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Mammary Implants Testing per ISO 14607 & ASTM F703

The U.S. Food and Drug Administration (FDA) regularly evaluates the risks associated with mammoplasty or breast augmentation procedures. Regulations and standardized testing are developed and continually updated based on available data to ensure patient safety. This article outlines the methodologies for mammary implant mechanical testing programs, including ASTM F703 and ISO 14607. 

Mammary or breast implants are prostheses that are used to change the geometry of a person’s breast. The procedure is known as mammoplasty or breast augmentation and is often performed for reconstructive purposes. Breast implants can be used to increase the size of the breast, restore breast volume, or improve asymmetry. Patients typically elect to have the procedure following physical trauma, mastectomies, or for cosmetic preferences. 

Several types of mammary implants exist and are categorized by the filler materials. The two most common are saline and silicone, both of which are encased by an elastomeric shell. Saline implants are filled with a sterile saline solution, while silicone implants are filled with a silicone gel. 

Development of mammary implant regulations

In the U.S., there are roughly 300,000 breast augmentations and 100,000 breast reconstruction procedures performed each year.[1] Breast implants have been around since 1962, and the results of the procedures provide varying benefits for patients. However, the implants aren’t without controversy due to patient safety concerns.  Breast implants are classified as Class III, which are higher risk devices and require Premarket Approval (PMA). 

In 1999, a report entitled “Safety of Silicone Breast Implants” reviewed the published literature and active studies. Although there was no evidence that breast implants created a direct, negative health impact, the report concluded that local health complications resulted in medical interventions and additional surgeries. FDA approved the first silicone gel implants in 2006 and with the absence of performance data, required six post-approval studies per manufacturer. Since then, the FDA has released an “Update on the safety of Silicone Gel-filled Breast Implants” outlining the partial results. The conclusion based on the available data at the time was that silicone implants have:

  • “…reasonable assurance of safety and effectiveness when used as labeled. Despite frequent local complications and adverse outcomes, the benefits and risks of breast implants are sufficiently well understood for women to make informed decisions about their use.”
  • “The longer a woman has breast implants, the more likely she is to experience local complications or adverse outcomes. Women with breast implants will need to monitor their breasts for local complications for the rest of their lives.”
  • “There is no apparent association between silicone gel-filled breast implants and connective tissue disease, breast cancer, or reproductive problems. Associations that are very rare or that take many years to manifest may not be detected using currently available data.”
  • “Women with breast implants may have a very small but increased likelihood of being diagnosed with anaplastic large cell lymphoma.”

For a full summary of the key findings, please read the article in full.[2]

In March 2019, a panel of FDA regulators, surgeons, researchers, and manufacturers joined a discussion regarding the risks of breast implants. Patients who have been adversely affected were invited to share their stories and concerns. The main concern revolved around textured surfaces of the breast implants and their link to Anaplastic Large Cell Lymphoma (ALCL). Several countries have already banned the kinds of implants causing concern, but the FDA has found no sufficient evidence that ALCL is linked to textured breast implants. The panel is evaluating next steps, but ultimately no restrictions or warnings have been added. The implants are considered to be safe as long as patients understand that complications are possible.[1]

Mammary implant test methods 

While the studies continue and more information is gathered, functional and mechanical evaluation of the breast implants is crucial. FDA released guidance in 2006, “Saline, Silicone Gel, and Alternative Breast Implants,” that defines device descriptions, preclinical, clinical, and labeling information for the premarket approval. The guidance includes testing requirements for these devices. ASTM F703[3], ASTM F2501, and ISO 14607[4] outline the recommended testing suites: 

  • Chemical Analysis – chemical testing, crosslink analyses, extractables, volatiles, heavy metals, and composition analysis of saline and silicone gel fillers
  • Toxicology – pharmacokinetic studies & toxicological testing
  • Mechanical testing – shell integrity, fatigue rupture testing, valve competency (if needed), burst pressure, cohesivity testing, bleed testing, stability, shelf life and packaging

Testing should be performed on sterilized (if necessary) final products.

Shell integrity testing

Tensile specimens are typically cut out of the shells in accordance with ASTM D412, cleaned, dried, and conditioned for at least three hours at 23 ± 2°C. The specimens are installed into grips and pulled until failure. ASTM F703 sets acceptance criteria of 11.12 N when tested using the ASTM D412, Die C, as well as for percent elongation and tensile set. Additional requirements exist if there are joints or seams within the test specimens.  ISO 14607 uses similar methods but has different acceptance criteria. 

Static rupture testing

ISO 14607 outlines the methods for static rupture resistance testing. Mammary implants are aligned into test platens and loaded at 5mm/min or slower until rupture is observed. It is important to use appropriately sized platens as the implants will extend horizontally and need to be continually supported. Consideration to the edges of the platens should also be evaluated so that the edges do not interfere with the lateral extension during testing. Force versus displacement is recorded until failure. 

Fatigue rupture testing

There are two test methods for fatigue rupture testing:

  1. The breast implant FDA guidance recommends replicating the above static configuration and performing testing in either constant force or displacement control. Force control is used more often to establish an AF/N (applied force to number of cycles) curve. Three samples are recommended per load level and are run to either failure or 6.5 million cycles, whichever comes first. Testing is typically performed using a sinusoidal profile at a frequency of 1 Hz. 
  2. ISO 14607 outlines parameters for a displacement controlled test that consists of 40mm of travel at a target frequency of 3.3 Hz. The test continues until 2 million cycles are reached or until failure is observed. 

As is the case for static testing, it is critical to use appropriately sized platens as the implants will extend horizontally and need to be continually supported. Consideration to the edges of the platens should also be evaluated so that the edges do not interfere with the lateral extension during testing. A rough edge can lead to tearing or premature failure of the test specimen, particularly in a fatigue configuration. 

Impact testing

Impact resistance is another mammary implant test method. In accordance with ISO 14607, a 4.4 kg mass is dropped vertically onto the test specimen from a calculated height. The implant must remain intact without rupture. 

Shelf life testing

Shelf life testing is also recommended by the guidance to understand the expiration dates of the implants.  The above testing methodologies are commonly performed at several time points to evaluate the differences due to the aging of the materials. These specimens can be aged in real-time or accelerated. 

Additional testing

Several additional test methods exist that are dependent on the type and features of breast implants. Valve competency testing is performed to evaluate whether fluid can be forced out of the implant during a reclining or other loading position. Bleed testing evaluates the diffusion of silicone gel through an intact shell.  Other methods also exist to evaluate gel cohesivity, and both ASTM F703 and ISO 14607 standards outline those methodologies. While these are the recommended testing methods, additional methods may be necessary depending on the design of each implant. 

The mammary implant test methods outlined above do not guarantee successful performance in vivo; however, diligent mechanical evaluation is a critical step in understanding how implants will behave under applied stresses. As more clinical data become available, these methods will be revised and updated to account for observations and patient outcomes. While benefits and risks continue to be assessed for breast implants, it is up to the patients to evaluate potential surgery and implant complications.   

Reference: 

[1] Perrone, M. (2019, March 24). FDA takes up decades-long debate over breast implant safety.

[2] FDA. (2018, July 16). Update on the Safety of Silicone Gel-Filled Breast Implants - Exec Sum. 

[3] ASTM F703-18 Standard Specification for Implantable Breast Prostheses

[4] ISO 14607:2018 Non-active surgical implants -- Mammary implants -- Particular requirements

 

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