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Release and molecular transport of cationic and anionic fluorescent molecules in mesoporous silica spheres.
KTH, School of Engineering Sciences (SCI), Applied Physics, Cell Physics.
KTH, School of Engineering Sciences (SCI), Applied Physics, Cell Physics.ORCID iD: 0000-0003-0578-4003
KTH, School of Engineering Sciences (SCI), Applied Physics, Cell Physics.
2008 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 24, no 19, 11096-102 p.Article in journal (Refereed) Published
Abstract [en]

We describe here a method for study of bulk release and local molecular transport within mesoporous silica spheres. We have analyzed the loading and release of charged fluorescent dyes from monodisperse mesoporous silica (MMS) spheres with an average pore size of 2.7 nm. Two different fluorescent dyes, one cationic and one anionic, have been loaded into the negatively charged porous material and both the bulk release and the local molecular transport within the MMS spheres have been quantified by confocal laser scanning microscopy. Analysis of the time-dependent release and the concentration profiles of the anionic dye within the spheres show that the spheres are homogeneous and that the release of this nonadsorbing dye follows a simple diffusion-driven process. The concentration of the cationic dye varies radially within the MMS spheres after loading; there is a significantly higher concentration of the dye close to the surface of the spheres (forming a "skin") compared to that at the core. The release of the cationic dye is controlled by diffusion after an initial period of rapid release. The transport of the cationic dye within the MMS spheres of the dye from the core to near the surface is significantly faster compared to the transport within the surface "skin". A significant fraction of the cationic dye remains permanently attached to the negatively charged walls of the MMS spheres, preferentially near the surface of the spheres. Relating bulk release to the local molecular transport within the porous materials provides an important step toward the design of new concepts in controlled drug delivery and chromatography.

Place, publisher, year, edition, pages
2008. Vol. 24, no 19, 11096-102 p.
URN: urn:nbn:se:kth:diva-11877DOI: 10.1021/la801179vISI: 000259673500084PubMedID: 18767822ScopusID: 2-s2.0-54549109154OAI: diva2:287237
QC20100727Available from: 2010-01-18 Created: 2010-01-18 Last updated: 2010-07-27Bibliographically approved
In thesis
1. Modeling Biophysical Mechanisms underlying Cellular Homeostasis
Open this publication in new window or tab >>Modeling Biophysical Mechanisms underlying Cellular Homeostasis
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Cellular homeostasis is the effort of all living cells to maintain their intracellular content when facing physiological change(s) in the extracellular environment. To date, cellular homeostasis is known to be regulated mainly by time-consuming active mechanisms and via multiple signaling pathways within the cells. The aim of this thesis is to show that time-efficient passive (physical) mechanisms also, under the control and regulation of bio-physical factors such as cell morphology and distribution and co-localization of transport proteins in the cell membrane, can regulate cellular homeostasis. This thesis has been developed in an interface between physics and biology and focuses on critical cases in which cells face physiologically unstable environments at their steady state and therefore may need a constituent effort to maintain their homeostasis. The main hypothesis here is that the cell geometry is oriented in such a way that cellular homeostasis is preserved in a given environment. For exploring these cases, comparative spatial models have been developed that combine transporting function of membrane proteins with simple versus complex geometries of cells. Models confirm the hypothesis and show that cell morphology, size of extracellular space and intercellular distances are important for a dynamic regulation of water and ion homeostasis at steady state. The main clue is the existence of diffusion limited space (DLS) in the bulk extracellular space (ECS). DLS can, despite being ECS, maintain its ionic content and water balance due a controlled function of transport proteins in the membrane facing part of DLS. This can significantly regulate cellular water and ion homeostasis and play an important role in cell physiology. In paper I, the role of DLS is explored in the kidney whereas paper II addresses the brain.

The response of cells to change in osmolarity is of critical importance for water homeostasis. Cells primarily respond to osmotic challenge by transport of water via their membranes. As water moves into or out of cells, the volumes of intra- and extracellular compartments consequently change. Water transport across the cell membrane is enhanced by a family of water channel proteins (aquaporins) which play important roles in regulation of both cell and the extracellular space dimensions. Paper III explores a role for aquaporins in renal K+ transport. Experimentally this role is suggested to be different from bulk water transport. In a geometrical model of a kidney principal cell with several DLS in the basolateral membrane, a biophysical role for DLS-aquaporins is suggested that also provides physiological relevance for this study. The biophysical function of water channels is then extensively explored in paper IV where the main focus has been the dynamics of the brain extracellular space following water transport. Both modeling and experimental data in this paper confirmed the importance of aquaporin-4 expressed in astrocytes for potassium kinetics in the brain extracellular space.

Finally, geometrically controlled transport mechanisms are studied on a molecular level, using silicon particles as a simplified model system for cell studies (paper V and VI). In paper V the role of electrostatic forces (around the nano-pores and in between the loaded material and the silicon surface) is studied with regard to transport processes.  In paper VI the roles of pore size and molecular weight of loaded material are studied. All together this thesis presents various modeling approaches that employ biophysical aspects of transport mechanisms combined with cell geometry to explain cell homeostasis and address cell physiology-based questions.   

Place, publisher, year, edition, pages
Stockholm: KTH, 2010. xii, 60 p.
Trita-FYS, ISSN 0280-316X ; 2010:01
National Category
Condensed Matter Physics
urn:nbn:se:kth:diva-11880 (URN)978-91-7415-546-4 (ISBN)
Public defence
2010-02-04, FA32, AlbaNova University Center, Roslagstullsbacken 21, KTH, Stockholm, 13:00 (English)
QC20100727Available from: 2010-01-21 Created: 2010-01-18 Last updated: 2010-07-27Bibliographically approved

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