| 1. |
- Ajaxon, Ingrid, 1983-
(författare)
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Can Bone Void Fillers Carry Load? : Behaviour of Calcium Phosphate Cements Under Different Loading Scenarios
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Calcium phosphate cements (CPCs) are used as bone void fillers and as complements to hardware in fracture fixation. The aim of this thesis was to investigate the possibilities and limitations of the CPCs’ mechanical properties, and find out if these ceramic bone cements can carry application-specific loads, alone or as part of a construct. Recently developed experimental brushite and apatite cements were found to have a significantly higher strength in compression, tension and flexion compared to the commercially available CPCs chronOS™ Inject and Norian® SRS®. By using a high-resolution measurement technique the elastic moduli of the CPCs were determined and found to be at least twice as high compared to earlier measurements, and closer to cortical bone than trabecular bone. Using the same method, Poisson's ratio for pure CPCs was determined for the first time. A non-destructive porosity measurement method for wet brushite cements was developed, and subsequently used to study the porosity increase during in vitro degradation. The compressive strength of the experimental brushite cement was still higher than that of trabecular bone after 25 weeks of degradation, showing that the cement can carry high loads over a time span sufficiently long for a fracture to heal. This thesis also presents the first ever fatigue results for acidic CPCs, and confirms the importance of testing the materials under cyclic loading as the cements may fail at stress levels much lower than the material’s quasi-static compressive strength. A decrease in fatigue life was found for brushite cements containing higher amounts of monetite. Increasing porosity and testing in a physiological buffer solution (PBS), rather than air, also decreased the fatigue life. However, the experimental brushite cement had a high probability of surviving loads found in the spine when tested in PBS, which has previously never been accomplished for acidic CPCs. In conclusion, available brushite cements may be able to carry the load alone in scenarios where the cortical shell is intact, the loading is mainly compressive, and the expected maximum stress is below 10 MPa. Under such circumstances this CPC may be the preferred choice over less biocompatible and non-degradable materials.
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| 2. |
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| 3. |
- Ajaxon, Ingrid, et al.
(författare)
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Compressive fatigue properties of an acidic calcium phosphate cement—effect of phase composition
- 2017
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Ingår i: Journal of materials science. Materials in medicine. - : Springer Science and Business Media LLC. - 0957-4530 .- 1573-4838. ; 28:3
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Tidskriftsartikel (refereegranskat)abstract
- Calcium phosphate cements (CPCs) are synthetic bone grafting materials that can be used in fracture stabilization and to fill bone voids after, e.g., bone tumour excision. Currently there are several calcium phosphate-based formulations available, but their use is partly limited by a lack of knowledge of their mechanical properties, in particular their resistance to mechanical loading over longer periods of time. Furthermore, depending on, e.g., setting conditions, the end product of acidic CPCs may be mainly brushite or monetite, which have been found to behave differently under quasi-static loading. The objectives of this study were to evaluate the compressive fatigue properties of acidic CPCs, as well as the effect of phase composition on these properties. Hence, brushite cements stored for different lengths of time and with different amounts of monetite were investigated under quasi-static and dynamic compression. Both storage and brushite-to-monetite phase transformation was found to have a pronounced effect both on quasi-static compressive strength and fatigue performance of the cements, whereby a substantial phase transformation gave rise to a lower mechanical resistance. The brushite cements investigated in this study had the potential to survive 5 million cycles at a maximum compressive stress of 13 MPa. Given the limited amount of published data on fatigue properties of CPCs, this study provides an important insight into the compressive fatigue behaviour of such materials.
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| 7. |
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| 8. |
- Barba, Albert, et al.
(författare)
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Impact of Biomimicry in the Design of Osteoinductive Bone Substitutes : Nanoscale Matters
- 2019
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Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 11:9, s. 8818-8830
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Tidskriftsartikel (refereegranskat)abstract
- Bone apatite consists of carbonated calcium-deficient hydroxyapatite (CDHA) nanocrystals. Biomimetic routes allow fabricating synthetic bone grafts that mimic biological apatite. In this work, we explored the role of two distinctive features of biomimetic apatites, namely, nanocrystal morphology (plate vs needle-like crystals) and carbonate content, on the bone regeneration potential of CDHA scaffolds in an in vivo canine model. Both ectopic bone formation and scaffold degradation were drastically affected by the nanocrystal morphology after intramuscular implantation. Fine-CDHA foams with needle-like nanocrystals, comparable in size to bone mineral, showed a markedly higher osteoinductive potential and a superior degradation than chemically identical coarse-CDHA foams with larger plate-shaped crystals. These findings correlated well with the superior bone-healing capacity showed by the fine-CDHA scaffolds when implanted intraosseously. Moreover, carbonate doping of CDHA, which resulted in small plate-shaped nanocrystals, accelerated both the intrinsic osteoinduction and the bone healing capacity, and significantly increased the cell-mediated resorption. These results suggest that tuning the chemical composition and the nanostructural features may allow the material to enter the physiological bone remodeling cycle, promoting a tight synchronization between scaffold degradation and bone formation.
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| 9. |
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| 10. |
- Fowler, Lee, et al.
(författare)
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Development of Antibacterial Ti-Cu-x Alloys for Dental Applications : Effects of Ageing for Alloys with Up to 10 wt% Cu
- 2019
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Ingår i: Materials. - Switzerland : MDPI. - 1996-1944. ; 12:23
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Tidskriftsartikel (refereegranskat)abstract
- Peri-implantitis, a disease caused by bacteria, affects dental implants in patients. It is widely treated with antibiotics, however, with growing antibiotic resistance new strategies are required. Titanium-copper alloys are prospective antibacterial biomaterials, with the potential to be a remedy against peri-implantitis and antibiotic resistance. The aim of this study was to investigate Ti-Cux alloys, exploring how Cu content (up to 10 wt%) and ageing affect the material properties. Electron microscopy, X-ray diffraction, hardness testing, bacteriological culture, and electrochemical testing were employed to characterize the materials. It was found that alloys with above 3 wt% Cu had two phases and ageing increased the volume fraction of Ti2Cu. An un-aged alloy of 5 wt% Cu showed what could be Ti3Cu, in addition to the α-Ti phase. The hardness gradually increased with increased Cu additions, while ageing only affected the alloy with 10 wt% Cu (due to changes in microstructure). Ageing resulted in faster passivation of the alloys. After two hours the aged 10 wt% Cu alloy was the only material with an antibacterial effect, while after six hours, bacteria killing occurred in all alloys with above 5 wt% Cu. In conclusion, it was possible to tune the material and antibacterial properties of Ti-Cux alloys by changing the Cu concentration and ageing, which makes further optimization towards an antibacterial material promising.
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| 11. |
- Fowler, Lee
(författare)
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Development of titanium-copper alloys for dental applications
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Titanium alloys find wide application in the medical implants industry, which includes areas of orthopaedic and dental implants. The reason for the popularity of the material is high mechanical strength, low density, and reported growth of bone onto the material, as well as corrosion resistance. Despite the general success of titanium materials, a drawback is that it is vulnerable to bacterial colonization, which can cause implant failure through inflammatory diseases. Peri-implantitis is one such disease, which can lead to irreversible bone loss and subsequently implant instability.This thesis focuses on the use of copper (Cu) as an antibacterial element in titanium alloys, where the purpose is designing inherently antibacterial materials.With an understanding that copper can reduce bacterial populations by ion release of Cu into solutions, as well as by direct contact of bacteria with Cu surfaces: studies on the effect of Cu ions on bacteria and cells were conducted, in addition to studies on Ti-Cux alloys.Varying Cu concentrations in solution were introduced to bacteria (Staphylococcus epidermidis) and cells (MC3T3 murine calvarial osteoblasts), and it was found that the lethal dosage for Cu ions was in the range from 9x10-5 to 9x10-6 g/ml, for bacteria and cells. The Cu ions were also found to cause a stress response for this bacteria at concentrations between 9x10-6 to 9x10-7 g/ml, and recommended to be avoided for implant materials.For Ti-Cux binary alloys, studies established that a 10wt%Cu alloy, which released 9x10-8 g/ml, reduced the bacterial population by 27 % in 6 hours in a direct contact test. This alloy was found to be composed of intermetallic (Ti2Cu) and hexagonal closed packed titanium (HCP-Ti) crystals. A separate study on aged heat treated Ti-Cux alloys, showed that an additional phase of Ti3Cu was present in lower volume fraction. The aged alloys of Ti-Cux showed higher volume fraction of Ti2Cu but only a slightly higher antibacterial ability, compared to those without ageing. The hardness of the Ti-Cux alloys was however detrimentally affected by ageing, especially for the 10wt%Cu alloy.Investigations on the alloying of Cu with an existing implant alloy, Ti-10wt%Ta-1.6wt%Nb-1.7wt%Zr (TNTZ), was also performed and at higher wt%Cu alloys with three-phased microstructures were present. Alloying of Cu in the TNTZ material increased hardness and with further development of this novel alloy, a potential biomaterial for clinical applications could be designed.In conclusion, the results of this thesis demonstrate that the use of Cu in proximity to cells and bacteria requires dose dependent consideration for material design, so that antibacterial materials can be developed that do not harm tissue. The appropriate design of alloys can also be performed so as to allow antibacterial ability to be achieved, along with ensuring appropriate mechanical and corrosion properties. Furthermore, Cu as an antibacterial element can be alloyed into various titanium alloy systems and with further development in this area; antibacterial alloys could benefit the implant industry and patients alike.
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| 12. |
- Fowler, Lee, et al.
(författare)
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Effect of copper ion concentration on bacteria and cells
- 2019
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Ingår i: Materials. - Switzerland : MDPI. - 1996-1944. ; 12:22
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Tidskriftsartikel (refereegranskat)abstract
- In the oral cavity, dental implants—most often made of commercially pure titanium—come in contact with bacteria, and antibacterial management has been researched extensively to improve patient care. With antibiotic resistance becoming increasingly prevalent, this has resulted in copper being investigated as an antibacterial element in alloys. In this study, the objective was to investigate the copper ion concentrations at which cyto-toxicity is avoided while bacterial inhibition is ensured, by comparing Cu ion effects on selected eukaryotes and prokaryotes. To determine relevant copper ion concentrations, ion release rates from copper and a 10 wt. % Cu Ti-alloy were investigated. Survival studies were performed on MC3T3 cells and Staphylococcus epidermidis bacteria, after exposure to Cu ions concentrations ranging from 9 × 10−3 to 9 × 10−12 g/mL. Cell survival increased from <10% to >90% after 24 h of exposure, by reducing Cu concentrations from 9 × 10−5 to 9 × 10−6 g/mL. Survival of bacteria also increased in the same range of Cu concentrations. The maximum bacteria growth was found at 9 × 10−7 g/mL, probably due to stress response. In conclusion, the minimum inhibitory concentrations of Cu ions for these prokaryotes and eukaryotes were found in the range from 9 × 10−5 to 9 × 10−6 g/mL. Interestingly, the Cu ion concentration correlating to the release rate of the 10 wt. % Cu alloy (9 × 10−8 g/mL) did not kill the bacteria, although this alloy has previously been found to be antibacterial. Further studies should investigate in depth the bacteria-killing mechanism of copper.
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| 13. |
- Fowler, Lee, et al.
(författare)
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Investigation of copper alloying in a TNTZ-Cux alloy
- 2019
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Ingår i: Materials. - Switzerland : MDPI. - 1996-1944. ; 12:22
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Tidskriftsartikel (refereegranskat)abstract
- Alloying copper into pure titanium has recently allowed the development of antibacterial alloys. The alloying of biocompatible elements (Nb, Ta and Zr) into pure titanium has also achieved higher strengths for a new alloy of Ti-1.6 wt.% Nb-10 wt.% Ta-1.7 wt.% Zr (TNTZ), where strength was closer to Ti-6Al-4V and higher than grade 4 titanium. In the present study, as a first step towards development of a novel antibacterial material with higher strength, the existing TNTZ was alloyed with copper to investigate the resultant microstructural changes and properties. The initial design and modelling of the alloy system was performed using the calculation of phase diagrams (CALPHAD) methods, to predict the phase transformations in the alloy. Following predictions, the alloys were produced using arc melting with appropriate heat treatments. The alloys were characterized using energy dispersive X-ray spectroscopy in scanning transmission electron microscopy (STEM-EDS) with transmission Kikuchi diffraction (TKD). The manufactured alloys had a three-phased crystal structure that was found in the alloys with 3 wt.% Cu and higher, in line with the modelled alloy predictions. The phases included the α-Ti (HCP-Ti) with some Ta present in the crystal, Ti2Cu, and a bright phase with Ti, Cu and Ta in the crystal. The Ti2Cu crystals tended to precipitate in the grain boundaries of the α-Ti phase and bright phase. The hardness of the alloys increased with increased Cu addition, as did the presence of the Ti2Cu phase. Further studies to optimize the alloy could result in a suitable material for dental implants.
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| 20. |
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| 21. |
- Hedenqvist, Patricia, et al.
(författare)
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The effect of housing environment on bone healing in a critical radius defect in New Zealand White rabbits
- 2020
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Ingår i: Plos One. - : Public Library of Science (PLoS). - 1932-6203. ; 15:5
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Tidskriftsartikel (refereegranskat)abstract
- In animal studies on bone healing, the effect of housing space and physical activity are seldom taken into account. Bone formation was evaluated in New Zealand White rabbits (mean ± SEM BW: 3.9 ± 0.11 kg) with a critical bone defect after 12 weeks of rehabilitation in pair-housing in 3 m2 large floor pens (Floor, n = 10) or standard single housing in 0.43 m2 cages (Cage, n = 10). In the randomised full-factorial study, a bone replica of calcium phosphate cement (CPC, n = 10) or autologous bone (AB, n = 10) was implanted in the unilateral 20 mm radius defect. Post-mortem, the oxidative capacity was measured by citrate synthase (CS) activity in M. quadriceps and the defect filling volume and density evaluated by microcomputer tomography (μ-CT). Histology sections were evaluated by subjective scoring and histomorphometry. Fourteen rabbits remained until the end of the study. Group Floor (n = 7; 3 CPC + 4 AB) had a higher CS activity and a larger bone defect filling volume and lower density by μ-CT measurements than group Cage (n = 7; 3 CPC + 4 AB). Three out of four rabbits in AB-Floor presented fusion of the defect with reorganisation of trabecular bone, whereas three of four in AB-Cage showed areas of incomplete healing. Floor rabbits had a higher score of bony fusion between the radius and ulna than Cage rabbits. There were no differences between groups in histomorphometry. The study found that a larger housing space increased physical activity and promoted bone formation. © 2020 Hedenqvist et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
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| 22. |
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| 23. |
- Jonsson, Henrik, 1987-, et al.
(författare)
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Crack nucleation and propagation in microcrystalline-cellulose based granules subject to uniaxial and triaxial load
- 2019
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Ingår i: International Journal of Pharmaceutics. - : Elsevier BV. - 0378-5173 .- 1873-3476. ; 559, s. 130-137
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Tidskriftsartikel (refereegranskat)abstract
- Cracking patterns in four kinds of granules, based on the common pharmaceutical excipient microcrystalline cellulose (MCC) and subject to compressive load, were examined. The initial pore structure and the location of initial failure under uniaxial compression were assessed using X-ray micro-computed tomography, whereas contact force development and onset of cracking under more complex compressive load were examined using a triaxial testing apparatus. Smoothed particle hydrodynamics (SPH) simulations were employed for numerical analysis of the stress distributions prior to cracking. For granules subject to uniaxial compression, initial cracking always occurred along the meridian and the precise location of the crack depended on the pore structure. Likewise, for granules subject to triaxial compression, the fracture plane of the primary crack was generally parallel to the dominant loading direction. The occurrence of cracking was highly dependent on the triaxiality ratio, i.e. the ratio between the punch displacements in the secondary and dominant loading directions. Compressive stresses in the lateral directions, induced by triaxial compression, prevented crack opening and fragmentation of the granule, something that could be verified by simulations. These results provide corroboration as well as further insights into previously observed differences between confined and unconfined compression of granular media.
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| 24. |
- Kotrschal, Alexander, et al.
(författare)
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Evolution of brain region volumes during artificial selection for relative brain size
- 2017
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Ingår i: Evolution. - : Wiley. - 0014-3820 .- 1558-5646. ; 71:12, s. 2942-2951
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Tidskriftsartikel (refereegranskat)abstract
- The vertebrate brain shows an extremely conserved layout across taxa. Still, the relative sizes of separate brain regions vary markedly between species. One interesting pattern is that larger brains seem associated with increased relative sizes only of certain brain regions, for instance telencephalon and cerebellum. Till now, the evolutionary association between separate brain regions and overall brain size is based on comparative evidence and remains experimentally untested. Here, we test the evolutionary response of brain regions to directional selection on brain size in guppies (Poecilia reticulata) selected for large and small relative brain size. In these animals, artificial selection led to a fast response in relative brain size, while body size remained unchanged. We use microcomputer tomography to investigate how the volumes of 11 main brain regions respond to selection for larger versus smaller brains. We found no differences in relative brain region volumes between large- and small-brained animals and only minor sex-specific variation. Also, selection did not change allometric scaling between brain and brain region sizes. Our results suggest that brain regions respond similarly to strong directional selection on relative brain size, which indicates that brain anatomy variation in contemporary species most likely stem from direct selection on key regions.
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| 25. |
- Lewin, Susanne, et al.
(författare)
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Additively manufactured mesh-type titanium structures for cranial implants : E-PBF vs. L-PBF
- 2021
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Ingår i: Materials & design. - : Elsevier. - 0264-1275 .- 1873-4197. ; 197
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Tidskriftsartikel (refereegranskat)abstract
- A patient-specific titanium-reinforced calcium phosphate (CaP–Ti) cranial implant has recently shown promising clinical results. Currently, its mesh-type titanium structure is additively manufactured using laser beam powder bed fusion (L-PBF). Nevertheless, an electron-beam (E-PBF) process could potentially be more time efficient. This study aimed to compare the geometrical accuracy and mechanical response of thin titanium structures manufactured by L-PBF (HIPed) and E-PBF (as-printed). Tensile test (ø = 1.2 mm) and implant specimens were manufactured. Measurements by μCT revealed a deviation in cross-sectional area as compared to the designed geometry: 13–35% for E-PBF and below 2% for L-PBF. A superior mechanical strength was obtained for the L-PBF specimens, both in the tensile test and the implant compression tests. The global peak load in the implant test was 457 ± 9 N and 846 ± 40 N for E-PBF and L-PBF, respectively. Numerical simulations demonstrated that geometrical deviation was the main factor in implant performance and enabled quantification of this effect: 34–39% reduction in initial peak force based on geometry, and only 11–16% reduction based on the material input. In summary, the study reveals an uncertainty in accuracy when structures of sizes relevant to mesh-type cranial implants are printed by the E-PBF method.
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| 26. |
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| 27. |
- Lewin, Susanne
(författare)
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Functional Aspects of Cranial Implants : Mechanical and Regenerative Properties
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In several neurosurgical procedures, the skull must be temporarily opened. The resulting bone defect can subsequently be reconstructed with a cranial implant. However, the complication rate of this surgical procedure is high (~20%). The most common complication for cranial implants is infection. Currently, the most frequently used implant materials are titanium alloys, PMMA or PEEK. An improved clinical outcome – in terms of increased bone regeneration, vascularization and soft tissue compatibility – could possibly be obtained through the use of bioactive and osteoconductive materials such as calcium phosphates (CaP).This thesis focuses on CaP–titanium composite (CaP–Ti) implants. This recently developed implant type is increasingly used with a promising outcome. However, a thorough understanding of its functional properties is lacking, something that is of high importance for their clinical use, but also for future biomaterial development. The overall aim of this thesis is to increase the knowledge of the in vivo functional aspects of CaP–Ti composite implants, with a specific focus on the mechanical and regenerative properties.The mechanical properties of the implant were investigated experimentally and numerically at quasi-static and impact loading rates. An important finding was that the titanium structure makes the CaP–Ti implant capable of cerebral protection in impact situations comparable to the one that was tested. Moreover, the mechanical response of the CaP–Ti implants could be predicted by the developed numerical models at both quasi-static and impact loading rates. The developed numerical framework makes an important contribution to future evaluations of patient-specific CaP–Ti cranial implant designs in various loading scenarios. A comparison of two additive manufacturing (3D-printing) processes demonstrated that lower geometrical accuracy and higher surface roughness made electron beam produced implants inferior in terms of mechanical strength, as compared to laser melted implants.In order to assess the regenerative properties, the volumetric balance of the implant was investigated by CT in ten patients. After one year, the total volume of the implant had decreased – mainly at the outside of the implants in the direction of the scalp. However, all patients had a volumetric increase at the interface between the implant and the bone defect. In a histological analysis of a retrieval specimen from one of the patients, the volumetric increase could be confirmed as bone regeneration, and the decrease as CaP degradation. Remodeling of the CaP into bone was also observed, but was not detected in the clinical CT. In retrieval specimens from an animal study, it was found that correlation of some µCT cross-sections to histology can result in improved and more robust quantitative µCT evaluations.
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| 28. |
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| 31. |
- Lind, Thomas, Docent, 1965-, et al.
(författare)
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Developmental low-dose exposure to bisphenol A induces chronic inflammation, bone marrow fibrosis and reduces bone stiffness in female rat offspring only
- 2019
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Ingår i: Environmental Research. - : Elsevier BV. - 0013-9351 .- 1096-0953. ; 177
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Tidskriftsartikel (refereegranskat)abstract
- Background: Developmental exposure to low doses of the endocrine disruptor bisphenol A (BPA) is known to alter bone tissue in young rodents, although how bone tissue is affected in aged animals is not well known. We have recently shown that low-dose developmental exposure to BPA increases procollagen type I N-terminal propeptide (P1NP) levels, a peptide formed during type 1 collagen synthesis, in plasma of 5-week-old female rat offspring while male offspring showed reduced bone size.Objective: To analyze offspring bone phenotype at 52 weeks of age and clarify whether the BPA-induced increase in P1NP levels at 5 weeks is an early sign of bone marrow fibrosis development.Methods: As in our 5-week study, pregnant Fischer 344 rats were exposed to BPA via drinking water corresponding to 0.5 mu g/kg BW/day (BPA0.5), which is in the range of human daily exposure, or 50 mu g/kg BW/day (BPA50) from gestational day 3.5 until postnatal day 22. Controls were given only vehicle. The offspring were sacrificed at 52 weeks of age. Bone effects were analyzed using peripheral quantitative and micro-computed tomography (microCT), 3-point bending test, plasma markers and histological examination.Results: Compared to a smaller bone size at 5 weeks, at the age of 52 weeks, femur size in male offspring had been normalized in developmentally BPA-exposed rats. The 52-week-old female offspring showed, like the 5-week-old siblings, higher plasma P1NP levels compared to controls but no general increasing bone growth or strength. However, 2 out of 14 BPA-exposed female offspring bones developed extremely thick cortices later in life, discovered by systematic in vivo microCT scanning during the study. This was not observed in male offspring or in female controls. Biomechanical testing revealed that both doses of developmental BPA exposure reduced femur stiffness only in female offspring. In addition, histological analysis showed an increased number of fibrotic lesions only in the bone man ow of female rat offspring developmentally exposed to BPA. In line with this, plasma markers of inflammation, Tnf (in BPA0.5) and Timpl (in BPA50) were increased exclusively in female offspring.Conclusions: Developmental BPA exposure at an environmentally relevant concentration resulted in female specific effects on bone as well as on plasma biomarkers of collagen synthesis and inflammation. Even a dose approximately eight times lower than the current temporary EFSA human tolerable daily intake of 4 mu g/kg BW/day, appeared to induce bone stiffness reduction, bone man ow fibrosis and chronic inflammation in female rat offspring later in life.
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| 32. |
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| 33. |
- Mellgren, Torbjörn, 1986-, et al.
(författare)
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Calcium Phosphate Microspheres as a Delivery Vehicle for Tooth-Bleaching Agents
- 2018
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Ingår i: Journal of Dental Research. - : SAGE PUBLICATIONS INC. - 0022-0345 .- 1544-0591. ; 97:3, s. 283-288
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Tidskriftsartikel (refereegranskat)abstract
- Bleaching of vital teeth has become common practice in cosmetic dentistry today. Tooth sensitivity and demineralization of the enamel are, however, common side effects associated with hydrogen and carbamide peroxide bleaching. This study investigated if calcium phosphate microspheres, which have remineralizing properties, could be used as an additive without hindering the diffusion of the bleaching agent and if the spheres could be used as a carrier for carbamide peroxide. A remineralizing agent could increase the safety of bleaching and decrease the severity of its side effects. Comparisons between current hydrogen peroxide diffusion studies and previously published work are difficult since many studies include challenging-to-replicate conditions or lack reporting of important parameters. Hence, a diffusion model was designed by Wu Lab (School of Dentistry, University of California, Los Angeles) to measure the diffusion flux and determine the diffusivity of hydrogen peroxide. Physical parameters (e.g., diffusivity) could then be used for direct comparison to the results obtained by future studies. Three whitening gels with increasing amounts of spheres were formulated and tested with 2 commercially available whitening gels. The flux of hydrogen peroxide through 1-mm discs of bovine enamel was measured at steady-state conditions, and the diffusivity was calculated. The results showed that the spheres could be used as a carrier for carbamide peroxide and that the amount of spheres did not affect the diffusivity of peroxide through the enamel discs. Hence, the microspheres are considered promising as an additive to minimize side effects in bleaching gel formulation.
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| 34. |
- Mellgren, Torbjörn, 1986-, et al.
(författare)
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Guided bone tissue regeneration using a hollow calcium phosphate based implant in a critical size rabbit radius defect
- 2021
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Ingår i: Biomedical Materials. - : Institute of Physics Publishing (IOPP). - 1748-6041 .- 1748-605X. ; 16:3
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Tidskriftsartikel (refereegranskat)abstract
- Long bone fractures are common and sometimes difficult to treat. Autologous bone (AB), bovine bone and calcium phosphates are used to stimulate bone growth with varying results. In the present study, a calcium phosphate cement (CPC) that previously showed promising grafting capabilities was evaluated for the first time in a long bone defect. A radius defect of 20 mm was created in 20 rabbits. The defect was filled by either a hollow CPC implant that had been manufactured as a replica of a rabbit radius through indirect 3D printing, or by particulate AB as control. Defect filling and bone formation was evaluated after 12 weeks by combining micro computed tomography (mu CT) and scoring of 3D images, together with histomorphometry and histology. The mu CT and histomorphometric evaluations showed a similar amount of filling of the defect (combining graft and bone) between the CPC and AB group, but the scoring of 3D images showed that the filling in the CPC group was significantly larger. Histologically the AB graft could not be distinguished from the new bone. The AB treated defects were found to be composed of more bone than the CPC group, including reorganised cancellous and cortical bone. Both the CPC and AB material was associated with new bone formation, also in the middle of the defect, which could result in closing of the otherwise critically sized gap. This study shows the potential for an indirectly 3D printed implant in guided bone regeneration in critically sized long bone defects.
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| 35. |
- Offermanns, Vincent, et al.
(författare)
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Effect of strontium surface-functionalized implants on early and late osseointegration: A histological, spectrometric and tomographic evaluation
- 2018
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Ingår i: Acta Biomaterialia. - : Elsevier BV. - 1742-7061 .- 1878-7568. ; 69, s. 385-394
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Tidskriftsartikel (refereegranskat)abstract
- Energy efficient sensing is one of the main objectives in the design of networked embedded monitoring systems. However, existing approaches such as duty cycling and ambient energy harvesting face challenges in railway bridge health monitoring applications due to the unpredictability of train passages and insufficient ambient energy around bridges. This paper presents ECOVIBE (Eco-friendly Vibration), an on-demand sensing system that automatically turns on itself when a train passes on the bridge and adaptively powers itself off after finishing all tasks. After that, it goes into an inactive state with near-zero power dissipation. ECOVIBE achieves these by: Firstly, a novel, fully passive event detection circuit to continuously detect passing trains without consuming any energy. Secondly, combining train-induced vibration energy harvesting with a transistor-based load switch, a tiny amount of energy is sufficient to keep ECOVIBE active for a long time. Thirdly, a passive adaptive off control circuit is introduced to quickly switch off ECOVIBE. Also this circuit does not consume any energy during inactivity periods. We present the prototype implementation of the proposed system using commercially available components and evaluate its performance in real-world scenarios. Our results show that ECOVIBE is effective in railway bridge health monitoring applications.
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| 36. |
- Robo, Céline, et al.
(författare)
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Functional properties of low-modulus PMMA bone cements containing linoleic acid
- 2021
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Ingår i: Journal of Functional Biomaterials. - : MDPI. - 2079-4983. ; 12:1
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Tidskriftsartikel (refereegranskat)abstract
- Acrylic bone cements modified with linoleic acid are a promising low-modulus alternative to traditional high-modulus bone cements. However, several key properties remain unexplored, including the effect of autoclave sterilization and the potential use of low-modulus cements in other applications than vertebral augmentation. In this work, we evaluate the effect of sterilization on the structure and stability of linoleic acid, as well as in the handling properties, glass transition temperature, mechanical properties, and screw augmentation potential of low-modulus cement containing the fatty acid. Neither 1H NMR nor SFC-MS/MS analysis showed any detectable differences in autoclaved linoleic acid compared to fresh one. The peak polymerization temperature of the low-modulus cement was much lower (28–30 °C) than that of the high-modulus cement (67 °C), whereas the setting time remained comparable (20–25 min). The Tg of the low-modulus cement was lower (75–78 °C) than that of the high-stiffness cement (103 °C). It was shown that sterilization of linoleic acid by autoclaving did not significantly affect the functional properties of low-modulus PMMA bone cement, making the component suitable for sterile production. Ultimately, the low-modulus cement exhibited handling and mechanical properties that more closely match those of osteoporotic vertebral bone with a screw holding capacity of under 2000 N, making it a promising alternative for use in combination with orthopedic hardware in applications where high-stiffness augmentation materials can result in undesired effects.
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- Wu, Dan, 1990-, et al.
(författare)
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The effect of two types of resorbable augmentation materials - a cement and an adhesive - on the screw pullout pullout resistance in human trabecular bone
- 2020
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Ingår i: Journal of the Mechanical Behavior of Biomedical Materials. - : Elsevier BV. - 1751-6161 .- 1878-0180. ; 110
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Tidskriftsartikel (refereegranskat)abstract
- Augmentation materials, such as ceramic and polymeric bone cements, have been frequently used to improve the physical engagement of screws inserted into bone. While ceramic, degradable cements may ultimately improve fixation stability, reports regarding their effect on early fixation stability have been inconsistent. On the other hand, a newly developed degradable ceramic adhesive that can bond with tissues surrounding the screw, may improve the pullout performance, ensure early stability, and subsequent bony integration. The aim of this study was to investigate failure mechanisms of screw/trabecular bone constructs by comparing non-augmented screws with screws augmented with a calcium phosphate cement or an adhesive, i.e. a phosphoserine-modified calcium phosphate. Pullout tests were performed on screws inserted into trabecular cylinders extracted from human femoral bone. Continuous and stepwise pullout loading was applied with and without real-time imaging in a synchrotron radiation micro-computed tomograph, respectively. Statistical analysis that took the bone morphology into account confirmed that augmentation with the adhesive supported significantly higher pullout loads compared to cement-augmented, or non-augmented screws. However, the adhesive also allowed for a higher injection volume compared to the cement. In-situ imaging showed cracks in the vicinity of the screw threads in all groups, and detachment of the augmentation materials from the trabecular bone in the augmented specimens. Additional cracks at the periphery of the augmentation and the bone-material interfaces were only observed in the adhesive-augmented specimen, indicating a contribution of surface bonding to the pullout resistance. An adhesive that has potential for bonding with tissues, displayed superior pullout resistance, compared to a brushite cement, and may be a promising material for cementation or augmentation of implants.
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| 41. |
- Zhu, Wei, et al.
(författare)
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Cemented injectable multi-phased porous bone grafts for the treatment of femoral head necrosis
- 2019
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Ingår i: Journal of materials chemistry. B. - : ROYAL SOC CHEMISTRY. - 2050-750X .- 2050-7518. ; 7:18, s. 2997-3006
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Tidskriftsartikel (refereegranskat)abstract
- Femoral head necrosis (FHN) can induce musculoskeletal disability. It presents a challenge from diagnostic and therapeutic points of view. Open surgery for the treatment of FHN is not an optimal route. To minimize the surgery window, an injectable material with a porous structure and bioactive nature is preferred. The fabrication of an injectable porous bone graft via a simple route was the aim of our study. Therefore, cemented multi-phased calcium phosphate porous granules have been studied with varied phase compositions, pore sizes and porosities, and degradation rates. Granules templated by PEG 100-600 mu m were chosen for cell toxicity and in vitro osteogenic potential testing. Rabbits, making up a femoral head necrosis model, were implanted with granule A. Mature cancellous bone tissue was observed in the femoral head defect after 2 months implantation. The results indicate that the newly formed injectable bioactive porous grafts could be a good candidate for the treatment of femoral head necrosis.
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