Nanostructured poly(ethylene glycol) thin films for silicon-based bio-microsystems

With the rapid evolution of the field of BioMEMS (biomedical micro electro mechanical system) technology in the recent years, silicon-based materials (e.g. silicon, glass, silicon dioxide, quartz) are gaining prominence for the development of microsystems for analytical and separation technologies. The interaction of a device with a biological environment leads to various challenges that have to be taken into account in order to allow its proper operation. It is known that silicon surfaces exposed to air or water develop a native oxide layer with surface silanol groups. These silanol groups are ionizable in water and make silicon surface negatively charged at neutral pH. A charged surface may create a streaming potential in the fluid flow and promote biofouling i.e. the strong tendency of proteins to physically adsorb to the surfaces. The adsorbed protein layer can mediate various biological responses such as cell attachment and activation, finally resulting in the formation of a fibrous capsule around the implanted device. All these events may interfere with the optimal operation of the device first by increasing its power consumption, and ultimating causing its failure and rejection by the host. Hence, it is desirable to control protein adsorption by surface modification with a biocompatible material/polymer. Poly(ethylene glycol) (PEG)/poly(ethylene oxide) (PEO), a water soluble, non-toxic, and non-immunogenic polymer, serves as an excellent coating material and has been shown to reduce protein adsorption and cell adhesion on synthetic surfaces. In this study, we develop and examine homogeneous and conformal PEG thin films created using a covalent coupling technique suitable for nano-meter feature size silicon-based microsystems, more particularly nanoporous silicon membranes. These films have been extensively characterized in terms of their ability to control protein adsorption and cell adhesion, and stability in vivo-like environment. Further in vivo implantation studies demonstrate improved performance of the PEG-coupled silicon membranes over unmodified silicon membranes.