Implications of sandblasting of 316 LVM stainless steel on its ion release, in vitro corrosion behavior and

biocompatibility

J.C. Galvn1, M. Multigner1, L. Saldaa2,3, M. Larrea1, A. Calzado-Martn3,2, C. Serra4, N. Vilaboa3,2, J.L. Gonzlez-

Carrasco1,2

1Centro Nacional de Investigaciones Metalrgicas (CSIC), Av. Gregorio del Amo 8, 28040 Madrid (Spain).

jcgalvan@cenim.csic.es, jlg@cenim.csic.es 2Centro de Investigacin Biomdica en Red en Bioingeniera, Biomateriales y Nanomedicina

(CIBER-BBN), Madrid (Spain). 3Hospital Universitario La Paz-IdiPAZ, Paseo de la

Castellana 261, 28046 Madrid (Spain). 4CACTI - Universidade de Vigo, Campus Lagoas-

Marcosende 15, 36310 Vigo (Spain). Introduction The austenitic stainless steel 316 LVM combines both good mechanic properties with a reasonable in vitro biocompatibility and in vivo tolerance. Thus, it is used for orthopedic applications. One method to improve the implant osseointegration is to increase the roughness by grit blasting. This study focus on the in vitro corrosion behavior, ion release and biocompatibility properties of 316 LVM steel modified by sandblasting, following two sandblasting processes of interest for the preparation of surgical implants which are based on the use of zirconia and alumina, respectively. Materials and methods Discs of 20 mm in diameter and 2 mm thick of 316LVM steel were grit blasted by the implant manufacturer (Surgival SL, Valencia, Spain). Blasting was performed with two different types of particles under a pressure of 350 KPa for 2 minutes. A first set of samples has been blasted using ZrO2 embedded in a silica vitreous phase microspheres sized between 125 m and 250 m. The second set of samples has been blasted with Al2O3 angular particles of around 750 m size. Topographic surface analysis of the as-processed specimens was determined with an interferometer optical profilometer. Due to the relatively high roughness of the blasted surfaces a Vertical Scanning Interferometry mode was used. Surface parameters were determined at 5X, 20X, and 50X magnifications, which yields fields of view of 1.092 mm2, 0.068 mm2, and 0.011 mm2, respectively. To get information of wider and more representative fields of view (4 mm2), stitching of the digital images obtained at 20X magnifications was used. Ra (nm), Rq (nm), Rz (nm), Rt (nm), and real surface area (mm2) were determined. The geometric surface area (A) was 6.41 cm2 for all the discs. The area increase corresponds to the ratio of measured surface area/scanned surface area and allows determining an index area. Microstructural characterization of surfaces and cross-sectional views were performed by using a scanning electron microscope (SEM) coupled with an energy dispersive X-ray (EDX) system for chemical analysis. The in vitro corrosion tests were carried out by soaking the blasted and non-blasted 316 LVM stainless steel specimens in the Ringers solution. Electrochemical impedance spectroscopy (EIS) tests were performed in a conventional electrochemical cell using a three electrodes set-up. Frequency scans were carried out by applying sinusoidal wave perturbations of 10mV in amplitude,

close to the corrosion potential. The analysed frequency was into the 100 kHz-1 mHz range. The impedance measurements were made after soaking the metal samples in the Ringers solution for 5 minutes and 24 hours. The impedance data were modelled with suitable electrical equivalent circuits and commercial computer programs based on complex nonlinear least-squares fitting methods. Inductively coupled plasma optical emission spectrometry (ICP-OES) has been applied to analyze the ion release. With this purpose, discs of stainless steel were incubated in 30 ml of Ringers solution in a humidified 5% CO2 atmosphere at 37C. To prevent bacterial contamination, this solution has been sterilized in an autoclave and samples exposed to UV radiation. Solution released ions were analyzed at regular intervals 24 h during 4 days. At each time interval, 23 ml of each solution was replaced by fresh solution aimed at similar blood that occurs in human body renewal process. This experimental setup was proposed by Yamamoto and Hiromoto [1], adapted to data given by Guyton and Hall [2]. The in vitro biocompatibilitiy of the samples was studied by using human mesenchymal stem cells from bone marrow (hMSCs). To evaluate cell attachment and proliferation, cells were cultured in growth medium on polished and both rough stainless steel 316 LVM surfaces. In order to study the ability of the surfaces to promote osteogenic maturation, cells were switched to the osteoblastic phenotype by incubation in osteogenic induction media and mineralized nodule formation was evaluated by means of Alizarin red staining. Results and discussion EIS show that the highest values of the impedance correspond to the polished specimens and the lowest to the alumina blasted specimens, thus a decrease in the corrosion resistance of the steel following grit blasting is envisaged. Implications of the larger area increase following blasting are not enough to explain this different behaviour and subsurface blasting-induced effects, playing a beneficial or detrimental role, will be discussed. Interestingly, impedance values increases with increasing the immersion time in Ringers solution, despite the high concentration of Cl- ions of this medium, which denotes an improvement of the corrosion protection likely due an increase in the thickness of the passive film in all the tested samples. Ion release rises for the blasted conditions and it could be partially related to the area increase. Finally, biocompatibility tests suggest that increases in surface roughness of stainless steel 316 LVM through blasting processes slow down the adhesion processes cells hMSCs to the material and the proliferation of those. That effect is most pronounced in areas with a higher degree of roughness. However, these topographical changes do not interfere with the maturation ability of hMSCs cells towards osteogenic lineage, which corroborates the usefulness of these materials for implant surgical. Acknowledgements This work was supported by the Ministry of Science and Innovation of Spain, MICINN (MAT2009-14695-C04-02, -04 and IPT-020000-2010-0001 Projects). References 1. A. Yamamoto, S. Hiromoto, Mater. Sci. Eng. C-Biomimetic Supramol. Syst. 29[5] (2009) 1559-1568. 2. A.C. Guyton, J.E. Hall, Textbook of Medical Physiology (11th edition), Elsevier Saunders, Philadelphia, PA (2006).

Abstract #1088, 219th ECS Meeting, 2011 The Electrochemical Society

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