Medical coatings are essential in modern healthcare. They modify device surfaces in order to enhance the safety and performance of many medical devices. Common medical-grade surface coatings include hydrophilic coatings as well as silicone, and antimicrobial types. These coatings are applied to device surfaces efficiently using high-throughput automated coating systems. These medical device coating systems include modules to apply coatings on the devices, such as spin coating equipment.
Automated systems consist of modular workstations, each performing specific tasks. For example, the coating application module controls the deposition of liquid coatings onto device surfaces. Each module or station is further divided into submodules based on coating application requirements.
There are multiple, compatible coating application methods that can be incorporated into automated systems, including spin coating.
In this article, we leverage Hydromer® Inc.’s 40+ years of experience to discuss spin coating equipment (as it relates to automated coating systems) in detail. The goal of this guide is to understand the different types of spin coater machines along with its critical parameters, and key components. We aim to provide valuable insights for Coating and Production Engineers, Operations Managers, and other professionals involved in medical device production.
Spin Coating Equipment Used in Automated Medical Device Coating Systems
The spin coating process is one of the several compatible coating application methods that is used to coat medical devices in automated systems.
What It Is
In this method, the coating material or solvent is spun at high speeds (usually >10 rotations per second = 600 rpm) using automated spin coaters (a type of spin coating equipment). Such a machine is designed to utilize the centrifugal force and the surface tension to apply coatings to numerous devices.
A spin coater is a compact device that efficiently produces thin, uniform coating layers. This type of coating equipment often outperforms other application modules in speed and consistency.
How the Spin Coating Process Works: The 4 Key Stages
Spin coater configurations vary based on production requirements, coating solution management, and automation level. However, the spin coating process steps remain consistent across configurations.
- Deposition: The process begins by dispensing a precise volume of coating solution onto the center of the substrate, which may be stationary or rotating slowly. This is achieved using a specialized nozzle or syringe pump.
- Spin Up: During acceleration, the substrate is rotated at high speeds by a controlled motor. Centrifugal forces spread the coating evenly across the surface. Maintaining the desired speed for a set time ensures uniformity.
- Spin Off: In this stage, the excess coating liquid is spun off the edges. The speed is kept constant until the desired coating thickness is achieved. In general, the higher the spin speed, the thinner the resulting films.
- Evaporation: In the final stage, solvents evaporate due to airflow and environmental exposure, resulting in a solid, thin coating across the substrate.
These are the four primary stages of the spin coating process. Each stage affects the film thickness and uniformity.
As expected, the utmost care needs to be taken during each stage. Defects in the coating layer can lead to unusable devices and/or serious post-procedural complications and patient discomfort.
Benefits of Using Spin Coating Equipment for Medical Device Coating Application
A spin coater machine is popular for quickly applying an ultra-thin layer of coatings to medical devices. Because of this, it is used by many OEMs and contract coating services.
Below are its main benefits over other methods, including dip coating equipment and spray coating equipment:
- Excellent Film Quality: Spin coaters deliver superior layer uniformity and thickness. At controlled speeds and correct settings, these coaters evenly distribute coatings across the device surface. Unlike dip and spray coaters, spin coater results depend primarily on spin speed and time. These parameters need to be established and controlled in the system.
- Design Simplicity: Spin coater machines are compact systems with minimal electromechanical components. They are easy to use and require little human intervention once set up. Spin coating application typically takes 10 to 60 seconds. This makes them ideal for research and rapid prototyping.
- Efficiency: When operated at optimal speeds, spin coaters minimize coating waste. High-speed spinning dries the coating through airflow, often reducing the need for post-deposition curing.
- Scalability: Spin coaters are cost-effective and can process multiple batches quickly. And with few process variables, the spin coating process is highly repeatable, making it easy to scale and integrate into semi- or fully-automatic equipment.
Medical Devices Compatible with Spin Coating Equipment
Spin coating equipment is well suited for applying coatings to medical devices with flat surfaces. However, it can also be used for many devices, including (but not limited to):
- Catheters
- Sheaths
- Certain implants
- Depositing coatings onto drug delivery systems
- And more
Key Components of an Automated Spin Coating Module
Spin coating is one of the most widely used thin-film deposition techniques across industries. One reason for this is that the equipment is simple to operate and features a straightforward design.
The main components of a spin coating module include:
1. Substrate Holder
The substrate holder, or spin chuck, secures the substrate during the spin coating process. It is mounted on the motor shaft, and its size varies based on substrate type and complexity.
The spin chuck usually uses a vacuum suction system, including pumps, lines, and ports, to hold the substrate securely and ensure proper centering.
2. Spindle Assembly
The spindle assembly, which includes a drive motor and precision components, provides the controlled rotational motion needed for coating application. It spins the substrate holder at speeds typically ranging from 500 to 6000 RPM or higher.
For reliable operation, spindle assemblies may use high-precision brushless DC, servo, or stepper motors.
3. Coating Management System
The coating management system comprises the reservoir, dispenser, syringe pump, and related components. It safely stores the coating solution and delivers it precisely to the substrate surface.
Dispensing failures can directly affect film thickness. Therefore, coating management and dispensing systems should be regularly monitored to prevent errors.
4. Spin Coating Process Chamber
The spin coating process occurs within an environment-controlled chamber. This component is fully enclosed during operation to prevent splashing at high speeds.
A chemically resistant bowl inside the chamber collects excess or splashed coating solution. It is connected to drainage channels for easy cleaning.
5. Exhaust System
Solvent-based coatings produce hazardous fumes, including alcohols, ketones, and other volatile compounds (VOCs). Spin coating chambers are sealed to prevent leaks and equipped with vapor extraction or exhaust systems to evacuate these fumes.
These systems maintain a safe working environment and prevent contamination or operator harm. Advanced systems, such as those from Hydromer®, include vapor filtration and chemical-resistant airflow features.
6. User Interface
The control system manages the entire spin coating process. Its user interface allows operators or engineers to set parameters such as rotation speed, acceleration profiles, spin time, and dispensing volume.
Sensors form the backbone of the control system. They monitor speed, deposition, and safety within the coating chamber. As a result, they ensure the stable and scalable operation of spin coating modules.
Critical Process Parameters of Spin Coating Equipment
The finished coating film is determined by the process parameters for the coating equipment. Spin coating requires attention to fewer process parameters compared to dip or spray coating methods. The critical parameters of the coating process include:
- Spin Speed: Spin speed is the most important parameter in this process. The higher the spin speed, the greater the centrifugal force. This leads to a uniform spread and thin film. Most spin coaters’ spin speed is set to 500 – 6000 RPM.
- Spin Time: The total duration for which the substrate is rotated also plays a crucial role in the outcome produced by the spin coaters. For example, the longer spin time allows greater solvent evaporation, leading to an ultra-thin coating layer. The time varies based on the coating material, but in most cases it is set to 10 to 60 seconds.
- Acceleration: The substrate must reach target RPM at a controlled rate to prevent uneven spreading or splashing. Equipment manufacturers, such as Hydromer®, Inc. program acceleration rates for reliability and scalability.
- Dispense Volume: The amount of coating solution released by the nozzle is also important when it comes to the spin coater. The volume is decided based on the substrate size and coating chemistry. Too little coating solution leads to incomplete surface coverage. Similarly, excessive dispense volume generally becomes the main reason for material wastage and edge buildup. In turn, this needs to be pinpointed.
- Coating Viscosity: Changes in viscosity significantly affect results across all application modules, including spin coaters. Viscosity should be monitored throughout the process. Higher viscosity produces thicker films, and lower viscosity results in thinner films.
- Environmental Conditions: Temperature and humidity influence key parameters like viscosity and solvent evaporation. Spin coating chambers use sensors to maintain optimal environmental conditions.
Types of Coatings That are Compatible with Spin Coating Equipment
Various medical equipment coatings are available to ensure devices meet required standards and operate safely within biological environments.
Not all medical coatings are compatible with spin coaters. Only liquid-based formulations are suitable, including the following:
- Hydrophilic Coatings For Medical Devices: These are polymer-based, water-loving, lubricious coatings. At their heart, they are used to create highly lubricious, low-friction surfaces. They ensure smooth insertion and navigation of invasive medical devices. They have gained massive popularity recently due to their customizability and multifunctional benefits. For example, at Hydromer®, Inc., we utilize our 40+ years of coating experience to customize these coatings for specific product requirements. They can be formulated to provide drug-eluting, antimicrobial, and thromboresistant properties, among others. When it comes to spin coating, the coating chemistry of hydrophilic formulations can be easily adjusted to ensure full compatibility with the coater equipment.
- Sol-Gel Coatings: Sol-gel coatings create a bioactive or protective oxide layer on the surface of medical devices. Their main purpose is to prevent corrosion, promote osseointegration, and allow drug delivery. A common example of these coatings is silica or titanium dioxide coating. When applied using spin coaters, the sol-gel coatings create ultra-thin oxide layers with good surface uniformity.
- Chitosan Coatings: Chitosan, a natural biopolymer derived from chitin, can be formulated as a low-viscosity aqueous coating. These coatings are fully compatible with spin coaters.
Hydromer®: Hydrophilic Medical Coating Manufacturer and Coating Equipment Supplier
Hydromer®, Inc. has formulated, manufactured and supplied advanced hydrophilic coatings for over 40 years. Our medical equipment portfolio includes high-performance semi- and fully-automated coating systems, friction testing machines, and custom-built equipment.
Our automated systems integrate with various coating application methods and curing processes, including Hydromer®’s proprietary UV curing technology, HydrUV™. Explore our full range of coating services to see how our solutions can support your products and production needs. Our services include contract R&D, formulation, analytical testing, and more.
We aim to help customers achieve efficient, high-volume device production.
Hydromer®, Inc Medical Coating Equipment
Our three most popular automated coating application solutions are:
- Hydrophilic Coating System: This automated system features integrated UV curing and is designed for applying hydrophilic coatings to medical devices. It requires only one or two operators and supports an annual capacity of 200,000 to 300,000 units.
- Fully Automated Coating System: This end-to-end solution is suitable for industrial applications and compatible with various medical-grade coatings. It requires a single operator and is ideal for large-scale production of complex devices such as catheters and guidewires.
- Friction Testing Equipment: Through years of manufacturing experience, we have developed a high-performance vertical and desktop friction tester. It is compliant with the industry standard YY/T 1898-2024. The equipment has been proven to measure the lubricity and durability of hydrophilic coatings accurately.
Contact our sales team to learn more about Hydromer® automated coating systems or to schedule a demonstration.
