Browsing by Subject "polyelectrolyte multilayers"
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Item Novel In Situ-Gelling, Alginate-based Composites for Injectable Delivery: Tuning Mechanical and Functional Characteristics(2014-07-24) Roberts, Jason RichardThe development of fully-implantable therapeutic and diagnostic devices represents a new paradigm in biomedical device design. However, designing materials that can perform as injectable matrices for the delivery of sensing and therapeutics chemistries while retaining control over sensor and drug release behaviors is a complex problem. The novel material described herein, microporous alginate composite (MPAC), allows for controllable in situ gelation?and hence enables injection?as well as encapsulation of functional elements such as sensing chemistries or therapeutics. As this material has never been described before, individual component materials, bulk mechanical and gelation properties, and sensing composite response characteristics were examined. The use of polyelectrolyte multilayers (PEMs) in fabrication of MPACs resulted in a porous composite in which macromolecules and nanoparticles were retained within the pores, while allowing for free movement of these materials. Entrapped enzyme molecules were shown to react with diffusing substrates from outside the matrix, confirming the ability of materials from within the pores to interact with small molecules in the local environment. Increasing numbers of PEMs used in composite fabrication was found to result in increased gelation times of hydrogels, while increasing particle concentration reduced gelation times. Changes in pH during MPAC gelation was also dependent on microsphere concentration and PEM numbers. After gelation, MPAC hydrogels immersed in water displayed complex swelling and stiffening behavior dependent on particle concentration and PEM numbers. Oxygen-sensing MPAC hydrogels displayed minor PEM-dependent behavior, while glucose-sensing MPAC hydrogels displayed strong dependence on concentration and PEM numbers. As concentrations increased, sensitivities increased and analytical ranges decreased indicating cooperative behavior among enzyme-containing pores. Utilizing low permeability nanofilms, sensitivities and ranges of sensors could be modulated based upon the number of layers used in fabrication. The development of this new composite system architecture permits an added level of control over injectable hydrogel physical and functional properties such as gelation time and sensor response characteristics. This added control could broaden the usage of alginate as an injectable material and lead to the development of a wide variety of new functional injectable devices.Item Polyelectrolyte Multilayers Containing Polyethylene-based Ionomers(2014-08-14) Huang, Hsiu-ChinLayer-by-Layer (LbL) assembly technique is a powerful approach to blend two or more materials to form new materials of thin films on any type of substrate, and the LbL film is called polyelectrolyte multilayers (PEMs). The assemblies are highly influenced by processing conditions and types of incorporated materials, and their morphology and chemical functionality can be controlled and tunable. The advantages allow people to design films with desired properties for a given application. This study uses linear polyethyleneimine (LPEI) and poly(ethylene-co-methacrylic acid) (EMAA) ionomer as main materials. EMAA ionomer is a commercial material known as Surlyn having ethylene as the major component, and dissolved in THF at 65? but becomes a colloidal dispersion when temperature goes down to room temperature. Water soluble LPEI solution has a large and changeable range of ionization degree by adjusting the solution pH, which also changes chain conformation. Oppositely, the ionomer has a low content of charged carboxylic acid groups, only 1.62 mole %, resulting in energetically favorable aggregation of ionic species. This study focuses on complexing the polymers having a drastically large difference in terms of ionization degree using LbL technique at a mixed THF-water solvent system. Via electrostatic interactions between LPEI and EMAA ionomers, the blends are successfully fabricated. Thermal, mechanical, and surface properties of the PEMs are investigated. For thermal properties, a new endothermic peak created in PEMs according to results of DSC overlaps with order-disorder transition peak and melting point of ionomer, resulting in an increase of latent energy. The interactions between the materials influence mechanical behavior; the PEMs exhibit higher stiffness and tensile strength, and are still tough. The most interesting and impressive performance of the blends is surface properties. Micro-sized holes and nano-scale structures (hierarchical morphology) found on the surfaces of LbL assemblies by SEM make the films very hydrophobic and superoleophilic to allow the films to separate water out from an oil-water emulsion. The film surfaces also show rose petal effect to pin water droplet of a high volume even though the surface is turn up side down. The work is the first demonstrator to use EMAA ionomers as a material in the LbL system. Many basic properties of the new complex are investigated and characterized, and these results are believed to benefit the development of novel materials in the future.