No description available.

<p>Mesenchymal stem cells have shown potential for success in gene therapy due to their ability to differentiate and their immunomodulatory properties <em>in vivo</em>. Although they have many inherent characteristics that are suitable for use within gene therapy, genetic modification of these cells is more difficult. Since MSCs are available in limited quantities and cannot be expanded indefinitely, the modification technique must ensure efficient expression of the transgene, a high cell survival rate and an intact ability to differentiate to various cell lineages. We optimized electroporation conditions for the genetic engineering of bone marrow-derived and umbilical cord blood-derived mesenchymal stem cells. MSCs engineered using electroporation conditions produced more transgene expression than cells engineered with cationic lipids in bone marrow-derived mesenchymal stem cells, but produced similar amounts in umbilical cord blood-derived mesenchymal stem cells. Optimal electroporation conditions also expressed more transgene than polymer based transfection reagent in umbilical cord blood-derived mesenchymal stem cells. Cell survival after optimal electroporation conditions was 67% in umbilical cord blood-derived mesenchymal stem cells. Most importantly, cells maintained their ability to differentiate into osteogenic, chondrogenic and adipogenic cell lineages. Electroporating umbilical cord blood-derived mesenchymal stem cells with a Factor IX containing plasmid lead to the FIX protein being expressed for over 12 days <em>in vitro</em>. This optimized electroporation protocol has created a fast, easy, economic and efficient method for genetically modifying mesenchymal stem cells without altering their ability to differentiate.</p> / Master of Applied Science (MASc)

Strategien zur Gewebsreparatur durch Zelltransplantate erfordern die Verfügbarkeit einer ausreichenden Menge von Zellen, die Schaffung konduktiver Mikrokulturbedingungen für die Integration und die Entwicklung des Implantats und die Entwicklung reproduzierbarer chirurgischer Technik für die klinische Anwendung des kultivierten Transplantats. In der vorliegenden Arbeit wurden mehrere Techniken der Zelltransplantation entwickelt und tierexperimentell erprobt. Unter Verwendung von Alginat wurde eine neue sequentielle Zellkulturtechnik für Knorpeltransplantate entwickelt. Der optimale Kompromiß zwischen der Matrixstabilisierung und einer ausreichenden Diffusionskapazität für die Zellfunktion wurde bei einer Mischung aus 0,6 % Alginat und 4,5 % Fibrin gefunden. Weitere untersuchte Matrixstrukturen zur Transplantation von Chondrozyten, wie die bioresorbierbaren Polymere, das Kollagen-Fibrin-Gel besitzen gegenüber der gegenwärtig kommerziell genutzten Methode hinsichtlich des chirurgischen Prozederes bei vergleichbaren histologischen Ergebnissen Vorteile. Die histomorphologischen Veränderungen und die Entwicklung des Transplantats in vivo werden durch die spezifischen Bedingungen der Transplantatumgebung beeinflußt. Dabei ist ein vollständiges zonales und sequentielles Remodeling von Knorpel-Knochendefekten nur bei nicht ausdifferenzierten Zellen (embryonale Chondrozyten, periostale Zellen) zu erkennen, da diese Zellen ein exzellentes chondrogenes und osteogenes Potential besitzen. Transplantate unter Verwendung von Chondrozyten zeigen dagegen nur eine sehr geringe Rekonstruktion des subchondralen Knochens. Periostale Zellen sind in vitro ohne Verlust des Phänotyps amplifizierbar und stellen daher eine optimale Zellquelle für das Tissue Engineering dar. Für das Bone Engineering ist die Kombination der osteokonduktiven Eigenschaften unterschiedlicher Trägermaterialien mit Zellen, die ein osteogenes Potential besitzen ein neuer Weg zur Optimierung des Prozesses der knöchernen Rekonstruktion, wie in Versuchen zur Rekonstruktion segementaler Ulnadefekte bei Kaninchen gezeigt werden konnte. Die Herstellung eines präossären stabilen aber formbaren Transplantats mit vielfältigen klinischen Einsatzmöglichkeiten ist unter Verwendung von biodegradierbaren Polymeren und von Fibrinbeads realisierbar. Der Einsatz von Wachstumsfaktoren, wie TGF-?1 und die zunehmenden Erkenntnisse zu den Zell-Zell- und Zell-Matrix-Interaktionen ermöglichen die verbesserte Generation ortsständigen Gewebes durch multipotente Zellen. Die immer komplexere und umfassendere Wiederholung der sich in der Ontogenese abspielenden Vorgänge durch die Techniken des Tissue Engineering, ermöglicht die Schaffung therapeutischer Optionen zur Behandlung von Knochen- und Knorpeldefekten, wo bisher keine existierten oder nur unzulänglich vorhanden waren. / Strategies for tissue repair by cell transplants require the availability of a sufficient amount of cells, the creation of conductive microculture conditions for the integration and development of the implant and the development of reproducible surgical techniques for the clinical application of the cultivated transplant. Within the frame of the present work, several techniques of cell transplantation were developed and tested by way of experiment. By using alginate, a new sequential cell culture technique was developed for cartilage transplants. The optimum compromise between the matrix stabilization and a sufficient diffusion capacity for the cell function was found with a mixture of 0.6 % of alginate and 4.5 % of fibrin. Further investigated matrix structures for the transplantation of chondrocytes, such as the bio-absorbable polymers, the collagen fibrin jelly show advantages compared with the method commercially applied at present regarding the surgical procedure with the gained histological results being comparable. The histomorphological changes and the development of the transplant within the living body are influenced by the specific conditions of the transplant environment. In this connection, a complete zonal and sequential remodeling of osteochondrodefects can only be detected for non-outdifferentiated cells (embryonic chondrocytes, periosteal cells) as these cells have an excellent chondrogenic and osteogenic potential. When using chondrocytes for transplants, however, the transplant only shows a very little restoration of the subchondral bone. Periosteal cells can be amplified in the living body without losing the phenotype, thus constituting an optimum cell source for tissue engineering. For the bone engineering, the combination of the osteoconductive properties of different carrier materials with cells having an osteogenic potential is a new way for optimizing the process of bone restoration as it was demonstrated in tests for the restoration of segmental ulnar defects occurring with rabbits. The generation of a preosteal stable, but mouldable transplant with manifold clinical possibilities of utilization can be realized by using biodegradable polymers and fibrin beads. The use of growth factors, such as TGF-?1, and the increasing knowledge of cell-cell and cell-matrix interactions enable the improved generation of stationary tissue by multipotent cells. The more and more complex and comprehensive repetition of processes going on in the ontogenesis by way of tissue engineering enables the creation of therapeutic options for the treatment of osteochondrodefects where hitherto none existed or just in a too small number.

Beim Tissue Engineering werden Erkenntnisse aus der Medizin, Biologie und Chemie mit Methoden der Ingenieurwissenschaften kombiniert, um biologische Ersatzgewebe herzustellen. Das Konzept besteht darin, aus körpereigenen Zellen einen vitalen und funktionalen Gewebeersatz zu fertigen. Hierbei werden körpereigene Zellen auf ein resorbierbares Gerüst transplantiert, in vitro zu einer stabilen Struktur gefestigt, um letztendlich ein vitales Ersatzgewebe implantieren zu können. Die Konstrukte für die menschliche Herzchirurgie sollten in das umgebende Gewebe einwachsen und haben das Potential sich wie gesundes Gewebe zu entwickeln und mitzuwachsen. / Tissue engineering combines knowledge from the fields of medicine, biology and chemistry with the methods of engineering to create artificial tissue. The concept is to produce vital and functional tissue from endogenous cells. These are seeded on to an absorbable scaffold and consolidated to form a stable structure in vitro, with the aim of eventually being able to produce substitute tissue for implantation. The constructs for human cardiac surgery need to embed into the surrounding tissue and, just like natural tissue, to have the potential to grow and develop.

Wound dressing plays an important role in wound recovery and collagen interacts with the human body in such a way that it has specific advantages compared to synthetic materials. The aim of the present study was to get an optimal crosslinking agent for collagen and so the mechanical, chemical and biochemical properties of crosslinked collagen materials were investigated. Fibroblast cells are important in the process of wound healing, so the interaction of human fibroblast cells with crosslinked collagen films were investigated as well. Collagen I was isolated from bovine achilles tendons and collagen films were formed using the isolated collagen I solution. Collagen films were crosslinked with glutaraldehyde (GA), genipin, hexamethylenediisocyanate (HMDC), 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide (EDC) at the equal concentration of 0.02 M and these crosslinked collagen films were compared with uncrosslinked collagen films (control). The surfaces of the crosslinked films were investigated using scanning electron microscopy (SEM). There was observable fibre structure on GA- and genipin-crosslinked collagen films. The tensile strength, elongation at break and low strain modulus of the crosslinked collagen films were investigated. The results showed that GA-, genipin- and HMDC-crosslinked collagen films obtained higher tensile strength than the control. Elongation at break of all the crosslinked collagen films became lower than the control. GA- and genipin-crosslinked collagen films obtained higher low strain modulus than other crosslinked collagen films and the control. The denaturation temperatures of all crosslinked collagen films were significantly higher than the control and the denaturation temperatures of GA- and genipin-crosslinked films were much higher than those of HMDC- and EDC-crosslinked films. All the crosslinked collagen films were resistant to the digestion of collagenase. These results suggest that all the crosslinking agents are effective and GA- and genipin-crosslinked films obtained more extensive crosslinking. The interaction of crosslinked collagen films with fibroblast cells was investigated, e.g. adhesion, proliferation and migration of fibroblast cells. The results demonstrated that the control, genipin- and EDC-crosslinked collagen films were conducive to cell adhesion. Fibroblast cells on the control, genipin- and EDC-crosslinked collagen films were able to proliferate after 24 hours, with increased growth after 48 hours. The fibroblast cells on the control, genipin- and EDC-crosslinked collagen films migrated directionally. The cells on genipin-crosslinked film initiated directional migration earlier than those on control- and EDC-crosslinked films. In summary, genipin crosslinked collagen films show high denaturation temperature, higher tensile strength and good biocompatibility for fibroblast cells adhesion, proliferation and migration. Genipin should be regarded as a suitable crosslinking agent for reconstituted collagen for use in wound dressing.

No description available.

A majority of all fractures in current US armed conflicts are open fractures, in which a soft tissue injury is sustained along with the bone fracture. Even with gold standard treatment, in which muscle flaps are used to cover bony defects, patients often do not regain normal function of their extremity, highlighting the necessity for tissue engineering strategies for this complex clinical problem. Due to a substantial amount of tissue damage and debridement treatment in composite injuries, a large volume of cells and extracellular matrix (ECM) proteins that are necessary for tissue healing are removed from the body. In the replacement of large volumes of tissue, nutrient transfer necessitates a vascular supply to maintain the viability of delivered cells. The objective of this project was to examine the regenerative potential of engineered matrix constructs and stem cells on composite bone & muscle defects. We hypothesized that stem cells delivered on engineered matrix constructs into the muscle defect will aid in muscle regeneration and promote bone healing, ultimately resulting in superior functional limb recovery. These studies established multiple preclinical platforms for testing tissue engineering strategies as well as models that can be used to gain insights on the healing of VML and composite VML/bone defects. From some of the insights gained on the vascularization of the defect sites, a vascular treatment strategy was tested within these platforms and shown to have varying results in the treatment of complex multi-tissue injuries.

Bone and cartilage constructs are often plagued with mechanical failure, poor nutrient transport, poor tissue ingrowth, and necrosis of embedded cells. However, advances in computer aided design (CAD) and computational modeling enable the design of scaffolds with complex internal michroarchitectures and the a priori prediction of their transport and mechanical properties, such that the design of constructs satisfying the needs of the tissue environment can be optimized. The goal of this research is to investigate the capability of additive manufacturing technologies to create designed microarchitectured tissue engineering scaffolds for bone and cartilage regeneration. This goal will be achieved by pursuing the following two objectives: (1) the manufacture of bioresorbable thermoplastic scaffolds by selective laser sintering (SLS) (2) and the manufacture of hydrogel scaffolds by large area maskless photopolymerization (LAMP). SLS is a laser based additive manufacturing method in which an object is built layer-by-layer by fusing powdered material using a computer-controlled scanning laser. LAMP is a massively parallel ultraviolet curing-based process that can be used to create hydrogels from a photomonomer on a large-scale (558x558mm) while maintaining extremely high feature resolution (20µm). In this research, SLS is used to process polycaprolactone (PCL) and composites of PCL with hydroxyapatite (HA) for bone tissue engineering applications while LAMP is used to process polyethylene glycol diacrylate (PEGDA) which can be used for hard and soft tissue applications.

This study explored hydrostatic pressure as a mechanobiological parameter to control in vitro endothelial cell tubulogenesis in 3-D hydrogels as a model microvascular tissue engineering approach. For this purpose, the present investigation used an endothelial spheroid model, which we believe is an adaptable microvascularization strategy for many tissue engineering construct designs. We also aimed to identify the operating magnitudes and exposure times for hydrostatic pressure-sensitive sprout formation as well as verify the involvement of VEGFR-3 signaling. For this purpose, we used a custom-designed pressure system and a 3-D endothelial cell spheroid model of sprouting tubulogenesis. We report that an exposure time of 3 days is the minimum duration required to increase endothelial sprout formation in response to 20 mmHg. Notably, exposure to 5 mmHg for 3 days was inhibitory for endothelial spheroid lengths without affecting sprout numbers. Moreover, endothelial spheroids exposed to 40 mmHg also inhibited sprouting activity by reducing sprout numbers without affecting sprout lengths. Finally, blockade of VEGFR-3 signaling abolished the effects of the 20-mmHg stimuli on sprout formation. Based on these results, VEGFR-3 dependent endothelial sprouting appears to exhibit a complex pressure dependence that one may exploit to control microvessel formation.

published_or_final_version / Orthopaedics and Traumatology / Master / Master of Philosophy