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How Hydrophilic Coatings Facilitate Minimally Invasive Surgery

By creating a lubricious surface, hydrophilic coatings reduce medical device stiction, aid in device positioning, and reduce the risk of infection.

Hinke Malda

The U.S. population is aging. According to The International Journal of Epidemiology, the number of older people in the United States is projected to increase by 135% between 2000 and 2050. Moreover, the population aged 85 and over—the group most likely to need health and long-term-care services—is projected to increase by 350%. The growing size of the aging population will likely lead to higher rates of chronic conditions such as diabetes and obesity, necessitating increased medical interventions, including minimally invasive surgeries.

As a result of this heightened healthcare challenge, demand will also grow for such medical devices as cameras, devices, and implants that can navigate through complex and sensitive parts of the body. Key to facilitating the insertion of such devices into tortuous and narrow vasculature and to help reduce tissue damage is the use of hydrophilic coatings.

Benefits of Hydrophilic Surfaces

Guidewires are inserted into the body through catheters featuring hydrophilic coatings.

Hydrophilic coatings have the ability to attract water molecules, creating a lubricious surface that reduces friction. For example, surgeries in which a long guidewire or catheter is snaked through the body have less impact on the patient if the device has a hydrophilic surface, reducing trauma and irritation at the insertion site and lessening tissue damage along the delivery path. This capability can also lead to increased patient comfort.

Maintaining a hydrophilic environment can also help alleviate the natural resistance that vascular inner surfaces exhibit as a result of stiction. Moreover, wetness and lubricity help a device such as a balloon catheter to slide through winding blood vessels, facilitating accurate positioning during such procedures as angioplasty or tuboplasty. In addition, hydrophilic coatings release low levels of particulates, lowering the chance of an allergic in vivo reaction. Last but not least, the lubricity created by a coating helps minimize bacterial colonization on the medical device, significantly reducing the chance of infection.

Lubricious coatings can be applied to catheters used to deliver a host of medical devices, including bare-metal stent grafts and drug-eluting stents, which are used for percutaneous coronary interventions. They can also be applied to catheters used in endovascular stent graft procedures used to treat abdominal aortic aneurysms. The neurovascular field has also begun to use catheters in innovative ways to reach blood vessels and aneurysms within the brain. Brain stents and aneurysm coils can be delivered through hydrophilic catheters and positioned without the need for highly invasive and dangerous craniotomies. Coated catheters can also be used to deliver insertion PEG tubes, pacemaker and implantable cardioverter-defibrillator leads, and chest drains.

Because many patients with aortic stenosis—an abnormal narrowing of the aortic valve—are elderly, ill, and at high risk of dying or being chronically debilitated from open-heart surgery, they can benefit from minimally invasive surgery using balloon catheters to deliver transcatheter heart valves. Transcatheter heart valves consist of a replacement valve, a metal frame, and a balloon catheter, all of which are fit into a delivery package about the width of a pencil. To insert such devices, surgeons make a small incision in the patient’s groin and thread the system through a catheter that is inserted through an artery into the heart. Once in place, the balloon expands, allowing the valve to be positioned in the heart. Given the great distance that a catheter must travel from the femoral and iliac arteries to the heart, a hydrophilic environment can facilitate the movement of the catheter and reduce tissue trauma.

Engineering Challenges

To develop coatings for medical device applications, engineers should aim for formulations that can make a device stronger, safer, longer lasting, and more cost-effective.

Choosing the right coating and coating supplier are critical decisions that engineers must make when selecting materials and designing medical devices. Understanding the types of coatings that can make a device stronger, safer, longer lasting, and more cost-effective are important criteria in the decision-making process.

In addition to the challenges associated with creating and manufacturing hydrophilic coatings, engineers are tasked with developing coating application processes, which are often customized to meet the specific needs of a medical device application. The coating process involves the use of reagents that are UV-cured using a standardized process, resulting in consistent quality and coating uniformity.

Engineers must also possess a fundamental molecular understanding of both the chemical science and application processes involved in developing coatings for medical device applications. Various methods can be employed for applying a coating to the medical device surface. For example, the use of a dip coating, spray, and plasma process—followed by a UV curing mechanism—allows the coating to dry rapidly, accelerating production, increasing yield rates, improving such properties as scratch and solvent resistance, and facilitating bonding.

Any company that provides surface modification services and hydrophilic coatings to the medical device market should meet ISO 13485 quality management system standards as well as ISO 10993 biocompatibility standards. Coating operations should also be performed in ISO Class 8 cleanrooms with an ISO 13485–compliant quality management system in place. In addition, medical device manufacturers benefit from having access to master files on record with FDA.

Conclusion

Among the aging population, baby boomers represent the largest population segment facing retirement. More affluent than previous retirement-age generations and more active, they are sparking a higher demand for quick and easy medical solutions, including minimally invasive surgeries. Such surgical techniques are less intrusive and promote faster healing times than more-invasive surgeries. They also cause less scarring and allow patients to return to normalcy quicker. If current industry trends persist, medical device manufacturers will continue to support minimally invasive surgeries by developing smaller devices and technologies.

As the development of miniaturized medical devices and technologies continues, it is important for coating developers and coating service providers to stay abreast of emerging trends. Thus, they will be able to solve current challenges, meet new needs, and provide fresh innovations that aid medical device engineers, surgeons, and patients.
 

Hinke Malda is the director of medical coatings at Exton, PA–based DSM Biomedical, where she leads research, application, product development, and marketing and sales teams. She has been with the company since 2006 and has served in several positions with increasing responsibilities. She received a master’s degree in chemistry from the University of Groningen and a PhD in chemical engineering and biomedical engineering from Eindhoven University of Technology. She is also a coinventor of several patents and the coauthor of many scientific articles. Reach Malda at [email protected].

 

To learn more about medical device coatings, visit DSM Biomedical (Booth #2711) at MD&M West, February 10–12 at the Anaheim Convention Center in Anaheim, CA.

 

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