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Working Principle of Ethylene Oxide Sterilization Indicator Ink

Date: Mar 10 2025  From: Star Color   

Ethylene Oxide (EO) sterilization is a widely used method for effectively eliminating microorganisms, ensuring the safety of medical devices. Accurately determining whether the sterilization process has achieved its intended results is critical. Ethylene Oxide sterilization indicator ink addresses this need by providing a visual color change during sterilization, offering a reliable monitoring solution for the healthcare industry.

‌I. Medical Validation Requirements for Sterilization Indicator Systems‌
Globally, over 20 billion medical devices undergo EO sterilization annually, highlighting its importance in healthcare. EO’s potent sterilizing capability penetrates various packaging materials, ensuring comprehensive sterilization for devices of diverse materials and shapes.

According to ISO 11135, EO sterilization requires specific conditions:

• Temperature: 30–60°C
• Humidity: 40–80% RH
• EO Concentration: 450–1200 mg/L
• Exposure Time: 1–6 hours

Under these conditions, EO effectively kills bacteria, viruses, and spores. The indicator ink detects EO concentration and undergoes an irreversible color change once sterilization parameters are met, providing trustworthy validation for the process.

‌II. Chemical Color-Changing Mechanism and Formulation Design‌

‌Functions and Technical Parameters of Components‌

• ‌Bromocresol Purple‌: A pH indicator with a color transition range at pH 5.2–6.8.
• ‌Citric Acid‌: Creates an acidic environment; particle size <10 μm ensures uniform dispersion.
• ‌Polyethylene Glycol (PEG)‌: Modulates reaction rate; molecular weight 4000–6000 balances control.
• ‌Nano Zinc Oxide‌: Humidity-sensitive catalyst with a surface area >50 m²/g for enhanced reactivity.

‌Reaction Equation and Color-Changing Principle‌
The esterification reaction between EO and citric acid lowers the system’s pH:
 ‌   HOOCCH₂C(OH)(COOH)CH₂COOH + EO → Esterification (pH decreases)
‌
When pH ≤5.4, bromocresol purple shifts from purple to bright yellow, visually indicating sterilization completion.

‌Intelligent Response Layer Design‌

• ‌Substrate Layer (PET Film)‌: Surface energy ≥45 mN/m ensures adhesion; thickness 50±5 μm balances strength and flexibility.
• ‌Microcapsule Isolation Layer‌: Gelatin-Arabic gum composite wall material with >92% encapsulation efficiency. Ruptures at 54±2°C to initiate the reaction.
• ‌Color-Developing Functional Layer‌: Solid content 22–25%, coating weight 8–10 g/m² for optimal performance.

‌III. Validation of Key Technical Indicators‌

‌Sensitivity Testing‌

• ‌EO Concentration Response‌:
  • At 600 mg/L and 25°C, color development time >6 h (non-compliant).
  • At 800 mg/L and 54°C, color development time ≤2 h (compliant).
• ‌Humidity Impact‌: At <30% RH, color development delay rate >40%, highlighting humidity’s critical role.

‌Stability Validation‌

• ‌High-Temperature Storage (60°C for 90 days)‌: pH threshold shift +0.15, within acceptable limits.
• ‌Light Aging (5000 lux for 200 hours)‌: ΔE <1.5, demonstrating excellent light resistance.
• ‌Cold Chain Transport (-20°C freeze-thaw cycles)‌: Coating delamination rate <3%, ensuring integrity.

‌
Ethylene Oxide sterilization indicator ink employs a precise chemical mechanism and optimized formulation to reliably validate sterilization effectiveness. Rigorous testing confirms its high sensitivity and stability, aligning with medical industry standards. It is indispensable for ensuring the safety of sterilized medical devices, pharmaceutical packaging, and laboratory supplies.

‌Zhongzhixing EO Sterilization Indicator Ink‌
Our eco-friendly, water-based formula minimizes VOC emissions and complies with international standards. Suitable for flexographic and gravure printing, it offers exceptional EO responsiveness, rapid color transition, and clear visual feedback. Trusted for medical devices, pharmaceutical packaging, and lab consumables, Zhongzhinking delivers precision and reliability in sterilization monitoring.

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