Viscosity and density play a crucial role in medical device coatings, directly impacting product cohesion, surface quality, and therapeutic effectiveness. Precise monitoring ensures consistency, compliance with global standards, and ultimately safer, more reliable devices for patients.
Table of Content
- 1. Introduction – The importance of monitoring the quality of coating across different devices
- 2. In-depth look at the medical device coating industry
- 2.1 Common coating processes across the medical industry
- 2.2 The importance of process control
- 3. The Rheonics solution
- 3.1 Implementing inline measurement for viscosity and density monitoring
- 4. References
Introduction - The importance of monitoring the quality of coating across different devices
The medical device industry is rapidly advancing, delivering innovative tools that enhance diagnostics, treatment, and patient outcomes. As these technologies evolve, the performance and safety of the devices themselves remain paramount. Many of these devices interact directly with human tissue or the vascular system, making it essential that they meet stringent quality and regulatory standards.
One critical aspect of device performance is the application of specialized coatings—such as hydrophilic, antimicrobial, or drug-eluting layers—that reduce friction, prevent infection, or enable targeted therapy. The quality of these coatings must be tightly controlled to ensure uniformity, adhesion, and functionality. In particular, monitoring and controlling the viscosity of coating fluids during manufacturing is essential to achieving consistent results and complying with international norms such as ISO 13485 and FDA requirements.
In-depth look at the medical device coating industry
The following are key examples of medical devices where coating quality—and the viscosity control that supports it—plays a vital role in both safety and effectiveness.
Catheters
Coating: Hydrophilic or antimicrobial coatings
Purpose: Reduce friction during insertion, improve patient comfort, or prevent infections
Viscosity Relevance: Consistent viscosity ensures even coating thickness and adhesion, avoiding excess buildup or patchiness that could impact performance.
Guidewires
Coating: Hydrophilic or fluoropolymer-based coatings
Purpose: Improve maneuverability within blood vessels and reduce trauma
Viscosity Relevance: Controlled viscosity is essential for achieving a uniform thin layer that does not interfere with mechanical properties or flexibility.
Stents
Coating: Drug-eluting or polymer coatings
Purpose: Deliver medication locally, reduce restenosis
Viscosity Relevance: Viscosity affects drug distribution, coating uniformity, and release kinetics. Precise control ensures therapeutic effectiveness and regulatory compliance.
Needles and Syringes
Coating: Silicone or lubricant coatings
Purpose: Reduce insertion force and improve patient comfort
Viscosity Relevance: Monitoring ensures the lubricant layer is consistent and functional without interfering with sterility or operation.
Orthopedic Implants
Coating: Antimicrobial, bioactive, or hydroxyapatite coatings
Purpose: Promote osseointegration, reduce infection risk
Viscosity Relevance: Controlled application is critical to ensure coatings remain bonded during sterilization and use.
Balloons for Angioplasty
Coating: Drug-coated or hydrophilic coatings
Purpose: Reduce restenosis, facilitate delivery
Viscosity Relevance: Consistent fluid properties ensure reproducible drug loads and effective balloon deployment.
Drug-Eluting Contact Lenses (DECLs)
Coating: Wetting agents or drug-delivery coatings
Purpose: Improve comfort, reduce contamination, or deliver medication
Viscosity Relevance: Critical to maintain coating integrity and uniformity for optical clarity, uniform protection from external pathogens, and therapeutic effect.
Common coating processes across the medical industry
Dip Coating
Dip coating involves immersing a medical device or component into a liquid coating material and then withdrawing it at a controlled speed, allowing a uniform film to form as the solvent evaporates. An example of this can be seen in the following video:
Viscosity is a critical parameter in this process because it directly affects coating thickness, smoothness, and uniformity. Real-time viscosity monitoring, ideally placed in the coating reservoir or circulation line, ensures that any fluctuations due to solvent evaporation or temperature changes are detected immediately.
Proper sensor placement allows operators to adjust solvent levels or process parameters on-the-fly, minimizing defects like drips, uneven coatings, or excessive buildup. Maintaining consistent viscosity translates to improved coating quality, better product consistency, and reduced rework or waste.
Spray Coating
Spray coating applies a fine mist of coating material onto a substrate through nozzles or atomizers, often used for applying thin, even layers on complex geometries. Viscosity plays a pivotal role in atomization efficiency. If the viscosity of the sprayed fluid is too high, the nozzle may clog or form droplets; if the opposite is true, the coating can run or sag. Inline viscosity sensors placed close to the spray nozzle feed line are ideal, as they provide immediate feedback on the fluid’s readiness for spraying. This enables precise adjustments to dilution or temperature before the material reaches the nozzle, ensuring optimal spray patterns, reduced overspray, and a high-quality, uniform finish. Accurate viscosity control results in more consistent product performance and reduces costly defects in medical coatings.
The importance of process control
Clinical Significance
Maintaining optimal viscosity in the coatings applied to medical devices is essential for ensuring consistent clinical performance and patient safety. Variations in viscosity can lead to uneven coating thickness, which may compromise the device’s functionality, durability, or therapeutic effectiveness. This is especially true in devices like drug-eluting stents, catheters, or orthopedic implants. Proper viscosity control helps achieve uniform surface coverage, reducing the risk of adverse patient outcomes such as thrombosis, infection, or device failure, and ultimately supports better clinical outcomes.
Economic Impact
Effective viscosity monitoring plays a key role in minimizing production costs and improving manufacturing efficiency. Uncontrolled viscosity can result in coating defects, increased scrap rates, and costly rework, all of which add to operational expenses. By maintaining viscosity within optimal ranges, manufacturers can reduce material waste, optimize production throughput, and improve overall yield. This translates into more predictable production cycles, lower costs per unit, and enhanced profitability for medical device manufacturers.
Regulatory Mandate
Viscosity control is a key element in meeting regulatory expectations for medical device manufacturing. Regulatory agencies such as the FDA, EMA, and other global bodies require manufacturers to establish robust process controls under Good Manufacturing Practices (GMP). Viscosity is often designated as a critical process parameter (CPP) due to its direct influence on coating quality and overall device performance. Incorporating viscosity monitoring within a Quality by Design (QbD) framework further strengthens regulatory compliance by demonstrating a thorough understanding of how process variables impact product quality. This proactive approach not only supports smoother regulatory submissions and inspections but also enhances product reliability and reduces the risk of non-conformances throughout the product lifecycle.
By controlling viscosity, manufacturers align with modern quality frameworks like PAT (Process Analytical Technology), ensure data integrity under 21 CFR Part 11 and EU Annex 11, support QbD principles under ICH, and meet ISO 13485:2016 quality management requirements. This comprehensive approach enhances product quality, regulatory compliance, and operational efficiency.
Accelerated R&D Cycles
Implementing precise viscosity monitoring during product development significantly shortens R&D timelines by enabling faster formulation optimization and process refinement. Real-time viscosity data allows researchers to quickly identify optimal coating parameters, reduce trial-and-error experimentation, and streamline scale-up activities. This data-driven approach supports rapid prototyping and iterative testing, ultimately accelerating time-to-market for new medical devices while ensuring robust product performance from early development stages.
The Rheonics solution
Rheonics offers a robust, fully integrated solution for inline viscosity and density measurement, enabling complete automation and control of coating processes. With their advanced inline sensors, the SRV and SRD, Rheonics ensures continuous real-time monitoring of fluid properties directly within the production line.
The SRV sensor provides highly accurate, real-time viscosity and temperature measurements, while the SRD sensor offers simultaneous measurement of density, viscosity, and temperature. Built to withstand harsh industrial environments and able to meet international sanitary requirements, both sensors deliver precise, repeatable, and reproducible readings without requiring recalibration throughout their operational lifetime.
Key Benefits:
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Continuous inline measurement of viscosity and density during production.
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No recalibration required, minimizing downtime and maintenance.
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Real-time data eliminates sampling delays, ensuring immediate process adjustments.
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High accuracy and repeatability improve product consistency and reduce waste.
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Supports full automation of medical coating and related processes.
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Reliable Under Challenging Conditions: Ideal for processes sensitive to temperature variations or minor solvent losses.
Patented Technology for Unmatched Performance:
Rheonics’ inline sensors are based on the balanced torsional resonator technology, which guarantees superior accuracy, especially at low viscosities common in coating applications. The sensors seamlessly integrate with existing Process Control Systems (PCS), allowing automatic adjustments and tight process control.
Implementing inline measurement for viscosity and density monitoring
Installation and integration recommendations
The following are examples of installation alternatives and recommendations relevant for different coating processes. It is important to mention that Rheonics’ sensors and accessories can be requested with a 3-A or EHEDG certification. More on this can be explored in the following articles:
Hygienic and Sanitary Process Viscometer and Density Meter for inline installation
https://rheonics.com/3-a-certified-rheonics-process-viscometer-and-density-meter/
Installation in trays or dishes
Some dip coating applications may involve using trays to hold the fluid during the dipping process. In these cases, Rheonics’ Type-SR sensors can be installed directly in the tray through the use of our HAW (MTK or OTK) and WFT weldolets. These are available with 3-A and EHEDG certification to meet industry requirements. Below are some example drawings of the mentioned accessories installed in fluid trays.
Installation in line
For medical applications involving coating fluids, perpendicular sensor installations are recommended to ensure accurate viscosity and density monitoring. The preferred approach is to position a Type-SR X3 or X5 probe at the center of the flow (variant selection is based on line size).
To achieve this, the WFT-15T can be used as a weld-on port, which is designed to match the 1.5” Tri-Clamp process connections present on the X3/X5-15T probes.
Alternatively, Rheonics’ clamped flow tee spool piece (FTP) with an integrated Tri-Clamp connection in varying line and port sizes can be used for a seamless hygienic integration.
For DN50 or DN80 sanitary lines, Varinline flanges are also offered under the X4 variant as a standardized solution compatible with both SRD and SRV sensors, as detailed in Rheonics’ hygienic installation guides.
Inline density and viscosity meter SRD Varinline flange options installation
Inline viscometer SRV Varinline flange options installation
Rheonics SRV-X4 flush hygienic sanitary inline viscometer
Rheonics SRD-X4 Flush sensor for hygienic and sanitary applications
Finally, one other alternative involves using the X1-12G probe variant alongside the HAW-12G-OTK2 weldolet. This alternative is ideal for small lines (2.5” to 3”) and provides the benefits of a hygienic installation in a small form factor.
Installation in tanks or reservoirs
In most coating applications, fluids are stored in tanks or reservoirs prior to use. Maintaining precise viscosity control during storage and preparation is essential to ensure that the applied coating layer consistently meets industry quality and performance standards.
Tank installation varies based on the vessel type. Most of the accessories mentioned above can be used for this purpose. Additionally, Rheonics offers other installation accessories such as the TMA-34N and the X5 Variant of probes. For a more in depth view of how sensors can be installed in tank, refer to the following articles:
Density and Viscosity Sensor installation in tank roofs or lids
Rheonics inline viscometer and density meter in tank and recirculation line for mixing processes
Integration
Multiple Analog and digital communication methods implemented in the sensor electronics make connecting to industrial PLCs and control systems straightforward.
Further details on this can be explored in our electronics and communications page or our communication connections section in our support portal.
References
DOVER™ Silver Coated 100% Silicone Foley Catheters | Byram Healthcare
PTFE Coating for Medical Needles | Medical Device Needle Coatings
Benefits of hydroxyapatite coatings on medical implants — HIMED
