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| 2. |
- Akhtar, Sultan
(författare)
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Transmission Electron Microscopy of Graphene and Hydrated Biomaterial Nanostructures : Novel Techniques and Analysis
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Transmission Electron Microscopy (TEM) on light element materials and soft matters is problematic due to electron irradiation damage and low contrast. In this doctoral thesis techniques were developed to address some of those issues and successfully characterize these materials at high resolution. These techniques were demonstrated on graphene flakes, DNA/magnetic beads and a number of water containing biomaterials. The details of these studies are given below.A TEM based method was presented for thickness characterization of graphene flakes. For the thickness characterization, the dynamical theory of electron diffraction is used to obtain an analytical expression for the intensity of the transmitted electron beam as a function of thickness. From JEMS simulations (experiments) the absorption constant λ in a low symmetry orientation was found to be ~ 208 nm (225 ± 9 nm). When compared to standard techniques for thickness determination of graphene/graphite, the method has the advantage of being relatively simple, fast and requiring only the acquisition of bright-field (BF) images. Using the proposed method, it is possible to measure the thickness change due to one monolayer of graphene if the flake has uniform thickness over a larger area.A real-space TEM study on magnetic bead-DNA coil interaction was conducted and a statistical analysis of the number of beads attached to the DNA-coils was performed. The average number of beads per DNA coil was calculated around 6 and slightly above 2 for samples with 40 nm and 130 nm beads, respectively. These results are in good agreement with magnetic measurements. In addition, the TEM analysis supported an earlier hypothesis that 40 nm beads are preferably attached interior of the DNA-coils while 130 nm beads closer to the exterior of the coils.A focused ion-beam in-situ lift-out technique for hydrated biological specimens was developed for cryo-TEM. The technique was demonstrated on frozen Aspergillus niger spores which were frozen with liquid nitrogen to preserve their cellular structures. A thin lamella was prepared, lifted out and welded to a TEM grid. Once the lamella was thinned to electron transparency, the grid was cryogenically transferred to the TEM using a cryo-transfer bath. The structure of the cells was revealed by BF imaging. Also, a series of energy filtered images was acquired and C, N and Mn elemental maps were produced. Furthermore, 3 Å lattice fringes of the underlying Al support were successfully resolved by high resolution imaging, confirming that the technique has the potential to extract structural information down to the atomic scale. The experimental protocol is ready now to be employed on a large variety of samples e.g. soft/hard matter interfaces.
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| 3. |
- Akhtar, Sultan, et al.
(författare)
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Visualization of functionalization of nano-particles and graphene in the TEM
- 2010
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Ingår i: Advanced Materials Workshop 2010.
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Konferensbidrag (refereegranskat)abstract
- Recently, the activity on functionalized nano-objects has strongly increased. Yet, there are, to our knowledge no techniques available that visualize the attachment of molecules to nano-entities such as nanoparticles and graphene. In this work, we show a methodology to analyse the attachment of molecules to nanoparticles and graphene. The difficulty of such transmission electron microscopy (TEM) characterization consists in the high beam sensitivity of these nanoobjects. We employed a high resolution- as well as diffraction contrast-imaging methods to characterize graphene. First, we have developed a method to measure the thickness of free-standing graphene-like layers. The refinement of these imaging techniques enabled the imaging of functionalized C60 (fullerene) on top of a few-layer graphene flake by TEM. We also developed a methodology to visualize the attachment of functionalized gold and magnetic nanoparticles (different sizes) to nonstained and unlabeled single strand DNA-coils. This technique can be used to understand the interaction of a large variety of functionalized nanoparticles with their solution environment and/or macromolecular structures for their large applications.
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| 7. |
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| 8. |
- Ferrari, Raffaele, et al.
(författare)
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Frontotemporal dementia and its subtypes: a genome-wide association study.
- 2014
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Ingår i: Lancet Neurology. - 1474-4465. ; 13:7, s. 686-699
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Tidskriftsartikel (refereegranskat)abstract
- Frontotemporal dementia (FTD) is a complex disorder characterised by a broad range of clinical manifestations, differential pathological signatures, and genetic variability. Mutations in three genes-MAPT, GRN, and C9orf72-have been associated with FTD. We sought to identify novel genetic risk loci associated with the disorder.
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| 16. |
- Li, Ling-Guang, 1982-, et al.
(författare)
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Dynamics of SiO2 Buried Layer Removal from Si-SiO2-Si and Si-SiO2-SiC Bonded Substrates by Annealing in Ar
- 2014
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Ingår i: Journal of Electronic Materials. - : Springer Berlin/Heidelberg. - 0361-5235 .- 1543-186X. ; 43:2, s. 541-547
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Tidskriftsartikel (refereegranskat)abstract
- Silicon-on-silicon-carbide substrates could be ideal for high-power and radiofrequency silicon devices. Such hybrid wafers, when made by wafer bonding, contain an intermediate silicon dioxide layer with poor thermal characteristics, which can be removed by high-temperature annealing in an inert atmosphere. To understand the dynamics of this process, removal of 2.4-nm-thick SiO2 layers from Si-SiO2-Si and Si-SiO2-SiC substrates has been studied at temperatures ranging from 1100A degrees C to 1200A degrees C. The substrates were analyzed by transmission electron microscopy, electron energy-loss spectroscopy, secondary-ion mass spectroscopy, and ellipsometry, before and after annealing. For oxide thickness less than 2.4 nm, the activation energy for oxide removal was estimated to be 6.4 eV, being larger than the activation energy reported for removal of thicker oxides (4.1 eV). Under the same conditions, the SiO2 layer became discontinuous. In the time domain, three steps could be distinguished: bulk diffusion, bulk diffusion with void formation, and bulk diffusion with disintegration. The void formation, predominant here, has an energetic cost that could explain the larger activation energy. The oxide remaining after prolonged annealing corresponds to one layer of oxygen atoms.
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| 17. |
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| 18. |
- Lidbaum, Hans, et al.
(författare)
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Reciprocal and real space maps for EMCD experiments
- 2010
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Ingår i: Ultramicroscopy. - : Elsevier BV. - 0304-3991 .- 1879-2723. ; 110:11, s. 1380-1389
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Tidskriftsartikel (refereegranskat)abstract
- Electron magnetic chiral dichroism (EMCD) is an emerging tool for quantitative measurements of magnetic properties using the transmission electron microscope (TEM), with the possibility of nanometer resolution. The geometrical conditions, data treatment and electron gun settings are found to influence the EMCD signal. In this article, particular care is taken to obtain a reliable quantitative measurement of the ratio of orbital to spin magnetic moment using energy filtered diffraction patterns. For this purpose, we describe a method for data treatment, normalization and selection of mirror axis. The experimental results are supported by theoretical simulations based on dynamical diffraction and density functional theory. Special settings of the electron gun, so called telefocus mode, enable a higher intensity of the electron beam, as well as a reduction of the influence from artifacts on the signal. Using these settings, we demonstrate the principle of acquiring real space maps of the EMCD signal. This enables advanced characterization of magnetic materials with superior spatial resolution.
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| 19. |
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| 20. |
- Pujari-Palmer, Shiuli, et al.
(författare)
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In vivo and in vitro evaluation of hydroxyapatite nanoparticle morphology on the acute inflammatory response
- 2016
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Ingår i: Biomaterials. - : Elsevier BV. - 0142-9612 .- 1878-5905. ; 90, s. 1-11
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Tidskriftsartikel (refereegranskat)abstract
- Biomedical implants have been widely used in bone repair applications. However, nanosized degradation products from these implants could elicit an inflammatory reaction, which may lead to implant failure. It is well known that the size, chemistry, and charge of these nanoparticles can modulate this response, but little is known regarding the role that the particle's morphology plays in inducing inflammation. The present study aims to investigate the effect of hydroxyapatite nanoparticle (HANPs) morphology on inflammation, in-vitro and in-vivo. Four distinct HANP morphologies were fabricated and characterized: long rods, dots, sheets, and fibers. Primary human polymorphonuclear cells (PMNCs), mononuclear cells (MNCs), and human dermal fibroblasts (hDFs) were exposed to HANPs and alterations in cell viability, morphology, apoptotic activity, and reactive oxygen species (ROS) production were evaluated, in vitro. PMNCs and hDFs experienced a 2-fold decrease in viability following exposure to fibers, while MNC viability decreased 5-fold after treatment with the dots. Additionally, the fibers stimulated an elevated ROS response in both PMNCs and MNCs, and the largest apoptotic behavior for all cell types. Furthermore, exposure to fibers and dots resulted in greater capsule thickness when implanted subcutaneously in mice. Collectively, these results suggest that nanoparticle morphology can significantly impact the inflammatory response.
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| 21. |
- Rubino, Stefano, et al.
(författare)
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A Simple Transmission Electron Microscopy Method for Fast Thickness Characterization of Suspended Graphene and Graphite Flakes
- 2016
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Ingår i: Microscopy and Microanalysis. - 1431-9276 .- 1435-8115. ; 22:1, s. 250-256
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Tidskriftsartikel (refereegranskat)abstract
- We present a simple, fast method for thickness characterization of suspended graphene/graphite flakes that is based on transmission electron microscopy (TEM). We derive an analytical expression for the intensity of the transmitted electron beam I-0(t), as a function of the specimen thickness t (t < < lambda; where lambda is the absorption constant for graphite). We show that in thin graphite crystals the transmitted intensity is a linear function of t. Furthermore, high-resolution (HR) TEM simulations are performed to obtain lambda for a 001 zone axis orientation, in a two-beam case and in a low symmetry orientation. Subsequently, HR (used to determine t) and bright-field (to measure I-0(0) and I-0(t)) images were acquired to experimentally determine lambda. The experimental value measured in low symmetry orientation matches the calculated value (i.e., lambda = 225 +/- 9 nm). The simulations also show that the linear approximation is valid up to a sample thickness of 3-4 nm regardless of the orientation and up to several ten nanometers for a low symmetry orientation. When compared with standard techniques for thickness determination of graphene/graphite, the method we propose has the advantage of being simple and fast, requiring only the acquisition of bright-field images.
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| 22. |
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| 23. |
- Rubino, Stefano, et al.
(författare)
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A site-specific focused-ion-beam lift-out method for cryo Transmission Electron Microscopy
- 2012
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Ingår i: Journal of Structural Biology. - : Elsevier BV. - 1047-8477 .- 1095-8657. ; 180:3, s. 572-576
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Tidskriftsartikel (refereegranskat)abstract
- The focused-ion-beam (FIB) is the method of choice for site-specific sample preparation for Transmission Electron Microscopy (TEM) in material sciences. A lamella can be physically lifted out from a specific region of a bulk specimen with submicrometer precision and thinned to electron transparency for high-resolution imaging in the TEM. The possibility to use this tool in life sciences applications has been limited by the lack of lift-out capabilities at the cryogenic temperatures often needed for biological samples. Conventional cryo-TEM sample preparation is mostly based on ultramicrotomy, a procedure that is not site-specific and known to produce artifacts. Here we demonstrate how a cooled nanomanipulator and a custom-built transfer station can be used to achieve cryo-preparation of TEM samples with the FIB, enabling high-resolution investigation of frozen-hydrated specimens in the TEM.
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| 24. |
- Rubino, Stefano, et al.
(författare)
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Cryo-electron Microscopy Specimen Preparation By Means Of a Focused Ion Beam
- 2014
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Ingår i: Journal of Visualized Experiments. - : MyJove Corporation. - 1940-087X. ; :89
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Tidskriftsartikel (refereegranskat)abstract
- Here we present a protocol used to prepare cryo-TEM samples of Aspergillus niger spores, but which can easily be adapted for any number of microorganisms or solutions. We make use of a custom built cryo-transfer station and a modified cryo-SEM preparation chamber2. The spores are taken from a culture, plunge-frozen in a liquid nitrogen slush and observed in the cryo-SEM to select a region of interest. A thin lamella is then extracted using the FIB, attached to a TEM grid and subsequently thinned to electron transparency. The grid is transferred to a cryo-TEM holder and into a TEM for high resolution studies. Thanks to the introduction of a cooled nanomanipulator tip and a cryo-transfer station, this protocol is a straightforward adaptation to cryogenic temperature of the routinely used FIB preparation of TEM samples. As such it has the advantages of requiring a small amount of modifications to existing instruments, setups and procedures; it is easy to implement; it has a broad range of applications, in principle the same as for cryo-TEM sample preparation. One limitation is that it requires skillful handling of the specimens at critical steps to avoid or minimize contaminations.
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| 26. |
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| 27. |
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| 28. |
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| 29. |
- Rubino, Stefano, 1978-, et al.
(författare)
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Energy-loss magnetic chiral dichroism (EMCD) : Magnetic chiral dichroism in the electron microscope
- 2008
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Ingår i: Journal of Materials Research. - 0884-2914 .- 2044-5326. ; 23:10, s. 2582-2590
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Forskningsöversikt (refereegranskat)abstract
- A new technique called energy-loss magnetic chiral dichroism (EMCD) has recently been developed [P. Schattschneider, et al. Nature 441, 486 (2006)] to measure magnetic circular dichroism in the transmission electron microscope (TEM) with a spatial resolution of 10 nm. This novel technique is the TEM counterpart of x-ray magnetic circular dichroism, which is widely used for the characterization of magnetic materials with synchrotron radiation. In this paper we describe several experimental methods that can be used to measure the EMCD signal [P. Schattschneider, et al. Nature 441, 486 (2006); C. Hébert, et al. Ultramicroscopy 108(3), 277 (2008); B. Warot-Fonrose, et al. Ultramicroscopy 108(5), 393 (2008); L. Calmels, et al. Phys. Rev. B 76, 060409 (2007); P. van Aken, et al. Microsc. Microanal. 13(3), 426 (2007)] and give a review of the recent improvements of this new investigation tool. The dependence of the EMCD on several experimental conditions (such as thickness, relative orientation of beam and sample, collection and convergence angle) is investigated in the transition metals iron, cobalt, and nickel. Different scattering geometries are illustrated; their advantages and disadvantages are detailed, together with current limitations. The next realistic perspectives of this technique consist of measuring atomic specific magnetic moments, using suitable spin and orbital sum rules, [L. Calmels, et al. Phys. Rev. B 76, 060409 (2007); J. Rusz, et al. Phys. Rev. B 76, 060408 (2007)] with a resolution down to 2 to 3 nm.
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| 30. |
- Rubino, Stefano, 1978-, et al.
(författare)
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In-situ contacting of nanosheets and remote EMCD
- 2009
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Ingår i: 2nd International Workshop on Remote Electron Microscopy and In Situ Studies, Gothenburg, Sweden 16-18 November 2009.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 31. |
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| 32. |
- Rubino, Stefano, 1978-, et al.
(författare)
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Simulation of magnetic circular dichroism in the electron microscope
- 2010
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Ingår i: Journal of Physics D. - : IOP Publishing. - 0022-3727 .- 1361-6463. ; 43:47, s. 474005-
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Tidskriftsartikel (refereegranskat)abstract
- As electron energy-loss spectroscopy (EELS) and x-ray absorption spectroscopy (XAS) probe the same transitions from core–shell states to unoccupied states above the Fermi energy, it should always be possible to apply the two techniques to the same physical phenomena, such as magnetic dichroism, and obtain the same information. Indeed, the similarity in the expression of the electron and x-ray cross-sections had been already exploited to prove the equivalence of x-ray magnetic linear dichroism and anisotropy in EELS, by noting that the polarization vector of a photon plays the same role as the momentum transfer in electron scattering. Recently, the same was proven true for x-ray magnetic circular dichroism (XMCD) by establishing a new TEM technique called EMCD (electron energy-loss magnetic chiral dichroism) (Schattschneider P et al 2006 Nature 441 486–8), which makes use of special electron scattering conditions to force the absorption of a circularly polarized virtual photon.The intrinsic advantage of EMCD over XMCD is the high spatial resolution of electron microscopes, which are readily available. Among the particular obstacles in EMCD that do not exist for synchrotron radiation, is the notoriously low signal and the very particular scattering conditions necessary to observe a chiral dichroic signal. In spite of that, impressive progress has been made in recent years. The signal strength could be considerably increased, and some innovations such as using a convergent beam have been introduced. EMCD has evolved into several techniques, which make full use of the versatility of the TEM and energy filtering, spectroscopy or STEM conditions (Rubino S 2007 Magnetic circular dichroism in the transmission electron microscope PhD Thesis Vienna University of Technology, Vienna, Austria).
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| 33. |
- Rubino, Stefano, et al.
(författare)
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Spatial Mapping of Elemental Distributions in Polypyrrole-Cellulose Nanofibers using Energy-Filtered Transmission Electron Microscopy
- 2010
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 114:43, s. 13644-13649
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Tidskriftsartikel (refereegranskat)abstract
- The energy-filtered transmission electron microscopy (EFTEM) technique has been used to study ion-exchange processes in conductive polymer composite nanofibers. The elemental distributions of carbon, nitrogen, oxygen, chlorine, boron, phosphorus, molybdenum, and sulfur within polypyrrole-cellulose nanofibers, used as potential controlled electrochemical solid phase extraction media, have been studied by EFTEM. The distribution of ions within the polypyrrole-cellulose nanofibers and the penetration depth of ions into the material as a function of the size and charge of the latter were investigated. Further, the spatial distribution of single stranded DNA hexamers inside polypyrrole-cellulose nanofibers was mapped subsequent to the electrochemically controlled extraction of DNA from a borate buffer solution. The results show that the EFTEM mapping technique provides unpreceded possibilities for studies of the distribution of ions inside conductive polymer composites.
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| 34. |
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| 35. |
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| 36. |
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| 37. |
- Rusz, Jan, et al.
(författare)
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First-principles theory of chiral dichroism in electron microscopy applied to 3d ferromagnets
- 2007
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 75:21, s. 214425-
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Tidskriftsartikel (refereegranskat)abstract
- Recently it was demonstrated [Schattschneider , Nature 441, 486 (2006)], that an analog of the x-ray magnetic circular dichroism experiment can be performed with the transmission electron microscope. The new phenomenon has been named energy-loss magnetic chiral dichroism. In this work we present a detailed ab initio study of the chiral dichroism in the Fe, Co, and Ni transition elements. We discuss the methods used for the simulations together with the validity and accuracy of the treatment, which, in principle, can apply to any given crystalline specimen. The dependence of the dichroic signal on the sample thickness, accuracy of the detector position, and the size of convergence and collection angles are calculated.
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| 38. |
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| 39. |
- Rusz, Ján, et al.
(författare)
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Influence of plural scattering on the quantitative determination of spin and orbital moments in electron magnetic chiral dichroism measurements
- 2011
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 83:13, s. 132402-
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Tidskriftsartikel (refereegranskat)abstract
- Recent quantitative measurements of the orbital to spin magnetic moment ratio m(L)/m(S) in electron magnetic circular dichroism (EMCD) experiments have given a m(L)/m(S) ratio that is larger than commonly accepted values. We demonstrate here that plural scattering may noticeably influence the m(L)/m(S) ratio. An equation is derived which describes its influence as a function of the spectral integrals of the plasmon scattering region and zero-loss peak. The influence of the electron-plasmon scattering can be removed when electron energy-loss spectra of the ionization edge are deconvoluted by the low-loss signal. For a bcc-Fe sample we obtain m(L)/m(S) = 0.04 after plasmon removal. We conclude that the plural scattering should be considered when extracting quantitative information from EMCD measurements.
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| 40. |
- Rusz, Jan, 1979-, et al.
(författare)
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Local electronic structure information contained in energy-filtered diffraction patterns
- 2011
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 84:6, s. 064444-
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Tidskriftsartikel (refereegranskat)abstract
- We analyze the information contained in energy-filtered diffraction patterns measured on core-level edges. By inversion of the sum rules for electron energy loss near edge structures we calculate the reciprocal space distribution of the contribution to the total signal originating from spin moment, orbital moment, spin-orbital interaction, and individual components of magnetic and spin-orbital anisotropy tensors. We demonstrate, in particular, that the diffraction patterns contain information about all three vector components of the spin and orbital magnetic moments.
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| 41. |
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| 42. |
- Rusz, Jan, et al.
(författare)
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Quantitative magnetic measurements with transmission electron microscope
- 2010
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Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853 .- 1873-4766. ; 322:9-12, s. 1478-1480
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Tidskriftsartikel (refereegranskat)abstract
- We briefly review the state-of-the-art electronmagnetic chiraldichroism experiments and theory with focus on quantitative measurements of the atom-specific orbital to spin moment ratio m(1)/m(s). Our approach of quantitative method, based on reciprocal space mapping of the magnetic signal, is described. We discuss additional symmetry considerations for m(1)/m(s) measurements, which are present due to dynamical diffraction effects. The selead to a preference for the 3-beam orientation of the sample. Further on, we describe a method of correcting a symmetries present due to imperfect 3-beam orientation-the so-called double-difference correction.
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| 43. |
- Schattschneider, Peter, 1950-, et al.
(författare)
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Detection of magnetic circular dichroism on the two-nanometer scale
- 2008
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 78:10, s. 104413-
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Tidskriftsartikel (refereegranskat)abstract
- Magnetic circular dichroism (MCD) is a standard technique for the study of magnetic properties of materials in synchrotron beamlines. We present here a scattering geometry in the transmission electron microscope through which MCD can be observed with unprecedented spatial resolution. A convergent electron beam is used to scan a cross sectional preparation of a Fe/Au multilayer sample. Differences in the energy-loss spectra induced by the magnetic moments of the Fe atoms can be resolved with a resolution of better than 2 nm. This is a breakthrough achievement when compared both to the previous energy-loss MCD resolution (200 nm) or the best x-ray MCD experiments (approximately 20 nm).
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| 44. |
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| 46. |
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| 47. |
- Thersleff, Thomas, et al.
(författare)
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Quantitative analysis of magnetic spin and orbital moments from an oxidized iron (110) surface using electron magnetic circular dichroism
- 2015
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 5
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Tidskriftsartikel (refereegranskat)abstract
- Understanding the ramifications of reduced crystalline symmetry on magnetic behavior is a critical step in improving our understanding of nanoscale and interfacial magnetism. However, investigations of such effects are often controversial largely due to the challenges inherent in directly correlating nanoscale stoichiometry and structure to magnetic behavior. Here, we describe how to use Transmission Electron Microscope (TEM) to obtain Electron Magnetic Circular Dichroism (EMCD) signals as a function of scattering angle to locally probe the magnetic behavior of thin oxide layers grown on an Fe (1 1 0) surface. Experiments and simulations both reveal a strong dependence of the magnetic orbital to spin ratio on its scattering vector in reciprocal space. We exploit this variation to extract the magnetic properties of the oxide cladding layer, showing that it locally may exhibit an enhanced orbital to spin moment ratio. This finding is supported here by both spatially and angularly resolved EMCD measurements, opening up the way for compelling investigations into how magnetic properties are affected by nanoscale features.
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| 48. |
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| 49. |
- Wessman, Per, et al.
(författare)
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Formulations for freeze-drying of bacteria and their influence on cell survival
- 2013
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Ingår i: Journal of Visualized Experiments. - : MyJove Corporation. - 1940-087X. ; :78
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Tidskriftsartikel (refereegranskat)abstract
- Cellular water can be removed to reversibly inactivate microorganisms to facilitate storage. One such method of removal is freeze-drying, which is considered a gentle dehydration method. To facilitate cell survival during drying, the cells are often formulated beforehand. The formulation forms a matrix that embeds the cells and protects them from various harmful stresses imposed on the cells during freezing and drying. We present here a general method to evaluate the survival rate of cells after freeze-drying and we illustrate it by comparing the results obtained with four different formulations: the disaccharide sucrose, the sucrose derived polymer Ficoll PM400, and the respective polysaccharides hydroxyethyl cellulose (HEC) and hydroxypropyl methyl cellulose (HPMC), on two strains of bacteria, P. putida KT2440 and A. chlorophenolicus A6. In this work we illustrate how to prepare formulations for freeze-drying and how to investigate the mechanisms of cell survival after rehydration by characterizing the formulation using of differential scanning calorimetry (DSC), surface tension measurements, X-ray analysis, and electron microscopy and relating those data to survival rates. The polymers were chosen to get a monomeric structure of the respective polysaccharide resembling sucrose to a varying degrees. Using this method setup we showed that polymers can support cell survival as effectively as disaccharides if certain physical properties of the formulation are controlled.
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| 50. |
- Wessman, Per, et al.
(författare)
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Impact of matrix properties on survival of freeze-dried bacteria
- 2011
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Ingår i: Journal of the Science of Food and Agriculture. - : Wiley. - 0022-5142 .- 1097-0010. ; 91:14, s. 2518-2528
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Tidskriftsartikel (refereegranskat)abstract
- Background: Disaccharides are in general first choice as formulation compounds when freezedrying microorganisms. Although polysaccharides and other biopolymers are considered too large to stabilize and interact with cell components in the same beneficial way as disaccharides, polymers have been reported to support cell survival. In the present study we compare the efficiency of sucrose, the polymers Ficoll, hydroxyethylcellulose, hydroxypropylmethylcellulose and polyvinylalcohol to support survival of three bacterial strains during freeze-drying. The initial osmotic conditions were adjusted to be similar for all formulations. Formulation characterization was used to interpret the impact that different compound properties had on cell survival. Results: Despite differences in molecular size, both sucrose and the sucrose based polymer Ficoll supported cell survival after freeze-drying equally well. All formulations became amorphous upon dehydration. Scanning electron microscopy and X-ray diffraction data showed that the discerned differences in structure of the dry formulations had little impact on the survival rates. The capability of the polymers to support cell survival correlated with the surface activity of the polymers in a similar way for all investigated bacterial strains. Conclusion: Polymer-based formulations can support cell survival as effectively as disaccharides if formulation properties of importance for maintaining cell viability are identified and controlled.
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