Browsing by Subject "biomaterials"

Now showing 1 - 4 of 4
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    Development and Applications of Gold Nanoparticles and Elastomeric Polymers as Biomaterials
    (2021-07) Siehr, Allison
    This thesis is focused on the development and applications of two different types of biomaterials: nanoparticles and polymers. In chapter 1, I briefly review these biomaterials. In chapter 2, we develop gold nanoparticles (GNPs) that can be driven to either self-assemble or remain colloidally stable using coiled-coil protein interactions. Control over the GNP self-assembly or stability is critical for specific biomedical applications. In chapter 3, we use the self-assembling GNPs to inhibit human immunodeficiency virus type-1 (HIV-1) by adding a targeting ligand for HIV-1. However, we found our GNPs are weak inhibitors of HIV-1. Methods to improve the inhibitor design are then discussed. In chapter 4, a biomaterials-based approach is used to elucidate the structures of HIV-1 and human T-cell leukemia virus type-1 (HTLV-1). A GNP immunolabeling strategy is used to identify HIV-1 and HTLV-1 envelope proteins, critical for viral entry and targets for vaccine development. However, the immunolabelling strategy was not robust, and alternative methods to study envelope proteins are discussed. Lastly, in chapter 5, a novel elastomeric polymer is evaluated for biomedical applications. PLA-PβMδVL-PLA polymers were synthesized in this work and shown to exhibit elastomeric properties. Next, the polymers were found to be biocompatible and biodegradable both in vitro and in vivo. Overall, this thesis demonstrates the development and applications of both gold nanoparticles and elastomeric polymers as biomaterials.
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    Modeling of blade cutting of viscoelastic biomaterials
    (2013-06) Peng, Yun
    The work in this thesis focuses on the modeling of blade cutting of viscoelastic materials. The blade cutting procedure is modeled in two stages. The first stage is the contact of the blade with the cutting material and the second stage is the fracture during continuous cutting. The modeling of the first stage is used to predict the initiation of the cutting fracture and the modeling of the second stage is use to characterize the cutting force during continuous fracture. Experiments that are used to determine the material parameters for the simulations and calculations of the cutting process are also carried out.The first stage is modeled as the area contact between the edge of the blade and cutting materials. It is modeled by applying the elastic-viscoelastic correspondence principle to the solutions for point load and then by performing a numerical integration scheme to extend the solutions to distributed pressure cases. The stress tensor was analytically obtained at any given point inside the viscoelastic material. The effect of slicing angles on the stress distribution is then evaluated. Using the principal stresses, the location of damage is predicted using Tresca's failure criterion. In the continuous damage stage, FEM simulation using ABAQUS is used as the modeling method. A bi-layered structure is applied to represent the tissue-bone structure which could be widely seen in a deboning process. In the simulation, the cutting force is monitored during the blade cuts through the interface. The dynamic change of the force pattern when the blade approaches the interface is analyzed in order to propose a control algorithm that prevents the blade cutting into bones. In order to provide realistic data for the simulation, several relaxation tests are designed to obtain the tensile relaxation modulus for biomaterials. Ligaments obtained from chicken wings and legs are used as specimens. The experimental data was theoretically fitted into a Burgers Model for the simulation and calculation. The model developed in this research can serve as a guideline for many applications such as the design of a surgical simulator to facilitate the training of new doctors and the intelligent control of a robot for deboning process to improve cutting yield and meat harvesting quality.
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    Peptide-functionalized hydrogels for three-dimensional cell culture
    (2016-06) Scott, Carolyn
    Biomimetic scaffolds have played a major role in the advancements in tissue engineering. In addition to mimicking the stiffness, nanofibrous structure, and biochemistry of the native extracellular matrix (ECM), reproducing the three-dimensional (3D) environment of the ECM has been shown to be extremely important. To this end, we designed a co-assembling peptide-amphiphile hydrogel system containing the fibronectin-mimetic PR_g peptide-amphiphile and an E2 diluent peptide-amphiphile for the entrapment and culture of cells in 3D. The E2 diluent peptide amphiphile was designed to screen charges on the PR_g and increase the kinetics of self-assembly in physiologically relevant solutions. Our study investigated two weight percent formulations, 0.5 and 1.0 wt %, and found that in both, entrapped fibroblasts survived encapsulation, proliferated, and deposited collagen IV and fibronectin ECM proteins. The 0.5 wt % gels had a modulus of 429 Pa and supported significantly more fibroblasts proliferation than the 1.0 wt % gels, which had a modulus of 809 Pa. The 1.0 wt% gels though, supported significantly higher mRNA expression and production of ECM proteins. This result indicates by tuning the wt % of our peptide-amphiphile hydrogels, we can encourage either rapid proliferation or ECM deposition. While peptide-amphiphiles are an attractive material for the design of cell scaffolds due to their ability to self-assemble into nanofibrous hydrogels and incorporate multiple biomimetic peptides, there are some limitations associated with these physical hydrogels. One such limitation is that the kinetics of assembly and the mechanical properties of the resulting hydrogels are dependent upon the peptide sequence. We found that the modulus of multifunctional peptide-amphiphile hydrogels ranged from 1000 to 6500 Pa, which was too broad a range to deconvolute the effect of the peptide signal and the effect of mechanical properties. To simplify our system and study the effects of combining ECM protein-mimetic and growth factor-mimetic peptides on the proliferation and function of pancreatic β-cells, peptide mimetics were covalently immobilized on plates. This study found that β-cells proliferate more and secreted significantly more insulin on peptide-functionalized compared to non-functionalized controls. The specific peptide mimetic or combination of peptide mimetics did not significantly affect insulin secretions, but literature suggests that other signals, including cell-cell signaling may play a more significant role in insulin secretion than ECM protein or growth factor signaling. A poly(ethylene glycol) dimethacrylate (PEGDM) hydrogel was functionalized with the laminin-mimetic IKVAV peptide at a 20 µM concentration to match the modulus of non-functionalized hydrogels. This system was used to determine if peptide-functionalization also had an effect in 3D. We found β-cells in IKVAV-functionalized hydrogels proliferated significantly more than β-cells in non-functionalized scaffolds, but no differences in insulin secretion were observed. Together, these studies demonstrate the ability of peptide mimetics to enhance cell proliferation and function of cells in 2D and 3D culture.
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    Wear and Fatigue Resistance: An In-Vitro Comparison of Three Materials for Vacuum-Formed Retainers
    (2022-06) Bitner, Timothy
    AbstractAim: To test the wear and fatigue resistance of three materials for the fabrication of vacuum-formed retainers in a simulated oral environment. Methods: Three materials were tested: Essix ACE, Taglus, and Zendura. To test wear resistance, 21 maxillary retainers of each material (63 overall) were mounted on zirconia models into an Artificial Resynthesis Technology machine to simulate wear in an oral environment. Each sample underwent 12,000 cycles of wear at 75 Newtons to simulate one year of retainer wear with moderate nighttime bruxing. Lateral movement was set to 2 mm with a frequency of 2 Hertz. Post-wear retainer thickness was measured using a digital micrometer and compared to baseline measurements to calculate the depth of wear. To test fatigue resistance, 15 maxillary retainers of each material (45 overall) were mounted and flexed at an angle of 25 degrees for 1825 cycles at a frequency of 1 Hertz to simulate one year of removing and reinserting a retainer at a rate of 5 times per day. Retainers were visually inspected for fractures. Pairwise t-tests with correction using Tukey’s method were conducted to determine which pairs of material groups were significantly different at α=0.05. Results: For the wear resistance test, the mean baseline thickness was 0.51 ± 0.033 mm, 0.492 ± 0.029 mm, and 0.515 ± 0.047 mm for Essix ACE, Taglus, and Zendura, respectively. The mean post-wear thickness was 0.354 ± 0.033 mm, 0.323 ± 0.038 mm, and 0.42 ± 0.027 mm for Essix ACE, Taglus, and Zendura, respectively. The overall wear was 0.155 ± 0.021 mm, 0.168 ± 0.031 mm, and 0.096 ± 0.033 mm for Essix ACE, Taglus, and Zendura, respectively. The wear depth of Zendura was significantly lower than both Essix ACE (P < 0.001) and Taglus (P < 0.001). There was no significant difference in wear depth between Essix ACE and Taglus (P = 0.312). Under the parameters set for the fatigue resistance test, visual fractures did not occur on any of the retainer materials for Essix ACE, Taglus, or Zendura. Conclusions: Under the assumption of moderate nighttime bruxing for one year, Zendura is the most resistant to wear among the materials tested. With the assumption of retainer removal and reinsertion five time daily for one year, all three materials tested exhibit the same ability to resist fatigue.