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Mechanism of lysozyme uptake in poly(acrylic acid) microgels
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Pharmacy. (Pharmaceutical Physical Chemistry)
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Pharmacy.
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Pharmacy.
2009 (English)In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 113, no 18, 6183-6193 p.Article in journal (Refereed) Published
Abstract [en]

The uptake of lysozyme by oppositely charged poly(acrylic acid)  microgels was investigated by micromanipulator-assisted light microscopy and confocal microscopy. Lysozyme was observed to distribute nonuniformly within the microgels, forming a core-shell structure with   considerably higher lysozyme concentration in the shell than in the core. The core-shell formation can be divided into two periods. During the first of these, the shell is formed during rapid microgel deswelling, and with no lysozyme diffusing into the microgel core. This   is followed by a second period, during which microgel deswelling is negligible and lysozyme diffuses into the microgel core. Thus, the shell which is initially formed as a result of fast lysozyme transport to the gel network and fast protein-microgel interactions is able to   carry a mechanical load and prevents deswelling during the latter core diffusion period. These two distinct regimes of lysozyme loading were also successfully described theoretically, demonstrating the importance of lysozyme cluster formation for the observed phenomena.

Place, publisher, year, edition, pages
American Chemical Society , 2009. Vol. 113, no 18, 6183-6193 p.
Keyword [en]
core-shell, deswelling, lysozyme, protein, microgel
National Category
Chemical Sciences
Research subject
Physical Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-101240DOI: 10.1021/jp900706kISI: 000265687500003OAI: oai:DiVA.org:uu-101240DiVA: diva2:212176
Available from: 2009-04-21 Created: 2009-04-21 Last updated: 2017-12-13Bibliographically approved
In thesis
1. Interaction Between Microgels and Oppositely Charged Proteins
Open this publication in new window or tab >>Interaction Between Microgels and Oppositely Charged Proteins
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis reports on interactions between microgels and oppositely charged proteins. Two types of negatively charged microgels are investigated: poly(acrylic acid) microgels of 60-80 µm in diameter, and colloidal poly(NIPAM-co-acrylic acid) microgels of around 1 µm in diameter. The proteins used are lysozyme and cytochrome c, which both have positive net charge. The experimental techniques used in the studies of the larger microgels are mainly micromanipulator-assisted microscopy and confocal microscopy, while the smaller microgels are studied mainly with dynamic light scattering.

It is observed that large amounts of protein are absorbed by the microgels, and that the uptake involves a substantial deswelling of the microgel. The uptake generally decreases as the ionic strength is increased, which is characteristic of electrostatic interactions. An ionic strength optimum is however observed in the case of lysozyme and poly(acrylic acid) microgels, where the highest uptake (10 gram lysozyme / gram microgel) is observed at ionic strength 40 mM. Cytochrome c uptake in poly(acrylic acid) microgels results in homogenous cytochrome c distribution throughout the microgel, whereas lysozyme uptake results in core-shell formation; the lysozyme concentration becomes much higher in the shell (outer part of the microgel) than in the core (inner part of the microgel). The shell constitutes a stress-bearing network which is sufficiently porous to allow protein diffusion through the shell. The different protein distributions are associated with different protein-protein interactions; strong protein-protein attraction promotes shell formation.

In the case of colloidal microgels, lysozyme uptake decreases the electrophoretic mobility and the colloidal stability of the microgels. The microgels flocculate as the uptake reaches charge ratio 0.6-0.7 (positive lysozyme charges/negative microgel charges), largely independent of ionic strength. Initial experiments on the combination of cytochrome c and colloidal microgels show that colloidal stability is maintained at a range of conditions (ionic strength, protein concentration) where flocculation occurred in the case of lysozyme.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2009. 71 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Pharmacy, ISSN 1651-6192 ; 98
Series
Keyword
microgel, protein, uptake, distribution, core-shell, colloidal stability
National Category
Physical Chemistry
Research subject
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-101246 (URN)978-91-554-7526-0 (ISBN)
Public defence
2009-06-05, B21, BMC, Husargatan 3, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2009-05-15 Created: 2009-04-21 Last updated: 2009-05-15Bibliographically approved

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Johansson, Christian

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