Smart materials with antifouling properties are relevant in many areas, for example in biomedical applications where it can be desirable to control the binding of cells. Curious to learn more about how such smart materials are developed and how QSense QCM-D is used in the material characterization, I reached out to Lucas Teunissen, Ph. D. - candidate in the group of professor Han Zuilhof, in the Laboratory of Organic Chemistry at Wageningen University & Research. Lucas’s research focus is on innovative polymer coatings, and in a recent study1 they developed a new thermoresponsive polymer brush that shows strong antifouling performance, and which could be of interest as a smart coating in biomedical applications.
In this post, I share what I learned from the interview with Lucas.
Development of innovative polymer coatings
My research mainly focuses on the development of innovative polymer coatings that can introduce specific properties to a target substrate, Lucas says. In contrast to typical polymer coatings, however, the type we employ are covalently bound polymers with high grafting density, so called polymer brushes, he explains.
Most polymer brushes are synthesized using a small number of monomers
Polymer brushes have been, and are, currently investigated intensively, Lucas says. The reason is that using controlled polymerization techniques, surface properties can be tailored with nanoscale precision. Although these controlled polymerization techniques are compatible with a vast range of (potential) monomers, most polymer brushes in scientific research are synthesized using a small number of well-established and thoroughly characterized monomers. In our research, and particularly in this study, we set out to contribute to the polymer brush research field by synthesis and characterization of polymer brushes synthesized from novel building blocks, Lucas says.
Synthesizing a new stimuli-responsive polymer for smart applications
One of the more recent developments regarding polymer brush coatings is the use of stimuli-responsive polymers to create so-called ‘smart’ applications, he continues. One of the most commonly employed responsive polymers is poly(N-isopropylacrylamide) (poly(NIPAM)), which reacts to changes in temperature. Despite many advantages, employing poly(NIPAM) limits the possibilities in terms of more complex polymer brush architectures, such as copolymer structures. Control over polymerization of NIPAM is not straightforward and synthesis of more complicated polymer brush architectures is therefore limited. It is therefore of significant interest to study new monomers that also bring about thermoresponsive properties, but do not exhibit the same limitations in terms of polymerization. As the number of alternative thermoresponsive polymers used in polymer brush research is limited, we aimed to synthesize and characterize a new thermoresponsive polymer brush, poly(N-2-(methacryloyloxyethyl)pyrrolidone) (poly(NMEP)), and investigate its potential for production of stimuli-responsive surfaces, Lucas says.
Developing a new antifouling polymer brush for biomedical applications
In a preliminary literature study, we came across a study that reported thermoresponsive properties of poly(NMEP) in solution, he continues. We decided to attempt to grow this polymer from a surface, using surface-initiated atom transfer radical polymerization (SI-ATRP), and study its thermoresponsive properties, Lucas explains. After successfully doing so, we wanted to show that it was indeed possible to create more complex polymer brush architectures using poly(NMEP) by synthesizing a block copolymer using poly(NMEP) as the base. Finally, the antifouling properties of the polymer brush against protein solutions were assessed to investigate its potential in biomedical applications.
Using QSense QCM-D analysis to assess polymer brush antifouling properties
The antifouling properties of the poly(NMEP) brushes were assessed using QCM-D where we exposed poly(NMEP)-modified QCM-D sensors to a flow of protein solutions and simultaneously, measured the amount of protein that adsorbed on the surface, Lucas says.
In brief, the experiments were executed as follows:
- An ATRP-initiator layer was firstly introduced to the QCM-D sensors from which polymerization was performed to produce poly(NMEP)-modified QCM-D sensors.
- The poly(NMEP)-modified sensors were mounted in our QSense Analyzer
- PBS buffer solution was pumped through the system.
- When the baseline was stable, the poly(NMEP)-modified sensors were exposed to a protein solution - either BSA, fibrinogen, or 10% human serum.
- After 15 minutes, the protein solution was switched back to the PBS buffer solution
- After stabilization of the signal, the amount of protein adsorbed on the poly(NMEP)-modified sensors could be calculated from the change in resonance frequency using the Sauerbrey equation
The QCM-D experiments showed that a poly(NMEP) coated surface greatly reduces the amount of protein that adsorbs on a surface, Lucas says. These results helped us judge the potential of the poly(NMEP) brushes as a component in biomedical devices.
A polymer brush with thermoresponsive properties and strong antifouling performance
This study was carried out to investigate a new thermoresponsive polymer brush based on NMEP, Lucas says. Our aim was to not only synthesize, but also to thoroughly characterize different aspects of the poly(NMEP) brushes in order to assess its potential as a component in biomedical devices.
We showed that Poly(NMEP) brushes exhibit thermoresponsive properties and we also demonstrated that it can be easily incorporated in more complex polymer brush architectures. The QCM-D experiments gave insight in the potential applicability for biomedical devices which now can be used by other researchers in the field when designing their polymer brush coatings.
To conclude, poly(NMEP) is a viable option when thermoresponsive properties in a polymer brush are desired, Lucas says. Apart from the thermoresponsive character, poly(NMEP) can be easily incorporated in more complex brush architectures. These properties, in combination with the strong antifouling performance, make poly(NMEP) brushes of great interest as a smart coating in biomedical devices, he concludes.