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Browsing by Author "Kipper, Matt, advisor"

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    Biomimetic and antimicrobial surfaces for orthopedic implants
    (Colorado State University. Libraries, 2021) Wigmosta, Tara, author; Kipper, Matt, advisor; Popat, Ketul, advisor; Giess, Brian, committee member; DeLong, Susan, committee member; Schenkel, Alan, committee member
    The number of total knee and hip replacement surgeries is expected to continue to rise in the United States. As such, the number of revision surgeries is also expected to rise. The two most common causes of failure for these implants is aseptic loosening, caused by incomplete osseointegration, and infection. Therefore, preventing infection while increasing the osteogenic properties of the surfaces used in orthopedic implants could reduce the number of revision surgeries. It is the goal of this work to create nanostructured surfaces that both increase mineralization and antimicrobial properties of titanium surfaces commonly used in orthopedic implants. To accomplish this, chitosan/heparin polyelectrolyte multilayers (PEMs), with the addition of either bone morphogenetic protein 2 (BMP-2) or gentamicin, were adsorbed onto titania nanotubes. BMP-2 has been used in clinical applications to increase osseointegration in spinal fusions, and gentamicin is effective against the most common pathogens found in infected orthopedic implants. Both heparin and chitosan are biocompatible and have antimicrobial properties. BMP-2 has a binding site for heparin that increases BMP-2's half-life in vitro. The first chapter summarizes the motivation and previous strategies used to increase osseointegration and antimicrobial properties of nanostructured biomimetic orthopedic implant surfaces. The first chapter concludes with a shift in hypothesis testing, outlining three different hypotheses: 1) surface modification(s) increase cytocompatibility and the osteogenic properties of mammalian bone cells; 2) surface modification(s) reduce bacterial adhesion, proliferation, and infection rate, without decreasing cytocompatibility; and 3) surface modification(s) provide a favorable environment in which mammalian cells can beat bacterial cells and colonize the surface first, thus increasing the osteogenic and antimicrobial properties of the surface. The testing of these hypotheses are explored in chapters 2 through 4. The second chapter explores hypothesis 1) by testing if BMP-2 released from chitosan/heparin PEM coated titania nanotubes surfaces induce an osteogenic response from rat bone marrow cells. Chapter 3 explores hypothesis 2) by testing if iota-carrageenan/chitosan and pectin/chitosan PEMs have antimicrobial properties against Pseudomonas aeruginosa (P. aeruginosa) and Staphylococcus aureus (S. aureus), and support rat bone marrow cell adhesion and proliferation. The last chapter explores hypothesis 3) by testing if gentamicin released from titania nanotubes coated with chitosan/heparin PEMs influences the "race to the surface" in favor of mammalian cells.
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    Brush-like surface using heparin/chitosan based nanoparticles for blood-contacting applications
    (Colorado State University. Libraries, 2013) Nijjar, Rajvir Singh, author; Kipper, Matt, advisor; Bailey, Travis, committee member; Reynolds, Melissa, committee member
    With increasing applications of biomedical implants, it is crucial to develop surfaces that are blood compatible, meaning they do not induce platelet or protein adhesion. Many implants that are currently used to treat a wide range of problems have one major drawback, they can induce thrombosis. The endothelial glycocalyx plays a crucial role in preventing thrombosis. Based on this idea, we set out to develop a surface that has a brush-like structure similar to that of the endothelial glycocalyx. We developed the surface by adsorbing negatively charged heparin/chitosan polyelectrolyte complex nanoparticles onto a heparin/tri-methylchitosan polyelectrolyte multilayer. The surface was then characterized using surface plasmon resonance (SPR), quartz crystal microbalance (QCM), atomic force microsocopy (AFM), scanning electron microscope (SEM), and polarization modulation-infrared reflection absorption spectroscopy (PM-IRRAS). Using these techniques we confirmed that we had created a surface with brush- like structure. Our hypothesis that the nanoparticles on the surface swell and form a brush-like structure when exposed to physiological conditions seems to be correct, as a result, we feel the surface we have developed could have a wide range of applications in the biomedical field.
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    Investigation of adipose-derived mesenchymal stem cells interaction with electrospun demineralized bone matrix nanofiber scaffolds
    (Colorado State University. Libraries, 2016) Yaprak Akgul, Selin, author; Kipper, Matt, advisor; Popat, Ketul, advisor; Bailey, Travis, committee member; Ehrhart, Nicole, committee member
    Nanofiber demineralized bone matrix (DBM) scaffolds were fabricated by electrospinning, and their ability to support cell adhesion and cell viability of murine adipose-derived mesenchymal stem cells (AD-MSCs) for short-term in culture media was investigated. Poly (ε-caprolactone) (PCL) scaffolds were used as control surfaces. Live cell stain calcein-AM and CellTiter 96® Non-Radioactive Cell Proliferation assays were used for cell adhesion and cell proliferation, respectively. DBM scaffolds supported greater cell adhesion compared to PCL nanofiber scaffolds. For cell viability, the two types of scaffolds behaved similarly. The results led to further research on DBM scaffolds. The ability to support osteoblastic differentiation of AD-MSCs for long-term (three weeks) in osteogenic differentiation media was also investigated. Both PCL scaffolds and DBM scaffolds seeded with no cells were used as control surfaces. The total protein content of viable AD-MSCs on the scaffolds was assessed by bicinchoninic acid (BCA) assay. Nanofiber scaffolds displayed increased levels of alkaline phosphatase (ALP) activity for the first week for all cases. ALP activity dropped after one week. Scanning electron microscopy (SEM) and alizarin calcium staining techniques were used to examine mineralization patterns qualitatively on DBM and PCL nanofiber scaffolds. DBM scaffolds deposited more calcium mineral than PCL scaffolds during three-week experiments. Mineralization was quantified by energy-dispersive X-ray spectroscope (EDS). After three weeks of culture, EDS revealed high calcium and phosphorus deposition on DBM scaffolds compared to PCL controls. The DBM scaffolds exhibited increased mineralization over three weeks, both with and without cells. These results demonstrate that the adhesion, proliferation, and osteogenic differentiation of AD-MSCs were influenced by DBM scaffolds.