Recent Advances in Coating Technology

Over the past few years, new coating formulations have emerged that eliminate the need to choose between high lubricity and low particulate generation.7But until recently these formulations could only be applied to medical devices through a two-coat application process, and many manufacturers are currently equipped only for single-coat processing. Fortunately, one-coat formulations are now available that substantially reduce particulate generation while maintaining the lubricity of previous best-in-class hydrophilic coatings (Figure 1).

These recently developed coating formulations may also offer economic benefits to manufacturers. The efficient use of polymers and cross-linkers in these coatings means they can often deliver improved performance while substantially reducing the amount of coating material used in manufacturing. Not only can this cut supply costs, it can also reduce production time in comparison to previous single- and multi-coat UV- and thermal-based coating processes (Figure 2). When evaluating new coating options, device manufacturers should work with suppliers to understand the total cost of technology adoption, including capital expenditures and operating costs.

Two-coat formulations may remain optimal for neurovascular and other devices that require the lowest possible generation of particulates, since these formulations deliver the best high-lubricity/low-particulate performance now available.

Increased Regulatory Attention

These advancements in hydrophilic coatings are timely, since regulatory agencies are focusing increased attention on promoting improved medical device coating durability and particulate reduction.

Regulatory focus on particulates is not new. Because particulates in the vasculature raise concerns about downstream emboli, attention has long been paid to reducing particulates during procedures.8 There are several areas of focus. In addition to the chemical formulation of coatings, device design, materials, manufacturing, and clinical procedural technique can affect the amount and size of particulates generated. Since 2015, FDA has increased its attention to particulate generation on both the manufacturing and clinical fronts.

Citing recent clinical data on particulates, in April, 2015, CDRH sent medical device manufacturers a request for information to enhance the agency’s understanding of the issue. Four months later, the agency followed up by issuing a communication to device manufacturers—“Critical to Quality (CtQ) Indicators: Hydrophilic Coated and Hydrophobic Coated Vascular and Neurological Devices”—which identified common features of coated devices that have the greatest impact on device safety and effectiveness, and how these features are typically controlled in design and manufacturing.9

In October, 2015, FDA issued a Safety Communication entitled “Lubricous Coating Separation from Intravascular Medical Devices,” followed by a Medical Product Safety Network (MedSun) final report entitled “Hydrophilic and Hydrophobic Coating on Medical Devices Used in the Vasculature.”10, 11  The report contained survey results from clinicians, and emphasized the importance of procedural technique in minimizing particulate generation.

Light obscuration equipment is used to count and size particulates from simulated use models.

In the wake of these communications, there has been an increase in FDA inspections directed toward manufacturing and quality control processes associated with coating.

The guidelines and standards used for evaluating coatings for medical devices have not changed since MDDI last reported on the issue.7 FDA recommends that manufacturers provide an interpretation of test data during device submission.12Manufacturers remain responsible for developing an appropriate particulate evaluation procedure.

In their communications to industry, FDA acknowledges the important role of hydrophilic coatings on intravascular devices in providing physicians greater maneuverability and reduced vessel fiction as an alternative to more invasive procedures and their accompanying risks.

Partnering for Optimal Results

Coating technology is highly specialized, and arriving at the optimal coating for a medical device only begins with the initial chemical formulation. To best meet the needs of different medical devices, even the most advanced formulations may require refinements during the optimization phase, and continued testing and analysis of coated devices through verification and validation. These tests include chemical characterization, coating thickness via scanning electron microscope (SEM), visualization of coating uniformity, lubricity and durability using standard industry methods, and biocompatibility testing of individual components and device/coating combinations. Testing and analysis may continue throughout the lifecycle of the production.

For these reasons, medical device manufacturers need to establish a close partnership with their coating provider as far upstream as possible in the product design process, ideally beginning at the concept phase. Since the coating is often the only part of a medical device that comes into contact with the patient, it should never be an afterthought.

FDA’s communication regarding CtQ Indicators for hydrophilic coating provides a useful framework for supplier/manufacturer partnership. Coating providers can help manufacturers characterize and control the quality of their coatings in several ways (Table 1). From the design phase forward, a close collaboration between the device manufacturer and the coating provider is critical. Coating providers may even be able to provide technical files to regulatory bodies that contain test data on similar approved devices to support the device application.

Table 1. FDA CtQ indicators for hydrophilic and hydrophobic coatings.