Pelvic organ prolapse (POP) is a common and debilitating disorder that negatively affects the quality of life for many women. Its prevalence is as high as 30-50% in the general population, involves the descent of the pelvic organs and causes symptoms in almost 25% of patients. A high number of them require surgical treatment, where prosthetic materials, such as polypropylene, could be used through abdominal approach. Unfortunately, symptomatic recurrences and mesh-related complications can occur after their use. In part, this may be due to the fact that meshes are still far from being optimized for this application. More data are needed before a translationally specific design for POP surgical treatment can be achieved.
While substantial consideration is devoted to the design and validation of biomaterials, the nature of their interactions with the surrounding (compromised) biological microenvironment is commonly neglected. Whereas materials and devices are designed to modulate specific functions for a given application and tissue bed, the definition of material -tissue interactions have rarely considered differences in target tissue. Identifying key parameters in the in vivo microenvironment under healthy and disease conditions may be key to highlight the main biochemical signal transduction pathways involved in the biocompatibility complex. Here, we have tried to address contributions from both cell cues and biomaterials, with an emphasis on human (pathological) fibroblasts derived from patients with POP .

Full thickness biopsies (>1 cm2) from the anterior vaginal wall were surgically excised from women suffering POP and healthy controls (n=5 both groups, based on information from previous studies) operated on for benign gynaecological pathology. Tissue collection was approved by the Clinical Ethics Committee and all participants signed a written informed consent. Biopsies were collected and immediately processed to isolate primary human vaginal fibroblasts by a double trypsin digestion. Experiments were carried out with fibroblast-derived cell lines within 3-8 passages and were repeated three times, using 3 technical replicates in each experiment. 
Fibroblasts were characterised and compared on the basis of their proliferative index, cell migration rates, morphological features (automatic quantification of area, circularity, and aspect ratio), cytoskeleton protein expression (immunofluorescence staining of vimentin, F-actin, and vinculin), inflammatory and ECM gene expression, and functional aspects such as their ability to respond to microenvironmental cues (type I collagen as a scaffold and substrates of varying stiffness). Finally, two types of surface modifications were created on polypropylene scaffolds to improve cell adhesion and morphology compared to a standard / ordinary polypropylene: a) different surface roughness in the microscale (lower roughness: Ra= 1.62±0.14µm; higher roughness: Ra=4.16±1.38µm); and b) surface functionalization by covalent immobilization of an arginylglycylaspartic acid (RGD), the most common peptide motif responsible for cell adhesion in the extracellular matrix.

Pure fibroblast cell lines (vimentin+/cytokeratin-) were successfully obtained from all processed tissues. In vitro, fibroblasts from prolapsed tissues revealed lower proliferation rates than fibroblasts from non-prolapsed tissues, as well as a differentiated morphology (larger areas and more elongated shape) and higher cell migration rates. In contrast to healthy cells, actin stress fibres were evident in POP fibroblasts under the microscope, whereas vinculin (a marker of focal adhesions) showed no differences. The expression of genes coding for ECM proteins (FBN1, POSTN and BGN) and HTR2A (receptor for serotonin), all up-regulated in tissues from patients affected by POP (as we have previously observed), was also higher in POP fibroblasts. Conversely, no differences in the expression of inflammatory genes were detected. This distinct phenotype of POP vs healthy fibroblasts resulted in a reduced adaptability to changes in substrate stiffness in terms of cell adhesion and viability, particularly in contact with the softest substrates (< 8 KPa), in which a significant proportion of cells were not able to survive. Furthermore, POP fibroblasts cultured on polypropylene scaffolds also exhibited less adhesive properties and therefore impaired cell viability, compared to healthy fibroblasts. However, increasing polypropylene surface roughness and functionalization by covalently attaching an RGD peptide clearly improved POP fibroblast adhesion and survival.

We have detected several phenotypical changes in fibroblasts derived from the vaginal wall of patients affected by prolapse, most of them related to their mechanical properties, such as the expression of cytoskeleton and extracellular matrix proteins. These alterations are possibly both cause and consequence of the overall phenotype of the prolapsed tissue, resulting in an impaired interaction with biomaterials and tissue repair. Our results reveal that the physico-chemical manipulation of a polypropylene surface certainly enhances cell adhesion and thus viability of POP fibroblasts.

Our contribution is based on the altered characteristics of the cells (fibroblasts) of the compromised POP host tissues, and the feasibility of surface modification of polypropylene devices (a polymer that is widely used in clinical practice). 
The results obtained can be potentially useful at least at two levels: a) the molecular mechanisms responsible for the maintenance of pelvic organ support structures are still poorly characterized; a better understanding of these mechanisms may help to identify women at risk and improve their prevention and treatment strategies; and, b) the response to the implantation of biomaterials can be improved by means of physicochemical modifications of the polymers used with an impact in the bioactivity zone. Overall, this can contribute to ameliorate the long-term treatment and repair of soft tissue defects.

Continence 2S2 (2022) 100244
DOI: 10.1016/j.cont.2022.100244