How Do Medical Injection Pen Injection Molding Accessories Ensure the Safety and Accurate Use of Injection Pens?

Why Medical Injection Pen Injection Molding Accessories Are Key to the Safe Operation of Injection Pens

In scenarios like self-injection for diabetes patients and precise drug administration in clinical settings, the stability and safety of medical injection pens are closely tied to medication efficacy and patient well-being. As core components of these pens—encompassing needle hubs, plungers, dose adjustment knobs, and sealing rings—injection molding accessories hold the key to ensuring safe pen operation, with their performance and quality acting as decisive factors. These accessories must meet the dual demands of “accurate drug delivery” and “safe human contact”: needle hubs need to form a sealed connection between the needle and the pen body, preventing drug leakage or intrusion of external contaminants; plungers must deliver consistent thrust transmission to avoid jamming or deviation during injection, guaranteeing precise dosing; sealing rings, meanwhile, must retain elasticity through repeated use to isolate the drug from the pen’s internal structure, warding off drug contamination or component corrosion.

Compared to standard injection-molded parts, medical injection pen accessories face far stricter requirements for material safety, dimensional precision, and corrosion resistance. A dimensional deviation exceeding 0.01mm could lead to dosage errors, while materials failing to meet medical sterility standards might trigger skin irritation or drug contamination. Thus, high-quality injection molding accessories serve as the foundation for injection pens to achieve “precise dosing and safe drug delivery,” and they represent a critical link in safeguarding patients’ medication safety.

Sterile Material Selection and Compliance Requirements for Medical Injection Pen Injection Molding Accessories

Material selection for medical injection pen injection molding accessories must center on “sterility, safety, and drug compatibility,” while also adhering to domestic and international medical regulatory standards. Priority is given to polymer materials that meet medical-grade criteria: for accessories in contact with drugs or the human body—such as needle hubs and sealing rings—medical-grade polypropylene (PP) or polycarbonate (PC) is commonly employed. Polypropylene boasts excellent chemical stability, resisting reactions with drugs and withstanding high-temperature sterilization (capable of enduring 121℃ moist heat sterilization); polycarbonate, on the other hand, combines high strength with transparency, making it ideal for accessories requiring drug visibility (like dose windows).

For plungers and other parts that bear repeated thrust, reinforced polyoxymethylene (POM) is a suitable choice, as its wear resistance and rigidity ensure no deformation or breakage during prolonged use. Material compliance must meet rigorous standards: components must pass biocompatibility tests (including cytotoxicity, sensitization, and irritation assessments) to ensure no adverse reactions when in contact with the human body. They must also align with the DMF filing requirements of the U.S. FDA, the MDR regulations for EU CE certification, and provisions for medical polymer materials in China’s “Regulations on the Supervision and Administration of Medical Devices,” which prohibit materials containing harmful substances like bisphenol A (BPA) and heavy metals. Furthermore, material suppliers must provide comprehensive Certificates of Conformity (CoC) and sterilization verification reports, ensuring the sterility and consistency of each material batch to safeguard accessory safety from the source.

Precision Control Technology and Parameter Setting for Medical Injection Pen Injection Molding Accessories

Medical injection pen injection molding accessories demand extremely high dimensional accuracy (typically with a tolerance range of ±0.005mm to ±0.01mm), achievable only through refined injection molding processes and parameter calibration. Mold design forms the basis of precision control: high-precision CNC machining is used to craft mold cavities, with surface roughness controlled below Ra0.02μm to ensure accessories have a smooth, burr-free surface. For thin-walled, deformation-prone parts (such as sealing rings with a thickness of just 0.5mm), cooling channels are integrated into the mold to uniformly regulate cavity temperature, preventing dimensional deviations caused by uneven cooling.

Injection parameters require dynamic adjustment based on material properties. Taking medical-grade PP as an example, the melting temperature must be controlled between 200℃ and 220℃—excessively high temperatures risk material degradation and the release of harmful substances, while excessively low temperatures lead to incomplete melting and material shortages. Injection pressure is set to 80MPa-100MPa, with holding pressure at 60%-70% of the injection pressure and a holding time of 5-8 seconds, ensuring accessories are dense and free of shrinkage voids. Cooling time is adjusted according to accessory thickness: 3-5 seconds for thin-walled components and 8-12 seconds for thick-walled parts (such as dose adjustment knobs with a thickness of 3mm) to prevent post-demolding deformation. Additionally, online dimensional inspection equipment (like laser diameter gauges) should be used during production, with key dimensions sampled and tested every 100 pieces to ensure deviations stay within allowable limits and prevent substandard accessories from entering subsequent processes.

Assembly Gap Optimization Techniques Between Medical Injection Pen Injection Molding Accessories and Pen Bodies

Excessively large assembly gaps between medical injection pen injection molding accessories and pen bodies can lead to drug leakage and loose components, while overly small gaps increase assembly resistance and may even cause component wear. Scientific methods are therefore needed to optimize gap sizes. First, gap requirements for different accessories must be clearly defined: the radial gap between the needle hub and pen body should be controlled at 0.005mm-0.01mm to ensure sealing performance while facilitating needle attachment and removal; the axial gap between the plunger and the pen body’s inner wall is set to 0.01mm-0.02mm, ensuring smooth plunger movement while preventing drug seepage into the pen body through gaps.

Optimization techniques combine “mold modification” and “assembly process adjustment”: if gaps are too large, mold cavity sizes can be reduced (modified by 1.2 times the gap deviation) or a thin wear-resistant coating (such as a 0.003mm-thick polytetrafluoroethylene coating) can be sprayed onto accessory surfaces to compensate for dimensional discrepancies. If gaps are too small, the holding pressure during injection can be moderately reduced by 5%-10% to minimize post-shrinkage dimensional deviations of accessories, or the pen body’s assembly holes can be slightly polished (with a polishing allowance not exceeding 0.005mm) to reduce assembly resistance. Additionally, mating surfaces of accessories and pen bodies must be cleaned before assembly to remove surface oil or dust, preventing gap accuracy issues caused by impurities; automated equipment should be used for precise alignment during assembly to avoid assembly deviations from manual operations, ensuring uniform and stable gaps.

Testing Methods for Drug Corrosion Resistance of Medical Injection Pen Injection Molding Accessories

Medical injection pen injection molding accessories are in long-term contact with drugs like insulin and growth hormones. Insufficient corrosion resistance can lead to material swelling and drug contamination, making standardized tests essential to verify their anti-corrosion performance. A common testing method is the “drug immersion test”: select drugs frequently used in injection pens (such as insulin solution with a concentration of 40U/mL), fully immerse accessories in the drug, place them in a 37℃ constant-temperature environment (simulating human body temperature), and remove them after 24 hours, 72 hours, and 168 hours respectively to test accessory weight change, dimensional deviation, and appearance. High-quality accessories should exhibit a weight change rate of less than 0.5%, a dimensional deviation of no more than 0.003mm, and no whitening, cracking, or swelling on their surfaces.

The “drug compatibility test” is equally critical: sample the immersed drug and test its purity using high-performance liquid chromatography (HPLC). If extractables from accessories (such as polymer degradation products) are detected, it is necessary to determine whether they exceed safety limits permitted by medical regulations; simultaneously, test the drug’s pH value and concentration changes to ensure no chemical reactions occur between accessories and the drug, which could compromise efficacy. Furthermore, a “repeated contact test” should be conducted: simulate the injection pen’s actual usage frequency (3 injections per day), allow accessories to repeatedly contact and separate from the drug, and test accessory elasticity and sealing performance after 30 days to ensure stable corrosion resistance during long-term use without functional failure.

Causes and Solutions for Demolding Defects of Medical Injection Pen Injection Molding Accessories

Medical injection pen injection molding accessories are prone to demolding defects such as flash, sink marks, bubbles, and material shortages during demolding. These defects not only affect appearance but may also lead to sealing failure and dosage deviations, requiring targeted analysis of causes and solutions. Flash is mostly caused by insufficient mold clamping force or excessive cavity gaps: if the mold clamping force is lower than the injection pressure (e.g., an injection pressure of 100MPa with a clamping force of only 80MPa), molten material may overflow from cavity gaps to form flash, and the clamping force needs to be increased to 1.2-1.5 times the injection pressure; if the cavity becomes worn after long-term mold use, leading to gaps, the cavity must be re-ground to restore sealing performance.

Sink marks often occur in areas of uneven accessory thickness (such as the reinforcing ribs of dose adjustment knobs). Due to slower cooling in thicker regions compared to thinner ones, differential shrink