Browsing by Subject "Hydrogels"

Now showing 1 - 20 of 26

A self-degradable hydrogel sensor for a nerve agent tabun surrogate through a self-propagating cascade
(Elsevier, 2021-09-22) Lee, Doo-Hee, Ph. D.; Valenzuela, Stephanie A.; Dominguez, Manuel N.; Otsuka, Mai; Milliron, Delia J.; Anslyn, Eric V.
Nerve agents that irreversibly deactivate the enzyme acetylcholin- esterase are extremely toxic weapons of mass destruction. Thus, developing methods to detect these lethal agents is important. To create an optical sensor for a surrogate of the nerve agent tabun, as well as a physical barrier that dissolves in response to this analyte, we devise a network hydrogel that decomposes via a self-propagating cascade. A Meldrums acid-derived linker is incor- porated into a hydrogel that undergoes a declick reaction in response to thiols, thereby breaking network connections, which re- leases more thiols, propagating the response throughout the gel. A combination of chemical reactions triggered by the addition of the tabun mimic initiates the cascade. The dissolving barrier is used to release dyes, as well as nanocrystals that undergo a spontaneous aggregation. Thus, this sensing system for tabun generates a phys- ical response and the delivery of chemical agents in response to an initial trigger.
Building hierarchical structure into synthetic extracellular matrices with peptoid crosslinked hydrogels
(2023-05-04) Morton, Logan D.; Rosales, Adrianne M.; Peppas, Nicholas; Lynd, Nathaniel; Suggs, Laura
The extracellular matrix (ECM) plays a critical role in supporting cellular behavior and tissue function. It provides a complex and dynamic network of proteins and polysaccharides that regulate cell adhesion, migration, proliferation, and differentiation. Natural ECMs are highly organized and hierarchical in structure, with specific biochemical and mechanical properties that vary across different tissues and organs. Mimicking the complexity of natural ECMs in synthetic materials is a major challenge in tissue engineering and regenerative medicine. Synthetic hydrogels, which are water-swollen networks of polymer chains, have emerged as a leading technology in creating synthetic, biomimetic ECMs. However, synthetic hydrogels typically lack the hierarchical structure and biochemical complexity of natural ECMs, which limits their ability to support cell behavior and tissue function or to model complex disease states that are seen in vivo. To address this challenge, research is being conducted on incorporating hierarchical structure and biochemical complexity into synthetic hydrogels. Peptoids are a promising class of peptidomimetics that can be designed to mimic the biochemical and physical properties of natural peptides and proteins. They are highly modular, with a wide range of chemistries that can be used to control their physical and biological properties. Additionally, peptoids are highly stable and resistant to enzymatic degradation, with extremely stable secondary structures that mimic those of peptides, including α-helices, making them attractive for biomedical applications. Herein, we designed peptoids of different secondary structures (helical, nonhelical, and unstructured) with different persistence lengths to decouple stiffness from other properties of the synthetic ECM system. We investigated the relationship between this molecular rigidity and hydrogel stiffness, demonstrating that the stiffness of the hydrogels could be tuned by adjusting the peptoid sequence and length independent of properties like swelling and permeability. We also examine how this range of stiffness impacts cellular behavior, especially for human mesenchymal stem cell (hMSC) manufacturing. We found that all peptoid crosslinked hydrogels were viable cell culture platforms in 2- and 3-dimensional culture for hMSCs and that the stiffness range achieved was significant enough to impact cellular behavior, with hMSCs grown on softer substrates proliferating more, producing more immunosuppressive and regenerative cytokines, and substantially altering their morphology. This work demonstrates the potential of peptoid crosslinked hydrogels as versatile scaffolds for tissue engineering, regenerative medicine, and disease modeling due to their similarities to native ECM with decoupled stiffness and mesh size.
Chemically modified hyaluronic acid biomaterials for cell culture and tissue engineering
(2016-12) Joaquin, Alysa Marie; Zoldan, Janeta; Suggs, Laura
The fate and behavior of cells is strongly dependent on the cell microenvironment, and this knowledge has been applied to the design of biomaterials to influence cell growth, morphology, and differentiation. However, a dearth of research specifically focused on the effects of material hydrophobicity on cell behavior indicates that this easily controllable material property is being overlooked. The field of tissue engineering has a need for cost-efficient, scalable methods to both increase stem cell stocks and control cell behavior, and hydrophobic biomaterials may be a robust solution to these needs. To evaluate the utility of hydrophobicity in controlling cell behavior, hyaluronic acid was modified with amines representing a wide range of hydrophobicity, resulting in twelve new materials. Both mouse embryonic stem cells (mESCs) and fibroblasts were cultured on these materials to evaluate the differences in pluripotent and differentiated cell behavior in response to hydrophobic materials. The viability of cells cultured on these materials was tested as an indicator of biocompatibility, and cell morphology and spreading area was evaluated to relate cell behavior to biomaterial hydrophobicity. Eight of the twelve materials proved to be biocompatible, and hydrophobic materials inhibited cell spreading; fibroblasts cultured on modified HA hydrogels grew in populations of both compact cell clusters and elongated, multi-polar morphologies, and cell spreading area increased as hydrophobicity decreased. Similarly, mESC spreading area increased with decreasing hydrophobicity; mESCs grown on the least hydrophobic HA hydrogels also multi-polar spreading, while mESCs cultured on the more hydrophobic materials grew exclusively in compact cell clusters. As the morphology of cells is often indicative of cell fate, and as hydrophobic materials tended to inhibit cell spreading, we expected that mESCs cultured on hydrophobic materials would maintain pluripotency. To this end, hybrid scaffolds composed of modified HA and gelatin were developed as a platform for stem cell pluripotency maintenance. The mESCs seeded into these scaffolds had a higher expression of the pluripotency marker SSEA-1 compared to control mESCs grown in complete medium after 24 hours, indicating that hydrophobicity is an important material property to consider in stem cell culture.
Composite nanogels for the triggerable release of chemotherapeutics
(2015-12) Peters, Jonathan Thomas; Peppas, Nicholas A., 1948-; Freeman, Benny; Johnston, Keith; Sanchez, Isaac; Zoldan, Janeta
The development of external stimuli responsive nanoparticles has progressed greatly since its inception in the seventies. However, apart from some clinical success for slow release delivery via liposomes, the technology has stalled for the delivery of chemotherapeutics due to a myriad of problems with cytocompatibility and premature diffusion of drug payload. The solution to cytocompatibility has been the coating of the system with polyethylene glycol. New methods have been developed to attach polyethylene glycol (PEG) tethers to the surface of otherwise unreactive particles. Surface hydrolysis of acrylamide containing polymers can be used to produce carboxylic acid functional groups near the surface of the polymeric nanoparticles. These nanoparticles can then be functionalized with PEG via EDC/NHS chemistry. The use of surface hydrolysis not only allows for reaction with these neutral polymers, but also provides greater control of PEG localization and leads to an unintrusive method to add the much needed stealth coating. In order to address the issue with premature release, new polymer systems have been developed. These systems are based around theory of hydrophobic interaction in order to improve the polymer/drug interaction in order to limit the unwanted diffusional release of drug payload. This interaction was addressed in a number of ways, focusing on both compartmentalization and copolymerization in order to develop nanogels that can entrap and withhold more drug from the surrounding area. An in depth look into the interactions that encourage drug uptake in these systems was performed by altering the copolymer chosen for these systems. This work looks into effects on phase transition, functional groups, hydrophobicity, and any structural changes that occur as a result of the polymerization scheme. After drawing conclusions on the interactions that encourage drug uptake, complex systems were devised to take advantage of these interactions. Core shell systems were designed to take advantage of the convective release of lower critical solution systems while still utilizing the mechanisms that improve drug retention. These systems were synthesized by two methods, emulsion polymerization and micelle crosslinking. These systems have been showed to improve the drug interaction and retention of doxorubicin as a model chemotherapeutic.
Conductive and recognitive hydrogels for biosensing applications
(2009-12) Bayer, Carolyn Louise; Peppas, Nicholas A., 1948-
Human disease processes are often characterized by a deviation from the normal physiological concentration of critical biomarkers. The detection of disease biomarkers requires the development of novel sensing methods which are sensitive, specific, efficient and low-cost. To address this need, a novel conductive and recognitive hydrogel composite material has been developed. This work investigated the fabrication methods, the chemical and physical composition, the sensing capabilities, and the biocompatibility of the proposed conductive and recognitive hydrogel composite materials. The conductive polymer was found to respond by changing conductivity in the presence of biomolecules. Specificity can then be incorporated into the system by integrating the conductive polymer with a molecularly imprinted hydrogel. The demonstration of a conductive and recognitive hydrogel composite is a step towards the integration of these materials into close-loop sensing and drug delivery systems.
Defined hydrogel microenvironments for optimized neuronal culture
(2010-05) Seidlits, Stephanie Kristin; Schmidt, Christine E.; Shear, Jason B.
Three-dimensional (3D) in vitro culture systems that provide controlled, biomimetic microenvironments would be a significant technological advance for both basic cell biology research and the development of clinical therapeutics (e.g., as in vivo cell delivery constructs). A variety of signals determine cell phenotype, including those from soluble factors, immobilized biomolecules, mechanical substrates, and culture geometry. My research seeks to create hydrogel culture systems that incorporate these signals in a defined, controllable manner. Specifically, I have focused on developing hydrogels based on the extracellular matrix (ECM) component hyaluronic acid (HA) with precisely specified mechanical, chemical and geometrical microenvironments. For example, the mechanical environment presented by HA hydrogels was tuned to span the threefold range measured for neonatal brain and adult spinal cord by modifying HA with varying numbers of photocrosslinkable methacrylate groups. These hydrogels were used to evaluate the effects of mechanical properties of a 3D culture paradigm on the differentiation of ventral midbrain-derived neural progenitor cells (NPCs) and results demonstrated that the mechanical properties of these scaffolds can assert a defining influence on differentiation. In addition, whole fibronectin was incorporated into HA hydrogels as an adhesive factor to encourage angiogenesis in 3D cultures, as interplay between endothelial cells and neurons is an important determining factor during NPC development and axonal regeneration after injury. To create spatially defined neuronal cultures in three-dimensions, multiphoton excitation (MPE) was used to photocrosslink protein microstructures within HA hydrogels. This method can be used to create complex, 3D architectures that provide both chemical and topographical cues to direct cell adhesion and guidance on size scales relevant to in vivo environments. Using this approach, both dorsal root ganglion cells (DRGs) and hippocampal NPCs could be guided along user-defined, 3D paths. In future studies, these strategies can be combined into a single hydrogel to create a culture microenvironment with multiple types of highly specified cues (i.e., chemical, topographical, and mechanical).
Design and development of an injectable, polymer-based immune priming center
(2010-05) Singh, Ankur; Roy, Krishnendu; Kwak, Larry W; Peppas, Nicholas A; Schmidt, Christine E; Suggs, Laura J; Williams III, Robert O
Immunotherapy, as a strategy to trigger immunity and eradicate a variety of chronic infectious diseases and cancers, has been explored for several decades with significant success in animal models. However, effective translation of these strategies into human clinical settings has proven elusive. Several cell-based anti-tumor therapies have progressed to clinical trials where antigen presenting dendritic cells (DCs) are isolated from patients, loaded with viral or tumor antigens and infused back in the patients. These ex-vivo “trained” DCs then present antigens to naïve T cells (adoptive therapy). However there exist several major limitations to this approach, including morbidity associated with patient cell isolation, high cost of ex vivo cell manipulation, time lag in “training” the immune cells, regulatory concerns, as well as the fact that ~ 90% of transplanted DCs die before they even home to lymph nodes. On the other hand, current immunotherapy approaches using recombinant proteins, synthetic peptides or nucleic acids, which "train" the immune cells in vivo to mount an immune response, have failed to address the tremendous challenge in generating efficient, sustained and protective immunity. There are two major challenges that must be overcome, (a) there exist relatively fewer numbers of immune cells at the sites of vaccine administration and given that these antigens themselves are weakly immunogenic, vaccine formulations must be tailored to attract large number of DCs to the immunization site and (b) immunologically, conventional nucleic acid or protein/peptide based vaccines do not elicit the required T helper type (Th) immunity along with a strong Cytotoxic T Lymphocyte (CTL) response against viral or tumor antigens and therefore new formulations must be able to “direct” the immune response towards a specific Th-type. Our goal was to design polymer-based sustained release formulations to addresses these challenges. Specifically, we have designed and developed delivery systems that can carry multiple biomolecules (nucleic acids, proteins, peptides, and chemoattractants) in a single injectable formulation. The delivery system promoted efficient migration of a large number of DCs to the site of injection and successful delivery of antigen resulting in activation of DCs. The multi-modal delivery system has the ability to bias or switch the immune response to the desired phenotype (e.g. Th1 or Th2) in a controlled manner. Using an infectious disease model against hepatitis B we have shown that co-encapsulation of Interleukin-10 (IL10) cytokine targeted siRNA within polymeric, surface-functionalized microparticles can further enhance DC activation and T cell proliferation in vitro as well as switch the hepatitis-specific immune response towards a strong Th1 phenotype in vivo. Further, in a weakly immunogenic A20 B cell lymphoma mouse model, a combination of microparticles and chemokine releasing in situ crosslinkable hydrogel provided significant Th1 type cellular immune response and delayed the onset of tumor development. Thus, the in situ crosslinkable hydrogel co-delivering microparticles and DC attracting chemokines creates an immune priming center with broad applications in a variety of disease models.
Design, development and optimization of methacrylic acid-based pH-responsive hydrogels for the oral delivery of model protein therapeutics
(2016-05) Steichen, Stephanie Danelle; Peppas, Nicholas A., 1948-; Baker, Aaron; Suggs, Laura; Watts, Alan; Yeh, Tim
Protein therapeutics have tremendous potential to treat a variety of debilitating diseases, however, due to their large size and low stability, their administration has been limited to injections. An orally delivered carrier capable of protecting the protein during its transit through the gastrointestinal tract could potentially overcome the limits of protein stability, improve oral bioavailability, and provide a more patient tolerated means of protein administration. A pH-responsive hydrogel system composed of methacrylic acid, N-vinyl pyrrolidone, and poly(ethylene glycol), designated as P((MAA-co-NVP)-g-EG), was developed. The effects of crosslinking lengths and density and incorporation of poly(ethylene glycol) tethers on swelling behavior and loading capability of protein therapeutics were evaluated. It was shown that P((MAA-co-NVP-g-EG) swelled to a greater extent than P(MAA-co-NVP) in equilibrium studies at neutral pH and showed a faster rate of swelling in dynamic conditions. Mesh sizes ranged from 400-650 Å, which was deemed sufficient for drug loading and release. Three therapeutic proteins were evaluated for their loading capability: insulin, porcine growth hormone (pGH), and ovalbumin. The weight loading efficiencies of the proteins were optimized by varying pH and ionic strength and ranged from 8-9% for insulin, 6-7% for pGH, and 4-5% for ovalbumin. There was no discernible effect of crosslinking density and length on loading. The incorporation of PEG tethers showed a significant improvement in loading of human GH, increasing weight-loading efficiencies from 4.5 to 6.4%. When exposed to simulated gastrointestinal conditions, the loaded microparticles released ~10% of their hGH payload at intestinal pH. The hydrogels were also evaluated for their safety in vitro and in vivo. No cytotoxicity was observed in two model intestinal cell lines at dosages less than 2.5 mg/mL. When exposed to C57Bl/6 mice at 66.7 mg/kg dose, the hydrogels triggered no inflammatory response and no deleterious effects on organ function after acute and long-term administration. In model intestinal epithelial layers, both P((MAA-co-NVP)-g-EG) and P(MAA-co-NVP) hydrogels significantly improved transport of hGH over hGH alone. In vivo studies performed in Sprague Dawley rats confirmed that hGH-loaded hydrogels yielded hGH bioavailabilities ranging from 0.46-4.8%. Therefore, these pH-responsive hydrogels show great promise for oral protein delivery.
Development of an injectable hydrogel electrode for the treatment of ventricular arrhythmias
(2022-08-16) Rodríguez-Rivera, Gabriel Josué; Cosgriff-Hernandez, Elizabeth; Rosales, Adrianne M.; Razavi, Mehdi; Peppas, Nicholas; Maynard, Jennifer
Ventricular arrhythmias (VA) are the leading cause of sudden death in the United States. The only effective treatment for VA is cardiac defibrillation, where a high-energy shock extinguishes the reentrant circuits that initiate and sustain VA. However, these high-energy shocks exceed the pain threshold. The primary goal of this research is to develop new painless strategies to extinguish reentrant VA. The current treatment requires large energy because the current leads capture the tissue from a single point far from the heterogeneous scarred tissue responsible for the electrical disruptions. We hypothesized that flexible electrodes that can access midmyocardium near the scarred area via the cardiac veins, we could terminate arrhythmias with low-energy shocks. However, there were no pacing electrodes small enough to navigate these tributaries to test this hypothesis. The focus of my dissertation was to develop a conductive hydrogel electrode that could be injected across the affected areas of the myocardium, filling the epicardial coronary veins and their mid-myocardial tributaries. When connected to a standard pacing lead, these hydrogels can then act as flexible electrodes that directly capture the previously inaccessible mid-myocardial tissue. Using in vitro and ex vivo models, we developed a hydrogel formulation with adequate viscosity and kinetics to form and retain the hydrogel in the cardiac veins to enable this approach. We tuned the hydrogel composition and combined new macromers chemistries with small molecules to obtain a biostable and biocompatible gel that matches the myocardium modulus. The conductivity is conferred by the ions on the hydrogel matrix and is above the target myocardium values. We demonstrated that the conductivity and network properties were retained after in vivo implantation and successful in vivo deployment demonstrated that the hydrogel electrode reaches cardiac veins and tributaries more deeply than current technologies allow. Feasibility of this approach was then confirmed with successful capture and pacing in a large animal model. This is the first report of an injectable electrode used to successfully pace the midmyocardium and mimic physiologic conduction. In vivo cardiac mapping studies showed fast and uniform capture along the hydrogel before and after myocardium ablation, as well as increased capture compared to traditional point pacing. As such, this injectable hydrogel electrode provides a novel way to improve current defibrillation strategies and opens opportunities for new therapeutic approaches. By capturing a larger area and deeper into the midmyocardium, this technology enhances new ways to study tissue activation that were not possible with current pacing leads.
Investigation of micro- and nanoscale hydrogels as protein receptors for use in diagnostic biosensors
(2017-06-20) Culver, Heidi Renee; Peppas, Nicholas A., 1948-; Anslyn, Eric V; Crooks, Richard M; Ren, Pengyu; Rylander, Henry G
Due to the high cost and environmental instability of antibodies, there is precedent for developing synthetic molecular recognition agents for use in diagnostic sensors. Molecular imprinting was first investigated as a method for improving selectivity of crosslinked polymer hydrogels. However, the lysozyme-imprinted polymers exhibited high cross-reactivity and did not afford the polymer with improved selectivity. Instead, the observed cross-reactivity prompted the investigation of charge-containing, non-imprinted polymers as differential protein receptors. To this end, a set nanogels were synthesized by copolymerizing N-isopropylacrylamide with methacrylic acid, followed by a post-synthesis modification. Specifically, a carbodiimide coupling scheme was used to introduce sulfate, guanidinium, secondary amine, or primary amine groups. As expected, modification of the ionizable groups in the network changed the physicochemical and protein binding properties of the nanogels. For high affinity protein-polymer interactions, turbidity of the nanogel solution increased, while for low affinity interactions minimal change in turbidity was observed. Thus, relative turbidity was used as input for multivariate analysis. Turbidimetric assays were performed in two buffers of different pH (i.e., 7.4 and 5.5), but comparable ionic strength, in order to improve differentiation. Using both buffers, it was possible to achieve 100% classification accuracy of eleven model protein biomarkers with as few as two of the nanogel receptors. Subsequently, these polymeric receptors were synthesized on the surface of silica-gold nanoshells to develop a diagnostic biosensor based on localized surface plasmon resonance (LSPR). In particular, the sensitivity of LSPR to changes in local refractive index was exploited to enable detection of three biomarkers (lysozyme, lactoferrin, and IgG) of Sjögren’s syndrome, an autoimmune disease that primarily affects the exocrine system. Overall, the polymer-gold nanomaterial composites developed in this dissertation provide a promising platform for developing affordable and environmentally robust diagnostic biosensors.
Linear and nonlinear poroviscoelasticity, and fracture properties of gelatin-based hydrogels
(2022-08-08) Chen, Si (Ph. D. in engineering mechanics); Ravi-Chandar, K.; Huang, Rui; Landis, Chad M.; Lu, Nanshu; Keitz, Benjamin
Hydrogels are polymer networks embedded in a solvent which is usually predominantly water. Due to the solvent diffusion and rearrangement of the polymer network, hydrogels exhibit poroelastic and viscoelastic behaviors. The two behaviors are usually coupled and may influence other mechanical properties, such as fracture. While there is much work on modeling and simulation of poroelasticity, viscoelasticity, and fracture, there is still a need for more experimental work that explores the response of the material and the calibration of the material response. In this dissertation, three large suites of experiments were performed under nonhomogeneous conditions to characterize the linear and nonlinear poroelasticity, viscoelasticity, and fracture in gelatin-based hydrogels. First, the poroelasticity of gelatin-based hydrogel of two different compositions is examined through drying and swelling experiments, achieved by adjusting the humidity levels in an environmentally controlled enclosure. The deformation of the specimens was quantified through Digital Image Correlation. The experimental measurements were compared with the simulations based on the Finite Element Method (FEM) implemented on the public domain code FEniCS, to provide a way to calibrate the material parameters both for linear and nonlinear poroelasticity. Second, the coupled poroelastic and viscoelastic behaviors of hydrogels were explored through simultaneous swelling/drying and creep experiments also in a controlled environment. This work showed that the decomposition of the volumetric and isochoric deformation provides a way to separate the poroelastic and viscoelastic behaviors. According to the experimental results, the volumetric deformation was dominated by water diffusion, and isochoric deformation was influenced by both viscoelasticity and poroelasticity. A nonlinear poroviscoelastic theory was developed based on a two-potential formulation under a thermodynamic framework, that successfully captured the coupled power-law creep and swelling/drying behaviors. Finally, the fracture behavior of hydrogels was explored under various conditions through poroelastic diffusion and viscoelastic creep. The viscoelastic J-like integral based on Schapery's theory was calculated from the measured displacement field and served as a characteristic parameter for crack growth in quasi-steady conditions. To further explore the poroelastic influence on the crack tip, fracture tests of immersed-crack-tip conditions were performed, which showed that water diffusion decreased the fracture energy.
Material design and molecular engineering of hydrogels for solar desalination
(2021-06-25) Zhou, Xingyi (Ph. D. in materials science and engineering); Yu, Guihua (Assistant professor); Korgel, Brian; Li, Wei; Zheng, Yuebing
Growing concern over water scarcity leads to increased research interest in advanced water purification technologies. Solar desalination, which utilizes solar energy to separate water and impurities through vaporization, enables the utilization of sustainable solar energy and abundant seawater to alleviate water scarcity. However, the essential process of solar desalination to remove impurities is energy-intensive. The vapor generation rate is limited due to insufficient solar absorption and thermal loss, lowering the freshwater production yield. Diffuse natural sunlight cannot satisfy the intrinsic energy consumption for rapid water vaporization. Therefore, developing new material platforms that can simultaneously provide high solar absorption, effective energy utilization, and low energy consumption for water vaporization to achieve highly efficient solar desalination under natural sunlight is anticipated. This dissertation adopts hydrogels as the new material platform for seawater desalination based on solar vapor generation (SVG). The unique water state in hydrogels could reduce energy consumption for water vaporization, facilitating vapor generation. To enable hydrogel materials for solar desalination as the vapor generators, rationally material and structural designs, as well as polymer network engineering are applied to achieve highly efficient freshwater production under natural conditions. Hydrogel-based solar vapor generators are constructed by introducing solar absorbers into polymeric networks of hydrogels to enable solar energy harvesting and conversion, providing thermal energy for vapor generation. To overcome the slow swollen rate of hydrogels during interfacial evaporation, different water pathways are constructed in hydrogel-based solar vapor generators to transport water to the evaporation surface for continuous vapor generation (Chapter 3). Moreover, the utilization of solar absorbers with different sizes and dimensions in hydrogels influences the water management and energy utilization efficiency of solar desalination, providing possibilities for enhanced SVG performance. The water state in hydrogels defines the vaporization behavior of water. Thus, the polymeric networks of hydrogels can be architected to tune the water state and further reduce the energy consumption of water vaporization. Polymeric chains with different hydrophilic functional groups are used to tailor the water-polymer interaction, varying the water state and phase change behaviors. Different polymeric networks, such as interpenetrating networks and copolymer networks, could be constructed for effective water management and further reduced evaporation energy consumption (Chapter 4). By incorporating functional components, the hydrogel-based solar vapor generators have also been endowed with multiple functionalities, such as antifouling, self-cleaning, and thermal responsiveness, to improve water collection and enable freshwater production from other water sources (Chapter 5). Finally, the development of hydrogel-based solar vapor generators is summarized and possible future directions are provided (Chapter 6).
Multiphoton lithography of mechanically and functionally tunable hydrogels
(2012-05) Spivey, Eric Christopher; Shear, Jason B.; Schmidt, Christine E.; Dunn, Andrew; Roy, Krishnendu; Tunnell, James
As one of the few 3D microfabrication techniques available to researchers, multiphoton lithography (MPL) has generated considerable interest in the scientific community. By allowing researchers to localize photochemistry to a femtoliter volume, MPL has permitted the fabrication of intricate, 3D microstructures from a range of materials, including protein hydrogels. MPL can be used to fabricate functional hydrogels on the scale of 100 μm, with features on the order of 1 μm. This dissertation examines existing MPL techniques to discover ways in which current processes can be modified to produce hydrogel products that are more useful for biomedical applications like tissue engineering. A new material is introduced that enables the fabrication of fully unconstrained hydrogel microstructures. In this context, A structure can be classified as “unconstrained” when it is free to translate and rotate without hindrance in three dimensions, and is not attached to the substrate or any other structure. New processes are demonstrated that permit the fabrication of larger MPL hydrogels without sacrificing feature resolution. This allows the fabrication of millimeter-scale, high aspect ratio structures with features smaller than 10 μm. Methods are described for tuning and measuring the mechanical properties of MPL-fabricated hydrogels, and ways of tuning the functional properties of the hydrogels are also examined.
Multiphoton techniques for dynamic manipulation of cellular microenvironments
(2014-08) Hernandez, Derek Scott; Georgiou, George; Shear, Jason B.; Schmidt, Christine; Ellison, Christopher; Contreras, Lydia; Thompson, Wesley
A multitude of biophysical signals, including chemical, mechanical, and contact guidance cues, are embedded within the extracellular matrix (ECM) to dictate cell behavior and determine cell fate. To understand the complexity of the cell-matrix interaction and how changes to the ECM contribute to the development of tissues or diseases, three-dimensional (3D), culture systems that can decouple the effects of these cues on cell behavior are required. This dissertation describes the development and characterization of approaches based on multiphoton excitation (MPE) to control the chemical, mechanical, and topographical presentation of micro-3D-printed (μ-3DP) protein hydrogels independently. Protein hydrogels were chemically functionalized via the MPE-induced conjugation of benzophenone-biotin without altering the physical properties of the matrix. Complex, immobilized patterns and chemical gradients were generated within protein hydrogels with a high degree of spatial resolution in all axes. Hydrogel surfaces were also labeled with adhesive moieties to promote localized Schwann cell adhesion and polarization. Laser shrinking, a method based on MPE to manipulate the topographical and mechanical presentation of protein hydrogels after fabrication, is also presented. Topographical features on an originally flat substrate are created with depths approaching 6 μm. The Young’s modulus of protein hydrogels can also be increased by 6-fold (~15 – ~90 kPa) using laser shrinking, and parameters can be adjusted to create continuous gradient profiles for studying durotaxis. At determined scan conditions, the two properties can be adjusted independently of each other. Most importantly, the physical properties of the hydrogels can be manipulated in situ to study the effects of dynamic changes to the substrates on cells. As a potential tool to monitor cellular responses to presented cues, fluorescent probes that detect nitric oxide are characterized. Collectively, these technologies represent a key advance in hydrogel tunability, as the platforms presented offer independent, dynamic, and spatiotemporal control of the chemical, mechanical, and topographical features of protein hydrogels. The introduced technologies expand the possibilities of protein hydrogels to clarify underlying factors of cell-matrix interactions that drive morphogenesis and pathogenesis, and are broadly applicable to a multitude of physiological systems.
Novel carriers for oral delivery of hemophiliac factor IX
(2016-05-04) Horava, Sarena DelVecchio; Peppas, Nicholas A., 1948-; Croyle, Maria; Freeman, Benny; Maynard, Jennifer A; Paul, Donald R
Current treatments for hemophilia B, a hereditary bleeding disorder characterized by the deficiency of coagulation factor IX (FIX), rely on injection-based administration that cause pain and discomfort, leading to noncompliance and risk of subsequent bleeding episodes. A non-invasive protein replacement therapy using an oral delivery system can both overcome such issues and improve access to treatment in developing countries. Oral delivery is a desirable route for protein therapeutics; however, two main challenges—increasing bioavailability and maintaining protein functionality—need to be addressed when designing a delivery platform. The overarching goal of this work presented here is to develop an oral delivery system for human factor IX (hFIX) as a convenient prophylactic treatment. Complexation hydrogels have been engineered to protect biologics from the harsh environment of the GI tract and deliver them to the small intestine for absorption. We have successfully developed pH-responsive hydrogel networks based on poly(methacrylic acid)-grafted-poly(ethylene glycol) [P(MAA-g-EG)] as delivery vehicles for hFIX. We have focused on optimizing the drug loading and release, as well as evaluating in vitro drug absorption and in vivo biocompatibility and biodistribution of the microcarrier. Tailoring the networks of P(MAA-g-EG) hydrogels improved the loading of hFIX within the microcarriers, which is critical for minimizing protein degradation. Optimizing the loading conditions by increasing the incubation time and using a reduced ionic strength buffer further improved the delivery potential of the microcarriers. The presence of the microcarriers significantly improved the in vitro absorption of hFIX. As an alternative strategy designed to further increase the delivery potential, we incorporated an enzymatically degradable component into the P(MAA-g-EG) microcarrier system. Evaluation of this degradable system demonstrated the increased levels of hFIX in intestinal conditions, which has the potential to promote the oral bioavailability of hFIX. We performed stability testing of lyophilized hFIX-loaded microparticles to determine the effects of storage conditions on hFIX release and activity. Lastly, in vivo biocompatibility and biodistribution studies were performed to establish the safety of multiple oral doses of P(MAA-g-EG) microparticles and to determine the residence time and clearance of these microcarriers. In vivo preclinical studies were critical for clinical applications of these drug delivery systems. This works shows that P(MAA-g-EG) microcarriers are promising candidates for the oral delivery of hFIX for treating hemophilia B.
Occlusion of the left atrial appendage using catheter-delivered hydrogels for prevention of thromboembolic phenomena
(2013-08) Zimbroff, Andrew David; Beaman, Joseph J.
The Left Atrial Appendage, once thought to be "a relatively insignificant portion of cardiac anatomy," has currently been realized to possess "important pathological associations [1a]" particularly in its role in promoting serious, frequent thromboembolic events common in individuals suffering from Atrial Fibrillation. Prior approaches to mitigating these events have either required invasive procedures, proved less than fully effective, or presented with problematic sequelae of their own. This work will present a new procedure that addresses both the prevention of the thromboembolic events and the correction of the shortcomings of the major prior methods utilized. A compliant hydrogel that can conform to the geometry of the appendage is proposed as a more effective method of occluding the chamber. This material would be transported to the LAA in liquid form via a multi-lumen catheter, and then solidify within the chamber to form a solid plug. Previous research has identified a candidate hydrogel, comprised of PEG-tetra-thiol and Dextran vinyl sulfone as a candidate hydrogel for this application. Experimental work has investigated fluid properties of the material, as well as degradation and swelling properties of the material. Results from this experimentation were used for fluid transport analysis, and for evaluation of anchoring force of the hydrogel within the chamber. Finally, subfunctions of the occlusion procedure were modeled and tested. During the actual procedure, a catheter balloon will isolate the appendage from the rest of the heart. A model was developed to study interactions between the appendage and this balloon. Additionally, due to fast solidification time, hydrogel components in the surgical procedure will be mixed in a mixing chamber at the tip of the catheter. Potential mixing chamber designs were modeled, and a ternary diffusion model was developed to better understand hydrogel mixing. Prototypes for both these subfunctions were built and tested as well. Additional analysis looked at the overall occlusion procedure, and how various subfunctions interacted with each other.
On the 3D contractile properties of the aortic heart valve interstitial cell in health and disease
(2022-05-02) Khang, Alex, Ph. D.; Sacks, Michael S.; Anseth, Kristi S; Baker, Aaron B; Cosgriff-Hernandez, Elizabeth M; Ferrari, Giovanni
Aortic valve interstitial cells (AVICs) are fibrobast-like cells that reside within all layers of the aortic valve (AV) and maintain extracellular matrix (ECM) turnover and remodeling. In disease, AVICs can undergo activation and take on a myofibroblastic phenotype characterized by increases in ECM deposition, remodeling, and cellular contractility brought about through expression of alpha-smooth muscle actin stress fibers (SFs). AVIC contractility via stress fibers is a physical indicator that reflects both AVIC activation level as well as biophysical state and is known to be correlated with crucial processes such as collagen deposition and ECM remodeling. My dissertation focuses on investigating the 3D contractile properties of AVICs within tissue-mimicking, 3D peptide-modified poly (ethlyene glycol) (PEG) hydrogels that crucially allow for direct visualization and assessment of AVIC behaviors. First, I used a flexure setup to quantify the contractile states of AVICs embedded within PEG gels, which showed similarity to our earlier native tissue work and demonstrated that the PEG gel environment reproduces many of the same functional characteristics as soft tissue. Then, I investigated the 3D contractile properties of AVICs in greater detail using 3D traction force microscopy and found that AVIC shape orientation and principal contractile direction were correlated. Further analysis showed that AVIC protrusions were the main drivers of AVIC contractile behaviors and that they deformed in a uniform, piston-like manner, indicative of highly-aligned underlying SFs. To gain deeper insight into SF architecture and contractile forces, I developed a 3D computational model of the contracting AVIC within a PEG hydrogel medium. First, the model predicted that AVICs stiffen the local material likely due to nascent ECM deposition. The local variations in hydrogel moduli were then incorporated with a mechanical model of the contracting AVIC which predicted that the greatest SF alignment and contractile force levels were localized at the AVIC protrusions, showing consistency with experimentation. Finally, I extended this approach to investigate intrinsic differences between AVICs extracted from human bicuspid AVs (BAVs) and structurally normal tricuspid AVs (NAVs) and found that AVICs from BAVs showed lower levels of activation as evidenced by lesser SF alignment and contractility. These findings suggest that intrinsic differences among the AVICs likely contribute to the increased rate of valve disease experienced by many BAV patients. In addition, this work highlights the importance of investigating cellular and sub-cellular differences among the BAV and NAV toward identifying targets for novel, non-surgical therapies.
Photopolymerizable scaffolds of native extracellular matrix components for tissue engineering applications
(2010-05) Suri, Shalu; Schmidt, Christine E.; Chen, Shaochen; Roy, Krishnendu; Suggs, Laura J.; Shear, Jason B.
In recent years, significant success has been made in the field of regenerative medicine. Tissue engineering scaffolds have been developed to repair and replace different types of tissues. The overall goal of the current work was to develop scaffolds of native extracellular matrix components for soft tissue regeneration, more specifically, neural tissue engineering. To date, much research has been focused on developing a nerve guidance scaffold for its ability to fill and heal the gap between the damaged nerve ends. Such scaffolds are marked by several intrinsic properties including: (1) a biodegradable scaffold or conduit, consisting of native ECM components, with controlled internal microarchitecture; (2) support cells (such as Schwann cells) embedded in a soft support matrix; and (3) sustained release of bioactive factors. In the current dissertation, we have developed such scaffolds of native biomaterials including hyaluronic acid (HA) and collagen. HA is a nonsulphated, unbranched, high-molecular weight glycosaminoglycan which is ubiquitously secreted by cells in vivo and is a major component of extracellular matrix (ECM). High concentrations of HA are found in cartilage tissue, skin, vitreous humor, synovial fluid of joints and umbilical cord. HA is nonimmunogenic, enzymatically degradable, non-cell adhesive which makes HA an attractive material for biomedical research. Here we developed new photopolymerizable HA based materials for soft tissue repair application. First, we developed interpenetrating polymer networks (IPN) of HA and collagen with controlled structural and mechanical properties. The IPN hydrogels were enzymatically degradable, porous, viscoelastic and cytocompatible. These properties were dependent on the presence of crosslinked networks of collagen and GMHA and can be controlled by fine tuning the polymer ratio. We further developed these hydrogel constructs as three dimensional cellular constructs by encapsulating Schwann cells in IPN hydrogels. The hydrogel constructs supported cell viability, spreading, proliferation, and growth factor release from the encapsulated cells. Finally, we fabricated scaffolds of photopolymerizable HA with controlled microarchitecture and developed designer scaffolds for neural repair using layer-by-layer fabrication technique. Lastly, we developed HA hydrogels with unique anisotropic swelling behavior. We developed a dual-crosslinking technique in which a super-swelling chemically crosslinked hydrogel is patterned with low-swelling photocrosslinked regions. When this dual-crosslinked hydrogel is swelled it contorts into a new shape because of differential swelling among photopatterned regions.
Polysaccharide decoration of complexation hydrogel networks for oral protein delivery
(2011-08) Phillips, Margaret Ann; Peppas, Nicholas A., 1948-; Maynard, Jennifer; Roy, Krishnendu; Rylander, H G.; Schmidt, Christine
Polysaccharide-decorated complexation hydrogels were investigated for use as oral insulin delivery systems. Several different polysaccharide modifications of poly(methacrylic acid-grafted-ethylene glycol) hydrogels were developed using dextran and pullulan. Polymerizable groups were added to the polysaccharides, dextran and pullulan, by methacrylation. These macromers were then copolymerized with methacrylic and poly(ethylene glycol) to form P(MAA-g-EG-co-Dextran) and P(MAA-g-EG-co-Pullulan) gels using a UV-initiated free radical polymerization. The synthesis of these materials was confirmed using Fourier transform-infrared spectroscopy. The pH-responsive swelling of these systems was investigated using dynamic and equilibrium swelling measurements. Swelling of polysaccharide-modified hydrogels occurred with increasing pH. In acidic conditions, these materials were in a collapsed state while in neutral conditions these materials were swollen. The ability to load insulin into these hydrogels using was demonstrated with loading efficiencies as high as 88% were observed for P(MAA-g-EG-co-Dextran 6000) hydrogel microparticles. Almost zero release of insulin occurred in acidic conditions while an increase in pH was shown to trigger release. The use of dextran and pullulan-modified complexation hydrogels for oral delivery applications was investigated using in vitro cellular viability assays and mucoadhesion experiments. These systems were shown to cause little cytotoxicity to an intestinal epithelium Caco-2 cell model over a range of concentrations as high as 1 mg/ml. The adherence of polysaccharide-modified hydrogels to reconstitituted mucin gels was quantified with the P(MAA-g-EG-co-Dextran 6000) performing the best. Further evaluation of polysaccharide-modified complexation hydrogels for oral insulin delivery was evaluated through in vitro insulin drug transport studies using a mucus-producing Caco-2/HT29-MTX co-culture model. The results showed that the P(MAA-g-EG-co-Dextran 6000) allowed transport of insulin across the cell monolayers and did not adversely affect the integrity of the epithelial monolayer.
Preferential Control of Forward Reaction Kinetics in Hydrogels Crosslinked with Reversible Conjugate Additions
(2020-05-13) FitzSimons, Thomas M.; Oentoro, Felicia; Shanbhag, Tej V.; Anslyn, Eric V.; Rosales, Adrienne M.
Molecular substitutions were used to demonstrate preferential control over the kinetic rate constants in a poly(ethylene glycol)-based hydrogel with two different reversible thia-conjugate addition reactions. A strong electron withdrawing nitrile group on the conjugate acceptor showed a 20-fold increase in the forward rate constant over a neutral withdrawing group, while the reverse rate constant only increased 6-fold. Rheometry experiments demonstrated that the hydrogel plateau modulus was primarily dictated by reaction equilibrium, while the stress relaxation characteristics of the hydrogel were dominated by the reverse rate constant. Furthermore, the dynamic crosslinking allowed the hydrogel to rapidly and spontaneously self-heal. These results indicate that decoupling the kinetic rate constants of bond exchange allow systematic control over dynamic covalent hydrogel bulk properties, such as their adaptability, stress relaxation ability, and self-healing properties.