Effects of chitosan coatings on polypropylene mesh for implantation in a rat abdominal wall model

Abstract

Hernia repair and pelvic floor reconstruction are usually accompanied with the implantation of a surgical mesh, which frequently results in a foreign body response with associated complications. An ideal surgical mesh that allows force generation of muscle tissues without significant granulation tissue and/or fibrosis is of significant clinical interest. The objective of the present study was to evaluate the in vitro and in vivo responses of a chitosan coating on polypropylene mesh (Ch-PPM) in comparison with commercially available meshes. We found that application of a 0.5% (w/v) Ch-PPM elicited preferential attachment of myoblasts over fibroblast attachment in vitro. Therefore, we test the hypothesis that 0.5% Ch-PPM will encourage skeletal muscle tissue ingrowth and decrease fibrosis formation in vivo. We implanted 0.5% Ch-PPM, collagen-coated polypropylene mesh (Pelvitex™; C.R. Bard), and polypropylene (Avaulta Solo(®); C.R. Bard) alone using a rat abdominal defect model. Force generation capacity and inflammatory response of each mesh were evaluated 2, 4, and 12 weeks postimplantation. We found that chitosan coating is associated with the restoration of functional skeletal muscle with histomorphologic characteristics that resemble native muscle and an early macrophage phenotypic response that has previously been shown to lead to more functional outcomes.

Figures

FIG. 1.

Scanning electron microscope (SEM) micrographs of mesh types (A) Avaulta Solo® C.R. Bard, knitted polypropylene mesh (PPM), (B) 0.3% Ch-PPM, (C) 0.5% Ch-PPM, (D) 0.7% Ch-PPM, (E) Pelvitex™, C.R. bard, collagen-coated polypropylene mesh (Col-PPM). Scale bar=300 μm. Ch-PPM, chitosan-coated PPM.

FIG. 2.

FTIR spectra of high molecular weight chitosan (600,000 MW) and uncoated PPM, 0.3% Ch-PPM, 0.5% Ch-PPM, 0.7% Ch-PPM. FTIR, Fourier transformation infrared spectroscopy. Color images available online at www.liebertpub.com/tea

FIG. 3.

(A) Total number of cells attached to mesh samples. “*” indicates significantly from control within time point, “+” indicates significantly different from 0.3% Ch-PPM within time point, “#” indicates significantly different from 0.5% Ch-PPM within time point, “%” indicates significantly different from 0.7% within time point, “α” indicates significantly different from 12-h time point within the same mesh type, and “β” indicates significantly different from 24-h time point within the same mesh type. (B) The ratio of myoblast:fibroblast (myo:fb) for mesh samples. The ratio was measured using the DiO:DiI fluorescence ratio. “*” indicates significantly different from control within time point, “#” indicates significantly different from 0.5% Ch-PPM within time point, and “α” indicates significantly different from 12-h time point within the same mesh type.

FIG. 4.

In situ force generation of mesh samples. Dashed line indicates force generation of native tissue. “+” indicates significantly different from 12-week PPM within time point, “α” indicates significantly different from 2-week Ch-PPM.

FIG. 5.

Comparison of representative tissue reactions to three test mesh articles at 12 weeks of postimplantation. (A) Ch-PPM. (B) PPM (Avaulta Solo, C.R. Bard, Inc.). (C) Col-PPM (Pelvitex; C.R. Bard, Inc.). Ch-PPM (A) is embedded in a narrow band of fibrous connective tissue (black arrows) and the individual fibers are cuffed by a moderate number of macrophages (white arrow heads) and multinucleate giant cells (star). In contrast, the PPM has invoked a severe inflammatory reaction and a wide band of fibrosis (between black arrows) with large foci of dystrophic mineralization (blue arrows). Note the large clusters of plasma cells (black arrow heads) and the numerous multinucleate giant cells (stars). The Col-PPM (C) is embedded in a wider band of fibrosis compared to the Ch-PPM (black arrows), but only a few inflammatory cells are present. All images in the left hand column taken at 4×magnification; scale bar=500 μm. All images in the right hand column taken at 40×magnification; scale bar=50 μm. Color images available online at www.liebertpub.com/tea

FIG. 6.

Tissue reaction over time to Ch-PPM. At 2 weeks (A) a thin layer of fibrosis (black arrows) and mixed inflammatory cells (white arrow heads), including neutrophils (green arrow heads), eosinophils (yellow arrow heads), macrophages (white arrow heads), and multinucleate giant cells (stars) surround the mesh. The degree of fibrosis is similar at 4 weeks (B) and 12 weeks (C), but the number of inflammatory cells is decreased and consists almost entirely of macrophages with rare multinucleate giant cells. Color images available online at www.liebertpub.com/tea

FIG. 7.

Immunolabeling of macrophage surface markers. Mesh materials were labeled with a pan macrophage marker (CD68, red), an M1 marker (CD86, yellow), and an M2 marker (CD206, green). All images taken at 40×magnification. Scale bar=100 μm. Color images available online at www.liebertpub.com/tea

FIG. 8.

Immunolabeling of monoclonal mouse anti-myogenin of (A) Ch-PPM, (B) PPM, and (C) Col-PPM. Expression of myogenin (dark brown regions) is limited to cells of skeletal muscle origin and indicates early stages of muscle growth. Qualitatively higher amounts of positive stain of myogenin are seen in Ch-PPM (arrows). All images taken at 10×magnification. Color images available online at www.liebertpub.com/tea