Date of Award
Doctor of Philosophy (PhD)
Biomedical and Chemical Engineering
biomaterials;Biomedical;liquid crystalline;materials;Shape-Memory Polymers
The overall objective of this work was to expand on the previous efforts carried out by other researchers to develop series of "smart" or stimulus-responsive shape-memory polymers for biomaterials applications. For this purpose, novel shape-memory polymers were fabricated and their macrostructure and microstructure were studied to understand their effects on overall shape-memory characteristics and mechanical properties of these materials. The advent of shape-memory polymers has significantly influenced the development and rapid growth of various functional polymers. Shape-memory polymers are used where the dynamic functions of polymers under an applied stimulus are required, and they find applications as catheters, sutures, drug delivery systems, and scaffolds in tissue regeneration, as well as aerospace applications. Each of these applications demands materials with unique chemical, physical, and mechanical properties to provide efficient functions. Consequently, a wide range of shape-memory polymers have been developed and investigated for these applications, but more research is required to optimize the overall property and function of these polymers. Furthermore, recent advances in the field of polymer science and shape-memory polymers, coupled with the novel characterization methods, necessitate the development of novel functional polymers for specific applications. This dissertation highlights various polymeric materials currently investigated for use in applications requiring shape-memory polymers. Chapter 1 gives an overview of biomaterials along with a background on shape-memory polymers. In the first case described in Chapter 2, epoxy-based triple shape-memory composites (TSMCs) were investigated, and the poly(ε-caprolactone) (PCL) compositional effect on triple shape-memory behavior was explored using heat and water stimuli. The TSMCs were developed using PIPS to achieve particle/matrix morphology. In Chapter 3, two newly TSMCs, one featuring a semicrystalline epoxy and the other featuring an amorphous epoxy, were explored, and the relationships between the morphology of TSMCs and their shape-memory characteristics were studied. Chapter 4 focuses on studying the effect of morphology on shape-memory behavior. This study reveals the effect of particle/matrix and co-continuous fiber/matrix morphology on triple shape-memory behavior of polymers with similar compositions. The knowledge, which was built upon the results of Chapter 2 through 4, would help in optimization of design strategy used for fabrication of triple shape memory polymers with enhanced shape fixing and recovery. In Chapter 5, an innovative "smart" anisotropic polymeric hydrogel was introduced which can be activated using hydration. The developed anisotropic hydrogel forms helicoids in response to hydration; and the dependence of the radius of curvature and the pitch of the formed helicoids on fiber angle orientation and thickness of hydrogel composites was evident. In Chapters 6 and Chapter 7, another class of shape memory polymers was investigated: liquid crystalline elastomer. Chapter 6 focuses on a new design strategy for fabrication of a hydrogel-forming liquid crystalline elastomer that exhibited soft shape memory properties in response to thermal and water stimuli. This approach involved incorporating liquid crystalline mesogens into the polymer networks to fabricate unique materials. The effect of liquid crystalline mesogens on thermal, mechanical, and shape memory performance of these unique materials was studied. Chapter 7 focuses on epoxy based liquid crystalline elastomers. Similar to Chapter 6, it was confirmed that unique and responsive smart materials can be fabricated using liquid crystalline mesogens. In this study, a better route to synthesize LCEs, based on epoxy chemistry with amenability to open air and catalyst-free synthesis, was introduced. Finally in Chapter 8, another class of responsive smart polymers: near infrared fluorescence shape memory web containing indocyanine green dye, was investigated. This approach presents a new design strategy, for incorporate dyes uniformly without manipulating their properties, to fabricate polymers with unique imaging and shape memory characteristics. For this study, incorporation of ICG dye into PVAc polymer was achieved using the electrospinning technique, yielding near infrared fluorescence polymeric material with high fluorescence intensity and uniform dye incorporation. All the aforementioned polymeric materials have great potentials for different applications and can significantly influence the growth and development of new biomaterials and medical devices. Chapter 9 discusses the conclusions and provides recommendations for future research and development for each chapter of the dissertation.
Torbati, Amir Hossein, "Soft Shape-memory Polymers As A Platform For Biomedical Applications" (2014). Dissertations - ALL. 1824.