Tissue - engineering as an adjunct to pelvic reconstructive surgery

This PhD-thesis is based on animal studies and comprises three original papers and unpublished data. The studies were con-ducted during my employment as a research fellow at the Department of Obstetrics and Gynecology, Herlev University Hospital, Denmark. New strategies for surgical reconstruction of pelvic organ pro-lapse (POP) are warranted. Traditional native tissue repair may be associated with poor long-term outcome and augmentation with permanent polypropylene meshes is associated with frequent and severe adverse effects. Tissue-engineering is a regenerative strategy that aims at creating functional tissue using stem cells, scaffolds and trophic factors. The aim of this thesis was to investigate the potential adjunctive use of a tissue-engineering technique for pelvic reconstructive surgery using two synthetic biodegradable materials; methoxypolyethyleneglycol-poly(lacticco-glycolic acid) (MPEG-PLGA) and electrospun polycaprolactone (PCL) - with or without seeded muscle stem cells in the form of autologous fresh muscle fiber fragments (MFFs). To simulate different POP repair scenarios different animal models were used. In Study 1 and 2, MPEG-PLGA was evaluated in a native tissue re-pair model and a partial defect model of the rat abdominal wall. We found that the scaffold was fully degraded after eight weeks. Cells from added MFFs could be traced and had resulted in the formation of new striated muscle fibers. Also, biomechanical changes were found in the groups with added MFFs. In Study 3, the long-term degradable electrospun PCL scaffold was evaluated in three rat abdominal wall models representing different loads on the scaffold. Surprisingly, cells from the MFFs did not survive. After eight weeks, a marked inflammatory foreign-body response was observed with numerous giant cells located between and around the PCL fibers which appeared not to be degraded. This response caused a considerable increase in the thickness of the mesh, resulting in a neotissue PCL construct with strength comparable to that of normal rat abdominal wall. The foreign-body inflammatory response did not differ between the groups in terms of cellularity, cell types or thickness, and no differences were found between groups when comparing biomechanical properties. In study 4, we modified a new transabdominal rabbit vaginal model to avoid the erosions known to occur following vaginal mesh implantation. A partial defect was created on the anterior vaginal wall in the vesico-vaginal space and on the anterior vaginal wall close to the cervix. This was a feasibility study aimed at obtaining results comparable to those seen in the rat model. The model was easy to perform and no vaginal erosions were observed.

In conclusion: In two rat abdominal wall models, cells from autologous MFFs, seeded on the quickly degradable MPEG-PLGA scaf-fold, survived implantation and contributed to the regenerative process by forming extra striated muscle fibers and influencing the biomechanical properties of the regenerated tissue. Consequently, MFFs seeded on an MPEG-PLGA scaffold is a potentially advantageous cell-delivering strategy to regenerate tissue at pelvic reconstructive surgery. In three rat abdominal wall models, a long-term degradable PCL scaffold caused a marked foreign-body response and formed a neo-tissue PCL construct that provided biomechanical tissue reinforcement to the abdominal wall, even at maximal load. Consequently, the PCL scaffold might be beneficial in pelvic reconstructive surgery, providing initial biomechanical rein-forcement, although long-term studies showing the tissue response at full degradation are required. Cells from the MFFs did not survive in or around the neo-tissue PCL construct, possibly because of the massive inflammatory response. Consequently, as a scaffold material, with the purpose of delivering cells to a specific anatomical site, the PCL scaffold seems poor. A transabdominal rabbit vaginal model was feasible and might be advantageous in the evaluation of meshes used for pelvic reconstructive surgery, especially when long-term studies are needed.