Towards the development of an in-vitro test to better predict fibrotic tendency of biomaterials prior to implantation.

Synthetic meshes used for pelvic floor repair have been associated with the complications of pain and erosion. Polypropylene is the most used biomaterial in pelvic floor repair and currently is the subject of significant morbidity and litigation. Biomaterial-induced fibrosis remains a challenging issue and has been suggested as a potential reason for biomaterial failure. Macrophages and fibroblasts play a central role in the body’s immunological response to implanted biomaterials.

During the healing process after implantation, macrophage phenotype ranges from pro-
inflammatory (M1) to anti-inflammatory/pro-fibrotic (M2) phenotypes. Mesh implanted in the pelvic floor is subject to mechano-chemical stress which our group has shown induces surface changes.
The study aimed to develop an in vitro model to measure macrophage and fibroblast response to biomaterials to help predict the risk of biomaterial induced fibrosis. A method was developed to culture macrophages on polypropylene mesh. This was combined with methods developed in our lab to simulate the mechano-chemical stress in vitro to assess macrophage response before and after application of these stresses. Genetic response of macrophages was assessed using qPCR. Fibroblasts were separately cultured in conditioned media collected from macrophage experiments and studied their response using qPCR and immunohistochemistry.

Surface changes were demonstrated on the mesh after exposure to mechano-chemical stress. Surface oxidation and helical defects were seen in the polymer. At the genetic level, macrophages cultured on mechano-chemically stressed mesh upregulated pro-inflammatory as well as pro-fibrotic genes. Fibroblasts cultured in conditioned media from macrophages cultured on mechano-chemically stressed mesh demonstrated increased alpha smooth muscle actin (α-SMA) production, a marker of myofibroblast differentiation. The results demonstrate a changing macrophage response as polypropylene is mechanochemically distressed. This is the first study that attempts to develop a novel in-vitro test combining mechanochemical stress testing with macrophages and fibroblasts to better understand biomaterial induced fibrosis.