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Polyelectrolyte polymer properties in relation to male contraceptive RISUG action.

Sohini Roy¹, Debidas Ghosh, Sujoy K Guha

¹School of Medical Science and Technology, Indian Institute of Technology, Kharagpur 721302, West Bengal, India. sohini.iitk@gmail.com

Colloids and Surfaces. B, Biointerfaces

|December 30, 2008

Summary

RISUG, a long-term hydrogel contraceptive, shows altered swelling in different pH and biological fluids. These changes enhance its retention and sperm-blocking effectiveness within the vas deferens.

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Area of Science:

Biomaterials Science
Reproductive Health
Polymer Chemistry

Background:

RISUG (styrene maleic anhydride-dimethyl sulfoxide) is a long-term hydrogel contraceptive effective when injected into the vas deferens.
It is currently undergoing advanced Phase III clinical trials in India.

Purpose of the Study:

To analyze the swelling characteristics of RISUG hydrogel in various pH buffers and biological fluids.
To understand how these characteristics influence its retention in the vas deferens.
To investigate the interaction of RISUG with biomolecules in biological fluids.

Main Methods:

Swelling studies in different pH buffers (e.g., pH 2-10) and biological fluids.
Analysis of diffusion modes (Fickian vs. non-Fickian) and swelling ratios.
Surface and structural analysis using Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), and Fourier-Transform Infrared Spectroscopy (FTIR).

Main Results:

RISUG exhibited significant variations in swelling degree and equilibrium swelling ratio with increasing pH, shifting from Fickian to non-Fickian diffusion.
Higher pH led to increased ionization of carboxylic groups, causing electrostatic repulsion, osmotic pressure, and increased free volume.
Lower pH stabilized the hydrogel due to limited carboxylic group dissociation.
SEM, AFM, and FTIR revealed structural loosening, increased porosity, and adsorption of biomolecules upon interaction with biological fluids.
AFM showed significant changes in surface roughness, indicating altered polymer-environment interactions.

Conclusions:

RISUG's swelling behavior is pH-dependent, influencing its stability and retention.
Interaction with biological fluids alters RISUG's structure and surface properties.
The observed swelling and increased surface roughness suggest enhanced resistance to sperm movement, supporting its contraceptive efficacy.