Acute and chronic particulate testing is required for most intravascular devices to mitigate potential health risks for patients. Additionally, coating integrity and durability are commonly evaluated for drug-eluting stents. Element’s cardiovascular device testing experts examine coatings and particulates in accordance with leading industry standards and guidance documents. 

Coating integrity and particulate shedding may affect patient safety, but they also affect device efficacy and therapeutic benefit, as in the case of drug-eluting stents. Regulatory bodies have not set acceptance limits for particulates, although some manufacturers set their own or use those specified in USP 788. 

Minimizing particulates and increasing coating lubricity can be two competing requirements, which presents challenges for device manufacturers. Our experts evaluate coatings and particulates intending to bring safe and reliable products to market. 

FDA guidance for coating & particulate testing

In addition to industry standards, there are several FDA guidance documents related to intravascular devices with recommendations for coating inspections and particulate testing. For example, “Coronary, Peripheral, and Neurovascular Guidewires – Performance Tests and Recommended Labeling,” a draft guidance document, has sections on coating integrity, particulate evaluation, and simulated use.

The guidance document “Non-Clinical Engineering Tests and Recommended Labeling for Intravascular Stents and Associated Delivery Systems” also contains useful information about baseline and simulated use testing of coating integrity and particulate evaluation. 

Coating integrity

Coating integrity inspections focus on detailed characterization of the device’s coated surfaces for defects, anomalies, or artifacts.  Unintended delamination, flaking, webbing, or degradation may impact the device’s clinical performance and should be characterized. FDA guidance documents listed above recommend inspections on the finished product that has been subject to all manufacturing processes, including sterilization. 

Inspections for coating integrity are recommended for baseline and simulated use conditions. For simulated use coating integrity assessments, devices are tracked through a tortuous path fixture that mimics challenging in vivo physiologic and anatomic conditions that the device might encounter during use, and they are then expanded in air or in an aqueous solution.

The number and size of defects observed need to be documented as part of the acceptable coating integrity discussion, and test reports should include details about the methods used to quantify defects. Counting the number of total defects per unit area and measuring representative and worst-case defect areas may also be included. 

Particulate testing

There are two main types of particulate evaluation: acute and chronic particulate testing. Acute particulate testing is related to the particulate matter released during simulated delivery and deployment of a device. Chronic particulates measurement takes place over a specified length of time that mimics the lifetime use of the device. 

Acute particulate testing 

FDA guidance documents and existing standards focus on acute particulate testing, outlining the assessment of particulates through either light obscuration or filtration/microscopy methods. Each method has its advantages and limitations. The light obscuration method has higher throughput but can only quantify particulates and categorize them by size. In contrast, the filtration/microscopy method can quantify particulates as well as identify them by color, shape, or composition. We employ the filtration/microscopy method that offers more flexibility in the evaluations requested by device manufacturers. 

Our Acute Particulate Testing of Bioresorbable Scaffolds article gives a more in-depth look at the baseline and simulated use testing of particulates generated from enzymatic or hydrolytic degradation.

Chronic particulate testing

We perform chronic particulate testing by integrating particle counting modules with our stent graft test systems and using individualized flow loops, flow meters, and filters for the mock vessels. Our flow loop design minimizes the flow compliance effect so that physiological radial strains for fatigue testing are maintained.

Filters for mock vessels are sampled at pre-determined intervals for analyzing particulates over long term fatigue tests. Since we have the filtration/microscopy capabilities in-house, we can perform these inspections on a fast turnaround basis while the durability test is running.

For more information about our coating and particulate testing for intravascular devices, or to request a quote, contact us today. 

Using a Scanning Electron Microscope (SEM) with automated particle size analysis, we can provide SEM photos for coating inspection and particle size analysis. Simulated use tracking fixtures are available to mimic worst case scenarios such as overlapped or bent stent configurations following a device’s instructions for use.

Key advantages include:

  • SEM photography to a magnification of 100,000x
  • Determining the effect of deployment on the device structure
  • Metallic fretting characterization
  • Automatic Feature Analysis (AFA) that provides information on the number and sizes of the particles via methods such as spectral analysis, line scans, and element mapping
  • Analyzing solid inorganic materials including metals and polymers
  • Large sample chamber for the examination of samples up to 100 long x 80mm wide x 25mm high

Several standards support coating inspections and particulate testing:

  • ASTM F2743 Standard Guide for Coating Inspection and Acute Particulate Characterization of Coated Drug-Eluting Vascular Stent Systems
  • AAMI TIR42 Evaluation of particulates associated with vascular medical devices
  • USP 788 Particulate Matter in Injections
  • ASTM F2477 Standard Test Methods for in vitro Pulsatile Durability Testing of Vascular Stents
  • ISO 25539-1 Cardiovascular implants – Endovascular devices – Part 1: Endovascular prostheses
  • ISO 25539-2 Cardiovascular implants – Endovascular devices – Part 2: Vascular stents
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