No description available.

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Materials science today is a multidisciplinary effort comprising an accelerated convergence of diverse fields spanning the physical, applied, and engineering sciences. This diversity promises to deliver the next generation of advanced functional materials for a wide range of specific applications. In particular, the past decade has seen a growing interest in the development of nanoscale materials for sophisticated technologies. Aqueous colloidal microgels have emerged as a promising class of soft materials for multiple biotechnology applications. The amalgamation of physical, chemical and mechanical properties of microgels with optical properties of nanostructures in hybrid composite particles further enhances the capabilities of these materials. This work covers the general areas of responsive polymer microgels and their composites, and encompasses methods of fabricating microgel-based drug delivery systems for controlled and targeted therapeutic applications. The first part of this thesis is devoted to acquainting the reader with the fundamental aspects of the synthesis, functionalization and characteristic properties of stimulus-responsive microgels constructed from poly(N-isopropylacrylamide) (poly(NIPAm)) and other functional comonomers. In particular, the role of electrostatics on the swelling-deswelling transitions of polyampholyte microgels upon exposure to a range of environmental stimuli including pH, temperature, and salt concentration are discussed. The templated synthesis of bimetallic gold and silver nanoparticles in zwitterionic microgels is also described. The latter part of this thesis focuses on the rational development of microgel-based drug delivery systems for controlled and targeted drug release. Specifically, the development of a biofunctionalized, pH-responsive drug delivery system (DDS) is illustrated, and shown to effectively suppress cancer cells when loaded with an anticancer agent. In another chapter, the design of tailored hybrid particles that combine the thermal response of microgels with the light-sensitive properties of gold nanorods to create a DDS for photothermally-induced drug release is discussed. The photothermally-triggered volume transitions of hybrid microgels under physiological conditions are reported, and their suitability for the said application evaluated. In another component of this work, it is explicitly shown that electrostatic interactions were not needed to deposit gold nanorods on poly(NIPAm)-derived particles, thereby eliminating the need for incorporation of charged functional groups in the microgels that are otherwise responsible for large, undesirable shifts and broadening of the phase transition.

<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

Materials science today is a multidisciplinary effort comprising an accelerated convergence of diverse fields spanning the physical, applied, and engineering sciences. This diversity promises to deliver the next generation of advanced functional materials for a wide range of specific applications. In particular, the past decade has seen a growing interest in the development of nanoscale materials for sophisticated technologies. Aqueous colloidal microgels have emerged as a promising class of soft materials for multiple biotechnology applications. The amalgamation of physical, chemical and mechanical properties of microgels with optical properties of nanostructures in hybrid composite particles further enhances the capabilities of these materials. This work covers the general areas of responsive polymer microgels and their composites, and encompasses methods of fabricating microgel-based drug delivery systems for controlled and targeted therapeutic applications. The first part of this thesis is devoted to acquainting the reader with the fundamental aspects of the synthesis, functionalization and characteristic properties of stimulus-responsive microgels constructed from poly(N-isopropylacrylamide) (poly(NIPAm)) and other functional comonomers. In particular, the role of electrostatics on the swelling-deswelling transitions of polyampholyte microgels upon exposure to a range of environmental stimuli including pH, temperature, and salt concentration are discussed. The templated synthesis of bimetallic gold and silver nanoparticles in zwitterionic microgels is also described. The latter part of this thesis focuses on the rational development of microgel-based drug delivery systems for controlled and targeted drug release. Specifically, the development of a biofunctionalized, pH-responsive drug delivery system (DDS) is illustrated, and shown to effectively suppress cancer cells when loaded with an anticancer agent. In another chapter, the design of tailored hybrid particles that combine the thermal response of microgels with the light-sensitive properties of gold nanorods to create a DDS for photothermally-induced drug release is discussed. The photothermally-triggered volume transitions of hybrid microgels under physiological conditions are reported, and their suitability for the said application evaluated. In another component of this work, it is explicitly shown that electrostatic interactions were not needed to deposit gold nanorods on poly(NIPAm)-derived particles, thereby eliminating the need for incorporation of charged functional groups in the microgels that are otherwise responsible for large, undesirable shifts and broadening of the phase transition.

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Mechanical stimulation plays a crucial role in promoting cell differentiation. However, applying physical force directly to cells requires complex equipment and a sterile environment, posing challenges. To overcome this, stimuli-responsive biomaterials or 4D scaffolds can serve as an alternative platform for mechanical stimulation. These scaffolds, fabricated using advanced 3D printing techniques, can apply the necessary force to cells. To optimize their functionality, bioactive molecules or extracellular matrices can be incorporated or decorated on their surfaces. This thesis proposal focuses on developing a versatile material platform that allows customization through systematic composition adjustment and on-demand printing, while also offering surface modification capabilities. The primary objective is to create a novel cell carrier platform using thermo-responsive polymers. By manipulating the additive monomer compositions, we can finely adjust properties such as the transition temperature of the polymers, tailoring them to specific requirements. Furthermore, this platform will enable the fabrication of complex three-dimensional biomaterial structures with controllable porosity, a critical aspect of biomaterial design. Leveraging the capabilities of three-dimensional printing technology, we can program and achieve desired porosity levels in the printed structures, providing enhanced flexibility for biomaterial design. The development of thermo-responsive scaffolds involved three distinct stages aimed at designing an optimized platform that effectively operates within the physiological range while ensuring cell viability. One of the key challenges was to achieve a balance between thermoresponsive behavior and biocompatibility. In the initial stage, we investigated the interplay between a crosslinkable three-armed macromer (trimethylolpropane triacrylate-TMPTA) and various monomers (N-isopropylacrylamide-NiPAAm, methyl methacrylate-MMA, dimethylaminoethyl acrylate-DMAEA, 4-acryloylmorpholine-AMO) using thermally induced solution polymerization. NiPAAm, known for its thermoresponsive properties, was selected despite its limited biocompatibility. DMAEA was chosen to adjust the polymer network transition temperature by introducing cationic charge, which disrupts the coil-globule effect of PNiPAAm and provides cell adhesiveness of the composition. Additionally, the hydrophilic monomer AMO was incorporated to further fine-tune the polymeric network. We examined the behavior of these components within the physiological range and their integration into the PNiPAAm network, establishing significant correlations between the transition temperature of the polymer and the crosslinker and monomers in their soluble condition. In the second stage of our research, we introduced photo-induced polymerization to enhance the crosslinking ratio. By utilizing this method, we successfully fabricated photo-polymerized mixtures (photoresists) into thermo-responsive discs, enabling us to study their swelling behavior between 37℃ and 25℃. Our findings revealed that the swelling behavior could be adjusted by varying the ratios of the crosslinker and monomers in the experimental groups. Through careful experimentation, we identified a suitable composition (3% w/w TMPTA, 80% w/w NiPAAm, 15% w/w DMAEA, 5% w/w AMO, and 4% w/w photo-initiator(PI)) that required minimal crosslinking incorporation while still retaining thermo-responsiveness. Furthermore, we conducted a preliminary biocompatibility study by fabricating the mixture into thin-films and cultivating them with L929 fibroblast cells. In the third and final stage, we utilized the optimized formulations from the previous stage to build thermo-responsive 3D scaffolds using continuous Digital Light Processing (cDLP) printing. We investigated the effects of various parameters, such as curing time and monomer composition, on the swelling property of the scaffolds. Additionally, we introduced glycofurol (GF) as a photo-polymerization solvent, which allowed us to produce scaffolds with improved resolution and reduced printing time. The resulting optimized scaffolds, with a composition of 3% w/w TMPTA, 80% w/w NiPAAm, 15% w/w DMAEA, 5% w/w AMO, 4% w/w PI, and 10 seconds per layer, exhibited the desired thermo-responsiveness. To further understand the mechanical properties and thermal dependencies of these scaffolds, we conducted rheological analysis. This analysis helped establish a relationship between the mechanical properties of the scaffolds and their response to temperature changes. To investigate the potential of cell stimulation through periodic changes, we conducted an experiment involving the seeding of L929 fibroblasts and C2C12 myoblasts on thermo-responsive 3D scaffolds. Our objective was to assess the ability of cells to proliferate on scaffolds with different compositions. Specifically, we examined two types of scaffolds: lattice scaffolds, characterized by a porous structure with a periodic network that enables cells to inhabit a 3D environment, and raft scaffolds, which feature a dense 3D structure designed for cells to reside on the surface for observation and evaluation. The lattice scaffolds were composed of ≥2% w/w DMAEA, while the raft scaffolds consisted of ≥5% w/w DMAEA. To evaluate cell proliferation, we conducted direct contact experiments and employed live/dead assays, subjecting the scaffolds to temperature switching conditions at 31℃ and 37℃. These experimental setups aimed to provide insights into the response and behavior of cells in the presence of thermo-responsive scaffolds with varying compositions. The results revealed favorable adhesion and spreading of the cells on the scaffolds. Interestingly, in our dynamic temperature experiment, we observed that myoblasts seeded on the scaffolds exhibited both proliferation and spreading, whereas myoblasts subjected to constant-temperature conditions did not show the same behavior. This suggests that the expansion and contraction of the scaffold, observed in previous experiments, may impact cell viability. Further investigation is needed to better understand this phenomenon. Additionally, we enhanced cell adhesiveness of the scaffolds by impregnating the scaffolds with poly-L-lysine and tested them with hASCs (human adipose-derived stem cells). Significant differences were observed between scaffolds with and without poly-L-lysine, highlighting the effectiveness of this approach. In conclusion, we have successfully developed a thermo-responsive 3D scaffold that exhibits a transition temperature within the physiological range, ensuring cell survival, and provides mechanical stimulation to the cells through the coil-globule effect without causing cell detachment. Among the formulations tested, the GF-printed formulation (3% w/w TMPTA, 80% w/w NiPAAm, 15% w/w DMAEA, 5% w/w AMO, and 4% w/w photo-initiator) with an exposure time of 10 seconds per layer showed the most promising results for cell cultivation under periodic changes in temperature, with a transition temperature of 36.3 °C ± 0.9 °C. Furthermore, we conducted direct cell contact experiments and confirmed the biocompatibility of the thermo-responsive macromer-based scaffolds. These findings demonstrate that this material platform offers a versatile and responsive material for mechanical stimulation of cells on three-dimensional scaffolds. These promising results suggest that this approach holds significant potential for tissue engineering applications and can be utilized to develop mechanical stimulation devices for various biomedical applications.:CHAPTER 1……………………..……………...…………………………..…4 Introduction CHAPTER 2……………………..…………………………..……………….29 Material and Methods CHAPTER 3……………………………………..…..……………………….52 Thermo-Responsive Polymer from Thermal Synthesis Studies CHAPTER 4…………………………………..……………………………...70 An Adjustable Thermo-Responsive Polymer from Photo Synthesis CHAPTER 5……………………………………………………………....….88 Fabrication of Thermo-Responsive Scaffolds from DLP Printing CHAPTER 6…………………...…………………………………………....107 3D Scaffold Biocompatibility Studies CHAPTER 7…………………...……………………………………………139 Discussions CHAPTER 8…………………...……………………………………………161 Summery APPENDIX…………………...………………………………………….…166 Bibliography, List of Publications, CV, Declaration of Authorship, Acknowledgements, Related publication

Protein therapeutics offer numerous advantages over small molecule drugs and are rapidly becoming one of the most prominent classes of therapeutics. Unfortunately, they are delivered almost exclusively by injection due to biological obstacles preventing high bioavailability via the oral route. In this work, numerous approaches to overcoming these barriers are explored. PH-Responsive poly(itaconic acid-co-N-vinylpyrrolidone) (P(IA-co-NVP)) hydrogels were synthesized, and the effects of monomer ratios, crosslinking density, microparticle size, protein size, and loading conditions were systematically evaluated using in vitro tests. P(IA-co-NVP) hydrogels demonstrated up to 69% greater equilibrium swelling at neutral conditions than previously-studied poly(methacrylic acid-co-N-vinylpyrrolidone) hydrogels and a 10-fold improvement in time-sensitive swelling experiments. Furthermore, P(IA-co-NVP) hydrogel microparticles demonstrated up to a 2.7-fold improvement in delivery of salmon calcitonin (sCT) compared to methacrylic acid-based systems, with a formulation comprised of a 1:2 ratio of itaconic acid to N-vinylpyrrolidone demonstrating the greatest delivery capability. Vast improvement in delivery capability was achieved using reduced ionic strength conditions during drug loading. Use of a 1.50 mM PBS buffer during loading yielded an 83-fold improvement in delivery of sCT compared to a standard 150 mM buffer. With this improvement, a daily dose of sCT could be provided using P(IA-co-NVP) microparticles in one standard-sized gel capsule. P(IA-co-NVP) was also tested with larger proteins urokinase and Rituxan. Crosslinking density provided a facile method for tuning hydrogels to accommodate a wide range of protein sizes. The effects of protein PEGylation were also explored. PEGylated sCT displayed lower release from P(IA-co-NVP) microparticles, but displayed increased apparent permeability across a Caco-2 monolayer by two orders of magnitude. Therefore, PEG-containing systems could yield high bioavailability of orally delivered proteins. Finally, a modified SELEX protocol for cellular selection of transcellular transport-initiating aptamers was developed and used to identify aptamer sequences showing enhanced intestinal perfusion. Over three selection cycles, the selected aptamer library showed significant increases in absorption, and from an initial library of 1.1 trillion sequences, 5-10 sequences were selected that demonstrated up to 10-fold amplification compared to the naïve library. These sequences could provide a means of overcoming the significant final barrier of intestinal absorption. / text