Publish Time: 2022-01-28 Origin: Site
Silk is coagulated by the silk fluid secreted from the silk glands in the silkworm. Silk fibroin is the main body of silk, accounting for about 70% to 80% of the silk quality. It is a natural biological macromolecule with no physiological activity. It is formed by connecting multiple amino bonds, and its molecular weight is generally considered to be about 3.7×105.
Silk fibroin contains 18 kinds of amino acids, of which glycine, alanine and serine account for about 85% of the total number of amino acids. chain, about 26 kD) of natural macromolecular fibrin.
A disulfide bond is formed between the cysteine ??residue at position 20 of the C-terminal of the H chain and the cysteine ??residue at position 172 of the L chain to bind the two. In addition, there is a glycoprotein (P25) with a molecular mass of about 30 kD and the complex of H chain and L chain is bound by hydrophobic interaction, and the molar ratio of H chain, L chain and P25 is 6: 6: 1 . In the H chain, 94% of the sequence is a highly repetitive crystalline region, and the remaining part includes the N-terminal sequence (signal peptide), the linking part between the crystalline regions, and the C-terminal sequence.
The amino acid sequence in the crystalline region is mainly composed of hexapeptide repeats (Gly-Ser-Gly-Ala-Gly-Ala), forming an anti-parallel β-sheet structure. Silk fibroin is composed of crystalline state and amorphous state in the aggregated state, and the crystalline state can be divided into silk I and silk II. The antiparallel β-sheet structure belongs to silkⅡ, which is an orthorhombic crystal system; silkⅠ is an intermediate form between α-helix and β-sheet, and the stereo conformation is crank-shaped. , the change of the solvent may make silk I into silk II.
In addition, there is a crystalline silk III, which is found in the silk fibroin film formed between the silk fibroin solution and the air interface, which is an intermediate form between silk I and silk II. The above-mentioned unique structure of silk fibroin makes it have many special properties. Silk fibroin not only has good biocompatibility and degradation properties, but also has the characteristics of easy processing and modification, non-toxic degradation products and low immunogenicity, and the mechanical strength of silk fibroin materials is also significantly better than other biological materials.
In recent years, many researchers have combined osteogenic seed cells and silk fibroin to prepare silk fibroin materials with bone repair ability. The silk fibroin in the materials can provide the required space and environment for cell growth, adhesion and differentiation. The research and development of silk fibroin-based bone repair materials has become one of the hot spots in bone tissue engineering research. At present, various forms of silk fibroin biomaterials, including silk fibroin membranes, silk fibroin nanofibers, silk fibroin hydrogels and silk fibroin porous materials Scaffolds have been widely used in the repair of bone loss and injury.
1. Research on the application of silk fibroin in the field of biosensors
A biosensor is an analysis system composed of biologically active material as a sensitive element and an appropriate transducer. Immobilization of biologically active enzymes is an essential step in the preparation of almost all types of biosensors. The silk fibroin membrane prepared from silk fibroin is an excellent immobilized enzyme carrier, and many studies have been reported in its application in biosensors. Silk fibroin membrane as an enzyme immobilization carrier began in 1978.
In 1989, the silk fibroin membrane-immobilized glucose oxidase biosensor was first applied to the analytical system. Now, silk fibroin membranes have been widely used in biosensors and other detectors as an excellent enzyme immobilizer. The reported enzymes immobilized with silk fibroin membranes include glucose oxidase (GOD), peroxidase (POD), urease, lipase, pectinase, catalase, saccharification, and superoxide dismutase. , Penicillin acylase, papain, phenylalanine lyase, β-glucosidase, etc.
In addition, the use of silk fibroin membranes for neurotransmitter sensors has also been reported. The charged properties of the silk fibroin film were studied. The research showed that the silk fibroin film is a polyamino acid film with amphoteric charging effect. The charge mainly comes from the charged groups on the side chains of basic amino acids and acidic amino acids. pH = around 4.5. Using the amphoteric charge characteristics of the silk fibroin film before and after the isoelectric point and the electrostatic interaction between the charges, it can be used to modify the electrode. Under the physiological condition of pH=7.4, the silk fibroin film exhibits the characteristic performance of a loaded electric film. Effectively eliminate the interference of anionic compounds.
The electrode was used the determination of neurotransmitter compound system, the neurotransmitter DA and 5-HT were measured, and the pH value charge selection effect of this modified electrode was verified. It has many advantages such as properties, which fully shows its broad prospects for the determination of biological substances and life science research.
2. Biological enzyme protectant
Organophosphorus pesticides can combine with cholinesterase in the body to form stable phosphorylated cholinesterase through organophosphate, thereby inhibiting the activity of cholinesterase in the human body, so that acetylcholine produced by normal nerve activity cannot be decomposed immediately. Human poisoning and death. Therefore, it is an effective anti-virus way to first react with the poison in vitro, so that it loses the ability to enter the body for destruction. With acetylcholinesterase as the detoxification enzyme and silk fibroin solution as the enzyme carrier, the treated fabric has good anti-virus effect, and can be stored for a long time under suitable temperature conditions, and when distilled water is used as the enzyme carrier, it can also be used. The fabric has good anti-virus effect, but its anti-virus effect becomes worse with the increase of time.
It shows that when the silk fibroin solution is used as the synthetic biological enzyme protectant, it can directly react with toxic substances (organophosphates) and combine into stable phosphorylated cholinesterase to block the damage of the toxic agents to the human body. Studies have shown that it is feasible to use silk fibroin solution as a biological enzyme protectant, which has a good anti-virus effect and can make the enzyme have a longer storage life.
3. Drug controlled release materials
5-Fluorouracil (5-FU) was embedded in silk fibroin membrane, and the drug release in silk fibroin 5-FU composite membrane was measured at different pH values. The results showed that the silk fibroin membrane could be used as a carrier for 5-FU and evenly embedded 5-FU. Due to the protection of the silk fibroin coating, the dissolution and release rate of 5-FU in the composite film slowed down and the release time was prolonged.
When the coated composite membrane is close to the isoelectric point of silk fibroin (pH=4.5), the release rate of 5-FU in solution is slower and the release time is longer, which indicates that adjusting the pH value of the external solution can regulate 5-FU release speed. The silk fibroin membrane with porous structure is prepared by freeze-drying method. The existence of a large number of capillaries in the membrane greatly improves the air permeability and moisture permeability of the silk fibroin membrane. The drug is applied in the porous silk fibroin membrane, and the existence of pores helps the controlled release of the drug.
4. Biomimetic materials
The "artificial skin" wound protective film made of silk fibroin film and fresh pig skin were compared in rabbits. The results showed that the performance of silk fibroin film was better than pig skin. In clinical trials of deep II degree wounds and superficial II degree wounds, it has good moisture permeability and adhesion to the wound surface, which promotes wound healing. In terms of biological properties, it has strong bactericidal properties, good adhesion between the drug silk fibroin film and the body surface, meets the requirements of wound covering and is non-toxic, has no irritating effect on the skin, and has a cytotoxicity. The protection and treatment of skin injury wounds such as plastic skin extraction areas can basically meet the application of scaffold materials, but they are far inferior to natural polymers in terms of biocompatibility and cell adhesion.
The biocompatibility and cell adhesion ability of scaffold materials are critical. Silk fibroin is favored as a natural polymer material with excellent biocompatibility. In recent years, the use of silk protein to modify some biopolymer materials has also attracted extensive attention of researchers.
Compared with other natural polymers, silk fibroin has obvious advantages. Studies have shown that it has good biocompatibility, non-toxic, non-polluting, non-irritating and biodegradable. Therefore, many scholars are devoted to research and develop new fields of silk fibroin application. Silk fibers have been used as textile fibers for thousands of years, and they have been used clinically, such as surgical sutures, for decades. Since silk fibroin was found to have unique physicochemical properties and good compatibility with the human body, it has been extensively studied as a food additive and in cosmetic applications. In recent years, it has been gradually discovered that silk fibroin has more potential, such as application in biosensing, biomedical materials, soft tissue compatible materials, tissue engineering and other fields, and new progress has also been made in traditional fields.