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| 2. |
- Abdulghani, Saba, et al.
(författare)
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The influence of initial pressurization and cup introduction time on the depth of cement penetration in an acetabular model.
- 2007
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Ingår i: Acta Orthopaedica. - : Medical Journals Sweden AB. - 1745-3682 .- 1745-3674. ; 78:3, s. 333-339
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Tidskriftsartikel (refereegranskat)abstract
- Background Acetabular cementation during total hip arthroplasty is considered difficult mainly due to the appearance and anatomy of the acetabulum. Improved cementation technique has been shown to improve the longevity of acetabular components. Method We designed a ceramic model to investigate the effect of varying the initial cement pressurization and cup introduction times on the depth of cement penetration. 4 groups were prepared, 2 of which involved varying initial cement pressurization and cup introduction times. Group 3 involved initial cement pressurization with no cup introduction, while group 4 involved cup introduction with no prior cement pressurization. Results and interpretation Most cement penetration occurred in the early pressurization phase, and we conclude that a relatively early and longer cement pressurization time and late cup introduction are positive factors for increased cement penetration in the acetabulum model.
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| 3. |
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| 4. |
- Camire, Christopher, et al.
(författare)
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Material characterization and in vivo behavior of silicon substituted alpha-tricalcium phosphate cement.
- 2006
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Ingår i: Journal of Biomedical Materials Research. Part B - Applied Biomaterials. - : Wiley. - 1552-4981 .- 1552-4973. ; 76B:2, s. 424-431
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Tidskriftsartikel (refereegranskat)abstract
- The possibility and biological effects of substituting silicon in a-tricalcium phosphate (alpha-TCP) by way of solid-state reaction have been evaluated. a-TCP powders with varying substitution amounts (1 and 5 mol % Ca2SiO4) were synthesized by reacting mixtures of CaCO3, Ca(2)P(2)O7, and SiO2, at a rate of 4 degrees C(min)(-1) to 1100 degrees C, left to dwell for 2 h and then heated to 1325 degrees C at 4 degrees C(min)(-1) and left to dwell for a period of 4 h. The powders were then rapidly quenched in air. Si incorporation could be verified by X-ray diffraction analysis, indicating an increase of the lattice volume with increasing Si content from 4284.1(8) to 4334(1) angstrom(3) for pure alpha-TCP and alpha-Si5%TCP, respectively. The hydrolysis of milled alpha-SiTCP powders was monitored by isothermal calorimetry, and the compressive strength of set cements was tested. The results showed changes in speed and amount of heat released during reactivity tests and a decrease in mechanical strength (60, 50, and 5 MPa) with increasing Si content. In vitro bioactivity of the set cements after soaking in simulated body fluid for 4 weeks was also tested. The formation of a bonelike apatite layer on the surface of the set cements could be observed and was thickest for 1% Si (20 mu m). These results were in good agreement with the in vivo studies performed, which showed strong evidence that the cement containing 1% silicon doped alpha-TCP enhanced mesenchymal cell differentiation and increased osteoblast activity compared with alpha-TCP. (c) 2005 Wiley Periodicals, Inc.
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| 5. |
- Hempel, Antje, et al.
(författare)
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The Ser/Thr protein kinase AfsK regulates polar growth and hyphal branching in the filamentous bacteria Streptomyces.
- 2012
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Ingår i: Proceedings of the National Academy of Sciences. - : Proceedings of the National Academy of Sciences. - 1091-6490 .- 0027-8424. ; 109:35, s. 2371-2379
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Tidskriftsartikel (refereegranskat)abstract
- In cells that exhibit apical growth, mechanisms that regulate cell polarity are crucial for determination of cellular shape and for the adaptation of growth to intrinsic and extrinsic cues. Broadly conserved pathways control cell polarity in eukaryotes, but less is known about polarly growing prokaryotes. An evolutionarily ancient form of apical growth is found in the filamentous bacteria Streptomyces, and is directed by a polarisome-like complex involving the essential protein DivIVA. We report here that this bacterial polarization machinery is regulated by a eukaryotic-type Ser/Thr protein kinase, AfsK, which localizes to hyphal tips and phosphorylates DivIVA. During normal growth, AfsK regulates hyphal branching by modulating branch-site selection and some aspect of the underlying polarisome-splitting mechanism that controls branching of Streptomyces hyphae. Further, AfsK is activated by signals generated by the arrest of cell wall synthesis and directly communicates this to the polarisome by hyperphosphorylating DivIVA. Induction of high levels of DivIVA phosphorylation by using a constitutively active mutant AfsK causes disassembly of apical polarisomes, followed by establishment of multiple hyphal branches elsewhere in the cell, revealing a profound impact of this kinase on growth polarity. The function of AfsK is reminiscent of the phoshorylation of polarity proteins and polarisome components by Ser/Thr protein kinases in eukaryotes.
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| 6. |
- Kjellson, Fred, et al.
(författare)
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Tensile properties of a bone cement containing non-ionic contrast media
- 2001
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Ingår i: Journal of Materials Science: Materials in Medicine. - 1573-4838. ; 12:10-12, s. 889-894
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Tidskriftsartikel (refereegranskat)abstract
- The addition of contrast media such as BaSO4 or ZrO2 to bone cement has adverse effects in joint replacements, including third body wear and particle-induced bone resorption. Ground PMMA containing particles of the non-ionic water-soluble iodine-based X-ray contrast media, iohexol (IHX) and iodixanol (IDX), has, in bone tissue culture, shown less bone resorption than commercial cements. These water-soluble non-ceramic contrast media may change the mechanical properties of acrylic bone cement. The static mechanical properties of bone cement containing either IHX or IDX have been investigated. There was no significant difference in ultimate stress between Palacos R (with 15.0 wt % of ZrO2) and plain cement with 8.0 wt % of IHX or IDX with mass median diameter (MMD) of 15.0 or 16.0 microm, while strain to failure was higher for the latter (p < 0.02). The larger particles (15.0 or 16.0 microm) gave significantly higher (p < 0.001) ultimate tensile strengths and strains to failure than smaller sizes (2.4 or 3.6 microm). Decreasing the amount of IHX from 10.0 wt % to 6.0 wt % gave a higher ultimate tensile strength (p < 0.001) and strain to failure (p < 0.02). Scanning electron microscopy (SEM) showed the smaller contrast media particles attached to the surface of the polymer beads, which may prevent areas of the acrylate bead surface from participating in the polymerization. In conclusion, the mechanical properties of bone cement were influenced by the size and amount of contrast medium particles. By choosing the appropriate amount and size of particles of water-soluble non-ionic contrast media the mechanical properties of the new radio-opaque bone cement can be optimized, thus reaching and surpassing given regulatory standards.
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| 7. |
- Lin, Zhaowei, et al.
(författare)
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Effects of BMP2 and VEGF165 on the osteogenic differentiation of rat bone marrow-derived mesenchymal stem cells.
- 2014
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Ingår i: Experimental and Therapeutic Medicine. - : Spandidos Publications. - 1792-1015 .- 1792-0981. ; 7:3, s. 625-629
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Tidskriftsartikel (refereegranskat)abstract
- Bone marrow-derived mesenchymal stem cells (MSCs) are dominant seed cell sources for bone regeneration. Bone morphogenetic proteins (BMPs) initiate cartilage and bone formation in a sequential cascade. Vascular endothelial growth factor (VEGF) is an essential coordinator of extracellular matrix remodeling, angiogenesis and bone formation. In the present study, the effects of the vascular endothelial growth factor 165 (VEGF165) and bone morphogenetic protein 2 (BMP2) genes on bone regeneration were investigated by the lentivirus-mediated cotransfection of the two genes into rat bone marrow-derived MSCs. The successful co-expression of the two genes in the MSCs was confirmed using quantitative polymerase chain reaction (qPCR) and western blot analysis. The results of alizarin red and alkaline phosphatase (ALP) staining at 14 days subsequent to transfection showed that the area of staining in cells transfected with BMP2 alone was higher than that in cells transfected with BMP2 and VEGF165 or untransfected control cells, while the BMP2 + VEGF165 group showed significantly more staining than the untransfected control. This indicated that BMP2 alone exhibited a stronger effect in bone regeneration than BMP2 in combination with VEGF165. Similarly, in inducing culture medium, the ALP activity of the BMP2 + VEGF165 group was notably suppressed compared with that of the BMP2 group. The overexpression of VEGF165 inhibited BMP2-induced MSC differentiation and osteogenesis in vitro. Whether or not local VEGF gene therapy is likely to affect bone regeneration in vivo requires further investigation.
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| 8. |
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| 9. |
- Nilsson, M, et al.
(författare)
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Biodegradation and biocompatability of a calcium sulphate-hydroxyapatite bone substitute.
- 2004
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Ingår i: Journal of Bone and Joint Surgery: British Volume. - 2044-5377. ; 86:1, s. 120-125
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Tidskriftsartikel (refereegranskat)abstract
- An injectable material consisting of calcium sulphate mixed with hydroxyapatite was investigated as a possible alternative to autograft in the restoration of bone defects. The material was studied both in vitro in simulated body fluid (SBF) and in vivo when implanted in rat muscles and into the proximal tibiae of rabbits. Variation in the strength and weight of the material during ageing in SBF was measured. Tissue response, material resorption and bone ingrowth were studied in the animal models. A good tissue response was observed in both the rat muscles and rabbit tibiae without inflammatory reactions or the presence of fibrous tissue. Ageing in SBF showed that during the first week carbonated hydroxyapatite precipitated on the surfaces of the material and this may enhance bone ingrowth.
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| 10. |
- Nilsson, Malin K, et al.
(författare)
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Factors influencing the compressive strength of an injectable calcium sulfate-hydroxyapatite cement.
- 2003
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Ingår i: Journal of Materials Science: Materials in Medicine. - 1573-4838. ; 14:5, s. 399-404
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Tidskriftsartikel (refereegranskat)abstract
- A biphasic injectable bone substitute, suitable for filling bone defects, that sets in the body, based on calcium sulfate and hydroxyapatite (HA), is presented. For applications in bone defects the compressive strength is important to assure support of the defect site during loading when the patient is weight bearing. To control the strength, the influence of four different factors; the liquid-to-powder (L/P) ratio, the HA particle morphology, the HA content and the amount of accelerator, were investigated. alpha-Calcium sulfate hemihydrate (CSH) and four different HA powders (three sintered and one spray-dried) were used. All differed in size and morphology. CSH and each HA powder were mixed together with distilled water to form the bone substitute. An accelerator, in form of calcium sulfate dihydrate, was added to the powder phase to obtain an adequate setting time. Cylindrical specimens were compression tested. A lower L/P-ratio gave stronger cement, but was more difficult to inject. The shape and the morphology of the HA particles influenced the strength, and reducing the amount of HA increased the strength. The amount of accelerator (calcium sulfate dihydrate) had no influence. (C) 2003 Kluwer Academic Publishers.
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