In this “AM in 10” video, we look at additive manufacturing (AM) and how it is used successfully for orthopaedic implants. As AM continues to mature, it will enable us to produce highly efficient and customised medical implants that are produced quickly and are cost-effective too. This means that more patients globally will have access to advanced medical care and be able to stay mobile as they grow older. Let’s look in more detail at this topic.
More hip and knee replacements required in the West
Advancements in orthopaedic implants have improved the well-being of hundreds of thousands of people over the many decades. An ageing population and rising rates of obesity in the West has led to increased pressure placed on many people’s joints. More younger people in their 40s and 50s are also needing implants such as new hips and knee joints and this means more people than ever require artificial implants to help with their mobility and quality of life.
The first hip replacements were performed in the 1970s and since then there have been significant advancements in this area. One of these advancements is the use of additive manufacturing (3D printing) and one of the benefits of additive manufacturing and orthopaedic implants is the ability to create customised implants for patients.
Customised orthopaedic implants
Additive manufacturing can be an expensive process and the cost of healthcare is an important consideration regardless of whether a nation has a public or private health care system. So why is AM a wise choice for this field? One of the key benefits of using additive manufacturing for medical implants is the ability to create internal prosthetics customised for each patient. Humans come in different shapes and sizes and the ability to create a customised implant means that once the part is surgically implanted it will last longer and provide the patient with substantially more comfort and mobility.
Medical implants and osseointegration
One of the issues with orthopaedic implants, particularly knee and hip implants is something known as osseointegration, which is a term relating to how the bone regrows into the implant after the implant operation.
To understand osseointegration we have to first have to understand Wolff’s Law, which was discovered by Juilias Wolff, a 19th Century anatomist who discovered that bone responds to the forces that are applied to it.
If a person’s bone bears large loading stresses, the bone will become stiffer and denser over time. Similarly, if the bone doesn’t receive large loading stresses, it will become less dense over time and this phenomenon has a big impact on the design of medical implants. For instance, if a dense and stiff metallic implant is used, such as a titanium hip stem, this implant will have a much larger stiffness modulus than the bone surrounding it.
If this isn’t carefully dealt with, the bone will start to remodel itself, become less dense around the implant and will achieve poor osseointegration. The outcome for the patient in this instance will not be good.
Lattice structures for implants
One way to improve osseointegration is to use specific meso-structural elements such as lattice structures that allow 3D printed implant designers to reduce the stiffness of the metal to something that’s more closely aligned to the stiffness of bone. The rough texture of the lattice structure can also:
- Aid in promoting osteointegration
- Allow nutrients to flow around the structure of the lattice
- Allow for soft tissue and bone regrowth
The most commonly used lattice structures for the creation of bone structures are called trabecular lattices or stochastic lattices. These lattices mimic the bone type called trabecular bone and at a basic level are essentially randomised foam.
Below (and also in the main video that relates to this blog), you can see a demo of the stochastic lattice feature of the Gen3D’s Sulis Lattice module which allows AM designers to control the density of a stochastic lattice and tailor the properties to specific medical implant applications.
Prototypes and surgical guides
Another reason why additive manufacturing and orthopaedic implants are so well aligned is that 3D printed prototypes and surgical guides allow the surgical team to better plan operations. These prototypes can significantly improve surgical outcomes.
Surgical implant prototypes are often printed using polymer processes such as medical-grade SLA or stereolithography. Multiple revisions can be completed based on patient scan data such as x-rays and CT scans which are then turned into a file and 3D printed. Then a plan of the operation can be discussed by the surgeons and the operating theatre staff.
The challenges of AM implants
Regulatory approval – Adding any new process into the field of medical devices needs regulatory approval, however, additive manufacturing in the orthopaedic space has been around for many years and there are plenty of suppliers that have regulatory approval for the use of 3D printed orthopaedic implants.
Loose powder – The 3D implant design must be delivered with great care. For example, ensuring that all of the powder has been removed from a newly printed and post-processed implant is essential because if any remains, and it is then used in surgery, it will cause extreme irritation of the soft tissue around the implant and ultimately revision surgery will be required.
The future of additive manufactured medical implants
Degradable implants – We will see more degradable implants and new biomaterials for use in orthopaedic implants. Biodegradable implants mean that over time as the patient’s bone integrates with the implant, the implant degrades and is replaced by the human bone structure.
Personalised implants – Currently, we customise implants for patient size but in the near future we will be able to customise for the patients’ age, gender, different bone density requirements and nutrient growth requirements. We will be able to take a patient-specific scan and test data then integrate it into our CAD software to design bespoke 3D printed implants for every patient.
If you’re interested in learning more about how Gen3D can help you design next-generation additive manufactured orthopaedic implants, get in contact at www.gen3d.com and one of our sales representatives or applications engineers will be happy to give you a demo of Sulis, and in particular the Lattice Module.