The microscopic distribution of hydrophilic polymers in interpenetrating polymer networks (IPNs) of medical grade silicone

Gregory N Smith,Erik Brok,Martin Schmiele,Kell Mortensen,Wim G Bouwman,Chris P Duif,Tue Hassenkam,Martin Alm,Peter Thomsen,Lise Arleth

doi:10.1016/j.polymer.2021.123671

Gregory N Smith, Erik Brok + Show 8 more

Open Access

https://doi.org/10.1016/j.polymer.2021.123671

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Abstract

By introducing hydrophilic polymers into silicone medical devices, highly beneficial biomedical properties can be realized. An established solution to introduce hydrophilic polymers is to form an interpenetrating polymer network (IPN) by performing the hydrogel synthesis in the presence of silicone swollen in supercritical carbon dioxide. The precise distribution of the two polymers is not known, and determining this is the goal of this study. Neutron scattering and microscopy were used to determine the distribution of the hydrophilic guest polymer. Atomic force microscopy revealed that the important length scale on the surface of these materials is 10–100 nm, and spin-echo small-angle neutron scattering (SESANS) on IPNs submerged in D2O revealed structures of the same scale within the interior and enabled quantification of their size. SESANS with hydration by D2O proved to be the only scattering technique that could determine the structure of the bulk of these types of materials, and it should be used as an important tool for characterizing polymer medical devices.

Highlights

Many medical devices are made of silicone elastomers due to their advantageous properties: soft and flexible, yet tough and robust, highly chemically resistant, and with good biocompatibility
Our goal is to develop tools that can be used regardless of the material complexity to reveal the morphology of the interpenetrating polymer network (IPN)
The structural complexity of these hydrophilic-hydrophobic IPNs demanded the use of many analytical techniques, with Atomic force microscopy (AFM) and spin-echo small-angle neutron scattering (SESANS) proving informative

Summary

Introduction

Many medical devices are made of silicone elastomers due to their advantageous properties: soft and flexible, yet tough and robust, highly chemically resistant, and with good biocompatibility. Due to the high surface tension of water [2], it is energetically favorable for cells to attach to surfaces rather than remain in the medium, and making the surface of medical devices more hydrophilic can alleviate this. Interpenetrating polymer networks (IPNs), net works of interlaced materials on a molecular scale that are not cova lently bonded and cannot be separated unless chemical bonds are broken [5], are another way to increase the surface tension of medical devices [4]. These are the type of materials that will be studied here

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