published_or_final_version / Paediatrics / Master / Master of Medical Sciences

Thesis(M.S.)--Auburn University, 2005. / Abstract. Vita. Includes bibliographic references.

No description available.

Two major problems preventing the clinical application of pancreatic islet transplantation were investigated. The problem of allograft rejection was studied in rats, made diabetic by streptozotocin treatment. It was shown that DA rats given LEW renal allografts and treated with cyclosporine accepted their grafts, and subsequently developed a strain-specific unresponsive state that allowed successful transplantation of LEW islets without further immunosuppression, whilst BN islets were rejected normally. The effect was demonstrated to be independent of the site of islet transplantation, and, once an islet allograft had been accepted, it was possible to remove the original renal allograft without affecting the transplanted islets. The effect was shown to apply to another strain combination (LEW into PVG), and also to animals made unresponsive to renal allografts by another method (donor-specific blood transfusion). The problem of separation of adequate numbers of viable islets from the pancreas was studied in the rat, dog, pig and human. To aid the investigation, supravital staining techniques were developed, using neutral red to identify the islets, and fluorescein diacetate and ethidium bromide to assess islet viability. A variety of islet isolation techniques were investigated, and a new technique for isolation of islets from the dog pancreas, yielding up to 160,000 islets from 1 pancreas with a maximum purity of 80%, was developed. The structural integrity and in vitro function of the isolated islets was demonstrated, but it was not possible to prevent diabetes by autotransplantation of islets to the portal vein of pancreatectomised dogs. A method for isolation of islets from the human pancreas was developed from that used in the dog, yielding up to 80,000 islets from a whole pancreas, with a maximum purity of 40%. The technique was shown to be both simple and reliable. The structural integrity and in vitro function of the isolated islets was demonstrated, and the viability of the islets proven by successful transplantation under the kidney capsule of nude mice.

Thesis (Ph. D.)--Rutgers University, 2009. / "Graduate Program in Materials Science and Engineering." Includes bibliographical references.

Thesis (M. Phil.)--University of Hong Kong, 2008. / Includes bibliographical references (leaves 151-192) Also available in print.

Thesis (M. Phil.)--University of Hong Kong, 2008. / Includes bibliographical references (leaves 151-192) Also available online.

Micrografting was used to study the restoration of symplasmic transport at the graft union and to examine the long-distance transport of macromolecules between scion and rootstock. New techniques were established, such as correlative imaging and single-cell analysis in microfluidic devices, to study graft development both in vivo and in vitro. Imaging of Arabidopsis homografts showed that a symplasmic domain develops in the callus stele whose function may be to contain the spread of auxin into the surrounding ground tissue. It was demonstrated, also, that recent reports of organelle transfer at the graft union cannot be explained by the formation of secondary plasmodesmata (PD) at the graft interface. While fused calli did not exchange organelles in vitro, large aggregates of the SIEVE-ELEMENT OCCLUSION RELATED protein fused to YFP (SEOR-YFP; 112 kDa) were unloaded from mature sieve tubes into living cells of the graft partner in vivo, suggesting that vascular remodelling may be a prerequisite for the exchange of organelles at the graft interface. Fusion proteins expressing organelle-targeting signals were found to translocate across the graft junction, unloading into cell files adjacent to the root protophloem. The phloem mobility of a given fusion protein was assessed using bioinformatic and statistical analysis of publicly available data. The size of a protein and its relative abundance in CCs both emerged as defining factors for subsequent phloem transport. The recipient tissue for phloem-unloaded macromolecules was identified as the phloem-pole pericycle (PPP). This cell layer is required to remove macromolecules from the terminus of the protophloem. Induced callose deposition at the PD that connect protophloem SEs to the PPP caused a restriction in unloading and a subsequent arrest in root growth. A non-cell autonomous protein of CC origin, NaKR1-1, is proposed to affect the unloading of macromolecules either by increasing the size exclusion limit (SEL) of PD within the PPP or by enabling a build-up in pressure at the protophloem terminus, due to SUC2 activity, thus allowing phloem unloading.

Osteoarthritis is a highly prevalent, debilitating disease characterized by the wear and degradation of articular cartilage. While many surgical interventions exist, few are consistently effective and those that are effective are not necessarily suitable for all patients. The objective of this dissertation is to improve patient care through the development of a new surgical technique and through basic science studies which seek to better understand articular cartilage wear initiation. Four studies, which address this objective are summarized below. Osteochondral allograft transplantation provides a safe and effective treatment option for large cartilage defects, but its use is limited partly due to the difficulty of matching articular surface curvature between donor and recipient. We hypothesize that bendable osteochondral allografts may provide better curvature matching for patella transplants in the patellofemoral joint. The finite element study presented in Chapter 2 investigates patellofemoral joint congruence for unbent and bendable osteochondral allografts, at various flexion angles. Finite element models were created for 12 femur-patella osteochondral allograft pairings. Two grooves were cut into the bony substrate of each allograft, allowing the articular layer to bend. Patellofemoral joints with either unbent (OCA) or permanently bent (BOCA) allografts were articulated from 40 to 70 degrees flexion and contact area was calculated. OCAs and BOCAs were then shifted 6 mm distally toward the tibia (S-OCA, S-BOCA) to investigate the influence of proximal-distal alignment on congruence. On average, no significant difference in contact area was found between native patellofemoral joints and either OCAs or BOCAs (p > 0.25), indicating that both types of allografts restored native congruence. This result provides biomechanical support in favor of an emerging surgical procedure. S-BOCAs resulted in a significant increase in contact area relative to the remaining groups (p < 0.02). The fact that bendable osteochondral allografts produced equally good results implies that these bendable allografts may prove useful in future surgical procedures, with the possibility of transplanting them with a small distal shift. Surgeons who are reluctant to use osteochondral allografts for resurfacing patellae based on curvature matching capabilities may be more amenable to adopting bendable osteochondral allografts. The recent development of bendable osteochondral allografts provides the potential for improved osteoarthritis treatment for joints whose current treatment is unsatisfactory. One such joint is the carpometacarpal joint in the thumb. While the current standard of care for carpometacarpal osteoarthritis, ligament reconstruction and tendon interposition, can reduce pain in the joint, it does not restore full joint function and mobility. A proposed alternative includes using an osteochondral allograft harvested from the femoral trochlea in a donor knee, machining grooves in the bone to allow the allograft to bend, and replacing the trapezium with this bent osteochondral allograft [1,2]. Chapter 3 of this dissertation discusses adjustments to the original design of the bendable allograft and the design of a custom surgical tool to perform the proposed surgery. Specification changes of the allograft included an overall size reduction in order to better fit within the carpometacarpal joint, minimum bone thickness requirements to avoid bone cracking during the surgical procedure, and a reduction from three grooves to two grooves, which provided sufficient bending yet avoided fracture of the allograft. The surgical tool was designed to be a custom forceps device, whose primary features included (1) jaws with an angled face to match the angle of allograft bending and (2) insertion holes for the Kirschner wire and compression screws used to anchor the allograft in the bent position. These customizations allow the tool to be used to bend the allograft, fix it in the bent configuration, and place the allograft in its proper position in the hand during anchoring of the bent allograft to the native trapezium. The final two studies presented in this dissertation focus on furthering our current understanding of wear and structure-function relationships of articular cartilage. We hypothesize that cartilage wears due to fatigue failure in reciprocating compression instead of reciprocating friction. Chapter 4 compares reciprocating sliding of immature bovine articular cartilage against glass in two testing configurations: (1) a stationary contact area configuration (SCA), which results in static compression, interstitial fluid depressurization and increasing friction coefficient during reciprocating sliding, and (2) a migrating contact area configuration (MCA), which maintains fluid pressurization and low friction while producing reciprocating compressive loading during reciprocating sliding. Contact stress, sliding duration, and sliding distance were controlled to be similar between test groups. SCA tests exhibited an average friction coefficient of μ=0.084±0.032, while MCA tests exhibited a lower average friction coefficient of μ=0.020±0.008 (p<10^(-4)). Despite the lower friction, MCA cartilage samples exhibited clear surface damage with a significantly greater average surface deviation from a fitted plane after wear testing (R_q=0.125±0.095 mm) than cartilage samples slid in a SCA configuration (R_q=0.044±0.017 mm, p=0.002), which showed minimal signs of wear. Polarized light microscopy confirmed that delamination damage occurred between the superficial and middle zones of the articular cartilage in MCA samples. The greatest wear was observed in the group with lowest friction coefficient, subjected to cyclical instead of static compression, implying that friction is not the primary driver of cartilage wear. Delamination between superficial and middle zones imply the main mode of wear is fatigue failure under cyclical compression, not fatigue or abrasion due to reciprocating frictional sliding. The final study of this dissertation, presented in Chapter 5, investigates the importance of collagen fibril distribution in articular cartilage computational models. Finite element models were created to approximate a bovine humeral head and replicate previous experimental loading conditions [3]. Five different finite element analyses were run, each using a different fibril distribution model. Three of the models used two, four, or eight discrete fibril bundles, while two models used continuous fibril distributions with either isotropic or depth-dependent ellipsoidal distributions. Two primary findings arose from this investigation. The first was the discovery that as the fibril distribution became more isotropic, the strain throughout the tissue decreased, even though the contact area between the articular surface and rigid platen remained relatively equal across distribution models. This suggests that computational models which approximate the collagen fibrils with an isotropic distribution may be underestimating the strain through the depth of the tissue. The second primary finding was that in the discrete distribution model with two fibril bundles, which followed the classically described Benninghoff structure [4], the greatest magnitude of shear strain during compressive loading was observed in the middle zone. However, the highest magnitude of shear strain observed in the isotropic fibril distribution model occurred in the deep zone near the subchondral surface. The observed results suggest that the type of fibril distribution used to model collagen in articular cartilage plays a role in depth-dependent strain magnitude and strain distribution.

No description available.