog. Polym. Sci. 26 (2001) 1561–1603,

https://doi.org/10.1016/s0079-6700(01)00021-1.

[3] W.K. Czaja, D.J. Young, M. Kawecki, R.M. Brown Jr., The future prospects of microbial cellulose in biomedical applications, Biomacromolecules 8 (2007) 1–12,https://doi. org/10.1021/bm060620d.

[4] D. Ciechanska, Multifunctional bacterial cellulose/chitosan composite materials for medical applications, Fibres Text. East. Eur. 12 (2004) 69–72.

[5] D.A. Schumann, J. Wippermann, D.O. Klemm, F. Kramer, D. Koth, H. Kosmehl, T. Wahlers, S. Salehi-Gelani, Artificial vascular implants from bacterial cellulose: pre-liminary results of small arterial substitutes, Cellulose 16 (2009) 877–885,https:// doi.org/10.1007/s10570-008-9264-y.

[6] S. Bielecki, H. Kalinowska, Biotechnological nanomaterials, Postep. Mikrobiol. 47 (2008) 163–169.

[7] J. Kucinska-Lipka, I. Gubanska, H. Janik, Polym. Bull. 72 (2015) 2399,https://doi.org/ 10.1007/s00289-015-1407-3.

[8] W. Czaja, A. Krystynowicz, S. Bielecki, R.M. Brown, Microbial cellulose - the natural power to heal wounds, Biomaterials 27 (2006) 145–151,https://doi.org/10.1016/j. biomaterials.2005.07.035.

[9] N. Petersen, P. Gatenholm, Bacterial cellulose-based materials and medical devices: current state and perspectives, Appl. Microbiol. Biotechnol. 91 (2011) 1277–1286,

https://doi.org/10.1007/s00253-011-3432-y.

[10] K. Kubiak, Celuloza Bakteryjna jako nanobiomateriał, 36 (2009) 649–662.

[11] K. Kowalska-Ludwicka, J. Cala, B. Grobelski, D. Sygut, D. Jesionek-Kupnicka, M. Kolodziejczyk, S. Bielecki, Z. Pasieka, Modified bacterial cellulose tubes for regener-ation of damaged peripheral nerves, Arch. Med. Sci. 9 (2013) 527–534,https://doi. org/10.5114/aoms.2013.33433.

[12] D. Ciechanska, J. Wietecha, D. Kazmierczak, J. Kazimierczak, Biosynthesis of modified bacterial cellulose in a tubular form, Fibres Text. East. Eur. 18 (2010) 98–104.

[13] D.W. Hutmacher, J.T. Schantz, C.X. Lam, K.C. Tan, T.C. Lim, State of the art and future directions of scaffold-based bone engineering from a biomaterials perspective, J. Tissue Eng. Regen. Med. 1 (2007) 245–260,https://doi.org/10.1002/term.24. [14] J.C. Courtenay, R.I. Sharma, J.L. Scott, Recent advances in modified cellulose for

tissue culture applications, Molecules 23 (2018)https://doi.org/10.3390/ molecules23030654.

[15] M. Ul-Islam, S. Khan, M.W. Ullah, J.K. Park, Bacterial cellulose composites: synthetic strategies and multiple applications in bio-medical and electro-conductivefields, Biotechnol. J. (2015)https://doi.org/10.1002/biot.201500106.

[16] Z. Cai, P. Chen, H.-J. Jin, J. Kim, The effect of chitosan content on the crystallinity, thermal stability, and mechanical properties of bacterial cellulose—chitosan com-posites, Proc. Inst. Mech. Eng. C J. Mech. Eng. Sci. 223 (2009) 2225–2230,https:// doi.org/10.1243/09544062jmes1480.

[17] S. Khan, M. Ul-Islam, M.W. Ullah, M. Ikram, F. Subhan, Y. Kim, J.H. Jang, S. Yoon, J.K. Park, Engineered regenerated bacterial cellulose scaffolds for application in in vitro tissue regeneration, RSC Adv. 5 (2015) 84565–84573.

[18] Jaehwan Kim, Z. Cai, Hyun Sook Lee, Gwang Seong Choi, Don Haeng Lee, Chulhee Jo, Preparation and characterization of a bacterial cellulose/chitosan composite for po-tential biomedical application, J. Polym. Res. 18 (2011) 739–744.

[19] V. Schumpelick, U. Klinge, Prosthetic implants for hernia repair, Br. J. Surg. 90 (2003) 1457–1458,https://doi.org/10.1002/bjs.4385.

[20] K. Turaga, R.J. Fitzgibbons, V. Puri, Inguinal hernias: should we repair? Surg. Clin. North Am. 88 (2008) 127–138,https://doi.org/10.1016/j.suc.2007.11.004. [21] W.Y. Lau, History of treatment of groin hernia, World J. Surg. 26 (2002) 748–759,

https://doi.org/10.1007/s00268-002-6297-5.

[22] J.D. Nathan, T.N. Pappas, Inguinal hernia: an old condition with new solutions, Ann. Surg. 238 (2003) S148–S157.

[23] E.U.H.T. Collaboration, Repair of groin hernia with synthetic mesh: meta-analysis of randomized controlled trials, Ann. Surg. 235 (2002) 322–332.

[24] U. Klinge, Mesh for hernia repair, Br. J. Surg. 95 (2008) 539–540,https://doi.org/10. 1002/bjs.6159.

[25] K.-Y. Lee, J.J. Blaker, A. Bismarck, Surface functionalisation of bacterial cellulose as the route to produce green polylactide nanocomposites with improved properties, Compos. Sci. Technol. 69 (2009) 2724–2733, https://doi.org/10.1016/j. compscitech.2009.08.016.

[26] Y. Bilsel, I. Abci, The search for ideal hernia repair; mesh materials and types, Int. J. Surg. 10 (2012) 317–321,https://doi.org/10.1016/j.ijsu.2012.05.002.

[27] D. Ciechanska, J. Kazimierczak, J. Wietecha, M. Rom, Surface biomodification of sur-gical meshes intended for hernia repair, Fibres Text. East. Eur. 20 (2012) 107–114.

[28] A.A. AF Turbak, A El-Kafrawy, FW Snyder. Solvent system for cellulose. U.S. Pat. 4,302,252 (1981).

[29] A.F. Turbak, Newer cellulose solvent systems, Wood Agric. Residues. Soltes E. (1983) 87–99.

[30] J.L. Ekmanis, GPC analysis of cellulose, Am. Lab. News. (Jan/Feb) (1987) 10–11.

[31] A.M. Kligman, D.A. Basketter, A critical commentary and updating of the guinea-pig maximization test, Contact Dermatitis 32 (1995) 129–134,https://doi.org/10.1111/ j.1600-0536.1995.tb00801.x.

[32] B. Magnusson, A.M. Kligman, Identification of contact allergens by animal assay. Guinea pig maximization test, J. Invest. Dermatol. 52 (1969) 268.

[33] Q.-P. Zhong, W.-S. Xia, Physicochemical properties of edible and preservativefilms from chitosan/cassava starch/gelatin blend plasticized with glycerol, Food Technol. Biotechnol. 46 (2008) 262–269.

[34] D. Gatahi, H. Wanyika, A. Kihurani, E. Gatebe, Effect of Biological Control Antagonists Adsorbed on Chitosan Immobilized Silica Nanocomposite on Ralstonia solanacearum and Growth of Tomato Seedlings, 2016https://doi.org/10.9734/AIR/2016/22742. [35] M. Bryjak, T. Janecki, I. Gancarz, K. Smolinska, Plazmowa modyfikacja membran

polimerowych, Membrany-teoria i praktyka III, Torun, 2009 64–79.

[36] A. Brzozowska-Stanuch, S. Rabiej, W. Stanuch, Wpływ warunków przyspieszonego starzenia-promieniowania UV i temperatury na poliamidy i polipropylen, Mech. Czas. Tech. 106 (1–M) (2009) (in Polish).

[37] L.G. Donaruma, Definitions in biomaterials, D. F. Williams, Ed., Elsevier, Amsterdam, 1987, 72 pp, J. Polym. Sci. Part C Polym. Lett. 26 (1988) 414,https://doi.org/10.1002/ pol.1988.140260910.

[38] D.F. Williams, On the mechanisms of biocompatibility, Biomaterials 29 (2008) 2941–2953,https://doi.org/10.1016/j.biomaterials.2008.04.023.

[39] F.G. Torres, S. Commeaux, O.P. Troncoso, Biocompatibility of bacterial cellulose based biomaterials, J. Funct. Biomater. 3 (2012) 864–878.

[40]H.G. Saravelos, T.C. Li, Physical barriers in adhesion prevention, J. Reprod. Med. 41 (1996) 42–51.

[41]R. Azziz, Microsurgery alone or with INTERCEED Absorbable Adhesion Barrier for pelvic sidewall adhesion re-formation. The INTERCEED (TC7) Adhesion Barrier Study Group II, Surg. Gynecol. Obstet. 177 (1993) 135–139.

[42] Y. Hu, J.M. Catchmark, Influence of 1-methylcyclopropene (1-MCP) on the produc-tion of bacterial cellulose biosynthesized by Acetobacter xylinum under the agitated culture, Lett. Appl. Microbiol. Department of Agricultural and Biological Engineering, Pennsylvania State University, State College, PA 16802, USA 2010, pp. 109–113,

https://doi.org/10.1111/j.1472-765X.2010.02866.x.

[43] B.S. Hungund, S.G. Gupta, Production of bacterial cellulose from Enterobacter amnigenus GH-1 isolated from rotten apple, World J. Microbiol. Biotechnol. 26 (2010) 1823–1828,https://doi.org/10.1007/s11274-010-0363-1.

[44] Us, Patent, and Google Patents.“Bacterial Cellulose Based ‘ Green ’ Composites.” (2016): 1–27. Print.

[45] N. Udpa, S.R. Iyer, R. Rajoria, K.E. Breyer, H. Valentine, B. Singh, S.P. McDonough, B.N. Brown, L.J. Bonassar, Y. Gao, Effects of chitosan coatings on polypropylene mesh for implantation in a rat abdominal wall model, Tissue Eng. Part A 19 (2013) 2713–2723.

[46] M. Ishihara, K. Obara, S. Nakamura, M. Fujita, K. Masuoka, Y. Kanatani, B. Takase, H. Hattori, Y. Morimoto, M. Ishihara, T. Maehara, M. Kikuchi, Chitosan hydrogel as a drug delivery carrier to control angiogenesis, Int. J. Artif. Organs 9 (2006) 8–16,

https://doi.org/10.1007/s10047-005-0313-0.

[47] G. Helenius, H. Backdahl, A. Bodin, U. Nannmark, P. Gatenholm, B. Risberg, In vivo biocompatibility of bacterial cellulose, J. Biomed. Mater. Res. A 76A (2006) 431–438,https://doi.org/10.1002/jbm.a.30570.