In a recent study published in Advanced Materials, researchers developed biocompatible, stimuli-responsive hydrogel implants for reversible fallopian tube occlusion, providing contraception and preventing endometriosis (uterine-like tissue grows outside the uterus).
Study: Reversible Mechanical Contraception and Endometriosis Treatment Using Stimuli-Responsive Hydrogels. Image Credit: Ws Studio1985/Shutterstock.com
Background
Fallopian tubes are essential for fertilization, making tubal ligation a common contraceptive method in the United States (U.S.), though over 10% of women regret it due to complications or the desire for children.
Reconnection is complex and often fails. Alternatives like the Essure device have faced issues. Stimuli-responsive hydrogels show promise for reversible tubal occlusion, offering effective contraception and potential endometriosis prevention by blocking retrograde menstruation (Menstrual blood flows backwards into the pelvic cavity). Further research is needed to improve their efficacy, safety, and reversibility.
About the study
All chemicals, except Formalin (ROTIHistofix 4%, ROTH) and Poly(ethylene glycol) di-photodegradable acrylate (PEGdiPDA) crosslinker, were obtained from Sigma-Aldrich. PEGdiPDA was synthesized and stored in the dark.
Purified N-(2-Hydroxyethyl) acrylamide (NHEA) and poly(ethylene glycol) diacrylate (PEGdiacrylate) were used for hydrogel preparation, injected into Teflon tubes, polymerized, and dried. Fresh fallopian tubes from SBZ Schlachtbetrieb Zürich AG were used either fresh or stored at -20 °C. Endometrial cells (12Z) and cell culture materials were sourced from Applied Biological Materials Inc (Abm).
Simulated oviduct fluid (SOF) was prepared, adjusting the pH to 7.2. Hydrogel master mixes with specific monomers and crosslinkers were stored and used to create gels, which were then tested for swelling in SOF.
Fourier-transform infrared spectra and Scanning electron microscopy (SEM) were used for analysis, while gel stability was tested in human peritoneal fluid. Rheological measurements assessed viscoelastic properties and degradation kinetics.
A 3D-printed uterus model simulated gel insertion using a hysteroscope. Gel cytotoxicity was tested with normal human dermal fibroblast (NHDF) cells using a lactate dehydrogenase (LDH) assay. In vivo feasibility studies in piglets involved hydrogel implantation and 21-day monitoring.
Burst pressure tests measured the effectiveness of hydrogel occlusion in fallopian tubes. Photolabile and thiol-degradable gels were degraded using light and glutathione solutions, respectively.
Histological analysis and experiments mimicking retrograde menstruation with endometrial cells and boar semen assessed hydrogel blockage. Data were statistically analyzed and presented as mean ± standard deviation.
Study results
The functional occlusion of the fallopian tube utilizing stimuli-degradable hydrogels effectively blocks the passage of sperm, oocytes, and endometrial cells, thus inhibiting fertilization and preventing the formation of endometrial plugs in the peritoneal cavity.
Two distinct but chemically related compositions of stimuli-degradable hydrogels were investigated. Both systems primarily comprised the superabsorbent poly(2-acrylamido-2-methyl-1-propanesulfonic acid) sodium salt (PAMPS) and poly(N-(2-hydroxyethyl) acrylamide) (PNHEA).
PAMPS provided high swelling ratios, while NHEA monomers prevented excessive swelling and instability. Two hydrogels with different degradation mechanisms, light versus reduction, were designed using different crosslinkers.
Photolabile hydrogels (PL-Gel) were formed with a PEG-based crosslinker, PEGdiPDA, in a 40 wt% mix of PAMPS and PNHEA. These hydrogels degraded under light irradiation (λ = 365 nm) within 30 minutes.
Thiol-degradable hydrogels (TD-Gels) were formed using a disulfide crosslinker, BAC, in a 25 wt% PAMPS and NHEA mix and degraded within 30 minutes when exposed to biocompatible glutathione (GSH). Both hydrogels were designed to degrade on a clinically relevant timescale, ensuring practical application for reversible tubal blockage.
Hydrogel placement was assessed using an application similar to the Essure device's surgical placement. Soft hydrogels were formed, dried, and inserted into the fallopian tube through a hysteroscope.
Upon contact with tissue, the hydrogels swelled, blocking the tube within hours. If tubal blockage reversal was desired, these hydrogels could be degraded using light or thiol-containing fluids.
The in situ swelling capacity and kinetics of the hydrogels were estimated by immersing them in SOF. The swelling plateau was reached within 4-6 hours, with final swelling ratios of 12 (PL-Gel) and 16 (TD-Gel).
The higher swelling equilibrium of TD-Gels was due to its lower polymer weight fraction and crosslinker concentration. The long-term stability of the hydrogels was demonstrated by incubating them in human peritoneal fluid and SOF, showing they remained intact for over six months.
Rheological analysis assessed the viscoelastic properties and degradation kinetics of the hydrogels. The hydrogels' storage moduli were comparable to porcine fallopian tube tissue, indicating no significant distortion due to swelling. PL-Gels showed faster degradation kinetics when swollen, which is advantageous for clinical application.
The cytocompatibility was assessed using an LDH release assay with fibroblast cells, showing negligible cytotoxicity of the hydrogels and their degradation products. Histological analysis of porcine fallopian tubes after in vivo implantation for three weeks showed good tissue compatibility and no significant damage or deformation.
The surgical application was simulated in a human-scale uterus model, successfully demonstrating the hydrogels' insertion using common gynaecological techniques. Ultrasound imaging confirmed effective blockage of the fallopian tubes.
Burst pressure tests showed that fully swollen hydrogels effectively blocked the fallopian tubes, withstanding pressures significantly higher than normal physiological pressures.
In vitro experiments demonstrated the hydrogels' potential to prevent retrograde menstruation and sperm passage, showing no cells or sperm could pass through the blocked fallopian tubes.
Conclusions
To summarize, this work proposed polymer materials with on-demand, triggerable degradation for reversible, swelling-mediated occlusion of fallopian tubes as a non-hormonal contraceptive and mechanical option for preventing endometrial cell migration.
The stimuli-responsive hydrogels demonstrated favorable swelling and viscoelastic properties, complete occlusion under physiological pressures, low stiffness, and negligible cytotoxicity.
Histological analysis of blocked fallopian tubes in a piglet model showed no damage, indicating a low risk of fibrosis. Degradation was achieved using photolabile or thiol-degradable crosslinks.
The hydrogels prevented endometrial cell passage and showed firm contact with fallopian tubes with no adverse effects. These materials offer a promising reversible contraceptive and potential endometriosis treatment.
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