Corrosion Behavior of Coated and Uncoated Bio Implants in SBF (Simulated Body Fluid)'.
Summary: Surgical implants used in medical applications are basically the specific type of stainless steel materials. Stainless steelhas been used widely and successfully for various types of trauma and orthopedic reconstructions. If an uncoated (bare) stainless steel metal piece is implanted in any part of the body, it will get corrode in Simulated Body Fluid (SBF) present inside the human body (a mixture of different salts). To overcome this problem a coating of Titanium Nitride (TiN) was developed on stainless steel bio-implants using physical vapor deposition (PVD) method. Both coated and uncoated implants were kept dipped in Simulated Body Fluid for five months. The samples were removed and tested for corrosion life assessment after every fifteen days using weight loss method.
Keywords: Simulated Body Fluid, Titanium Nitride, Chromium oxide, Corrosion.
In human body a large number of chemical reactions occurring continuously to sustain its viability. These chemical reactions produce an abundance of oxidizing agents, which creates an unfriendly environment for metals and alloys. Even the most corrosion-resistant materials are not immune to the forces of nature and undergo some degree of corrosion . Some metals like stainless steel may decay at a finite rate, whereas others like gold and platinum are extremely corrosion-resistant. During the corrosion process, a coupled oxidation-reduction reaction takes place, in which one species gains electrons (oxidizing agent) while the other donates electrons (reducing agent). This reaction occurs spontaneously when energy is released by the reaction. Most implanted metals, such as titanium, cobalt-chromium, and stainless steels, have a tendency to lose electrons in solution, and as a result, they have a high potential to corrode [2, 3].
The result is dissolution of the metal and formation of metallic ions. Metal implants have become essential biomedical therapeutic tools in a variety of treatments. Metal implants are composed of a variety of metals, depending on function and location. Medical grade stainless steel, chromium-cobalt and titanium alloys are the most frequently used materials. Aluminum, chromium, cobalt, iron, manganese, molybdenum, nickel, titanium, vanadium and zirconium are the most frequent metals used for metal implants . There are various applications for metal implants, including vascular and digestive stunts, internal fracture treatments, face and dental surgery, and orthopedic joint replacements . Under macroscopic observation, human tissue may appear to be chemically inert; however, at the molecular level, human tissue is a dynamic environment for immersed metals. Metals implanted into this saline environment inevitably undergo corrosion.
The degradation of these metals can produce harmful effects both locally and systemically within the human body . Significant developments have been taking place to provide suitable biomaterials from metals/ alloys, ceramics bio-glasses, and polymers with minimal reaction and rejection by body [7-9]. The most corrosion resistant of the implant materials presently employed is titanium and its alloys. Various methods have been used to evaluate the corrosion resistance of implant materials in the laboratory involving either qualitative measurements of implantation of devices into experimental animals (in vivo) or quantitative electrochemical measurements in simulated body fluid (in vitro) or a combination of both where qualitative and quantitative corrosion measurements of implants are made in vivo . The electrochemical evaluations were performed to investigate the corrosion behavior of SS-304 uncoated and coated by 45S5 bioglass using melting and sol-gel techniques .
To achieve this purpose, the samples were dipped in SBF (as electrolyte) at 37+-1 degC (the body temperature). The bioactivity of the metallic implants made of 304 SS coated by 45S5 bioactive-glass layers was investigated by imprisoning in SBF solution. The coated specimens were immersed in 100 ml of SBF for 14 days in an incubator at 37 degC. These samples were then brought out from the incubator and desiccated at room temperature . In present study the Titanium nitride coatings on stainless steel implants were investigated for corrosion in prepared composition of Simulated Body Fluid and compared with uncoated implants.
Results and Discussion
Several types of stainless steels are commercially available. Although in practice the most common is 316L (ASTM F138, F139) . Stainless steel 316L has the following composition Fe (balance), less than 0.03% C, 16-18.5% Cr, 10-14% Ni, 2-3% Mo, less than 2% Mn, less than 1% Si, less than 0.045% P, less than 0.03% S.
In SBF both coated and uncoated bio implants exhibit different type of behaviors. The coated samples showed an enhanced corrosion resistance in comparison with un-coated ones .
For Coated Implants
Initial weights of the implants were: Implant A = 3.53 g
Implant B = 2.63 g
Implant C = 2.79 g
Table-1: Table showing variation in weight for TiNcoated bio implants.###
Weight of A
Weight of B
Weight of C
In coated bio implants no surface corrosion was observed throughout the study because the titanium nitride coating provides an extra protective layer. The results showed very little variations in weight in case of TiN coated implants (Fig. 1).
For Uncoated Implants
Initial weights of the implants were: Implant D = 3.29 g Implant E = 3.16 g
The corrosion behavior of various implants and the role of the surface oxide film to avoid corrosion are discussed. Surface modification of implants by coating is considered to be the best solution to combat corrosion and to enhance the life span of the implants .
The results showed that the uncoated implants were readily corroded in the Simulated body fluid (SBF) as compared to the TiN coated implants. This is due to the fact that the TiN coated implants offer good corrosion resistance for bio implant as compared to uncoated implants.
It forms an adherent protective layer (TiO2) and remains passive under physiological conditions. Titanium implants remained virtually unchanged in appearance and offered better corrosion resistance.
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|Author:||Iqbal, Waqas; Zahra, Naseem; Alam, Shahzad; Habib, Farzana; Irfan, Muhammad|
|Publication:||Journal of the Chemical Society of Pakistan|
|Date:||Jun 30, 2013|
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