Speaking of the development of biological materials, it can be divided into the following four stages:
①18th century: the enlightenment stage of artificial bone research using natural materials (such as willow branches, wood, hemp, ivory and precious metals) as bone repair materials;
②19th century: the natural development stage of using precious metals such as pure gold, pure silver and platinum;
③The middle of the 20th century: the use of cobalt-chromium aluminum alloy, pure titanium, titanium alloy, and organic glass and other polymer materials for clinical exploration;
④ 1960s: The rapid development stage of bioceramics emerging.
Bioceramics refers to a type of ceramic materials used for specific biological or physiological functions, that is, ceramic materials that are directly used in the human body or related to the human body, such as biology, medicine, and biochemistry. Broadly speaking, all ceramic materials belonging to bioengineering are collectively referred to as bioceramics. Bioceramic materials are classified into bioactive ceramic materials and bioinert ceramic materials according to their combination with tissues. The fundamental difference between the two is whether the implant can form a chemical bond with living tissue after implantation. This article first briefly introduces bio-inert ceramic materials.
1. The characteristics of biologically inert ceramic materials:
After the material is implanted in the organism, it cannot form a chemical bond with the active tissue, but is surrounded by the fibrous connective tissue membrane. The fibrous connective tissue membrane separates the implant from the normal tissue at the repair site, and the implant remains permanently in the body as a foreign body. Although bio-inert ceramic materials cannot chemically bond with human tissues, due to their good mechanical properties, excellent wear resistance and chemical stability, bio-inert ceramic materials are still an important type of alternative hard tissue repair materials. How to improve the fracture toughness of biologically inert ceramic materials, overcome their brittleness, and introduce biologically active ingredients to improve their combination with human tissues is the main content of biologically inert ceramic materials.
2. Classification of biological inert ceramics:
Bio-inert medical ceramic materials include oxide ceramics, non-oxide ceramics, glass ceramics, etc. They have stable chemical properties, good biocompatibility, corrosion resistance in the body, no degradation, and no chemical combination with human tissues. The commonly used bio-inert ceramics in clinical practice include alumina ceramics, zirconia ceramics, and zirconia toughened alumina ceramics. Among them, oxides of Al, Mg, Ti, and Zr are most widely used. Bio-inert ceramics generally have high strength and wear resistance, and are mainly used in medical treatment to make artificial joints, artificial bones, oral implants, all-ceramic teeth and dental crowns.
(1) Alumina (Al2O3) ceramic materials
Alumina has many crystal forms, among which the high-temperature crystal form α-Al2O3 has the best thermal and chemical stability. The density of α-Al2O3 is 3.99g/cm3, which is lighter than common biomedical products such as stainless steel, titanium and titanium alloys. metallic material. α-Al2O3 is a crystal dominated by ionic bonds, with strong bonding force, which makes Al2O3 have a high melting point (2050°C), hardness, chemical resistance and elastic modulus.
As early as 1969, alumina ceramic was used as a permanent implantable bone prosthesis to be implanted into the femur of adult mongrel dogs. It was found that polycrystalline alumina ceramics showed inertness and superior resistance to any environment including biological environments. Abrasion and high compressive strength. Alumina ceramics are extremely stable in the human body, have high hardness, and are hardly abraded. This makes alumina ceramics the first biologically inert ceramic materials to be used in clinical applications.
(2) Zirconia (ZrO2) ceramic materials
Zirconia is an oxide ceramic with the highest fracture toughness at room temperature and is widely used as a structural material. Compared with alumina ceramics, zirconia ceramics have higher room temperature strength and fracture toughness, lower elastic modulus, but the hardness and wear resistance are not as good as alumina ceramics.
Due to its excellent biocompatibility, zirconia has high fracture toughness and strength, and low elastic modulus. It is currently mainly used in artificial joints, tooth roots, crowns and all-ceramic teeth in the medical field. The highest dental restoration material. When paired with polyethylene for artificial joints, its friction and lubrication performance is similar to alumina. Zirconia ceramic has higher fracture toughness, and the clinical fracture rate of zirconia femoral head prosthesis is lower than that of alumina ceramic femoral head.
3. The advantages and disadvantages of biologically inert ceramic materials:
The main advantages of biologically inert materials used in artificial hip joints:
Wear-resistant, able to resist abrasive wear and third body wear well;
High strength, which can meet the requirements of material strength for weight-bearing parts repair;
High hardness, no creep phenomenon, stable structure;
The surface of the microcrystalline structure can be processed with high polishing;
Good hydrophilicity and excellent lubrication performance;
Stable chemical properties, excellent corrosion resistance, almost no ion release;
Biologically inert, not easy to cause cellular reactions;
Bacteria are not easy to adhere to the surface;
Surface degradation is slow.
Disadvantages of bio-inert ceramics
The characteristics of bio-inert ceramics being wrapped by fibrous tissue in the body or forming fibrous tissue interface with bone tissue affects the application of this material in bone defect repair, because there is a fibrous tissue interface between bone and material, which hinders the material and bone. The combination also affects the osteoconductivity of the material. Long-term retention in the body produces structural defects, which makes the bone tissue mechanically weak.