Mechanosensitivity of astrocytes on optimized polyacrylamide gels analyzed by quantitative morphometry
Pouria Moshayedi,
Luciano da F. Costa,
Andreas Christ,
Stephanie P. Lacour,
James Fawcett,
Jochen Guck,
Kristian Franze
JOURNAL OF PHYSICS-CONDENSED MATTER
22
(19)
194114
(2010)
| Journal
Cells are able to detect and respond to mechanical cues from their environment. Previous studies have investigated this mechanosensitivity on various cell types, including neural cells such as astrocytes. In this study, we have carefully optimized polyacrylamide gels, commonly used as compliant growth substrates, considering their homogeneity in surface topography, mechanical properties, and coating density, and identified several potential pitfalls for the purpose of mechanosensitivity studies. The resulting astrocyte response to growth on substrates with shear storage moduli of G' = 100 Pa and G' = 10 kPa was then evaluated as a function of coating density of poly-D-lysine using quantitative morphometric analysis. Astrocytes cultured on stiff substrates showed significantly increased perimeter, area, diameter, elongation, number of extremities and overall complexity if compared to those cultured on compliant substrates. A statistically significant difference in the overall morphological score was confirmed with an artificial intelligence-based shape analysis. The dependence of the cells' morphology on PDL coating density seemed to be weak compared to the effect of the substrate stiffness and was slightly biphasic, with a maximum at 10-100 mu g ml(-1) PDL concentration. Our finding suggests that the compliance of the surrounding tissue in vivo may influence astrocyte morphology and behavior.
Monitoring of laser micromanipulated optically trapped cells by digital
holographic microscopy
Bjoern Kemper,
Patrik Langehanenberg,
Alexander Hoeink,
Gert von Bally,
Falk Wottowah,
Stefan Schinkinger,
Jochen Guck,
Josef Kaes,
Ilona Bredebusch, et al.
JOURNAL OF BIOPHOTONICS
3
(7)
425-431
(2010)
| Journal
For a precise manipulation of particles and cells with laser light as well as for the understanding and the control of the underlying processes it is important to visualize and quantify the response of the specimens. Thus, we investigated if digital holographic microscopy (DHM) can be used in combination with microfluidics to observe optically trapped living cells in a minimally invasive fashion during laser micromanipulation. The obtained results demonstrate that DHM multi-focus phase contrast provides label-free quantitative monitoring of optical manipulation with a temporal resolution of a few milliseconds.<br> [GRAPHICS]<br> Laser micromanipulation monitoring of optically trapped pancreas tumor cells by quantitative digital holographic phase contrast. The arrows in the false colour coded quantitative phase contrast images indicate the impact of the treatment with focussed laser light.
Mesenchymal Stem Cell Mechanics from the Attached to the Suspended State
John M. Maloney,
Dessy Nikova,
Franziska Lautenschlaeger,
Emer Clarke,
Robert Langer,
Jochen Guck,
Krystyn J. Van Vliet
Human mesenchymal stem cells (hMSCs) are therapeutically useful cells that are typically expanded in vitro on stiff substrata before reimplantation. Here we explore MSC mechanical and structural changes via atomic force microscopy and optical stretching during extended passaging, and we demonstrate that cytoskeletal organization and mechanical stiffness of attached MSC populations are strongly modulated over >15 population doublings in vitro. Cytoskeletal actin networks exhibit significant coarsening, attendant with decreasing average mechanical compliance and differentiation potential of these cells, although expression of molecular surface markers does not significantly decline. These mechanical changes are not observed in the suspended state, indicating that the changes manifest themselves as alterations in stress fiber arrangement rather than cortical cytoskeleton arrangement. Additionally, optical stretching is capable of investigating a previously unquantified structural transition: remodeling-induced stiffening over tens of minutes after adherent cells are suspended. Finally, we find that optically stretched hMSCs exhibit power-law rheology during both loading and recovery; this evidence appears to be the first to originate from a biophysical measurement technique not involving cell-probe or cell-substratum contact. Together, these quantitative assessments of attached and suspended MSCs define the extremes of the extracellular environment while probing intracellular mechanisms that contribute to cell mechanical response.
The biophysics of neuronal growth
Kristian Franze,
Jochen Guck
REPORTS ON PROGRESS IN PHYSICS
73
(9)
094601
(2010)
| Journal
For a long time, neuroscience has focused on biochemical, molecular biological and electrophysiological aspects of neuronal physiology and pathology. However, there is a growing body of evidence indicating the importance of physical stimuli for neuronal growth and development. In this review we briefly summarize the historical background of neurobiophysics and give an overview over the current understanding of neuronal growth from a physics perspective. We show how biophysics has so far contributed to a better understanding of neuronal growth and discuss current inconsistencies. Finally, we speculate how biophysics may contribute to the successful treatment of lesions to the central nervous system, which have been considered incurable until very recently.
Micro and nanotechnology for biological and biomedical applications
This special issue contains some of the current state-of-the-art development and use of micro and nanotechnological tools, devices and techniques for both biological and biomedical research and applications. These include nanoparticles for bioimaging and biosensing, optical and biophotonic techniques for probing diseases at the nanoscale, micro and nano-fabricated tools for elucidating molecular mechanisms of mechanotransduction in cell and molecular biology and cell separation microdevices and techniques for isolating and enriching targeted cells for disease detection and diagnosis. Although some of these works are still at the research stage, there is no doubt that some of the important outcomes will eventually see actual biomedical applications in the not too distant future.
Physical insight into light scattering by photoreceptor cell nuclei
Moritz Kreysing,
Lars Boyde,
Jochen Guck,
Kevin J. Chalut
A recent study showed that the rod photoreceptor cell nuclei in the retina of nocturnal and diurnal mammals differ considerably in architecture: the location of euchromatin and heterochromatin in the nucleus is interchanged. This inversion has significant implications for the refractive index distribution and the light scattering properties of the nucleus. Here, we extend previous two-dimensional analysis to three dimensions (3D) by using both a numerical finite-difference time-domain and an analytic Mie theory approach. We find that the specific arrangement of the chromatin phases in the nuclear core-shell models employed have little impact on the far-field scattering cross section. However, scattering in the near field, which is the relevant regime inside the retina, shows a significant difference between the two architectures. The "inverted" photoreceptor cell nuclei of nocturnal mammals act as collection lenses, with the lensing effect being much more pronounced in 3D than in two dimensions. This lensing helps to deliver light efficiently to the light-sensing outer segments of the rod photoreceptor cells and thereby improve night vision. (C) 2010 Optical Society of America
The cavity-to-cavity migration of leukaemic cells through 3D
honey-combed hydrogels with adjustable internal dimension and stiffness
Joakim da Silva,
Franziska Lautenschlaeger,
Easan Sivaniah,
Jochen Guck
Whilst rigid, planar surfaces are often used to study cell migration, a physiological scenario requires three-dimensional (3D) scaffolds with tissue-like stiffness. This paper presents a method for fabricating periodic hydrogel scaffolds with a 3D honeycomb-like structure from colloidal crystal templates. The scaffolds, made of hydrogel-walled cavities interconnected by pores, have separately tuneable internal dimensions and adjustable gel stiffness down to that of soft tissues. In conjunction with confocal microscopy, these scaffolds were used to study the importance of cell compliance on invasive potential. Acute promyelocytic leukaemia (APL) cells were differentiated with all-trans retinoic acid (ATRA) and treated with paclitaxel. Their migration ability into the scaffolds' size-restricted pores, enabled by cell softening during ATRA differentiation, was significantly reduced by paclitaxel treatment, which interferes with cell shape recovery. These findings demonstrate the usability of the scaffolds for investigating factors that affect cell migration, and potentially other cell functions, in a realistic 3D tissue model. (C) 2009 Elsevier Ltd. All rights reserved.
Biophotonic techniques for the study of malaria-infected red blood cells
Jakob M. A. Mauritz,
Alessandro Esposito,
Teresa Tiffert,
Jeremy N. Skepper,
Alice Warley,
Young-Zoon Yoon,
Pietro Cicuta,
Virgilio L. Lew,
Jochen Guck, et al.
Investigation of the homeostasis of red blood cells upon infection by Plasmodium falciparum poses complex experimental challenges. Changes in red cell shape, volume, protein, and ion balance are difficult to quantify. In this article, we review a wide range of optical techniques for quantitative measurements of critical homeostatic parameters in malaria-infected red blood cells. Fluorescence lifetime imaging and tomographic phase microscopy, quantitative deconvolution microscopy, and X-ray microanalysis, are used to measure haemoglobin concentration, cell volume, and ion contents. Atomic force microscopy is briefly reviewed in the context of these optical methodologies. We also describe how optical tweezers and optical stretchers can be usefully applied to empower basic malaria research to yield diagnostic information on cell compliance changes upon malaria infection. The combined application of these techniques sheds new light on the detailed mechanisms of malaria infection providing potential for new diagnostic or therapeutic approaches.
Mechanical difference between white and gray matter in the rat
cerebellum measured by scanning force microscopy
Andreas F. Christ,
Kristian Franze,
Helene Gautier,
Pouria Moshayedi,
James Fawcett,
Robin J. M. Franklin,
Ragnhildur T. Karadottir,
Jochen Guck
JOURNAL OF BIOMECHANICS
43
(15)
2986-2992
(2010)
| Journal
The mechanical properties of tissues are increasingly recognized as important cues for cell physiology and pathology. Nevertheless, there is a sparsity of quantitative, high-resolution data on mechanical properties of specific tissues. This is especially true for the central nervous system (CNS), which poses particular difficulties in terms of preparation and measurement. We have prepared thin slices of brain tissue suited for indentation measurements on the micrometer scale in a near-native state. Using a scanning force microscope with a spherical indenter of radius similar to 20 mu m we have mapped the effective elastic modulus of rat cerebellum with a spatial resolution of 100 mu m. We found significant differences between white and gray matter, having effective elastic moduli of K=294 +/- 74 and 454 +/- 53 Pa, respectively, at 3 mu m indentation depth (n(g) = 245, n(w)=150 in four animals, p < 0.05; errors are SD). In contrast to many other measurements on larger length scales, our results were constant for indentation depths of 2-4 mu m indicating a regime of linear effective elastic modulus. These data, assessed with a direct mechanical measurement, provide reliable high-resolution information and serve as a quantitative basis for further neuromechanical investigations on the mechanical properties of developing, adult and damaged CNS tissue. (C) 2010 Elsevier Ltd. All rights reserved.
Detection of Plasmodium falciparum-infected red blood cells by optical
stretching
Jakob M. A. Mauritz,
Teresa Tiffert,
Rachel Seear,
Franziska Lautenschlaeger,
Alessandro Esposito,
Virgilio L. Lew,
Jochen Guck,
Clemens F. Kaminski
JOURNAL OF BIOMEDICAL OPTICS
15
(3)
030517
(2010)
| Journal
We present the application of a microfluidic optical cell stretcher to measure the elasticity of malaria-infected red blood cells. The measurements confirm an increase in host cell rigidity during the maturation of the parasite Plasmodium falciparum. The device combines the selectivity and sensitivity of single-cell elasticity measurements with a throughput that is higher than conventional single-cell techniques. The method has potential to detect early stages of infection with excellent sensitivity and high speed. (C) 2010 Society of Photo-Optical Instrumentation Engineers. [DOI: 10.1117/1.3458919]
Critical review: cellular mechanobiology and amoeboid migration
Jochen Guck,
Franziska Lautenschlaeger,
Stephan Paschke,
Michael Beil
Cell motility is important for tissue homeostasis and plays a central role in various pathologies, notably inflammation and cancer. Research into the critical processes involved in cell migration has so far mostly focused on cell adhesion and proteolytic degradation of the extracellular matrix. However, pharmacological interference with these processes only partially blocks cell motility in vivo. In this review we summarize the arising evidence that the mechanical properties of the cell body have a major role to play in cell motility-especially in a low-adhesion, amoeboid-like migration mode in three-dimensional tissue structures. We summarize the processes determining cell mechanics and discuss relevant measurement technologies including their applications in medical cell biology.
Contact
Cell Physics Division Prof. Vahid Sandoghdar Acting Division Head
Max Planck Institute for the Science of Light Staudtstr. 2 91058 Erlangen, Germany
