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Incorporating chemical functionality into polymer systems allows for material properties and interactions to be more precisely controlled, expanding their scope for use/improvement in biomedical and other applications. In this body of work, several polymer platforms, including polyethylene glycol (PEG)-based hydrogels and thermoplastic polyurethanes (TPUs), are chemically modified with functional reagents, e.g. quaternary ammonium compounds (QACs), and their ability promote specified properties and/or interactions are examined.Post-Fabrication, QAC-Functionalized Thermoplastic Polyurethanes for Contact-Killing Catheter Applications: Catheter-related infections are an estimated $2.3 billion annual burden to the U.S. healthcare system, and result in approximately 28,000 deaths per year. To combat these infections, a TPU containing an allyl ether side-chain functionality (allyl-TPU) that allows for rapid and convenient surface modification with antimicrobial QACs is explored. A series of quaternary ammonium thiol compounds (Qx-SH) possessing various hydrocarbon tail lengths (8 – 14 carbons) are synthesized and attached to the allyl-TPU surface using thiol-ene “click” chemistry, and antimicrobial testing of the QAC-functionalized TPUs reveal that Q8-SH is most effective against various bacteria. A prototype catheter is extruded and functionalized (post-fabrication) with Q8-SH, and biofilm formation tests demonstrate its ability to inhibit biofilm accumulation.Ionomers for Tunable Softening of Thermoplastic Polyurethane: Plasticizer migration and leaching leads to changes in material properties over time and produces environmental concerns. Thermoplastic polyurethane (TPU) sulfonate ionomers with quaternary ammonium counterions are synthesized to achieve soft TPUs without the use of low molecular weight plasticizers. The incorporation of a functional sulfonate monomer containing bulky ammonium counterions along the polymer backbone reduces the durometer hardness of the TPU by interfering with the polar interactions of the hard segment, and disrupting the crystallinity. The synthetic procedure allows for facile tuning of the mechanical properties by increasing both the steric bulk of the counterion the feed ratio of ionic monomer, which decreases the durometer hardness of the TPU. The thermo-mechanical properties for a series of TPU ionomers are evaluated, and a 35-point decrease in the shore A durometer is achieved using a tetradecylammonium counterion at 7.5 mol% incorporation.Control of Mesh Size and Modulus by Kinetically Dependent Cross-linking in Hydrogels: Suitable control substrates are needed to probe the effects of mechano-transduction on stem cell differentiation. To address this, a hydrogel platform that utilizes tetra-polyethylene glycol (PEG) with modified chain ends for control of cross-linking kinetics and affords a range of substrate elasticities while maintaining the chemical composition of the gel is explored. Rheology and SANS experiments are performed to demonstrate how variations in cross-linking kinetics can be used to precisely control the modulus and microstructure of a gel, and the results indicate that increased structural heterogeneity results in lower moduli hydrogels. |
