Poly(ethylene glycol): protein-repulsive or albumin-compatible?

Area of Science:

• Biomaterials Science
• Surface Chemistry
• Immunology

Background:

• Poly(ethylene glycol) (PEG) and poly(ethylene oxide) (PEO) segments are widely used to impart 'stealth' properties to foreign materials.
• This stealth effect is commonly attributed to the repulsion of all proteins by PEG via the excluded volume effect, reducing immune system recognition.

Purpose of the Study:

• To challenge the prevailing hypothesis that protein repulsion solely explains the stealth effect of PEG/PEO segments.
• To investigate the specific interactions between PEG segments and key plasma proteins, particularly albumin and fibrinogen.

Main Methods:

• Literature review on protein-PEG interactions.
• Experimental assessment of albumin and fibrinogen compatibility with PEG in phosphate-buffered saline.
• Comparison of interactions at physiologically relevant concentrations.

Main Results:

• Albumin and PEG were found to be compatible at room temperature and relevant concentrations.
• Fibrinogen and PEG exhibited phase separation, indicating incompatibility.
• PEG with molar masses >= 8000 did not accommodate albumin, aligning with excluded volume predictions.

Conclusions:

• The stealth effect of PEG/PEO segments is primarily driven by their compatibility with albumin, the dominant plasma protein.
• This albumin-PEG compatibility creates a 'chameleon' effect, masking foreign materials from immune recognition.
• The interaction mechanism shifts from simple repulsion to specific protein accommodation based on PEG characteristics and protein type.