Dissertation
Development of crystalline and polymeric materials for stimuli-responsive and biomedical applications
University of Iowa
Doctor of Philosophy (PhD), University of Iowa
Spring 2023
DOI: 10.25820/etd.007062
Abstract
Crystal engineering is important for the design of materials and devices with targeted physical properties. Control of crystal size, morphology, and intermolecular interactions of the lattice, dynamic and static, enables precise engineering of the material’s bulk properties such as adsorption, bioavailability, or elasticity using reversible chemical bonds. For example, the crystal packing and hence the crystallite size may be modified by altering the synthesis conditions or including a modulator without creating or breaking covalent bonds. Such atomic and nanoscale modifications in turn significantly affected the adsorption and mechanical properties of one class of absorbent material, soft porous crystals such as metal-organic frameworks (MOFs), used in a variety of applications in fluid separation and chemical sensing due to their modularity and high selectivity.
This thesis represents the first study to demonstrate size-dependent mechanical properties of MOFs, determined by atomic force microscopy (AFM) nanoindentation. The results showed that reducing crystal size to the nanoscale can result in increased or decreased Young’s modulus depending on the system under study. The observed change in mechanical properties explains previously reported size-dependent variations in gas adsorption of ZIF-8. The study demonstrates how downsizing crystalline metal-organic materials can lead to specific and adjustable physical properties. We also show how a combination of techniques including AFM nanoindentation, scanning electron microscopy energy dispersive X-ray spectroscopy, IR spectroscopy, and gas physisorption analysis can enable correlations between intermolecular structure, bulk elasticity, and the gas adsorption behavior of materials. Using highly basic triethylamine during the synthesis of ZIF-8 leads to a lower number of interframework hydrogen bonds and a higher number of missing linker defects, which play an integral role in the observed mechanical and gas adsorption anomalies.
The thesis also demonstrates that the size-dependent mechanical phenomena are widespread across a broad category of MOFs. Soft porous nanocrystals of the structure [Cu2(bdc)2(bpy)]n with a shape-memory effect have been shown to exhibit a significant increase in elastic modulus when compared to their microcrystalline counterparts. These findings suggest that crystal downsizing is a promising strategy for tailoring the mechanical properties of MOFs, opening new avenues for their use in a variety of applications.
Moreover, a novel AFM nanoindentation methodology is developed to determine the hardness of nanomaterials. The technique is developed on nanocrystals of acetylsalicylic acid using atomic force microscopy (AFM) nanoindentation. The results show that the nanocrystals exhibited a transition from elastic to plastic deformation, and the values of Young’s modulus and hardness for aspirin nanocrystals were found to be approximately 3 GPa and 0.3 GPa, respectively. This study highlights the successful implementation of the AFM nanoindentation technique in accurately determining the hardness of nanomaterials at sub 100 nm indentations.
Related to biomedical defense applications, we discuss the challenge of maintaining dental and medical readiness in the military due to dental caries. To combat this issue, dental restoratives are a simple and effective solution and can be used as self-applied first aid. The study aims to evaluate the shear bond strength of two dental restorative materials to human teeth with two different fluoride treatments, as well as the hardness and biofilm formation on teeth after fluoride varnish application. The findings indicate that the combination of silver diamine fluoride with light cured methacrylate dental resins and resin-modified glass ionomer cements is a promising treatment option for dental caries in military settings.
Intermolecular interactions are the fabric of co-crystals formed from two or more molecules. Pharmaceutical co-crystals offer enhanced drug properties and multimodal capability by stabilizing one or more active pharmaceutical ingredient (API) with co-crystal formers (coformers) in the solid state. Varying the coformers of the target API(s) allows the control of noncovalent interactions (e.g., hydrogen bonds, π-effects, electrostatic forces) between atoms in the co-crystal lattice. Increased quantity and magnitude of intermolecular forces in the co-crystal compared to the individual component leads to increased stability, bioavailability, and controllable release of API. Here, we develop an approach to developing a topical form of tranexamic acid (TXA) in the form of a cocrystal. Four different cocrystals of TXA were synthesized and the coformers tested for their individual contribution to cytotoxicity and antimicrobial activity. The 1:1 cocrystal of TXA and gallic acid (GAA) was found to be a promising candidate for drug development due to its ability to induce blood clot formation and enhanced antibacterial activity. An optimized form of the TXA-GAA cocrystal has the potential to be incorporated into a solid form for use in a topical medical device, providing slow or extended release of the API.
Details
- Title: Subtitle
- Development of crystalline and polymeric materials for stimuli-responsive and biomedical applications
- Creators
- Aladen Tiba
- Contributors
- Leonard R MacGillivray (Advisor)Alexei V Tivanski (Advisor)Ned B Bowden (Committee Member)F Christopher Pigge (Committee Member)Lewis L Stevens (Committee Member)
- Resource Type
- Dissertation
- Degree Awarded
- Doctor of Philosophy (PhD), University of Iowa
- Degree in
- Chemistry
- Date degree season
- Spring 2023
- Publisher
- University of Iowa
- DOI
- 10.25820/etd.007062
- Number of pages
- xvii, 120 pages
- Copyright
- Copyright 2023 Aladen Tiba
- Language
- English
- Date submitted
- 04/24/2023
- Date approved
- 06/30/2023
- Description illustrations
- illustrations, graphs
- Description bibliographic
- Includes bibliographical references (pages 108-120).
- Public Abstract (ETD)
- Recent interest in nanomaterials, which are one billionth of a meter in size, has been fueled by their size-dependent physical and chemical properties, making them valuable for biomedical, pharmaceutics, electronics, and energy science applications. However, it is not possible to study the properties of larger materials and then apply them to the nanoscale, as size reduction to the nanoscale can result in remarkably different properties. As a result, there is a need for nanoscale studies that measure and manipulate these unique properties and correlate them to their atomic structures. Due to the inherent size limitations of nanomaterials, traditional macroscopic methods cannot be employed. Atomic force microscopy (AFM) is a versatile microscopic technique that can be used to visualize and quantify the size and shape of nanomaterials. The AFM can also measure and apply extremely small forces or currents to nanomaterials, enabling investigation of physical properties like elasticity and conductivity, and novel approaches for measuring interactions between extended structures to predict their behavior during gas adsorption or in device applications. In this context, we have investigated the mechanical properties of various porous materials across different size ranges, including metal-organic frameworks of various chemical structures. We have also developed a method for accurately determining the hardness and yield strength of nanomaterials, which traditionally requires probing a bulk material. When several experimental methods are combined, novel correlations between bulk properties and nanostructure can be determined and used to guide functional applications of important materials.
- Academic Unit
- Chemistry
- Record Identifier
- 9984428940102771
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