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Friday, April 16th, 2021

Ian Coates

Assessing the Impact of Block-Selective Homopolymers on the Diffusion of Payloads Through Polymeric Gels

The goal of this project is to investigate the impact of a gel-miscible polymer additive on gel nanostructure, gel mechanical behavior, and sodium bis(2-ethylhexyl) sulfosuccinate (AOT) release rate. Characterizing gels’ mechanical behavior and release of AOT through these gels will benefit future applications like transdermal drug delivery through informed structure-property (i.e., nanostructure-diffusion) relationships. Previous work in our group has shown that gel nanostructure is tuned by varying the amount of gel-forming SEBS copolymer. The purpose of this project is to further investigate methods of gel nanostructure tuning by identifying the impact of a discrete phase-selective polymer on organogel properties. Specifically, the impact of additive polymer concentration of gel nanostructure, mechanical response, and diffusivity will be studied. The current work uses Fourier-transform infrared spectroscopy (FTIR) to track changes in gel AOT concentration over time for gels with ranging homopolymer concentrations. The acquired data is modeled using Fick’s laws to yield a diffusion coefficient for each gel formulation. We hypothesize that the aforementioned nanostructure trends are the culprit for our observation that diffusion of AOT decreases with increasing polystyrene additive polymer concentration. Understanding these relationships will provide key insight for biomedical and agricultural payload delivery applications.

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Monday, April 12th, 2021

Emily Tully

Location Dependent Mechanical Behavior of Aponeurosis Tissue Under Uniaxial Tensile Stretch

Aponeurosis is a connective tissue that serves as an extension of tendon, attaching to muscle fibers that do not fully extend to the tendon. The material properties of aponeurosis – and thus its mechanical function in the body – are poorly understood. The goal of this work was to perform uniaxial tensile testing to measure the mechanical response of aponeurosis tissue as a function of thickness and location from tendon to muscle. Ten samples measuring ~60mm by 10mm were cut with tissue fibers running lengthwise, and the thickness was measured every 5mm. Uniaxial tensile testing was completed on a custom planar biaxial material testing system with digital image correlation (DIC) to track sample strain. The average nominal (engineering) stress and Lagrange strain values were determined for two regions: the thinner section that connects to muscle fibers and the thicker section that connects to the tendon tissue. Linearized moduli were determined at each time point by dividing nominal stress by Lagrange strain. Paired t-tests (p<0.05) were performed on the Lagrange strain and linearized moduli at each time point. Statistical results indicated that there is no significant difference in the strain of an aponeurosis sample at different thicknesses, but that under greater tensile loads, aponeurosis may exhibit higher moduli corresponding to thinner sections. These results show the material properties of aponeurosis tissue are inhomogeneous and can be used to develop more accurate simulations of muscle-tendon unit mechanical function. Such simulations provide necessary insight into how healthy versus impaired muscle drives the movement of vertebrates.

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Sunday, April 11th, 2021

Wutt Kyi

Effect of White Matter Stimulation on Clinical Outcomes in Thalamic Deep Brain Stimulation for Essential Tremor

Deep brain stimulation (DBS) is a surgical procedure where electrodes are implanted in the brain before stimulating the tissue with electricity. DBS of the ventral intermediate (VIM) nucleus of the thalamus and the subthalamic nucleus (STN) are established treatments for the motor symptoms of essential tremor (ET) and Parkinson disease (PD), respectively. Motor outcomes, such as tremor, rigidity, and bradykinesia, after VIM and STN DBS can vary considerably across patients and strongly depend on the location of stimulation relative to the surgical target. Previous research suggests that stimulation of the white matter (WM) tracts lateral to the VIM, the gray matter (GM) target, results in better DBS outcomes. The objective of this retrospective study is to determine how the spread of stimulation to WM during VIM DBS relates to therapeutic and non-therapeutic outcomes in ET patients. For the first phase of this research, a MATLAB algorithm that can differentiate brain tissues, such as WM, GM, and cerebrospinal fluid, from medical imaging based on tissue anisotropy was developed. Patient-specific tissue anisotropy was derived from diffusion tensor imaging data acquired for individual patients who received DBS (n = 22). To evaluate the performance of the algorithm, it has been trained and tested across both ET and PD patient data sets. This algorithm can be used to differentiate brain tissues in any region of interest. The modeling framework utilized in this study could be used to identify optimal stimulation sites on an individual basis, thereby improving clinical outcomes.

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Sunday, April 11th, 2021

Anthony Orlando

Mechanics of Wax-based Gels with varying Polymer Concentration: An Overview

Wax-based polymer gels have the potential to vastly improve the shelf life of transdermal drug patches. It can be reasoned, and addressed with future testing, that diffusivity of wax-based gels in the solid wax phase is relatively negligible and only becomes significant once the material transitions to the gel phase. The gel phase of this type of material is comparable to amorphous mineral oil-based gels. If the melting point of the wax-based gels is constrained between human body temperature and room temperature, diffusion of the payload in gels can be controlled to only occur when the patch is in contact with the human skin. Our first step in studying wax-based polymer gels is their mechanical behavior. Testing of both the solid wax and gel phases of the wax-based gels will provide foundational physical properties of the gels and aid in moving them towards application in the medical industry.

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Sunday, April 11th, 2021

Thomas Matsumura

Title: Measuring Lower Limb Muscle Activity and Kinematics in Variable Foot Strike Gaits

Abstract: Anterior knee pain affects roughly a quarter of the population, and many cases go untreated. Joint pain is a complex condition, but is influenced by morphology, kinematics (motion), and joint load imbalances, which are driven by muscle forces. To develop a better understanding of the interactions between kinematics and muscle activity patterns, non-invasive surface EMG sensors will be used on the lower limbs of pain-free subjects to measure muscle activation during different activities and gait patterns, including normal walking, toe-in/toe-out walking, and box jumps. Sensors are placed on the subject’s knee extensor muscles, hamstrings, dorsiflexors, and plantar flexors, which are the muscle groups that are most associated with knee loads. Data processing includes rectification, smoothing, and statistical analysis between different activities. Comparing these data will allow us to determine activities that lead to changes in surface EMG signals, and thus muscle forces, and how these changes may affect knee joint loads. We will then examine how those with no history of patellofemoral pain and those with a history of pain differ in muscle activation patterns. We hope that the data collected and subsequent analysis can help us determine how joint loads may be reduced in subjects with anterior knee pain may be reduced by gait retraining, physical therapy, or surgical interventions.

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Saturday, April 10th, 2021

Cameron Hong

Assessing Solvent Viscosity Impact on the Physical Characteristics of Polymeric Organogels

Traditionally, studies of polymeric organogels focus on the impact of polymer factors on the gels’ mechanical and transport properties. Alternatively, this study seeks to assess the impact of altering solvent viscosity, while holding polymer factors constant. The gels in this study were composed of styrene-ethylene-butylene-styrene (SEBS) triblock copolymer, oleic acid (OA), and mineral oil. Samples were formulated at 10, 20, and 30 wt% SEBS copolymer for each mineral oil, varying in viscosity from ~30 mPa*s to ~500 mPa*s. Uniaxial mechanical testing was performed to determine Gc, the contributions of physical crosslinks, i.e., micelles, to stress, and Ge, the contributions of chain entanglements to stress. Modeling the data from these experiments showed that Gc and Ge only varied with polymer concentration. In a separate set of experiments, Fourier Transform Infrared Spectroscopy (FTIR) was used to track the diffusion of OA out of the gel. Through modeling the release of OA with time using a Fickian diffusion model, the diffusion coefficients for formulations at varying solvent viscosities were determined. Notably, the results of the FTIR experiments conform to behavior predicted by the Stokes-Einstein equation. The results from these two sets of experiments allows for a higher degree of tunability than previously available. The results from this study will be of particular use in development of transdermal drug delivery devices.

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Saturday, April 10th, 2021

Michael Duncan

Title: Gas-Phase Chemical Ionization Orbitrap Mass Spectrometry
Michael Duncan
Advisor: Douglas B. Collins
The most common method of analysis for trace gases in air employs chemical ionization-time of flight mass spectrometry (CI-TOF-MS). Transportable CI-TOF-MS instruments have relatively low mass resolving power (m/Δm 50,000, allowing for the exact monoisotopic mass to be determined. However, Orbitrap instruments are most commonly designed to analyze sprayed liquid samples. Atmospheric chemists commonly need to analyze the molecular composition of gases that include a variety of large organic molecules that have a similar mass to charge ratios as one another, making it difficult to accurately identify them using a CI-TOF-MS. This project set out to design a chemical ionization apparatus for Orbitrap mass spectrometry and allow for the analysis of gaseous samples. The design has been focused on low costs, modularity, and adaptability, all in order to keep the horizon of users and use cases as broad as possible. Analyte ions will be formed by ion-molecule reactions within a cone-shaped flow reactor. Reagent ions will be supplied to the ion-molecule reactor using a continuous soft x-ray photoionization process. Computer-aided design in Solidworks along with rapid prototyping with 3D printing has allowed for conceptualization, realization, and testing of key components before fabrication. The first machined prototype is the next major step that will provide the opportunity to test the concept.

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Saturday, April 10th, 2021

Jaden Lee

Using Finite Element Modeling to Investigate the Effect of Mechanical Loading on Muscle Microstructure

Clinical treatments for muscle conditions such as muscle atrophy and cerebral palsy require an understanding of the mechanical properties of the impaired tissue. The extracellular matrix (ECM) is a collagen-based, honeycomb-like structure present throughout muscle tissue that greatly influences muscle stiffness. Although many studies have investigated the mechanical properties of muscle tissue and the ECM, there is scarce literature on the effect of different loading conditions on the functionality of the ECM. The goal of this study is to develop a finite element model of a muscle fascicle unit in order to understand how muscle stiffness may be dictated by the ECM. We hypothesize that the geometric parameters and material properties of the ECM such as thickness, fiber alignment, and hyperelasticity impact the mechanical properties of muscle tissue subject to various mechanical loading conditions. A transversely uniform representative volume element of muscle tissue was developed in Solidworks using a Voronoi-based cross-section. The model was discretized into tetrahedral finite elements using an open-source meshing package. Using FEBio, we will simulate the effects of uniaxial and biaxial stretching on the element with variations in ECM geometric and material properties. This theoretical model will then be used to link tissue-level mechanical function (stiffness) to tissue microstructure, thus providing insight into how impaired muscle may differ mechanically and structurally from healthy muscle.

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Saturday, April 10th, 2021

Keith Grega

Impact of Screw Type on Torque During Slipped Capital Femoral Epiphysis Screw Removal

Slipped Capital Femoral Epiphysis (SCFE) is a disorder that occurs in adolescents in which the femoral head slips with respect to the femoral neck. SCFE can lead to abnormal hip mechanics which may result in the need for realignment of the femoral head through surgery. Percutaneous in situ fixation is the most common treatment for SCFE, where the femoral head is realigned on the neck through screw insertion to prevent further deformity during adolescence. The topic of screw removal is quite controversial. If the screws are left in the patient, there is the potential that fractures may occur later in life due to stress risers, yet screw removal requires a second surgical operation. In addition, there is no standard screw that is used for the procedure. Different physicians prefer various types of screws including titanium vs. non-titanium, cannulated vs. non-cannulated and threaded vs. partially-threaded. Therefore, the purpose of this research project is to determine the amount of torque required to remove various types of orthopaedic screws after closure of the physis. This analysis will quantify how various screws perform during screw removal and provide insight into tissue damage that may occur due to screw removal. The ultimate goal of this study is to determine the optimal screw to use during the procedure that will cause the least amount of damage after bone growth has occurred around the screw.

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Saturday, April 10th, 2021

Jake Schaefer

The Mechanical Properties of Ramming Animal Horn Shapes

One of the most common, yet very dangerous injuries in the world of sports are concussions, which are caused by brain cavity accelerations. Concussions can lead to serious health conditions such as Chronic Traumatic Encephalopathy or CTE, which is a degenerative brain disease that can be fatal. Unlike humans, male Bighorn Sheep are capable of, and frequently do, ram heads at high velocities repeatedly without exhibiting clear signs of CTE. It is apparent that the biomechanical structure and function of their skull and horns play an important role in ramming and possible prevention of CTE. It has been shown in previous studies that after impact, oscillations of the horns could dissipate kinetic energy and reduce brain cavity accelerations. As a result, it is hypothesized that the unique shape of the horns could be a contributing factor to this energy dissipation. In order to test this hypothesis, a drop test will be conducted with a loaded container. On it will be attached ram horn shapes as well as miscellaneous shapes. It is expected that when the horn models are attached to the cylinder, the max acceleration on the container will be less than when the other shapes are attached. Based on the findings, the efficacy of bighorn sheep-like horn shapes as a possible energy dissipating structure will be determined. If it is seen to be effective, such structures could lead to designs that will reduce accelerations due to impact in many cases, such as automotives, sports, and construction.

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