Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Immobilization of protein via PEG chains
YKI – Ytkemiska institutet.
1992 (English)In: Poly(Ethylene Glycol) Chemistry: Biotechnical and Biomedical Applications / [ed] Harris, J.M., New York: Plenum Press , 1992, 303-324 p.Chapter in book (Refereed)
Abstract [en]

INTRODUCTION; Grafting of poly(ethylene glycol) (or PEG) to solid surfaces has been recognized as a technique for obtaining low protein adsorption and low cell adhesion characteristics. 1,2 For instance, PEG coating is reported to give a marked suppression of plasma protein adsorption and platelet adhesion leading to reduced risk of thrombus formation, as demonstrated both in vitro and in vivo.35 The inert character of PEG surfaces is believed to be due to the solution properties of the polymer, its molecular conformation in aqueous solution, and the fact that it is completely noncharged. The oxyethylene unit,—OCH2CH2—, has a meansquare dipole moment of 1.13 mD2 and a C—O—C bond angle of 110°, not far from the H—O—H angle.6 The structural similarity with water and the strong hydrogen bonding to the ether oxygen atoms explain its complete solubility in water. (Interestingly, its homologs polyoxymethylene and polyoxypropylene, as well as its isomer polyacetaldehyde, are nonsoluble in water.) PEG's ability to prevent proteins and other biomolecules from approaching the surface can be considered a steric stabilization effect. Steric stabilization usually has two contributions, an elastic term and an osmotic term. The elastic, or volume restriction component, results from the loss of conformational entropy when two surfaces approach each other, caused by a reduction in the available volume for each polymer segment.7 Thus, when a protein approaches the PEGmodified surface a repulsive force develops due to loss of conformational freedom o the poly(ethylene glycol) chains. The osmotic interactions, or mixing interactions, arise from the increase in polymer concentration on compressing two surfaces.8 When a protein or another large molecule in water solution approaches the surface, the number of available conforrnations of the PEG segments is reduced due to compression or interpenetration of polymer chains and an osmotic repulsive force develops.9 Whether interpenetration or compression or both occur depends on the density of PEG chains. If the PEG grafting is dense it is probable that compression is preferred to interpenetration, while if the grafting is less dense interpenetration is likely to dominate. For a number of applications attachment of proteins and other biomolecules to PEGgrafted surfaces is of interest. In solidphase immunoassay and in extracorporeal therapy, antibodies or other bioactive molecules immobilized to a support interact with cells or molecules in a specimen, e.g., a body fluid such as blood, plasma, or urine. In bioorganic synthesis an enzyme is linked to a solid matrix which may subsequently be used as a slurry, packed into columns or used in a membrane reactor. Implants and artificial organs need to be biocompatible and tissue and osseointegration may be improved by attachment of growth stimulation agents, such as collagen, to the surfaces. The applications mentioned above, immunoassay, extracorporeal therapy, enzymatic synthesis, and implants, are all based on a specific interaction between a biomolecule, usually a protein, and a cell or another biomolecule in an aqueous solution. When a solidphase technique is employed it is important that the biornolecule is attached to the support in such a way that its biological properties are not destroyed. For instance, enzymatic activity can be completely lost if the coupling affects the active site,l° and the antigenrecognizing ability of an antibody can be destroyed by binding to the Fab segment.ll Furthermore, it is an advantage if the underlying surface, the background, is inert in the sense that strong interaction with the immobilized molecule is avoided and that nonspecific adsorption of molecules from solution is minimized. Strong attraction forces, e.g., due to hydrophobic interactions, between a protein and a surface could eventually lead to such a strong change in protein conformation that the biological activity is lost. Nonspecific adsorption is a wellknown problem in solidphase diagnostics and is the prime reason for the lack of accuracy of some of these tests. (See Section 19.4.1 for further discussion). Immobilization of the biologically active molecule to free ends of grafted PEG chains offers an attractive way of avoiding the problem of attraction by the underlying surface. Both gradual deformation of the attached molecule and nonspecific adsorption of other molecules or particles will be minimized. Provided that the immobilization procedure used gives minimal distortion of the biological properties and that the layer of immobilized molecules is not so dense that crowding phenomena appear,l2 the procedure would be expected to lead to products with high activity and good stability (see Figures I and 2). The characteristic features of the PEG layer (i.e., hydrophilicity, freedom of electrostatic charges, and rapid motion of the hydrated chains), being valuable in terms of avoiding interaction between proteins and the surface, cause considerable difficulties when it comes to immobilization efficiency. Even with very reactive end groups on the PEG chains, coupling of the biomolecule in solution is rendered difficult by the energy barrier involved in close approach of a protein to a dense PEG layer. Thus, coupling of proteins and other biomolecules to PEG-grafted surfaces is not trivial. This paper discusses two approaches to the problem and gives some examples of procedures used.

Place, publisher, year, edition, pages
New York: Plenum Press , 1992. 303-324 p.
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:ri:diva-13601OAI: oai:DiVA.org:ri-13601DiVA: diva2:989915
Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2016-09-29Bibliographically approved

Open Access in DiVA

No full text

By organisation
YKI – Ytkemiska institutet
Natural Sciences

Search outside of DiVA

GoogleGoogle Scholar

Total: 16 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
v. 2.27.0