Kartik M. Varadarajan

Bio: Kartik M. Varadarajan is an academic researcher from Harvard University. The author has contributed to research in topics: Femur & Medicine. The author has an hindex of 25, co-authored 82 publications receiving 1657 citations. Previous affiliations of Kartik M. Varadarajan include MAKO Surgical Corp. & General Electric.

Differences of Knee Anthropometry Between Chinese and White Men and Women

Abstract: Whether there are differences in knee anthropometry between Asian and white knees remains unclear. Three-dimensional knee models were constructed using computed tomography or magnetic resonance imaging of healthy Chinese and white subjects. The morphologic measurements of the femur included mediolateral, anteroposterior dimensions, and aspect ratio. The tibial measurements included mediolateral, medial/lateral anteroposterior dimension, aspect ratio, and posterior slope of medial/lateral plateau. The results showed that Chinese knees were generally smaller than white knees. In addition, the femoral aspect ratio of Chinese females was significantly smaller than that of white females (1.24 ± 0.04 vs 1.28 ± 0.06). Tibial aspect ratio differences between Chinese and white males (1.82 ± 0.07 vs 1.75 ± 0.11), though significant, were likely a reflection of differences in knee size between races. These racial differences should be considered in the design of total knee arthroplasty prosthesis for Asian population.

Multifunctional performance of carbon nanotubes and graphene nanoplatelets reinforced PEEK composites enabled via FFF additive manufacturing

Abstract: The study is focused on multifunctional performance of carbon nanotubes (CNT) and Graphene nanoplatelets (GNP) reinforced PEEK composites enabled via fused filament fabrication (FFF) additive manufacturing (AM) utilizing in-house nanoengineered filaments. Thermo-physical, mechanical and wear characteristics of electro-conductive PEEK nanocomposites are reported. The coefficient of thermal expansion (CTE) is found to decrease by 26% and 18% with the incorporation of 5 wt% GNP and 3 wt% CNT into PEEK polymer, respectively. The decrease in CTE provides better dimensional stability to resulting nanocomposite structures. Due to uniform dispersion of CNT and GNP in the PEEK matrix, the crystallization temperature and degree of crystallinity are both increased. The 3D printed PEEK nanocomposites reveal interfacial voids between the beads and intra-bead pores and thus exhibit lower density compared to that of the 3D printed neat PEEK. Young's and storage moduli are found to increase by 20% and 66% for 3 wt% CNT loading and by 23% and 72% for 5 wt% GNP loading respectively. However, the PEEK nanocomposites exhibit similar tensile strength to that of neat PEEK. The coefficient of friction obtained from fretting wear tests is found to decrease by 67% and 56% for 1 wt% CNT and 3 wt% GNP loaded PEEK nanocomposites, respectively and the decrease is attributed to reduced hardness and increased porosity. Multifunctional performance of carbon nanostructures reinforced AM-enabled PEEK composites demonstrated here makes them suitable for a range of applications such as orthopedics, oil and gas, automotive, electronics and space.

Microarchitected 3D printed polylactic acid (PLA) nanocomposite scaffolds for biomedical applications.

Abstract: Anti-bacterial scaffolds made of copper, bronze and silver particles filled PLA nanocomposites were realized via fused filament fabrication (FFF), additive manufacturing. The thermal, mechanical and biological characteristics including bioactivity and bactericidal properties of the scaffolds were evaluated. The incorporation of bronze particles into the neat PLA increases the elastic modulus up to 10% and 27% for samples printed in 0° and 90° configurations respectively. The stiffness increases, up to 103% for silver filled PLA nanocomposite scaffolds. The surface of scaffolds was treated with acetic acid to create a thin porous network. Significant increase (~20-25%) in the anti-bacterial properties and bioactivity (~18-100%) is attributed to the synergetic effect of reinforcement of metallic/metallic alloy particles and acid treatment. The results indicate that PLA nanocomposites could be a potential candidate for bone scaffold applications.

Patient-adapted and improved articular implants, designs and related guide tools

Abstract: Methods and devices are disclosed relating improved articular models, implant components, and related guide tools and procedures. In addition, methods and devices are disclosed relating articular models, implant components, and/or related guide tools and procedures that include one or more features derived from patient-data, for example, images of the patient's joint. The data can be used to create a model for analyzing a patient's joint and to devise and evaluate a course of corrective action. The data also can be used to create patient-adapted implant components and related tools and procedures.

FDM-Based 3D Printing of Polymer and Associated Composite: A Review on Mechanical Properties, Defects and Treatments.

Abstract: Fused deposition modelling (FDM) is one of the fastest-growing additive manufacturing methods used in printing fibre-reinforced composites (FRC). The performances of the resulting printed parts are limited compared to those by other manufacturing methods due to their inherent defects. Hence, the effort to develop treatment methods to overcome these drawbacks has accelerated during the past few years. The main focus of this study is to review the impact of those defects on the mechanical performance of FRC and therefore to discuss the available treatment methods to eliminate or minimize them in order to enhance the functional properties of the printed parts. As FRC is a combination of polymer matrix material and continuous or short reinforcing fibres, this review will thoroughly discuss both thermoplastic polymers and FRCs printed via FDM technology, including the effect of printing parameters such as layer thickness, infill pattern, raster angle and fibre orientation. The most common defects on printed parts, in particular, the void formation, surface roughness and poor bonding between fibre and matrix, are explored. An inclusive discussion on the effectiveness of chemical, laser, heat and ultrasound treatments to minimize these drawbacks is provided by this review.

Morphological Muscle and joint parameters for musculoskeletal modelling of the lower extremity

Abstract: Background: To assist in the treatment of gait disorders, an inverse and forward 3D musculoskeletal model of the lower extremity will be useful that allows to evaluate if–then scenarios. Currently available anatomical datasets do not comprise sufficiently accurate and complete information to construct such a model. The aim of this paper is to present a complete and consistent anatomical dataset, containing the orientations of joints (hip, knee, ankle and subtalar joints), muscle parameters (optimum length, physiological cross sectional area), and geometrical parameters (attachment sites, ‘via’ points). Methods: One lower extremity, taken from a male embalmed specimen, was studied. Position and geometry were measured with a 3D-digitizer. Optotrak was used for measurement of rotation axes of joints. Sarcomere length was measured by laser diffraction. Findings: A total of 38 muscles were measured. Each muscle was divided in different muscle lines of action based on muscle morphology. 14 Ligaments of the hip, knee and ankle were included. Interpretation: The presented anatomical dataset embraces all necessary data for state of the art musculoskeletal modelling of the lower extremity. Implementation of these data into an (existing) model is likely to significantly improve the estimation of muscle forces and will thus make the use of the model as a clinical tool more feasible.

The electrical properties of polymer nanocomposites with carbon nanotube fillers

Abstract: The electrical properties of polymer nanocomposites containing a small amount of carbon nanotube (CNT) are remarkably superior to those of conventional electronic composites. Based on three-dimensional (3D) statistical percolation and 3D resistor network modeling, the electrical properties of CNT nanocomposites, at and after percolation, were successfully predicted in this work. The numerical analysis was also extended to investigate the effects of the aspect ratio, the electrical conductivity, the aggregation and the shape of CNTs on the electrical properties of the nanocomposites. A simple empirical model was also established based on present numerical simulations to predict the electrical conductivity in several electronic composites with various fillers. This investigation further highlighted the importance of theoretical and numerical analyses in the exploration of basic physical phenomena, such as percolation and conductivity in novel nanocomposites.