Doctor of Philosophy, University of Toledo, 2022, Chemical Engineering

Polysaccharides have attracted much attention in the field of bone tissue engineering as natural scaffolds that mimic the physiological structure of the extracellular matrix (ECM) and provide glycosaminoglycan-like environments with nontoxic degradation products. Moreover, the use of polysaccharides is not limited to mimicking the 3D structure of the ECM but also as bioactive natural macromolecules that can stimulate cell-signalling. Gellan gum (GAGR) is a naturally occurring polysaccharide with repeating units of D-glucose, D-glucuronic acid, and L-rhamnose. Due to its biocompatibility and biodegradability, GAGR has been investigated in biomedical applications, food processing, pharmaceutics, and tissue engineering. In this research, GAGR is investigated not only as a scaffold but also as a bioactive material that stimulates bone regeneration. Culturing pre-osteoblast cells with GAGR resulted in a significant upregulation of genes related to osteogenesis and chondrogenesis, in addition to collagen type I protein formation, which is the main component in the ECM. Thus, to deliver GAGR, various formulations of GAGR, hyaluronic acid, and β-tricalcium phosphate were fabricated. The objective was to develop an ionically crosslinked gel that can be injected and allows GAGR to disintegrate over time from its network structure. Then, the possibility of GAGR diffusion and adsorption in human bone was investigated in vitro by the standard diffusion cell chamber and adsorption isotherms. In vivo, the cross-linked GAGR gel was injected into the femur bone of an ovariectomized rat model. GAGR gel-injected sites showed a significant increase in inward bone growth, resulting in thicker cortical bone, as well as an increase in number of blood vessels. A simulation of the in vivo study using finite element model (COMSOL Multiphysics v 5.4) showed a qualitative agreement to the experimental results, and revealed a significant effect of GAGR molecular weight and adsorption on (open full item for complete abstract)

Committee: Dong-Shik Kim (Committee Chair); Joshua Park (Committee Member); Eda Yildirim-Ayan (Committee Member); Maria Coleman (Committee Member) Subjects: Chemical Engineering

Master of Science, University of Toledo, 2022, Chemical Engineering

The current study investigated the antibacterial activities of low acyl gellan gum (LA-GAGR) and its derivative, Mini-GAGR through two different methods. The first method involves the measurement of antibacterial activities of suspended LA-GAGR and Mini-GAGR in a liquid phase to determine their minimum inhibitory concentrations (MIC). The concentrations used for LA-GAGR and Mini-GAGR were 0.002 %, 0.003 %, and 0.015 %. As LA-GAGR and Mini-GAGR concentrations increased, their antibacterial activities became significantly high. The results also showed that LA-GAGR had a greater antibacterial activity than Mini-GAGR. The second method was via the growth inhibition experiment where 1.5% of LA-GAGR and 3% of Mini-GAGR in a gel phase were compared with two different types of polysaccharides, 2% chitosan and 7% dextran. Before running the growth inhibition experiment, confirmation of similar rheological properties for all samples was made. LA-GAGR, Mini-GAGR, chitosan and dextran showed similar rheological properties with gel-like behavior. The result of the growth inhibition experiment showed that the largest inhibition zone was formed in chitosan. While LA-GAGR has some inhibition zone, unlike Mini-GAGR where the gel is colorless, dextran did not inhibit the bacterial growth and allowed the bacteria to colonize on its gel.

Committee: Dong-Shik Kim Dr (Advisor); Joshua Park Dr (Committee Member); Maria Coleman Dr (Committee Member) Subjects: Biology; Biomedical Research; Chemical Engineering; Microbiology

Master of Science, University of Toledo, 2019, Chemical Engineering

Low acyl gellan gum (LA-GAGR) is a microbial polysaccharide that forms a viscoelastic gel when mixed with hyaluronic acid and β-tri- calcium phosphate (TCP). The effects of concentrations of the cross-linker (TCP) and LA-GAGR on the rheological properties and decomposition of the gels were studied. The degree of cross-linking of LA-GAGR was controlled with TCP content to determine its effects on the viscoelastic properties and release rate of LA-GAGR from the gel. The gels appeared thicker and opaquer with increasing TCP concentration. Three concentrations, 0.0 wt%, 0.5 wt%, and 1.0 wt% of TCP were examined with 0.15 wt% and 0.30 wt% of LA-GAGR. 5 wt% TCP is a maximum weight percentage that can be added to LA-GAGR, above which the TCP begins to precipitate out. Flow sweep tests showed that all tested gels are shear thinning and that the gel made with 1.0 wt% TCP and 0.30 wt% LA-GAGR displayed the highest viscosity with the experimental value of 675 Pa·s at 0.1 s-1. However, gels made with 0.0 wt% TCP and 0.15 wt% LA-GAGR showed the lowest viscosity, 5.8 Pa·s at 0.1 s-1. The gel made with 0.0 wt% TCP and 0.15 wt% LA-GAGR exhibited the lowest loss and storage moduli of 0.5 Pa and 0.056 Pa, respectively. The gel made with 1.0 wt% TCP and 0.30 wt% LA-GAGR exhibited the highest loss and storage moduli of 116 Pa and 437.8 Pa, respectively. The gels made with 0.30 wt% LA-GAGR and TCP concentrations of 0.5 wt% and 1.0 wt% showed typical viscoelastic behaviors. For the release rates of LA-GAGR the gels, the gel made with 1.0 wt% TCP and 0.30 wt% LA-GAGR exhibited the lowest average release rate of 0.10 mg h-1, releasing all of LA-GAGR within 13 days. The low degree of crosslinking, due to the decrease of TCP, decreased the decomposition time of the gel to 8 days for the gel containing 0.30% LA-GAGR, 0.5% TCP. The properties of the gels varied depending on the method of mixing. When components were added gradually during mixing, the gel resulted in thicker and opaquer gels w (open full item for complete abstract)

Committee: Dong-Shik Kim (Committee Chair); Joshua Park (Committee Member); Maria Coleman (Committee Member) Subjects: Biochemistry; Biomedical Engineering; Biomedical Research; Chemical Engineering; Chemistry

Master of Science, University of Toledo, 2018, Chemical Engineering

The release of low acyl gellan gum from a controlled release system was evaluated at 0, 0.5, 1% concentration of tri-calcium phosphate. Release rates of 6.387, 0.345, and 0.679 mg/h of low acyl gellan gum were obtained for the 0, 0.5, and 1% tri-calcium phosphate, respectively. Additionally, rheological properties were obtained for the 0.5% TCP gel and 1% TCP. Moreover, low acyl gellan gum was enzymatically cleaved into two smaller molecular weight products, named midi-GAGR and mini-GAGR. Rheological testing revealed molecular weights of approximately 5,500 Da and 1,300 Da for midi-GAGR and mini-GAGR, respectively. Furthermore, the antioxidant capacities of both products were evaluated using DPPH assay. Midi-GAGR was able to scavenge 23% of free radicals, while mini-GAGR scavenged 13%. The polysaccharide low acyl gellan gum has shown promise to be engineered to fit clinical applications.

Committee: Dong-Shik Kim (Committee Chair); Joshua Park (Committee Member); Yakov Lapitsky (Committee Member) Subjects: Chemical Engineering