UMD Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/3
New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a given thesis/dissertation in DRUM.
More information is available at Theses and Dissertations at University of Maryland Libraries.
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Item Electroadhesion of Hydrogels to Biological Tissues: A Discovery that Could Enable Sutureless Surgery(2022) Borden, Leah Klein; Raghavan, Srinivasa R; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This study concerns the topic of electroadhesion (EA), which refers to adhesion induced by an electric field. Previous research had demonstrated that a DC electric field could be used to adhere a cationic hydrogel to an anionic hydrogel. Here, we extend this phenomenon to new systems. First, we adhere cationic gels to animal (bovine) tissues by simply applying a DC field of ~ 10 V across a gel-tissue pair for 10 to 20 s. This adhesion persists indefinitely after the electric field is removed. Moreover, if the field is re-applied with reversed polarity, the EA is eliminated, and the materials can be separated. Because tissues have anionic character, only cationic gels can be stuck to them by EA. We also show that gels can be stuck over cuts or tears in tissues using EA, which can enable tissue repair (surgery) to be performed without the need for sutures or staples. Electroadhesion goes far beyond just bovine tissues. We have found that gels can be adhered by EA to tissues from various animals, including mammals (e.g., cow, pig, mouse); birds (e.g., chicken); fish (e.g., salmon); reptiles (e.g., lizards); amphibians (e.g., frogs), as well as various invertebrates (e.g., shrimp, worms). In addition, gels can also be adhered to plant tissue, including fruits (e.g., plums) and vegetables (e.g.; carrot), and also to fungi (mushrooms). In mammals, EA is strong for certain tissue types, such as arteries, intestines, and cornea across a range of species. Conversely, weak or no adhesion is observed with other mammalian tissues such as adipose and brain. These differences reveal some common themes in regard to EA: for instance, the higher the fraction of anionic polymers (proteins and/or polysaccharides) in the biological material, the higher the EA strength. Interestingly also, because tissues often have anisotropic structure, adhesion by EA can be strong in one tissue orientation, but weak or non-existent in the perpendicular one. Lastly, we delve into the mechanism behind EA. The EA strength between a cationic gel and an anionic material (gel or tissue) can be systematically enhanced in several ways. These include increasing the polymer concentration in the cationic gel as well as the cationic charge density. We also conduct experiments to unravel the contributions to EA from the charged polymer chains and the counterions. When cationic and anionic gels are contacted in the EA orientation and a high voltage of ~ 100 V is applied, the gels undergo “zipping”, i.e., they rapidly lock into adhesion due to electrostatic interactions in a manner that resembles the closing of a zip. Our findings suggest the following sequence of events for EA between gels. First, the DC field pulls counterions away from the gel-gel interface, which strongly polarizes the cationic and anionic chains at the interface. These chains then form a dense electrostatic complex (ESC), leading to adhesion of the gels. When the field is turned off, the ESC persists because it is thermodynamically stable. This explains why the adhesion remains strong and can even be permanent. Future work will investigate the applicability of EA towards surgeries, first in animals, and then potentially in humans.Item COCHLEAR IMPLANTATION: PATH PLANNING ALGORITHMS AND DYNAMICS(2022) Poley, Celeste; Balachandran, Balakumar; Krieger, Axel; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The focus of this dissertation is on incorporating robotics into pediatric cochlear implantation surgery. Since the 1980s, over 300,000 cochlear implantation surgeries have been performed worldwide, both in adults and children alike. For this dissertation research, surgical constraints in the operating theater are of utmost importance for the health and safety of the patient. As the field moves toward minimally invasive surgery, the issues that come with this, such as the loss of the natural field of view and the loss of tactile sense can create significant hurdles for surgeons. Medical robotics can be used to decrease the limitations of such surgical procedures since a desirable attribute of surgical robots is dexterity. Medical robotics can be used to can be used to counter these limitations, by taking advantage of the dexterity of surgical robots. These robots can be used in complex working environments for surgical procedures such as cochlear implantation surgery (CIS). The author's dissertation contains simulation, analytical, and numerical research, through which the effects of dynamics within the path planning algorithms on simulated and modeled cochlear implantation surgery have been studied. A novel path planning algorithm has been developed by making use of Rapidly-exploring Randomized Trees (RRT), and subsequently incorporating Sequential Quadratic Programming. The goal in utilizing a path planning algorithm (PPA) would be to increase safety and aid surgeons in a tightly constrained environment of pediatric temporal bone, which differs in geometry and size from adult temporal bones, and to positively impact the surgical procedure and recuperation from surgery. This algorithm was chosen for use in the tight spaces presented by pediatric patient anatomy and to address patient specific constraints or abnormalities that arise with cochlear implantation surgery in cases of congenital deafness, to add an extra layer of safety for patients. This method allows for more torque handling in tiny and heavily constrained environments, and prevents nicking of delicate anatomy, such as the cranial facial nerve, which can cause facial muscle paralysis if exposed to the slightest damage. The testing of the planning algorithm is carried out in a programming environment. These models are based on geometric equations describing the inner ear anatomy, based on data collected as a part of this dissertation work. Through this doctoral dissertation research, the author has developed several novel methods and innovative techniques to improve associated path planning algorithm. Since cochlear implantation surgeries are moving in the direction of minimally invasive surgery, it would be a beneficial goal to improve the surgery by including a path planning algorithm and a simulated robotic system to help reach the dissertation's goal of simulating the drilling done for cochlear implantation surgery, and with the ultimate goal of improving patient outcome and minimizing time to recovery.Item Racial/Ethnic Disparities in Amputation and Revascularization: The Roles of Socioexonomic Reighborhood Stress and Allostatic Load(2020) Hughes, Kakra; Sehgal, Neil J; Health Services Administration; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Blacks are several times more likely to undergo a leg amputation as compared to Whites. This is because while peripheral artery disease (PAD), the most common cause of amputation, is more likely to be treated by revascularization (restoration of blood flow) in Whites, PAD is more likely to be treated by amputation in Blacks. Whereas an ongoing debate argues as to whether this disparity is primarily a sociologic versus a biologic phenomenon, I proposed that there are socioeconomic neighborhood stressors that create more severe PAD and renders individuals less likely to undergo successful revascularization and more likely to undergo amputation. Three specific aims are addressed in this dissertation resulting in three manuscripts. In Study 1, utilizing the Nationwide Inpatient Sample Database (NIS) in a retrospective study design, I determined that among patients admitted to the hospital for severe PAD, low socioeconomic status (SES) correlates positively with the likelihood of amputation, but paradoxically correlates negatively with the severity of PAD. In Study 2, I used the National Health and Nutrition Examination Survey, in a cross-sectional study design, to evaluate if there was a relationship between PAD severity, as determined by the ankle-brachial index (ABI) and the level of allostatic load. I did not identify an association. In Study 3, I employed the Nationwide Readmission Databases to show that low SES positively correlates with readmission for amputation following surgical revascularization. Findings from these three papers indicate that there is a positive correlation between low SES and the likelihood of amputation both upon initial admission as well as during subsequent follow up after surgical revascularization. I was unable to establish a clear relationship between PAD severity and allostatic load. The paradoxical finding that low SES individuals present with less severe manifestation of PAD signifies that there are yet-to-be-established factors involved in this complex disparity. This dissertation underscores the dominant role of social determinants of health and submits that in order to adequately address this amputation-revascularization disparity and avoid unnecessary amputations, major investments need to be made not only in healthcare, but also in America’s social infrastructure.Item Polymeric Materials for Hemostatic and Surgical Sealant Applications(2015) Behrens, Adam Michael; Kofinas, Peter; Bioengineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Commercial hemostatic agents and surgical sealants do not meet the current clinical need. The available options suffer from a variety of shortcomings including high costs, short shelf lives, difficult preparations, and concerns over safety. This work aims to utilize synthetic polymers to develop alternative approaches that have the potential to improve outcomes from traumatic injuries and surgeries while minimizing risk and cost. The first aspect of this research focuses on the development of hemostatic hydrogel particles. These spherical hydrogels with a narrow size distribution were synthesized via inverse suspension polymerization. A cationic monomer was utilized in the hydrogel formulation to facilitate rapid swelling, leading to the formation a physical barrier to blood loss. Coagulation studies demonstrated the ability to cause localized aggregation through charge interactions with erythrocytes while reducing clotting activity in the bulk. This mechanism allows the hydrogel to quickly block blood flow and may mitigate thrombotic complications at distal sites. Hemostatic efficacy was exhibited by decreases in both the time to hemostasis and mass of blood loss in rat liver puncture and tail amputation injury models when compared to compression with gauze alone. The second aspect of this research focuses on the development of a synthetic surgical sealant. This work is centered on the investigation of a polymer fiber mat deposition method called solution blow spinning. This fabrication technique allows for the rapid in situ generation of polymer fibers, offering the ability to conformally deposit polymeric materials directly on the surgical site of interest. Solution blow spinning was utilized to deposit a body temperature responsive, biodegradable polymer blend. Above a critical temperature, the two phase fibrous polymer mat transitioned into a one phase polymer film. This transition resulted in plasticization and promoted polymer-substrate interaction, leading to increased adhesion. Sealant efficacy was demonstrated in a cecal intestinal anastomosis mouse model, where the polymer blend was used to supplement sutures. Both burst pressure and survival rate were significantly improved over the suture-only control.Item OPTICAL COHERENCE TOMOGRAPHY FOR NEUROSURGEY AND CANCER RESEARCH(2014) Liang, Chia-Pin; Chen, Yu; Bioengineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Optical Coherence Tomography (OCT) provides non-labeling, real-time and high resolution images, which has the potential to transform the paradigm of surgical guidance and preclinical animal studies. The design and development of OCT devices for neurosurgery guidance and novel imaging algorithms for monitoring anti-cancer therapy have been pursued in this work. A forward-imaging needle-type OCT probe was developed which can fit into minimally invasive tools (I.D. ~ 1mm), detect the at-risk blood vessels, and identify tissue micro-landmarks. This promising guidance tool improves the safety and the accuracy of needle-based procedures, which are currently performed without imaging feedback. Despite the great imaging capability, OCT is limited by the shallow imaging depth (1-2 mm). In order to address this issue, the first MRI compatible OCT system has been developed. The multi-scale and multi-contrast MRI/OCT imaging combination significantly improves the accuracy of intra-operative MRI by two orders (from 1mm to 0.01 mm). In contrast to imaging systems, a thin (0.125 mm), low-cost (1/10 cost of OCT system) and simple fiber sensor technology called coherence gated Doppler (CGD) was developed which can be integrated with many surgical tools and aid in the avoidance of intracranial hemorrhage. Furthermore, intra-vital OCT is a powerful tool to study the mechanism of anti-cancer therapy. Photo-immunotherapy (PIT) is a low-side-effect cancer therapy based on an armed antibody conjugate that induces highly selective cancer cell necrosis after exposure to near infrared light both in vitro and in vivo. With novel algorithms that remove the bulk motion and track the vessel lumen automatically, OCT reveals dramatic hemodynamic changes during PIT and helps to elucidate the mechanisms behind the PIT treatment. The transformative guidance tools and the novel image processing algorithms pave a new avenue to better clinical outcomes and preclinical animal studies.