3D Bioprinted Degradable Meshes for Pelvic Reconstructive Surgery.

Abstract

Introduction: Introduction: Non-degradable synthetic meshes for treating pelvic organ prolapse (POP) have been banned in many countries due to the adverse events associated with transvaginal surgery. There is a growing interest and focus on degradable materials as an alternative approach. Irrespective of the material choice, all implants elicit a foreign body response (FBR). It is crucial that this response leads to an overall healing response to the success of the implanted graft. We recently designed tissue-engineered 3D printed degradable mesh using poly e-caprolactone (PCL) bioprinted with endometrial Mesenchymal stem/stromal cells (eMSC) for POP repair. Objective(s): The aim of this study was to extend our knowledge and investigate the key 3D design considerations that impact the foreign body response to implanted meshes in a small animal model. The study also aimed to uncover the key molecular mediators that drive the foreign body response. Furthermore, we wanted to explore, the feasibility and fate of using them as vaginal implants in a large animal model of POP. Method(s): Molten PCL was 3D printed with melt-electrowritten (MEW) program on a GESIM bioprinter. Hierarchical geometries were fabricated by two-way stacking of the strands at a fiber spacing of 1 mm and 0.5 mm with 3 different interlayer angles of 90o, 45o or 22.5o both individually and combined to screen 10 different mesh constructs including a negative control scaffold fabricated in a thin sheet without porosity. The mechanical and biophysical properties of mesh were characterised using scanning electron microscopy and uniaxial tensile testing. For immune response studies, meshes were implanted subcutaneously in immunocompetent mice and explanted at 1 and 6 wks. The macrophage response was determined using immunofluorescence of CD206, F4/80 and CCR7. Histology and expression of 96 genes involved in the regulation of angiogenesis, inflammation, extracellular matrix, cell adhesion and collagen were assessed using Fluidigm Biomark qPCR. For vaginal performance validation, meshes were transvaginally sutured in our parous sheep model for POP. Immunohistochemistry and electron microscopy were used to visualize new ECM and blood vessels around implants. Result(s): The lowest angular interlayer angle; 22.5o reveals a fibrous mesh architecture with the pore size of 47.3 +/- 4.5 mum. The mesh morphology study by electron microscopy reveals the fiber diameter to be 18.86 +/- 2.16 mum. Meshes printed at 45o and 22.5o had higher tensile strength under dry conditions. Meshes that were printed at 45o and 22.5o showed better tissue integration indicated by the greater number of host cell penetration, leading to deposition of tissue healing collagen inside the mesh, particularly 6 weeks after implantation. Our qPCR on-going analysis is looking at the up and down-regulated genes at 1 and 6 weeks. The number of CCR7 M1 and CD206 M2 macrophages revealed that the pattern and geometry of the layer-by-layer deposition of the MEW meshes mediated macrophage polarization and the extent of the foreign body reaction. In parous sheep vaginas, similar effects were seen with evidence of angiogenesis and tissue integration that mirrored the foreign body response in the mouse model. Conclusion(s): This study shows that the geometric design of degradable meshes fabricated by 3D printing directly impacts the foreign body response in vivo. The basic parameters in mesh design particularly influence host cells during the acute inflammatory stage and continue to impact the ECM synthesis, angiogenic and anti-inflammatory response in close proximity of the mesh. From a tissue engineering perspective, MEW feature on a 3D printer allows rational design of meshes and holds significant potential as alternative surgical constructs for the treatment of POP.