Chemical and Biomolecular Engineering Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2751
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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 TISSUE ADHESIVE, SPRAYABLE POLYMER BLENDS AS ADJUVANT SURGICAL TOOLS(2022) Erdi, Metecan; Kofinas, Peter; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Commercial materials deployed in surgery for treatment of high-impact clinical pathologies suffer from shortcomings stemming from a combination of poor mechanical properties, difficulty in precise application, and non-specific prevention mechanisms. Work in this dissertation seeks to counteract these concerns through a multitude of blending approaches with biodegradable polymers and therapeutic agents for improved outcomes following traumatic tissue injury. The polymer blends were spray deposited using solution blow spinning, a method of fiber production where material rapidly accumulates onto target tissue substrate and forms a stable interface. The first thrust of this dissertation hones on deposition of a biocompatible, wet tissue adhesive. These tissue adhesives were fabricated through molecular weight ratio blends of poly(lactide-co-caprolactone) (PLCL), a synthetic, biodegradable copolymer with viscoelastic properties fostering pressure-dependent adhesion. High molecular weight PLCL endowed the composite material with rigidity and inherent cohesive strength, while low molecular weight PLCL induced spreadability and adhesive strength. Such optimized material behavior presented an ability to not only adhere to hydrophilic surfaces, but also demonstrated an ability to act as a media for biocompatible and complete wound healing. Efficacy as an adhesive in wound dressings was exhibited through spray deposition of blend adhesives to bandage substrates in a porcine partial thickness burn wound model and comparison with a poly(urethane)-based clinical control material. The second thrust of this dissertation focuses on development of an effectively applied barrier material for prevention of post-operative fibrotic scar tissue termed as adhesions. Rapid generation of tissue-conformal polymer fibers through solution blow spinning yields a material that is inherently flexible, thereby counteracting the brittle architecture of a sheet-like film currently deployed in surgery. Prevention of asymmetric fibrosis was accomplished through tuned surface biodegradation via high and low molecular weight PLCL blends. This strategy seeks to physically prevent prolonged retention of adhesion-generating molecules at the site of injury, as well as biologically counteract underlying inflammatory processes through controlled release of a therapeutic, apolipoprotein mimetic peptide from composite PLCL fiber mat. Adhesion prevention efficacy was qualified in high impact pre-clinical mouse models of cecal ligation and cecal anastomosis, and compared to pre-fabricated, dried hydrogel barrier and aqueous therapeutic suspension controls. Both adhesion severity and resultant wound healing response were significantly improved versus no treatment and clinically adopted controls.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 INTERFACIAL CONSIDERATIONS FOR DROPLET PCR LAB-ON-CHIP DEVICES(2015) Pandit, Kunal; White, Ian M; Raghavan, Srinivasa R; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Lab-on-chip devices have the potential to decentralize the current model of diagnostics to point-of-care diagnostics. Easy to use, low cost, rapid infectious disease diagnostic tools could especially impact and improve healthcare in low resource areas. Micro-total-analytical-systems could also enable smarter medical decisions, quicker patient recoveries, and cheaper healthcare costs in fully developed settings. Significant innovations to standard technologies used today will help realize the promise of lab-on-chip devices. In this work, innovative technologies compatible with current lab-on-chip devices were investigated to simplify their operation, decrease their complexity, and reduce their cost. The interfacial aspects that dominate microfluidic systems, and in particular droplet polymerase chain reaction (PCR) devices, are emphasized. Droplet PCR utilizing microfluidic technology has largely been automated, but sample preparation methods prior to amplification remains a laborious process. We have developed particles that condense the many steps of sample preparation into a single buffer protocol. The particles were made by crosslinking chitosan, a pH responsive biopolymer. DNA was electrostatically and sterically adsorbed to the beads at pH 8.5. Furthermore, amplification of DNA directly off the beads was demonstrated eliminating the need to desorb DNA into solution. Implementation of these particles will drastically simplify droplet PCR lab-on-chip devices. We also characterized the adsorption of polymerase at the oil-water interfaces of droplets and identified a surfactant to prevent the loss of polymerase in solution. The pendant drop technique was used to observe the change in interfacial tension due to adsorption of Taq Pol and/or surfactants to the interface. PCR performance of two surfactants, Brij L4 and ABIL EM90, were predicted from equilibrium interfacial tension measurements. Brij L4, a surfactant that had never been used with PCR, prevented polymerase adsorption and enabled more efficient PCR than ABIL EM90, a popular PCR surfactant. Lastly, we ambitiously designed a system to conduct droplet PCR without oil or surfactants. Droplets were generated on-chip by adapting a co-flow droplet generating device previously developed in our group. Then droplets were immobilized on-chip in hydrodynamic traps. Two different modes of trapping were demonstrated, indirect and direct. Also, all aspects of an air continuous phase droplet PCR device were considered such as protein adsorption to channel walls and droplet evaporation during thermal cycling.Item Development and Biophysical Characterization of HK Polymer for siRNA Delivery to Tumor in a Mouse Model(2014) Chou, Szu-Ting; Mixson, Archibald J; Seog, Joonil; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Delivery has been the major obstacle for nucleic acid therapeutics, including the RNA interference (RNAi) approach. Mixson's lab has been focused on the development of a non-viral peptide-based delivery system, HK (histidine-lysine) polymers, which have shown promise as carriers of plasmids and small interference RNA (siRNA) in several cell lines and in tumor-bearing models. In a previous study, a four-branched peptide, denoted H3K(+H)4b, with the predominant repeating -HHHK- sequence in the branch, has been shown to be the most effective and least toxic carrier in vitro and in vivo. Building on these results, I utilized different approaches including several structure and stability molecular characterization methods to study polyplex and to develop more effective carriers for improved therapy with siRNAs targeting malignancies. To understand the role of histidine in the stability of the H3K(+H)4b/siRNA polyplex, the physicochemical properties were investigated. With the use of isothermal titration calorimetry and heteronuclear single quantum coherence NMR, histidines were shown to form hydrogen bonds with siRNA, which enhanced the stability and biological activity of the polyplexes. In addition, to enhance resistance to nucleases and to target the tumors selectively, H3K(+H)4b was chemically modified with different patterns of polyethylene glycol (PEG) and cyclic RGD (Arg-Gly-Asp, cRGD) peptide conjugates. The luciferase marker gene expressed stably by tumor xenografts in mouse models was targeted in order to evaluate the efficacy of HK carriers of siRNA that differed in location and number of cRGD-PEG attachments. The most effective carrier was (RGD-PEG)4H3K(+H) (RP-HK), which has a cRGD-PEG on each of its four terminal branches. Consistent with its prolonged stability, as observed by pharmacokinetic studies, the RP-HK polyplex down-regulated luciferase activity in tumor xenografts by nearly 70% compared with the untreated group. Subsequently, the RP-HK polyplex was used to target the Raf-1 oncogene, an important mediator of tumor cell growth and angiogenesis. As in the luciferase studies, the polyplex reduced Raf-1 mRNA by more than 75%, and more importantly, the treatment inhibited the tumor growth by 60% in a mouse model. We anticipate that further design and engineering of HK carriers will improve the predictability and therapeutic activity of siRNA polyplexes in cancer treatment.