Gas Permeation, Mechanical Behavior and Cytocompatibility of Ultrathin Pure and Doped Diamond-Like Carbon and Silicon Oxide Films

Juergen Lackner,Marcin Kot,Eleonore Fröhlich,Claudia Meindl,Annelie-Martina Weinberg,Caterina Czibula,Lukasz Major,Christian Teichert,Clemens Kittinger,Alexander Fian,Wolfgang Waldhauser,Christian Wolf

doi:10.3390/coatings3040268

Abstract

Protective ultra-thin barrier films gather increasing economic interest for controlling permeation and diffusion from the biological surrounding in implanted sensor and electronic devices in future medicine. Thus, the aim of this work was a benchmarking of the mechanical oxygen permeation barrier, cytocompatibility, and microbiological properties of inorganic ~25 nm thin films, deposited by vacuum deposition techniques on 50 µm thin polyetheretherketone (PEEK) foils. Plasma-activated chemical vapor deposition (direct deposition from an ion source) was applied to deposit pure and nitrogen doped diamond-like carbon films, while physical vapor deposition (magnetron sputtering in pulsed DC mode) was used for the formation of silicon as well as titanium doped diamond-like carbon films. Silicon oxide films were deposited by radio frequency magnetron sputtering. The results indicate a strong influence of nanoporosity on the oxygen transmission rate for all coating types, while the low content of microporosity (particulates, etc.) is shown to be of lesser importance. Due to the low thickness of the foil substrates, being easily bent, the toughness as a measure of tendency to film fracture together with the elasticity index of the thin films influence the oxygen barrier. All investigated coatings are non-pyrogenic, cause no cytotoxic effects and do not influence bacterial growth.

Highlights

Finding materials with both high biocompatibility and low or controllable gas permeation is a great challenge for using microelectronics and microfluidics in in vivo sensors
2500 MPa and a tensile strength of 120 MPa at >150% strain. They are well suitable for future microelectronic applications due to a high dielectric strength of
Thin films of about 25 nm thickness were deposited on 50 μm thin PEEK foils in order to protect against oxygen permeation through the polymer

Summary

Introduction

Finding materials with both high biocompatibility (cytocompatibility, hemocompatibility, etc.) and low or controllable gas permeation is a great challenge for using microelectronics and microfluidics in in vivo sensors. Microelectronic devices are generally based on a large number of materials for electronics and printed circuit boards, including ceramics and polymers for chip and resistor housings, metal and semiconductors for the chip itself, metals (Al, Ni-Au, Pd-Au, Cu, Pd-Cu, etc.) for circuit paths, fiber reinforced epoxy binders, polyimide and polyurethane foils for dielectrics and various glues. Dense packaging for any in vivo use is essential to prevent permeation/diffusion of body fluids into the electronic components. This saves the electronics from biological fluids as well as the tissue from any (corrosion) contaminants from the electronics. Polymers like polydimethylsiloxane, parylene-C and polymethyl methacrylate have been applied on silicon based devices due to easy manufacturing, sufficiently high mechanical properties and bio-inertness

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