Thermoplastic bioactive composite – with special reference to dissolution behaviour and tissue response

Bioactive glasses are surface-active ceramic materials which support and accelerate bone growth in the body. During the healing of a bone fracture or a large bone defect, fixation is often needed. The aim of this thesis was to determine the dissolution behaviour and biocompatibility of a composite consisting of poly(ε-caprolactone-co-DL-lactide) and bioactive glass (S53P4). In addition the applicability as an injectable material straight to a bone defect was assessed. In in vitro tests the dissolution behaviour of plain copolymer and composites containing bioactive glass granules was evaluated, as well as surface reactivity and the material’s capability to form apatite in simulated body fluid (SBF). The human fibroblast proliferation was tested on materials in cell culture. In in vivo experiments, toxicological tests, material degradation and tissue reactions were tested both in subcutaneous space and in experimental bone defects. The composites containing bioactive glass formed a unified layer of apatite on their surface in SBF. The size and amount of glass granules affected the degradation of polymer matrix, as well the material’s surface reactivity. In cell culture on the test materials the human gingival fibroblasts proliferated and matured faster compared with control materials. In in vitro tests a connective tissue capsule was formed around the specimens, and became thinner in the course of time. Foreign body cell reactions in toxicological tests were mild. In experimental bone defects the specimens with a high concentration of small bioactive glass granules (<45 μm) formed a dense apatite surface layer that restricted the bone ingrowth to material. The range of large glass granules (90-315 μm) with high concentrations formed the best bonding with bone, but slow degradation on the copolymer restricted the bone growth only in the superficial layers. In these studies, the handling properties of the material proved to be good and tissue reactions were mild. The reactivity of bioactive glass was retained inside the copolymer matrix, thus enabling bone conductivity with composites. However, the copolymer was noticed to degradate too slowly compared with the bone healing. Therefore, the porosity of the material should be increased in order to improve tissue healing.

Wood as a model material for medical biomaterials. In vivo and in vitro studies with bone and Betula pubescens Ehrh

Novel biomaterials are needed to fill the demand of tailored bone substitutes required by an ever‐expanding array of surgical procedures and techniques. Wood, a natural fiber composite, modified with heat treatment to alter its composition, may provide a novel approach to the further development of hierarchically structured biomaterials. The suitability of wood as a model biomaterial as well as the effects of heat treatment on the osteoconductivity of wood was studied by placing untreated and heat‐treated (at 220 C , 200 degrees and 140 degrees for 2 h) birch implants (size 4 x 7mm) into drill cavities in the distal femur of rabbits. The follow‐up period was 4, 8 and 20 weeks in all in vivo experiments. The flexural properties of wood as well as dimensional changes and hydroxyl apatite formation on the surface of wood (untreated, 140 degrees C and 200 degrees C heat‐treated wood) were tested using 3‐point bending and compression tests and immersion in simulated body fluid. The effect of premeasurement grinding and the effect of heat treatment on the surface roughness and contour of wood were tested with contact stylus and non‐contact profilometry. The effects of heat treatment of wood on its interactions with biological fluids was assessed using two different test media and real human blood in liquid penetration tests. The results of the in vivo experiments showed implanted wood to be well tolerated, with no implants rejected due to foreign body reactions. Heat treatment had significant effects on the biocompatibility of wood, allowing host bone to grow into tight contact with the implant, with occasional bone ingrowth into the channels of the wood implant. The results of the liquid immersion experiments showed hydroxyl apatite formation only in the most extensively heat‐treated wood specimens, which supported the results of the in vivo experiments. Parallel conclusions could be drawn based on the results of the liquid penetration test where human blood had the most favorable interaction with the most extensively heat‐treated wood of the compared materials (untreated, 140 degrees C and 200 degrees C heat‐treated wood). The increasing biocompatibility was inferred to result mainly from changes in the chemical composition of wood induced by the heat treatment, namely the altered arrangement and concentrations of functional chemical groups. However, the influence of microscopic changes in the cell walls, surface roughness and contour cannot be totally excluded. The heat treatment was hypothesized to produce a functional change in the liquid distribution within wood, which could have biological relevance. It was concluded that the highly evolved hierarchical anatomy of wood could yield information for the future development of bulk bone substitutes according to the ideology of bioinspiration. Furthermore, the results of the biomechanical tests established that heat treatment alters various biologically relevant mechanical properties of wood, thus expanding the possibilities of wood as a model material, which could include e.g. scaffold applications, bulk bone applications and serving as a tool for both mechanical testing and for further development of synthetic fiber reinforced composites.

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.

The Impact of Foreign Direct Investment Inflows on the Economic Growth of Bangladesh. The Roles of Infrastructural Facilities

Foreign direct investment (FDI) inflow has been a key concern for Bangladesh to obtain additional support for the economic development. The Government of Bangladesh continuously competing with other South Asian countries and putting more effort to increase the number of FDI inflows in the country. From the country’s perspective, the constant increasing rate of economic growth shows a positive outcome of FDI inflow. However, the country still not performing up to the mark to pull enough FDI inflows to its potential. Thus, this study discusses about the major determinants and factors affecting FDI inflows in Bangladesh. Among those determinants and factors, infrastructural facility is considered as the most important to affect FDI inflows. FDI inflow is fundamentally depending upon infrastructural facilities to achieve its desire success. Foreign investors take this issue very seriously because based on this they can measure their ease of doing business in the host country. Despite of providing a large market size, due to having weak and lack of infrastructural facilities, Bangladesh is facing trouble in drawing attention of the foreign investors. In order to make the infrastructural facilities happen, it is highly required to organize each of the systems under of it. The body of this study discussed about the weak infrastructures in Bangladesh such as transport and communication, power and energy, education system, and governance services. Improvement in one of these systems cannot provide valuable positive changes on FDI inflows. It requires improvement in all the weak systems to grasp multinational companies and attract foreign investors. On the basis of this research problem, research questions are established. Both qualitative and quantitative methods are used to answer the research questions. Furthermore, several theories have been applied to justify possible scenarios from the research problem. In addition, the history in between Bangladesh, trade liberalization, and FDI inflows is presented briefly.

The Impact of Foreign Direct Investment Inflows on the Economic Growth of Bangladesh. The Roles of Infrastructural Facilities

Foreign direct investment (FDI) inflow has been a key concern for Bangladesh to obtain additional support for the economic development. The Government of Bangladesh continuously competing with other South Asian countries and putting more effort to increase the number of FDI inflows in the country. From the country’s perspective, the constant increasing rate of economic growth shows a positive outcome of FDI inflow. However, the country still not performing up to the mark to pull enough FDI inflows to its potential. Thus, this study discusses about the major determinants and factors affecting FDI inflows in Bangladesh. Among those determinants and factors, infrastructural facility is considered as the most important to affect FDI inflows. FDI inflow is fundamentally depending upon infrastructural facilities to achieve its desire success. Foreign investors take this issue very seriously because based on this they can measure their ease of doing business in the host country. Despite of providing a large market size, due to having weak and lack of infrastructural facilities, Bangladesh is facing trouble in drawing attention of the foreign investors. In order to make the infrastructural facilities happen, it is highly required to organize each of the systems under of it. The body of this study discussed about the weak infrastructures in Bangladesh such as transport and communication, power and energy, education system, and governance services. Improvement in one of these systems cannot provide valuable positive changes on FDI inflows. It requires improvement in all the weak systems to grasp multinational companies and attract foreign investors. On the basis of this research problem, research questions are established. Both qualitative and quantitative methods are used to answer the research questions. Furthermore, several theories have been applied to justify possible scenarios from the research problem. In addition, the history in between Bangladesh, trade liberalization, and FDI inflows is presented briefly

The Middle East in the American quest for world order : ideas of power, economics, and social development in United States foreign policy, 1953-1961

Doctoral dissertation, University of Tampere

Predicting body weight from body measurements of pre-pubertal Ayshire heifers

Selostus: Hiehojen elopainon määrittäminen mittauksin alkukasvatusvaiheessa

The role of presidential advisory systems in US foreign policy-making : the case of the National Security Council and Vietnam, 1953-1961

Doctoral dissertation, University of Joensuu