The reorientation of poly(2-dimethylamino ethyl methacrylate) after environment stimuli improves hydrophilicity and resistance of protein adsorption

https://doi.org/10.1016/j.jcis.2007.08.017Get rights and content

Abstract

There is a dense poly(2-dimethylamino ethyl methacrylate) (PDMAEMA) layer on the surface of poly(acrylonitrile and 2-dimethylamino ethyl methacrylate) (PAN-DMAEMA) membrane. The contact angle measurement indicated that the hydrophilicity of membrane increases at higher pH value and ionic strength. The reorientation of PDMAEMA after environment stimuli results in further enrichment of ester groups on the membrane surface according to XPS analysis. The amount of adsorbed bovine serum albumin (BSA) on PAN-DMAEMA membrane is dramatically decreased at higher pH value and ionic strength. A viewpoint based on the minimizing electrostatic interactions between PDMAEMA groups after environment stimuli leading to the conformation switch of PDMAEMA chains from stretched to shrunk states, which results in higher surface enrichment of ester groups enhancing hydrophilic property of the PAN-DMAEMA membrane, was put forward to explain the resistance of protein adsorption on the membrane.

Graphical abstract

The reorientation of PDMAEMA and the existence of exchanged ions make the membrane more hydrophilic, so that BSA adsorption is remarkably decreased at higher pH value and ionic strength.

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Introduction

Protein adsorption is the initial step in biofouling processes and is a widespread phenomenon afflicting a variety of medical, biotechnological, and industrial systems [1], [2], [3]. The control of protein adsorption at material surfaces is still a challenge in current research. When a protein approaches an interface or a surface, the energies of interactions between them contains contributions from van der Walls, electrostatic, hydrophobic, and hydrogen-bonding terms. To achieve protein resistance for an interface, a series of different driving forces for protein adsorption must be eliminated. Whitesides groups prepared self-assembled monolayers presenting substrates with various functional groups to test the resistance of protein adsorption of those substrates. They observed the following properties among protein resistant substrates: hydrophilicity, the ability to accept hydrogen bonding, the inability to donate hydrogen bonding, and a net neutral charge [4], [5], [6]. Extensive research has been focused on the development of physical and chemical strategies for effective antifouling surfaces through modifying material surfaces using hydrophilic molecules, such as poly(ethylene glycol) and zwitterionic molecules [7], [8], [9], [10], [11], [12], [13].

Polyelectrolytes are highly hydrophilic; many studies have been carried out for surface modification with polyelectrolytes to enhance hydrophilicity and antifouling properties [14], [15]. Poly(2-dimethylamino ethyl methacrylate) is a weak polyelectrolyte, whose degree of ionization can be switched at around neutral pH. PDMAEMA is a stimuli-responsive polymer; there is a conformation transition of PDMAEMA from stretched to shrunk states after changes of temperature, pH, and ionic strength in aqueous solutions [16], [17], [18], [19], [20], [21]. PDMAEMA was able to condense the structure of plasmid DNA yielding polymer/plasmid complex, which has the highest transfection efficiency and cytotoxicity [19], [20]. Bovine serum albumin (BSA) can be adsorbed on PDMAEMA layer; the larger BSA uptake was likely due to the electrostatically driven adsorption at solution pH of 5.7; but BSA repulsion (desorption) from the PDMAEMA layer was observed when net electrostatic attractions were eliminated [21]. PDMAEMA displays the resistance of protein adsorption at higher solution pH and/or ionic strength; this is a simple and arbitrary to demonstrate the resistance of protein adsorption of PDMAEMA with only eliminating electrostatic interactions, since there is relatively little known about the molecular basis of PDMAEMA. The detailed study on the molecular mechanism of PDMAEMA switch form the adsorption to repulsion of protein is significant, since the controlled protein adsorption on PDMAEMA has potential applications in controlled drug delivery, biomacromolecular separation, water treatment, and so on.

In the present work, a weak polyelectrolyte membrane was prepared using poly(acrylonitrile and 2-dimethylamino ethyl methacrylate) (PAN-DMAEMA) copolymer by phase inversion in a wet process. The surface segregation during aqueous-based coagulation renders the arrangement of hydrophilic polymer of PDMADMA on the membrane surface, creating a dense PDMAEMA layer that provides an appropriate platform to study protein adsorption [12], [13], [22], [23]. The amount of adsorbed BSA on PAN-DMAEMA membrane is remarkably decreased at higher pH value and ionic strength in solutions. A significant observation is that the reorientation of PDMAEMA after environment stimuli enhances its hydrophilic property, which is an important factor for resisting protein adsorption of PDMAEMA.

Section snippets

Materials

Acrylonitrile (AN) was purchased from Damao Chemical Co. (Tianjin, China) and distilled before use. 2-Dimethylamino ethyl methacrylate (DMAEMA) was purchased from Xinyu Chemical Co. (Wuxi, China). Azobisisobutyronitrile (AIBN), N,N-dimethyl formamide (DMF), and poly(vinyl alcohol) (PVA, degree of polymerization is 1700) were purchased from Kewei Chemical Co. (Tianjin, China). Other reagents were all of analytical grade and used without further purification.

Synthesis of PAN-DMAEMA copolymer

A random copolymer containing AN and

Formation of PDMAEMA layer on the membrane surface

PAN-DMAEMA copolymer was synthesized by aqueous phase precipitation polymerization. The weight percentages of C, N, and H elements in PAN-DMAEMA copolymer were 66.3, 22.7, and 6.5 wt% from an elemental analyzer. The composition of PAN-DMAEMA copolymer was 91.6 mol% AN and 8.4 mol% DMAEMA. PAN-DMAEMA membrane was prepared through a simple aqueous-based immersion precipication process. The surface segregation during aqueous-based coagulation renders the arrangement of hydrophilic polymer of

Conclusion

The surface segregation during aqueous-based coagulation renders the arrangement of hydrophilic polymer of PDMADMA on the membrane surface, creating a dense PDMAEMA layer that provides an appropriate platform to study protein adsorption. The amount of adsorbed BSA on PAN-DMAEMA membrane is dramatically decreased at higher solution pH and ionic strength. The transition of PDMAEMA chains from stretched to shrunk conformation in response to environment stimuli results in surface enrichment of

Acknowledgements

This research was funded by Tianjin Natural Science Foundation (No. 07JCYBJC00900); Key Laboratory of Colloid and Interface Chemistry (Shandong University). We also thank Miss He for help in the XPS measurements.

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