Untitled Quiz

Role of Implant Biomaterials

• Implants are used to recover physical function, specifically mechanical function, of tissues or organs.
• Implants are designed to provide physical support, but they do not have other biological functions.

General Mechanical Properties

• Implant biomaterials are subjected to complex mechanical environments in the body.
• Common mechanical properties include Young's modulus, yield strength, ultimate tensile strength, fracture toughness, and elongation at break.
• Young's modulus is determined by the chemical bonding of atoms and molecules and is important for predicting how a material will respond to stress.
• Other mechanical properties such as yield strength, ultimate tensile strength, fracture toughness, and elongation at break are all influenced by the microstructure of the material.

Elasticity, Resilience, and Hardness

• Elasticity refers to a material's ability to return to its original shape after deformation.
• Resilience refers to the amount of energy a material can store during elastic deformation.
• Hardness is a measure of the material’s resistance to wear and friction, which is often measured using the Rockwell or Brinnell hardness tests.

Failure

• It's critical to understand the reasons behind material failure to ensure safe and effective biomaterial use.
• The fracture mechanism depends on the working conditions and can be influenced by fatigue, stress corrosion cracking, or a combination of both.
• Fatigue occurs when a material undergoes repeated stress cycles, which can lead to progressive structural damage.
• Stress Corrosion Cracking is a sudden brittle fracture of normally ductile materials when exposed to tensile stress in a corrosive environment.

Essential Properties for Orthopedic Implants

• Orthopedic implants must possess specific characteristics to function safely and successfully at load-bearing sites:
  • No Toxicity: This is synonymous with excellent corrosion resistance.
  • Suitable Mechanical Strength: The implant must be strong enough to withstand the forces experienced in the body.
  • High Wear Resistance: This prevents wear particles from causing inflammation and loosening of the implant.
  • Osseo-integration Ability: The implant must be able to bond with surrounding bone to prevent implant loosening.

Mechanical Working Environments of Implants

• Fatigue: A common problem for orthopedic implants. Cyclic loading during activities like walking or running can lead to fatigue.
• Fretting Fatigue and Corrosion Fretting Fatigue: Occur due to the combination of cyclic stress and friction in the implant's working environment.
  • Fretting Fatigue: Occurs when a foreign body is pressed against a material undergoing cyclic stress, producing oxide debris causing microscopic cracks at the contact site.
  • Corrosion Fatigue: A combination of fatigue and corrosion.

Wear of Joints

• Wear is an inevitable problem in joint replacements, leading to aseptic loosening.
• Wear particles attract macrophages, which engulf the particles and release enzymes and metabolites that damage the implant.

Osseo-Integration

• Osseo-integration is the ability for an implant to bond to surrounding bone, essential for the longevity of permanent orthopedic implants.
• Failure to osseo-integrate can lead to fibrous tissue formation around the implant, promoting loosening.
• Factors such as surface chemistry, roughness, and topography influence osseo-integration.

Conclusion

• The internal environment in the body is harsh for metallic materials, highlighting the need for biomaterial design that addresses mechanical and chemical challenges.