Application of the hottest degradable polymer mate

The application of degradable polymer materials in medical devices

biomaterials play an important role in disease treatment and medical care. According to the properties of materials, biomaterials can be divided into inert materials and degradable materials. At present, the development of biomaterials shows a trend from inert to degradable (hydrolysis and enzymatic degradation), This shows that many bioinert instruments that play a temporary therapeutic role (helping the body repair or regenerate damaged tissues) will be replaced by biodegradable materials

compared with inert materials, biodegradable polymer materials are a more ideal material for medical devices. Inert devices generally have the problems of poor long-term compatibility and the need for secondary surgery, while biodegradable polymer devices do not have these defects. In the past 20 years, there have been some new medical technologies in biomedicine, including tissue engineering, drug controlled release, regenerative medicine, gene therapy and Biological Nanotechnology. These new medical technologies all need biodegradable polymer materials as support, and they also promote the development of biodegradable polymer materials accordingly

degradable polymer materials need to have good compatibility in the whole degradation process, mainly including the following points:

no continuous inflammation or toxic reaction after implantation in human body

suitable degradation cycle

in the process of degradation, it has mechanical properties corresponding to the treatment or tissue regeneration function

degradation products are non-toxic and can be excreted out of the body through metabolism or osmosis

machinability. There are many factors that affect the biocompatibility of degradable polymer materials. Some properties of the materials themselves, such as the shape and structure of implants, hydrophilicity and lipophilicity, water absorption, surface energy, molecular weight and degradation mechanism, need to be considered

this paper reviews the properties and degradation characteristics of several commonly used degradable polymer materials, including polyglycolide, polylactic acid, (glycolide lactide) copolymer, polycaprolactone, Polydioxanone, polyhydroxy fatty acid ester, polytrimethylene carbonate, polyurethane and polyether urethane, and their applications in medical devices, including implants, tissue engineering scaffolds, drug controlled release carriers, etc

polyglycolide (PGA)

PGA is the first synthetic degradable polymer material used in clinical medicine. It has a high degree of crystallinity (45% - 55%), which makes it have a large tensile modulus of elasticity. PGA is insoluble in organic solvents to avoid users from adding other functional solvents in future needs. The glass transition temperature (TG) is between 35 ~ 40 ℃, and the melting point (TM) is higher than 200 ℃. It can be processed and molded by extrusion, injection molding and molding. PGA was first developed into absorbable suture due to its good fiber forming property

in 1969, the first synthetic degradable suture Dexon approved by FDA was made of PGA. Because PGA has appropriate degradation to avoid quality problems, excellent initial mechanical properties and biological activity, PGA non-woven fabric has been widely studied as a scaffold material for tissue regeneration. At present, a scaffold material containing PGA non-woven fabric is being used in clinical trials

in addition, PGA dural substitute is also under study, because it has the ability to help tissue regeneration and close the skin under the seamless suture. The high crystallinity of PGA makes it have excellent mechanical properties. Among the biodegradable polymer materials used in clinic, self reinforced PGA is the hardest, and its modulus is close to 12.5gpa. PGA has also been developed as an internal fixation system (biofix) because of its good initial mechanical properties. PGA is degraded by random breaking (hydrolysis) of ester bonds in the chain segment. Under hydrolysis, the mechanical properties of PGA decreased in 1 ~ 2 months, and the mass loss occurred in 6 ~ 12 months. In vivo, PGA is degraded into glycine, which can be directly excreted from the body through urine or metabolized into carbon dioxide and water. The application of PGA in biomedicine is limited by its high degradation rate, acidity and insoluble degradation products, but these shortcomings can be overcome by copolymerization with other monomers

polylactic acid (PLA)

lactide (LA) is a chiral molecule, and there are two stereoisomers: L-LA and d-la. Their homopolymers are semi crystalline. Racemic La (DL – LA) is a mixture of L – La and D – La, and its polymer is random. The crystallinity (0% ~ 37%) of poly L-LA (PLLA) is determined by molecular weight and processing parameters. Its TG is 60 ~ 65 ℃ and TM is about 175 ℃. Because its hydrophilicity is worse than PGA, its degradation rate is lower than PGA

plla has high tensile strength, low elongation at break and high tensile modulus of elasticity (close to 4.8gpa), and is an ideal medical load-bearing material, such as bone fixation instruments. PLLA bone fixation devices on the market now include bioscrew, bio anchor, meniscalstinger, etc. In addition, PLLA can also be made into high-strength surgical suture. In 1971, PLLA surgical suture was approved to market by FDA, which has better performance than Dexon. PLLA can also be used in other medical fields, such as ligament repair and reconstruction, drug-eluting stents, targeted drug delivery, etc. In 2007, FDA approved an injectable PLLA product (Sculptra) for the treatment of facial fat loss or atrophy caused by human immunodeficiency virus (HIV). The degradation rate of PLLA is slow. The complete degradation of high molecular weight PLLA in vivo takes 2 ~ 5.6A. Factors such as crystallinity and porosity can affect its degradation rate

under hydrolysis, the mechanical properties of PLLA decreased within 6 months, but the mass loss occurred after a long time. Therefore, in order to obtain better degradation performance, researchers copolymerized L-LA with GA or dl-la. Resomerlr708 is a random copolymer obtained by copolymerization of L – La and DL – La (mass ratio 70:30)

pdlla formed random copolymers because of the random distribution of L-LA and d-la. The strength of TG decreased significantly between 55 and 60 ℃, which was caused by the random arrangement of molecular chains. Under hydrolysis, the mechanical properties of PDLLA decreased within 1 ~ 2 months, and the mass loss occurred within 12 ~ 16 months. Compared with PLLA, PDLLA has the characteristics of low strength and high degradation rate. It is an ideal material for drug delivery carrier and tissue regeneration scaffold (low strength). PLA is degraded by random breaking (hydrolysis) of ester bonds in the chain segment. The primary degradation product is lactic acid, which is a by-product of normal human metabolism. Through citric acid cycle, lactic acid can be further degraded into carbon dioxide and water

copolymer (PLGA)

the study found that PLGA was a random copolymer when the mass ratio of La to GA was 25/75~75/25. The study of LER et al. Showed that PLGA with the mass ratio of La to GA of 50/50 had the fastest degradation rate

PLGA with different monomer mass ratios has been widely used in clinic. PLGA with the trade name purasorbplg is a semi crystalline copolymer, in which the mass ratio of La to GA is 80/20; The mass ratio of L-LA to GA in multi strand suture Vicryl is 10/90. Its upgraded version of vicrylrapid has also been launched, and the degradation speed of the upgraded version after irradiation is faster

panacryl is another commercial PLGA suture. In addition, PLGA is also used in other medical fields, such as silk (vicrylmesh), skin grafting materials and dural substitutes. Tissue engineering skin grafting uses vicrylmesh as scaffold material. The ester bond in PLGA breaks due to hydrolysis, and its degradation rate is affected by many factors, such as the mass ratio of La to GA, molecular weight, material shape and structure, etc. PLGA has the characteristics of easy processing and controllable degradation rate. It has been approved by FDA to be applied to human body, and has been widely studied in the fields of controllable drug/protein transport system, tissue engineering scaffold and so on. PLGA can promote cell adsorption and proliferation, which makes it have potential tissue engineering applications. Many studies have prepared micron nano PLGA three-dimensional scaffolds. Figure 1 lists three PLGA structures obtained by different methods

polycaprolactone (PCL)

PCL is a semi crystalline linear polyester made of relatively cheap monomers ε- Caprolactone（ ε- CL) is obtained directly by ring opening polymerization. PCL has good processability, is easily soluble in many organic solvents, and has low TM (55 ~ 60 ℃) and TG (– 60 ℃). The tensile strength of PCL is very low (23mpa), and the elongation at break is very high (700%). In addition, it can be copolymerized with a variety of polymers. The degradation cycle of PCL is 2 ~ 3a, and it is often used as a long-term drug controlled release carrier. Among them, micron nano PCL drug transport carrier is in the research stage

pcl is also used as tissue engineering scaffold material. Eng et al. Used three different methods to increase the hydrophilicity of PCL, and then blended it with polyethylene glycol (PEG) to make anisotropic hydrogel fiber scaffold. This scaffold has good biocompatibility and controllable structure, and is a potential scaffold material for heart valve tissue engineering. Zhaojing et al. Prepared micellar nanoparticles of PCL-PEG copolymer, which can be used as the transport carrier of picophyllin (anticancer drug). 70% of the drug can be released in vitro (37 ℃) and phosphate buffer (PBS, ph=7.4) in 96h, which is very consistent with Higuchi equation. Therefore, PCL-PEG copolymer nanoparticles containing PPP are expected to become injection preparations. Because the degradation rate of PCL is very slow, in order to obtain a faster degradation rate, researchers have developed several types of copolymers containing PCL. take ε- The copolymerization of Cl and dl-la can obtain a faster degradation rate. Similarly, ε- CL can also be copolymerized with GA to make surgical suture. Its hardness is smaller than PGA. Monofilament suture monacryl is such a product

in addition ε- The multiblock copolymer composed of Cl, La, GA and PEG can be used in drug controlled release systems. It is mainly used as the carrier of small and medium-sized bioactive molecules (synbiosys). Ng et al. Found a method to prepare PCL based small interfering RNA (siRNA) carrier. The preparation process is simple and convenient, and it has a significant inhibitory effect on tumor cell proliferation

Polydioxanone (PDS)

although PLA and PGA can be made into general-purpose degradable multifilamentary suture, multifilamentary suture has a high risk of infection in use, and multifilamentary suture also has large friction when penetrating tissue, so many researchers are looking for polymer materials suitable for making monofilament suture. PDS is a degradable polymer material suitable for monofilament suture. In the 1980s, the first PDS monofilament suture PDS came into the market. In addition, PDS fixing screws (orthosorbablepins) are also used in orthopedics, which are mainly used for the fixation and repair of small bones and cartilage. PDS is a colorless semi crystalline polymer, which can be obtained by ring opening polymerization of p-dioxanone, with Tg of – 10 ~ 0 ℃

as a member of polyester, its degradation is also achieved through the random fracture of ester bonds in the chain. High crystallinity and hydrophilicity make PDS have moderate degradation rate. In vivo, PDS is degraded to glyoxylic acid, which can be excreted through urine, and can also be further degraded to glycine, which is consistent with GA degradation products. Compared with PGA, the tensile elastic modulus of PDS (close to 1.5gpa) is very low. Under hydrolysis, the mechanical properties of PDS decreased within 1 ~ 2 months, and the mass loss occurred within 6 ~ 12 months

polyhydroxy fatty acid ester (P