Thesis (Ph. D.)--Biomedical Engineering, Georgia Institute of Technology, 2008. / LaPlaca, Michelle, Committee Chair ; McDevitt, Todd, Committee Member ; Lee, Robert, Committee Member ; Archer, David, Committee Member ; Lambert, Nevin, Committee Member.

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Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(工学) / 甲第14264号 / 工博第3015号 / 新制||工||1448(附属図書館) / 26591 / UT51-2008-T24 / 京都大学大学院工学研究科高分子化学専攻 / (主査)教授 岩田 博夫, 教授 伊藤 紳三郎, 教授 大嶋 正裕 / 学位規則第4条第1項該当

Meniscus damage is very common and eventually leads to the deterioration of the entire knee joint. The goal of this study was to provide evidence that supports a proof of concept for a decellularized porcine meniscal xenograft to be used as a treatment method for meniscal injury as a partial or full meniscus transplant. This research adapted an antigen removal protocol for articular cartilage to produce decellularized xenografts in 48% of the time and with no significant difference in DNA content as other current methods. DNA and GAG content, and the compression moduli were significantly lower in the xenograft than the control, but collagen content remained the same. Tensile modulus and ultimate tensile stress were significantly higher for the xenograft than the control. Crosslinking analysis was performed and 0.2% genipin was found to have a significantly higher degree of crosslinking than the rest.

Full thickness wounds, such as deep burns, need restoration of both the dermal and epidermal layers of the skin. In normal wound healing, re-epithelialization occurs by migration and proliferation of keratinocytes from the wound edges and by differentiation of stem cells from remaining hair follicles. Restoration of dermis occurs by influx of growth factors secreted by macrophages, platelets, and fibroblasts; by fibroblast proliferation and subsequent synthesis and remodeling of collagenous dermal matrix. In the case of full-thickness acute burn injuries and chronic wounds (e.g. pressure ulcers, venous ulcers and diabetic foot ulcers), these processes are defective. With the principles of tissue engineering in mind (to correct, improve and maintain tissues and their functions), researchers have developed promising materials and methods to make it possible to restore either the dermal (Integra® DRT, Alloderm®) or the epidermal layer (split thickness skin grafts (STSG), cultured epithelial autografts (CEA), autologous keratinocytes in single cell suspension). It is now well established that superior results are obtained if both dermal and epidermal components are combined, for example in a bilayered skin equivalent. Apligraf® is recommended for use on venous ulcers and is the only bilayered living skin equivalent currently approved by the FDA. Studies on different factors affecting the wound healing capacity as well as techniques in use provide valuable information for further development. In this licentiate thesis, we evaluated different transplantation techniques for delivering cultured human keratinocytes in single cell suspension, a measure becoming more frequently used in addition to STSG and CEA for restoring the epidermal layer of the skin. We found that the pressure device, commonly used to spray cell suspension onto the wound with pressures as high as 200 kPa, killed around 0% of the cells. In comparison, an ordinary syringe with the attachment of a spray nozzle showed almost 90% viable cells post transplantation and provided an equally good distribution of the cell suspension. We also studied different silver containing dressings regarding silver accumulation in human skin. In addition, we graded the re-epithelialization to evaluate whether the dressings caused any delay in the wound healing process. We found that the silver dressings tested, with few exceptions, caused dermal accumulation of silver, primarily aggregated around blood vessels. We could also show that most of the dressings had negative effect on the re-epithelialization. For the restoration of the dermal layer of the skin, Integra® DRT functions as a scaffold for guided tissue regeneration of the dermis. We had the possibility to study a case of necrotizing fasciitis were the treatment consisted of the use of Integra® DTR together with sub-atmospheric pressure (after initial surgical debridement) and later transplantation of split thickness skin grafts. This measure proved to be safe as well as giving satisfactory pliable and aesthetically acceptable result.

Hydrogels have been extensively studied for use in applications such as tissue engineering, drug delivery systems, wound dressing, actuators, valves, and sensors in Micromechanical Systems (MEMS), among others. Thermo-responsive hydrogels in particular pose various advantages such as their capability to respond to an external stimulus and reverse the response when the stimulus is removed and the ability to imbibe a significant amount of solvent and increase their volume by over 1000%. Extensive research has been conducted to tune and improve hydrogel's rate and degree of swelling and mechanical properties. Previous work showed that when synthetic clay (Laponite) is cross-linked with a well-known thermo-responsive hydrogel composed of N- Isopropylacrylamide (NIPA) the mechanical properties of the hydrogel network improved. It was demonstrated that increasing the cross-linker concentration will increase the stiffness of the hydrogel network, but the swelling ratio will decrease. This imposes a tradeoff between two desirable properties, swelling ratio, and mechanical strength. In this work, a unique thermo-responsive nanocomposite hydrogel was synthesized with two types of synthetic clays, Laponite XLG and its modified version (with ionic dispersant) Laponite XLS, at different concentrations to explore the interrelation of the two clays synthesized with the NIPA gel with respect to the gel's microstructures, mechanical properties, swelling degree, and kinetics. It was found that the N-Isopropylacrylamide (NIPA) gel cross-linked with the combined synthetic clays XLS and XLG exhibited improved mechanical properties and swelling ratios at equilibrium. The Young Modulus improved by 247% (from 24.6 kPa to 85.3 kPa) and the swelling ratio at equilibrium exhibited an improvement of 35% (from 605% to 814%) when compared to N-Isopropylacrylamide (NIPA) cross-linked with either of the clays separately. The short and extended time swelling was characterized and compared with mathematical models to understand the swelling kinetics of the combined gels.

Osteoarthritis (OA) is the most common form of arthritis, often thought of as a disease of the elderly, but post traumatic OA predominantly impacts younger individuals. Articular cartilage is the tissue that coats the end of your bones in synovial joints. Since cartilage has limited healing capacity, defects, or injuries to it progressively erodes down to the subchondral bone. Unfortunately, current treatment options all have limitations, particularly for younger patients. Cartilage has a specific zonal architecture that is distinguished by the different cell morphologies and arrangements, biochemical composition, and mechanical properties. 3D bioprinting is a tissue engineering technique that involves the simultaneous extrusion of biomaterials and cells to fabricate constructs. The layer-by-layer nature of 3D bioprinting and the frequent use of hydrogels as biomaterials make it a promising technique to engineer zonal articular cartilage. The goal of this dissertation was to develop and use novel human reporter chondrocytes to determine optimal combinations of biomaterials to 3D bioprint both the middle-deep and surface zones of articular cartilage. Human articular chondrocytes were transduced with either a type II collagen promoter- or lubricin promoter-driven Gaussia luciferase. Upon promoter stimulation, luciferase is secreted by the cells enabling a high-throughput, temporal, assessment of either type II collagen or lubricin. The human chondrocyte reporter system was combined with a Design of Experiment approach which streamlined the process of biomaterial optimization. To 3D bioprint the deep zone, an optimal combination of gelatin methacrylate (GelMA) and hyaluronic acid methacrylate (HAMA) was determined based on type II collagen promoter-driven luminescence, chondrocyte mobility and biomaterial stiffness. While an optimal combination of GelMA and oxidized methacrylated alginate (OMA) was determined for the surface zone based on lubricin promoter-driven luminescence, lubricin secretion, and construct shape fidelity. Together these results highlight the effectiveness of human reporter chondrocyte optimization for 3D bioprinting zonal cartilage.

Despite advancements of modern medicine, the number of patients with the the end-stage kidney disease keeps growing, and surgical procedures to establish and maintain a vascular access for hemodialysis are rising accordingly. Surgical access of choice remains autogenous arteriovenous fistula, whereas approach “fistula first at all costs” leads to failure in certain subgroups of patients. Modern synthetic vascular grafts fail to deliver long-term results comparable with AV fistula. With all that in mind, this work has an aim of developing a new alternative vascular graft, which can be used for hemodialysis access using the methods of TE, especially electrospinning technique. It is hypothesized that electrospun scaffold, made of PCL and collagen type I may assemble mechanical properties similar to native blood vessels. Seeding such electrospun scaffolds with human microvascular endothelial cells (hmvECs) and preconditioning with shear stress and continuous flow might achieve sufficient endothelial lining being able to resist acute thrombosis. One further topic considered on-site infections, which represents one of the most spread complications of dialysis therapy due to continuous needle punctures. The main hypothesis was that during electrospinning process, polymers can be blended with antibiotics with the aim of producing scaffolds with antimicrobial properties, which could lead to reducing the risk of on-site infection on one side, while not affecting the cell viability. / Trotz der Fortschritte in der modernen Medizin wächst die Zahl der Patienten mit Nierenerkrankungen im Endstadium weiter, und die chirurgischen Verfahren zur Herstellung und Aufrechterhaltung eines Gefäßzugangs für die Hämodialyse nehmen entsprechend zu. Der chirurgische Zugang der Wahl bleibt eine autogene arteriovenöse Fistel, während der Ansatz „Fistel zuerst um jeden Preis“ bei bestimmten Untergruppen von Patienten zum Versagen führt. Moderne synthetische Gefäßtransplantate liefern keine mit AV-Fisteln vergleichbaren Langzeitergebnisse. Vor diesem Hintergrund zielt diese Arbeit darauf ab, ein neues alternatives Gefäßtransplantat zu entwickeln, das für den Zugang zur Hämodialyse unter Verwendung der TE-Methoden, insbesondere der Elektrospinntechnik, verwendet werden kann. Es wird angenommen, dass ein elektrogesponnenes Gerüst aus PCL und Kollagen Typ I ähnliche mechanische Eigenschaften wie native Blutgefäße aufweisen kann. Die Besiedelung solcher elektrogesponnener Gerüste mit menschlichen mikrovaskulären Endothelzellen (hmvECs) und das Vorkonditionieren mit Scherbeanspruchung und kontinuierlichem Fluss könnte eine ausreichende Endothelialisierung erreichen, um eine akute Thrombose vermeiden zu können. Ein weiteres Thema waren lokale Infektionen, die eine der am weitesten verbreiteten Komplikationen der Dialysetherapie aufgrund kontinuierlicher Nadelstiche darstellen. Die Haupthypothese war, dass Polymere während des Elektrospinnprozesses mit Antibiotika gemischt werden können, um Gerüste mit antimikrobiellen Eigenschaften herzustellen, die dazu führen können, dass das Risiko einer Infektion vor Ort auf einer Seite verringert wird, ohne die Lebensfähigkeit der Zellen zu beeinträchtigen.

Knorpeldefekte gelten in der Medizin als besonders schwierig zu beheben, da das avaskuläre und aneurale hyaline Knorpelgewebe nur über sehr begrenzte Selbstheilungskräfte verfügt. Die Entwicklung neuer klinischer Therapien für eine erfolgreiche Regeneration bis hin zum vollständigen Ersatz von beschädigtem oder erkranktem Knorpel stellt daher das Ziel umfangreicher Forschung dar. Darüber hinaus zeichnet sich Knorpel durch eine organisierte, zonale Zell-Matrix-Verteilung und -Dichte aus, die möglichst naturgetreu nachgebildet werden muss, um einen adäquaten Gelenkknorpelersatz zu schaffen. Das dreidimensionale Bioprinting von humanen mesenchymalen Stromazellen (hMSCs) in Hydrogelen ist hierbei ein vielversprechender Ansatz. Es sind jedoch umfangreiche Studien erforderlich, um herauszufinden, wie 3D-Stammzellkonstrukte mit unterschiedlichen Zelldichten und Zell-Zell-Wechselwirkungen in einer gedruckten Hydrogel Matrix interagieren. Deshalb wurde in dieser Arbeit untersucht, ob die mesenchymalen Stromazellen in Form von Einzelzellen oder Sphäroiden durch das Extrusionsdruckverfahren in ihrer Proliferationsfähigkeit und ihrem chondrogenen Differenzierungspotential beeinträchtigt werden. Hierfür wurden in dieser Arbeit sowohl das Zellüberleben als auch Proliferations- und Differenzierungsmarker in gedruckten und nicht gedruckten Proben mit Einzelzellkonzentrationen von 2-20 Millionen Zellen sowie bei Sphäroiden mit ca 4000 Zellen/Sphäroid untersucht. Es konnte gezeigt werden, dass das extrusionsbasierte Druckverfahren keine negativen Auswirkungen auf die Überlebensfähigkeit und die Proliferation der hMSCs hat. Zum Nachweis der chondrogenen Differenzierung wurden mehrere Experimente durchgeführt. Durch die Expression von Typ-II-Kollagen und Aggrecan sowie durch die Quantifizierung von GAG welches zu einem großen Teil in der ECM von Knorpelgewebe zu finden ist, konnte bestätigt werden, dass die mesenchymalen Stromazellen durch den Druckprozess ihr chondrogenes Differenzierungspotential nicht einbüßen. Die beim 3D-Bioprinting auftretenden Scherkräfte scheinen die in-vitro Chondrogenese sogar ohne chemische Stimulation durch TGF-β1 anzustoßen. Außerdem zeigten die Sphäroidgruppen ein höheres chondrogenes Differenzierungspotential als die Einzelzellgruppen. Um dies im Zusammenhang mit dem 3D Extrusionsdruckverfahren zu bestätigen, erscheint es sinnvoll, weitere Versuche mit noch höheren Zellkonzentrationen in Form von Sphäroiden durchzuführen. Zusammenfassend zeigte sich in dieser Arbeit, dass das extrusionsbasierte Druckverfahren in Alginat/Gelatine Hydrogelen keine Zellschädigung verursacht und weder die chondrogene Differenzierung von Einzelzellen noch von Sphäroiden beeinträchtigt. / Cartilage defects are considered particularly difficult to repair in medicine, since avascular and aneural hyaline cartilage tissue has only very limited self-healing capabilities. The development of new clinical therapies for successful regeneration to complete replacement of damaged or diseased cartilage therefore represents the goal of extensive research. In addition, cartilage is characterized by an organized, zonal cell-matrix distribution and density that must be replicated as closely as possible to nature in order to create an adequate articular cartilage replacement. Three-dimensional bioprinting of human mesenchymal stromal cells (hMSCs) in hydrogels is a promising approach in this regard. However, extensive studies are needed to determine how 3D stem cell constructs interact with different cell densities and cell-cell interactions in a printed hydrogel matrix. Therefore, this work investigated whether the mesenchymal stromal cells in the form of single cells or spheroids are affected in their proliferative capacity and chondrogenic differentiation potential by the extrusion printing process. For this purpose, cell survival as well as proliferation and differentiation markers were investigated in this work in printed and non-printed samples with single cell concentrations of 2-20 million cells and in spheroids with approximately 4000 cells/spheroid. It was shown that the extrusion-based printing process had no negative effects on the survival and proliferation of hMSCs. Several experiments were performed to demonstrate chondrogenic differentiation. By expressing type II collagen and aggrecan and quantifying GAG which is largely found in the ECM of cartilage tissue, it was confirmed that the mesenchymal stromal cells do not lose their chondrogenic differentiation potential by the printing process. The shear forces involved in 3D bioprinting appear to trigger in vitro chondrogenesis even without chemical stimulation by TGF-β1. In addition, the spheroid groups showed a higher chondrogenic differentiation potential than the single cell groups. To confirm this in the context of the 3D extrusion printing process, it seems reasonable to perform further experiments with even higher cell concentrations in the form of spheroids. In summary, this work showed that the extrusion-based printing process in alginate/gelatin hydrogels does not cause cell damage and does not affect the chondrogenic differentiation of either single cells or spheroids.

Articular cartilage provides a near frictionless surface for the articulating ends of bones. Cartilage functions to lubricate and transmit compressive forces resulting from joint loading and impact. If damaged, whether by traumatic injury or disease, cartilage lacks the ability for self-repair. This study explores the production of scaffoldree cartilage and investigates the effect of Tissue Growth Technologies’ CartiGen Bioreactor on the cartilage. Chondrocyte and bone marrow-derived stem cell (BMSC) attachment to chitosan is also investigated in hopes of producing a bilayered construct for osteochondral repair. Results demonstrate that culturing of scaffoldree cartilage in the CartiGen bioreactor resulted in an enhancement of the scaffoldree cartilage’s biomechanical and biochemical properties and that the chitosan microspheres were able to successfully support porcine chondrocyte and BMSC attachment. Results from both studies are encouraging for future work involving tissue engineered cartilage.