Thermoplastic polyurethane elastomer (TPU) materials have better biocompatibility and stability than those of traditional medical materials such as PE, PP, TPE, PVC and silicone rubber, as well as excellent mechanical properties and processing properties, and the material is not Containing plasticizers, it has received more and more attention and application in the medical industry in recent years.
Human tissue and blood pose considerable challenges to the elastic materials implanted in medical devices: such materials must withstand long-term exposure to adverse aqueous environments at body temperature, and these devices must minimize patient complications. Materials must minimize coagulation, rejection, tissue inflammation, and toxic chemicals entering the body to meet the safety of implantable medical devices. In addition, the elastomer must have sufficient strength to produce a smaller, shape and size product according to the designer's requirements.
The chemical structural feature of TPU is that the macromolecular chain contains repeating urethane segments, wherein the macromolecular chain is composed of a flexible segment (soft satin) and a rigid segment (hard segment). The soft segment is typically composed of an oligomeric polyol and the hard segment is composed of a diisocyanate and a small molecule chain extender. The strong classical action between the hard segments promotes the hard segment aggregation into the microdomains, resulting in microphase separation, thus giving the TPU elastomer excellent physical properties and good biodegradability. In addition, since the basic component of blood is protein, the polypeptide chain constituting the protein contains several amide bonds, which are similar in polarity to the carbamate in the TPU macromolecular chain, so the TPU elastomer material and the organism have a good biological phase. Capacitive and blood compatibility. These characteristics make TPU materials more and more widely used in the medical field, especially in the selection of medical device elastomer materials implanted in the human body, TPU is more indispensable.
Medical grade TPU classification and characteristics
Medical grade TPU is usually divided into two categories: aliphatic and aromatic. The diisocyanate for polymerization generally has aromatic 4,4'-diphenylmethane diisocyanate (MDI) and aliphatic methylene dicyclohexyl diisocyanate (H12MDI); the polyol has polytetramethylene ether glycol ( PTMEG), polycarbonate diol (PCDL); chain extender is 1,4-butanediol (BDO).
Medical grade TPU has excellent properties, including: high tensile strength, up to 28~69MPa; high elongation at break, up to 250%~700%; wide hardness range - Shore hardness 62A~84D, even higher Good biological stability; good wear resistance and hydrolytic stability; good bonding performance; constant elastic properties at low temperature, resistant to bending; can be sterilized by irradiation with ethylene oxide and gamma rays.
At the same time, compared with other common medical materials, medical grade TPU elastomer has obvious advantages, such as: more resistant to bending than TPE, easy to bond, easier to coextrus with other materials, better biostability and compatibility; Rubber has better mechanical properties and processing properties, and the same strength wall thickness can be thinner, thus reducing the suffering of patients; less plasticizer than PVC, lower adsorption of liquid, better biocompatibility and compatibility, and physical Better performance.
Lubrizol's medical grade TPU elastomer
The medical grade is different from the industrial and civilian grade TPU elastomers. Due to its stringent performance requirements and strict purity requirements, only a few large companies in the world have been commercialized. Lubrizol has become the most comprehensive and most commercially available medical grade product in the world due to the acquisition of TPU elastomers and related companies such as Noveon and Dow Chemical. A supplier of TPU elastomers, whose products have been used in the medical industry for more than 30 years. In the domestic and global markets, Lubrizol's medical-grade TPU elastomer-related certification tests (USP Class VI, MEM Elution and other related tests) are the most comprehensive, which almost occupy the implant-grade TPU elastomer. main market.
Pellethane, Tecoflex, Tecothane, Carbothane and Isoplast are used for five medical grade TPU grades with excellent overall performance. Among them, Pellethane is suitable for short-term applications, such as infusion tubes, infusion tube drip buckets, indwelling needle extension tubes and slit protective sleeves; Tecoflex is resistant to yellowing, can be customized in color and is added with barium sulfate and barium sulfate, suitable for short- and medium-term applications. Such as central venous catheters, catheters, nasal feeding catheters, gastric endoscopy catheters and cardiac assist devices; Tecothane can be customized in color and added with barium sulfate and tungsten sulfate, suitable for medium and long-term medical applications, such as central venous catheters, catheters , nasal feeding catheter, gastric endoscopy catheter and cardiac assist device; Carbothane is resistant to yellowing, excellent oxidation resistance, hydrolysis resistance, good biocompatibility, customizable color and addition of barium sulfate and tungsten sulfate, suitable for A variety of medical applications that have been implanted in the human body for a long time; Isoplast has high tensile strength and impact resistance and is suitable for applications requiring hard polymers, impact modification, transparency and fiberglass filling.
Medical grade TPU elastomer application
For many years, PVC has become a popular material for the manufacture of medical bags and medical catheters that require extremely high flexibility due to their relatively low price and excellent anti-kink properties. But over the years, researchers around the world have consistently discovered that PVC can have a detrimental effect on patients. PVC medical devices contain a large amount of phthalate plasticizers, which are easily migrated into blood or other liquids in medical catheters or medical bags, causing patients to be exposed to phthalate. Extremely high. In addition, in view of the use of medical devices for the delivery of liquid medicine or blood, medical devices such as catheters and medical bags must be incinerated after use to avoid the risk of improper disposal of biologically contaminated waste, but incineration of PVC will release nearly 75 A harmful substance that causes harm to human bodies and incineration equipment. Therefore, many health systems in the world have promised to completely eliminate PVC from hospitals.
TPU elastomer is an excellent alternative to PVC because it does not contain plasticizers and there is no risk of phthalate migration from medical devices to liquids or humans. In addition, TPU elastomers are easily incinerated and do not release corrosive substances and other hazardous chemicals. From a material point of view, the strength of the TPU elastomer is also significantly higher than that of PVC and other alternative materials, and it can be made into thin-walled catheters and medical bags with higher internal compressive strength. Medical devices made with them are not only more durable, they use less material, but are also less likely to be damaged in a frequently used hospital environment. TPU elastomers have better transparency than other potential PVC alternatives such as ethylene vinyl acetate (EVA) and thermoplastic polyolefin elastomers (TPO) to ensure that they are not inferior to the aesthetics of PVC.
● implantable medical device
TPU elastomers have become the material of choice for the manufacture of medical catheters, especially for medical catheters that need to be introduced into the human body, due to their good biocompatibility and stability, high strength, low friction factor and good flexibility. In order to adapt to the human body structure, some medical catheters have an outer diameter of only about 3 mm; in order to pass different chemical liquids, they are often designed as a porous structure, and at most, up to 9 holes can be achieved, and some holes are still shaped holes, and between the holes and the holes The interval is less than 0.5mm; in order to ensure the stability and reliability of the liquid medicine, the outer diameter of the tube and the size of each small hole are required to be stable, and the tube wall is absolutely not allowed to be broken during the injection or threading process; In order to ensure the smoothness of catheter insertion and reduce the discomfort of the patient, it is also required that the outer wall of the catheter must be smooth, and after entering the human body, the catheter needs to be more compliant due to the influence of body temperature; in order to monitor the catheter in the human body at any time during the operation. The position is to ensure the correctness of the insertion route, and the tube material needs to be filled with 20%~40% of barium sulfate as an X-ray contrast agent. For the application requirements of these medical catheters, the TPU can be well satisfied.
Although some implantable medical devices can also choose silicone rubber, silicone rubber is not suitable for making porous structures, and the wall thickness is much thicker than that of polyurethane elastomer materials to achieve the same strength requirements, which will cause more pain to patients. . Therefore, in the field of implantable medical devices, TPU elastomers are the best choice for materials that can satisfy both excellent biostability and compatibility and high mechanical strength.
For decades, PVC has been widely used in medical device manufacturing due to its low cost and excellent softening properties. However, in recent years, with the deepening of medical research, the drawbacks of PVC as a medical material have been continuously discovered, and medical device manufacturers around the world have gradually begun to get rid of dependence on PVC.
At the same time, TPU elastomers are gaining more and more applications in the medical field by replacing PVC and surpassing other materials due to their excellent biocompatibility and stability, as well as excellent mechanical properties and processing properties.