BIOMATERIALS IN IMPLANTS_030400_030457_031013.pptx

Biomaterials used

1. BIOMATERIALS IN IMPLANTS INTRODUCTION; IN 1992, Brane mark developed a threaded implant design made of pure titanium that showed direct contact with the bone. Hence forth popularity of implants reached new heights. Currently the implant materials available are diverse. Success and longevity of implants depends on the 4 B’s Biomaterial Biomechanics Biological tissue Body serviceability. NOTE : A biomaterial is any substance other than drugs that can be used for any period of time as part of a system that treats, augments, or replaces any tissue, organ or function of the body.

2. Classification of Implant Biomaterials Metal and Metal alloys These include; Titanium Titanium alloys Cobalt, chromium, molybdenum alloy Austenitic steel and surgical steel Precious metals (Gold, platinum, palladium) Iron, chromium, nickel alloy

3. 2. Ceramic s and carbon These include; Aluminum oxide (alumina, sapphire) Zirconium oxide Titanium oxide Calcium phosphate ceramics Glass ceramic 3. Polymers Poly methyl metha acrylate (PMMA) Poly tetra fluoro ethylene (PTFE) Poly ethylene terapthylate (Dacron) Poly sulphone.

4. 4. Composites These are a combination or polymers and other synthetic biomaterials; they include: Carbon – PTFE Carbon – PMMA Alumina - PTFE

5. BIOLOGICAL CLASSIFICATION Biomaterials are classified basing on tissue response; Bio tolerant; polymers (Fibrous tissue encapsulation at implant interface) Bio inert e.g. Titanium, titanium alloy, alumina, and zirconium Bio active e.g. Glass ceramics, (direct chemical bonding of implant with surrounding bone).

6. Requirement for ideal implant material Any material intended for use as an implant must meet 2 basic criteria; Biocompatibility with living tissue Bio functionality with regard to force transfer.

7. Properties of implants Implant properties can be categorized into two major categories; Bulk properties Surface properties BULK PROPERTIES; Modulus of elasticity; measure of change in dimension (stain) with respect to stress. Tensile, compressive, shear, strength. An implant material should have high tensile, compressive, shear strength to fractures and improve function stability. Yield and fatigue strength; yield strength is the magnitude of stress at which a material shows initial permanent deformation. Fatigue strength is the stress at which a material fractures under repeatitive loading. An implant should have high yield strength and fatigue strength to prevent brittle fracture.

8. . Ductility, refers to relative ability of a material to deform plasticity under the tensile stress before it fractures. Hardness and toughness, amount of energy required to cause fracture, increased toughness prevents fracture of the implants. Electrical & thermal conductivity, should be minimum to prevent thermal expansion, contraction and oral galvanism.

9. Surface properties Surface tension and surface energy, this determines the wettability of implant by wetting fluid (blood) and cleanliness of implant surface. Biocompatibility, ability of a material to perform with an appropriate biological response with a specific application. It depends on, corrosion resistance and cytotoxicity of corrosion product Corrosion resistance: This is the deterioration of a material cause by reaction with its environment. Types include; stress corrosion; failure by cracking due to stress. Fretting corrosion; due to micro motion or rubbing contact within the corrosive environment. Crevice corrosion; occurs in narrow region e.g. implant screw bone interface. Pitting corrosion; occurs in surface pit, metal ions dissolve and combine with Cl ions. Galvanic corrosion, occurs between 2 dissimilar metals in contact within an electrolyte resulting in current flow. Electrochemical corrosion; in this anodic oxidation and cathodic reduction takes place resulting in metal deterioration as well as charge transfer via electrons.

10. Cytotoxicity of corrosion Toxicity of implant materials depends on toxicity of corrosion products which depends on; Amount of corroded material dissolved by corrosion per unit time. Amount of corroded material removed by metabolic activity in the same unit time. Amount of corrosion particles deposited in the tissue. NOTE : Both increased corrosion and resistance and decreased toxicity of corrosion products contribute to biocompatibility.

11. BIOMATERIALS What are the properties of the following biomaterials? Titanium Titanium alloys Cobalt, chromium, molybdenum alloy Iron chromium, Nickel based alloy Precious metals Ceramics Bio inert ceramics Bio active ceramics Polymers

12. Surface characterization & preparation of implants Passivation ; refers to enhancement and stabilization of oxide layer to prevent corrosion. Performed by immersion in 40% nitric acid. Used for CoCr implant. Acid etching ; in this the surface is treated with nitric or hydrofluoric acid. Results in clean surface with roughened texture for increased tissue adhesion. Sand blasting ; sand particles are used to get a roughened surface texture with Increases surface area Increased attachment strength at bone implant interface.