8 Polymer Materials to Manufacture Medical Devices
Medical equipment can be subdivided into in vitro diagnostics, medical consumables, medical equipment, and pharmaceutical equipment. Due to its low cost, easy processing, light weight and toughness, plastics are widely used in medical devices.
Not all polymers are suitable for the medical device industry, and some are now used on a large scale, but they actually have hidden dangers and are gradually being replaced. According to the different use environments of medical devices, the requirements for polymer materials are different, but generally speaking, they should have the following properties:
- Good physical and mechanical properties, which can meet the requirements of physiological function and use environment;
- It can withstand the sterilization process without affecting its biological and mechanical properties;
- Good forming performance, easy to process into various shapes and low cost;
- The polymer is medical grade, with low heavy metal content, and low content of solubles and solubles;
- Non-toxic to the body, no pyrogenic reaction, no “three causes” (carcinogenic, teratogenic, gene mutation) effects, no damage to adjacent tissues, no interference with the body’s immune mechanism, and no calcification of the surface of the material;
- When the material is in contact with blood, it has good anticoagulant performance, does not cause reduction of blood cells after hemolysis, does not cause protein denaturation in the blood, and does not damage the formed components of the blood;
- When the material is implanted in the body, it has sufficient chemical stability and physiological inertia, and the physical and mechanical properties do not change significantly (excluding degradable materials).
At present, common polymer materials include PVC, PE, PP, PS, ABS, PC, fluoroplastics, TPE, etc.
PVC is a low-cost amorphous plastic with excellent chemical resistance and antimicrobial properties. Because its melting temperature is very close to the decomposition temperature, the glass transition temperature is high, the material is hard, and the processing is difficult. Therefore, plasticizers and other additives are generally added to the PVC resin to make hard, soft and Transparent product.
According to market estimates, about 25% of medical plastic products are PVC. Medical applications include: blood bags, hemodialysis tubes, breathing masks, oxygen tubes, bag infusion sets, urine bags, etc. Especially in repairing and implanting medical applications, it can be used for artificial ears and noses, mainly using its light weight, non-irritating to the skin, softness and tissue matching, and resistance to sweat, saliva and solvents.
Many disposable products in health services are made of flexible PVC.
However, it has also been proved that PVC as a polar material has an adsorption effect on certain drugs and thus affects the curative effect. It also has a very small amount of carcinogenic vinyl chloride monomer. Its main plasticizer DEHP is easy to precipitate and bring health risks. For this reason, the current Polyurethane materials are mostly used to make interventional catheters.
PE is the largest polymer material in the product. It is cheap, non-toxic, tasteless, excellent in chemical resistance, and has good biocompatibility. It is a non-polar material and has a small amount of drug adsorption. According to density and molecular chain side chain, it can be divided into HDPE, LDPE, LLDPE, UHMWPE, etc.
HDPE polymer chains have fewer side chains, and the chains can be compressed more densely, so it has higher crystallinity, molecular weight and density, and its mechanical strength is better than LDPE. It is often used in injection molded parts. The maximum operating temperature is 100°C, and it can be boiled for sterilization. Mainly used to make artificial lungs, artificial trachea and other artificial organs, orthopedic repair materials and disposable medical supplies.
HDPE is suitable for blow molding
LDPE has many side chains, so the relative molecular weight is small, crystallinity and density are low, and it has good flexibility, impact resistance and transparency. It is mainly used for blending with other plastics, medical packaging bags, and veins. Infusion container, etc.
In addition to the general characteristics of PE, UHMWPE (ultra-high molecular weight polyethylene) also has high impact resistance, strong abrasion resistance (the crown of plastic), low friction coefficient, biological inertness and good energy absorption characteristics, and its chemical resistance The performance is comparable to PTFE, and it is an ideal material for artificial hips and artificial joints.
PP looks like PE and is also a non-polar material. It is more transparent and lighter than PE, and has higher strength and hardness than PE. It has excellent chemical resistance, fatigue resistance, good heat resistance, and can be sterilized at a temperature above 100°C. It is easy to process and has no environmental stress cracking problems.
Medical PP has high transparency, good barrier properties and radiation resistance, and uses include disposable syringes, connectors, transparent plastic covers, straws, parenteral nutrition packaging, dialysis films, etc.
Non-PVC material with PP as the main body is a substitute for the widely used PVC material. PP film is usually welded into bags by heat sealing method, and its processing technology is more complicated than that of high-frequency welding PVC bags. Non-PVC large infusion bags are produced using fully automatic equipment to ensure stable process and reliable quality.
04 PS and K resin
PS is the third largest plastic species after PVC and PE. It is usually processed and applied as a single-component plastic. Its main characteristics are transparent, hard, but brittle and fragile, and have a high coefficient of thermal expansion. In recent decades, the development of modified polystyrene and styrene-based copolymers has overcome the shortcomings of polystyrene to a certain extent. K resin is one of them.
K resin is a low-cost transparent amorphous polymer made by copolymerization of styrene and butadiene. CA and SAN often have a light blue or light yellow color, while K resin is colorless and transparent. Odorless, non-toxic, lower density than PS, and higher impact resistance than PS. K resin is biocompatible and can be sterilized with ethylene oxide gas or ultraviolet rays. According to the number of butadiene components, different hardness can be distinguished.
K resin is mainly used in medical plastic products with difficult processing technology, high technical content, and high added value, such as artificial lung-oxygenator greenhouse, arterial outlet, reclaimer arterial outlet, heart suction head, aorta Intubation, blood filter, breather, thermostat, etc. At the same time, K resin meets the requirements of Class VI-50 of the US Pharmaceutical Packaging Law.
ABS is manufactured by co-polyacrylonitrile and styrene in the presence of polybutadiene (latex). The higher the acrylonitrile content, the higher the strength and the better the chemical resistance, but it also means that the lower the butadiene content, the lower the impact strength.
ABS has certain rigidity, hardness, impact resistance and chemical resistance, radiation resistance and ethylene oxide disinfection resistance. It is mainly used in medical applications as surgical tools, roller clamps, plastic needles, tool boxes, diagnostic devices and hearing aid housings. , Especially the shells of some large-scale medical equipment.
The typical characteristics of PC are toughness, strength, rigidity and heat-resistant steam sterilization. These characteristics make PC a priority choice for blood dialysis filters, surgical tool handles and oxygen tanks (when in surgical heart surgery, this instrument can remove blood from the Carbon dioxide, increase oxygen). The medical applications of PC also include needle-free injection systems, perfusion instruments, blood centrifuge bowls and pistons. Taking advantage of its high transparency, the usual myopia glasses are made of PC.
Fluoroplastics used in medicine are mainly PTFE. PTFE is a highly crystalline polymer with high density, the lowest known coefficient of friction and the best chemical resistance of all plastics, good biocompatibility and anticoagulant properties, no decomposition, no adverse reactions and aging when implanted in the body Not obvious, excellent heat resistance, continuous use temperature of 260 ℃, high temperature sterilization can be used.
Therefore, PTFE is widely used in medicine, such as artificial heart, lung, blood vessel, heart valve, various tubular organs, such as artificial trachea, esophagus, bile duct, urethra and artificial peritoneum, dura mater and artificial skin.
Thermoplastic elastomers (TPE) are soft thermoplastics with low elastic modulus and high toughness. Their chemical structure is composed of thermoplastic hard segments and elastic soft segments. The key difference from traditional rubber is the lack of or between the molecular chains. There is only very slight crosslinking.
Thermoplastic polyurethanes called TPE-U or TPU are partially crystalline and come in two different variants, the first based on polyester and the second based on polyether. The latter has excellent low-temperature flexibility and resistance to hydrolysis, anticoagulation, and antimicrobial attack. It can be used for medical catheters, artificial hearts, oxygen masks, drug release equipment, IV connectors, sphygmomanometers, rubber sacs, and skin delivery. Medicinal wound cloth.
The S in TPE-S or TPS is the abbreviation of styrene block copolymer. Usually TPS is based on SBS and SEBS. The latter has better heat resistance, mechanical properties and UV resistance, and has high transparency, non-polarity, It can be sterilized by steam, ethylene oxide and ultraviolet rays, and is non-toxic. It can replace PVC for disposable infusion tubes, blood bags and other medical flexible equipment.