No description available.

Thesis (doctoral)--Lund University, 1993. / Added t.p. with thesis statement inserted.

Thesis (M. S.)--Bioengineering, Georgia Institute of Technology, 2010. / Committee Chair: Chaikof, Elliot; Committee Member: Conticello, Vincent; Committee Member: Jo, Hanjoong. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Thesis (doctoral)--Lund University, 1993. / Added t.p. with thesis statement inserted.

No description available.

Tissue engineering is an interdisciplinary field that aims to restore, maintain, or improve diseased or damaged tissues. Electrospinning has become one of the most popular means to fabricate a scaffold for various tissue engineering applications as the process is extremely versatile and inexpensive. The ability for electrospinning to consistently create nanofibrous structures capable of mimicking the native extracellular matrix (ECM) is the basis behind why this technique is so successful in tissue engineering. Cardiovascular disease has been the leading cause of death in the United States for over 100 years, and because of this, the need for coronary artery replacements is in serious demand. More specifically, small diameter vessels (<6 mm I.D.) are most needed, due to the fact that they are most often affected and the current clinical replacements provide less than optimal long-term patency and regenerative ability. Tissue engineering of vascular grafts has been investigated for over 50 years, however, synthetic replacements made of Dacron® and expanded-poly(tetrafluoroethylene) (e-PTFE) still remain the clinical standard. This study examines a variety of different ways to alter different characteristics of electrospun constructs, to create scaffolds that would be favorable for use as a blood vessel replacement; the end goal being the creation of an acellular bioresorbable vascular graft that would provide sufficient mechanical support to withstand physiological forces, as well as ample biocompatibility to allow host cells to infiltrate and regenerate the graft as the structure degrades. As a way of tailoring the mechanical and thermal properties of a scaffold to be more conducive to that of a native artery, a novel co-polymer was created from the random copolymerization of two monomers; 1,4-Dioxan-2-one (DX) and DL-3-methyl-1,4-dioxan-2-one (DL-3-MeDX) were mixed at different ratios and electrospun, forming nanofibrous scaffolds that exhibited different mechanical and thermal properties. Next, scaffolds were electrospun from natural and synthetic polymers, and the potential for these materials to elicit the formation of an acute thrombotic occlusion was investigated by quantifying tissue factor expression from monocytes using a novel technique. Tissue factor expression by monocytes on the electrospun natural and synthetic polymer scaffolds was compared to that of e-PTFE to determine their potential for use as vascular graft materials. Platelet-rich plasma (PRP), a naturally occurring blood component which is comprised of supraphysiologic concentrations of autologous growth factors, was activated and lyophilized to form a preparation rich in growth factors (PRGF). PRGF was electrospun for the first time, to create a scaffold that would mimic the role of the native ECM in the wound healing cascade. Characterization of these scaffolds proved their bioactivity was enhanced, with cell infiltration occurring throughout the structures in as little as 3 days. Lastly, PRP/PRGF and/or heparin were incorporated into electrospun PCL scaffolds as a means of enhancing the regenerative potential and reducing the thrombogenic potential of the scaffolds, while supplying the constructs with mechanical stability. The release of several pro-regenerative growth factors and chemokines from the PRP incorporated scaffolds was analyzed and the effect of PRP and heparin on scaffold degradation characteristics was determined. Additionally, cell proliferation, migration, sprout formation, and chemokine release were evaluated, and results from these experiments proved the addition of PRP could enhance the regenerative potential of the electrospun scaffolds. The results from this study reveal the variety of ways in which a number of characteristics of an electrospun scaffold can be altered to create a more ideal bioresorbable vascular graft that has the potential to be regenerated within the body, while providing enough mechanical support for this to occur over time.

A promising approach to overcome thrombus and neointima formation on vascular grafts is to create a functional, quiescent monolayer of endothelial cells on the surface of implants. Surface topography of these implants is proven to enhance cell attachment and to reduce the inflammation associated with a smooth surface. Photoembossing is a relatively new, simple, environment-friendly and cost-effective technique to create surface topographies, since there is no etching step or mould needed. In this study, photopolymer films are photoembossed through contact mask photoembossing, while fibres are photoembossed through holographic lithography. Surface relief textures of ridges and grooves with various pitch sizes and heights are successfully obtained through both methods. Furthermore, we introduce this technique to fabricate, for the first time, reproducible surface textures on electrospun fibres. Human umbilical vein endothelial cells (HUVECs) are used in the study. Three different systems are investigated: non-degradable PMMA-TPETA, semi-degradable PLGA-TPETA and fully degradable PLGA-PEGDA-DTT, for different applications and therapeutic requirements. Both non-degradable PMMA-TPETA photopolymer and semi-degradable PLGA-TPETA photopolymer are shown to improve biocompatibility compared to PMMA and PLGA, respectively. Photoembossed films made from these two photopolymers show significantly improved cell attachment and proliferation, IV with a water contact angle around 70º. It is shown that the pitch size of surface topographies affects cell adhesion and migration in the wound healing assay study. Interaction between HUVECs and fibres shows that cells grow from their initial locations at fibre crossings. Focal adhesions are seen to be more aggregated on the surface textured fibres, while those on the glass cover slips are more dispersed near the edge of the cell membrane. The appearance of F-actin in the cytoplasm is also seen to be influenced by the surface topography, where changes in the diameter of the fibre and its surface texture result in F-actin rearrangement. Our study shows that a surface textured, fully degradable, gel-like photopolymer PLGA-PEGDA-DTT has great potential to be further developed for tissue engineering applications.

Each year, more than one million prosthetic vascular grafts are implanted. Well-over 50 % of these artificial vessels are of the small caliber variety with an inner diameter less than or equal to 10 mm. The challenge rests in implanting these synthetic substitutes into a hemodynamic environment with a high downstream resistance and low rates of flow. Over the course of four interrelated studies, we investigated the healing properties of small caliber prosthetic vascular grafts. All of these studies were conducted using baboons. First, we documented the difference in healing response between three different types of vascular grafts: (1) autologous artery (2) allogeneic vessel (3) prosthetic ePTFE. This comparison furnished an important model of graft healing. Proliferating endothelial cells were localized to the top 10 % of the neointima, while the proliferating smooth muscle cells were identified within the lower 10 % of the neointima. Secondly, we examined the effects of changing a prosthetic grafts material properties and how that change impacts healing of the grafts surface. These ultrastructural changes were introduced by radially stretching a porous 60 mm ePTFE vascular graft. Radially stretching the graft material decreased the void fraction, reduced the potential for transmural ingrowth, and changed the healing characteristics of the implanted vessels. Thirdly, we investigated the effect of a changing hemodynamic environment upon the healing of a vascular graft with uniform material properties. The changing hemodynamics were generated with a stenotic model. Under sub-acute conditions, an inverse relationship failed to exist between intimal thickening and wall shear stress. Lastly, the details of this hemodynamic environment were documented with computational fluid dynamics (CFD). The computational grids were constructed using three sets of geometric information: (1) incorporating the ideal material dimensions of the implanted vessel (2) utilizing contour information from pressure-perfused histologic cross-sections (3) applying geometric information form detailed MRI imaging. MRI imaging information provided the best description of the vessels hemodynamic environment. With this computational information, correlations were made between the intimal thickening and hemodynamic parameters.

The research presented here deals with synthetic materials for application in tissue engineering, primarily poly(ethylene glycol) (PEG) and poly(dimethyl siloxane)star (PDMS)star. Tissue engineering seeks to repair or replace damaged tissue through implantation of cell encapsulated in an artificial scaffold. Cell differentiation and extracellular matrix (ECM) deposition can be influenced through a wide variety of in vitro culture techniques including biochemical stimuli, cell-cell interactions, mechanical conditioning and scaffold physical properties. In order to systematically optimize in vitro conditions for tissue engineering experiments, the individual effects of these different components must be studied. PEG hydrogels are a suitable scaffold for this because of their biocompatibility and biological "blank slate" nature. This dissertation presents data investigating: the effects of glycosaminoglycans (GAGs) as biochemical stimuli on pig vocal fold fibroblasts (PVFfs); the effects of mechanical conditioning and cell-cell interactions on smooth muscle cells (SMCs); and the effects of scaffold physical properties on SMCs. Results show that GAGs influence PVFf behavior and are an important component in scaffold design. Hyaluronic acid (HA) formulations showed similar production in collagen I and III as well as reduced levels of smooth muscle a-actin (SMa-actin), while chondroitin sulfate (CSC) and heparin sulfate showed enriched collagen III environments with enhanced expression of SMa-actin. A physiological flow system was developed to give comprehensive control over in vitro mechanical conditioning on TEVGs. Experiments performed on SMCs involved creating multi-layered TEVGs to mimic natural vascular tissue. Constructs subjected to mechanical conditioning with an endothelial cell (EC) layer showed enhanced expression of SMC differentiation markers calponin h1 and myocardin and enhanced deposition of elastin. Consistent with other studies, EC presence diminished overall collagen production and collagen I, specifically. Novel PDMSstar-PEG hydrogels were studied to investigate the effects of inorganic content on mesenchymal stem cell differentiation for use in TEVGs. Results agree with previous observations showing that a ratio of 5:95 PDMSstar: PEG by weight enhances SMC differentiation markers; however, statistically significant conclusions could not be made. By studying and optimizing in vitro culture conditions including scaffold properties, mechanical conditioning and multi-layered cell-cell interactions, TEVGs can be designed to maximize SMC differentiation and ECM production.

Thesis (Ph.D)--Biomedical Engineering, Georgia Institute of Technology, 2008. / Committee Chair: Elliot Chaikof; Committee Member: Marc Levenston; Committee Member: Robert Nerem; Committee Member: Vincent Conticello; Committee Member: Yadong Wang. Part of the SMARTech Electronic Thesis and Dissertation Collection.