Statement of Purpose

As a mechanical student, I would like to extend toward biomechanical engineering. I have noticed that over the past decades, dramatic advancements in the knowledge of knee mechanics have led to design modifications that appear to be durable. Significant advances have occurred in the type and quality of the metals, polyethylene, and more recently, ceramics used in the prosthesis manufacturing process, leading to improved longevity. In my senior year, I conducted a special topic research in Orthopaedic Engineering and Movement Analysis Lab. I collaborated with National University of Taiwan Hospital’s orthopedic surgeons, participated in several discussion sessions with physicians and engineers, and deeply understood that: in order to seek a major breakthrough in medicine-engineering techniques, a viewpoint from purely the perceptive of engineers or physicians is not adequate. Rather, the researcher needs a comprehensive understanding of the practical applications of engineering theories, techniques, as well as clinical medicine.

I expect to develop more sustained and functionally better total knee arthroplasty requiring patients to undergo only one definitive procedure in their lifetime. From previous literatures, I discover that majority of research was focused in identifying and redesigning functional movement period’s tibial component, the location where the peak value of von Mises stress occurs. Although this method diminishes the peak value of von Mises stress and ensures that the entire component can withstand the stress, it exceeds the material’s yielding stress value and leads to plastic deformation. Previous researches have rarely considered the damage caused by stress.

Stress damage is a critical factor to consider in the design of total knee arthroplasty. I believe that after finite element analysis of total knee arthroplasty’s 3D finite element model, an integral analysis has to be conducted on each element on the type of stress in different phases. Then, which tibial component’s area of the entire phase can bear the most energy is calculated. The objective of this post-handling process is to avoid the concentration toward reducing the peak value of von Mises stress, while ignoring the fact that other areas can absorb more energy in the function movement cycle. Also, the component can be more easily damaged than regions bearing the peak value of von Mises stress. Eventually, the data is recalculated based on the region of the highest energy absorbed. I further hope to integrate my concepts with traditional design directions, and identify the optimal equilibrium of the two design concepts in order to extend the life of total knee arthroplasty.

I am confident that my thoughts can be converted into a feasible research plan and I can work most efficiently to achieve my objective. Because I am familiar with Biomechanics, Advanced Dynamics, Mechanics of Solids, and Optimization, I understand how to transform fluoroscopy medical image, through image comparison, to obtain the correct 3D position of total knee arthroplasty in different phases, as well as establish 3D finite element model, analyze with finite element package, and write programs to execute post-handling measures. In college, I nourished my computer and engineering problem-solving skills. I was also familiar with MATLAB programming language and specialized in two finite element packages: ABAQUS and MSC.Marc. I can also modify 3D model through Geomagic Studio.

I graduated from National Taiwan Universeity’s Department of Mechanical Engineering and received complete training in engineering. In my 4 college years, I took a total of 159 credits and averaged a GPA of 3.6/4.0. My GPA in my last two years even topped 4.0. In order to satisfy my interest in biology and medicine, I studied Introduction to Biomedical Engineering and General Biology, and research Optimization in Biomechanical Engineering. In these subjects, I averaged close to 90. Meanwhile, I proactively studied the related literatures of sports hazards and understood that osteoarthritic destruction of the knee is the most common reason for total knee replacement. Mechanical derangements, ligamentous instability, fracture into a joint, and cartilage destruction are the causes of osteoarthritis. My reason for taking Biomechanical Engineering was built on the hope to help patients of sports hazards receive better treatment and restore as much as possible their normal joint functions.

In university, my special topic was to discuss replacing total knee arthroplasty patients’ functional movement (going up stairs), ligaments’ force condition and  ligament stress, compare total knee arthroplasty’s posterior cruciate substituting (PS type) and posterior cruciate retaining (CR type). My total knee arthroplasty 3D finite element model hypothesized that the Co-Cr-Mo alloy’s femur component was simulated as rigid body. I set the UMWPE material’s tibial component as isotropic, homogeneous, and allowed for large deformation’s non-linear elastic material. Also, ligaments were simulated as non-linear spring according to computer programs, and for lateral collateral ligament, I only selected one fiber bundle. Posterior cruciate ligament was classified into anterior bundle and posterior bundle, and medial collateral ligament was classified into anterior bundle, oblique bundle and deep bundle. I analyzed the model with MSC.Marc and obtained the following major findings:

1. During the entire sports process, PS type’s lateral collateral ligament and anterior bundle of medial collateral ligament stress was greater than that of CR.

2. PS type and CR type’s von Mises stress both occurred at stance phase 70%.

3. PS type’s peak value of von Mises stress was larger than that of CR.

The above findings can help us examine the two types of total knee arthroplasty and I expect these results to be beneficial toward the design of total knee arthroplasty. Recently, my research group has established vivo knee joint’s 3D finite element ligament model through MRI image, as well as analyzed unloading flexion motion’s ligament stress.

In the Optimization in Biomechanical Engineering, I worked on a bone remodeling project. I connected MSC.Marc and MATLAB to simulate human calcaneus in walking’s (70% stance) loading condition and explored how trabecular architecture of calcaneus adapts to its orientation and density in response to its strain energy state. I extracted calcaneus’s mid-stream’s sagital plane to build my analysis. Boundary conditions include forces of Plantar Fascia, Plantar ligaments, Achilles tendon and two joint capsules.

The essential idea was that above a certain level of strain energy density bone mass was increased, and below a certain threshold excessive bone remodeling could be seen, and in between these two levels the bone structure was maintained. The result of bone density distribution is similar to the real bone. My professor rated me as “excellent”. The numerical simulation in this research was a quick and convenient way to quantify the long-term bone morphological changes, which could shorten the research period for the related problems and save a large amount of experimental expenditures.

My ultimate academic goal is to pursue the MS/PhD degree at Stanford University to enrich my theoretical knowledge and skills to be an outstanding researcher. I hope to join your Skeletal Tissue Associated Research (STAR) Laboratory and study bone remodeling. I possess the simulation skills of the development of bone cross-sectional morphology under the influence of pressures and tensile strains applied directly to bone surfaces. My experience told me that stimulus reference value plays a key role in bone remodeling’s stimulus reference value. I expect to share my experiences and techniques of completing the calcaneus model with laboratory engineers. I further wish to co-work and complete the promixal fermur project, as well as extend the research territory to other important bones of the human body.

I am also interested to join the knee meniscectomy and osteoarthritis biomechanics projects. My special topic of arthroplasty has allowed me to possess the background knowledge of total knee arthroplasty. In order to understand how the mechanics of meniscectomy lead to the tissue degeneration of osteoarthritis, I can help deal with finite element modeling of the knee under dynamic loading conditions by being attentive to the studies of: How do altered contact area and pressures affect stresses and strains within the articular cartilage? How would the stresses and strains within the cartilage influence surface failure and tissue development?

I believe that I posses the particular type of personality a successful researcher requires: I am always obsessed with figuring out a problem, having determination, perseverance, intellectual rigor, spiritual fortitude, and being capable of hard work. I plan to join a top research organization in Stanford University , where I can contribute to the cutting edge in biomechanics and work together with topnotch talents. I am ready to perform in your program both academically and mentally.