| 11. |
- Dånmark, Staffan
(författare)
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Polyester scaffold: Material design and cell-protein-material interaction
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Tissue engineering has emerged as a valid approach for the regeneration and restoration of bone defects. The concept of bone tissue engineering includes degradable scaffolds, osteogenic cells and osteoinductive growth factors either alone or in any combination of these three. The scaffold bulk material and its design, in particular, are essential for reaching clinically relevant treatments. It is essential that the scaffold is biocompatible and acts as a temporary extra-cellular matrix with a porous 3-dimensional structure, supporting adhesion, proliferation and differentiation of osteogenic cells. Yet another criterion of the scaffold is that is must have sufficient mechanical stability to maintain structural integrity and protect the cells with a gradual transfer of mechanical load to the developing tissue. At the same time, the scaffolds needs to be bioresorbable with a controllable degradation rate depending on its application and the rate of tissue regrowth. In this thesis, aliphatic polyester scaffolds have been modified and shown to be suitable for bone tissue engineering applications. In addition, a new microfluidic device for live imaging of cell behavior within porous 3-dimensional scaffolds has been developed. Highly porous and degradable aliphatic polyester scaffolds with varying pore sizes and interconnected pores were fabricated. The polyesters assayed were random co-polyesters poly(L-lactide-co-ε-caprolactone) [poly(LLA-co-CL)] and poly(L-lactide-co-1,5-dioxepan-2-one) [poly(LLA-co-DXO] and the homopolymer poly(L-lactide) [poly(LLA)]. The inherently different polymers yielded scaffolds with a wide range of properties with respect to surface chemistry, thermal properties, mechanical stability and degradation rate. The polyester scaffolds were shown to support the increased proliferation of bone marrow-derived stromal cells (BMSC) as well as enhanced osteogenic differentiation, with increased levels of osteocalcin gene expression, which emphasized their potential to act as cells carriers in bone tissue engineering. The potential of poly(LLA-co-CL) scaffolds and common biomedical polyesters in bone tissue engineering was further enhanced by surface functionalization. This involved two different methods of immobilization of bone morphogenetic protein-2 (BMP-2), a potent bone-growth-inducing factor, to the assayed polyesters. The first method used BMP-2 immobilized to heparin functionalized polyesters, while the second method covalently bonded BMP-2 to grafted linker groups on polyesters. Both immobilization techniques retain the bioactivity of BMP-2, and growth-factor-modified polyesters showed an increasing expression of osteogenic genes and production of osteocalcin in osteoblasts-like cells as well as increased proliferation in the mouse cell line, C3H10T1/2. The rate of degradation of electron-beam-sterilized polyester scaffolds and the subsequent loss of mechanical stability were strongly dependent on the chemical, physical and macroscopic architecture of the samples. The degradation rate and loss of mechanical integrity were much greater in porous scaffolds with hydrophilic co-monomers. By incorporating hydrophobic co-monomers with a limited ability to crystalize instead of hydrophilic co-monomers, the mechanical stability was retained for a longer time during the degradation process. The polyester supported spreading and flattened the morphology of both BMSC and osteoblast-like cells. The early cell adhesion to synthetic surfaces is mainly governed by the proteins adsorbed from its surrounding fluids. Early adhesion of BMSC to blood-plasma-coated polyesters was limited, despite the ability of the polyesters to adsorb adhesive proteins and expression of appropriate integrins on BMSC. However, adhesion to a purified adhesive matrix protein on the polyesters did occur, suggesting that pretreatment of polyester scaffolds with adhesive proteins or peptides is a feasible way to enhance the efficiency of cell loading into polyester scaffolds. Polyester scaffolds were combined with microfluidics and soft lithography to develop a new method for high-resolution imaging of live cells within porous scaffolds. The microfluidic device was used to frequently follow live cell proliferation and differentiation on the same spatial location within 3-dimansional porous scaffolds over a period of more than four weeks. This device is attractive for the evaluation of cells and materials intended for tissue engineering. We conclude that degradable aliphatic co-polyester scaffolds carefully designed with respect to macroscopic structure, bulk material and surface chemistry are able to meet the specific requirements of various bone tissue engineering applications. In addition, microfluidic devices permit reoccurring high resolution imaging of live cells within porous scaffolds and have a potential as a method of evaluating tissue engineering constructs.
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| 12. |
- Faxälv, Lars, et al.
(författare)
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Putting polyphosphates to the test: evidence against platelet-induced activation of factor XII
- 2013
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Ingår i: Blood. - Washington, USA : American Society of Hematology. - 0006-4971 .- 1528-0020. ; 122:23, s. 3818-3824
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Tidskriftsartikel (refereegranskat)abstract
- The recent claim that stimulated platelets activate the intrinsic pathway of coagulation by the release of polyphosphates has been considered a breakthrough in hemostasis research. In little more than 3 years, the original publication by Muller et al has been cited greater than100 times. However, none of the citing articles has sought to independently validate this potentially paradigm-shifting concept. To this end, we performed extensive experimentation in vitro and in vivo in an attempt to verify the claim that factor XII (FXII) is primarily activated by stimulated platelets. In contrast to the original assertion, platelet-derived polyphosphates were found to be weak activators of FXII, with a FXIIa-generating activity of less than10% compared with equivalent concentrations of kaolin. Using different coagulation assays, it was shown that platelet contribution to whole blood coagulation was unrelated to the generation of activated FXII in vitro. Additionally, key results used to verify the hypothesis in the original study in vivo were found to be irreproducible. We conclude that platelet-derived polyphosphates are not physiologically relevant activators of FXII.
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| 13. |
- Fischer, Marion, et al.
(författare)
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The ability of surface characteristics of materials to trigger leukocyte tissue factor expression.
- 2010
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Ingår i: Biomaterials. - : Elsevier BV. - 1878-5905 .- 0142-9612. ; 31:9, s. 2498-507
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Tidskriftsartikel (refereegranskat)abstract
- Biomaterial-induced thrombosis is usually attributed to blood coagulation initiated by contact phase and platelet-related reactions. Considering the major role of extrinsic initiation in blood coagulation in vivo, we studied the material related-induction of this pathway by investigating the relevance of surface properties for the expression of Tissue Factor (TF), a critical initiator of the extrinsic pathway of coagulation. We incubated materials with self-assembled monolayers of alkylthiols (SAMs) displaying various ratios of -CH(3), -OH, and -COOH terminations with fresh heparinized whole human blood in vitro. The transcription of TF-mRNA in leukocytes showed clear differences in relation to surface properties and increased over time. In addition, a positive correlation between TF transcription and its presence on leukocytes, granulocyte activation, and complement activation was found. Cells displaying the highest TF expression after material contact had significantly lower intracellular TF, pointing to previous TF release. Yet under the conditions of our whole blood incubation set-up within the limited time frame the observed initiation of the extrinsic pathway did not trigger blood coagulation.
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| 14. |
- Forsgren, Johan, 1981-
(författare)
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Functional Ceramics in Biomedical Applications : On the Use of Ceramics for Controlled Drug Release and Targeted Cell Stimulation
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Ceramics are distinguished from metals and polymers by their inorganic nature and lack of metallic properties. They can be highly crystalline to amorphous, and their physical and chemical properties can vary widely. Ceramics can, for instance, be made to resemble the mineral phase in bone and are therefore an excellent substitute for damaged hard tissue. They can also be made porous, surface active, chemically inert, mechanically strong, optically transparent or biologically resorbable, and all these properties are of interest in the development of new materials intended for a wide variety of applications. In this thesis, the focus was on the development of different ceramics for use in the controlled release of drugs and ions. These concepts were developed to obtain improved therapeutic effects from orally administered opioid drugs, and to reduce the number of implant-related infections as well as to improve the stabilization of prosthetic implants in bone.Geopolymers were used to produce mechanically strong and chemically inert formulations intended for oral administration of opioids. The carriers were developed to allow controlled release of the drugs over several hours, in order to improve the therapeutic effect of the substances in patients with severe chronic pain. The requirement for a stable carrier is a key feature for these drugs, as the rapid release of the entire dose, due to mechanical or chemical damage to the carrier, could have lethal effects on the patient because of the narrow therapeutic window of opioids. It was found that it was possible to profoundly retard drug release and to achieve almost linear release profiles from mesoporous geopolymers when the aluminum/silicon ratio of the precursor particles and the curing temperature were tuned.Ceramic implant coatings were produced via a biomimetic mineralization process and used as carriers for various drugs or as an ion reservoir for local release at the site of the implant. The formation and characteristics of these coatings were examined before they were evaluated as potential drug carriers. It was demonstrated that these coatings were able to carry antibiotics, bisphosphonates and bone morphogenetic proteins to obtain a sustained local effect, as they were slowly released from the coatings.
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| 15. |
- Hammarström, Per, et al.
(författare)
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An Auto-Catalytic Surface for Conformational Replication of Amyloid Fibrils-Genesis of an Amyloid World?
- 2011
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Ingår i: Origins of life and evolution of the biosphere. - : Springer Verlag (Germany). - 0169-6149 .- 1573-0875. ; 41:4, s. 373-383
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Tidskriftsartikel (refereegranskat)abstract
- Amyloid fibrils are composed of self assembled stacked peptide or protein molecules folded and trapped in a stable cross-beta-sheet conformation. The amyloid fibrillation mechanism represents an intriguing self-catalyzed process rendering replication of a molecular conformational memory of interest for prebiotic chemistry. Herein we describe how a solid surface can be rendered auto-catalytic for fibrillation of a protein solution. We have discovered that a hydrophobic silicon or glass surface can be made to continuously fibrillate solutions of insulin monomers under stressed conditions (pH 1.6, 65 degrees C). It was found that the surface acts as a platform for the formation of nascent seeds that induce fibril replication on and at the surface. This autocatalytic effect stems from a layer a few insulin molecules thick representing an oligomeric layer of misfolded, conformationally trapped, insulin molecules that rapidly through epitaxial growth catalyze the rate determining step (nucleation) during fibril replication. This autocatalytic layer is generated by the protein-solid surface interaction and conformational changes of the adsorbed protein during exposure at the air-water interface. The resulting autocatalytic surface thus both initiates local conformational molecular self-replication and acts as a reservoir for fibril seeds budding off into solution spreading fibril replication entities to the surrounding medium. The possibility of catalysis of the conformational replication process by minute amounts of nucleation sites located on a recruiting surface can evade the issue of dramatic concentration dependence of amyloidogenesis.
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| 16. |
- Harmankaya, Necati, 1983, et al.
(författare)
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Healing of complement activating Ti implants compared with non-activating Ti in rat tibia.
- 2012
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Ingår i: Acta biomaterialia. - : Elsevier BV. - 1878-7568 .- 1742-7061. ; 8:9, s. 3532-40
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Tidskriftsartikel (refereegranskat)abstract
- Recent studies have revealed that ozone ultraviolet (UVO) illumination of titanium (Ti) implants improves bone-implant anchorage by altering the physico-chemical and immune activating properties of the titanium dioxide (TiO(2)) layer. In the present rat tibia model, the authors compared the early events of inflammation and bone formation around UVO-treated Ti and complement activating immunoglobin g (IgG)-coated Ti. Machined Ti and machined Ti coated with a physical vapour-deposited Ti layer were used as references. Screw-shaped test and reference implants were implanted into rat tibia and harvested after 1, 7 and 28 days. Messenger RNA expression of implant adhered cells and peri-implant tissue ~250 μm from the surface were subsequently analysed with regard to IL-1β, TNF-α, osteocalcin, cathepsin K, BMP-2 and PDGF. Separate implants were retrieved after 7 and 28 days for removal torque measurements, and histological staining and histomorphometric analysis of bone area and bone-to-implant contact. While enhanced expression of inflammatory markers, TNF-α and IL-1β, was observed on IgG-coated surfaces throughout the observation time, UVO-treated surfaces indicated a significantly lower early inflammatory response. In the early phases (1 and 7 days), the UVO-treated surfaces displayed a significantly higher expression of osteoblast markers BMP-2 and osteocalcin. In summary, complement activating Ti implants elicited a stronger inflammatory response than UVO-treated Ti, with low complement activation during the first week of healing. In spite of this, the UVO-treated Ti induced only marginally more bone growth outside the implants.
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| 17. |
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| 18. |
- Harmankaya, Necati, 1983, et al.
(författare)
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Raloxifene and alendronate containing thin mesoporous titanium oxide films improve implant fixation to bone.
- 2013
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Ingår i: Acta biomaterialia. - : Elsevier BV. - 1878-7568 .- 1742-7061. ; 9:6, s. 7064-73
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Tidskriftsartikel (refereegranskat)abstract
- This study tested the hypothesis that osteoporosis drug-loaded mesoporous TiO2 implant coatings can be used to improve bone-implant integration. Two osteoporosis drugs, Alendronate (ALN) and Raloxifene (RLX), were immobilized in nanoporous oxide films prepared on Ti screws and evaluated in vivo in rat tibia. The drug release kinetics were monitored in vitro by quartz crystal microbalance with dissipation and showed sustained release of both drugs. The osteogenic response after 28days of implantation was evaluated by quantitative polymerase chain reaction (qPCR), removal torque, histomorphometry and ultrastructural interface analysis. The drug-loaded implants showed significantly improved bone fixation. In the case of RLX, stronger bone-remodelling activity was observed compared with controls and ALN-loaded implants. The ultrastructural interface analysis revealed enhanced apatite formation inside the RLX coating and increased bone density outside the ALN coating. Thus, this novel combination of a thin mesoporous TiO2 carrier matrix and appropriate drugs can be used to accelerate implant fixation in trabecular bone.
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| 19. |
- Jämstorp Berg, Erik, 1980-
(författare)
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Diffusion Controlled Drug Release from Slurry Formed, Porous, Organic and Clay-derived Pellets
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Coronary artery disease and chronic pain are serious health issues that cause severe discomfort and suffering in society today. Antithrombotic agents and highly potent analgesics play a critical role in improving the recovery process for patients being treated for these diseases. This thesis focuses on the design and study of pellet-based drug dosage forms which allow diffusion-controlled delivery of drugs with the aim of achieving optimal therapeutic outcomes.A wet slurry process was used to mix the drug and the polymer and/or clay precursor excipients into a paste. The pellets were then shaped via ionotropic gelation (alginate hydrogel beads/pellets), extrusion/spheronization (halloysite clay pellets) or geopolymerization.The decrease in the drug diffusion rate in the alginate beads was affected by the drug's molecular size and charge and the characteristics (such as concentration and chemical structure) of the surrounding alginate gel.The halloysite clay pellets provided sustained release of the highly potent drug fentanyl at both gastric pH 1 and intestinal pH 6.8. As expected, crushing the pellets reduced the diffusion barrier, resulting in more rapid release (dose dumping).The use of mechanically strong geopolymer gels was investigated as a potential means of preventing dose dumping as a result of crushing of the dosage form. Variations in the synthesis composition resulted in drastic changes in the microstructure morphology, the porosity, the mechanical stability and the drug release rate. Pore network modeling and finite element simulations were employed to theoretically evaluate the effects of porosity and drug solubility in the geopolymer structure on the drug release process. Fitting the model parameters to experimental data showed that increased average pore connectivity, a greater pore size distribution, and increased drug solubility in the pellet resulted in an increased drug release rate. Furthermore, incorporation of pH-sensitive organic polymers in the geopolymer structure reduced the high drug release rate from the pellets at gastric pH. These results indicate that geopolymers have potential for use in pellet form; both the release rate of the drug and the mechanical stability of the pellets can be optimized to prevent dose dumping.
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| 20. |
- Karlsson, Johan, 1984, et al.
(författare)
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Localized controlled drug delivery from mesoporous implants
- 2014
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Ingår i: Technical Proceedings of the 2014 NSTI Nanotechnology Conference and Expo, NSTI-Nanotech 2014. Washington, DC, United States, 15-18 June 2014. - 9781482258271
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Konferensbidrag (refereegranskat)abstract
- Mesoporous materials possess both a well-defined topography on the nanometer scale, and they may serve as hosts for drugs. In this work, titanium implants coated with mesoporous TiO2 thin films have been evaluated both in vitro and in vivo. Material characterization showed that, long-range ordered mesoporous TiO2, with a pore-size of 6 nm, and a narrow pore-size distribution were obtained. An in vivo study demonstrated that the films were robust enough to withstand the implantation procedure. The in vitro apatite formation experiments showed that formation of apatite was higher on the mesoporous surface compared to its nonporous counterpart. In a separate in vivo study, two osteoporosis drugs, alendronate (ALN) and raloxifene (RLX), were immobilised into the nanoporous oxide films. The in vitro drug release tests carried out showed a sustained release of both drugs. The osteogenic response after 28 days of implantation of the drug-loaded implants showed a significantly improved bone fixation.
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