Browsing by Author "Gatenholm, Paul"
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- Creation of Ovalbumin Based Scaffolds for Bone Tissue RegenerationFarrar, Gabrielle (Virginia Tech, 2009-04-24)Bio-based materials are a viable alternative to synthetic materials for tissue engineering. Although many bio-based materials have been used, Ovalbumin (OA) has not yet been researched to create 3D structures that promote cellular responses. Micro-porous scaffolds are a promising construct for bone tissue regeneration; therefore OA crosslinked with three different concentrations (10%, 15% and 20%) of glutaraldehyde (GA) was used in this research. After fabrication, a porous morphology was observed using SEM. Average pore sizes were found to be comparable to scaffolds previously shown to promote cellular response. A TNBS assay determined percent crosslinking in the scaffolds, however there was no significant difference in percent crosslinking despite differing GA concentrations used. Possible explanations include an excess of GA was used. Using DSC, a glass transition temperature (Tg) was found for control indicating the scaffolds are amorphous. Average dry and wet compressive strengths were also found. As expected, differing GA concentrations had no significant effect on Tg and average compressive strengths due to an excess used. Scaffolds were mechanically tested at 37°C with no significant difference found; therefore these scaffolds can be used in the body. It was shown through cell studies that MC3T3-E1 pre-osteoblast cells significantly increased in number on the 10% and 15% scaffolds, therefore cell proliferation occurred. Because of a positive cellular response, 10% GA scaffolds were used for differentiation studies that showed an increase in osteocalcin at 21 days and alkaline phosphatase levels for scaffolds cultured for 14 days. Overall OA scaffolds have shown to be a promising 3D construct for bone tissue regeneration.
- Electromagnetic Control of Biological AssemblySano, Michael B. (Virginia Tech, 2010-04-23)We have developed a new biofabrication process in which the precise control of bacterial motion is used to fabricate customizable networks of cellulose nanofibrils. This work describes how the motion of Acetobacter xylinum can be controlled by electric fields while the bacteria simultaneously produce nanocellulose, resulting in networks with aligned fibers. Since the electrolysis of water due to the application of electric fields produces the oxygen in the culture media far from the liquid-air boundary, aerobic cellulose production in 3D structures is readily achievable. Five separate sets of experiments were conducted to demonstrate the assembly of nanocellulose by Acetobacter xylinum in the presence of electric fields in micro and macro environments. This work demonstrates a new concept of bottom up material synthesis by control of a biological assembly process.
- Electrospun Nanocellulose: A New BiomaterialRodriguez Rivera, Katia Argelia (Virginia Tech, 2011-09-23)Science and engineering studies on biocompatible implantable materials for tissue and organ repair have recently focused on polymeric materials to serve as scaffolds for cellular integration. Cellulose in many forms has been demonstrated as potential biopolymer for tissue engineering; however, it has not been previously electrospun into a scaffold for tissue engineering applications. The overall goal of this research project was to produce electrospun cellulose acetate (CA) nanofibers with specific architectures and surface chemistries to be evaluated as scaffolds for tissue regeneration. The size and morphology of electrospun CA was impacted by polymer concentration, solvent system, and solution flow rate. The conversion of CA electrospun scaffolds into regenerated cellulose by exposure to NaOH ethanol solution was successful for scaffolds produced at polymer solution flow rate of at least 1 mL/h. The regeneration process resulted in minimal degradation of the cellulose while retaining the original fiber structure of the scaffold. In vitro cytotoxicity evaluation of the fibrous cellulose scaffolds on a culture of mouse fibroblast (L-929) cells indicated that this material posed no threat to mammalian cells. Electrospun cellulose scaffolds with different architectures and surface chemistries were designed and evaluated to enhance scaffold properties and cell adhesion. The morphology of the partially regenerated cellulose revealed only a broad diffraction peak for the scaffold material, while the fully regenerated cellulose showed a characteristic semi-crystalline cellulose II diffraction pattern. Fiber orientation and porosity of the scaffolds were controlled by electrospining CA solution onto the edge of a rotator wheel and laser microablation, respectively. Bioactivity of the scaffolds was shown to be enhanced via scaffold surface modification with either anionic or cationic functional groups. Biomimetic Ca-P crystal mineralization on electrospun cellulose fibers was produced by means of carboxymethyl cellulose (CMC) adsorption and treatments with simulated body fluid (SBF) or phosphate buffer saline (PBS) solutions. Porosity and Ca-P crystals enhanced osteoprogenitor cell adhesion on the electrospun cellulose scaffolds. Cationic modification by trimethyl ammonium betahydroxy propyl (THAMP) derivation and adsorption of extracellular matrix proteins on cellulose fibers promoted adhesion and proliferation of neural-like (PC12) and myoblast (C2C12) cells. Differentiation of myoblast cells (C2C12) towards myotubes on electrospun cellulose scaffolds was controlled by surface chemistry and mechanical properties. Together these studies showed great potential for cellulose acetate to be electrospun and converted into a viable biocompatible tissue engineering scaffolds.
- Microporous bacterial cellulose as a potential scaffold for bone regenerationZabrowska, Magdalena; Bodin, Aase; Bäckdahl, Henrik; Popp, Jenni; Goldstein, Aaron; Gatenholm, Paul (2010-01)Nanoporous cellulose biosynthesized by bacteria is an attractive biomaterial scaffold for tissue engineering due to its biocompatibility and good mechanical properties. However, for bone applications a microscopic pore structure is needed to facilitate osteoblast ingrowth and formation of a mineralized tissue. Therefore, in this study microporous bacterial cellulose (BC) scaffolds were prepared by incorporating 300–500 lm paraffin wax microspheres into the fermentation process. The paraffin wax microspheres were subsequently removed, and scanning electron microscopy confirmed a microporous surface of the scaffolds while Fourier transform infrared spectroscopy verified the elimination of paraffin and tensile measurements showed a Young’s modulus of approximately 1.6 MPa. Microporous BC and nanoporous (control) BC scaffolds were seeded with MC3T3-E1 osteoprogenitor cells, and examined by confocal microscopy and histology for cell distribution and mineral deposition. Cells clustered within the pores of microporous BC, and formed denser mineral deposits than cells grown on control BC surfaces. This work shows that microporous BC is a promising biomaterial for bone tissue engineering applications.
- Modification of Wood Fiber with Thermoplastics by Reactive Steam-ExplosionRenneckar, Scott Harold (Virginia Tech, 2004-07-16)For the first time, a novel processing method of co-refining wood and polyolefin (PO) by steam-explosion was scientifically explored for wood-thermoplastic composites without a coupling agent. Traditional studies have addressed the improvement of adhesion between components of wood thermoplastic composites through the use of coupling agents such as maleated PO. The objective of this study was to increase adhesion between wood and PO through reactive processing conditions of steam-explosion. PO characteristics, such as type (polyethylene or polypropylene), form (pellet, fiber, or powder) and melt viscosity were studied along with oxygen gas content of the steam-explosion reactor vessel. Modification of co-processed wood fiber was characterized in four studies: microscopy analysis of dispersion of PO with wood fiber, sorption properties of co-processed material, chemical analysis of fractionated components, and morphological investigation of co-processed material. Two additional studies are listed in the appendices that relate to adsorption of amphiphilic polymers to the cellulose fiber surface, which is one hypothesis of fiber surface modification by co-steam-explosion. Microscopy studies revealed that PO melt viscosity was found to influence the degree of dispersion and uniformity of the steam-exploded material. The hygroscopic nature of the co-processed fiber declined as shown by sorption isotherm data. Furthermore, a water vapor kinetics study found that all co-refined material had increased initial diffusion coefficients compared to the control fiber. Chemical changes in fractionated components were PO-type dependent. Lignin extracted from co-processed wood and polyethylene showed PO enrichment determined from an increase of methylene stretching in the Fourier Transform infrared subtraction spectra, while lignin from co-processed wood and polypropylene did not. Additionally, extracted PO showed indirect signs of oxidation as reflected by fluorescence studies. Solid state nuclear magnetic resonance spectroscopy revealed a number of differences in the co-processed materials such as increased cellulose crystallinity, new covalent linkages and an alternative distribution of components on the nanoscale reflected in the T1Ï relaxation parameter. Steam-explosion was shown to modify wood fiber through the addition of "non-reactive" polyolefins without the need for coupling agents. In light of these findings, co-refining by steam-explosion should be viewed as a new reactive processing method for wood thermoplastic composites.
- Three-dimensional bioprinting of biosynthetic cellulose (BC) implants and scaffolds for tissue engineering(United States Patent and Trademark Office, 2014-04-08)A novel BC fermentation technique for controlling 3D shape, thickness and architecture of the entangled cellulose nano-fibril network is presented. The resultant nano-cellulose based structures are useful as biomedical implants and devices, are useful for tissue engineering and regenerative medicine, and for health care products. More particularly, embodiments of the present invention relate to systems and methods for the production and control of 3-D architecture and morphology of nano-cellulose biomaterials produced by bacteria using any biofabrication process, including the novel 3-D Bioprinting processes disclosed. Representative processes according to the invention involve control of the rate of production of biomaterial by bacteria achieved by meticulous control of the addition of fermentation media using a microfluidic system. In exemplary embodiments, the bacteria gradually grew up along the printed alginate structure that had been placed into the culture, incorporating it. After culture, the printed alginate structure was successfully removed revealing porosity where the alginate had been placed. Porosity and interconnectivity of pores in the resultant 3-D architecture can be achieved by porogen introduction using, e.g., ink-jet printer technology.