Hydrophilic Biodegradable Coatings For Implants & MedTech

A growing trend in the medical field is the use of biodegradable polymers in medical devices, such as implants. One example is hydrophilic, biodegradable polymers being used to develop hydrophilic medical coatings that are used on implants and other devices. As medical technology develops, these biodegradable materials may also be used to develop temporary implants and medical devices. These would be made of biodegradable materials that can safely break down in the body.  In order to accomplish this any medical coating applied to degradable devices must also be biodegradable. As a result, hydrophilic biodegradable coatings are quickly becoming one of the most researched biomedical topics lately. ^1,2 

In this article we will dive into hydrophilic coatings that are made from biodegradable materials. We discuss the science behind biodegradable hydrophilic polymers, how they degrade over time, and their medical uses. In this article we will focus specifically on chitosan, polyvinyl alcohol (PVA), and polyethylene glycol (PEG) based systems. If you are a biomedical engineer or original equipment manufacturer you will not want to miss learning about this fascinating technology! 

Role of Hydrophilic Coatings in Biodegradable Medical Devices 

Hydrophilic medical coatings, such as those by Hydromer®, Inc. (a leading hydrophilic coating company) are widely used in all types of medical devices, not just biodegradable applications. Their widespread use is tied to their ability to greatly help enhance the safety and performance of devices by:  

• Reducing friction (serving as lubricious coatings) 
• Allowing navigation of devices through tortuous pathways in the body
• Improving biocompatibility
• Improving drug delivery from device surfaces
• Provide antimicrobial properties 
• And more

These are all very important when creating safe, high performance equipment for the medical  device industry. 

However, when hydrophilic coatings are combined with biodegradability they provide an additional advantage, which we can call “controlled disappearance.”

Biodegradable medtech devices work effectively while they are in use. Then, they safely degrade into harmless substances. In order for biodegradable devices to use hydrophilic coatings, the coatings themselves must also be biodegradable. As a result, this is what we will explore in this article, starting with the science behind these coatings.

Critical Requirements Of Hydrophilic Biodegradable Coatings^1,2

The effectiveness of biodegradable, hydrophilic medical coatings rests on three connected principles: hydrophilicity, biodegradability, and biocompatibility. These three requirements are briefly covered below. 

1. Hydrophilicity:
   • Hydrophilic surfaces attract and retain water, forming a lubricious, water-loving layer with high wettability and low friction
   • These surfaces are less prone to protein adhesion and clotting 
   • Hydrophilicity helps in reducing tissue irritation, trauma, etc
   • Hydrophilicity improves lubricity for smooth device insertion and navigation through tortuous pathways
2. Biodegradability:
   • Biodegradable coatings must successfully break down (degrade) over time into byproducts via hydrolysis, enzymatic activity, or environmental triggers
   • It is important that the byproducts formed after degradation should be non-toxic and easily cleared from the human body
3. Biocompatibility:
   • Both the hydrophilic coating and its degradation byproducts must be safe for surrounding tissues
   • It cannot be cytotoxic or cause inflammatory responses

When all achieved, these three properties make hydrophilic, biodegradable coatings extremely valuable for certain applications. These include temporary implants, dissolvable drug vehicles, and wound-healing devices.

Polymers Used for Hydrophilic Biodegradable Coatings

Chitosan, Polyvinyl alcohol (PVA) and Polyethylene glycol (PEG) are three polymer systems used in the formulation of biodegradable coatings that are hydrophilic. 

We discuss each of these polymers below, including some of their notable properties and advantages.

Chitosan Polymer^3-5

Chitosan comes from a natural substance called chitin. Chitin is found in the shells of crustaceans like crabs and shrimp. 

Medical coatings are made from chitosan due to the polymer’s beneficial qualities. These coatings are used in a range of medical devices, including wound dressings, surgical implants, and drug delivery systems. 

This polymer is also used to formulate biodegradable hydrophilic coatings. It is safe, biocompatible, and can naturally break down in the human body. 

The advantages of Chitosan for use in biodegradable medical coatings include:

• Hydrophilicity: Chitosan has a number of hydroxyl and amino groups on its polymeric structure that interact strongly with water
• Biocompatibility: This polymer is safe for human tissues and does not cause toxic reactions
• Biodegradability: It naturally breaks down into non-toxic byproducts
• Antibacterial Properties: Chitosan can inhibit the growth of germs, reducing the risk of infections
• Film-Forming Ability: Can be easily processed into thin film hydrophilic coatings
• Moisture Retention: Helps maintain a hydrated environment, which is beneficial for wound healing and lubrication

Learn more about Chitosan Hydrophilic Medical Coatings.

Polyvinyl Alcohol (PVA) ^6-8

Polyvinyl alcohol (PVA) is a synthetic, water-soluble polymer.  It is widely used in biodegradable hydrophilic coatings. This polymer is produced by the hydrolysis of polyvinyl acetate, and has an abundance of hydroxyl (–OH) groups in its structure.  This makes it strongly hydrophilic and capable of forming hydrogen bonds with water and biological tissues. 

The advantages of PVA polymer for use in biodegradable medical coatings include: 

• Excellent Hydrophilicity: PVA provides excellent water absorption and lubricity, helping reduce friction and protein adhesion
• Biocompatibility: Well tolerated by tissues and its degradation products are non-toxic
• Film-Forming Ability: Easily processed into thin, uniform coatings which can be applied to various substrates
• Controlled Degradation: Degradation can be controlled via crosslinking or blending, allowing coatings to last days to weeks
• Drug Loading Capacity: PVA hydrogels can incorporate and release drugs, making them valuable for drug-eluting coatings

Polyethylene Glycol ^9-11 

Polyethylene glycol (PEG) is a water-loving (hydrophilic) polymer. It is well-known for its ability to repel proteins. PEG creates a thick layer of water around itself through hydrogen bonding. This helps stop proteins from sticking to its surface and prevents cells from attaching. 

PEG is often called a “stealth” polymer because of its ability to resist protein adsorption and avoid detection by the immune system. 

The advantages of PEG polymer for use in biodegradable medical coatings include: 

• Hydrogel Formation: Crosslinked PEG networks provide lubricity and swelling capacity
• Biodegradability: Can be incorporated into degradable copolymers such as PVP, polyesters, or polycarbonates
• Drug Delivery: Hydrophilic coatings formulated with PEG can control the release of drugs or growth factors from device surfaces
• Proven Track Record in Medical Applications: Has been used extensively in medical devices, drug delivery systems, and pharmaceuticals
• Functionalization: PEG chains can easily be functionalized with reactive groups, allowing for further modifications, such as drug immobilization
• Biocompatibility: Considered non-toxic and has a good safety profile
• Cost-effective: PEG is relatively inexpensive and its supply is widely available

You can learn more about the uses and benefits of PEG Hydrophilic Coatings.

Curing and Application Methods for Hydrophilic Biodegradable Coatings ^12-16

Coating application method and curing type strongly influences the coating’s durability and degradation profile. 

Common application and curing approaches for these coatings include:

• Solvent Casting and Dip Coating: Simple immersion techniques allow for uniform coating formation 
• UV Curing: UV curing is a process that uses ultraviolet (UV) light to start a chemical reaction called photopolymerization. This reaction changes liquid materials into solid forms very quickly when compared to thermal curing.
• Layer-by-Layer (LbL) Assembly: Alternating layers of charged polymers are used to make very thin and precise coatings that can break down at different rates
• Crosslinking: Ionic (e.g., calcium crosslinked alginate), covalent (e.g., glutaraldehyde), or enzymatic crosslinking modifies the stability and degradation rates of the coating 
• Surface Grafting and Plasma Activation: Can be used to attach biodegradable polymers directly to device substrates, improving adhesion

The choice of coating method depends on the substrate material (metal, polymer, ceramic) and the desired degradation timeframe (profile).

Biodegradation Profiles

All biodegradable hydrophilic coatings do not have uniform degradation profiles. These coatings can be engineered to degrade in days, weeks, or months. The degradation profile depends on the specific application and is controlled through the formulation of the coating.

There are several factors influencing the degradation timeframe of a coating. These include:

• pH and Enzyme Presence: Acidic or enzymatic environments can accelerate breakdown for biodegradable polymers
• Crystallinity: Polymers that have a crystalline structure degrade slower than amorphous polymers
• Crosslink Density: Polymers that have higher crosslinking tend to degrade slowly
• Blending: Mixing hydrophilic polymers with hydrophobic polymers can influence the breakdown rate of the coating 

Below are just some examples scenarios of where a different degradation rate may be required based on the application: 

• Longer duration: A biodegradable vascular stent coating may be designed to dissolve within 6–12 months.
• Prolonged drug release: A drug delivery coating for infection prevention might be intended to degrade in 2–4 weeks. The coating may release antibiotics only during the critical healing phase. Drug-eluting stents may also fall into this category.
• Immediate drug release within tissues: Wound-healing films may degrade within minutes to hours, synchronizing with tissue regeneration.

Safety and Regulatory Benchmarks ^17,18

Biodegradable coating performance can be fine tuned based on formulation and application. However, safety is a non-negotiable requirement. 

Key benchmarks to consider for these coatings include (but may not be limited to):

• ISO 10993 biocompatibility testing: Cytotoxicity, sensitization, and irritation assays
• Hemocompatibility: Ensures coatings do not trigger clotting or hemolysis
• FDA guidelines: Focus on demonstrating predictable degradation, non-toxicity, and safe clearance from the body

7 Medical Devices That Use Hydrophilic Biodegradable Coatings

Below are seven examples of medical devices where biodegradable, hydrophilic coatings are useful.

1. Drug-Eluting Stents and Vascular Implants ¹⁹

• Use: Coronary or peripheral stents are covered with special hydrophilic biodegradable materials (like PVP or PEG) that contain medicines to prevent cell growth
• Advantages: These stents help stop the blood vessels from narrowing again by controlling how the medicine is released. As the coating breaks down naturally, it reduces the chances of long-term inflammation and blood clots.

2. Orthopedic Implants and Bone Fixation Devices ²⁰

• Use: Devices like screws, pins, and bone scaffolds are coated with hydrophilic biodegradable materials to make them safer and easier to insert.
• Advantage: These hydrophilic biodegradable coatings help the bone connect with the implant, reduce injury during insertion, and eliminate the need for a second surgery to remove the implant.

3. Catheters and Guidewires ²¹

• Use: Hydrophilic biodegradable coatings are applied to catheters for urinary, blood vessel, or nerves to make them slippery. 
• Advantage: This reduces pain during insertion and reduces the risk of harmful bacteria. Since the coating breaks down, it doesn’t permanently change the device’s surface, lowering the chances of negative reactions within the body.

4. Wound Healing and Tissue Engineering Scaffolds ²²

• Use: Scaffolds, meshes, or dressings are covered with hydrophilic biodegradable coatings. These work to deliver growth factors, antibiotics, or stem cells.
• Advantage: These coatings help cells stick, move, and keep the wound moist while they slowly disappear.

5. Bioresorbable Vascular Scaffolds (BVS) ²³

• Use: These are fully biodegradable stents coated with a hydrophilic coating that helps with placement and drug delivery.
• Advantage: They act as temporary support for arteries and completely dissolve, leaving the blood vessel in its natural state. Because they break down naturally and safely they eliminate the need for surgical removal. 

6. Ophthalmic Devices ²⁴

• Use: Hydrophilic biodegradable coatings are used in intraocular lenses or drug-delivering eye implants.
• Advantage: This type of hydrophilic coating makes the surfaces more comfortable and allows for effective drug delivery. The enzymes present in eye tears help in breaking down  these inserts naturally without leaving any residue.

7. Neural and Soft-Tissue Implants ²⁵

• Use: Hydrophilic biodegradable coatings are used on devices like electrodes, nerve guides, or soft tissue repair tools.
• Advantage: These coatings improve biocompatibility. These coatings also allow for controlled release of drugs to help reduce inflammation or scarring.

Hydromer®’s Role in Advancing Biodegradable Hydrophilic Coatings

Hydromer®, Inc. is a trusted industry-leader in developing and supplying safe and innovative hydrophilic medical coatings for a wide range of medical applications. Our coating experts have the capability to develop custom, biodegradable and non-biodegradable medical coatings for a wide range of medtech applications. 

We have been a trusted partner to leading OEMs, startups, and CMOs for 40+ years. So if you need a custom medical coating, regulatory consulting, or contract coating services then turn to Hydromer, Inc.  

Contact our coating experts now to get started on your custom coating project. 

Conclusion

Biodegradable coatings that are also hydrophilic help make medical devices better and safer. They provide many benefits, such as reducing friction, preventing unwanted growth (fouling), and delivering drugs. They also degrade naturally and disappear safely from the human body after their use. 

The main materials used to create biodegradable hydrophilic coatings include chitosan, PVA, and PEG-based polymers. Companies like Hydromer, Inc. are able to formulate specific solutions that meet the needs of healthcare providers and safety regulations.

New medical devices focus on being temporary, safe, and effective. As a result, biodegradable hydrophilic coatings are expected to be very important in the future of medical and biomedical technologies.

References

Click here to see all references for this article.

1. Niemczyk A, El Fray M, Franklin SE. Friction behaviour of hydrophilic lubricious coatings for medical device applications. Tribology International. 2015/09/01/ 2015;89:54-61. doi:https://doi.org/10.1016/j.triboint.2015.02.003

2. La Porte RJ. Hydrophilic polymer coatings in the development and manufacture of medical devices. University of Massachusetts Lowell; 1996.

3. Obaid NA, Alzahrani AM, Alaryni BA, et al. Effectiveness of Chitosan Coating Catheter in Preventing Catheter-Associated Urinary Tract Infection (CAUTI). 

4. Prabha S, Sowndarya J, Ram P, et al. Chitosan-Coated Surgical Sutures Prevent Adherence and Biofilms of Mixed Microbial Communities. Current microbiology. Feb 2021;78(2):502-512. doi:10.1007/s00284-020-02306-7

5. Peers S, Montembault A, Ladavière C. Chitosan hydrogels for sustained drug delivery. Journal of Controlled Release. 2020/10/10/ 2020;326:150-163. doi:https://doi.org/10.1016/j.jconrel.2020.06.012

6. Alexandre N, Costa E, Coimbra S, et al. In vitro and in vivo evaluation of blood coagulation activation of polyvinyl alcohol hydrogel plus dextran‐based vascular grafts. Journal of biomedical materials research Part A. 2015;103(4):1366-1379. 

7. Chandran MR, Usha R. Bio Evaluation of Lantibiotic Nisin Loaded Polyvinyl Alcohol–Sodium Alginate Crosslinked Hydrogel As Novel Dental Temporary Filling Material. Journal of Pure & Applied Microbiology. 2023;17(4)

8. Rostami F, Yekrang J, Gholamshahbazi N, Ramyar M, Dehghanniri P. Under-eye patch based on PVA-gelatin nanocomposite nanofiber as a potential skin care product for fast delivery of the coenzyme Q10 anti-aging agent: in vitro and in vivo studies. Emergent Materials. 2023;6(6):1903-1921. 

9. Sabel-Grau T, Tyushina A, Babalik C, Lensen MC. UV-VIS Curable PEG Hydrogels for Biomedical Applications with Multifunctionality. Gels. Mar 5 2022;8(3)doi:10.3390/gels8030164

10. Yeh S-L, Deval P, Tsai W-B. Fabrication of Transparent PEGylated Antifouling Coatings via One-Step Pyrogallol Deposition. Polymers. 2023;15(12). doi:10.3390/polym15122731 

11. Zhu J. Bioactive modification of poly(ethylene glycol) hydrogels for tissue engineering. Biomaterials. Jun 2010;31(17):4639-56. doi:10.1016/j.biomaterials.2010.02.044

12. Tan Q, Ji J, Barbosa MA, Fonseca C, Shen J. Constructing thromboresistant surface on biomedical stainless steel via layer-by-layer deposition anticoagulant. Biomaterials. 2003;24(25):4699-4705. 

13. Tang X, Yan X. Dip-coating for fibrous materials: mechanism, methods and applications. Journal of Sol-Gel Science and Technology. 2017/02/01 2017;81(2):378-404. doi:10.1007/s10971-016-4197-7

14. Soucek MD, Ren X. UV-Curable Coating Technologies. In: Tiwari A, Polykarpov A, eds. Photocured Materials. The Royal Society of Chemistry; 2014:0.

15. Kushibiki T, Mayumi Y, Nakayama E, et al. Photocrosslinked gelatin hydrogel improves wound healing and skin flap survival by the sustained release of basic fibroblast growth factor. Scientific Reports. 2021/11/29 2021;11(1):23094. doi:10.1038/s41598-021-02589-1

16. Liu L, Gao Y, Zhao J, et al. A Mild Method for Surface-Grafting PEG Onto Segmented Poly(Ester-Urethane) Film with High Grafting Density for Biomedical Purpose. Polymers. 2018;10(10). doi:10.3390/polym10101125 

17. ISO. Biological evaluation of medical device. International Standard Organization. 2017;

18. Nalezinková M. In vitro hemocompatibility testing of medical devices. Thrombosis Research. 2020/11/01/ 2020;195:146-150. doi:https://doi.org/10.1016/j.thromres.2020.07.027

19. Udriște AS, Burdușel AC, Niculescu A-G, Rădulescu M, Grumezescu AM. Coatings for Cardiovascular Stents—An Up-to-Date Review. International Journal of Molecular Sciences. 2024;25(2). doi:10.3390/ijms25021078 

20. Kumar M, Kumar R, Kumar S. Coatings on orthopedic implants to overcome present problems and challenges: A focused review. Materials Today: Proceedings. 2021;45:5269-5276. 

21. Edwards PA, Price M, Nimchuk N, Mahon J. Novel Water Loving Coatings (WLC) Lubricious and Durable Guidewires. 2017; Accessed 2/1/2025. https://doi.org/10.1115/DMD2017-3434 2017 Design of Medical Devices Conference

22. Thai NLB, Beaman HT, Perlman M, Obeng EE, Du C, Monroe MBB. Chitosan Poly(vinyl alcohol) Methacrylate Hydrogels for Tissue Engineering Scaffolds. ACS Applied Bio Materials. 2024/12/16 2024;7(12):7818-7827. doi:10.1021/acsabm.3c01209

23. Singh R, Bathaei MJ, Istif E, Beker L. A review of bioresorbable implantable medical devices: Materials, fabrication, and implementation. Advanced Healthcare Materials. 2020;9(18):2000790. 

24. Liu S, Zhao X, Tang J, Han Y, Lin Q. Drug-eluting hydrophilic coating modification of intraocular lens via facile dopamine self-polymerization for posterior capsular opacification prevention. ACS Biomaterials Science & Engineering. 2021;7(3):1065-1073. 

25. Spearman BS, Agrawal NK, Rubiano A, Simmons CS, Mobini S, Schmidt CE. Tunable methacrylated hyaluronic acid-based hydrogels as scaffolds for soft tissue engineering applications. Journal of biomedical materials research Part A. Feb 2020;108(2):279-291. doi:10.1002/jbm.a.36814