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.
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Item Sutureless Anastomosis: Electroadhering a Hydrogel Sleeve Over Cut Pieces of Tubular Tissue(2024) Grasso, Samantha Marie; Raghavan, Srinivasa R; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Recently, our lab demonstrated that cationic gels could be adhered to animal tissues by applying an electric field (10 V DC, for ~ 20 s). This phenomenon, termed electroadhesion (EA), could potentially be used to repair injured tissues without sutures. An extreme injury is when a tube in the body (e.g., a blood vessel or an intestine) is cut into two segments. The surgical process of joining the segments is termed anastomosis, and thus far has only been done clinically with sutures. Here, we explore the use of EA for performing sutureless anastomoses in vitro with bovine aorta and chicken intestine. For this purpose, we make a strong and stretchable cationic gel in the form of a sleeve (i.e., a hollow tube). By using a custom plastic mold, we control both the sleeve diameter and wall thickness. A sleeve with a diameter matching that of the tubular tissue is slipped over the cut segments of the tube, followed by application of the DC electric field. Thereby, the sleeve becomes strongly adhered by EA to the underlying tube. Water or blood is then flowed through the repaired tube, and we record the burst pressure Pburst of the tube. We find that Pburst is > 80 mm Hg and close to the Pburst of an intact (uncut) tube. In comparison to the sleeve, a long strip of the gel attached around the cut tubular pieces allows a much lower Pburst. Thus, our study shows that gel-sleeves adhered by EA could enable anastomoses to be performed in the clinic without the need for sutures.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 Characterizing the combined effect of electrostatics and polymer adhesion for elastomer-based electroadhesives(2019) Chen, Simpson Abraham; Bergbreiter, Sarah; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This dissertation presents work done in the fabrication and characterization of polymer-based electroadhesives to understand the underlying mechanisms of electroadhesion with the inclusion of soft polymers as the functional surface material. Electrostatic models for parallel plate and interdigitated electrodes provide insight into the effect of design parameters on electric fields. However, little work has been done to model how electrostatic force affect adhesion in soft electroadhesives while accounting for their mechanical and material properties. To this end, a basic friction model is presented to describe the critical shear force for a single electrode electroadhesive. The effect of voltage, contact area, dielectric thickness, and bulk thickness on shear adhesion is explored. It was shown that within a range of design parameters the basic friction model could accurately predict the critical shear force and with stiff dielectric layers higher compliance improved adhesion. However, improved models are required to cover behavior over a larger parameter space. To move beyond friction-based modeling, the combined effect of polymer adhesion and electrostatic force on conductive polymer layers is explored through performing JKR tack tests. Tack tests can measure the intrinsic adhesive property of a polymer, called the critical energy release rate. By performing JKR tack tests with two different tack systems, a rigid probe contacting a soft elastic surface and a soft probe contacting a rigid surface, it was shown that the combination of the two adhesion mechanisms can be described as a superposition of the critical energy release rate of the polymer and electrostatic force. Using these findings, a design framework is developed to combine gecko adhesives with electrostatics to increase the controllable adhesion range. Textured electroadhesives with arrays of spherical bumps were fabricated and showed an increase in adhesion up to 20x. The textured electroadhesives were also mounted onto 3D printed mounts to pick up various objects weighing from 2g to 60g. The work presented here provides a theoretical and design framework for future soft electroadhesives to build upon for applications from climbing robots to pick and place manufacturing.