In recent years, the global medical device industry has maintained rapid and stable growth, with an average growth rate of about 4%, which is higher than the national economic growth rate over the same period. The United States, Europe, and Japan jointly occupy the main market position in the global medical device market. The United States is the world's largest producer and consumer of medical devices, and its consumption is firmly in the leading position in the industry. Among the world's top medical device giants , The United States has the largest number of medical device companies and accounts for the largest proportion.
This article mainly introduces commonly used medical engineering plastics, which are composed of materials with easy-to-process shapes. These plastics tend to be relatively expensive relative to weight, because most materials are lost due to debris during processing.
Introduction to common engineering plastics in the medical field
Acrylonitrile Butadiene Styrene (ABS)
The terpolymer is made of SAN (styrene-acrylonitrile) and butadiene synthetic rubber. From its structure, the main chain of ABS can be BS, AB, AS, and the corresponding branch chain can be AS, S, AB and other components.
ABS is a polymer in which the rubber phase is dispersed in the continuous phase of the resin. Therefore, it is not simply a copolymer or mixture of these three monomers, SAN (styrene-acrylonitrile), which gives ABS hardness and surface finish, butadiene gives For its toughness, the ratio of these three components can be adjusted as needed. Plastics are usually used to make 4-inch thick plates and 6-inch diameter rods, which can be easily bonded and laminated to form thicker plates and components. Due to its reasonable cost and easy processing, it is a popular material for computer numerical control (CNC) manufacturing prototypes.
ABS is often used to blister large-scale medical equipment shells. In recent years, ABS filled with glass fiber has been used in more places.
Acrylic resin (PMMA)
Acrylic resin is actually one of the earliest medical device plastics, and is still commonly used in the molding of anaplastic restorations. *Acrylic is basically polymethyl methacrylate (PMMA).
Acrylic resin is strong, clear, processable and bondable. One common method of bonding acrylic is to solvent bonding with methyl chloride. Acrylic has almost unlimited kinds of rods, sheet and plate shapes, and various colors. Acrylic resins are particularly suitable for light pipes and optical applications.
Acrylic resin for signage and display can be used for benchmark tests and prototypes; however, care must be taken to determine the medical grade version before using it in any clinical trials. Commercial grade acrylic resins may contain UV resistance, flame retardants, impact modifiers and other chemicals, making them unsuitable for clinical use.
Polyvinyl chloride (PVC)
PVC has two forms, rigid and flexible, depending on whether or not plasticizers are added. PVC is usually used for water pipes. The main disadvantages of PVC are poor weather resistance, relatively low impact strength, and the weight of the thermoplastic sheet is quite high (specific gravity 1.35). It is easily scratched or damaged, and has a relatively low thermal deformation point (160).
Unplasticized PVC is produced in two main formulations: Type I (corrosion resistance) and Type II (high impact). Type I PVC is the most commonly used PVC, but in applications requiring higher impact strength than Type I, Type II has better impact resistance and slightly reduced corrosion resistance. In applications requiring high-temperature formulations, polyvinylidene fluoride (PVDF) for high-purity applications can be used at approximately 280°F.
Medical products made of plasticized polyvinyl chloride (plasticizedpvc) were originally used to replace natural rubber and glass in medical equipment. The reason for the substitution is: plasticized polyvinyl chloride materials are more easily sterilized, more transparent, and have better chemical stability and economic effectiveness. Plasticized polyvinyl chloride products are easy to use, and because of their own softness and elasticity, they can avoid damaging the sensitive tissues of the patient and avoid making the patient feel uncomfortable.
Polycarbonate (PC)
Polycarbonate (PC) is the toughest transparent plastic and is very useful for prototype medical devices, especially if UV curing bonding is to be used. PC has several forms of rod, plate and sheet, it is easy to combine.
Although more than a dozen performance characteristics of a PC can be used alone or in combination, seven are most often relied on. PC has high impact strength, transparent water transparency, good creep resistance, wide operating temperature range, dimensional stability, wear resistance, hardness and rigidity, despite its ductility.
PC is easily discolored by radiation sterilization, but radiation stability grades are available.
Polypropylene (PP)
PP is a light-weight, low-cost polyolefin plastic with a low melting point, so it is very suitable for thermoforming and food packaging. PP is flammable, so if you need fire resistance, look for flame retardant (FR) grades. PP is resistant to bending, commonly known as "100-fold glue". For applications that require bending, PP can be used.
Polyethylene (PE)
Polyethylene (PE) is a commonly used material in food packaging and processing. Ultra-high molecular weight polyethylene (UHMWPE) has high wear resistance, low friction coefficient, self-lubricity, surface non-adhesion and excellent chemical fatigue resistance. It also maintains high performance at extremely low temperatures (for example, liquid nitrogen, -259°C). UHMWPE starts to soften around 185°F and loses its abrasion resistance.
Since UHMWPE has a relatively high expansion and contraction rate when temperature changes, it is not recommended for close tolerance applications in these environments.
Due to its high surface energy, non-adhesive surface, PE may be difficult to bond. Components are easiest to fit together with fasteners, interference or snaps. Loctite produces cyanoacrylate adhesives (CYA) (LoctitePrism surface-insensitive CYA and primer) for bonding these types of plastics.
UHMWPE is also used in orthopedic implants with great success. It is the most commonly used material in the acetabular cup during total hip arthroplasty and the most common material in the tibial plateau component during total knee arthroplasty. It is suitable for highly polished cobalt-chromium alloy. *Please note that the materials suitable for orthopedic implants are special materials, not industrial versions. Medical grade UHMWPE is sold under the trade name Lennite by Westlake Plastics (Lenni, PA).
Polyoxymethylene (POM)
DuPont's Delrin is one of the most well-known POMs, and most designers use this name to refer to this plastic. POM is synthesized from formaldehyde. POM was originally developed in the early 1950s as a tough, heat-resistant non-ferrous metal substitute, commonly known as "Saigang". It is a tough plastic with a low coefficient of friction and high strength.
Delrin and similar POM are difficult to bond, and mechanical assembly is best. Delrin is commonly used for machined medical device prototypes and closed fixtures. It is highly processable, so it is very suitable for prototypes of machining equipment that require strength, chemical resistance, and materials that meet FDA standards.
One disadvantage of Delrin is its sensitivity to radiation sterilization, which tends to make POM brittle. If radiation sterilization, snap fit, plastic spring mechanism and thin section under load may break. If you want to sterilize B-POM parts, please consider using EtO, Steris or autoclaves, depending on whether the device contains any sensitive components, such as electronic devices.
Nylon (PA)
Nylon is available in 6/6 and 6/12 formulations. Nylon is tough and heat resistant. Identifiers 6/6 and 6/12 refer to the number of carbon atoms in the polymer chain, and 6/12 is a long-chain nylon with higher heat resistance. Nylon is not as processable as ABS or Delrin (POM) because it tends to leave sticky chips on the edges of parts that may need to be deburred.
Nylon 6, the most common is cast nylon, which was developed by DuPont before World War II. However, it was not until 1956, with the discovery of compounds (co-catalysts and accelerators) that cast nylon became commercially viable. With this new technology, the polymerization speed is greatly increased, and the steps required to achieve polymerization are reduced.
Due to fewer processing restrictions, cast nylon 6 provides one of the largest array sizes and custom shapes of any thermoplastic. Castings include bars, tubes, tubes and plates. Their size ranges from 1 pound to 400 pounds.
Nylon materials have mechanical strength and skin-friendly feel that ordinary materials do not have. However, medical equipment foot drop orthoses, rehabilitation wheelchairs, and medical nursing beds usually require parts with a certain load-bearing capacity, so PA66+15%GF is generally selected.
Fluorinated Ethylene Propylene (FEP)
Fluorinated ethylene propylene (FEP) has all the desirable properties of tetrafluoroethylene (TFE) (polytetrafluoroethylene [PTFE]), but has a lower survival temperature of 200°C (392°F). Unlike PTFE, FEP can be injection molded and extruded into bars, tubes and special profiles by conventional methods. This becomes a design and processing advantage over PTFE. Bars up to 4.5 inches and plates up to 2 inches are available. The performance of FEP under radiation sterilization is slightly better than that of PTFE.
High-performance engineering plastics
Polyetherimide (PEI)
Ultem 1000 is a thermoplastic polyetherimide high-heat polymer, designed by General Electric Company for injection molding. Through the development of new extrusion technology, manufacturers such as A. L. Hyde, Gehr and Ensinger produce various models and sizes of Ultem 1000. Ultem 1000 combines excellent processability and has cost saving advantages compared to PES, PEEK and Kapton in high heat applications (continuous use up to 340°F). Ultem is autoclavable.
Polyetheretherketone (PEEK)
Polyetheretherketone (PEEK) is a trademark of Victrex plc (UK), a crystalline high-temperature thermoplastic with excellent heat and chemical resistance, as well as excellent wear resistance and dynamic fatigue resistance. It is recommended for electrical components that require high continuous operating temperature (480°F), and extremely low emissions of smoke and toxic fumes exposed to flames.
PEEK meets Underwriters Laboratories (UL) 94 V-0 requirements, 0.080 inches. The product has extremely strong resistance to gamma radiation, even exceeding that of polystyrene. The only common solvent that can attack PEEK is concentrated sulfuric acid. PEEK has excellent hydrolysis resistance and can operate in steam up to 500°F.
Polytetrafluoroethylene (PTFE)
TFE or PTFE (polytetrafluoroethylene), usually called Teflon, is one of the three fluorocarbon resins in the fluorocarbon group, which is composed entirely of fluorine and carbon. The other resins in this group, also known as Teflon, are perfluoroalkoxy fluorocarbon (PFA) and FEP.
The forces that bind fluorine and carbon together provide one of the strongest known chemical bonds among closely symmetrically arranged atoms. The result of this bond strength plus chain configuration is a relatively dense, chemically inert, and thermally stable polymer.
TFE resists heat and almost all chemical substances. Except for a few foreign species, it is insoluble in all organic matter. Its electrical performance is very good. Although it has high impact strength, compared with other engineering thermoplastics, its wear resistance, tensile strength and creep resistance are low.
TFE has the lowest dielectric constant and lowest dissipation factor of all solid materials. Due to its strong chemical connection, TFE is almost unattractive to different molecules. This results in a friction coefficient as low as 0.05. Although PTFE has a low coefficient of friction, it is not suitable for load-bearing orthopedic applications due to its low creep resistance and low wear properties. Sir John Charnley discovered this problem in his pioneering work on total hip replacement in the late 1950s.
Polysulfone
Polysulfone was originally developed by BP Amoco and is currently manufactured by Solvay under the trade name Udel, and polyphenylsulfone is sold under the trade name Radel.
Polysulfone is a tough, rigid, high-strength transparent (light amber) thermoplastic that can maintain its properties in a wide temperature range from -150°F to 300°F. Designed for FDA-approved equipment, it has also passed all USP Class VI (biological) tests. It meets the drinking water standards of the National Sanitation Foundation, up to 180°F. Polysulfone has very high dimensional stability. After exposure to boiling water or air at 300°F, the linear dimensional change is usually one-tenth of 1% or less. Polysulfone has high resistance to inorganic acids, alkalis and salt solutions; even at high temperatures under moderate stress levels, it has good resistance to detergents and hydrocarbon oils. Polysulfone is not resistant to polar organic solvents such as ketones, chlorinated hydrocarbons and aromatic hydrocarbons.
Radel is used for instrument trays that require high heat resistance and high impact strength, and for hospital autoclave tray applications. Polysulfone engineering resin combines high strength and long-term resistance to repeated steam sterilization. These polymers have proven to be alternatives to stainless steel and glass. Medical grade polysulfone is biologically inert, has a unique long life in the sterilization process, can be transparent or opaque, and is resistant to most common hospital chemicals.
