Biocompatible Ceramics

Biocompatible ceramics refer to a type of ceramic materials used for specific biological or physiological functions, that is, ceramic materials directly used in the human body or biology, medical research, biochemistry, etc. directly related to the human body. As a bioceramic material, the following characteristics are required: biocompatibility, mechanical compatibility, excellent affinity with biological tissues, anti-thrombosis, sterilization, and physical and chemical stability.

Applications:

Bioceramic materials can be divided into bio-inert ceramics (such as Al₂O₃, ZrO₂) and bioactive ceramics (such as dense hydroxyapatite, bioactive glass). Bio-inert ceramics mainly refer to ceramic materials with stable chemical properties and good biological compatibility. such as alumina, zirconia and medical carbon materials. The structure of these ceramic materials is relatively stable, the intermolecular bonds are strong, and they all have high strength, wear-resistance and chemical stability. Bioactive ceramics include surface bioactive ceramics and bioabsorbent ceramics. Biosurfactant ceramics usually contain hydroxyl groups and are porous, so the biological tissue can grow into and bond firmly with its surface. There are several kinds of bioactive ceramics, such as bioactive glass, hydroxyapatite ceramics, tricalcium phosphate ceramics. The characteristic of bioabsorbent ceramics is that it can be partially or completely absorbed by organisms to induce the growth of new bone. At present, hydroxyapatite (HA) and tricalcium phosphate (TCP) are widely studied and applied in bioabsorbent ceramics.

• Alumina bioceramics: The c-axis direction of single crystal alumina has high bending strength, good wear resistance and good heat resistance, so it can be directly fixed with bone. It can be used as artificial bone, tooth root, joint and bolt. Due to the extremely thin fibrous membrane formed on the surface of the alumina ceramic implanted into the human body, there is no chemical reaction at the interface, so it is often used for total hip reduction and repair and the connection between femur and hip.
• Zirconia ceramics: They are bio-inert ceramics with ZrO₂ as the main component, and their remarkable characteristics are high fracture toughness, high fracture strength and low elastic modulus. Zirconia (ZrO₂), inert in the physiological environment, has extremely high chemical and thermal stability, and has good biocompatibility. Zirconia, like alumina, has good biocompatibility and is used to replace tooth roots, bones, femoral joints, composite ceramic artificial bones, valves, etc.

Figure 1. Zirconia ceramic layer for enamel restoration.

• Bioactive Glass & Glass-ceramics: The main component of bio-glass ceramics is CaO-Na₂O-S iO₂-P₂O₅, which contains more calcium and phosphorus than ordinary glass, and can naturally and firmly bond with the bone chemically. It has unique properties that are different from other biomaterials. It can rapidly undergo a series of surface reactions at the implantation site, which ultimately leads to the formation of a carbonate-based apatite layer. Bioglass ceramics have good biocompatibility, and can be implanted into the body without reaction such as rejection and tissue necrosis. At present, this kind of material is mostly used to repair small bones in the ear, which has a good effect on hearing restoration.

Figure 2. Bioactive glass-ceramic

• Calcium phosphate bioactive ceramics: Calcium phosphate ceramic (CPC) is an important type of bioactive ceramic materials. At present, the most researched and applied are hydroxyapatite (HA) and tricalcium phosphate (TCP). Calcium phosphate ceramic contains two components, CaO and P₂O₅, and is an important inorganic substance that constitutes the human hard tissue. After being implanted into the human body, its surface can be combined with human tissue through bonds to achieve complete affinity. In addition to these two, calcium phosphate bioceramics also include degradable and absorbing zinc-calcium-phosphorus oxide (ZCAP) ceramics, zinc sulfate-calcium phosphate (ZSCAP) ceramics, aluminum calcium phosphate (ALCAP) ceramics and iron-calcium- Phosphorus oxide (FECAP) ceramics, etc.

Figure 3. Calcium phosphate bioactive ceramics

References:

1. Hench LL.(1991) "Bioceramics: from concept to clinic." Journal of the American Ceramic Society. 74:1487-510.
2. Best S, Porter A, Thian E, Huang J.(2008) "Bioceramics: past, present and for the future." Journal of the European Ceramic Society. 28:1319-27.