No description available.

Cell adhesion and growth are central issues in the otherwise promising method of endothelialization of materials for improving blood compatibility. To improve cell adhesion to biomaterial surfaces, surface modification with cell adhesion peptides is often used. In particular, arginine-glycine-aspartic acid (RGD), long recognized as a peptide sequence that plays and important role in cell adhesion, has been covalently attached to surfaces to enhance cell adhesion. In this work, the effect of the orientation of the cell adhesion peptide immobilized on the surface was studied through using gold surfaces, which can be readily modified with thiols and sulfur-containing groups. Peptide orientation was controlled by the placement of the cysteine (C) at either the C- or N-terminus, Two cell adhesion peptides, the non-specific RGD and more endothelial cell specific REDV (arginine-glutamic acid-aspartic acid-valine), were studied for their effect on the surface chemical and biological properties, including effects on the interactions with the endothelial cell line ECV304. Vitronectin adsorption to the modified surfaces was specifically examined as a possible reason for differences noted. The results suggest that peptide orientation plays an important role in the interactions of cells and proteins to the modified surfaces. Peptides with the cysteine at the N-terminus showed increased adhesion of endothelial cells from the ECV304 line, with the greatest adhesion noted consistently on the CREDV-modified surfaces. Differences in surface chemistry as evaluated by x-ray photoelectron spectroscopy were also found higher levels of bonded peptide when the thiol-containing cysteine was in the N-terminal position. These results suggest that the secondary structure of the peptide can be used to enhance or to limit its reaction with the surface. Furthermore, while cell adhesion was noted during culture in the absence of serum, significant increases in the numbers of adherent cells were noted on all surfaces when the cells were grown in the presence of serum. Immunoblotting and culture with antibodies demonstrated that this increase in the adhesion of the cells is likely mediated primarily by the cell adhesion peptide vitronectin. / Thesis / Master of Engineering (ME)

Rheological modification is frequently cited as a key application for hyperbranched polymers. However, the high degree of branching in these polymers restricts entanglement and the resultant mechanical properties suffer. Longer distances between branch points may allow entanglements. Highly branched polymers, where linear units are incorporated between branch points, are synthesized with an oligomeric A2 plus a monomeric B3. Higly branched polymers differ from traditional hyperbranched polymers in that every monomeric repeating unit of a hyperbranched polymer is a potential branch point, which is not true for highly branched polymers. The oligomeric A2 plus B3 synthetic methodology was used for the synthesis of highly branched ionenes and polyurethanes. Highly branched ionenes, which have a quaternary ammonium salt in the main chain, were synthesized with a modified Menshutkin reaction. The oligomeric A2 was comprised of well-defined telechelic tertiary amine endcapped poly(tetramethylene oxide). Reduced mechanical properties were observed for highly branched polymers compared to linear counterparts. Highly branched polyurethanes were synthesized with polyether soft segments including poly(ethylene glycol), poly(tetramethylene glycol), and poly(propylene glycol). Degree of branching was determined via a novel 13C NMR spectroscopy approach, which is described herein. The classical degree of branching was supplemented with an alternative degree of branching equation, which was tailored for highly branched architectures. The melt and solution viscosities of highly branched poly(ether urethane)s were orders of magnitude lower than the linear analogs. For the first time, the presence of entanglements was confirmed for highly branched polymers. Doping the highly branched polyurethane with lithium perchlorate, a metal salt, resulted in a significantly higher melt viscosity. The ionic conductivity of the highly branched polyurethane when doped with a metal salt was orders of magnitude higher than the linear analog. Soybean oil was oxidized for synthesis of soy-based polyol monomers. Three regimes were determined, and for the first time, a correlation between hydroxyl number and a resonance from the double bonds of soybean oil in 1H NMR spectroscopy was described. The relationship was used to accurately describe oxidation of soybean oil with time, temperature, and air flow rate. Soybean oil oxidation was catalyzed, and tack-free films were formed. / Ph. D.

Thesis (doctoral)--Lund University, 1997. / Added t.p. with thesis statement inserted.

Thesis (doctoral)--Lund University, 1997. / Added t.p. with thesis statement inserted.

Polymer nanocomposites are a going part of Materials Science and Engineering. These new composite materials exhibit dimensional and thermal stability of inorganic materials and toughness and dielectric properties of polymers. Development of nanocomposites become an important approach to create high-performance composite materials. In this study silica, fly ash, silica nanotubes and carbon black particles have been added to modify polyurethane foam and thermoplastic polyurethanes. It has been found that the addition of silica can diminish the size of foam bubbles, resulting in an increased stiffness of the material, increase of the compressive strength, and greater resistance to deformation. However, the uniformity of bubbles is reduced, resulting in increased friction of the material. Fly ash added to the foam can make bubbles smaller and improve uniformity of cells. Therefore, the material stiffness and compressive strength, resistance to deformation, and has little impact on the dynamic friction of the material. Adding nanotubes make bubble size unequal, and the arrangement of the bubble uneven, resulting in decreased strength of the material, while the friction increases. After the addition of carbon black to the polyurethane foam, due to the special surface structure of the carbon black, the foam generates more bubbles during the foaming process changing the foam structure. Therefore, the material becomes soft, we obtain a flexible polyurethane foam. The results of mechanical properties determination of the thermoplastic polyurethane that adding particles may increase the stiffness and wear resistance of the thermoplastic polyurethane, while the tensile properties of the material are reduced. This phenomenon may be due to agglomeration of particles during the mixing process. Possibly the particles cannot be uniformly dispersed in the thermoplastic polyurethane.

No description available.

The aim of this study was to design and synthesise thermoplastic biodegradable and biocompatible polyurethanes for tissue engineering applications. A secondary aim was to tailor a range of degradation rates of the polyurethanes to suit a broad spectrum of tissue engineering applications. Various factors were systematically investigated in order to provide a means of controlling mechanical, thermal and degradation properties of the polyurethanes. The factors investigated included variation of the hard segment percentage, the diisocyanate, the soft segment macrodiol as well as the chain extender. Soft segment macrodiols were synthesised for this study including a poly(γ-butyrolactone) macrodiol which has been used to make biodegradable aliphatic poly(ester-urethane) for the first time. A novel range of degradable chain extenders was also developed and has been reported. The polymers were characterised using Gel Permeation Chromatography (GPC), Instron tensile testing, Differential Scanning Calorimetry (DSC) and Shore hardness. Cell culture testing was performed as was a three-month degradation study which showed the polyurethanes to be biocompatible and biodegradable respectively. Selected materials were shown to be suitable for scaffold fabrication using Fused Deposition Modelling (FDM), and the scaffolds made were further shown to support primary fibroblast growth in vitro.

Thesis (Ph. D.)--School of Textile and Fiber Engineering, Georgia Institute of Technology, 2004. Directed by Haskell Beckham. / Vita. Includes bibliographical references (leaves A1-A2).

Bone graft substitute is a continuously developing field in orthopedics. When compared to tradition biomaterial in the field such as PLA or PCL, elastomer like polyurethane offers advantages in its high elasticity and flexibility, which establish an intimate contact with surrounding bones. This tight contact can provide a stable bone-material interface for cell proliferation and ingrowth of bone. The aim of this study is to evaluate the osteogenesis capabilities of a porous polyurethane scaffold in a critical size bone defect. In this study, a porous scaffold synthesized from segmented polyurethane is put under in vitro and in vivo tests to evaluate its potential in acting as a bone graft substitute for critical size bone defects. In vitro results indicate osteoblast-like cells are proliferating on the polyurethane scaffold during the 21-days experiment. Cells express their normal morphology when seeded on polyurethane under fluorescent staining. Although cells show a relatively lower cell activity then that seeded on culture plate, they share a similar alkaline phosphatase activity profile with the controls during the experiment period. In the in vivo animal model, reconstructed images from micro CT scanning indicates there are bone ingrowth inside the scaffold. Histology also indicates a tight interface has formed between bone and polyurethane, with osteogenic cells proliferating on the surface. The result has indicates polyurethane is a potential material for orthopedics in acting as a bone graft substitute. / published_or_final_version / Orthopaedics and Traumatology / Master / Master of Philosophy