Topology Optimization & Additive Manufacturing are Pushing the Boundaries of Personalized Healthcare

We’re entering the era of personalized healthcare. One-size-fits-all solutions are being replaced by treatments tailored precisely to the needs of the individual.
 
One of the driving forces behind this transformation in patient care is provided by the combination of additive manufacturing and topology optimization. Otherwise known as 3D printing, the ability of additive manufacturing to enable one-off production of an almost unlimited array of shapes and forms has attracted plenty of attention. But in terms of delivering customized devices and products quickly and efficiently, it is only part of the story.
 
Realizing the full potential of additive manufacturing invariably demands the effective use of topology optimization. Already widely employed in the transportation sector, topology optimization is a powerful software design tool that enables optimized distribution of materials within user-defined constraints such as available space, loads, and functionalities. Together, these two technologies are already delivering impressive results in use cases that include anatomical modeling, medical and dental device design, prosthetics, orthotics, and orthopedic implants. As innovative materials and techniques are developed and costs fall, even more exciting possibilities are being put within reach.
 
In this article, the aim is to highlight the efficiency with which topology optimization and additive manufacturing can now help the healthcare sector turn the promises of personalized treatment into dramatically improved outcomes for patients. It will also look at some of the hurdles that still need to be overcome to extend the opportunities available. A recent study involving the custom design of a femur implant will help illustrate these themes.
 

Replicating the Work of Nature

Over the past two decades, industries such as automotive and aerospace have embraced the ability of topology optimization to deliver better and faster design outcomes. Typically, this has been in conjunction with traditional manufacturing techniques such as casting. In many respects, the characteristics and capabilities of topology optimization are an even better fit for additive manufacturing and the healthcare sector. Nature is a fantastic design engineer, and topology optimization is often likened to a free-form, organic process. By providing designers with the means to replicate the highly efficient, naturalistic, complex geometries and shapes that biology produces organically within the human body, topology optimization offers compelling benefits in areas such as orthopedic implants. For example, the truss and lattice structures that topology optimization generates on the designer’s PC closely mirror the characteristics of natural bone growth. Given the obvious need for a device such as an implant to be designed and manufactured as closely as possible to match the structure it will replace, that’s a hugely powerful core attribute.
 

Designing for 3D Print

Equally significant is the fact that topology optimization can optimize both the design itself, and its manufacturability. In other words, topology optimization provides the designer with the best design outcome for a given manufacturing process. Inevitably, prior to the emergence of additive manufacturing, the ability to create highly naturalistic and organic shapes was often constrained by the production processes available. 3D printing makes it feasible to manufacture the best mathematical solution created by topology optimization, or something very close.
 

Optimizing the Benefits of Additive Manufacture

For all its benefits, additive manufacturing is not a silver bullet. The design-for-manufacturing capabilities of topology optimization are just as valuable here. Issues such as angle overhang, where an area of the design is unsupported and therefore potentially difficult to print, remain critical in determining the ability to successfully manufacture the desired product. Significantly, topology optimization enables such factors to be considered as early as possible in the design journey. Moreover, tools are available that simulate the additive manufacturing process in granular detail. Faults caused by the printing process such as distortion, poor surface quality and snap lines can therefore be predicted and addressed.
 

The Bioprinting Revolution is Here

Not surprisingly, healthcare research and development are flourishing. For example, 3D bioprinting offers new opportunities to create human tissue, ultimately, human organs from scratch. In this area, topology optimization’s ability to model and simulate highly complex combinations of hard and soft materials such as skin, cartilage, and bone, and design structures that will support and facilitate the future growth of implants using biomaterials, will be critical in enabling the healthcare sector to take advantage of these advances. In areas such as reconstructive surgery, the potential to deliver truly life-changing outcomes for individual patients is clear.
 

Proving the Benefits of Topology Optimization

In some of these fields, there is obviously more work to be done before innovative new techniques are ready for wider deployment. But in areas such as orthopedic implants, adoption of topology optimization and additive manufacturing is already gathering momentum and making a significant impact on treatment efficacy. A recent study in which a femur implant was designed using topology optimization (and compared against a healthy femur) helps illustrate the reasons behind this growth. But before looking at the outcomes, it is worthwhile considering the multiple challenges faced by designers and manufacturers working in such fields.

Addressing the Challenges of Orthopedic Implant Design and Manufacturing

Top of the list is the need to secure regulatory approvals. In this respect, significant progress is being made in terms of the recognition of simulation-based evidence by bodies such as the FDA. Material specification is also a critical design factor; the finished product must not cause an adverse tissue reaction within the patient. Implant strength is another major issue. For example, according to the National Hospital Discharge Survey (NCHS), between 2000 and 2010, the number of hip replacements carried out in the U.S. doubled for people between the ages of 45 and 64. However, up to 20 percent of patients may require revision surgery because of a complication of the new implant/bone complex.
 
The most common cause is loosening of the implant stem, often the result of bone resorption or loss of bone mass. Given the number of younger, active patients that are needing this type of treatment, extending their longevity is a rising priority. By enabling the application of a wide array of load cases, and thereby reducing stress shielding in the surrounding bone, topology optimization has a key role to play. In the case of the femur implant, five load cases were applied: standing, stance, walking up and down stairs, and jogging. A two-stage optimization process, optimizing both the solid sections and areas of lattice-based design, resulted in the optimized femoral stem shape shown in Figure 1.
 
Compared to a generic implant, the use of topology optimization reduced stress shielding by 57 percent. In addition, fatigue life simulated to be more than ten million cycles, and with a minimum wall thickness of 0.5mm and an overhang angle smaller than 45 degrees, the design’s manufacturability using additive methods was confirmed.
 
There’s a compelling logic to personalized healthcare. After all, nothing is more personal than an individual human body, and as science provides us with ever-greater opportunities to do so, treatment will increasingly cater to the unique demands of each patient. The trend is both broad and powerful, especially in areas like drug development. As far as topology optimization and additive manufacturing are concerned, one of the most significant barriers to wider adoption is a simple lack of awareness of the possibilities. The rapid evolution of 3D printing promises an exciting future, but it is important to note that the tools and opportunities used to provide better patient outcomes are very much relevant today, too. Topology optimization is not a novel concept. Neither is additive manufacturing. Together, these proven technologies offer a holistic, end-to-end solution that opens the door to a completely new approach to healthcare.