Browsing by Subject "hydrogel"
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Item Development of hyaluronic acid – poly(ethylene glycol) hydrogels towards hematopoietic differentiation of mouse embryonic stem cells(2009-08) Erickson, Kathryn Marie; Roy, Krishnendu; Suggs, LauraThe fields of tissue engineering, regenerative medicine, and stem cell engineering are rapidly growing. However, these fields must overcome several obstacles before they can make a significant impact on treating cellular disorders. Two major hurdles that must be addressed are: determining how to control the pluripotency of stem cells and developing systems for high-throughput culture of stem cells. The prospect of using a cell source capable of differentiating into cells of any tissue in the body (embryonic stem cells) has received enormous interest in recent years. The pluripotent attribute of embryonic stem cells seems ideal but developing methods to drive embryonic stem cells to specific lineages, including the hematopoietic lineage, is a complex process dependent on multiple intrinsic and extrinsic factors including chemical, cellular, and environmental signaling. With regards to environmental signaling, the use of three-dimensional culture systems such as scaffolds and hydrogels, have been utilized in an attempt to drive lineage-specific differentiation in a synthetic, biomimetic microenvironment. To determine specific environmental factors responsible for hematopoietic differentiation a systematic biological and engineering process must be implemented. A biodegradable hydrogel composed of the hyaluronic acid, a polysaccharide abundant in the bone marrow microenvironment, and the synthetic polymer, poly(ethylene glycol) was formulated to culture mouse embryonic stem cells (mESCs). Photoencapsulation of mESCs did not significantly decrease cellular viability or proliferation. The FACS data was inconclusive however, from gene expression studies, it was determined that the hydrogel culture system promoted differentiation of mESCs as evidenced by a down-regulation of the gene encoding for stem cell maintenance transcription factor, Oct-3/4. Furthermore, embryoid bodies, necessary for in vitro differentiation were observed in the hydrogel systems. Although an increase in the gene encoding for the cell surface marker, c-kit was up-regulated, the surface marker, sca-1 was not up-regulated. Up-regulation of both c-kit and sca-1 is necessary for the development of hematopoietic progenitor cells. Results indicate that the differentiation of mESCs into the hematopoietic lineage was unsuccessful but differentiation in these hydrogel systems did occur. Future cell marker and gene expression studies are necessary to determine which cell lineage the encapsulated mESCs are differentiating into before the effects of incorporating other environmental, cellular, and chemical factors can be investigated.Item Effect of pH on the Properties of Hydrogels Cross-Linked via Dynamic Thia-Michael Addition Bonds(ACS Publications, 2021-12-28) FitzSimons, Thomas M.; Anslyn, Eric V.; Rosales, Adrienne M.Hydrogels cross-linked with dynamic covalent bonds exhibit time-dependent properties, making them an advantageous platform for applications ranging from biomaterials to self-healing networks. However, the relationship between the cross-link exchange kinetics, material properties, and stability of these platforms is not fully understood, especially upon addition of external stimuli. In this work, pH was used as a handle to manipulate cross-link exchange kinetics and control the resulting hydrogel mechanics and stability in a physiologically relevant window. Poly(ethylene glycol)-based hydrogels were cross-linked with a reversible thia-Michael addition reaction in aqueous buffer between pH 3 and pH 7. The rate constants of bond exchange and equilibrium constants were determined for each pH value, and these data were correlated with the resulting mechanical profiles of the bulk hydrogels. With increasing pH, both the forward and the reverse rate constants increased, while the equilibrium constant decreased. These changes led to faster stress relaxation and less stiff hydrogels at more basic pH values. The elevated pH values also led to an increased mass loss and a faster rate of release of an encapsulated model bovine serum albumin fluorescent protein. The connection between the kinetics, mechanics, and molecular release profiles provides important insight into the structure−property relationships of dynamic covalent hydrogels, and this system offers a promising platform for controlled release between physiologically relevant pH values.Item Effect of pH on the Properties of Hydrogels Cross-Linked via Dynamic Thia-Michael Addition Bonds(ACS Publications, 2021-12-28) FitzSimons, Thomas M.; Anslyn, Eric V.; Rosales, Adrienne M.Hydrogels cross-linked with dynamic covalent bonds exhibit time-dependent properties, making them an advantageous platform for applications ranging from biomaterials to self-healing networks. However, the relationship between the cross-link exchange kinetics, material properties, and stability of these platforms is not fully understood, especially upon addition of external stimuli. In this work, pH was used as a handle to manipulate cross-link exchange kinetics and control the resulting hydrogel mechanics and stability in a physiologically relevant window. Poly(ethylene glycol)-based hydrogels were cross-linked with a reversible thia-Michael addition reaction in aqueous buffer between pH 3 and pH 7. The rate constants of bond exchange and equilibrium constants were determined for each pH value, and these data were correlated with the resulting mechanical profiles of the bulk hydrogels. With increasing pH, both the forward and the reverse rate constants increased, while the equilibrium constant decreased. These changes led to faster stress relaxation and less stiff hydrogels at more basic pH values. The elevated pH values also led to an increased mass loss and a faster rate of release of an encapsulated model bovine serum albumin fluorescent protein. The connection between the kinetics, mechanics, and molecular release profiles provides important insight into the structure−property relationships of dynamic covalent hydrogels, and this system offers a promising platform for controlled release between physiologically relevant pH values.Item A Sustainable Additive Approach for the Achievement of Tunable Porosity(University of Texas at Austin, 2018) Lau, Sharon; Yeazel, Taylor; Miller, Ana; Pfister, Nathan; Rivero, Iris V.This study aims to design a green additive approach for the fabrication of controlled porosity on hydrogels. Although hydrogels have been of common use in tissue engineering, the generation of controllable porosity remains an issue due to their swelling and degradation properties. Hydrogels in this study were fabricated by physical cross-linking and the porosity was generated by casting the solution in a 3D printed mold prior to physical cross-linking. This approach eliminates the use of chemical cross-linking compounds which are often toxic and not environmentally friendly. Polyvinyl alcohol was selected to validate this technique due to its biocompatibility and adequate mechanical properties. The microstructure, mechanical properties and deformation of the porous hydrogels were characterized. Results revealed that the proposed bioplotting technique reduced variation of pore size and allotted for the realization of controlled and tunable pore structures.