Coatings on Knee Implants

Introduction

The human knee joint is experiencing various issues, particularly cartilage damage known as Osteoarthritis (OA), due to changes in lifestyle. Total knee replacement surgery is a common treatment for this condition, where an implant is surgically attached to the knee joint. The implants used in knee replacement surgeries are typically made of bio-compatible materials like stainless steel or titanium alloys. While these implants provide relief to patients, daily activities can gradually lead to wear between the implants. As a result, wear debris affects the knee joint and causes pain for the patient. To address this problem, tribological studies are conducted to examine the wear rate and friction between the implants. Nanotechnology is then utilized as a solution to minimize these effects. Applying nano coatings on knee implants reduces friction and wear, ultimately improving the implant’s lifespan [1].

Fig-1 The figure showing the cartilage damage in the knee joint, and the implant replaced at that joint [2]

Knee Implants

An implant is a device designed to support and strengthen damaged parts of the human body. Common types of implants include those used in knee joints, hip joints, and dental procedures, which are biocompatible with the body. Currently, knee replacement procedures are particularly important. Knee replacement, also known as knee arthroplasty, involves the use of implants made from bio-compatible metals and ceramics. This procedure is commonly performed on individuals aged 45-65 who suffer from osteoarthritis. Knee replacements provide relief to patients, and the lifespan of the implants can range from 15 to 20 years. Surgeons typically use materials such as stainless steel, titanium alloys, Co-Cr alloys, tantalum alloys, composites, ceramics, and polymers for these implants [3].

Challenges with the Knee Implants

Approximately 80-85% of knee replacements have a long lifespan, lasting for many years. However, daily activities contribute to wear and friction between the implants, causing significant pain and reduced joint fluid. Extensive studies have been conducted to examine the amount of friction and wear debris generated under different conditions in these implants. Wear is considered a limiting factor for the longevity of the implant. Unfortunately, current orthopedic implant materials hinder patients from resuming their normal lives. To address this issue and minimize wear debris, Nanotechnology has been introduced. By applying a thin film or coating of bio-compatible material on the implant, excellent results have been achieved in orthopedic implants, promoting bone growth and reducing complications [4].

Fig-2 The Image of the failed polyethylene components from total knee prosthesis [5]

How to overcome this challenge – Nanocoatings

Coating involves applying a thin film to enhance the properties of a surface or substrate. It improves functionalities such as reducing friction, increasing temperature and radiation resistance. Coatings are typically applied through methods like vapor deposition, spraying, and roll-to-roll processes. While most coatings have micron-scale thickness, Nano coatings offer better results. At the Nano level, materials exhibit unique properties that are impossible to achieve at the micro level. Nano coatings enhance material functionalities, including reducing friction, improving corrosion resistance, extending the lifespan of medical implants, and incorporating anti-bacterial properties. Furthermore, many Nano coatings are eco-friendly and do not release toxic gases into the atmosphere [6].

Fig-3 Types and effects of osteogenic coatings on titanium implants [6]

Why Nano-coatings

Metal components can be safeguarded from moisture, salt spray, and oxidation by applying nano-coatings with anti-corrosive properties, resulting in extended durability. These coatings are also water-repellent and non-stick, making them suitable for creating waterproof surfaces in the food packaging industry. In healthcare, nano-coatings serve as essential anti-bacterial agents to prevent infections. Additionally, nano-coatings possess anti-abrasive qualities, providing strength to materials in scenarios where lubricants are not employed.

Reference

[1] Kennedy, F.E., 2013. Biomechanics of the hip and knee: implant wear. In Wear of orthopaedic implants and artificial joints (pp. 56-92). Woodhead Publishing.

[2] https://medlineplus.gov/ency/article/002974.htm

[3] https://www.healthline.com/health/total-knee-replacement-surgery/outcomes-statistics-success-rate

[4] Kumar, K.S., Meenakshi, C.V.R. and Ramana, S.V., 2020. Nano Coatings on Knee Implants–A Tribological Review. Materials Today: Proceedings, 22, pp.2088-2092.

[5] Grecu, D., Antoniac, I., Trante, O., Niculescu, M. and Lupescu, O., 2016. Failure analysis of retrieved polyethylene insert in total knee replacement. biomaterials, 6, pp.12-15.

[6] Lu, X., Wu, Z., Xu, K., Wang, X., Wang, S., Qiu, H., Li, X. and Chen, J., 2021. Multifunctional coatings of titanium implants toward promoting osseointegration and preventing infection: Recent developments. Frontiers in Bioengineering and Biotechnology, 9, p.783816.