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| 2. |
- Björkman, Frida, et al.
(författare)
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Regular moist snuff dipping does not affect endurance exercise performance
- 2017
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Ingår i: Plos One. - : Public Library of Science (PLoS). - 1932-6203. ; 12:7
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Tidskriftsartikel (refereegranskat)abstract
- Physiological and medical effects of snuff have previously been obtained either in cross-sectional studies or after snuff administration to non-tobacco users. The effects of snuff cessation after several years of daily use are unknown. 24 participants with >2 years of daily snuff-use were tested before and after >6 weeks snuff cessation (SCG). A control group (CO) of 11 snuff users kept their normal habits. Resting heart rate (HR) and blood pressure (BP) were significantly lower in SCG after snuff cessation, and body mass was increased by 1.4 +/- 1.7 kg. Total cholesterol increased from 4.12 +/- 0.54 (95% CI 3.89-4.35) to 4.46 +/- 0.70 (95% CI 4.16-4.75) mM L-1 in SCG, due to increased LDL, and this change was significantly different from CO. Resting values of HDL, C-reactive protein, and free fatty acids (FFA) remained unchanged in both groups. In SCG group, both HR and BP were reduced during a four-stage incremental cycling test (from 50 to 80% of VO(2)max) and a prolonged cycling test (60 min at 50% of VO(2)max). Oxygen uptake (VO2), respiratory exchange ratio, blood lactate (bLa) and blood glucose (bGlu) concentration, and rate of perceived exertion (RPE) were unchanged. In CO group, all measurements were unchanged. During the prolonged cycling test, FFA was reduced, but with no significant difference between groups. During the maximal treadmill running test peak values of VO2, pulmonary ventilation (VE), time to exhaustion and bLa were unchanged in both groups. In conclusion, endurance exercise performance (VO(2)dmax and maximal endurance time) does not seem to be affected by prolonged snuff use, while effects on cardiovascular risk factors are contradictory. HR and BP during rest and submaximal exercise are reduced after cessation of regular use of snuff. Evidently, the long-time adrenergic stress on circulation is reversible.
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| 4. |
- Brown, Toby D, et al.
(författare)
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Melt electrospinning of poly(ε-caprolactone) scaffolds : phenomenological observations associated with collection and direct writing.
- 2014
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Ingår i: Materials science & engineering. C, biomimetic materials, sensors and systems. - : Elsevier BV. - 0928-4931 .- 1873-0191. ; 45
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Tidskriftsartikel (refereegranskat)abstract
- Melt electrospinning and its additive manufacturing analogue, melt electrospinning writing (MEW), are two processes which can produce porous materials for applications where solvent toxicity and accumulation in solution electrospinning are problematic. This study explores the melt electrospinning of poly(ε-caprolactone) (PCL) scaffolds, specifically for applications in tissue engineering. The research described here aims to inform researchers interested in melt electrospinning about technical aspects of the process. This includes rapid fiber characterization using glass microscope slides, allowing influential processing parameters on fiber morphology to be assessed, as well as observed fiber collection phenomena on different collector substrates. The distribution and alignment of melt electrospun PCL fibers can be controlled to a certain degree using patterned collectors to create large numbers of scaffolds with shaped macroporous architectures. However, the buildup of residual charge in the collected fibers limits the achievable thickness of the porous template through such scaffolds. One challenge identified for MEW is the ability to control charge buildup so that fibers can be placed accurately in close proximity, and in many centimeter heights. The scale and size of scaffolds produced using MEW, however, indicate that this emerging process will fill a technological niche in biofabrication.
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| 6. |
- Cai, Yixiao, et al.
(författare)
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Strategy towards independent electrical stimulation from cochlear implants : Guided auditory neuron growth on topographically modified nanocrystalline diamond
- 2016
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Ingår i: Acta Biomaterialia. - : Elsevier BV. - 1742-7061 .- 1878-7568. ; 31, s. 211-220
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Tidskriftsartikel (refereegranskat)abstract
- Cochlear implants (CI) have been used for several decades to treat patients with profound hearing loss. Nevertheless, results vary between individuals, and fine hearing is generally poor due to the lack of discrete neural stimulation from the individual receptor hair cells. A major problem is the deliverance of independent stimulation signals to individual auditory neurons. Fine hearing requires significantly more stimulation contacts with intimate neuron/electrode interphases from ordered axonal re-growth, something current CI technology cannot provide.Here, we demonstrate the potential application of micro-textured nanocrystalline diamond (NCD) surfaces on CI electrode arrays. Such textured NCD surfaces consist of micrometer-sized nail-head-shaped pillars (size 5 5 lm2) made with sequences of micro/nano-fabrication processes, including sputtering, photolithography and plasma etching.The results show that human and murine inner-ear ganglion neurites and, potentially, neural progenitor cells can attach to patterned NCD surfaces without an extracellular matrix coating. Microscopic methods revealed adhesion and neural growth, specifically along the nail-head-shaped NCD pillars in an ordered manner, rather than in non-textured areas. This pattern was established when the inter-NCD pillar distance varied between 4 and 9 lm.The findings demonstrate that regenerating auditory neurons show a strong affinity to the NCD pillars, and the technique could be used for neural guidance and the creation of new neural networks. Together with the NCD’s unique anti-bacterial and electrical properties, patterned NCD surfaces could provide designed neural/electrode interfaces to create independent electrical stimulation signals in CI electrode arrays for the neural population.
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| 7. |
- Detta, Nicola, et al.
(författare)
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Melt electrospinning of polycaprolactone and its blends with poly(ethylene glycol)
- 2010
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Ingår i: Polymer international. - : Wiley. - 0959-8103 .- 1097-0126. ; 59:11, s. 1558-1562
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Tidskriftsartikel (refereegranskat)abstract
- Melt electrospinning is one aspect of electrospinning with relatively little published literature, although the technique avoids solvent accumulation and/or toxicity which is favoured in certain applications In the study reported, we melt-electrospun blends of poly(epsilon-caprolactone) (PCL) and an amphiphilic diblock copolymer consisting of poly(ethylene glycol) and PCL segments (PEG-block PCL) A custom-made electrospinning apparatus was built and various combinations of instrument parameters such as voltage and polymer feeding rate were investigated Pure PEG-block-PCL copolymer melt electrospinning did not result in consistent and uniform fibres due to the low molecular weight, while blends of PCL and PEG-block-PCL, for some parameter combinations and certain weight ratios of the two components, were able to produce continuous fibres significantly thinner (average diameter of ca 2 mu m) compared to pure PCL The PCL fibres obtained had average diameters ranging from 6 to 33 mu m and meshes were uniform for the lowest voltage employed while mesh uniformity decreased when the voltage was increased This approach shows that PCL and blends of PEG block-PCL and PCL can be readily processed by melt electrospinning to obtain fibrous meshes with varied average diameters and morphologies that are of interest for tissue engineering purposes.
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| 8. |
- Edin, Emil
(författare)
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Effect of Stress Relief Annealing: Part Distortion, Mechanical Properties, and Microstructure of Additively Manufactured Austenitic Stainless Steel
- 2022
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Additive manufacturing (AM) processes may introduce large residual stresses in the as-built part, in particular the laser powder bed fusion process (L-PBF). The residual stress state is an inherent consequence of the heterogeneous heating and subsequent cooling during the process. L-PBF has become renowned for its “free complexity” and rapid prototyping capabilities. However, it is vital to ensure shape stability after the component is removed from the build plate, which can be problematic due to the residual stress inducing nature of this manufacturing process. Residual stresses can be analyzed via many different characterization routes (e.g. X-ray and neutron diffraction, hole drilling, etc.), both quantitatively and qualitatively. From an industrial perspective, most of these techniques are either prohibitively expensive, complex or too slow to be implementable during the early prototyping stages of AM manufacturing.In this work a deformation based method employing a specific geometry, a so called “keyhole”-geometry, has been investigated to qualitatively evaluate the effect of different stress relief annealing routes with respect to macroscopic part deformation, mechanical properties and microstructure. Previous published work has focused on structures with open geometry, commonly referred to as bridge-like structures where the deformation required for analysis occurs during removal from the build plate. The proposed keyhole-geometry can be removed from the build plate without releasing the residual stresses required for subsequent measurement, which enables bulk manufacturing on single build plates, prior to removal and stress relief annealing. Two L-PBF manufactured austenitic stainless steel alloys were studied, 316L and 21-6-9. Tensile specimen blanks were manufactured and the subsequent heat treatments were carried out in pairs of keyhole and tensile blank. Both a contact (micrometer measurement), and a non-contact (optical profilometry) method were employed to measure the residual stress induced deformation in the keyholes. The annealing heat treatment matrix was iteratively expanded with input from the deformation analysis to find the lowest temperature at which approximately zero deformation remained after opening the structure via wire electrical discharge machining. The lowest allowable annealing temperature was sought after to minimize strength loss. After stress relief annealing at 900 ℃ for 1 hour, the 316L keyhole-geometry was considered shape stable. The lateral micrometer measurement yielded a length change of 1 µm, and a radius of 140 m (over the 22 mm top surface) was assigned from curve fitting the top surface height profiles. The complementary microstructural characterization revealed that this temperature corresponded to where the last remains of the cellular sub-grain structures disappears. Tensile testing showed that the specimen subjected to the 900 ℃ heat treatment had a marked reduction in yield stress (YS) compared to that of the as-built: 540 MPa → 402 MPa, whereas ultimate tensile strength (UTS) only reduced slightly: 595 MPa → 570 MPa. The ductility (4D elongation) was found to be ~13 % higher for the specimen heat treated at 900 ℃ than that of the as-built specimen, 76% and 67% respectively. For alloy 21-6-9 the residual stress induced deformation minimum (zero measurable deformation) was found after stress relief heat treatment at 850 ℃ for 1 hour. Slight changes in the microstructure were observable through light optical microscopy when comparing the different heat treatment temperatures. The characteristic sub-grain features associated with alloy 316L were not verified for alloy 21-6-9. Similar to the results for 316L, UTS was slightly lower for the tensile specimen subjected to the heat treatment temperature required for shape stability (850 ℃) compared to the as-built specimen: 810 MPa → 775 MPa. The measured ductility (4D elongation) was found to be approximately equal for the as-built (47%), and heat treated (48%) specimen. As-built material exhibited a YS of 640 MPa while the heat treated specimen had a YS of 540 MPa. For alloy 21-6-9, the lateral micrometer deformation measurements were compared with stress relaxation testing performed at 600 ℃, 700℃ and 800 ℃. Stress relaxation results were in good agreement with the results from the lateral deformation measurements. The study showed that for both steel alloys, the keyhole method could be successfully employed to rapidly find a suitable stress relief heat treatment route when shape stability is vital.
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| 9. |
- Edin, Emil, et al.
(författare)
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Rapid method for comparative studies on stress relief heat treatment of additively manufactured 316L
- 2022
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Ingår i: Materials Science & Engineering. - : Elsevier. - 0921-5093 .- 1873-4936. ; 847
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Tidskriftsartikel (refereegranskat)abstract
- The additive manufacturing method laser powder bed fusion (L-PBF) is known to introduce large residual stresses in the built component. Optimization of process parameters and subsequent heat treatment is crucial to relieve these residual stresses. However, many of the available tools used to analyze these residual stresses are either prohibitively expensive, or too time consuming for initial prototyping stages.A qualitative method for rapid evaluation of the effectiveness of stress relief heat treatment of L-PBF manufactured 316L has been tested. Residual stress induced distortion has been measured with contact and non-contact methods to study the effect of different stress relief heat treatment temperatures (600 – 950 °C, fixed holding time: 1 h). Over the examined temperature interval, at which deformation was measured, distinct differences were observable at each temperature with both methods. Based on the distortion, shape stability was considered reached after subjecting the test geometry to a heat treatment temperature of 900 °C for 1 hour. Complementary mechanical testing and microstructural characterization were carried out to provide a more general understanding of the implications of each heat treatment temperature. Microstructural characterization revealed that complete dissolution of the cellular sub-grain features occurred at the same temperature as where the minimum magnitude of distortion was obtained.
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| 10. |
- Edin, Emil, et al.
(författare)
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Stress relief heat treatment and mechanical properties of laser powder bed fusion built 21-6-9 stainless steel
- 2023
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Ingår i: Materials Science and Engineering A. - : Elsevier. - 0921-5093 .- 1873-4936. ; 868
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Tidskriftsartikel (refereegranskat)abstract
- In this work, the effectiveness of residual stress relief annealing on a laser powder bed fusion (L-PBF) manufactured austenitic stainless steel, alloy 21-6-9 was investigated. Residual stress levels were gauged using geometrical distortion and relaxation testing results. In the investigated temperature interval (600–850 °C), shape stability was reached after subjecting the as-built material to an annealing temperature of 850 °C for 1 h. Microstructural characterization and tensile testing were also performed for each annealing temperature to evaluate the alloy's thermal stability and the resulting tensile properties. In the as-built state, a yield strength (YS) of 640 MPa, ultimate tensile strength (UTS) of 810 MPa and 4D elongation of 47% were measured. Annealing at 850 °C for 1 h had little measurable effect on ductility (48% 4D elongation) while still having a softening effect (UTS = 775 MPa, YS = 540 MPa). From the microstructural characterization, cell-like features were observed sporadically in the annealed condition and appeared stable up until 800 °C after which gradual dissolution began, with the last remnants disappearing after subjecting the material to 900 °C for 1 h.
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