• Nu S-Au Găsit Rezultate

ELECTROCHEMICAL STUDY ON CORROSION RESISTANCE IN PHYSIOLOGICAL MEDIA OF NITINOL WIRE USED AS BIOIMPLANT

N/A
N/A
Protected

Academic year: 2022

Share "ELECTROCHEMICAL STUDY ON CORROSION RESISTANCE IN PHYSIOLOGICAL MEDIA OF NITINOL WIRE USED AS BIOIMPLANT "

Copied!
7
0
0

Text complet

(1)

ELECTROCHEMICAL STUDY ON CORROSION RESISTANCE IN PHYSIOLOGICAL MEDIA OF NITINOL WIRE USED AS BIOIMPLANT

DANIELA TARNITAa, DAN TARNITAb, BOGDAN OPREAc, ADRIANA SAMIDEd*

aUniversity of Craiova, Faculty of Mechanics, Department of Applied Mechanics, Calea Bucuresti 107, Craiova, Romania

bUniversity of Medicine and Pharmacy, Department of Orthopedics Surgery, Craiova, Romania

cUniversity of Medicine and Pharmacy, Department of Morphological Sciences, Petru Rares 2, Craiova, Romania

dniversity of Craiova, Faculty of Sciences, Department of Chemistry, Calea Bucuresti 107i, Craiova, Rmania

The characterization of Nitinol (NiTi) wire corroded in some physiological media is discussed according to electrochemical measurements, such as: potentiodinamic curves, Tafel polarization and polarization resistance technique. The morphology of the surface was examined using microscopic images. All the experimental data show that the physiological serum (PS) has a more pronounced corrosive character as compared to 5 % glucose solution and 10 % Aminosteril solution. The results obtained through polarization curves indicate that the potential of corrosion in pitting (Ecp) decrease from 1045 mV in aminosteril to 440 mV in glucose and 216 mV in physiological serum. Moreover, for the NiTi tested in Aminosteril, corrosion current density (icorr) significantly decreases and polarization resistance (Rp) increases in a considerable manner as compared to their values which were obtained in PS and glucose. These results were discussed according to the formation of passive films; their stability strongly depends on the corrosive action of the artificial physiological media in the order: Physiological serum (PS) < 5% Glucose solution <<10 % Aminosteril solution.

(Received October 23, 2012; Accepted December 18, 2012) Keywords: nitinol; electrochemical; bioimplant

1. Introduction

The corrosion of bioimplants implies the interaction between an implant (a metal or an alloy) and the physiological medium, and is influenced both by the metal properties and the environment. From a thermodynamic and kinetic point of view, the theory of corrosion in liquid mediums implies the principles of electrochemistry, of diffusion and dissolution. Various forms of corrosion are met which can be appreciated and interpreted depending on certain factors such as:

the pH of the medium, the nature of the bioimplant and temperature [1-12].

As a result of the electrochemical reactions on the metallic surface, certain elements in the alloy pass from the metallic form into an ionic form [6-12]. These materials must be biocompatible and resistant to biological fluids. They must not produce adverse reactions in the human body and must not degrade while being used [1-6].

Nitinol (Nickel Titanium Naval Ordinance Laboratory) is an alloy of an almost equal mixture of nickel and titanium. It was invented in the late 1960s and it belongs to a group of materials referred to as “smart materials” because of their unique physical properties that make

*Corresponding author: [email protected]

(2)

Nitinol so remarkable: shape-memory and super-elasticity. The most important shape memory alloy used in biomedical applications, Nitinol is able to fulfill functional requirements related not only to their mechanical reliability, but also to its chemical reliability and its biological reliability [13,14]. Nitinol offers the possibility of designing and fabricating orthopaedic implants with great advantages such as high biocompatibility, superelasticity, the memory shape effect, resistance to corrosion and wear, resistance to torsion, invariable stress effects, dynamic interference, fatigue resistance and MRI compatibility. Nitinol's extraordinary ability to accommodate large strains, fatigue life and the ability to be electrically heated for shape recovery coupled with its physiological and chemical compatibility with the human body have made it one of the most commonly used materials in medical device engineering and design. In the last years, NiTi technology has contributed to significant improvements in orthopaedics and orthodontics. Its use is now overcoming the limits in designing smaller, more efficient minimally invasive tools and devices [13-20].

NiTi applications in orthopedics currently include internal fixation by the use of fixatives, compression bone stables used in osteotomy and fracture fixation, rods for the correction of scoliosis, shape memory expansion staples used in cervical surgery, staples in small bone surgery, and fixation systems for suturing tissue in minimal invasive surgery [13-20].

Although several studies have demonstrated the good corrosion resistance and biocompatibility of NiTi, the high nickel content of the alloy (55 weight % Ni) and its possible dissolution by corrosion still remains a concern [19, 20]. Tissues in the human body contain water, dissolved oxygen, proteins and various ions, such as chloride and hydroxide, and they present an aggressive environment to metals or alloys used for implantation [21, 22]. Corrosion resistance of a metallic implant is thus an important aspect of its biocompatibility [21]. In addition to the release of ions in the physiological environment, the corrosion process will also result in the deterioration of dimensional parameters of the corroding body. NiTi corrosion behaviour can be significantly improved after specific surface treatments such as electropolishing.

In this study the behavior of Nitinol (NiTi) in physiological serum (PS), glucose and aminosteril solutions is discussed according to electrochemical measurements and microscopic images related to morphology of surfaces before and after corrosion tests.

2. Experimental

The Nitinol used had the following composition (wt. %): 50 % Ni and 50 % Ti. Before corrosion the samples were degreased with acetone and dried. Physiological serum (0.9 % NaCl), 5 % glucose and 10 % aminosteril were used as aggressive media for corrosion tests. All the mentioned solutions were bought from pharmacy, being used as perfusion solutions in medical treatment. The composition of 10 % Aminosteril containing amino acids and other electrolytes is shown in Table 1.

For electrochemical measurements a standard cell has been used with a working electrode (surface 0.314 cm2) made of NiTi wire, a platinum auxiliary electrode (surface 1 cm2) and a Ag/AgCl reference electrode. The electrode made of NiTi was polished with metalographic paper, washed in distilled water, degreased in acetone and dried in warm air. The potentiodinamic polarization was conducted with a scan rate of 1 mV.s-1, in an electrochemical system, VoltaLab 40, with a personal computer and VoltaMaster 4 software. The immersion time of the plates in the respective media was 4 minutes in open circuit, at room temperature.

The morphology of the Nitinol surface before and after treatment in the above mentioned solutions was examined using a metallographic microscope Euromex, with Canon camera and included software.

(3)

Table 1. Composition of 10 % Aminosteril solution.

Electrolyte Concentration (g/L) L-isoleucine

L-leucine L-lysine L-lysine

(monohydrochloride) L-methionine

L-phenylalanine L-threonine L-thryptophan L-valine L-arginine L-histidine L-alanine L-proline L-malic acid Glycine NaOH KCl KOH 85%

MgCl2.6H2O

4.67 7.06 5.97 7.46 4.10 4.82 4.21 1.82 5.92 10.64

2.88 15.00 15.00 8.08 15.95 1.200 0.683 0.716 1.017

3. Results and discussion Potentiodynamic curves

The polarization curves of Nitinol in physiological serum (PS) and glucose are presented in Fig.1a. The study of the response given by Nitinol polarization in physiological serum (PS) and glucose solutions, simulating the body fluid conditions indicate that the critical potential in pitting (Ecp) is shifted to higher value, when the corrosion process of Nitinol carried out in glucose. It has also been observed that the critical potential in pitting (Ecp) decreases from 440 mV in glucose to 216 mV in physiological serum. Polarization curve of nitinol in aminosteril solution is shown in Fig.1b. Note that, in this case, the corrosion process occurs at low current densities, of the order of microamps, and Ecp reaches a high value of 1045 mV. Thus, we can say that in aminosteril, Nitinol corrosion occurs more slowly than in PS or glucose. This can be explained according to the composition of aminosteril solution, which contains aminoacids and bases (NaOH and KOH) that favor spontaneous passivation of nitinol, up to a potential of 1045 mV.

(4)

Fig. 1. Potentiodynamic curves of NiTi obtained in different artificial physiological media:

a – physiological serum (PS) and glucose solutions; b – aminosteril solution

Tafel polarization

Corrosion currents (icorr) were calculated by extrapolation of anodic and cathodic Tafel lines to the corrosion potential (see Fig.2, Tafel Diagram).

The polarization curves presented in Fig.2 show that:

(i) for NiTi corroded in glucose solution, the corrosion potential (Ecorr) was shifted in the positive direction; (ii) to the potential of -270 mV, the anodic process of NiTi corroded in glucose solution is significantly modified than that of nitinol corroded in PS; (iii) from

-270 mV to the critical pitting potential (Ecp), anodic polarization curves overlap, indicating in both cases, the formation of passive film on the surface; over Ecp, NiTi becomes active, indicating the beginning of passive film destruction, this phenomenon being more pronounced in PS; (iv) from Fig.2 it can be seen that the polarization curves of nitinol in aminosteril solution were shifted in the area of very low currents, less than 50 μA, as compared to those of nitinol corroded in PS or glucose; this can be associated with a significant decrease of corrosion current.

The corrosion currents (μA cm-2) were obtained using VoltaMaster 4 software and these are presented in Fig.4.

Fig. 2. Tafel diagram of NiTi coroded in various artificial physiological media a

0 1 2 3

-0.5 0 0.5 1

E ( V vs. Ag / AgCl ) i ( mA / cm2 )

Nitinol / PS nitinol / glucose

b

0 4 8 12 16 20

-0.5 0.5 1.5 2.5 3.5

E (V vs.Ag/AgCl) i (μA cm-2 )

Nitinol / Aminosteril

-4 -3 -2 -1 0 1 2 3

-1.5 -0.5 0.5 1.5

E (V vs.Ag/AgCl) log i (mA cm-2 )

-2 -1 0 1 2 3

log i (μA cm-2 ) Nitinol / PS

Nitinol / glucose Aminosteril

(5)

Polarization resistance technique

Using the polarization resistance technique the corrosion resistance of NiTi was evaluated in this media simulating body fluids. Various composition of environments (Clions, glucose and aminoacids) affected the corrosion resistance of NiTi. The results showed that the aminosteril solution is the least corrosive medium for Nitinol, and because of high Cl ions content, PS is the most corrosive one. The polarization curves obtained in the potential ranges near to corrosion potentials were recorded with a scan rate of 1 mV s-1. The linearization was accomplished in the domain of over-voltages values ± 10 mV (Fig.3). The slopes (di/dE) E→Ecorr of the lines from Fig.3 represent the polarization conductance. Polarization resistances (Rp - Ω cm2) were calculated using relation 1 and these are presented in Fig.4.

corr p

E E

di 1

dE

R

  

 

 

(1)

Fig. 3. Potentiodynamic curves near Ecorr of NiTi obtained in different artificial physiological media: a – physiological serum (PS) and glucose solutions;

b – aminosteril solution

Fig. 4. The numerical values of corrosion currents and polarization resistances obtained for NiTi in different artificial physiological media

From Fig.4 it can be seen that for NiTi corroded in aminosteril, high polarization resistance was obtained, as compared to NiTi corroded in PS and glucose. This is probably due to

a y = 3.3576x + 2504.1 R2 = 0.9961

y = 1.3968x + 663.08 R2 = 0.9995

-200 -100 0 100

-800 -700 -600 -500 -400 -300

E (mV vs.Ag/AgCl)

i (μA cm-2 ) Nitinol / PS

Nitinol /glucose b

y = 0.0848x + 46.571 R2 = 0.9962

-20 -10 0 10 20

-800 -700 -600 -500 -400

E (mV vs.Ag/AgCl) i (mA cm-2 )

Nitinol / Aminosteril

0 10 20 30 40 50

i (μA cm -2 )

0 4000 8000 12000

Rp ( cm 2 ) icorr

Rp

icorr 43.2 17.9 1.09

Rp 297 715 11792

PS glucose aminosteril

(6)

the inh solutio films f aminos

tested passiva before are pre small d

eviden sugges of gluc PS, bu bonds desorp layer i and inh

observ in ami be reac used a and po were o

hibitory actio on, forming a formed in PS steril confirm

Surface m The electr using the m ation on the (Fig.5a) and esented. Unc

defects (Fig.

Fig. 5. Mi physiolog The result nce of corros sting that the cose the mic ut a non-unifo

such as hy ption is facil is evidenced

hibitory effe 4. Concl While cor ved that the u It has also nosteril to 4 ched in the h s a bioimplan In case of olarization re obtained in P

on of variou a surface la S and glucose ms that a very morfology

rochemically microscopic im

corroded ele d after corro corroded sam

5a).

icroscopic ima gical serum; c ts of micro sion spots, w e passive film crograph show form passive ydrogen bon itated and th

in Fig.5d. p ct of amino a lusions rrelating the used physiolo been observ 40 mV in gl human body nt with no m f Niti corrod

esistance inc PS and gluco

us aminosteri ayer with bet e. The corros y slowly atta

-corroded N mages, whic ectrode in th osion in PS ( mple did not s

ages of NiTi su c – after corro

scopy for c which affect m formed on

w evidence o film is nuan ding interac he passive fi providing a g

acids gives to

data obtain ogical serum ved that the p

lucose and 2 under norm major risks.

ed in amino reases in a c ose. In this re

il componen tter adheranc sion current ack of amino

NiTi samples ch indicate th hese solution (Fig.5b), in g show any par

urface: a – be osion in glucos corroded sam t the NiTi su n the surface

of corrosion nced. Glucose

ctions, sugge film is partia good passiva o NiTi high

ned by the u m has a quite h potential of c 216 mV in ph mal condition

osteril, corros considerable egard, when

nts. Thus, Ni ce and stabil (icorr) value o oacids occure

s in PS, gluc he formation ns. The micro

glucose (Fig.

rticular featu

efore corrosio se; d – after c mple in phy urface. Corr e was extens n spots less in

e interacts w esting that a ally destroye

ation of NiT corrosion res

used electro high corrosiv corrosion in hysiological ns, thus the m

sion current manner as c the Nitinol

iTi is passiv lity as comp of 1.09 μA o ed.

cose and am of superfici oscopic imag .5c) and in a ure in micros

n; b – after co corrosion in am

ysiological rosion spots

ively damag ntense than t with NiTi surf at high pote d. The form Ti surface. To

sistance in am

chemical me ve action.

pitting decre serum. Thes material we h density sign compared to is immersed

vated in amin pared to the

obtained for

minosteril we ial film prov ges of NiTi aminosteril ( scopic imagin

orrosion in minosteril

serum (PS) are much n ged. In the pr

those was sh face sites, vi entials, the g mation of a u

ogether, ads minosteril.

methods it ha ease from 10 se potentials have studied nificantly de their values d in PS soluti

nosteril passive NiTi in

ere also viding a surface Fig.5d) ng than

, show nuanced

resence hown in a labile glucose uniform sorption

as been 045 mV

cannot can be ecreases s which ion, the

(7)

surface layer is not stable and the composition can be changed by incorporation of ions and molecules.

The results of microscopy for corroded sample in PS, show evidence of corrosion spots, and the formation of a non-uniform film on the Nitinol surface was observed. In the presence of glucose corrosion spots have a lower intensity, but passive film has an irregularly distribution on the surface. On microscopic image of NiTi corroded in aminosteril is observed a passive film which has an uniform distribution on the surface. The composition of passive film and inhibitory effect of amino acids provide a very high corrosion resistance of NiTi in aminosteril.

As a general conclusion, in this study, the results were discussed according to the formation of passive films; their stability strongly depends on the corrosive action of the artificial physiological media in the order: Physiological serum (PS) < 5% Glucose solution <<10 % Aminosteril solution.

References

[1] T. Hanawa, Corr. Eng. 49, 687 (2000).

[2] T. Hanawa, Sci. and Tech. Adv. Mat. 3, 289 (2002).

[3] T. Hanawa, K. Asami, K. Asaoka, J. Biomed. Mater. Res. 40, 530 (1998).

[4] T. Hanawa, S. Hiromoto, A. Yamamoto, N. Maruyama, K. Nakazawa, Min. Met. & Mat.

Soc. 39, 145 (2001).

[5] T. Hanawa, Rec. Res. Dev. Biomat. 37, 11 (2002).

[6] A. Samide, C. Negrila, A. Ciuciu, Digest J. Nanomaer. Biostruct. 5, 1001 (2010).

[7] A. Samide, I. Bibicu, B. Oprea, N. Cioatera, A. Ciuciu, J. Optoelectron. Adv. Mater.

10, 1431 (2008).

[8] I. Bibicu, A. Samide, B. Oprea, B. Tutunaru, J. Optoelectron. Adv.Mat. 10, 2156 (2008).

[9] B. Tutunaru, A. Samide, I. Bibicu, M. Preda, J. Optoelectron. Adv. Mat. 11, 3400 (2007).

[10] B. Tutunaru, A. Samide, M. Preda, Rev. Chim. 55, 757 (2004).

[11] B.Tutunaru, A. Samide, M. Preda, Rev. Chim. 58, 927 (2007).

[12] B. Tutunaru, A. Samide, M. Preda, Preda, Rev. Chim. 56, 934 (2005).

[13] R. Venugopalan, C. Trépanier, Min. Invas. Ther & Allied Technol. 9, 67 (2000).

[14] S. Lu, Medical applications of Ni–Ti in China. Engineering aspects of shape memory alloys.

Jordan Hill, Oxford: Butterworth-Heinemann (1990).

[15] J. Haasters, G. Salis-Solio, G. Bonsmann, The use of Ni–Ti as an implant material in orthopedics. Engineering aspects of shape memory alloys. Jordan Hill, Oxford: Butterworth- Heinemann (1990).

[16] T. G. Frank, W. Xu, A. Cuschieri, Shape memory applications in minimal access surgery-the Dundee experience. Proceedings 2nd International Conference on Shape Memory and

Superelastic Technologies, 509 (1997).

[17] D. Tarnita, D. Bolcu, C. Berceanu, F. Cismaru, J. Optoelectron. Adv. Mater. 12, 2323 (2010).

[18] D. Tarnita, D.N. Tarnita, N. Bizdoaca, I. Mindrila, I, Vasilescu, Rom. J. Morph. Embr.

50, 15 (2009).

[19] D. Tarnita, D. N. Tarnita, R. Tarnita, C. Berceanu, F. Cismaru, Mater. Sci. Eng. Tech. Special Edition Biomaterials, 40, 1 (2009).

[20] S . A. Shabalovskaya, J. Bio. Med. Mater. Res. 6, 297 (1996).

[21] J. Ryhänen, M. Kalliomen, W. Serlo W et al. Bone healing and mineralization, implant corrosion and trace metals after nickel–titanium shape memory metal intramedullary fixation.

J. Bone Mineral Res. (in press).

[22] L. L. Shrier, R.A. Jarman, O. T. Burstein, Corrosion–metal/environment reactions. 3rd edn.

Jordan Hill, Oxford: Butterworth-Heinemann, (1995).

Referințe

DOCUMENTE SIMILARE

rnetric sþacets X^rbsþectiael,y Y are-NS-isomorþkic, tken the corresþond'ing quoti,ent sþaces læ ønd, lo øre homeomorþhic.. Rernarh

For the quasioperations the interval arithmetic is not inclusion mono- tonic.. \Miss' Berlin ected with inversability of complex ervals) is the scope of the

The Magnetoresistance effect is caused by the double exchange action between Mn 3+ and Mn 4+ ions [13] , The magnetoresistance peak value M RP of reduced samples B2-B4

The corrosion characteristic of CuZn coated AZ91 alloy shifts slowly to the anodic region which is attributed that this shifting is evidence in the forming of a thin high

Instead for the cyclic voltammograms of both types of truffles recorded on the nickel electrode in both reaction media, a reversible process can be noticed in which the anodic

In order to improve mechanical properties of hip prostheses, these have been coated with different materials, which have superior properties. In order to improve mechanical

Identity is thus constructed in interaction, which means that out of a whole host of potential identity features, those features become salient which permit a differentiation of

Key words: Christian philosophy, Catholicism, Protestantism, Orthodoxy, Russian Religious Philosophy, theology, unitotality, apophatics.. Vladimir