Bioceramics refers to a kind of ceramic materials used for specific biological or physiological functions, that is, directly used for human body or directly related to biological, medical, biochemical and other ceramic materials. As a bioceramic material, it needs to have the following conditions: biocompatibility, mechanical compatibility, excellent affinity with biological tissue, antithrombotic, sterilization and good physical and chemical stability.
Bioceramic materials can be divided into bio inert ceramics (such as Al2O3, ZrO2, etc.) and bioactive ceramics (such as dense hydroxyapatite, bioactive glass, etc.).
Bio inert ceramics are mainly ceramic materials with stable chemical properties and good biocompatibility. Such as alumina, zirconia and medical carbon materials. This kind of ceramic materials have stable structure, strong bonding force in molecules, and high strength, wear resistance and chemical stability.
1. Alumina Bioceramics
The c-axis direction of single crystal alumina has high bending strength, good wear resistance and heat resistance, which can be directly fixed with bone. It has been used as artificial bone, root, joint and bolt. And the bolt is not rusty and will not dissolve harmful ions. Unlike the metal bolt, it does not need to be taken out of the body. Because of the thin fibrous membrane formed on the surface of alumina ceramic implanted in human body, there is no chemical reaction at the interface, and it is mostly used in the whole hip restoration and the connection of femur and hip bone. The monocrystal alumina produced by the flame melting method has high strength, good wear resistance, and can be finely processed to make artificial root, fracture fixator, etc. Polycrystalline alumina, namely corundum, with high strength, is used to make artificial hip joint, artificial bone, artificial tooth root and joint. The mechanical properties of single-crystal alumina ceramics are better than that of polycrystalline alumina, which are suitable for the parts with negative weight and high wear-resistant requirements, but its disadvantage lies in the difficulty of processing. Chinese ceramics can completely meet the ISO standard in laboratory research, but there is still a certain gap in clinical application, and the materials do not meet the ISO standard.
(ISO requirements for medical alumina implants)
Clinical application of single crystal alumina
Compared with alumina polycrystalline ceramics, it has higher mechanical strength and is not easy to break. It can also be used as a fixation material for damaged bone. It is mainly used to make artificial bone screws, which have higher strength than the artificial bone screws made of metal materials. It can be processed into a variety of teeth with small size and high strength. Because alumina single crystal has good affinity with human protein and strong binding force, it is conducive to the attachment of gingival mucosa and different tooth materials.
2. Zirconia ceramics
Zirconia bioceramics is a kind of bio inert ceramics with ZrO2 as the main component, which is characterized by high fracture toughness, high fracture strength and low elastic modulus. Zirconia (ZrO2) has very high chemical and thermal stability (TM = 2953k). It is inert in physiological environment and has good biocompatibility. There are three allotropes in pure zirconia, under certain conditions, crystal transformation (phase transformation) can take place. Under the action of external force, the transformation process from t phase to M phase needs to absorb high energy, which makes the stress at the crack tip relax, increases the resistance of crack diffusion and toughens, so it has very high fracture toughness.
Part of stable zirconia, like alumina, has good biocompatibility, high stability in human body, and higher fracture toughness and wear resistance than alumina, which is beneficial to reduce implant size and realize low friction and wear, and is used to manufacture root, bone, femoral joint, composite ceramic artificial bone, valve, etc.
(comparison of properties of alumina and zirconia ceramics for surgical implantation)
Biomedical application: Based on the excellent biocompatibility, good fracture toughness, high fracture strength and low elastic modulus of zirconia ceramics, it is suitable for making artificial joints that need to bear high shear stress. The wear rate of zirconia / zirconia pair is 5000 times of that of alumina / alumina pair, but it shows good friction and wear performance when the friction pair of zirconia / UHMWPE is formed.
Bioactive ceramics include surface bioactive ceramics and bioabsorbable ceramics, also known as biodegradable ceramics. Biosurfactant ceramics usually contain hydroxyl groups and can also be made porous. Biological tissue can grow in and bond with its surface firmly. The characteristics of biosurfactant ceramics are that they can absorb part or all of them, and can induce the growth of new bone in the organism. Bioactive ceramics have bone conductivity. As a scaffold, they can form bone on its surface. They can also be used as a shell of a variety of substances or to fill bone defects. Bioactive ceramics include bioactive glass, hydroxyapatite ceramics, tricalcium phosphate ceramics and so on.
1． Bioactive Glass & Glass-ceramics
The main component of Bioglass ceramics is cao-na2o-sio2-p2o5, which contains more calcium and phosphorus than ordinary window glass, and can combine with bone naturally and firmly. It has unique properties different from other biomaterials. It can produce a series of surface reactions at the implant site, which eventually leads to the formation of carbonate based phosphorite layer. Bioglass ceramics have good biocompatibility, no rejection, inflammation and tissue necrosis reaction, and can form osseous combination with bone; it has strong binding strength with bone, good interface binding ability and rapid osteogenesis. At present, this kind of material has been used to repair the ossicles of the ear, which has a good effect on the recovery of hearing. However, due to the low strength, it can only be used in the parts of human body with little stress. At present, the method of preparing bioactive glass is mainly prepared by sol-gel method. The material prepared by this method has special chemical composition, nanocluster structure and micropore, so its specific surface area is larger, and its biological activity is better than other Bioglass and glass ceramics. Because of the good purity, high uniformity, good bioactivity and specific surface area, the sol-gel method has better research and application value. Especially, bioactive glass porous materials have a good prospect in bone tissue engineering scaffolds.
The most remarkable feature of bioactive glass and glass ceramics is that after implantation into human body, the surface condition changes dynamically with time, and the bioactive HCA layer is formed on the surface, which provides a bonding interface for tissues.
A. Composition: bioactive glass mainly consists of SiO2, Na2O, Cao, P2O5, etc. Bioactive glass ceramics are polycrystals obtained by controlling crystallization on the basis of bioactive glass. Compared with the traditional Na CA SI system glass, it has three characteristics: low SiO2 content, high Na2O and CaO content, and high CaO / P2O5 ratio.
B. Properties: fast surface reaction; amorphous two-dimensional structure makes the strength and fracture toughness low; elastic modulus (30-35mpa) is low, close to cortical bone; Machinable biological glass has good processing performance.
C. Preparation process: the preparation process of bioactive glass is basically the same as the traditional glass preparation process, including weighing, mixing, fusion, melting, homogenization, glass formation, etc. Glass ceramics also need to control glass nucleation and grain growth under a certain heat treatment system.
D. Clinical application: a) 45S5 bioactive glass is used for small bone replacement of middle ear, jaw defect repair, periodontal defect repair, bone ridge maintenance implant, without cell damage, degradation products and infection. b) Ceravital bioactive glass ceramics is a kind of bioactive glass ceramics with low sodium and potassium, which is used in middle ear surgery. c) Apatite wollastonite active glass-a-wgc has been successfully used in tens of thousands of patients as a spinal prosthesis, chest and frontal bone repair and bone defect repair. d) MBGC, a kind of Machinable bioactive glass, is mainly used in maxillofacial, spinal, alveolar hard tissue repair and oral repair. It is characterized by excellent machinability and osseointegration.
2. Calcium phosphate bioactive ceramics
Calcium phosphate ceramic (CPC) is an important kind of bioactive ceramic materials. At present, hydroxyapatite (HA) and tricalcium phosphate (TCP) are the most studied and applied materials. Calcium phosphate ceramics contain two components, Cao and P2O5. It is an important inorganic material to form human hard tissue. After implanted into human body, its surface and human tissue can be completely compatible through bond. Among them, ha is very similar to human bone and teeth in composition and structure, with high mechanical properties and low solubility in human physiological environment; TCP has a good combination with bone, no rejection reaction, and the dissolution degree in aqueous solution is much higher than ha, which can be slowly degraded and absorbed by body fluids, providing rich calcium and phosphorus for the growth of new bone and promoting the growth of new bone. In addition, calcium phosphate bioceramics also include zinc calcium phosphorus oxide ceramics (ZCAP), zinc sulfate calcium phosphate ceramics (zscap), aluminum calcium phosphate ceramics (Alcap) and iron calcium phosphorus oxide ceramics (FeCap).
A. Overview of composition and physicochemical properties
Calcium phosphate compounds are usually classified according to the Ca / P atomic ratio (CA / P ratio). Calcium phosphate ceramics are the general term of calcium phosphate ceramics with different Ca / P ratios.
The structure of various calcium phosphate compounds at high temperature is related to their calcium phosphorus ratio, temperature, heating speed, atmosphere and other factors; the different synthesis process will also affect their thermal properties (mainly their thermal stability).
All kinds of calcium phosphate compounds have certain solubility. The solubility products of dicalcium phosphate, tricalcium phosphate and hydroxyapatite are as follows:
Calcium hydrophosphate PK = 6.57
Tricalcium phosphate PK = 28.7
Hydroxyapatite PK = 57.8
The solubility of dicalcium phosphate in water is the strongest, followed by tricalcium phosphate and hydroxyapatite. Therefore, the bone repair materials made of dicalcium phosphate and tricalcium phosphate can be gradually dissolved and precipitated into hydroxyapatite.
B. Hydroxyapatite ceramics
Hydroxyapatite, or HA or HAP for short, is the main inorganic component of vertebrate bone and tooth, which is similar to natural apatite mineral in composition and structure, in the form of lamellar microcrystalline. It is used as a bone substitute for bone transplantation. Ha has good biocompatibility. It is not only safe and non-toxic, but also can conduct bone growth. Ha can make bone cells adhere to its surface. With the growth of new bone, this junction area gradually shrinks, and ha becomes a part of bone through the outer layer of crystal. New bone can grow from the junction of HA implant and original bone along the surface or internal through pores of the implant. Ha bioactive ceramics are typical bioactive ceramics, which can form chemical bond with tissue on the interface after implantation. The bonding mechanism between HA bioactive ceramics and bone is not the same as that of Bioglass, which needs to form silicon rich layer on its surface, and then form intermediate bonding band to achieve bonding. After the dense hydroxyapatite ceramics were implanted into the bone, the osteoblasts directly differentiated on its surface to form a bone matrix, producing an amorphous electron density band with a width of 3-5 μ M. the collagen fiber bundle grew into this area and between the cells, and the bone salt crystallization took place in this amorphous band. As the mineralization matures, the amorphous band shrinks to 0.05-0.2 μ M. the bond between hydroxyapatite implant and bone is realized by this very narrow bond band.
After the HA coated artificial joint was implanted into the body, the surrounding bone tissue could be deposited directly on the surface of hydroxyapatite, and formed chemical bond with the calcium and phosphorus ions of hydroxyapatite, which was closely combined, without fibrous membrane in the middle. Ha bioceramics were implanted into soft tissues such as muscles or ligaments or surrounded by a thin layer of connective tissue, without inflammatory cells and micro capillaries. When it is used for percutaneous implantation, it can close to the epithelial tissue in the neck without inflammation and infection. Therefore, ha bioactive ceramics are also suitable for skin piercing devices and soft tissue repair.
The preparation of HA ceramics can be obtained from the decomposition of animal bone tissue and artificial synthesis, the latter is divided into wet and solid reaction. The most commonly used method is reaction coprecipitation, which is to prepare calcium raw material and phosphate or phosphoric acid into a liquid of appropriate concentration. According to the Ca-P atom ratio of 1.67, under the environment of pH > 7, control the appropriate temperature for reaction synthesis. The precipitate is dehydrated and dried, and calcined at high temperature to produce a light green aggregate, with a purity of 99.5% Above, its chemical composition is mainly: Cao, P2O5. Single ha has poor formability and sintering property, and is easy to deform and crack. Adding ZrO2 + Y2O3, ZnO and CPM composite reagent containing magnesium salt, etc. can make it have good biocompatibility, enough mechanical strength and non-toxic. Continuous hip sintering is an effective method to prepare high density HA with theoretical density. This kind of material is mainly used for the repair and replacement of biological hard tissue, such as oral implant, alveolar ridge heightening, periodontal bag filling, frontal and facial bone defect repair, ear bone replacement and so on. As the mechanical strength is not high enough, it is only used for the above parts that do not bear large load. Due to the excellent strength and toughness of natural bone, people think of improving the performance of bioceramic bone repair materials through bionic approach. The model of bone microstructure proposed by Landis et al. Has been widely used, although there are still some details not verified by experiments.
Among the calcium phosphate compounds, apatite has been studied most, and its general formula is M10 (xO4) 6z2. M - is a divalent metal ion, xO4 - is a pentavalent anion, and Z - is a monovalent anion. Next, we will discuss the hydroxyapatite ceramics in detail.
Properties and application of hydroxyapatite ceramics
The structure of the synthesized hydroxyapatite is similar to the biological bone tissue, so the synthesized hydroxyapatite has the same properties as the biological hard tissue. For example, CA: P ≈ 1.67, density ≈ 3.14, mechanical strength greater than 10MPa, non-toxic to biology, no stimulation, good biocompatibility, not absorbed, can induce new growth.
Hydroxyapatite has been used in alveolar, bone defect, repair and filling of brain surgery at home and abroad to make otoacoustic bone chain and plastic materials. In addition, it can be made into artificial bone nucleus to treat bone tuberculosis.
3. Tricalcium phosphate
At present, β - TCP, which is widely used in biodegradation ceramics, is a kind of high-temperature phase of calcium phosphate. It belongs to the ternary system and has a Ca-P atom ratio of 1.5. The biggest advantage of β - TCP is its good biocompatibility, direct fusion with bone after implantation, without any local inflammatory reaction and systemic toxicity.
Calcium phosphorus ratio plays an important role in determining the solubility and absorption trend in vivo, so compared with HA, TCP is easier to dissolve in vivo, and its solubility is about 10-20 times higher than ha. The degradation rate of β - TCP implanted in vivo can vary with its surface structure, crystal structure, porosity and implanted animals, and its strength often decreases with degradation. It has been proved that changing pore size and material purity can slow down degradation rate and improve biological strength.
Compared with other ceramics, β - TCP ceramics are more similar to the properties and structures of human bone and natural teeth in vivo. The dissolution of hydroxyapatite is harmless, and the formation of new bone depends on the supplement of calcium and phosphate ions from body fluid, which can produce decomposition, absorption and precipitation reactions at the bone interface, and achieve solid combination.
The disadvantage of β - TCP ceramics is that its mechanical strength is too low to withstand the impact of force. Mixing β - TCP with other materials to make biphase or multiphase ceramics is one of the methods to improve its mechanical strength. It is generally believed that the bone conduction effect of biphasic Calc ium phosphate (BCP) is better than that of single HA or TCP, which can combine the advantages of high strength of HA and good biodegradability of TCP, and the chemical composition is similar to that of bone. Bruder et al. Inoculated bone marrow stroma cells (BMS) on porous BCP and successfully repaired 21 mm long segmental defect of canine femur. Fu Rong et al found that BMS cultured on BCP could express osteoblasts better, which indicated that BCP was more suitable for bone tissue engineering matrix materials.
With the progress of society, human beings are no longer satisfied with simply imitating the shape of human organs, but pursuing new materials with perfect functions. Bioceramics has become an indispensable part in the field of medicine. At present, many researches have been carried out in the field of materials science. With the rapid development of modern science and the improvement of technology, the preparation methods of bioceramics are becoming more and more feasible. A variety of C A-P ceramics combined with organic materials are used as scaffolds for bone tissue engineering in clinical trials, such as TCP + collagen, nanocrystalline HA + collagen, TCP + platelet rich plasma, etc. There are two kinds of shape memory alloy: self expanding and balloon expanding. The ideal biomedical material for biliary stricture caused by advanced malignant tumors should be non-toxic, non sensitizing, non irritant, non genotoxic and non carcinogenic. Therefore, it is very important to understand the biological response of biomedical materials to human body. These reactions mainly include tissue reaction, blood reaction and immune reaction.
Through continuous research and development, more excellent properties of bioceramics will be developed and applied. In a word, bioceramics have great research space and broad development prospects.
On 2018-08-08 11:45:46
