Compared with glass and metal materials, the main characteristics of plastics are:
1, the cost is low, can be reused without disinfection, suitable for use as a raw material for the production of disposable medical devices;
2, the processing is simple, the use of its plasticity can be processed into a variety of useful structures, and metal and glass is difficult to manufacture into complex structure of products;
3, tough, elastic, not as easy to break as glass;
4, with good chemical inertness and biological safety.
These performance advantages make plastics widely used in medical devices, mainly including polyvinyl chloride (PVC), polyethylene (PE), polypropylene (PP), polystyrene (PS), polycarbonate (PC), ABS, polyurethane, polyamide, thermoplastic elastomers, polysulfone and polyether ether ketone. Blending can improve the performance of plastics, so that the best performance of different resins are reflected, such as polycarbonate /ABS, polypropylene/elastomer blending modification.
Due to contact with liquid medicine or contact with the human body, the basic requirements of medical plastics are chemical stability and biosafety. In short, the components of plastic materials can not be precipitated into the liquid medicine or the human body, will not cause toxicity and damage to tissues and organs, and is non-toxic and harmless to the human body. In order to ensure the biosafety of medical plastics, medical plastics usually sold in the market are certified and tested by medical authorities, and users are clearly informed which grades are medical grade.
Medical plastics in the United States usually pass FDA certification and USPVI biological detection, and medical grade plastics in China are usually tested by Shandong medical device Testing Center. At present, there are still a considerable number of medical plastic materials in the country without a strict sense of biosafety certification, but with the gradual improvement of regulations, these situations will be more and more improved.
According to the structure and strength requirements of the device product, we choose the right type of plastic and the right grade, and determine the processing technology of the material. These properties include processing performance, mechanical strength, cost of use, assembly method, sterilization, etc. The processing properties and physical and chemical properties of several commonly used medical plastics are introduced.
Seven commonly used medical plastics
1. Polyvinyl chloride (PVC)
PVC is one of the most productive plastic varieties in the world. PVC resin is white or light yellow powder, pure PVC is atactic, hard and brittle, rarely used. According to different uses, different additives can be added to make PVC plastic parts show different physical and mechanical properties. Adding an appropriate amount of plasticizer to PVC resin can make a variety of hard, soft and transparent products.
Hard PVC does not contain or contains a small amount of plasticizer, has good tensile, bending, compressive and impact resistance, can be used as a structural material alone. Soft PVC contains more plasticizers, and its softness, elongation at break and cold resistance are increased, but the brittleness, hardness and tensile strength are reduced. The density of pure PVC is 1.4g/cm3, and the density of PVC plastic parts with plasticizers and fillers is generally in the range of 1.15~2.00g/cm3.
According to market estimates, about 25% of medical plastic products are PVC. This is mainly due to the low cost of the resin, the wide range of applications, and its easy processing. PVC products for medical applications are: hemodialysis pipes, breathing masks, oxygen tubes and so on.
2. Polyethylene (PE, Polyethylene)
Polyethylene plastic is the largest variety in the plastic industry, milky, tasteless, odorless and non-toxic glossy waxy particles. It is characterized by cheap price, good performance, can be widely used in industry, agriculture, packaging and daily industry, and occupies a pivotal position in the plastic industry.
PE mainly includes low density polyethylene (LDPE), high density polyethylene (HDPE) and ultra-high molecular weight polyethylene (UHDPE) and other varieties. HDPE has fewer branch chains on the polymer chain, higher relative molecular weight, crystallinity and density, greater hardness and strength, poor opacity, high melting point, and is often used in injection parts. LDPE has many branch chains, so the relative molecular weight is small, crystallinity and density is low, with better softness, impact resistance and transparency, often used for blowing film, is currently widely used PVC alternative. HDPE and LDPE materials can also be mixed according to the performance requirements. UHDPE has high impact strength, low friction, resistance to stress cracking and good energy absorption characteristics, making it an ideal material for artificial hip, knee and shoulder connectors.
3. polypropylene (PP, polypropylene)
Polypropylene is colorless, odorless and non-toxic. Looks like polyethylene, but is more transparent and lighter than polyethylene. PP is a thermoplastic with excellent properties, with small specific gravity (0.9g/cm3), non-toxic, easy to process, impact resistance, anti-deflection and other advantages. It has a wide range of applications in daily life, including woven bags, films, turnover boxes, wire shielding materials, toys, car bumpers, fibers, washing machines and so on.
Medical PP has high transparency, good barrier and radiation resistance, so that it has a wide range of applications in the medical equipment and packaging industry. Non-PVC materials with PP as the main body are currently widely used as alternatives to PVC materials.
4. Polystyrene (PS) and K resin
PS is the third largest plastic variety after polyvinyl chloride and polyethylene, usually used as a single-component plastic processing and application, the main characteristics are light weight, transparent, easy to dye, molding processing performance is good, so widely used in daily plastics, electrical parts, optical instruments and cultural and educational supplies. Its texture is hard and brittle, and it has a high coefficient of thermal expansion, which limits its application in engineering. In recent decades, modified polystyrene and styrene-based copolymers have been developed to overcome the shortcomings of polystyrene to a certain extent. K resin is one of them.
K resin is made of styrene and butadiene copolymerization, it is an amorphous polymer, transparent, tasteless, non-toxic, density of 1.01g/cm3 (lower than PS, AS), higher impact resistance than PS, transparency (80 ~ 90%) good, thermal deformation temperature of 77℃, The amount of butadiene contained in K material, its hardness is also different, due to the good fluidity of K material, processing temperature range is wide, so its processing performance is good.
The main uses in daily life include cups, LIDS, bottles, cosmetic packaging, hangers, toys, PVC substitute material products, food packaging and medical packaging supplies
5. ABS, Acrylonitrile Butadiene Styrene copolymers
ABS has certain rigidity, hardness, impact resistance and chemical resistance, radiation resistance and ethylene oxide disinfection resistance.
ABS in the medical application is mainly used as surgical tools, drum clips, plastic needles, tool boxes, diagnostic devices and hearing aid housing, especially some large medical equipment housing.
6. Polycarbonate (PC, Polycarbonate)
The typical characteristics of PCS are toughness, strength, rigidity, and heat-resistant steam sterilization, which make PCS preferred as hemodialysis filters, surgical tool handles, and oxygen tanks (when used in surgical heart surgery, this instrument can remove carbon dioxide from the blood and increase oxygen);
Other applications of PC in medicine 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.
7. PTFE (Polytetrafluoro ethylene)
Polytetrafluoroethylene resin is a white powder, waxy appearance, smooth and non-stick, is the most important plastic. PTFE has excellent properties that are not comparable to general thermoplastics, so it is known as "plastic king". Its friction coefficient is the lowest among plastics, has good biocompatibility, and can be made into artificial blood vessels and other directly implanted devices.
Post time: Oct-25-2023