Surface mineralization of fibrous polyester scaffolds for bone tissue engineering purposes

Despite the remarkable ability of bone to remodel and spontaneously regenerate, the body is incapable of self-healing in case of a critical sized bone defect caused by severe trauma or after a bone tumor resection. In such a case a surgical intervention is needed. Concerns regarding autogeneic and allogeneic bone tissue transplantation necessitate the search for synthetic bone tissue engineering alternatives. Such a bone substitute or scaffold has to be biocompatible, bioactive and biodegradable so that the implant material can integrate with the surrounding bone matrix, promote bone formation and finally be replaced by newly generated bone tissue. Additionally, in order to allow cell in-growth, vascularization and efficient transport of nutrients, oxygen, growth factors and metabolites, the scaffold should be porous with a high degree of interconnectivity. In this thesis, two biodegradable polyesters, poly(ε-caprolactone) (PCL) and poly(D,L-lactide) (PDLLA), were processed by means of electrospinning and 3D plotting. As such, four potential bone tissue engineering scaffolds were fabricated: electrospun PCL, electrospun PDLLA, 3D plotted PCL and a multiscale PCL scaffold fabricated by combining electrospinning and 3D plotting. In order to enhance the bioactivity of these scaffolds, a surface coating with an apatite was applied. The apatite structure is chemically comparable to the mineral phase found in natural bone and acts as an excellent cell support to maintain desirable cell-substrate interactions. Moreover, as bone apatite has carbonate content of 3 – 13 weight percent (wt%), and several studies showed that the cell adhesion, proliferation and metabolic activity of bone cells was increased on apatites with a high carbonate content, the incorporation of carbonate in the apatite lattice of the coating was of interest. In the first part of the thesis, the electrospun PCL and PDLLA scaffolds were coated with a thin and homogenous primer layer of calcium deficient hydroxyapatite (CDHAp). Coating was achieved in two steps: activation and nucleation. During the first step, reactive groups were created on the fiber surface. These served as nucleation points for apatite deposition during the second step in which the samples were alternately dipped in calcium and phosphate rich solutions. A cell study was conducted to determine whether the CDHAp coating enhanced cell viability. CDHAp coated electrospun PCL and PDLLA demonstrated to be a good substrates for cell attachment and growth of MC3T3-E1 cells. In the second part of the thesis, coating of the 3D PCL scaffold with hydroxyapatite with various carbonate contents was achieved. Analysis of the cell viability and adhesion of MC3T3-E1 cells showed that a hydroxyapatite coating with a carbonate content of at least 10 wt% carbonate improved the osteogenic cell response when compared to uncoated 3D plotted PCL scaffolds and scaffolds coated with a hydroxyapatite with a lower carbonate content. In the final part of the thesis the previously optimized protocols for the coating of electrospun and 3D plotted PCL were combined for the coating of the innovative multiscale scaffold with hydroxyapatite with a low and medium carbonate content. Seeding of MC3T3-E1 cells on these coated II scaffolds showed that the cells reached confluence after 1 day of culture and formed a monolayer after 7 days of culture. Moreover, the cells were able to infiltrate and colonize the interior of the scaffold

The Backup of Wind Power: Analysis of the Parameters Influencing the Wind Power Integration in Electricity Generation Systems (De backup van windenergie: analyse van de invloedsparameters voor de integratie van windenergie in elektriciteitsopwekkingsystemen).

Het onderzoek in deze thesis, waarbij de impact van windenergie op elekt riciteitsopwekkingsystemen wordt bestudeerd, heeft een gemeenschappelijk doel, namelijk het bestaan bewijzen van de interactie tussen windenergi e en systemen en het analyseren van deze interactie. Windturbines, net a ls elke andere eenheid voor elektriciteitsopwekking, kan niet enkel op z ichzelf bekeken worden. Voor een correcte interpretatie van de uitbating van systemen met windenergie, moet de dynamische context begrepen worde n. Het onderzoek naar windenergie in elektriciteitsopwekkingsystemen wordt gevoerd volgens drie criteria, namelijk operationele kost, betrouwbaarhe id van het systeem en broeikasgasemissie reductie. Verscheidene cruciale parameters die de impact van wind op deze drie criteria beïnvloeden, zo als windsnelheid- en vraagprofielen, systeemontwerp, brandstofprijzen en het totaal geïnstalleerd vermogen aan windturbines, worden beschouwd. D e wederzijdse invloed van windenergie en het elektriciteitsopwekkingsyst eem kan binnen lange en korte termijn gezien worden. Het intermitterende karakter van wind, dat wordt opgebouwd uit variabiliteit en relatieve o nvoorspelbaarheid is gerelateerd aan deze opsplitsing in respectievelijk lange en korte termijn. Zowel variabiliteit als onvoorspelbaarheid geef t aanleiding tot een noodzaak voor backup van windenergie. De innovatieve aspecten van het onderzoek in deze thesis zijn drieledig. Ten eerste biedt het een algemeen kader voor windenergie en elektricite itsopwekkingsystemen, gebaseerd op literatuuronderzoek en analyses over windsnelheid, windenergie en systeemaspecten. Het doel hiervan is een go ede achtergrond te verschaffen voor de studie van windenergie. In de twe ede plaats levert de thesis nieuwe invalshoeken en methodes voor het ond erzoek van windenergie, zoals de impact van onevenwichtskosten van vier verschillende Europese tariefontwerpen, het gebruik van energieopslag, h et aanhouden van reserves, de invloed van de systeemsamenstelling op de integratie van windturbines en het bepalen van de bijdrage van windturbi nes tot het systeemvermogen. De methodes zijn uitgebouwd om eenvoudig br uikbaar te zijn voor verder onderzoek. Tenslotte verschaft deze thesis n ieuwe inzichten door het toepassen van vermelde methodes op praktische g evallen. Deze inzichten zorgen voor een beter begrip van de vele aspecte n die meespelen bij de interactie tussen windenergie en elektriciteitsop wekkingsystemen, van de voornaamste parameters die hierbij in rekening m oeten gebracht worden en van de kritische kwesties die kunnen ontstaan.wind; power; electricity; generation; systems; cost;

The Backup of Wind Power: Analysis of the Parameters Influencing the Wind Power Integration in Electricity Generation Systems (De backup van windenergie: analyse van de invloedsparameters voor de integratie van windenergie in elektriciteitsopwekkingsystemen)

Het onderzoek in deze thesis, waarbij de impact van windenergie op elekt riciteitsopwekkingsystemen wordt bestudeerd, heeft een gemeenschappelijk doel, namelijk het bestaan bewijzen van de interactie tussen windenergi e en systemen en het analyseren van deze interactie. Windturbines, net a ls elke andere eenheid voor elektriciteitsopwekking, kan niet enkel op z ichzelf bekeken worden. Voor een correcte interpretatie van de uitbating van systemen met windenergie, moet de dynamische context begrepen worde n. Het onderzoek naar windenergie in elektriciteitsopwekkingsystemen wordt gevoerd volgens drie criteria, namelijk operationele kost, betrouwbaarhe id van het systeem en broeikasgasemissie reductie. Verscheidene cruciale parameters die de impact van wind op deze drie criteria beïnvloeden, zo als windsnelheid- en vraagprofielen, systeemontwerp, brandstofprijzen en het totaal geïnstalleerd vermogen aan windturbines, worden beschouwd. D e wederzijdse invloed van windenergie en het elektriciteitsopwekkingsyst eem kan binnen lange en korte termijn gezien worden. Het intermitterende karakter van wind, dat wordt opgebouwd uit variabiliteit en relatieve o nvoorspelbaarheid is gerelateerd aan deze opsplitsing in respectievelijk lange en korte termijn. Zowel variabiliteit als onvoorspelbaarheid geef t aanleiding tot een noodzaak voor backup van windenergie. De innovatieve aspecten van het onderzoek in deze thesis zijn drieledig. Ten eerste biedt het een algemeen kader voor windenergie en elektricite itsopwekkingsystemen, gebaseerd op literatuuronderzoek en analyses over windsnelheid, windenergie en systeemaspecten. Het doel hiervan is een go ede achtergrond te verschaffen voor de studie van windenergie. In de twe ede plaats levert de thesis nieuwe invalshoeken en methodes voor het ond erzoek van windenergie, zoals de impact van onevenwichtskosten van vier verschillende Europese tariefontwerpen, het gebruik van energieopslag, h et aanhouden van reserves, de invloed van de systeemsamenstelling op de integratie van windturbines en het bepalen van de bijdrage van windturbi nes tot het systeemvermogen. De methodes zijn uitgebouwd om eenvoudig br uikbaar te zijn voor verder onderzoek. Tenslotte verschaft deze thesis n ieuwe inzichten door het toepassen van vermelde methodes op praktische g evallen. Deze inzichten zorgen voor een beter begrip van de vele aspecte n die meespelen bij de interactie tussen windenergie en elektriciteitsop wekkingsystemen, van de voornaamste parameters die hierbij in rekening m oeten gebracht worden en van de kritische kwesties die kunnen ontstaan.nrpages: 276status: publishe

Impact of large amounts of wind power on the operation of an electricity generation system: Belgian case study

Wind power can have considerable impacts on the operation of electricity generation systems. Energy from wind power replaces other forms of electricity generation, thereby lowering overall fuel costs and greenhouse gas (GHG) emissions. However, the intermittency of wind power, reflected in its variability and relative unpredictability restrains the full potential benefits of wind power. The variable nature of wind power requires power plants to be ready for bridging moments of low wind power output. The occurrence of forecast errors for wind speed necessitates sufficient reserve capacity in the system, which cannot be used for other useful purposes. These forecast errors inevitably cause efficiency losses in the operation of the system. To analyse the extent of these impacts, the Belgian electricity generation system is taken as a case and investigated on different aspects such as technical limitations for wind power integration and cost and GHG emissions' reduction potential of wind power under different circumstances. © 2010 Elsevier Ltd.status: publishe

Impact of large amounts of wind power on the operation of an electricity generation system : Belgian case study

Wind power can have considerable impacts on the operation of electricity generation systems. Energy from wind power replaces other forms of electricity generation, thereby lowering overall fuel costs and greenhouse gas (GHG) emissions. However, the intermittency of wind power, reflected in its variability and relative unpredictability restrains the full potential benefits of wind power. The variable nature of wind power requires power plants to be ready for bridging moments of low wind power output. The occurrence of forecast errors for wind speed necessitates sufficient reserve capacity in the system, which cannot be used for other useful purposes. These forecast errors inevitably cause efficiency losses in the operation of the system. To analyse the extent of these impacts, the Belgian electricity generation system is taken as a case and investigated on different aspects such as technical limitations for wind power integration and cost and GHG emissions’ reduction potential of wind power under different circumstances

Effect of the generation mix on wind power introduction

The specific needs and ensuing costs for wind power integration into electricity generation systems depend to a large extent on the operation, composition and behaviour of the electricity generation system. The differences in the considered systems greatly influence the outcomes regarding wind power integration. The generation mix is studied here. Analyses are performed using a mixed integer linear programming model so as to get more insight in the consequences of the design and operation of electricity generation systems including wind power by looking at three distinct case systems. The model takes into account a multitude of technical specificities of the operation of an electricity generation system. The results show several aspects that are strongly related to the composition of electricity generation systems that influence the integration of wind power in the systems. These aspects range from the composition of the system to more specific technical parameters of the power plants and their operation, such as the marginal power plant and the greenhouse gas emission levels. The results shed some light on the reasons for the divergence in wind power integration studies. Moreover, it can help in gaining insights in the future development of electricity generation systems where wind power is being introduced. © 2009 The Institution of Engineering and Technology.status: publishe

Influence of massive heat-pump introduction on the electricity-generation mix and the GHG effect: Comparison between Belgium, France, Germany and The Netherlands

To evaluate the environmental impact of massive heat-pump introduction on greenhouse gas (GHG) emissions, dynamic simulations of the overall electricity-generation system have been performed for Belgium. The simulations are carried out with Promix, a tool that models the overall electricity-generation system. For comparison, three heating devices are considered, namely conventional boilers, heat pumps and electrical resistance heating. The introduction of electric heating at the expense of classic heating increases the demand for electricity and generates a shift of emissions from fossil-fuel heating systems to electrical power plants. The replaced classic fossil-fuel-fired heating represents emissions of about 300 kton. With regard to the heat-pump scenarios, both direct heat-pump heating with a coefficient of performance (COP) of 2.5 and accumulation heat-pump heating with a COP of 5 are investigated. The results of the simulations reveal that the massive introduction of heat-pump heating is favourable to the environment. In Belgium, the largest reductions in GHG emissions occur with heat pumps for direct heating, combined with newly commissioned combined cycle (CC) gas-fired plants or with accumulation heat-pump heating. These scenarios bring about overall GHG emission reductions of approximately 200 kton compared with the reference case with conventional heating for the years 2000 and 2010. The amount of additional electricity-related emissions depends on the considered heating device. In 2010, the scenario with accumulation heat pumps results in an overall decrease of Belgian GHG emissions by 0.15% compared with the reference scenario. The expansion of the electricity-generation system with new CC plants has an important favourable impact on GHGs as well. In most cases, the combination of higher electricity demand and the construction of new gas-fired CC plants will lead to lower overall GHG emissions. Copyright © 2007 John Wiley & Sons, Ltd.status: publishe

Possible Impact of Electric Cars on Electricity Spot Prices

International audienc

Considerations on the backup of wind power: Operational backup

The introduction of wind power into an electricity-generation system on a large scale brings about challenges for the evolution and operation of this system: backup for wind power becomes a necessity. This paper defines various elements that come into play when considering backup for electricity generation from wind power. The backup is split up in capacity backup and operational backup. The focus is set on the short-term, operational aspects of the backup provision. The effects of several short-term operation related parameters are defined and analysed. Most relevant parameters for the operation and needs for wind power backup are the load profiles, the wind power output profiles and the total amount of installed wind power. These are analysed by means of a Mixed Integer Linear Programming (MILP) model through two different methods for operational backup provision, comparing the incremental cost, generated by both methods. The first method applies wind power backup through a 100% provision of additional spinning reserves. The second method does not foresee any spinning reserve and relies on the balancing by the Transmission System Operator (TSO). Both methods result in different additional charges that are being affected by the said parameters. Both the wind profile and the total amount of installed wind power are positively related to the relative cost increase. The load profile is negatively correlated to this increase. The relationship between these parameters and the development of the incremental cost provides an understanding that allows finding better equilibria in the operational backup of wind power.Wind power Backup Operational Electricity-generation system Short run MILP

Applying Markov chains for the determination of the capacity credit of wind power

Investments in wind power occur everywhere in the world. The value of these investments for integration in an electricity generation system cannot be determined in the same way as conventional electricity sources due to the variable and relative unpredictable nature of wind power. Wind power can only to some limited extend be centrally dispatched. To look at the long term value of investments in wind power, the term capacity credit can be used. It defines the level of conventional generation that can be replaced by wind power generation. Using four adequacy indices, namely Loss-of-load Expectancy (LOLE), Loss of Energy Expectation (LOEE), Loss-of-load Frequency (LOLF) and Expected Interruption Cost (EIC), the Peak load Carrying Capability (PLCC) is established for different sizes and locations of wind power in a system. The PLCC can be seen as a way to quantify the capacity credit of wind power since it determines how much the load can be increased for a given level of wind power investment, while maintaining the system reliability. The adequacy indices are found to vary depending on size and location of wind power investments, therefore causing the PLCC to change accordingly. A Monte Carlo approach is used for determining the indices. Expected and unexpected outages of system elements are simulated and evaluated against system load. Wind power data are generated through Markov chains, based on actual meteorological data from Belgian weather measurement sites, thereby preserving the same statistical properties as the original data.status: publishe