# Tailoring polymethylhydrosiloxane as candidate material for vitreous humour substitution: physical properties and in vitro toxicity

## TL;DR

This paper explores PMHS as a potential substitute for vitreous humour, showing it has suitable physical properties and is non-toxic.

## Contribution

The study introduces a novel synthesis approach for PMHS with controlled viscosity and evaluates its in vitro toxicity for the first time.

## Key findings

- Low-viscosity PMHS has a surface tension of 20 milliN/m and a refractive index of 1.3960.
- PMHS samples are transparent and non-irritant, indicating potential for vitreous humour substitution.
- Basic diethyl ether solvent produces higher viscosity PMHS compared to acidic dichloromethane.

## Abstract

Polymethylhydrosiloxane (PMHS) has been considered to be developed as an alternative material of polydimethylsiloxane (PDMS) for vitreous humour substitution. This polymer production begins with hydrolysis of dichloromethylsilane (DCMS), as raw material, which continues through condensation polymerization. Previous research reported the synthesis of PMHS using an acid solvent with different temperature variations and indicated that low-viscosity PMHS can be produced through condensation at 15–20 °C. However, this process requires a very long polymerization time. Meanwhile, synthesis using a higher temperature of 50 °C required a catalyst. The influence of solvents, one of the important synthesis temperatures, on the synthesis process of PMHS has not been explored. Furthermore, the toxicity of this material has not been reported. In this study, PMHS with low- and medium-viscosity were synthesized from DCMS with different solvents and additional control of the condensation temperature to accelerate the polymerization. Utilizing a basic diethyl ether (DE) solvent facilitates a higher viscosity value than an acidic dichloromethane (DCM) solvent. All PMHS samples were characterized by a viscometer, refractometer, surfgauge, UV–Vis, FTIR, and NMR spectroscopy. The in vitro hen’s egg chorioallantoic membrane (HET-CAM) toxicity test of PMHS was also conducted. A low-viscosity PMHS sample had a surface tension of 20 milliN/m and a refractive index of 1.3960, while medium-viscosity had 21 milliN/m and 1.3982. All samples were ~ 100% transparent, had typical functional groups of PMHS, and did not show signs of being irritant (non-toxic). Therefore, PMHS has the potential to be developed as a new material for vitreous humour substitution.