3D printing helps improve biocompatibility of metallic implants

“New alloys can be designed and implemented without a long lead-time in critical areas such as spinal devices, dental and craniomaxillofacial devices, as well as other load-bearing applications”Amit Bandyopadhyay

With over half of all commercial biomedical implants containing metal, a new study by researchers at Washington State University, the Mayo Clinic, and Stanford University Medical Center has shown the value of using 3D printing to identify new alloys that improve upon metals that have been in surgical use for decades.

As reported in Materials Today [Mitra et al. Mater. Today (2020) DOI: 10.1016/j.mattod.2020.11.021], 3D printing was used to assess a range of new and more effective alloys in implants – mainly used in orthopedic, dental, fracture management, spinal and cardiovascular applications. The three main alloys are currently employed in biomedical implants: stainless steel, titanium, and cobalt–chrome were originally developed by the automotive and aerospace industries for their strength, fatigue, corrosion resistance, and not for their biological performance.

A common problem with metallic implants is metal ion hypersensitivity and a lack of favorable tissue materials interaction for faster healing. Different coatings have been used to improve the surface properties of implants, which have worked to an extent, but a lack of strong bonding with the base metal is common, which has resulted in many interfacial failures, leading to revision surgeries. This drove the multi-disciplinary team to explore how best to design new alloys specifically to improve their biocompatibility (i.e., biological performance).

Their straightforward approach based on 3D printing technology could be a game-changer, as it allows for parts to be made with complex shapes, flexible design, and the ability to customize. This could also reduce healing time and increase the lifetime of implants. As team leader Amit Bandyopadhyay told Materials Today, “New alloys can be designed and implemented without a long lead-time in critical areas such as spinal devices, dental and craniomaxillofacial devices, as well as other load-bearing applications”.

Existing implants coated with tantalum demonstrate the metal has excellent biocompatibility, with applications as a coating to enhance tissue–materials interactions. As tantalum has a very high density and a very high melting point, and is much more expensive than titanium, the addition of tantalum to titanium was tried via 3D printing. While processing tantalum is a major challenge, a titanium–tantalum alloy can be processed efficiently while keeping to a similar density. Tests showed that an alloy of 90% titanium and 10% tantalum exhibited similar biological performance as 100% tantalum, indicating that only a small fraction of tantalum would be sufficient.

The team is now looking at potential new alloys to help stop infections on implants' surfaces to minimize many painful revision surgeries, particularly for patients with bone disorders.