Hydrophilic coatings are used to enhance the safety and performance of medical devices. The overall hydrophilicity, properties, and performance of a coating is largely determined by their polymer chemistry. Coatings manufacturers use different polymer chemistries to formulate coatings with specific properties and functionalities. Polyacrylamide hydrophilic coatings, based on polyacrylamide polymer, is one polymer used for medical coatings. For example, crosslinking polyacrylamide (PAM/PAAm) with polyethylene glycol (PEG) creates a coating that combines the mechanical strength of PAM with the impressive biocompatibility and flexibility of PEG.
If you are interested in other polymers we cover several of them at a high level in our comprehensive guide on hydrophilic polymers and chemistries. This article, however, is intended to focus solely on polyacrylamide (PAM). Our goal is to help you understand PAM’s chemical structure and what differentiates it from other hydrophilic polymers used for medical coatings. We will also discuss where PAM-based coatings are used in medical applications as well as their benefits.
Chemical Structure and Composition of Polyacrylamide (PAM)
Polyacrylamide is a water-soluble, linear polymer with numerous hydrophilic amide groups (–CONH₂).1 Such a composition makes it a perfect fit for hydrogels that are commonly used for medical devices and implants.
PAM is a synthetic polymer derived from polymerizing acrylamide.1 Here’s how:
The Acrylamide Monomer
The acrylamide monomer consists of vinyl (CH₂=CH–) and amide (–CONH) groups.
The structure of the acrylamide monomer is as follows:
CH₂=CH–CONH₂
The carbon-carbon double bond (C=C) of the vinyl group is reactive. It allows free-radical polymerization. As such, many monomers are connected together through the process of polymerization.
Result of Polymerization: Polyacrylamide
Once the carbon-carbon double bond from the acrylamide monomer opens, a linear polymer consisting of repeating –CH₂–CH– units is formed through polymerization.2
The structure of the polyacrylamide polymer is:
–[CH2–CH(CONH2)]n–
Where ‘n’ is the degree of polymerization. It also represents the number of repeating acrylamide units (–CH₂–CH(CONH₂)–)6.
Each unit has a pendant amide group (–CONH₂), capable of forming hydrogen bonds with water. The length or molecular weight determines the viscosity, flexibility, and coating ability of PAM.3
Also, it is helpful to note that each amide group can absorb water that is thousands of times its own weight.
Properties of Polyacrylamide (PAM)
Polyacrylamides polymer has high hydrophilicity. It has excellent mechanical and chemical stability. As a result, it is known for improving the functionality and lifetime of medical devices.
Physical Properties of Polyacrylamide
Polyacrylamide are crosslinked polymers that can be easily processed into coatings. They can absorb a tremendous amount of water compared to their weight.1 They also exhibit high optical clarity at the same time, which is useful for many diagnostic procedures.
- Appearance: Polyacrylamide for medical devices is a white and odorless solid or powder.
- Swellability: It is a highly soluble polymer that easily swells in the presence of water and biological fluids.
- Density: In contrast to other hydrophilic polymers, polyacrylamide’s density is ~1.3 g/cm³. It is known to be moderately dense.
- Thermal Stability: Polyacrylamide can withstand temperatures up to 200°C.
Chemical Properties of Polyacrylamide (PAM) Polymer
Polyacrylamide forms a highly stable, thin hydrogel or hydrophilic film on the surface of the medical devices. The film is non-toxic and non-irritating when completely processed.
- Amide Groups: The presence of amide groups ensures strong hydrogen bonds.
- Non-Ionic1: The polyacrylamide is a neutral polymer. It does not react with the biological tissues. Hence, PAM has been proven to have excellent biocompatibility.
- Hydrolysis: It can create carboxylate groups (–COO⁻) under normal conditions.4 Such behaviour helps this polymer alter charges to increase swelling and adhesion.
- Stability: The C-C bond of polyacrylamide cannot be broken under normal biological conditions.2
Polyacrylamide (PAM) vs. Other Hydrophilic Polymers
Polyacrylamide is commonly known as PAM or PAAm. This polymer is not as popular as other hydrophilic polymers, such as polyvinylpyrrolidone (PVP) and polyethylene glycol (PEG). However, polyacrylamide do serve as the best polymer choice in certain cases. This polymer is mainly combined with other hydrophilic polymers to create advanced formulations that possess multiple properties.
Here are some reasons why Polyacrylamide may be used as well as how it compares to other hydrophilic polymers used for medical coatings.
1. Excellent Hydrophilicity
Polyacrylamide has multiple hydrogen bonds present across each acrylamide monomer. These bonds create a dense hydration layer that traps a tremendous amount of water molecules. Moreover, such a layer can easily stabilize water to increase wettability, surface hydration, and biocompatibility.4
The result is a highly effective and extremely lubricious layer on the surface of medical devices. For example, a PAM-coated guidewire offers a lower coefficient compared to a PEG- or PVP-coated guidewire.
2. High Water-Retention
Water retention is a critical property of hydrophilic coatings. It is directly linked to the reliability of these coatings.
The amide group of acrylamide contains a carbonyl oxygen (C=O), which is a hydrogen bond acceptor, and amide hydrogens (–NH₂), which are hydrogen bond donors. Both of them play a critical role in interacting strongly with the surrounding hydrogen (δ⁺) and oxygen (δ⁻) atoms present in nearby water molecules.
Such interactions strongly attract and bind water molecules for a longer period of time vs some other hydrophilic polymers.
3. Good Adhesion To Certain Substrates
Amide groups are polar, and they have an excellent ability to form hydrogen bonds.5 As a result, polyacrylamide interacts strongly with substrates that have hydroxyls (–OH) on their surface. It is an excellent choice for medical devices consisting of metals and glass.
Most polyacrylamide-based hydrophilic coatings are durable and less prone to delamination, which is a common issue.
On the other hand, polymers like PEG can accept hydrogen bonds, but they fail to donate them.7 This can lead to one-sided, secondary interactions, which may make adhesion weaker.
4. Adjustable Mechanical Strength
Polyacrylamide-based coatings are tunable in nature. Their softness, flexibility, and strength can be easily controlled by varying chemical composition and structure.8
- Soft and gel-like hydrophilic coatings can be made by keeping the crosslinking density low. This allows the coating to better mimic biological tissues.
- In contrast, using high-density crosslinking provides excellent strength and wear resistance.
5. High Optical Clarity
Polyacrylamide forms a transparent, homogeneous film on the surface of the substrates. Such optical clarity is essential for medical devices that are used for diagnostic purposes, such as those that include a lens.
The optical performance of PAM is exceptional under hydrated states. This is because it does not separate into regions of different refractive index.9 On the other hand, PEG or PVP may phase-separate at higher molecular weights.
Customization of Polyacrylamide-Based Hydrophilic Coatings
Customization is one of the major differentiators of polyacrylamide. These hydrophilic polymers can be chemically modified to offer different properties for a specific application.
The reason is the highly reactive amide groups that are ready for copolymerization and grafting. As discussed previously, even adjusting the crosslinking density can significantly change the coating’s overall properties.
Coating manufacturers have the following options when it comes to customizing polyacrylamide (PAM):
- Copolymerization
- Surface Grafting
- Functional Additives
They can also play around with the layer thickness, chain length, and monomer ratios to alter the properties.
Here are a few customizations that have been popular over the past few decades:
- PAM-PEG: The combination of polyacrylamide with polyethylene glycol (PEG) offers excellent mechanical strength and antifouling properties for coatings.
- PAM-Zwitterion Blend: This is useful for improving protein resistance in coatings to avoid blood clotting.
- PAM-Chitosan Blend: Such a blend drastically improves mechanical strength and thermal stability for coatings used in dynamic biological environments.
Medical Devices Coated with Polyacrylamide Hydrogel
Polyacrylamide is best suited for a variety of medical devices that come in contact with biological tissues. This polymer is non-toxic and non-carcinogenic. It can also be easily customized to provide antimicrobial and antifouling properties.
Below is a quick list of some medical devices that are suitable for polyacrylamide hydrophilic coatings:
- Catheters: Catheter surfaces must be highly lubricious for safe insertion and navigation through complex anatomical pathways. Polyacrylamide-based catheter coatings offer a low-friction surface. This drastically reduces tissue trauma and improves patient comfort during the catheter’s intended functions. These coatings can be used on a wide variety of catheters, including cardiac, balloon, urinary9, and vascular catheters. Learn more about hydrophilic catheter coatings.
- Guidewires: Similar to catheters, PAM polymer formulations ensure a low-friction surface. This helps provide the safe and smooth insertion and navigation of guidewires. Learn more about hydrophilic guidewire coatings.
- Implants: Customized PAM-based hydrophilic formulations offer a variety of benefits for medical implants. A few of them include smooth deployment, enhanced tissue integration, and minimized inflammatory response.
- Lenses: Medical lenses are coated with polyacrylamide-based hydrophilic coatings in order to achieve exceptional optical clarity. Such coatings play a critical role during diagnostic operational procedures.
This coating is helpful for medical devices and applications that require best-in-class lubricity, adhesion, mechanical strength, or optical clarity.
Consulting with a coatings expert is a good idea if you are unsure of the best type of polymer coating for your device. Contact the coatings team at Hydromer® for a project review or technical consulting. We can help develop a custom hydrophilic coating to meet your specific product requirements.
Hydromer®: Customized Polyacrylamide-Based Hydrophilic Coatings Manufacturer
Hydromer, Inc., has long been recognized as a global leader in hydrophilic coatings technology. We have 40+ years of experience formulating, manufacturing, and supplying clinically proven hydrophilic medical coatings to device manufacturers worldwide.
We deliver custom hydrophilic coating solutions that help OEMs bring innovative products to market. Our multifunctional Polyacrylamide-based hydrophilic coatings can be customized to meet your product’s specific safety and performance requirements.
Our coatings team uses a range of hydrophilic polymers, including Polyacrylamide to develop coatings with best-in-class performance and safety.
Hydromer medical coatings exhibit the following properties:
- Long-lasting hydrophilicity
- High lubricity
- High wettability
- Antimicrobial
- Drug-eluting capabilities
- Biocompatibility
- Low particulate
- Enhanced adhesion
- High durability
- Thromboresistance to reduce blood clotting
Get in Touch
Are you looking for more than just another coatings supplier? We are a full-service partner to many leading device manufacturers. We can develop a custom coating to meet your specific product goals and regulatory requirements. But what sets us apart from our competitors is the extensive range of support services we offer to our customers, including:
- Research and Development (R&D) services
- Contract coating services
- Specialized Analytical Testing
- Custom Machine Building
- Turn-key Operations
- Technology Transfer Services
- Technical consulting and support services
Contact our team of coating experts today with questions or to learn more about our coatings and services.
References
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2. Xiong, C., Wei, F., Li, W., Liu, P., Wu, Y., Dai, M., & Chen, J. (2018). Mechanism of polyacrylamide hydrogel instability on High-Temperature Conditions. ACS Omega, 3(9), 10716–10724. https://doi.org/10.1021/acsomega.8b01205
3. Klein, Joachim & Conrad, Klaus‐Dieter. (2003). Characterisation of poly(acrylamide) in solution. Die Makromolekulare Chemie. 181. 227 – 240. 10.1002/macp.1980.021810120.
4. Mohamed, M. H., & Mohyaldinn, M. E. (2024). Polyacrylamide-Based Solutions: A Comprehensive Review on Nanomaterial Integration, Supramolecular Design, and Sustainable Approaches for Integrated Reservoir Management. Polymers, 17(16), 2202. https://doi.org/10.3390/polym17162202
5. Deng, Y., Xu, Y., Nie, L., & Huang, Y. (2023). Crosslinked Polymer Coatings of Poly (Acrylic Acid-co-acrylamide)/Polyethyleneimine (P(AA-co-AAm)/PEI) on Titanium Alloy with Excellent Lubrication Performance for Artificial Joints. Coatings, 14(1), 28. https://doi.org/10.3390/coatings14010028
6. Hydrophilic Coating Polymers and Chemistries: Complete Guide. https://hydromer.com/hydrophilic-coating-polymers-chemistries-guide/#:~:text=Repeating%20acrylamide%20units%20(%E2%80%93CH%E2%82%82%E2%80%93CH(CONH%E2%82%82)%E2%80%93).
7. Such, G. K., Johnston, A. P. R., & Caruso, F. (2010). Engineered hydrogen-bonded polymer multilayers: from assembly to biomedical applications. Chemical Society Reviews, 40(1), 19–29. https://doi.org/10.1039/c0cs00001a
8. Wang, Y., Zhang, R., Qiao, Z., Dou, B., Xu, H., Meng, F., & Huang, J. (2025). Polyacrylamide-Based Hydrogel with Biocompatibility and Tunable Stiffness for Three-Dimensional Cell Culture. ACS Applied Bio Materials. https://doi.org/10.1021/acsabm.4c01846
9. Cai, Y., Li, J., Gu, R., Yang, H., Chen, Y., Li, Y., Qu, D., Wang, R., & Wang, D. (2025). Preparation of Antibacterial and Antiadhesive Urinary Catheters with Robust Double-Network Gelatin-Polyacrylamide-Ag Nanoparticle Hydrogel Coatings. ACS Applied Polymer Materials. https://doi.org/10.1021/acsapm.4c03678
