Development of Craniofacial Bone Defect Reconstruction Implant Based on Fibre-Reinforced Composite with Photopolymerisable Resin Systems. Experimental studies in vitro and in vivo.

Reconstruction of defects in the craniomaxillofacial (CMF) area has mainly been based on bone grafts or metallic fixing plates and screws. Particularly in the case of large calvarial and/or craniofacial defects caused by trauma, tumours or congenital malformations, there is a need for reliable reconstruction biomaterials, because bone grafts or metallic fixing systems do not completely fulfill the criteria for the best possible reconstruction methods in these complicated cases. In this series of studies, the usability of fibre-reinforced composite (FRC) was studied as a biostable, nonmetallic alternative material for reconstructing artificially created bone defects in frontal and calvarial areas of rabbits. The experimental part of this work describes the different stages of the product development process from the first in vitro tests with resin-impregnated fibrereinforced composites to the in vivo animal studies, in which this FRC was tested as an implant material for reconstructing different size bone defects in rabbit frontal and calvarial areas. In the first in vitro study, the FRC was polymerised in contact with bone or blood in the laboratory. The polymerised FRC samples were then incubated in water, which was analysed for residual monomer content by using high performance liquid chromatography (HPLC). It was found that this in vitro polymerisation in contact with bone and blood did not markedly increase the residual monomer leaching from the FRC. In the second in vitro study, different adhesive systems were tested in fixing the implant to bone surface. This was done to find an alternative implant fixing system to screws and pins. On the basis of this study, it was found that the surface of the calvarial bone needed both mechanical and chemical treatments before the resinimpregnated FRC could be properly fixed onto it. In three animal studies performed with rabbit frontal bone defects and critical size calvarial bone defect models, biological responses to the FRC implants were evaluated. On the basis of theseevaluations, it can be concluded that the FRC, based on E-glass (electrical glass) fibres forming a porous fibre veil enables the ingrowth of connective tissues to the inner structures of the material, as well as the bone formation and mineralization inside the fibre veil. Bone formation could be enhanced by using bioactive glass granules fixed to the FRC implants. FRC-implanted bone defects healed partly; no total healing of defects was achieved. Biological responses during the follow-up time, at a maximum of 12 weeks, to resin-impregnated composite implant seemed to depend on the polymerization time of the resin matrix of the FRC. Both of the studied resin systems used in the FRC were photopolymerised and the heat-induced postpolymerisation was used additionally.

Calculation of the critical crack size for cold form rectangular hollow section tube (CRHS) under bending load at -40º C temperature

To predict the capacity of the structure or the point which is followed by instability, calculation of the critical crack size is important. Structures usually contain several cracks but not necessarily all of these cracks lead to failure or reach the critical size. So, defining the harmful cracks or the crack size which is the most leading one to failure provides criteria for structure’s capacity at elevated temperature. The scope of this thesis was to calculate fracture parameters like stress intensity factor, the J integral and plastic and ultimate capacity of the structure to estimate critical crack size for this specific structure. Several three dimensional (3D) simulations using finite element method by Ansys program and boundary element method by Frank 3D program were carried out to calculate fracture parameters and results with the aid of laboratory tests (loaddisplacement curve, the J resistance curve and yield or ultimate stress) leaded to extract critical size of the crack. Two types of the fracture which is usually affected by temperature, Elastic and Elasti-Plastic fractures were simulated by performing several linear elastic and nonlinear elastic analyses. Geometry details of the weldment; flank angle and toe radius were also studied independently to estimate the location of crack initiation and simulate stress field in early stages of crack extension in structure. In this work also overview of the structure’s capacity in room temperature (20 ºC) was studied. Comparison of the results in different temperature (20 ºC and -40 ºC) provides a threshold of the structure’s behavior within the defined range.

Repair of segmental bone defects with fiber-reinforced composite: a study of material development and an animal model on rabbits

The Repair of segmental defects in load-bearing long bones is a challenging task because of the diversity of the load affecting the area; axial, bending, shearing and torsional forces all come together to test the stability/integrity of the bone. The natural biomechanical requirements for bone restorative materials include strength to withstand heavy loads, and adaptivity to conform into a biological environment without disturbing or damaging it. Fiber-reinforced composite (FRC) materials have shown promise, as metals and ceramics have been too rigid, and polymers alone are lacking in strength which is needed for restoration. The versatility of the fiber-reinforced composites also allows tailoring of the composite to meet the multitude of bone properties in the skeleton. The attachment and incorporation of a bone substitute to bone has been advanced by different surface modification methods. Most often this is achieved by the creation of surface texture, which allows bone growth, onto the substitute, creating a mechanical interlocking. Another method is to alter the chemical properties of the surface to create bonding with the bone – for example with a hydroxyapatite (HA) or a bioactive glass (BG) coating. A novel fiber-reinforced composite implant material with a porous surface was developed for bone substitution purposes in load-bearing applications. The material’s biomechanical properties were tailored with unidirectional fiber reinforcement to match the strength of cortical bone. To advance bone growth onto the material, an optimal surface porosity was created by a dissolution process, and an addition of bioactive glass to the material was explored. The effects of dissolution and orientation of the fiber reinforcement were also evaluated for bone-bonding purposes. The Biological response to the implant material was evaluated in a cell culture study to assure the safety of the materials combined. To test the material’s properties in a clinical setting, an animal model was used. A critical-size bone defect in a rabbit’s tibia was used to test the material in a load-bearing application, with short- and long-term follow-up, and a histological evaluation of the incorporation to the host bone. The biomechanical results of the study showed that the material is durable and the tailoring of the properties can be reproduced reliably. The Biological response - ex vivo - to the created surface structure favours the attachment and growth of bone cells, with the additional benefit of bioactive glass appearing on the surface. No toxic reactions to possible agents leaching from the material could be detected in the cell culture study when compared to a nontoxic control material. The mechanical interlocking was enhanced - as expected - with the porosity, whereas the reinforcing fibers protruding from the surface of the implant gave additional strength when tested in a bone-bonding model. Animal experiments verified that the material is capable of withstanding load-bearing conditions in prolonged use without breaking of the material or creating stress shielding effects to the host bone. A Histological examination verified the enhanced incorporation to host bone with an abundance of bone growth onto and over the material. This was achieved with minimal tissue reactions to a foreign body. An FRC implant with surface porosity displays potential in the field of reconstructive surgery, especially regarding large bone defects with high demands on strength and shape retention in load-bearing areas or flat bones such as facial / cranial bones. The benefits of modifying the strength of the material and adjusting the surface properties with fiber reinforcement and bone-bonding additives to meet the requirements of different bone qualities are still to be fully discovered.

Small-size pines suitability for glueboards

The aim of the research was to evaluate the suitability of small-size pine as a raw material for glueboard. A further aim was to investigate claims that dead knots and the twisting of the heartwood cause, quality problems in the but of the small-size pine. The theoretical framework of the study details the whole manufacturing process from raw material to the finished article; the description of the qualities of raw material, the sawing and drying processes as well as the making of the glueboard. The solve the research problem the following figures were calculated: amount of small-size pines, the yield and quality of sawn timber which can be used for making glueboard as well as the variables which affect the various stages of the process. The results show that about half of the timber from the thinning process was suitable material for sawing. The most common problem with the unsuitable timber was form defects of the stem. The average usage ratio of sawing was 2,31 k-m3/m3. 87,97 % of the sawn timber could be used for the production of glueboard. The unsuitability of sawn timber for making glueboard was mainly caused by breakage and the twisting of the heartwood. Dead knots were small and did not effect the quality of the but of the small-size pine. It can therefore be concluded that small-size pine is suitable raw material for glueboard.

The Effects of Endocrine Disrupters on Fetal Male Rat Testicular and Adrenal Development

Many of the reproductive disorders that emerge in adulthood have their origin during fetal development. Numerous studies have demonstrated that exposure to endocrine disrupting chemicals can permanently affect the reproductive health of experimental animals. In mammals, male sexual differentiation and development are androgen-dependent processes. In rat, the critical programming window for masculinization occurs between embryonic days (EDs) 15.5 and 19.5. Disorders in sex steroid balance during fetal life can disturb the development of the male reproductive tract. In addition to the fetal testis, the adrenal cortex starts to produce steroid hormones before birth. Glucocorticoids produced by the adrenal cortex are essential for preparing the fetus for birth. In the present study, the effects of exposure to endocrine disrupters on fetal male rat testicular and adrenal development were investigated. To differentiate the systemic and direct testicular effects of endocrine disrupters, both in vivo and in vitro experiments were performed. The present study also clarified the role of desert hedgehog signalling (Dhh) in the development of the testis. The results indicate that endocrine disrupters, diethylstilbestrol (DES) and flutamide, are able to induce rapid steroidogenic changes in fetal rat testis under in vitro conditions. Although in utero exposure to these chemicals did not show overt effects in fetal testis, they can induce permanent changes in the developing testis and accessory sex organs later in life. We also reported that exposure to antiandrogens can interfere with testicular Dhh signalling and result in impaired differentiation of the fetal Leydig cells and subsequently lead to abnormal testicular development and sexual differentiation. In utero exposure to tetrachlorodibenzo-p-dioxin (TCDD) caused direct testicular and pituitary effects on the fetal male rat but with different dose responses. In a study in which the effects of developmental exposure to environmental antiandrogens, di-isononylphthalate and 1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene (p,p^’-DDE), on fetal male rat steroidogenesis were investigated, chemicals did not down-regulate testicular or adrenal steroid hormone synthesis or production in 19.5-day-old fetal rats. However, p,p^’-DDE-treatment caused clear histological and ultrastructural changes in the prenatal testis and adrenal gland. These structural alterations can disturb the development and function of fetal testis and adrenal gland that may become evident later in life. Exposure to endocrine disrupters during fetal life can cause morphological abnormalities and alter steroid hormone production by fetal rat Leydig cells and adrenocortical cells. These changes may contribute to the maldevelopment of the testis and the adrenal gland. The present study highlights the importance of the fetal period as a sensitive window for endocrine disruption.

Distribution and role of macrophytes in coastal lagoons : implications of critical shifts

Crossroads, crucibles and refuges are three words that may describe natural coastal lagoon environments. The words refer to the complex mix of marine and terrestrial influences, prolonged dilution due to the semi-enclosed nature and the function of a habitat for highly diverse plant and animal communities, some of which are endangered. To attain a realistic picture of the present situation, high vulnerability to anthropogenic impact should be added to the description. As the sea floor in coastal lagoons is usually entirely photic, macrophyte primary production is accentuated compared with open sea environments. There is, however, a lack of proper knowledge on the importance of vegetation for the general functioning of coastal lagoon ecosystems. The aim of this thesis is to assess the role of macrophyte diversity, cover and species identity over temporal and spatial scales for lagoon functions, and to determine which steering factors primarily restrict the qualitative and quantitative composition of vegetation in coastal lagoons. The results are linked to patterns of related trophic levels and the indicative potential of vegetation for assessment of general conditions in coastal lagoons is evaluated. This thesis includes five field studies conducted in flads and glo-flads in the brackish water northern Baltic Sea. Flads and glo-flads are defined as a Baltic variety of coastal lagoons, which due to an inlet threshold and post-glacial landuplift slowly will be isolated from the open sea. This process shrinks inlet size, increases exposure and water retention, and is called habitat isolation. The studied coastal lagoons are situated in the archipelago areas of the eastern coast of Sweden, the Åland Islands and the south-west mainland of Finland, where land-uplift amounts to ca. 5 mm/ per year. Out of 400 evaluated sites, a total of 70 lagoons varying in inlet size, archipelago position and anthropogenic influence to cover for essential environmental variation were chosen for further inventory. Vegetation composition, cover and richness were measured together with several hydrographic and morphometric variables in the lagoons both seasonally and inter-annually to cover for general regional, local and temporal patterns influencing lagoon and vegetation development. On smaller species-level scale, the effects of macrophyte species identity and richness for the fish habitat function were studied by examining the influence of plant interaction on juvenile fish diversity. Thus, the active election of plant monoand polycultures by fish and the diversity of fish in the respective culture were examined and related to plant height and water depth. The lagoons and vegetation composition were found to experience a regime shift initiated by increased habitat isolation along with land-uplift. Vegetation composition altered, richness decreased and cover increased forming a less isolated and more isolated regime, named the vascular plant regime and charophyte regime, respectively according to the dominant vegetation. As total phosphorus in the water, turbidity and the impact of regional influences decreased in parallel, the dominance of charophytes and increasing cover seemed to buffer and stabilize conditions in the charophyte regime and indicated an increased functional role of vegetation for the lagoon ecosystem. The regime pattern was unaffected by geographical differences, while strong anthropogenic impact seemed to distort the pattern due to loss of especially Chara tomentosa L. in the charophyte regime. The regimes were further found unperturbed by short-time temporal fluctuations. In fact the seasonal and inter-annual dynamics reinforced the functional difference between the regimes by the increasing role of vegetation along habitat isolation and the resemblance to lake environments for the charophyte regime. For instance, greater total phosphorus and chlorophyll a concentrations in the water in the beginning of the season in the charophyte regime compared with the vascular plant regime presented a steeper reduction to even lower values than in the vascular plant regime along the season. Despite a regional importance and positive relationship of macrophyte diversity in relation to trophic diversity, species identity was underlined in the results of this thesis, especially with decreasing spatial scale. This result was supported partly by the increased role of charophytes in the functioning of the charophyte regime, but even more explicitly by the species-specific preference of juvenile fish for tall macrophyte monocultures. On a smaller species-level scale, tall plant species in monoculture seemed to be able to increase their length, indicating that negative selection forms preferred habitat structures, which increase fish diversity. This negative relationship between plant and fish diversity suggest a shift in diversity patterns among trohic levels on smaller scale. Thus, as diversity patterns seem complex and diverge among spatial scales, it might be ambiguous to extend the understanding of diversity relationships from one trophic level to the other. All together, the regime shift described here presents similarities to the regime development in marine lagoon environments and shallow lakes subjected to nutrient enrichment. However, due to nutrient buffering by vegetation with increased isolation and water retention as a consequence of the inlet threshold, the development seems opposite to the course along an eutrophication gradient described in marine lagoons lacking an inlet threshold, where the role of vegetation decreases. Thus, the results imply devastating consequences of inlet dredging (decreasing isolation) in terms of vegetation loss and nutrient release, and call for increased conservational supervision. Especially the red listed charophytes would suffer negatively from such interference and the consequences are likely to also deteriorate juvenile fish production. The fact that a new species to Finland, Chara connivens Salzm. Ex. Braun 1835 was discovered during this study further indicates a potential of the lagoons serving as refuges for rare species.

Ferromagnetic properties of pyrolytic nanocarbon

The work reported in this thesis is dedicated to irreversible magnetic properties in pyrolytic nanocarbon samples. Based on atomic force microscope images, the samples consist of carbon clusters with radius 30..120 nm. These are treated as single-domain nanoparticles. Magnetic hysteresis, field cooled, zero field cooled and thermoremanent magnetization measurements were performed using an RF SQUID magnetometer and ferromagnetic behaviour was observed. Analysis suggests that the ferromagnetic ordering is associated with defects in a thin surface layer, whose thickness is independent of particle size. Critical radius for single-domain particles, critical radius for coherent rotation, magnetic layer thickness, distance between elementary magnetic moments, saturation magnetization, exchange stiffness constant and anisotropy energy density are also presented.

The effects of maternal hyperglycemia on human umbilical vascular gene expression and neonatal rat lung development

Background: Maternal diabetes affects many fetal organ systems, including the vasculature and the lungs. The offspring of diabetic mothers have respiratory adaptation problems after birth. The mechanisms are multifactorial and the effects are prolonged during the postnatal period. An increasing incidence of diabetic pregnancies accentuates the importance of identifying the pathological mechanisms, which cause the metabolic and genetic changes that occur in offspring, born to diabetic mothers. Aims and methods: The aim of this thesis was to determine changes both in human umbilical cord exposed to maternal type 1 diabetes and in neonatal rat lungs after streptozotocin-induced maternal hyperglycemia, during pregnancy. Rat lungs were used as a model for the potential disease mechanisms. Gene expression alterations were determined in human umbilical cords at birth and in rat pup lungs at two week of age. During the first two postnatal weeks, rat lung development was studied morphologically and histologically. Further, the effect of postnatal hyperoxia on hyperglycemia-primed rat lungs was investigated at one week of age to mimic the clinical situation of supplemental oxygen treatment. Results: In the umbilical cord, maternal diabetes had a major negative effect on the expression of genes involved in blood vessel development. The genes regulating vascular tone were also affected. In neonatal rat lungs, intrauterine hyperglycemia had a prolonged effect on gene expression during late alveolarization. The most affected pathway was the upregulation of extracellular matrix proteins. Newborn rat lungs exposed to intrauterine hyperglycemia had thinner saccular walls without changes in airspace size, a smaller relative lung weight and lung total tissue area, and increased cellular apoptosis and proliferation compared to control lungs, possibly reflecting an aberrant maturational adaptation. At one and two weeks of age, cell proliferation and secondary crest formation were accelerated in hyperglycemia-exposed lungs. Postnatal hyperoxic exposure, alone caused arrested alveolarization with thin-walled and enlarged alveoli. In contrast, the dual exposure of intrauterine hyperglycemia and postnatal hyperoxia resulted in the phenotype of thick septa together with arrested alveolarization and decreased number of small pulmonary arteries. Conclusions: Maternal diabetic environment seems to alter the umbilical cord gene expression profile of the regulation of vascular development and function. Fetal hyperglycemia may additionally affect the genetic regulation of the postnatal lung development and may actually induce prolonged structural alterations in neonatal lungs together with a modifying effect on the deleterious pulmonary exposure of postnatal hyperoxia. This, combined with the novel human umbilical cord gene data could serve as stepping stones for future therapies to curb developmental aberrations.

Finite size effects in superconducting nanocomposites

The present Master’s thesis presents theoretical description of the extraodinary behavior of the confined Indium nanoparticles. Superconducting properties of nanoparticles and nanocomposites are extensively reviewed. Special attention has been paid to phase fluctuation, shell and disordered effects. The experimental data has been obtained and provided by Dmitry Shamshur from Ioffe Physical Technical Institute. The investigated material represents a highly ordered system of silicate spheres filled with indium metal, where the In nanoparticles are interconnected between each other. Bulk indium is a superconductor with crititcal superconducting temperature Tc0 = 3:41 K. But indium nanoparticles exhibit different behavior, the critical temperature rise by approximately 20% up to 4.15 K. As well as transition of the indium particles to type-II superconductivity with high critical magnetic fields. Such diversity is explained by finite size effects which originate from nanosize of the samples.