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M. Warga, P. Szurman, S. Grisanti, F. Ziemssen, R.T. Kaczmarek, K.U. Bartz–Schmidt; Influence of Sterilization on the Water Absorption of Silicone Encoating of Intraocular Microelectronic Devices . Invest. Ophthalmol. Vis. Sci. 2006;47(13):1069.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate the water absorption and insulation properties of silicone rubber as an encapsulant for microelectronic devices that have been sterilized either by steam or by ethylene oxide.
To test the long–term function four steam–sterilized and ten ethylene oxide sterilized silicone encapsulated Intraocular Vision Aids (IoVA) were implanted in thirteen pigmented rabbits and followed–up for up to 21 months. To confirm and quantify the moisture absorption of the silicone embedding in the dependence of the different sterilization procedures in vitro experiments were performed. Six explanted micro arrays were stored in water and weight changes were measured. In a second experiment silicone encapsulated silica gel as a humidity indicator was sterilized either by steam or ethylene oxide.
Three of the steam–sterilized microelectronic devices showed a functional loss three days after implantation in the rabbit eye. The fourth one maintained its function for up to 6 months, but only after the inductive energy supply was adjusted. The 10 ethylene oxide sterilized micro arrays in contrast maintained wireless stimulation by inductive energy transmission for up to 21 months. Steam sterilization of the microelectronic devices led to a weight gain of 2% due to water absorption, while in the ethylene oxide group the weight gain was maximal 0,3%. Encapsulated silica gel stained positive for water absorption after steam sterilization.
Silicone rubber has a proven biocompatibility and is therefore often used in implant medicine to encapsulate microelectronic devices. Although being water repellent silicone rubber is permeable for water vapour. One should keep in mind that sterilization procedure of the encapsulation could change the water absorption and insulation properties. According to our results ethylene oxide sterilization is recommended to assure long–term function of the silicone encapsulated microelectronic unit.
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