Two series monodispersed nanoparticles of hydroxylpropyl cellulose (HPC) and functionalized poly-N-isopropylamide (PNIPAM) particles have been synthesized and used as building blocks for creating three-dimensional networks, with two levels of structural hierarchy. The first level is HPC nanoparticles were made from methacrylated or degradable cross-linker attached HPC. These nanoparticles could be stabilized at room temperature by residual methacrylate or degradable groups are present both within and on the exterior of HPC nanoparticles. Controlled release studies have been performed on the particle and networks .The nearly monodispersed nanoparticles have been synthesized on the basis of a natural polymer of hydropropylcellulose (HPC) with a high molecular weight using the precipitation polymerization method and self-assembly of these particles in water results in bright colors. The HPC nanoparticles can be potential using as crosslinkers to increase the hydrogels mechanical properties, such as high transparency and rapid swelling/de-swelling kinetics. The central idea is to prepare colloidal particles containing C=C bonds and to use them as monomers - vinylparticles, to form stable particle assemblies with various architectures. This is accomplished by mixing an aqueous suspension of hydrogel nanoparticles (PNIPAM-co-allylamine) with the organic solvent (dichloromethane) to grow columnar crystals. The hydrogels with such a unique crystal structure behavior not only like the hydrogel opals, but also have a unique property: anisotropy.

A huge discrepancy between the number of patients on the waiting list for organ transplants and the actual available donors has led to search for alternative approaches to substitute compromised or missing tissues and organs. Tissue engineering is a promising alternative to organ transplantation with the aim to fabricate functional organs through the use of biological or biocompatible scaffolds. Nanogels made from self-assembling ultrashort peptides are promising biomaterials for a variety of biomedical applications. Our group at KAUST is interested in the development of novel synthetic peptide-based biomaterials that combine the advantages of both natural and synthetic hydrogels for various applications. In this study, we have investigated two compounds of a novel class of rationally designed ultrashort peptides, Ac-IVFK-NH2 (Ac-Ile-Val-Phe-Lys-NH2) and Ac-IVZK-NH2 (Ac-Ile-Val-Cha-Lys-NH2). These compounds have an innate tendency to self-assemble into nanofibrous hydrogels which can be used as 3D scaffolds, for example for the fabrication of 3D skin grafts for wound healing. We have evaluated the efficacy of the peptide scaffolds in treating full-thickness wounds in minipigs. Additionally, we assessed the ability of these scaffolds in supporting skeletal muscle tissue proliferation and differentiation. We found that our innovative nanogels supported a substantial increase in human dermal fibroblast and myoblast growth and cells viability, and supported myoblast differentiation. Also, microscopic observation of the direct contact of keratinocytes and fibroblasts revealed enhancement in keratinocytes proliferation. In addition, we demonstrated the ability of human umbilical vein endothelial cells to form tube like structure within peptide nanogels using immunofluorescence staining. Moreover, we successfully produced artificial 3D vascularized skin substitutes using these peptide scaffolds. We selected these peptide nanogels and were able to produce in situ silver nanoparticles within the nanogels, solely through UV irradiation, with no reducing agent present. We then assessed the efficacy of the silver nanoparticle-containing peptide nanogels on minipigs with full-thickness excision wounds. The application of the peptide nanogels on full thickness minipig wounds demonstrated that the scaffolds were biocompatible and did not trigger wound inflammation, and thus safe for topical application. The effect of nanogels, both with and without the addition of the silver nanoparticles, revealed that the scaffold itself has a high potential to act as an antibacterial agent. Interestingly, the effect of the peptide nanogels on wound closure was comparable to that of standard care hydrogels. Furthermore, we have demonstrated that both peptides can act as printable bioinks which opens up the possibility of 3D bioprinting of different cell types in the future. We believe that the described results represent an advancement in the context of engineering skin and skeletal muscle tissue, thereby providing the opportunity to rebuild missing, failing, or damaged parts.

Hydrogels are hydrophilic, three-dimensional polymeric networks prepared through chemical or physical conjugation. Hydrogels are recognized for their tunable properties, specifically through changes in the backbone of the polymers, such as 1) modifying the number of hydrophobic chain lengths, 2) adding or removing cleavable linkages, 3) varying reactive-end groups, 4) increasing or decreasing the weight percent of the hydrogel, and 5) combining two or more hydrogel networks into one, namely creating an interpenetrating network. We synthesized and characterized on- and off-demand, dissolvable hydrogels for use as burn wound dressings, polypectomy bandages, and vascular occlusion devices, and within interpenetrating networks. The hydrogels are composed of PEG-based crosslinkers, and PEI-based hyperbranched macromers which were prepared in high yields. In context of burn wound dressings, there is an unmet need for an adherent dressing with ease of removal, such as a dissolvable hydrogel dressing. In a model of in vivo porcine burn wounds, our hydrogel shows superior burn healing relative to traditional dressings such as sterile gauze pad and non-adherent foam dressings. When our hydrogel was removed, no newly formed tissue adhered to the dressing, and immunohistochemical stains exhibit improved inflammation and necrosis. When our hydrogel was used as an in vivo polypectomy sealant, we observed ease of application and adhesion to the colon, despite peristalsis. In in vitro studies, we observe no migration of bacteria through the hydrogel. As a vascular occlusion device, our hydrogels withstand an ex vivo burst pressure of up to 440mmHg on average, over 3x that of arterial pressure. Furthermore, we prepared an interpenetrating network from two hydrogel formulations both using SN2 chemistry with tunable mechanical properties. The hydrogel formulations highlighted in this work vary in gelation, mechanical properties, swelling, dissolution, and adhesion based on the structure of the polymer and reactive groups. These hydrogels represent a future direction in wound dressings and sealants as they prevent bacterial migration into an open wound, adhere to tissue, provide a moist wound environment, demonstrate structure-function relations allowing for tunable mechanical properties, and are biocompatible. / 2022-03-10T00:00:00Z

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The research of this dissertation is formulated in two fields, i.e., the theoretical and computational studies of circumferential wrinkling on soft nanofibers and the swelling mechanics study of a bi-layered spherical hydrogel containing a hard core. Continuous polymer nanofibers have been massively produced by means of the low-cost, top-down electrospinning technique. As a unique surface instability phenomenon, surface wrinkling in circumferential direction is commonly observed on soft nanofibers in electrospinning. In this study, a theoretical continuum mechanics model is developed to explore the mechanisms of circumferential wrinkling on soft nanofibers under uniaxial stretching. The model is able to examine the effects of elastic properties, surface energy, and fiber radius on the critical axial stretch to trigger circumferential wrinkling and to discover the threshold fiber radius to initiate spontaneous wrinkling. In addition, nonlinear finite element method (FEM) is further adopted to predict the critical mismatch strain to evoke circumferential wrinkling in core-shell polymer nanofibers containing a hard core, as a powerful computational tool to simulate controllable wrinkling on soft nanofibers via co-electrospinning polymer nanofibers incorporated with nanoparticles as the core. The studies provide rational understanding of surface wrinkling in polymer nanofibers and technical approaches to actively tune surface morphologies of polymer nanofibers for particular applications, e.g. high-grade filtration, oil-water separation, polymer nanocomposites, wound dressing, tissue scaffolding, drug delivery, and renewable energy harvesting, conversion, and storage, etc. Furthermore, hydrogels are made of cross-linked polymer chains that can swell significantly when imbibing water and exhibit inhomogeneous deformation, stress, and, water concentration fields when the swelling is constrained. In this study, a continuum mechanics field theory is adopted to study the swelling behavior of a bi-layered spherical hydrogel containing a hard core. The problem is reduced into a two-point boundary value problem of a 2nd-order nonlinear ordinary differential equation (ODE) and solved numerically. Effects of material properties on the deformation, stress, and water concentration fields of the hydrogel are examined. The study offers a rational route to design and regulate hydrogels with tailorable swelling behavior for practical applications in drug delivery, leakage blocking, etc.

No description available.

Microencapsulation of stem cells in hydrogel for use in therapeutic applications has been shown to improve cell retention at the site of injuries due to their mechanical and immunoprotective properties. These microscale droplets (cocoons) can be produced at high throughputs within microfluidic channels. Currently, the ability for cells to egress hydrogel cocoons is under investigation. This egress can correlate with therapeutic efficacy, and so promoting or inhibiting the egress of cells can be a vital component of viable treatments. Previously, a second hydrogel layer was shown to reduce egress, but issues involving cell proliferation were unchanged. We propose a microfluidic process to encapsulate cells in two layers of thermoresponsive hydrogels, in which the inner core melts at physiological temperatures to form hollow cocoons that allow cells free motion inside the immunoprotective shell. We hypothesize that the open volume would increase cell viability and proliferation, without increasing cell egress due to the uninterrupted hydrogel shell. In this project the encapsulation of NIH 3T3 cells in hollow agarose cocoons was achieved. 3T3 cells were first encapsulated in thermoreversible gelatin which were then re-encapsulated in agarose through the use of a flow-focusing microfluidic channel with on-chip mixing of two inlet flows to produce hollow cocoons. The production of these cocoons showed the potential of high throughput, monodisperse samples with future investment. Preliminary investigation in the behavior of the encapsulated cells showed that the cells maintain high viability over the course of 48 hours. There are early indications that the hollow nature of correctly formed cocoons can limit cell egress, and may allow for proliferation in the cocoon.

Thesis(M.Sc.(Chemistry)) -- University of Limpopo, 2020 / An extensive search for a highly efficient, reusable, and non-toxic adsorbent materials for the removal of organic dyes from wastewater continues to be of great importance to the world. Activated carbon is the most widely used adsorbent material for treating dye contaminants from water owing to its high removal capacity and large surface area. However, activated carbon is expensive and not easy to regenerate. Hence, the use of biodegradable, non-toxic, and cost-effective biopolymer-based hydrogel adsorbents has attracted great attention. These adsorbents have high swelling capacity and number of adsorptive functional groups to allow adsorption of methylene blue dye. Hence in this work, we present carboxymethyl cellulose crosslinked with poly (acrylic acid) incorporated with magnetic cloisite 30B clay (CMC-cl-pAA/Fe3O4-C30B) and sodium alginate crosslinked with poly (acrylic acid) incorporated with zinc oxide (SA-cl pAA/ZnO) hydrogel nanocomposites (HNCs) for the removal of methylene blue from aqueous solution. The hydrogel nanocomposites were synthesised through in situ free radical polymerisation. The structural properties of the prepared materials were studied using Fourier transform infrared (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), and dynamic mechanical analysis (DMA). The FTIR and XRD confirmed the successful synthesis of the CMC-cl-pAA and SA-cl-pAA hydrogels, Fe3O4-C30B and ZnO nanoparticles (NPs) and their hydrogel nanocomposites. Furthermore, the co-existence of the metal oxide nanoparticles in the CMC-cl-pAA and SA-cl-pAA hydrogel matrices was confirmed by XRD. The SEM revealed that upon the incorporation of the Fe3O4- C30B NPs onto CMC-cl-pAA, the resulting material showed spherical particles of the magnetite nanoparticles on the irregular shaped hydrogel structure. As well as on the SA-cl-pAA after modification by ZnO nanoparticles, the spherical ZnO particles were embedded on the hydrogel surface. The successful modification with metal oxide nanoparticles was also confirmed by the presence of characteristic elements of the incorporated materials on the EDS. The TEM coupled with selected area electron diffraction (SAED) confirmed the presence of Fe3O4-C30B on the hydrogel structure, in which circular bright dotted lines were observed corresponding to light diffracted by the lattice planes of different energies on the Fe3O4 structure. The thermogravimetric analysis was conducted to study the thermal stability of the materials, the results showed that the incorporation of Fe3O4-C30B and ZnO nanoparticles on CMC-cl-pAA and SA-cl-pAA hydrogels, respectively improved their thermal stability. Furthermore, DMA was used to study the mechanical stability of the prepared hydrogels and their composites. In the case of CMC-cl-pAA hydrogel, the storage modulus of CMC-cl pAA/Fe3O4-C30B nanocomposite was higher than of the hydrogel, indicating improved mechanical stability, and on SA-cl-pAA hydrogel the storage modulus decreased, indicating a decrease in mechanical stability on the SA-cl-pAA/ZnO HNC. Consequently, the swelling studies revealed that the SA/AA/ZnO HNC was highly efficient for water uptake in comparison to SA/AA hydrogel. Whereas, CMC-cl pAA/Fe3O4-C30B had lower swelling capacity than CMC-cl-pAA hydrogel. Various factors influencing the adsorption of adsorbents were systematically investigated. The kinetics, isotherms, and thermodynamics of adsorption were examined, and results showed that equilibrium data fitted the Langmuir isotherm model, and the adsorption kinetics of MB followed pseudo-second-order model in both the CMC-based HNC and SA-based HNC. Maximum adsorption capacities of 1129 and 1529.6 mg/g were achieved for SA/AA hydrogel and SA/AA/ZnO HNC, respectively, in 0.25 g/L MB solution at pH 6.0 within 40 min. Whereas maximum capacities of 1165 mg/g (pH 5) and 806.51 mg/g (pH 7) for CMC-cl-pAA hydrogel and CMC-cl-pAA/Fe3O4- C30B HNC, respectively. Thermodynamic parameters for SA/AA and CMC-cl-pAA hydrogels exhibited exothermic adsorption processes and their nanocomposites SA/AA/ZnO and CMC-cl-pAA/Fe3O4-C30B exhibited endothermic nature of the adsorption processes, respectively. Moreover, the CMC-cl-pAA/Fe3O4-C30B NCH showed improved mechanical and thermal properties as compared to CMC-cl-pAA hydrogel. In contrast, the SA/AA/ZnO HNC presented outstanding reusability with relatively better adsorption efficiencies than SA/AA hydrogel. / Sasol bursary and National Research Foundation (NRF)

Indiana University-Purdue University Indianapolis (IUPUI) / The pancreas is a vital organ that secretes key metabolic hormones and digestive enzymes. In pancreatic ductal adenocarcinoma (PDAC), one of the leading causes of cancer-related death in the world, limited advances in diagnosis or therapies have been made over decades. Key features of PDAC progression include an elevated matrix sti ness and an increased deposition of extracellular matrices (ECM), such as hyaluronic acid (HA). Understanding how cells interact with components in the tumor microenvironment (TME) as PDAC progresses can assist in developing diagnostic tools and therapeutic treatment options. In recent years, hydrogels have proven to be an excellent platform for studying cell-cell and cell-matrix interactions. Utilizing chemically modi ed and naturally derived materials, hydrogel networks can be formed to encompass not only the components, but also the physicochemical properties of the dynamic TME. In this work, a dynamic hydrogel system that integrates multiple click chemistries was developed for tuning matrix physicochemical properties in a manner similar to the temporally increased matrix sti ness and depositions of HA. Subsequently, these dynamic hydrogels were used to investigate how matrix sti ening and increased HA presentation might a ect survival of PDAC cells and their response to chemotherapeutics.