| 1. |
- Pulkkinen, Hertta, et al.
(författare)
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Recombinant human type II collagen as a material for cartilage tissue engineering.
- 2008
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Ingår i: International Journal of Artificial Organs. - : Wichtig Editore Srl. - 0391-3988 .- 1724-6040. ; 31:11, s. 960-969
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Tidskriftsartikel (refereegranskat)abstract
- PURPOSE: Collagen type II is the major component of cartilage and would be an optimal scaffold material for reconstruction of injured cartilage tissue. In this study, the feasibility of recombinant human type II collagen gel as a 3-dimensional culture system for bovine chondrocytes was evaluated in vitro.METHODS: Bovine chondrocytes (4x106 cells) were seeded within collagen gels and cultivated for up to 4 weeks. The gels were investigated with confocal microscopy, histology, and biochemical assays.RESULTS: Confocal microscopy revealed that the cells maintained their viability during the entire cultivation period. The chondrocytes were evenly distributed inside the gels, and the number of cells and the amount of the extracellular matrix increased during cultivation. The chondrocytes maintained their round phenotype during the 4-week cultivation period. The glycosaminoglycan levels of the tissue increased during the experiment. The relative levels of aggrecan and type II collagen mRNA measured with realtime polymerase chain reaction (PCR) showed an increase at 1 week.CONCLUSION: Our results imply that recombinant human type II collagen is a promising biomaterial for cartilage tissue engineering, allowing homogeneous distribution in the gel and biosynthesis of extracellular matrix components.
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| 2. |
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| 3. |
- Adolfsson, E., et al.
(författare)
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Evaluation of bone ingrowth in Free Form Fabricated scaffolds
- 2008
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Ingår i: Key Engineering Materials. - 1662-9795.
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Tidskriftsartikel (refereegranskat)abstract
- Colloidal processing was used to cast zirconia and hydroxyapatite materials. The cast materials reached densities around 99% when sintered at 1500°C and 1200°C respectively. By controlling the colloidal process the sintered density of hydroxyapatite was also reduced to around 80% when the same sintering condition was used. The casting process was combined with free form fabrication to prepare designed scaffolds with identical macroporosity. These scaffolds were used to evaluate the early bone tissue response in rabbit femur. After six weeks of implantation the bone area in scaffolds of zirconia and hydroxyapatite were compared. In scaffolds of hydroxyapatite the bone area was roughly three times larger compared to corresponding scaffolds of zirconia. When the scaffolds of hydroxyapatite also contained an open microporosity of around 20% the amount of bone was even more pronounced. The results showed the importance of the material composition and the microstructure on the bone regenerating performance of scaffolds.
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| 8. |
- Almqvist, Sofia, 1980, et al.
(författare)
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Ex Vivo Study of the Angiogenic Effect of the Extracellular Matrix Protein Amelogenin
- 2008
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Ingår i: Abstract, The 9th New Jersey Symposium on Biomaterials Science and regenerative medicine, New Jersey, USA. ; 29-31 October
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Konferensbidrag (refereegranskat)abstract
- Introduction: Angiogenesis is crucial for wound healing but is often impaired in chronic wounds. The process is dependent on the interaction of endothelial cells and the extracellular matrix (ECM), which is mediated by cell membrane integrins. Amelogenin is an extracellular matrix protein that has been reported to promote formation of granulation tissue and repair of chronic venous leg ulcers and elevate the pro-angiogenic vascular endothelial growth factor in dermal fibroblasts.1-3 This study investigated the effect of amelogenin on angiogenesis in an ex vivo sprouting assay and related the findings to the cell surface integrin expression. Methods: Chick aortic arch assay: Transverse sections of the aortic arch of 13-day-old chick embryos were attached and sealed with Matrigel to the bottom of a 48-well plate. Amelogenin was added (0.01 mg/ml, 0.1 mg/ml and 1 mg/ml) in serum-free endothelial basal growth medium. Porcine serum albumin was used as control for unspecific protein effects. The plates were incubated at 37°C and sprouting was assessed at 24 h and 48 h by microscopy and scored from 0 to 6 (arbitrary units) by a blinded observer. Integrin assay: Human dermal microvascular endothelial cells (Promocell) were seeded in complete cell growth medium alone or supplemented with 0.1 mg/ml, 1 mg/ml amelogenin or 20 µg/ml fibronectin. After 24 h incubation in 37°C, cells were gently harvested with the non-enzymatic buffer (EDTA/PBS). Upregulated integrins/subunits were detected by an Integrin-Mediated Cell Adhesion Array (Chemicon), where cells expressing specific integrins (α1, α2, α3, α4, α5, αv, β1, β2, β3, β4, β6, αvβ3, αvβ5 and α5b1) are captured by surface immobilized antibodies. Results and Discussion: Amelogenin at 0.1 mg/ml significantly (p = 0.001) increased micro-vessel outgrowth by 76 % from the explants compared with control explants after 48 h of incubation. No significant sprouting was observed with the non-specific protein control porcine serum albumin or medium only. The preliminary data from the integrin assay show that amelogenin at 0.1 mg/ml also displays a broad up-regulation of several integrins/subunits. This result is comparable to the positive control, fibronectin, an ECM protein involved in all phases of tissue repair. Taken together, the present observations suggest that the angiogenic effects might be explained by the cell binding properties of amelogenin. Conclusions: Amelogenin stimulated micro-vessel outgrowth in the chick aortic arch assay possibly through up-regulation of several integrins and subunits important for cell interaction with the ECM. The pro-angiogenic property may contribute to the beneficial effects reported after treatment of chronic ulcers with the novel ECM therapy containing amelogenin. Acknowledgements: The studies were supported by the Swedish Research Council (grant K2006-73X-09495-16-3), Mölnlycke Health Care AB, the VINNOVA VinnVäxt Program Biomedical Development in Western Sweden, and the Danish Medical Research Council (22-02-0287). References: 1. Mirastschijski U. et al. (2004) Wound Repair Regen. 12:100-108. 2. Vowden P. et al. (2006) Wound Repair Regen. 14:240-248. 3. Ågren M. S. et al. (2007) Wound Repair Regen. 15:A139.
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| 9. |
- Almqvist, Sofia, 1980, et al.
(författare)
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In Vitro Effect of Amelogenin on Selected Cell Mediators from Human Monocytes
- 2008
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Ingår i: 8th World Biomaterials Congress, Amsterdam, The Netherlands.
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Konferensbidrag (refereegranskat)abstract
- Introduction: Inflammation is an integral part of the normal wound healing response. Besides clearing the wound of invading microbes and debris, inflammatory cells are believed to be crucial coordinators of the repair process, acting both as phagocytes and as a major source of growth factors and other signals [1]. In non-healing skin ulcers the repair process is stuck in the inflammation phase [2]. Excessive inflammation can reflect an imbalance in the transformation of phenotype between the classically activated, inflammatory macrophage and the alternatively activated macrophage involved in immunosuppression and tissue repair [3]. Amelogenin is a hydrophobic extracellular matrix protein that under physiological conditions will self assemble into nanospheres which in turn may form larger aggregates. Treatment with amelogenin has shown enhanced skin wound healing in an in vivo study in rabbits [4]. In addition, amelogenin has been proposed to have anti-inflammatory properties by attenuation of lipopolysaccharide (LPS)- and peptidoglucan-induced production of selected pro-inflammatory cytokines by human blood cells [5]. The present study was initiated to determine the effects of amelogenin on human monocyte secretion of factors which modulate both inflammation and tissue repair. Materials and Methods: Lyophilized amelogenin from Biora AB (Malmö, Sweden) was dissolved in 17 mM acetic acid. Human monocytes were obtained from six healthy blood donors by isolation using the separation gradient PercollTM in two steps according to Pertoft et al. [6]. The isolated monocytes were cultured for 24 h at 37ºC with 5% CO2 and 95% humidity. Thereafter the supernatants and non-adherent cells were removed. Fresh medium (RPMI, 5% foetal bovine serum, antibiotics) containing amelogenin, 0, 0.01, 0.1 and 1.0 mg/ml, and with or without addition of LPS, was added to the wells in triplicates. The plates were again incubated for 24 h. The supernatants were analyzed with commercial human ELISA assays for tumour necrosis factor- (TNF-), interleukin-10 (IL-10), macrophage inflammatory protein-1 (MIP-1), monocyte chemoattractant protein-1 (MCP-1), vascular endothelial growth factor (VEGF), and insulin like growth factor-1 (IGF-1). Results: Amelogenin treatment markedly altered the expression of factors by human monocytes. Amelogenin significantly reduced LPS-induced TNF- secretion, whereas the IL-10 expression was increased. Monocyte secretion of the two inflammatory chemokines MIP-1 and MCP-1 (Figure; mean ± SEM, n=6) was also affected by amelogenin treatment. Furthermore, amelogenin significantly increased monocyte secretion of VEGF (Figure; mean ± SEM, n=6) and IGF-1, although to a lesser extent, after 24 h culture. Conclusions: The amelogenin effects correlate to protein concentration, however not in a dose dependent manner, but instead the cell responses may reflect a concentration related difference in self assembly of the amelogenin protein. The observed changes in cytokine and chemokine expression are markedly affected by simultaneous LPS-induced inflammation activation, revealing possible anti-inflammatory properties of the amelogenin protein. In addition, the several-fold increase in VEGF-levels by monocytes provides a possible mechanism for the observed pro-angiogenic effect in vivo [4]. These in vitro results indicate that the extracellular matrix protein amelogenin by virtue of its interaction with human monocytes may modulate inflammation and tissue repair. Acknowledgements: The support from the Swedish Research Council (grant K2006-73X-09495-16-3), Mölnlycke Health Care Group AB and the VINNOVA VinnVäxt Program Biomedical Development in Western Sweden, is gratefully acknowledged. References: 1. Martin, P., et al. Trends Cell Biol., 15, 599, 2005. 2. Ågren, M.S., et al. Acta Derm Venereol Suppl (Stockh). 210, 3, 2000. 3. Duffield, J.S. Clin Sci (Lond), 104, 27, 2003 4. Mirastschijski, U., et al. Wound Repair Regen., 12, 100, 2004. 5. Myhre, A.E., et al. J Periodontal Res., 41, 208, 2006. 6. Pertoft, H., et al. J Immunol Methods., 33, 221, 1980.
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| 10. |
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| 11. |
- Andersson, Marcus, 1975, et al.
(författare)
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Effect of molecular mobility of polymeric implants on soft tissue reactions: An in vivo study in rats
- 2008
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Ingår i: Journal of Biomedical Materials Research Part A. - : Wiley. - 1552-4965 .- 1549-3296. ; 84A:3, s. 652-660
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Tidskriftsartikel (refereegranskat)abstract
- Although numerous different polymers are used as implants or otherwise studied for many other biotechnical applications, there is a lack of basic models that correlate polymer characteristics with foreign body reactions. This study aims at developing one such model by systematically studying surface molecular mobility of polymeric implants in soft tissues in vivo. Changing the length of the alkyl side chain of poly(alkyl methacrylates) (PAMAs), provides an interesting opportunity to study the surface molecular mobility with minimal changes of the hydrophobicity of the surface. Thus, in this study three different PAMAs, with increasingly surface mobility; poly (isobutyl methacrylate) (PIBMA), poly(butyl methacrylate) (PBMA), and poly(lauryl methacralate) (PLMA) along with pure titanium (Ti) substrates were implanted in the dorsum of Sprague-Dawley rats. Inflammatory cell recruitment, cell adhesion, and cytokine release were studied after 1, 3, and 28 days of implantation. Total number of inflammatory cells in the exudate was measured but no correlation between surface mobility and cell recruitment where found. However, the number of surface associated cells where significantly lower on the surfaces with high molecular mobility (PLMA and PBMA). The histological evaluation performed after 28 days revealed thicker fibrous capsule and a higher number of blood vessels on the low molecular mobility surface (PIBMA). After 28 days the cell activity was higher on the high molecular mobility surfaces (PLMA and PBMA) compared with PIBMA, based on the cytokine release. None of the surfaces induced any significant cell-death. On the basis of the results of this study we conclude that there is a significant difference in biological response to surfaces with different in molecular mobility. This might affect the wound healing process and the biocompatibility of biomaterials. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res, 2007 -------------------------------------------------------------------------------- Received: 13 March 2006; Revised: 15 December 2006; Accepted: 29 January 2007 Digital Object Identifier (DOI) 10.1002/jbm.a.31389 About DOI
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| 12. |
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| 13. |
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| 14. |
- Bolind, Pia, 1953, et al.
(författare)
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Retrieved implants from irradiated sites in humans: a histologic/histomorphometric investigation of oral and craniofacial implants
- 2006
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Ingår i: Clinical implant dentistry and related research. - Hamilton, Ont. : Wiley. - 1523-0899 .- 1708-8208. ; 8:3, s. 142-50
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Tidskriftsartikel (refereegranskat)abstract
- PURPOSE: The aim of this report was to quantitatively and qualitatively evaluate the tissue response to bone-anchored implants retrieved from irradiated sites in patients. MATERIALS AND METHODS: The material consists of 23 consecutively received Branemark implants (Nobel Biocare AB, Goteborg, Sweden) placed in pre- or postoperatively irradiated sites. Twenty-two of the 23 implants were suitable for histologic evaluation of undecalcified sections in the light microscope. RESULTS: The oral implants with shorter time in situ demonstrated sparse bone to implant contact with mainly dense connective tissue in the interface. However, for implants with longer time in situ, high amounts of bone-implant contact and bone fill of threads were noted. The mean values of bone-implant contact and bone area within the thread were calculated to 40% (16-94) and 70% (13-96), respectively. The craniofacial implants, with the exception of two implants lined with a capsular formation, demonstrated mature and newly formed bone at the bone-implant interface. The mean value for bone-metal contact was calculated to 45 and 53% for two specimens. The mean value for bone area within the thread ranged from 65 to 88% for three specimens. CONCLUSION; The possibility to achieve bone anchorage of implants in irradiated tissue was supported by the findings in this study. However, due to limited material, conclusions with regard to radiation dose and bone tissue response to implants cannot be stated.
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| 15. |
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| 16. |
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| 17. |
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| 18. |
- Ekblad, Alf, et al.
(författare)
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Forest soil respiration rate and d13C is regulated by recent above ground weather conditions
- 2005
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Ingår i: Oecologia. - : Springer Science and Business Media LLC. - 0029-8549 .- 1432-1939. ; 143:1, s. 136-142
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Tidskriftsartikel (refereegranskat)abstract
- Soil respiration, a key component of the global carbon cycle, is a major source of uncertainty when estimating terrestrial carbon budgets at ecosystem and higher levels. Rates of soil and root respiration are assumed to be dependent on soil temperature and soil moisture yet these factors often barely explain half the seasonal variation in soil respiration. We here found that soil moisture (range 16.5-27.6% of dry weight) and soil temperature (range 8-17.5 degrees C) together explained 55% of the variance (cross-validated explained variance; Q2) in soil respiration rate (range 1.0-3.4 micromol C m(-2) s(-1)) in a Norway spruce (Picea abies) forest. We hypothesised that this was due to that the two components of soil respiration, root respiration and decomposition, are governed by different factors. We therefore applied PLS (partial least squares regression) multivariate modelling in which we, together with below ground temperature and soil moisture, used the recent above ground air temperature and air humidity (vapour pressure deficit, VPD) conditions as x-variables. We found that air temperature and VPD data collected 1-4 days before respiration measurements explained 86% of the seasonal variation in the rate of soil respiration. The addition of soil moisture and soil temperature to the PLS-models increased the Q2 to 93%. delta13C analysis of soil respiration supported the hypotheses that there was a fast flux of photosynthates to root respiration and a dependence on recent above ground weather conditions. Taken together, our results suggest that shoot activities the preceding 1-6 days influence, to a large degree, the rate of root and soil respiration. We propose this above ground influence on soil respiration to be proportionally largest in the middle of the growing season and in situations when there is large day-to-day shifts in the above ground weather conditions. During such conditions soil temperature may not exert the major control on root respiration.
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| 19. |
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| 26. |
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| 27. |
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| 28. |
- Eriksson, Cecilia, et al.
(författare)
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Time-of-flight secondary ion mass spectrometric analysis of the interface between bone and titanium implants.
- 2008
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Ingår i: Rapid communications in mass spectrometry : RCM. - : Wiley. - 0951-4198 .- 1097-0231. ; 22:7, s. 943-9
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Tidskriftsartikel (refereegranskat)abstract
- Implant healing into bone tissue is a process where the mature bone grows towards and eventually fuses with the implant. In this study we investigated implant healing during 4 weeks with focus on the implant-tissue interface. Our main interest was to study the mineralization process around the implant. Titanium discs were implanted in rat tibia for 2 and 4 weeks. After implantation cross sections of bone and implant were made using a low-speed saw equipped with a diamond wafering blade. One section from each sample was stained with basic fuchsin and micrographed by light microscopy (LM). The other section was analyzed with imaging time-of-flight secondary ion mass spectrometry (TOF-SIMS) using a Bi(3)(+) cluster ion source. This ion source has recently been shown to enable identification of high-mass hydroxyapatite (HA) fragment ions (m/z 291-653) in bone samples. The LM images were used to identify areas suitable for TOF-SIMS analysis. Three areas were selected for mass spectral analysis, corresponding to interface region, bone and soft tissue, from which positive ion spectra were recorded. In the areas identified as bone, high-mass HA fragments ions were found after both 2 and 4 weeks. In the soft tissue area, no high-mass ions were found after 4 weeks. However, after 2 weeks HA-related ions were identified in mineralized spots in areas defined as soft tissue. After 4 but not after 2 weeks, high-mass HA fragment ions were found in the interface region. In conclusion, differences were observed regarding mineralization between 2 and 4 weeks of implantation and between different regions surrounding the implants. Imaging TOF-SIMS analysis using a Bi(3)(+) cluster as ion source enables identification of high-mass HA fragment ions at implant-tissue interfaces in bone. This technique might therefore be useful for biocompatibility assessment and for studying the mineralization process at implant surfaces.
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| 29. |
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| 33. |
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| 34. |
- Gullfot, Fredrika, 1967-
(författare)
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Synthesis of xyloglucan oligo- and polysaccharides with glycosynthase technology
- 2009
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Xyloglucans are polysaccharides found as storage polymers in seeds and tubers, and as cross-linking glycans in the cell wall of plants. Their structure is complex with intricate branching patterns, which contribute to the physical properties of the polysaccharide including its binding to and interaction with other glycans such as cellulose. Xyloglucan is widely used in bulk quantities in the food, textile and paper making industries. With an increasing interest in technically more advanced applications of xyloglucan, such as novel biocomposites, there is a need to understand and control the properties and interactions of xyloglucan with other compounds, to decipher the relationship between xyloglucan structure and function, and in particular the effect of different branching patterns. However, due to the structural heterogeneity of the polysaccharide as obtained from natural sources, relevant studies have not been possible to perform in practise. This fact has stimulated an interest in synthetic methods to obtain xyloglucan mimics and analogs with well-defined structure and decoration patterns. Glycosynthases are hydrolytically inactive mutant glycosidases that catalyse the formation of glycosidic linkages between glycosyl fluoride donors and glycoside acceptors. Since its first conception in 1998, the technology is emerging as a useful tool in the synthesis of large, complex polysaccharides. This thesis presents the generation and characterisation of glycosynthases based on xyloglucanase scaffolds for the synthesis of well-defined homogenous xyloglucan oligo- and polysaccharides with regular substitution patterns.
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| 35. |
- Jarmar, T., et al.
(författare)
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Characterization of the surface properties of commercially available dental implants using scanning electron microscopy, focused ion beam, and high-resolution transmission electron microscopy
- 2008
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Ingår i: Clinical Implant Dentistry and Related Research. - : Wiley. - 1523-0899 .- 1708-8208. ; 10:1, s. 11-22
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: Since osseointegration of the respective implant is claimed by all manufacturing companies, it is obvious that not just one specific surface profile including the chemistry controls bone apposition. PURPOSE: The purpose was to identify and separate out a particular set of surface features of the implant surfaces that can contribute as factors in the osseointegration process. MATERIAL AND METHODS: The surface properties of several commercially available dental implants were extensively studied using profilometry, scanning electron microscopy, and transmission electron microscopy. Ultrathin sections prepared with focused ion beam microscopy (FIB) provided microstructural and chemical data which have not previously been communicated. The implants were the Nobel Biocare TiUnite (Nobel Biocare AB, Goteborg, Sweden), Nobel Biocare Steri-Oss HA-coated (Nobel Biocare AB, Yorba Linda, CA, USA), Astra-Tech OsseoSpeed (Astra Tech AB, Molndal, Sweden), Straumann SLA (Straumann AG, Waldenburg, Switzerland), and the Branemark Integration Original Fixture implant (Branemark Integration, Goteborg, Sweden). RESULTS: It was found that their surface properties had differences. The surfaces were covered with crystalline TiO(2) (both anatase and rutile), amorphous titanium oxide, phosphorus doped amorphous titanium oxide, fluorine, titanium hydride, and hydroxyapatite, respectively. CONCLUSION: This indicates that the provision of osseointegration is not exclusively linked to a particular set of surface features if the implant surface character is a major factor in that process. The studied methodology provides an effective tool to also analyze the interface between implant and surrounding bone. This would be a natural next step in understanding the ultrastructure of the interface between bone and implants.
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| 36. |
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| 37. |
- Jarmar, Tobias, et al.
(författare)
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Injectable bone cements for vertebroplasty studied in sheep vertebrae with electron microscopy
- 2008
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Ingår i: Key Engineering Materials. - 1662-9795.
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Tidskriftsartikel (refereegranskat)abstract
- Vertebral compression fractures were simulated by making a hole into sheep vertebrae and by injecting a stabilizing material. The injectable bio-ceramic Xeraspine™ was evaluated together with a commercially available PMMA (Vertebroplastic™) as the reference material. The Vertebrae were harvested after 7 days and prepared for microscopy. The samples were deposited with gold on the surface and thereafter subjected to SEM and EDX analysis. It was found that the Xeraspine-bone interface was composed of a mixture of elements. The Vertebroplastic implant was embedded in a carbon containing tissue, likely a soft tissue capsule. The Xeraspine sample was subjected to high resolution analysis in the TEM combined with EDX measurements. The TEM sample was prepared with a novel technique for preparation of the tissue-material interface (FIB). In the TEM analysis it was found that the interface region consists of ZrO2 together with a mixture possibly consisting of katoite and apatite formed during setting and/or originating from the boneapatite.
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| 38. |
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| 39. |
- Jarmar, T., et al.
(författare)
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Technique for preparation and characterization in cross-section of oral titanium implant surfaces using focused ion beam and transmission electron microscopy
- 2008
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Ingår i: Journal of Biomedical Materials Research Part A. - : Wiley. - 1552-4965 .- 1549-3296. ; 87:4, s. 1003-9
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Tidskriftsartikel (refereegranskat)abstract
- The surface properties of materials are believed to control most of the biological reactions toward implanted materials. To study the surface structure, elemental distribution, and morphology, using transmission electron microscopy (TEM) techniques, thin foils of the surface (in cross-section) are needed. These have been cumbersome to produce, in particular, from the normally irregular screw-shaped metal implants. Focused ion beam (FIB) microscopy has been developed partly for TEM sample preparation, mainly within the microelectronics industry. Our study describes a method based on FIB for producing electron transparent foils/sections from a metal implant for TEM analysis. Using a screw-shaped titanium dental implant, it was demonstrated that thin foils can be prepared with submicron specificity and from almost any surface geometry. A comparison of different lift-out techniques showed that the in situ lift-out preparation technique allowed plasma cleaning and produced particularly good samples with excellent yield. The titanium oxide on the implant surface was analyzed using energy-filtered TEM (EFTEM) and high-resolution TEM (HRTEM) and the TiO(2) rutile phase being determined via the lattice parameters. This study provides the first set of data for the optimization of a new route for preparation and analysis of biomaterial surfaces and interfaces.
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| 40. |
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| 41. |
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| 42. |
- Johansson, Martin, et al.
(författare)
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The Healing Process of an Ileostomy to a Percutaneous Titanium Implant: a Short Term Experimental Study on animals
- 2008
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Ingår i: Abstract, 8th World Biomaterials Congress, Amsterdam, The Netherlands.
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Konferensbidrag (refereegranskat)abstract
- Introduction: Many diseases such as e.g. ulcerative colitis, colorectal cancer, familial adenomatous polyposis as well as bladder cancer often require surgery with removal of all or part of the intestines or urinary bladder with construction of an abdominal stoma. External stoma appliances or internal ileal pouches have to be used for collection of bowel contents and urine, respectively. It is hypothesized that by attachment of the intestine to a percutaneous implant, a fully continent stoma might be achieved. Such an attachment needs to be instantaneous, permanent and leakage free. As of today there is no implant or structure known to merge with intestine. The principal aim of the present study was to evaluate the tissue response to a newly designed implant. Apart from the healing process of the abdominal tissues to the implant surface, special focus was directed to the adherence of the ileal serosa to the inner surface of the implant. Conclusions: The present results demonstrate convincingly that the serosal side of the intestine may attach and merge with the internal structure of the implant. These studies provide a basis for optimization of the surgical procedure prior to long-term trials.
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| 43. |
- Kou, Wen, 1979-, et al.
(författare)
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Numerical modeling of the fracture process in a three-unit all-ceramic fixed partial denture
- 2007
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Ingår i: Dental Materials. - : Elsevier BV. - 0109-5641 .- 1879-0097. ; 23:8, s. 1042-1049
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Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVES: The main objectives were to examine the fracture mechanism and process of a ceramic fixed partial denture (FPD) framework under simulated mechanical loading using a recently developed numerical modeling code, the R-T(2D) code, and also to evaluate the suitability of R-T(2D) code as a tool for this purpose. METHODS: Using the recently developed R-T(2D) code the fracture mechanism and process of a 3U yttria-tetragonal zirconia polycrystal ceramic (Y-TZP) FPD framework was simulated under static loading. In addition, the fracture pattern obtained using the numerical simulation was compared with the fracture pattern obtained in a previous laboratory test. RESULTS: The result revealed that the framework fracture pattern obtained using the numerical simulation agreed with that observed in a previous laboratory test. Quasi-photoelastic stress fringe pattern and acoustic emission showed that the fracture mechanism was tensile failure and that the crack started at the lower boundary of the framework. The fracture process could be followed both in step-by-step and step-in-step. SIGNIFICANCE: Based on the findings in the current study, the R-T(2D) code seems suitable for use as a complement to other tests and clinical observations in studying stress distribution, fracture mechanism and fracture processes in ceramic FPD frameworks.
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| 44. |
- Kroon, Martin, et al.
(författare)
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A new constitutive model for multi-layered collagenous tissues
- 2008
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Ingår i: Journal of Biomechanics. - : Elsevier BV. - 0021-9290 .- 1873-2380. ; 41:12, s. 2766-2771
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Tidskriftsartikel (refereegranskat)abstract
- Collagenous tissues Such as the aneurysmal wall or the aorta are multi-layered structures with the mean fibre alignments distinguishing one layer from another. A constitutive representation of the multiple collagen layers is not yet developed, and hence the aim of the present study. The proposed model is based on the constitutive theory of finite elasticity and is characterized by an anisotropic strain-energy function which takes the material structure into account. The passive tissue behaviour is modelled and the related mechanical response is assumed to be dominated by elastin and collagen. While elastin is modelled by the neo-Hookean material the constitutive response of collagen is assumed to be transversely isotropic for each individual layer and based on an exponential function. The proposed constitutive function is polyconvex which ensures material stability. The model has five independent material parameters, each of which has a clear physical interpretation: the initial stiffnesses of the collagen fabric in the two principal directions, the shear modulus pertaining to the non-collagenous matrix material, a parameter describing the level of nonlinearity of the collagen fabric, and the angle between the principal directions of the collagen fabric and the reference coordinate system. An extension-inflation test of the adventitia of a human femoral artery is simulated by means of the finite element method and an error function is minimized by adjusting the material parameters yielding a good agreement between the model and the experimental data.
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| 45. |
- Kumar, Ashok, et al.
(författare)
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Affinity binding of cells to cryogel adsorbents with immobilized specific ligands : effect of ligand coupling and matrix architecture
- 2005
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Ingår i: Journal of Molecular Recognition. - : Wiley. - 0952-3499 .- 1099-1352. ; 18:1, s. 84-93
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Tidskriftsartikel (refereegranskat)abstract
- The capture of human acute myeloid leukemia KG-1 cells expressing the CD34 surface antigen and the fractionation of human blood lymphocytes were evaluated on polyvinyl alcohol (PVA)-cryogel beads and dimethyl acrylamide (DMAAm) monolithic cryogel with immobilized protein A. The affinity ligand (protein A) was chemically coupled to the reactive PVA-cryogel beads and epoxy-derivatized monolithic cryogels through different immobilization techniques and the binding efficiency of the cell surface receptors specific antibody-labeled cells to the gels/beads was determined. The binding of cells to monolithic cryogel was higher (90-95%) compared with cryogel beads (76%). B-lymphocytes, which bound to the protein A-cryogel beads, were separated from T-lymphocytes with yields for the two cell types 74 and 85%, respectively. About 91% of the bound B-cells could be recovered without significantly impairing their viability. Our results show differences in the percentage of cell-binding to the immunosorbents caused by ligand density, flow shear forces and bond strength between the cells and the affinity surface once distinct chemical coupling of protein A, size of beads, sequence of antibody binding to protein A adsorbents, morphology and geometry of surface matrices were compared.
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| 46. |
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| 47. |
- Lindberg, Fredrik, et al.
(författare)
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Hydroxylapatite growth on single-crystal rutile substrates
- 2008
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Ingår i: Biomaterials. - : Elsevier BV. - 0142-9612 .- 1878-5905. ; 29:23, s. 3317-3323
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Tidskriftsartikel (refereegranskat)abstract
- Titanium is widely used as an implant material. In addition to the bulk properties of titanium, the biological response is to a large degree controlled via the surface. The native amorphous titanium oxide that forms spontaneously on the surface gives a very good biological response. Lately it has been shown that crystalline titanium oxides (rutile and anatase) have in vitro bioactive properties. In addition to its potential for new materials development, this finding also opens up for the possibility of studying the mechanisms of bioactivity on materials with strictly controlled surfaces. In this paper the mechanisms behind the in vitro bioactivity are studied, using rutile single crystals. Three single-crystal rutile substrates: (100), (110), and (001), and a polycrystalline rutile substrate obtained by physical vapour deposition were soaked in a phosphate buffered saline solution for up to 4 weeks. The hydroxylapatite films that formed were analysed by X-ray diffraction, scanning electron microscopy, focused ion beam, and transmission electron microscopy. The hydroxylapatite grew faster on the (001) surface than on the other two. It was also found that on the (001) surface the direction of fast growth in hydroxylapatite was aligned parallel to the surface. This is in contrast to the (110) rutile surface where the fast growth of the hydroxylapatite crystal was directed outwards from the surface. The (100) face had poor adhesion at the interface. The orientations of the precipitated crystallites play a significant role in the faster coverage of the (001) rutile face. Based on the experimental results, a model for the hydroxylapatite growth process is given.
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| 48. |
- Lindholm-Sethson, Britta, et al.
(författare)
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Effects of pH and fluoride concentration on the corrosion of titanium
- 2008
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Ingår i: Journal of Biomedical Materials Research Part A. - : Wiley. - 1549-3296 .- 1552-4965. ; 86A:1, s. 149-159
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this investigation was to confirm and summarize the corrosion behavior of titanium in saline solution at different pH and fluoride concentration, and to characterize the surface films and the stability of a passive and aged titanium surface using open circuit potential measurements, electrochemical impedance spectroscopy, and anodic polarization curves. The results from the electrochemical measurements were related to titanium released after 2-min brushing with saline solutions with different pH and fluoride concentration, that is, simulating tooth brushing with fluoride containing prophylactic substances. Titanium was analyzed using atomic adsorption spectrophotometry. The pH in the saline solution was varied between 4 and 7 with additions of sodium fluoride up to 1.0 wt %. The presence of fluoride in solution was unfavorable for the stability of titanium and led to corrosion and the release of titanium especially at low pH. The combination of low pH and presence of fluoride ions in solution destroyed a passive film on the titanium surface even after aging for 170 h in neutral saline solution. The results do not necessarily imply the occurrence of biological soft tissue related effects even if a physical contact between titanium and the surrounding milieu is prevalent. To provide a general understanding of electrochemical techniques in biomaterial research, much effort was put in the qualitative description of the results, with the intention to provide a broader understanding of especially the impedance method to other researchers. (c) 2007 Wiley Periodicals, Inc. J Biomed Mater Res, 2007.
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| 49. |
- Lööf, Jesper, 1977-
(författare)
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Calcium-Aluminate as Biomaterial : Synthesis, Design and Evaluation
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis different aspects of calcium-aluminate (CA) as biomaterial are presented. Calcium aluminate is a chemically bonded ceramic with inherent properties making it suitable for use as biomaterial in some applications. In this thesis the emphasis is put on the basic chemical, physical and mechanical properties that may be achieved using the CA system as well as synthesis of the CA raw material. The basis for using CA in any application is the synthesis of the raw material. Different synthesis routes for producing CA are presented with focus on high temperature routes and the micro-structural and phase development during synthesis. As a base for further understanding of the CA properties a thorough outline of the reaction chemistry for CA is presented also including a description of how the reactions may be controlled and how formulations can be designed. The surface reactions of CA when subjected to simulated body fluid showed that CA is in vitro bioactive. An in vivo study in teeth also indicates that CA produces apatite at the tooth material interface. Dental materials are subjected to a harsh environment in the mouth with high mechanical forces, erosion and thermal changes. Also the demands on precise handling characteristics are high. For these reasons the in vitro evaluation of physical and mechanical properties are important. In this work several mechanical and physical properties of Ca-based formulations for dental applications has been tested using different methods. Some attention is also put on the specific characteristics of CA and the difficulties that arise when new material classes needs to be tested according to consensus standard methods. Finally studies on a CA-based formulation intended for Vertebroplasty is presented. The studies include basic mechanical properties as well as testing the material in an in vitro model utilising synthetic cancellous bone.
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| 50. |
- Mak, Wing Cheung, et al.
(författare)
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Real time observation of diffusion and bioaffinity binding processes in single polyelectrolyte-coated microcapsules : A fluorescence-based approach
- 2007
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Ingår i: Colloids and Surfaces B. - : Elsevier. - 0927-7765 .- 1873-4367. ; 60:1, s. 125-130
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Tidskriftsartikel (refereegranskat)abstract
- We report on using fluorescence microscopy to study, visualize and determine the diffusion phenomena into and bioaffinity binding within single microcapsules in real time by using biotin–fluorescein as diffusive species and encapsulated avidin as binding partner. Microcapsules were constructed by entrapment of avidin within an agarose matrix and encapsulated with polyelectrolyte layers by Layer-by-Layer (LbL) polyelectrolyte self assembly. A “ring” of high fluorescence intensity advancing with time towards the capsule centre was observed during incubation of capsules with fluorescent-labeled biotin. Fluorescence intensity was build up in capsule areas where binding to avidin occurred and was visualized in real time. A model for the diffusion process in microcapsules was developed and experimental data was plotted and fitted well with trends predicted by the model. The value of the diffusion coefficient for biotin–fluorescein was determined to be 3.5 × 10−8 cm2/s, which is comparable to literature values of similar sized molecules.
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