CORROSION RESISTANCE OF METALLIC BIOMATERIALS IN SIMULATED BODY FLUIDS

The field of biomaterials is of immense importance for the mankind as the very existence and longevity of some of the less fortunate human beings. The field of biomaterials is not new and as early as 4000 years back the Egyptians and Romans have used linen for sutures, gold and iron for dental applications and wood for toe replacement but with very little knowledge about the problem of corrosion. Currently, the availability of better diagnostic tools and advancements in the knowledge on materials as well as on surgical procedures, implantology has assumed greater significance and bioimplants are commonly used in dentistry, orthopedics, plastic and reconstructive surgery, ophthalmology, cardiovascular surgery, neurosurgery, immunology, histopathology, experimental surgery, and veterinary medicine. Various classes of materials such as metals, alloys, polymers ceramics and composites have been widely used to fabricate the bioimplants. These implants encounter different biological environments of very different physico-chemical nature and their interaction with the tissues and bones is a complex problem. Corrosion, the steady degradation of materials by electrochemical attack is of great concern particularly when a metallic implant is placed in the aggressive electrolytic environment of the human body. The implants face severe corrosion environment which includes blood and other constituents of the body fluid which encompass several constituents like water, sodium, chlorine, proteins, plasma, amino acids along with mucin in the case of saliva .The aqueous medium in the human body consists of various anions such as chloride, phosphate, and bicarbonate ions, cations like Na+ , K+ , Ca2+, Mg2+ etc., organic substances of low-molecular-weight species as well as relatively high molecular-weight polymeric components, and dissolved oxygen . The biological molecules upset the equilibrium of the corrosion reactions of the implant by consuming the products due to anodic or cathodic reaction. Proteins can bind themselves to metal ions and transport them away from the implant surface upsetting the equilibrium across the surface double layer that is formed by the electrons on the surface and excess cations in the solution.