The main characteristics of medical plastics
Biocompatibility:Ensuring Safe Body ResponseBiocompatibility is the ability of a material to have an appropriate host response when used for its intended medical purpose. Therefore, medical plastics must be non-toxic, non-hazardous or non-immunogenic when in contact with human tissue or fluids. Some of the key considerations for biocompatibility of medical plastics include:Cytotoxicity-Materials must not produce toxic effects on living cells. Leachables and extractables must be below hazardous levels. Sensitization - Plastics should not cause allergic reactions after implantation. Sensitization tests are performed using animal models. Irritation and Inflammation-Medical plastics should not cause irritation, swelling, injury, or inflammatory reactions in the body. These are evaluated by skin irritation studies. Blood compatibility-Medical plastics must be tested for hemolysis. If the device involves blood contact, the plastic must not induce thrombosis, embolism, red blood cell rupture, etc. Carcinogenicity-Materials must not promote cancerous tumors when implanted. A two-year animal carcinogenicity study was conducted. Genotoxicity-Plastics must not damage cellular DNA or cause mutations. Tests like the Ames test identify genotoxins. Sterilization Residues - After sterilization, plastics should not retain toxic residues. They must not be leached out later.
Non-permeability:Resistance to diffusion of substances Non-permeability refers to the ability of a plastic to act as an effective barrier. This prevents various substances from diffusing through it. This is critical for those plastics used in fluid handling, sealing and conveying applications. Key Aspects of Non-Permeability:Water Permeability - Medical tubing, fluid bags, catheters, etc. must not allow water to be transmitted or absorbed from the medical device. This may affect the performance and characteristics of the medical device. Permeability - Oxygen masks, anesthesia equipment and intravenous tubing should not allow gas to diffuse. This may result in variations in concentration. Select medical plastics with low permeability. Chemical permeability-Drug elution devices rely on plastics to diffuse active agents at controlled calibrated rates. They should be impermeable to other chemicals. Microbial permeability-Plastic matrices should act as a barrier to microbial transmission. Microporosity compromises sterility. Leachable permeability-Plastics cannot diffuse from the material into fluids or surrounding tissues. Plastic components that can leach are additives, fillers, and plasticizers. Factors that affect permeability include crystallinity, cross-linking, polarity, fillers, and molecular structure. Higher density and cross-linked plastics provide lower permeability.
Sterilization resistance:Preventing the spread of infectionMedical devices and equipment require repeated sterilization in hospitals. This helps prevent the spread of infection. Medical grade plastics must withstand frequent sterilization by heat, radiation, steam and chemicals. There must be no change in visual appearance, physical properties, or mechanical properties. Key considerations include:Heat Resistance - Plastics withstand repeated autoclave or dry heat sterilization cycles. They must retain their properties even after these sterilization processes. Examples include tensile strength, impact resistance and other mechanical properties. Radiation Resistance - Gamma or electron beam radiation can degrade polymers. This can occur through chain breakage, oxidation and cross-linking. Suitable plastics should be able to resist high sterilization doses. Chemical Resistance-Chemical sterilizing agents should not have degrading effects over time. Examples include cracking, hydrolysis, leaching, and swelling. Sterilant Absorption-Residual sterilants should not leach from the plastic and cause toxicity. Aeration/extraction procedures may be required. Appearance - Sterilization should not significantly alter the appearance of the plastic. For example, optical clarity, reflectivity, or color, or cause yellowing/chalking. For safe medical use, plastics can resist damage during repeated sterilization. This can be achieved in the presence of additives. Examples include antioxidants, stabilizers, radio-opaque agents, etc.
Lightweight:Easy handlingLightweight plastics help reduce fatigue and improve ergonomics for medical professionals. They do this by making devices and equipment easier to handle and carry. For patients, lightweight plastics in medical products can minimize weight burdens. For example, in prosthetics and mobility aids. Here are some key aspects:Low density - Medical plastics such as polyethylene, polypropylene, acrylic and ABS have a density of between 0.85 - 1.2 g/cm3. This is lower than metals such as steel (8 g/cm3). High Strength to Weight Ratio - Medical plastics can be formulated and designed to achieve high strength and stiffness relative to their low mass. This allows for reduced measurements and weight savings. Easier handling - Devices made from lightweight plastics reduce wrist strain. They are more comfortable for prolonged surgical procedures that require maneuvering. Portability - Portable devices with plastic frames and housings are easier to transport and use. Examples include wheelchairs, patient monitors, etc. Ergonomics - Customized plastics make handheld devices easier to use and reduce fatigue issues. Examples include handles, grips and housings. Patient comfort-Lightweight plastics reduce the burden of carrying for patients. Examples include plastic prosthetics, braces and implants.
Durability:Maintaining Performance Throughout the LifecycleMedical devices made of plastic need to maintain performance throughout their expected lifespan. This is despite the pressures of their routine cleaning, handling, transportation and sterilization. Key aspects of durability include:Tensile Strength - Plastics used in load-bearing applications require high strength and stiffness. This helps to withstand mechanical forces during use without permanent deformation or cracking. Creep resistance - Medical components such as plastic tubing and equipment housings are subjected to repeated bending. These materials should be fatigue resistant. Impact and abrasion resistance - Good toughness and abrasion resistance help external components. For example, plastic housings can withstand knocks and scratches during daily use. Dimensional Stability - Plastic should maintain tight dimensional tolerances over time. This should be free of any warping. Examples include precision fittings and components. Chemical resistance - Medical plastics need to be resistant to cleaning agents, disinfectants and body fluids. They must not break or expand/shrink excessively. Choose medical grade plastics that are chemically resistant. UV/weathering resistance - Plastic devices must maintain performance even when exposed to the outdoors. Examples include light, humidity, and other environmental conditions during storage and use. Select medical grade plastics with good weathering resistance.
