Pelvic organ prolapse (POP) is a debilitating urogynaecological disorder affecting 1 in 4 women across all age groups [1]. Vaginal birth is the leading cause of POP due to the dynamic progression of the fetus through the birth canal. This results in major trauma to the pelvic organ support structures due to overstretching of the puboccygeus muscle, pudental nerve and suspensory ligaments and urinary/anal sphincter injury [2]. Until recently, surgical reconstruction using non-degradable light weight meshes was the most common treatment option for POP, however, due to unacceptable post-surgical complications, these meshes have now been banned in Australia, New Zealand, USA and UK. We have been developing injectable therapeutic hydrogel therapies that can be administered to injured patients following a traumatic birth injury. 
We hypothesise that this alternative hydrogel-based prophylactic treatment will promote vaginal healing in a rat vaginal balloon injury model that simulates birth associated damage. This study aims to investigate the use of extracellular vesicle mimetics (EVMs) for their therapeutic efficacy for traumatic birth injury. EVMs are lipid-bilayer nanoparticles that contain bioactive agents specific to the parent cells. This study develops an injectable therapy using these nanoparticles as novel therapeutic agents for the potential treatment of traumatic vaginal childbirth injuries.

Human umbilical cord-derived mesenchymal stem cells (UCMSCs) were expanded in vitro. EVMs were generated by the serial extrusion of UCMSCs through a series of polycarbonate membranes of decreasing pore size. A vaginal birth induced injury model was developed in virgin Sprague-Dawley rats (8 weeks) by inserting an 8F Foley catheter and inflating for 2 hrs with 5 ml sterile PBS. Cell-derived EVMs were isolated and loaded in Alginate/Aloe Vera hydrogel to prepare an injectable dose in a 31 g insulin syringe. Balloon-injured rats served as a control. After 1 and 6 wks, collected vaginal tissue was fixed in Formalin, embedded in Paraffin, followed by 6 µm sectioning and staining by H&E, Masson’s Trichrome, Harts elastin fibre staining and histomorphological assessments, namely vaginal thickness, pattern and number of rugae. In addition, immunohistologic staining was performed to assess immune cell recruitment around the injection sites. Immunomodulation due to Alginate/Aloe Vera/EVMs injection was assessed by quantifying pan macrophage CD68+, pro-inflammatory CCR7+ and anti-inflammatory CD206+ macrophages. Statistical analysis was performed using Graph Pad Prism V7.0 and data were presented in mean ± SEM.

Vaginal trauma after SBI was evidenced by increased vaginal diameter and inflammatory response. Vaginal trauma was evident by a consistent increased vaginal diameter (7.63 ± 0.25 mm) compared to uninjured rats (4.51 ± 0.13 mm) (P<0.0001). At 6 wks, total collagen area at the injured site was increased for rats treated with eMSCs/hydrogel (1.96 ± 0.13 mm2) compared to the control group of injured rats (1.05 ± 0.04 mm2) and similarly, the muscularis area was increased in the damaged vaginas of rats injected with eMSCs/hydrogel (1.66 ± 0.13 mm2) compared to the control injured rats with no treatment (0.6 ± 0.06 mm2). Untreated tissues showed a significant reduction of smooth muscle content, increased elastin and increased tissue stiffness, indicative of fibrotic healing.

Local injection with hydrogel (Alginate/Aloe Vera) or with EVMs in hydrogel (Alginate/Aloe Vera/EVMs T) had a significant impact on birth injury reversal. Our data suggested that the prophylactic injections into damaged vagina modulates the inflammatory tissue response resulting in increased collagen and decreased elastic fibres. The increase in the collagen and muscularis area for the treated group should lead to a favourable healing with strengthening of the damaged vaginal floor. Alginate/aloe vera /EVM significantly minimised the loss of smooth muscle and reduced elastin content, comparable to an uninjured control vagina.

This is the first study to investigate whether stem cell-derived extracellular vesicle mimetics (EVMs) can have therapeutic potency for treating vaginal birth injury. Immediate treatment of severe vaginal birth trauma with therapeutic EVMs delivered in Alginate/Aloe Vera hydrogel may be a potential new treatment strategy for healing birth injury and preventing future POP in women.

Mukherjee S et al. Biomacromolecules 2019; 20 (1):454-68
DeLancey JO et al. Obstet Gynecol. 2003 Jan; 101(1):46-53