SIMULIA is proud to work with a variety of women in the engineering field, both as employees and clients. Our new Women in Engineering series will highlight some of these outstanding contributors to the field of simulation. Today we are proud to introduce Dr. Cheryl Liu, Senior Principal Engineer at Stryker.

The human body is capable of incredible things, but it is not infallible. Injuries and age can cause damage to joints, resulting in pain and reduced function. The bright side, however, is that medical technology has advanced to the point that many of these parts can be repaired or replaced, allowing people to maintain their mobility.

With any sort of medical implant, great care must be taken to make sure that the implant functions properly and works in synchrony with the rest of the body. Fortunately, medical technology has advanced to the point that implant concepts can be thoroughly evaluated and optimized in a virtual environment before they are tested and approved by regulatory agencies and placed inside the patient.

Simulation for Implants and Surgical Tools

“We see the value of biomechanics simulation,” says Dr. Cheryl Liu, a Keynote Presenter at the 2021 Americas Regional User Meeting and Senior Principal Engineer at the medical technology company Stryker. “We also see the value of representing the patient and their abilities. We need a library of such models to understand how the implant will perform inside a variety of patients. So when we design implants, we can use these tools to iterate designs.”

Simulation can also demonstrate how implants will perform to surgeons and patients and assess how a surgical tool will function in surgery. For example, according to Dr. Liu, simulation can and should be leveraged more broadly to improve surgical tools by reducing weight and noise. Testing tools for ease of use, safety, effectiveness and endurance is of the utmost importance, especially with the development of robotic surgeries.

“With the CT scan that’s behind the robotic procedures, we have a 3D model created for the patient’s bones,” says Dr. Liu. “If we can understand the patient’s biomechanics and be able to predict what kind of kinematic outcome we can get when a surgeon places an implant a certain way, we can find the optimal implant positioning for that specific individual so they improve their function post-operatively.”

The Stryker team uses multiple simulations to design an implant so that they can both understand how the new design is meeting performance requirements in key areas, and to understand the risk of potential performance issues in other areas.

The Future of Patient-Specific Medicine

Not every patient has a unique implant designed for them; rather, Stryker works from an extensive library of proven successful models and uses simulation to determine which model, size and placement will work in each case. True patient-specific simulation models, says Dr. Liu, are the Holy Grail – models that take into consideration a patient’s limb alignment, bone geometry, soft tissue constraints, and range of motion.

“We don’t want to sacrifice the accuracy of the model by simplifying so much that it loses that patient-specific natural conditions,” says Dr. Liu. “But at the same time, a true patient specific simulation model that can be used intraoperatively needs to be solved efficiently. We need to partner with our software providers and companies like SIMULIA to help us improve the efficiency of the software so that we can achieve real-time solutions.”

Stryker is building a library of patient-specific models by collecting comprehensive anatomical and gait lab data from a sample of individuals of varying age, gender, fitness, and size. That data is then used to calibrate and validate the models. Included in the gathered data is information about how joints such as the knee move during different activities like walking downhill or doing a knee bend. For a patient that regularly plays sports, the medical team needs to determine what type and positioning of the implant will allow them the best range of motion to play tennis, for example. Simulation helps them to make this decision.

Stryker chose to work with SIMULIA software, specifically Abaqus, to meet the challenging requirements of implant design and selection.

“If what we need is a static bending analysis on implants, most software can do it,” says Dr. Liu. “But we also need to be able to simulate dynamic impact. We want to simulate constraints from soft tissue and activities of daily living. We want to simulate material failure and fracture. All these advanced features really require advanced software that has been developed and verified for these applications. We see Abaqus as our high end simulation software that can help us solve these advanced simulation needs.”

A Constant Learning Process

Dr. Liu feels that her career path was determined when she traveled from China to the United States to attend graduate school at the University of Notre Dame’s Department of Aerospace and Mechanical Engineering. There were few female engineering students at her undergraduate school in China, but in graduate school she had the opportunity to work with several talented female engineering peers. Dr. Liu earned her Ph.D. in biomechanics and joined SIMULIA in 2006. She began working at Stryker in 2014, where she found that many diverse leaders in the company.

Dr. Liu has worked on constructing cardiovascular stent analysis training material and was involved in the Abaqus knee simulator and the Living Heart Project while at SIMULIA, prior to joining Stryker. Her expertise in simulation and life sciences has contributed to her successful career, one that she enjoys greatly. She encourages other young women and girls to pursue engineering, despite any obstacles that may arise.

“If you are interested in solving problems and developing your skills and continuing to learn, and never end that process, I think this is the right career,” she says. “You will never be bored. You will always have new perspectives, new knowledge, and new challenges to work on. This work makes me excited about this career and that’s how I sustain myself.

“I encourage curiosity because that’s how you learn and grow professionally. Even though I’m in the knee or joint replacement division, I’m always curious about what our other divisions are working on. I help them solve their problems as well, and in the process, I learn a lot. I think that’s what really is beneficial as a career, is that you are never going to get bored.”

Dr. Liu believes that the future of the industry lies in real time simulation, whether in the form of physics-based simulation or machine learning and artificial intelligence. This will require a great deal of data to feed into the development of models and algorithms, which can benefit from the consistent progress of simulation software such as Abaqus.

“I love simulation because it enables innovation in our industry. Coming up with better designs is better for patients, better for our surgeon customers. Simulation is faster and reduces risk. It’s a no-brainer. I’d be surprised if any medical device companies are not doing it. I think this is a great tool that all the industry should adopt.”