Direct Comparison between Ring-Opening Polymerization and Hydrolysis-Condensation Methods in the Synthesis of Polydimethylsiloxane as a Vitreous Substitute: A Systematic Literature Review

Polydimethylsiloxane (PDMS) is a polymer with outstanding biocompatibility, chemical stability, gas permeability, and optical clarity properties. It is suitable for various applications, including as a vitreous substitute in retinal surgery. PDMS provides optical stability and transparency, essential for maintaining adhesion between the retina and the retinal pigment epithelium. The main methods for synthesizing PDMS are ring-opening polymerization (ROP) and hydrolysis-condensation, both of which produce PDMS with a wide range of properties that can be tailored by adjusting the synthesis parameters. While ROP is typically performed with cyclic siloxanes such as octamethylcyclotetrasiloxane (D4), hydrolysis-condensation uses precursors such as dichlorodimethylsilane (DCDMS). This study compares the ROP and hydrolysis-condensation methods for PDMS synthesis, focusing on their effectiveness in achieving a specific viscosity range, a key parameter for vitreous replacement applications. The effectiveness of each method in achieving specific viscosity ranges for vitreous substitute applications is compared. The results indicate that ROP requires only 1 synthesis step and operates at higher temperatures (150 - 200 °C), yielding PDMS with viscosities ranging from 0.58 to 9.36 Pa·s, influenced by factors such as KOH concentration, reaction time, and D4 purity. In contrast, hydrolysis-condensation involves a 2-step process with viscosities between 0.57 and 4.49 Pa·s, affected by more complex parameters, including the DCDMS:DCM volume ratio, reaction time, and temperature during hydrolysis. Both methods achieved close refractive index values (1.3989 - 1.4048), although the surface tension varied with sample viscosity (19 - 23 mN/m). Comparative analysis reveals that although ROP is more suitable for producing high-purity PDMS efficiently. These findings contribute to understanding PDMS synthesis methods and their implications for vitreous substitute applications. Recommendations for future research on this topic include the need to conduct further biocompatibility tests such as in vivo tests and stability tests of PDMS samples. HIGHLIGHTS Polydimethylsiloxane (PDMS) stands out for its biocompatibility, chemical stability, optical clarity, and gas permeability, making it ideal for vitreous substitute applications in retinal surgery. PDMS serves as an intraocular tamponade agent, offering optical clarity, inertness, and maintaining adhesion between the retina and retinal pigment epithelium, mimicking native vitreous properties. The study compares ring-opening polymerization (ROP) and hydrolysis-condensation methods, enabling tunable PDMS properties for specific applications. Efficient synthesis of high-performance PDMS tailored for biomedical applications. GRAPHICAL ABSTRACT