Titanium implants’ surface functionalization by pulsed laser deposition of TiN, ZrC and ZrN hard films

Highlights

• TiN/Ti, ZrN/Ti, ZrC/Ti samples were grown using the PLD technique at room temperature.

• The corrosion resistance of TiN/Ti, ZrN/Ti, ZrC/Ti samples was measured by linear sweep voltametry and electrochemical impedance spectroscopy.

• After 32 days of immersion in simulated body fluid, ZrN and ZrC layers have assured a good protection of Ti substrate against corrosion.

Abstract

Thin films of TiN, ZrC, and ZrN were deposited at room temperature on highly polished Ti and Si samples using the pulsed laser deposition technique. Grazing incidence X-ray diffraction investigations showed that films were nanocrystalline, with grain sizes from 5 to 12 nm and under compression. Simulations of X-ray reflectivity curves acquired from the samples indicated that the deposited layers were dense and smooth. Electrochemical tests performed in simulated body fluid showed that the deposited coatings significantly improved the corrosion resistance of Ti samples. The comparative study found out that the best sample was ZrN/Ti, its corrosion current after 32 days immersion in simulated body fluids being half of that measured for the bare Ti sample and in the same time almost unchanged from the initial value.

Introduction

Ti and its alloys are widely used as biomaterials for various prostheses and orthopedic devices that are implanted in the human body [1]. They are distinguished by their low specific weight, acceptable mechanical properties, affordable cost and good biocompatibility [1], [2]. One of the main problems of these implants is that their average life-time, which could usually range from 10 to maximum 25 years, is significantly shorter than people's life expectancy. Most patients must undergo at least one if not more surgical revisions for the implants during their life-time. Unfortunately, the older the patient, the higher are the health risks associated with the procedure. It is therefore very important to find innovative solutions that could prolong the life of Ti implants and reduce the risks of inflammation. Ti, as well as all other materials that are used for body implants, has several drawbacks. When present for very long periods of time immersed in the corrosive body fluids, there is a slow out-diffusion process of Ti ions into the body, especially if wear occurred for the implanted metal parts [3], [4]. The relatively low hardness, high coefficient of friction and high wear rates are also specific drawbacks for Ti based implants and prostheses, which have been long recognized, studied and addressed by the scientific community [5], [6].

There are many articles describing various surface treatments or coatings that could be deposited on prosthesis to increase their corrosion resistance, osseointegration and biocompatibility and to reduce the wear rates and the resulting debris quantity and size [7], [8], [9], [10]. Some of the coatings materials that were studied as protective coatings for various applications, including biomedical ones, have been TiN [8], [9], [10], [11], [12], ZrN [13], [14], [15] and, more recently, ZrC [16]. Very good quality thin films of these materials in terms of structure, composition and mechanical properties were obtained using the pulsed laser deposition (PLD) technique on substrates there were heated at temperatures from 300 to 500 °C [17], [18], [19], [20]. In this article, taking into account the possibility of using such materials as protective coatings for Ti-based implants, we describe the use of the PLD technique to deposit TiN, ZrN, and ZrC at room temperature on pure Ti samples. Room temperature deposition is a much simpler technological solution than deposition on heated substrates because the complicated 3D shape of implants would make uniform heating a complex and difficult task. We further investigated their structure and electrochemical properties when immersed in simulated body fluid (SBF) to evaluate their potential application as coatings for implants.