4 Accelerated Life Tests for Anodized Aluminum Medical Devices

Posted July 28, 2017
By Losone Kaba

An Overview of Performance Testing Procedures for MICRALOX® Coated Medical Devices

Current sulfuric anodizing specifications for aluminum are based on a range of factors relevant for industrial usage, such as coating thickness and weight, salt water spray corrosion, and abrasion resistance. While meaningful for certain applications, they are a poor fit for the life cycle of anodized medical devices where the aluminum articles require regular cleaning and sterilization; these processes expose aluminum articles to strong chemistries.

Anodized Aluminum Medical Devices Testing.jpgThese traditional specifications are built around military standards and they fail to predict performance in use and/or introduce inconsistencies with non-military design specifications—a common complaint in ensuring that quality standards and specifications are adhered to for use in medical applications. 

This blog presents a series of easy-to-adopt accelerated testing protocols specifically for medical applications, that when used, provide consistent and comprehensive quality assurance on how the anodic coating will perform. As such, we recommend that these protocols become the basis for performance specifications for anodic coated aluminum devices used in the medical industry.

For a more detailed discussion on the procedures and protocols involved with the 4 accelerated life tests, read: Accelerated Life Tests for Anodized Aluminum Medical Devices. 

Testing MICRALOX®

MICRALOX® is a patented aluminum oxide coating with a micro-crystalline barrier that revolutionizes aluminum anodizing. MICRALOX® produces a long lasting, virtually indestructible surface that delivers dramatically superior chemical corrosion resistance and eliminates color fading due to super-heated steam, and is an excellent alternative to stainless steel, plastic, and other materials.

Reusable aluminum anodized medical devices undergo relentless sterilization conditions that can degrade the anodized finish. MICRALOX® was created to counter the effects of harsh sterilization procedures. We know medical devices anodized with MICRALOX® will maintain superior corrosion resistance and color because we relentlessly test it. Here is an overview of the procedures for the 4 accerlated life tests we implement to ensure MICRALOX® coating’s long-lasting performance on medical devices remains intact.  

1. HCl Bubble Test (Low pH)

In the HCl Bubble Test, the anodic coating is immersed in a dilute HCl solution. The coating is visually monitored for up to two hours. If the coating succumbs to chemical attack, the HCl solution reacts with the Al substrate, and bubbles of H2 are released that are visually apparent. Qualitatively, coating failure occurs when the first continuous stream of H2 bubbles is observed on the coating surface. The HCl Bubble Test is a known for testing anodized coatings, and coating vendors often supply HCl Bubble Test corrosion‐resistance results. 

Acceptance Criteria

PASS: There are no hydrogen bubbles generated under the attack of a strong acid within 2 hours of immersion. It indicates a high quality of anodized aluminum.

FAIL: Anodized aluminum generates hydrogen bubbles within 2 hours of immersion. It indicates a poor anodized aluminum.

HCI Bubble Test  P_F.jpeg

2. Extreme Alkaline Resistance Test (High pH 13.5) 

This test is primarily used as one of the performance tests for MICRALOX® coating’s performance. Processed samples or parts are tested by partially immersing the parts into a beaker with 200 mL of a fully transparent solution, stored at a cool temperature (40°-70° F). The samples or parts are placed in the beaker for 10 minutes so that a significant portion of the part’s surface area interact with the solution, usually by hanging the parts vertically. The surface of the parts or samples are checked for change in appearance (polishing is not allowed) between each immersion interval and after rinsing in clean water. If there is any change in appearance on the samples or parts, this is considered a fail.

Acceptance Criteria

Extreme Alkaline Resistance Test P_F.jpeg

PASS: No changes in appearance and the samples do not look dull.

FAIL: The samples look dull and there are changes in the appearance.

3. Hot Etch Performance Test 

This test determines the performance of the anodic coating when exposed to a high-pH solution for extended times. Parts are observed at set intervals until failure: 1, 2, 5, 20, and 25 minutes. Parts are observed after rinsing in clean water.

Acceptance Criteria

Anodized Aluminum Hot Etch Performance Test.jpeg

4. Autoclave Sterilization Testing

Procedure

  1. Perform a sterilization cycle in the TUTTNAUER sterilization unit with the following criteria:
  • High-temperature gravity steam cycle
  • Temperature: 270° F (132° C)
  • Minimum exposure time: 30 minutes 
  1. Remove samples from autoclave; inspect and record the surface appearance of all samples
  2. Repeat total, up to 100 cycles
  3. If at any time during the testing the samples show signs of excessive discoloration, the test may be stopped for those samples; discoloration will be judged by the operator and include such things as:
    • bare aluminum showing
    • heavy pitting
    • heavy corrosion
    • fading
    • markings not identifiable, and or color not identifiable

Acceptance Criteria

  • Measure L*, a*, b*, and ΔE values using color spectrometer
  • PASS: ΔE < 5 of the original surface coating is discolored after 100 cycles
  • FAIL: ΔE >5 of the original surface coating is discolored after autoclaving, up to 100 cycles 

MICRALOX®, our revolutionary coating technology for medical device components, produces a long lasting, virtually indestructible surface, which delivers dramatically superior chemical and corrosion resistances and eliminates color-fading due to super-heated steam. For a more detailed discussion on the procedures and protocols involved with the 4 accelerated life tests for anodized aluminum medical devices, read this white paper: Accelerated Life Tests for Anodized Aluminum Medical Devices

I’ll Read More About the 4 Tests