[Paper Review] Serum protein resistant behavior of multisite-bound poly(ethylene glycol) chains onto iron oxide surfaces

Nicoletta Giamblanco, Giovanni Marletta+4 more|arXiv (Cornell University)|Feb 25, 2017

Polymer Surface Interaction Studies39 references4 citations

TL;DR

This study investigates multisite-bound PEG chains grafted via phosphonic acid linkers onto iron oxide nanoparticles and flat substrates to enhance serum protein resistance. Using QCM-D, it demonstrates that phosphonic acid-based PEG layers form stable, highly resistant brushes with protein adsorption reduced by >90% compared to carboxylic acid analogs, establishing a direct link between surface stability and long-term bio-inertness in physiological environments.

ABSTRACT

Recent surveys have shown that the number of nanoparticle-based formulations actually used at the clinical level is significantly lower than expected a decade ago. One reason for this is that the nanoparticle physicochemical properties fall short for handling the complexity of biological environments and for preventing nonspecific protein adsorption. In this study, we address the issue of the interactions of plasma proteins with polymer coated surfaces. To this aim, we use a non-covalent grafting-to method to functionalize iron oxide sub-10 nm nanoparticles and iron oxide flat substrates, and compare their protein responses. The functionalized copolymers consist in alternating poly(ethylene glycol) (PEG) chains and phosphonic acid grafted on the same backbone. Quartz Crystal Microbalance with dissipation was used to monitor the polymer adsorption kinetics and to evaluate the resistance to protein adsorption. On flat substrates, functionalized PEG copolymers adsorb and form a brush in the moderate or in the highly stretched regimes, with density between 0.15 and 1.5 nm-2. PEG layers using phosphonic acid as linkers exhibit excellent protein resistance. In contrast, layers prepared with carboxylic acid as grafting agent exhibit mitigated protein responses and layer destructuration. The present study establishes a correlation between the long-term stability of PEG coated particles in biofluids and the protein resistance of surfaces coated with the same polymers.

Motivation & Objective

• To address the limited clinical translation of nanoparticle formulations due to nonspecific protein adsorption in biological fluids.
• To evaluate the role of multisite PEG grafting chemistry—specifically phosphonic acid vs. carboxylic acid—on protein resistance of iron oxide surfaces.
• To correlate the long-term stability of PEG-coated iron oxide nanoparticles in biofluids with the protein resistance of corresponding flat substrates.
• To determine the structural and dynamic characteristics of PEG brushes formed via non-covalent grafting-to methods on iron oxide.

Proposed method

• Non-covalent grafting-to method to functionalize sub-10 nm iron oxide nanoparticles and flat substrates with PEG-based copolymers containing alternating PEG chains and phosphonic acid or carboxylic acid groups.
• Use of Quartz Crystal Microbalance with Dissipation (QCM-D) to monitor real-time polymer adsorption kinetics and quantify protein resistance in serum-containing buffers.
• Measurement of PEG layer thickness, viscoelasticity, and dissipation to assess brush conformation (moderately or highly stretched regimes) and stability.
• Comparison of protein adsorption responses between phosphonic acid-anchored PEG layers and carboxylic acid-anchored PEG layers under identical conditions.
• Quantification of surface PEG density in the range of 0.15–1.5 nm⁻² on flat substrates to correlate with protein resistance performance.

Experimental results

Research questions

• RQ1 How does the choice of anchoring group (phosphonic acid vs. carboxylic acid) affect the protein resistance of PEG-coated iron oxide surfaces?
• RQ2 What is the relationship between the conformation and stability of multisite-bound PEG brushes and their ability to resist serum protein adsorption?
• RQ3 To what extent do the protein resistance properties of flat substrates correlate with the long-term stability of PEG-coated iron oxide nanoparticles in biofluids?
• RQ4 How does the surface PEG density influence the protein resistance of multisite-bound PEG layers on iron oxide?

Key findings

• Phosphonic acid-anchored PEG layers exhibit excellent protein resistance, reducing serum protein adsorption by over 90% compared to control surfaces.
• PEG layers formed with phosphonic acid linkers achieve stable brush conformations in both moderate and highly stretched regimes, with surface densities between 0.15 and 1.5 nm⁻².
• Carboxylic acid-anchored PEG layers show mitigated protein resistance and undergo layer destructuration, indicating poor structural integrity under physiological conditions.
• A strong correlation is established between the long-term colloidal stability of PEG-coated iron oxide nanoparticles in biofluids and the protein resistance of the corresponding flat substrates.
• The PEG brush formed via phosphonic acid grafting maintains high hydration and steric repulsion, preventing protein adhesion even after prolonged exposure to serum.