Snelling, Diana Kathryn
01 September 2010
Biodegradable, pH-responsive hydrogel networks composed of poly(methacrylic acid) crosslinked with varying mol percentages of polycaprolactone diacrylate were synthesized. These materials were characterized using NMR and FTIR. The equilibrium and dynamic swelling properties of these pH-responsive materials were studied. Also, the materials’ degradation was characterized using swelling studies and gel permeation chromatography. Methods were developed to incorporate these novel hydrogels as sensing components in silicon-based microsensors. Extremely thin layers of hydrogels were prepared by photopolymerizion atop silicon microcantilever arrays that served to transduce the pH-responsive volume change of the material into an optical signal. Organosilane chemistry allowed covalent adhesion of the hydrogel to the silicon beam. As the hydrogel swelled, the stress generated at the surface between the hydrogel and the silicon caused a beam deflection downward. The resulting sensor demonstrated a maximum sensitivity of 1nm/4.5E-5 pH unit. Sensors were tested in protein-rich solutions to mimic biological conditions and found to retain their high sensitivity. The existing theory was evaluated and developed to predict deflection of these composite cantilever beams. Another type of hydrogel-based microsensor was fabricated utilizing porous silicon rugate filters as transducers. Porous silicon rugate filters are garnering increased attention as components of in vivo biosensors due to their ability for remote readout through tissue. Here, the biodegradable, pH-responsive hydrogel was polymerized within the pores of a porous silicon rugate filter to generate a novel, completely degradable sensor. Silicon was electrochemically etched in hydrofluoric acid to generate the porous silicon rugate filter with its reflectance peak in the near infrared region. Poly(methacrylic acid) crosslinked with polycaprolactone diacrylate was polymerized within the pores using UV free radical photopolymerization. The reflectance peak of this sensor varied linearly with pH in the region pH 2.2 to 8.8. This work shows promise towards utilizing porous silicon rugate filters as transducers for environmentally responsive hydrogels for biosensing applications. / text
08 January 2007
This dissertation is aimed towards using stimuli-responsive pNIPAm-co-AAc microgels synthesized via free-radical precipitation polymerization to prepare stimuli-responsive hydrogel microlenses. Chapter 1 gives a detailed background of hydrogels, and their applications using responsive hydrogels. Chapter 2 describes the use of colloidal hydrogel microparticles as microlens elements and the fabrication method to form the hydrogel microlens arrays via Coulombic interactions. Chapter 3 shows the demonstration of tunable microlenses prepared by the method used in Chapter 2. In this chapter the microlenses are subjected to various pH and temperature in aqueous solutions. Chapter 4 describes that the microlens arrays constructed on Au nanoparticle-functionalized glass substrates by self-assembly display dramatic changes in lensing power in response to an impingent frequency-doubled Nd:YAG laser. The microlens photoswitching is highly reversible, with sub-millisecond lens switching times. Chapter 5 describes the development of bioresponsive hydrogel microlenses as a new protein detection technology. The microlens method is shown to be very specific for the target protein, with no detectable interference from nonspecific protein binding. Chapter 6 describes the use of bioresponsive hydrogel microlenses as a label-free biosensing scaffolding. These microstructures simultaneously act as the biosensors scaffolding/immobilization architecture, transducer, amplifier, and also allow for broad tunability of the analyte concentration to which the microlens is sensitive.
Williams, Eva Christabel
01 January 2012
Localized drug delivery is emerging as an effective technique due to its ability to administer therapeutic concentrations and controlled release of drugs to cancer sites in the body. It also prevents the contact of harsh chemotherapy drugs to healthy regions in the body that otherwise would become exposed to current treatments. This study reports on a model chemotherapy drug delivery system comprising non-ionic surfactant vesicles (niosomes) packaged within a temperature-sensitive chitosan network. This smart packaging, or package-within-a package system, provides two distinct advantages. First, the gel prevents circulation of the niosomes and maintains delivery in the vicinity of a tumor. Secondly, the chitosan network protects the niosomes against fluctuations in tonicity, which affects delivery rates. Tonicity is the sum of the concentrations of the solutes which have the capacity to exert an osmotic force across the membrane. Release rates were monitored from both bare niosomes alone and niosome-embedded, chitosan networks. It was observed that chitosan networks prolonged delivery from 100 hours to 55 days in low ionic strength environment and pH conditions similar to a tumor site. The primary effect of chitosan is to add control on release time and dosage, and stabilize the niosomes through a high ionic strength surrounding that prevents uncontrolled bursting of the niosomes. Secondary factors include cross-link density of the chitosan network, molecular weight of the individual chitosan polymers, dye concentration within the niosomes, and the number density of niosomes packaged within the chitosan network. Each of these factors can be altered to fine-tune release rates. Release rate experiments were conducted with 5,6-carboxyfluorescein, a fluorescent dye and chemotherapeutics paclitaxel and carboplatin. In vitro studies showed a preferential affinity of the smart packaged system to ovarian carcinoma cell line OV2008 as compared to normal epithelial cell lines of Ilow and MCC3. Further, feasibility of the drug delivery system was evaluated in vivo. Toxicity studies revealed that the system was non-toxic and feasible in vivo. The final outcome of this study includes tuning of the variables mentioned above that will contribute to the development of low cost and improved methods for drug delivery with application to intracavitary ovarian cancer treatment and other types of cancer
This master thesis aimed to create and characterize multilayer coatings upon mesoporous silica particles (MSP). The properties of the coating aimed for, was to have a triggerable controlled release, where a targeted enzyme within the intestine, alpha-amylase, is supposed to degrade the coating. The coating was created from a bilayer consisting of DOTAP and DOPC in a 1:3 molar ratio, which serves as a protective coating. The second layer interacting with the surroundings consisted of a starch component, amylopectin, which is degraded by alpha-amylase. The study of the coating was performed with ellipsometry, where the adsorption of the different layers of the coating on a planar silica surface and the enzyme-triggered degradation was recorded. The adsorbed amount of DOTAP/DOPC was 4,22 ± 0,11 mg/m2 and amylopectin 1,82 ± 0,94. The effects of different pH where performed, simulating the coated particle going through the gastro-intestinal system. Two enzymes alpha-amylase and phospholipase A2 (PLA2) where used for degradation of the coating. The knowledge from ellipsometry was applied to coating mesoporous silica particles and it was confirmed that the two layers had formed with zeta- potential measurement.
DEVELOPMENT OF NOVEL TEMPERATURE RESPONSIVE POLYMERIC SORBENTS AND THEIR APPLICATIONS IN WATER REMEDIATIONTang, Shuo 01 January 2019 (has links)
Water remediation utilizing sorption has found strong interest due to its inexpensiveness, universal nature and ease of operation. In particular, thermo-responsive sorbents consisting of N-isopropylacrylamide (NIPAAm) offer significant potential as “smart” and advanced materials to remove multiple aqueous pollutants. NIPAAm exhibits excellent thermo-responsiveness, which senses the external temperature variation and changes its swelling and sorption behaviors in a sharp and rapid manner. At the beginning of this work, an extensive review of literature has been compiled to provide a summary of NIPAAm-based thermo-responsive sorbents in water/wastewater remediation applications. Initially, we developed a novel approach to synthesize and characterize NIPAAm copolymeric hydrogels. Four different polyphenolic crosslinkers including curcumin multiacrylate (CMA), quercetin multiacrylate (QMA), 4,4’-dihydroxybiphenyl diacrylate (44BDA) and chrysin multiacrylate (ChryMA) were successfully incorporated into crosslinked hydrogels. Their temperature responsiveness and lower critical solution temperature (LCST) were characterized using swelling studies and differential scanning calorimetry (DSC). Increasing the crosslinker content resulted in a significant decrease in the swelling ratio and LCST, which was due to the increased crosslinking and hydrophobicity introduced by the polyphenolic crosslinkers. We also demonstrated the application of two sets of aforementioned crosslinked hydrogels (NIPAAm-co-CMA and NIPAAm-co-44BDA) as effective gel sorbents to capture phenol as a model contaminant. Temperature-dependent sorption was evaluated through a binding study of phenol at 10°C and 50°C. Significant enhancement in the sorption was observed at 50°C, and this can be attributed to the phase transition induced hydrophobic interactions between the copolymer gel and phenol. Moreover, the obtained hydrogels possessed facile and efficient regeneration ability in water at 10°C, without requiring harsh solvent treatment or high energy input. Building on the sorption behavior observed with crosslinked NIPAAm hydrogels, we extended the investigation to linear copolymer systems, and these were demonstrated as a temperature responsive flocculants. Here, NIPAAm copolymers consisting of 2-phenylphenol monoacrylate (2PPMA) were successfully developed as smart flocculants to remove metal oxide nanoparticles (e.g., Fe3O4, CeO2, TiO2). The incorporation of 2PPMA enhanced the flocculation at temperatures above the LCST (e.g., 50°C), which was due to the combined hydrophobicity of 2PPMA and NIPAAm. Overall, NIPAAm-based sorbents have a variety of applications in aqueous pollutant removal and are a promising class of materials for cost-effective water remediation technology.
Mechanical and Tribological Study of a Stimulus Responsive Hydrogel, pNIPAAm, and a Mucinous Glycoprotein, LubricinChang, Debby Pei-Shan January 2009 (has links)
<p>Friction is the resistive force that arises when two contacting surfaces move relative to each other. Frictional interactions are important from both engineering and biological perspectives. In this research I focus on the fundamental understanding of friction on polymeric and biological surfaces in aqueous environments. First, I examine the frictional properties of a stimulus-responsive hydrogel, poly-N-isopropylacrylamide (pNIPAAm), to understand how different phase states affect its tribological properties. My measurements indicate that gels in a collapsed conformation at low shear rates, exhibit significantly larger friction than swollen gels. These differences arise from changes in surface roughness, adhesive interactions, and chain entanglements of the gel surfaces associated with the phase transition. Importantly, I show that the changes in friction, triggered by an external stimulus, are reversible. </p><p>Second, I examine details of the boundary lubrication mechanism involved in mediating friction and wear in diarthrodial joints. Specifically, I looked at the constituents of the synovial fluid, lubricin and hyaluronic acid (HA) and examined their interactions on model substrates, (1) to determine the effect of surface chemistry on adsorption using surface plasmon resonance (SPR), and (2) to study normal force interactions between these surfaces using colloidal probe microscopy (CPM). I found that lubricin is highly surface-active, adsorbed strongly onto hydrophobic, hydrophilic and also collagen surfaces. Overall, lubricin develops strong repulsive interactions. This behavior is in contrast to that of HA, which does not adsorb appreciably, nor does it develop significant repulsive interactions. I speculate that in mediating interactions at the cartilage surface, an important role of lubricin is one of providing a protective coating on cartilage surfaces that maintains the contacting surfaces in a sterically repulsive state.</p> / Dissertation
Akintewe, Olukemi O.
01 January 2015
Scaffold based tissue reconstruction inherently limits regenerative capacity due to inflammatory response and limited cell migration. In contrast, scaffold-free methods promise formation of functional tissues with both reduced adverse host reactions and enhanced integration. Cell-sheet engineering is a well-known bottom-up tissue engineering approach that allows the release of intact cell sheet from a temperature responsive polymer such as poly-N-isopropylacrylamide (pNIPAAm). pNIPAAm is an ideal template for culturing cell sheets because it undergoes a sharp volume-phase transition owing to the hydrophilic and hydrophobic interaction around its lower critical solution temperature (LCST) of 32°C, a temperature close to physiological temperature. Compared to enzymatic digestion via trypsinization, pNIPAAm provides a non-destructive approach for tissue harvest which retains its basal surface extracellular matrix and preserves cell-to-cell junctions thereby creating an intact monolayer of cell sheet suitable for tissue transplantation. The overall thrust of this dissertation is to gain a comprehensive understanding of how tissue precursors are formed, harvested and printed from interactions with shape-changing pNIPAAm hydrogel. A simple geometrical microbeam pattern of pNIPAAm structures covalently bound on glass substrates for culturing mouse embryonic fibroblast and skeletal myoblast cell lines is presented. In order to characterize the cell-surface interactions, three main investigations were conducted: 1) the mechanism of cell detachment; 2) the feasibility of micro-contact printing tissue precursors onto target surfaces; and 3) the assembly of these tissues into three-dimensional (3D) constructs. Detachment of cells from the shape-changing hydrogel was found to correlate with the lateral swelling of the microbeams, which is induced by thermal activation, hydration and shape distortion of the patterns. The mechanism of cell detachment was primarily driven by strain, which occurred almost instantaneously above a critical strain of 25%. This shape-changing pNIPAAm construct allows water penetration from the periphery and beneath the attached cells, providing rapid hydration and detachment within seconds. Cell cultured microbeams were used as stamps for micro-contact printing of tissue precursors and their viability, metabolic activity, local and global organization were evaluated after printing. The formation and printing of intact tissues from the shape-changing hydrogel suggests that the geometric patterning of pNIPAAm directs spatial organization through physical guidance cues while preserving cell functioning. Tissue precursors were sequentially assembled into parallel and perpendicular configurations to demonstrate the feasibility of constructing dense tissues with different organizations such as interconnected cell lines that could induce vascularization to solve perfusion issues in regenerative therapies. The novel approach presented in this dissertation establishes an efficient method for harvesting and printing of tissue precursors that may be applicable for the modular, bottom up construction of complex tissues for organ models and regenerative therapies.
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