1. Introduction

Medical injection-molded parts are widely used in various medical devices and instruments, such as syringes, infusion sets, and surgical instrument handles. These injection-molded parts not only need to meet strict initial performance requirements but also must maintain stable performance throughout their entire service life to ensure the safety and effectiveness of medical operations. However, due to the influence of multiple factors, medical injection-molded parts may experience performance degradation during long-term use, such as aging, deformation, and strength reduction. Therefore, formulating effective strategies for maintaining long-term performance is of utmost importance in the medical industry.

2. Factors Influencing the Long-Term Performance of Medical Injection-Molded Parts

2.1 Material Selection

The material is the foundation for determining the performance of medical injection-molded parts. Different plastic materials have distinct chemical structures, physical properties, and aging characteristics. For example, polypropylene (PP) has good chemical stability and heat resistance but is prone to aging and degradation under long-term ultraviolet exposure. Polycarbonate (PC) has high strength and transparency but is sensitive to certain chemicals and may experience stress cracking. Additionally, the additives in the material, such as plasticizers, stabilizers, and antioxidants, also affect the long-term performance of injection-molded parts. Improper selection or unreasonable addition amounts of additives can lead to additive migration and failure, thereby impacting the performance of the injection-molded parts.

2.2 Injection Molding Process

Injection molding process parameters, such as injection temperature, injection pressure, holding pressure time, and cooling time, have a significant impact on the internal structure and performance of medical injection-molded parts. Unreasonable injection molding processes can result in defects within the injection-molded parts, such as residual stress, pores, and cracks, which can serve as starting points for performance degradation during long-term use. For example, excessively high injection temperatures can cause material degradation, reducing the strength and heat resistance of the injection-molded parts. Insufficient injection pressure can lead to incomplete melt filling, resulting in shrinkage cavities and non-uniform density, affecting the dimensional stability and mechanical properties of the injection-molded parts.

2.3 Environmental Factors

Medical injection-molded parts are exposed to various environmental factors during use, such as temperature, humidity, light, and chemicals. High-temperature environments can accelerate the aging and degradation of materials, reducing the strength and toughness of injection-molded parts. High-humidity environments can cause material moisture absorption, leading to dimensional changes and performance degradation. Ultraviolet exposure can trigger photochemical oxidation reactions in certain plastic materials, causing color changes, surface crazing, and performance deterioration. Contact with chemicals, such as disinfectants and drugs, can cause material swelling, corrosion, or stress cracking.

2.4 Mechanical Stress

Medical injection-molded parts are subjected to various mechanical stresses during use, such as tension, compression, bending, and torsion. Long-term mechanical stress can cause fatigue damage to the injection-molded parts, gradually accumulating into cracks and ultimately leading to part failure. For example, surgical instrument handles are frequently subjected to repeated bending stresses during use. If the handle lacks sufficient strength and toughness, it is prone to fracture.

3. Strategies for Maintaining Long-Term Performance of Medical Injection-Molded Parts

3.1 Material Optimization

• Select Appropriate Materials: Based on the usage environment and performance requirements of medical injection-molded parts, choose plastic materials with good aging resistance, chemical stability, mechanical properties, and biocompatibility. For example, for injection-molded parts that need to be exposed to ultraviolet light for a long time, modified plastics with ultraviolet absorbers can be selected. For parts in contact with chemicals, materials with good chemical corrosion resistance should be chosen.
• Optimize Additive Formulations: Select and add additives reasonably to ensure compatibility and stability with the material. Additives such as antioxidants, light stabilizers, and heat stabilizers can be added to improve the anti-aging performance of the material. Toughening agents and reinforcing agents can be added to enhance the mechanical properties of the material. At the same time, strictly control the addition amount of additives to avoid negative impacts on material performance due to excessive additives.

3.2 Process Control

• Optimize Injection Molding Process Parameters: Determine the optimal injection molding process parameters through experiments and simulation analysis to ensure a uniform internal structure and defect-free injection-molded parts. Advanced injection molding technologies, such as hot runner technology and gas-assisted injection molding technology, can be adopted to improve the quality and performance stability of injection-molded parts.
• Control Mold Temperature: Mold temperature has a significant impact on the cooling rate and crystallinity of injection-molded parts. Proper control of mold temperature can reduce residual stress within the injection-molded parts and improve dimensional stability and mechanical properties. For example, for crystalline plastics, a higher mold temperature can promote crystallization, increasing the strength and hardness of the injection-molded parts. However, for non-crystalline plastics, excessively high mold temperatures may cause material degradation.
• Post-Processing Techniques: Perform appropriate post-processing on injection-molded parts, such as annealing and humidity conditioning, to eliminate residual stress and improve material performance. Annealing involves heating the injection-molded parts to a certain temperature and holding for a period of time, followed by slow cooling to make the molecular structure within the material more uniform and reduce residual stress. Humidity conditioning involves placing the injection-molded parts in an environment with a certain humidity to allow them to absorb a certain amount of moisture and achieve dimensional stability.

3.3 Environmental Management

• Control Usage Environment: Strive to create a suitable usage environment for medical injection-molded parts and avoid long-term exposure to harsh environments such as high temperature, high humidity, strong light, and chemicals. For example, for medical equipment used outdoors, sun protection and rain protection measures should be taken. For injection-molded parts in contact with chemicals, they should be cleaned and dried promptly to avoid chemical residue.
• Select Appropriate Packaging Materials: Choose packaging materials with good protective properties, such as moisture-proof, light-proof, and anti-static packaging bags or boxes, during storage and transportation to reduce the impact of environmental factors on injection-molded parts. At the same time, pay attention to the sealing of the packaging materials to prevent air, moisture, and dust from entering the packaging.

3.4 Regular Inspection and Maintenance

• Establish an Inspection System: Develop a regular inspection plan to test and evaluate the performance of medical injection-molded parts. Inspection items can include appearance inspection, dimensional measurement, physical property testing (such as strength, hardness, and toughness), and chemical property testing (such as chemical corrosion resistance and biocompatibility). Through regular inspection, timely detect performance changes and potential problems of injection-molded parts and take corresponding measures for treatment.
• Maintenance and Replacement: Based on the inspection results and usage conditions, perform maintenance and replacement on medical injection-molded parts. For injection-molded parts with slight performance degradation, repair and reinforcement measures can be taken for maintenance. For parts with severe performance degradation or those that cannot be repaired, timely replacement should be carried out to ensure the safety and effectiveness of medical equipment.

4. Conclusion

Maintaining the long-term performance of medical injection-molded parts is an important issue in the medical industry. By comprehensively applying strategies such as material optimization, process control, environmental management, and regular inspection and maintenance, the long-term performance stability of medical injection-molded parts can be effectively improved, and their service life can be extended, ensuring the safety and effectiveness of medical equipment. In practical applications, personalized long-term performance maintenance plans should be formulated according to the specific conditions and usage requirements of medical injection-molded parts, and continuously optimized and improved to adapt to the constantly developing needs of the medical industry. At the same time, strengthening cooperation and communication with material suppliers and research institutions and jointly conducting research on the performance of medical injection-molded parts and technological innovation will provide stronger support for the development of the medical industry.