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Browsing by Author "Cooke, Shelley L."

Now showing 1 - 4 of 4
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    Bioactive Cellulose Nanocrystal-Poly(epsilon-Caprolactone) Nanocomposites for Bone Tissue Engineering Applications
    Hong, Jung Ki; Cooke, Shelley L.; Whittington, Abby R.; Roman, Maren (2021-02-25)
    3D-printed bone scaffolds hold great promise for the individualized treatment of critical-size bone defects. Among the resorbable polymers available for use as 3D-printable scaffold materials, poly(epsilon-caprolactone) (PCL) has many benefits. However, its relatively low stiffness and lack of bioactivity limit its use in load-bearing bone scaffolds. This study tests the hypothesis that surface-oxidized cellulose nanocrystals (SO-CNCs), decorated with carboxyl groups, can act as multi-functional scaffold additives that (1) improve the mechanical properties of PCL and (2) induce biomineral formation upon PCL resorption. To this end, an in vitro biomineralization study was performed to assess the ability of SO-CNCs to induce the formation of calcium phosphate minerals. In addition, PCL nanocomposites containing different amounts of SO-CNCs (1, 2, 3, 5, and 10 wt%) were prepared using melt compounding extrusion and characterized in terms of Young's modulus, ultimate tensile strength, crystallinity, thermal transitions, and water contact angle. Neither sulfuric acid-hydrolyzed CNCs (SH-CNCs) nor SO-CNCs were toxic to MC3T3 preosteoblasts during a 24 h exposure at concentrations ranging from 0.25 to 3.0 mg/mL. SO-CNCs were more effective at inducing mineral formation than SH-CNCs in simulated body fluid (1x). An SO-CNC content of 10 wt% in the PCL matrix caused a more than 2-fold increase in Young's modulus (stiffness) and a more than 60% increase in ultimate tensile strength. The matrix glass transition and melting temperatures were not affected by the SO-CNCs but the crystallization temperature increased by about 5.5 degrees C upon addition of 10 wt% SO-CNCs, the matrix crystallinity decreased from about 43 to about 40%, and the water contact angle decreased from 87 to 82.6 degrees. The abilities of SO-CNCs to induce calcium phosphate mineral formation and increase the Young's modulus of PCL render them attractive for applications as multi-functional nanoscale additives in PCL-based bone scaffolds.
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    Effects of Therapeutic Radiation on Polymeric Scaffolds
    Cooke, Shelley L. (Virginia Tech, 2014-01-16)
    High levels of ionizing radiation are known to cause degradation and/or cross-linking in polymers. Lower levels of ionizing radiation, such as x-rays, are commonly used in the treatment of cancers. Material characterization has not been fully explored for polymeric materials exposed to therapeutic radiation levels. This study investigated the effects of therapeutic radiation on three porous scaffolds: polycaprolactone (PCL), polyurethane (PU) and gelatin. Porous scaffolds were fabricated using solvent casting and/or salt leaching techniques. Scaffolds were placed in phosphate buffered saline (PBS) and exposed to a typical cancer radiotherapy schedule. A total dose of 50 Gy was broken into 25 dosages over a three-month period. PBS was collected over time and tested for polymer degradation through high performance liquid chromatography (HPLC) and bicinchoninic acid (BCA) protein assay. Scaffolds were characterized by changes in microstructure using Scanning Electron Microscopy (SEM), and crystallization using Differential Scanning Calorimetry (DSC). Additionally, gelatin ε-amine content was analyzed using Trinitrobenzene Sulfonic Acid Assay (TNBSA). Gelatin scaffolds immersed in PBS for three months without radiation served as a control. Each scaffold responded differently to radiation. PCL showed no change in molecular weight or microstructure. However, the degree of crystallinity decreased 32% from the non-irradiated control. PU displayed both changes in microstructure and a decrease in crystallinity (85.15%). Gelatin scaffolds responded the most dramatically to radiotherapy. Samples were observed to swell, yet maintain shape after exposure. As gelatin was considered a tissue equivalent, further studies on tissues are needed to better understand the effects of radiotherapy.
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    Investigation into Polyurethane at Varying Dose Rates of Ionizing Radiation for Clinical Application
    Cooke, Shelley L.; Whittington, Abby R. (Hindawi, 2018-10-01)
    Polyurethanes (PUs) are commonly used materials for medical devices. These devices are exposed repeatedly to radiation when patients undergo radiotherapy treatments. It has been found that peripherally inserted central catheters (PICCs) and central venous catheters (CVCs) fail at an increased rate (14.7% and 8.8%, respectively) when radiated. Currently, little research is available on increased failure seen in conjunction with radiation, but complex in vivo environments within a human patient make it difficult to isolate effects of individual variables. This research investigated effects of radiation in an aqueous environment to determine whether radiation combined with a mimicked in vivo environment is sufficient to change PU devices. The following dose rates were used in this study: 3.2 Gy·min−1, 4.5 Gy·min−1, 44 Gy·min−1, and 833 Gy·min−1. Samples were characterized in four main ways: cellular response, physical changes, chemical changes, and mechanical changes. Results reveal normal cellular response at all dose rates, indicating dose rate does not alter cellular adhesion or proliferation, and biocompatibility of the material is not being altered. Results from physical, chemical, and mechanical effects confirm that varying dose rates alone do not initiate material changes, which negates the hypothesis that varying dose rates of radiation contribute to the complications in PICC and CVCs.
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    Investigation into the Stability of Biomedical Grade Silicone and Polyurethane Exposed to Ionizing Radiation
    Cooke, Shelley L. (Virginia Tech, 2018-09-12)
    Clinical studies suggest radiation dose and dose rate cause increased failure of medical implants however, little evidence supports this claim and due to the complexity of an in vivo environment, separating variable implants is difficult. Before beginning to understand material changes in vivo, a systematic study of silicone and polyurethane exposed to radiation is needed to verify whether radiation is a major variable contributing to material changes. This research fills a gap within the current literature by investigating low dose therapeutic radiation and varying dose rates at sterilization dose and answers questions on whether radiation in an aqueous environment alone is enough to significantly alter material properties. This is the first research to apply a water environment to therapeutic doses and the first to investigate a range of dose rates for clinical applications. Biomedical grade silicone and polyurethane films will be exposed to both types of radiation in an aqueous environment separately and analyzed for changes. The limited current literature combined with standards for biomedical devices will be used to characterize changes seen in materials. The first strategy used to explore the compliance of biomedical grade polymers employs low doses of therapeutic radiation ranging between 0 Gy and 80 Gy. Analysis of these low doses results in confirming cellular, mechanical and chemical stability of silicone and polyurethane. The second strategy used to investigate silicone and polyurethane exposed materials to 25 kGy (sterilization dose) of gamma irradiation at varying dose rates (3.2 - 833 Gy/min). Results from these studies conclude that varying the dose rate causes slight changes in both materials but not significant enough to alter bulk material properties. In conclusion, the results from this research reveal that both silicone and polyurethane maintain their stability at low doses and varying dose rates of irradiation while in an aqueous environment. This indicates that increased failure rates seen in silicone and polyurethane materials in vivo when exposed to radiation cannot be contributed to radiation alone. With the highly complex environment medical devices are exposed to in vivo, each variable that may contribute to failure should be investigated individually before combining to fully understand the mechanisms of material failure. This study indicates that the environment may play a larger role in material change and there is a need for updates to medical device standards.