Medical and Bioengineering

The applications of alumina (Al₂O₃), zirconia (ZrO₂), silicon carbide (SiC), and silicon nitride (Si₃N₄) in medicine and bioengineering fully demonstrate the exceptional performance of advanced ceramics as biomaterials.

These materials are favored in the medical field due to their shared unique advantages:

1. Excellent biocompatibility: This is paramount. They do not cause significant immune rejection, toxicity, or inflammatory reactions when in contact with human tissue, blood, and body fluids, and can safely exist in the human body for long periods of time.

2. Excellent mechanical properties:

• High hardness and wear resistance: These significantly reduce the generation of implant wear debris, which is key to the success of joint implants.
• High compressive strength: These materials can withstand the immense loads generated by human activity.

3. Extremely high chemical inertness: They are resistant to acids, alkalis, and corrosion, and are extremely stable in the complex physiological environment of the body. They do not degrade or release harmful ions, resulting in an extremely long service life.

4. Hydrophilicity and lubricity: The surface of some ceramics (such as alumina) can form a liquid film with liquid, with an extremely low friction coefficient, which is very suitable for joint interfaces.

Although all four materials are ceramics, their application depth and focus in the medical field vary.
1. Alumina (Al₂O₃)

• Alumina is the earliest, most classic, and most widely used bioceramic, particularly as a material for the ball heads of hip prostheses.
• Advantages: Extremely high hardness, excellent wear resistance, good biocompatibility, and a long history of clinical success.
• Specific applications: Artificial hip and knee joints, dental implants, bone screws, and intermediate components.

2. Zirconia (ZrO₂)

• ZrO₂, through phase transformation toughening, has a fracture toughness far superior to that of alumina, defying the perception of ceramics as "brittle." Advantages: Extremely high fracture toughness and flexural strength (closest to metal), wear resistance, excellent aesthetics (color and transparency similar to natural teeth), and biocompatibility.
• Specific Applications: Dental restorations, artificial hip joints, and femoral head bearings.

3. Silicon Nitride (Si₃N₄)

• Silicon nitride is an emerging bioceramic with great potential, boasting several properties considered superior to traditional materials.
• Advantages: Bone-like friction properties (facilitating osseointegration), osteogenic properties (promoting bone growth), excellent infection resistance (surface structure inhibits bacterial adhesion), visibility (no artifacts in X-rays and CT scans, facilitating postoperative observation), high strength and toughness.
• Specific Applications: Spinal fusion cages (this is the most revolutionary application of silicon nitride), bone graft substitutes, and small joint replacements.

4. Silicon Carbide (SiC)

• Silicon carbide's medical applications tend to be more focused on encapsulation rather than direct load-bearing, leveraging its unparalleled chemical inertness and biocompatibility.
• Advantages: Extreme chemical inertness and stability (virtually no degradation in the body), excellent biocompatibility, high hardness, and semiconductor properties.
• Specific Applications: Encapsulation coatings for long-term implantable medical devices, orthopedic coatings, and microelectromechanical systems (MEMS).