Medical injection-molded parts, as core components in medical devices, medical consumables, and drug delivery systems, have their material selection directly related to the safety, effectiveness, and reliability of products. Compared with ordinary injection-molded parts, medical injection-molded parts need to meet more stringent standards in material selection, covering aspects such as biocompatibility, chemical stability, sterilization adaptability, physical properties, and traceability.

I. Biocompatibility: The Foundation of Material Safety

Biocompatibility is the primary requirement for material selection of medical injection-molded parts. It refers to the ability of a material not to cause toxicity, sensitization, irritation, or immune responses when in contact with human tissues or blood in specific application scenarios. According to the ISO 10993 series standards issued by the International Organization for Standardization (ISO), medical materials need to pass a full range of tests, including cell cytotoxicity (MTT assay), sensitization (skin patch test), and pyrogen (limulus amoebocyte lysate test), to ensure their safety for the human body. For example, polyether ether ketone (PEEK) is widely used in orthopedic implants due to its excellent biocompatibility and high strength; polycarbonate (PC), after passing multiple safety verifications, is often used in transparent parts such as dialyzer housings and medical masks.

Biocompatibility also involves the long-term adaptability of materials to the biological environment. For instance, materials implanted in the body need to have anticoagulant properties to avoid hemolysis or thrombosis; materials in contact with blood need to prevent protein denaturation or a decrease in blood cells. In addition, the degradation products of materials must also be non-toxic and harmless to avoid the release of harmful substances during long-term use.

II. Chemical Stability: A Barrier Against Environmental Corrosion

Medical injection-molded parts often need to withstand the erosion of disinfectants, drugs, and body fluids, so materials must have excellent chemical stability. For example, polytetrafluoroethylene (PTFE) is used in vascular catheters and tracheal intubation tubes due to its strong chemical inertness; polypropylene (PP) is resistant to acids and alkalis and is widely used in products such as syringes and infusion bottles. The choice of materials should be determined according to specific application scenarios:

• Moist Heat Sterilization: Materials that can withstand high temperatures are required. For example, polyphenylsulfone (PPSU) can withstand moist heat sterilization at 121°C for 15-30 minutes without deformation, making it suitable for surgical instrument boxes.
• Ethylene Oxide Sterilization: Materials should have low adsorption of ethylene oxide to avoid residual risks. Medical silicone is often used in seals due to its low adsorption.
• Irradiation Sterilization: Materials need to be resistant to high doses of radiation. For example, medical-grade PC can withstand large-dose radiation disinfection without yellowing or performance degradation.

III. Sterilization Adaptability: The Key to Ensuring Sterile Use

Medical injection-molded parts need to be sterilized to ensure a sterile state, so materials must be compatible with different sterilization methods. For example:

• High-Temperature Steam Sterilization: Requires materials that are heat-resistant and dimensionally stable, such as PEEK and PPSU.
• Ethylene Oxide Sterilization: Materials with low adsorption should be selected to avoid the retention of sterilizing agents, such as silicone and some special plastics.
• Gamma Ray or Electron Beam Irradiation Sterilization: Materials need to be radiation-resistant and not produce toxic degradation products, such as PC and polyimide (PI).

The choice of materials also needs to consider the impact of sterilization on physical properties. For example, some materials may soften and deform at high temperatures, while others may become brittle under irradiation. Therefore, experimental verification of the performance stability of materials after sterilization is required.

IV. Physical Properties: The Guarantee for Meeting Functional Requirements

The physical properties of medical injection-molded parts need to meet specific functional requirements, including strength, hardness, elasticity, transparency, etc. For example:

• High-Strength Requirements: Orthopedic implants need to select high-strength materials, such as PEEK and titanium alloy composites.
• High-Transparency Requirements: Dialyzer housings and infusion bags need to select transparent materials, such as PC and polymethyl methacrylate (PMMA).
• Elastic Requirements: Catheters and seals need to select elastic materials, such as polyurethane (PU) and thermoplastic elastomers (TPE).
• Wear Resistance Requirements: Artificial joint components need to select wear-resistant materials, such as ultra-high molecular weight polyethylene (UHMWPE).

In addition, the processability of materials also needs to be considered. For example, materials should be easy to injection-mold and have high dimensional stability after molding to meet the strict precision requirements of medical products.

V. Traceability: The Support for Full Life-Cycle Management

Medical injection-molded parts need to achieve full life-cycle traceability, so material selection should support data recording and tracking. For example:

• Raw Material Traceability: Data such as supplier, batch number, and quality report need to be recorded to ensure a reliable material source.
• Production Process Traceability: Process parameters and inspection data need to be recorded to facilitate problem investigation and quality improvement.
• Product Flow Traceability: Implantable components need to accurately record their flow to facilitate recalls or investigations of adverse events.

The choice of materials also needs to consider the feasibility of marking and labeling. For example, laser marking or QR code marking requires the material surface to be easy to process and the marked information to be durable and non-fading.

VI. Environment and Cost: Balancing Performance and Economic Considerations

The material selection of medical injection-molded parts also needs to consider environmental factors and cost-effectiveness. For example:

• Environmental Protection: Priority should be given to biodegradable or recyclable materials, such as polylactic acid (PLA) for disposable medical devices.
• Cost: On the premise of meeting performance requirements, materials with lower costs should be selected, such as PP and PE for non-implantable products.
• Supply Chain Stability: Suppliers with stable supply and reliable quality should be selected to avoid production disruptions due to material shortages.

Conclusion

The material selection of medical injection-molded parts is a multi-dimensional and stringent process. It is necessary to comprehensively consider factors such as biocompatibility, chemical stability, sterilization adaptability, physical properties, traceability, as well as environmental and cost factors. Through scientific material selection and strict control, the safety, effectiveness, and reliability of medical injection-molded parts can be ensured, providing solid support for the development of the medical industry.