Ian Wark Research Institute
ARC Special Research Centre
ARC Special Research Centre
Research Area: Coatings, polymer surfaces, interface science, surface analysis, biocompatible coatings
Degree: Honours
Supervisors: Prof Hans Griesser and
Prof Clive Prestidge
Description: This project aims to study and interpret how the dielectric barrier properties of ultrathin polymeric coatings affect interfacial interactions between solid synthetic materials suitable for biomedical device applications ('biomaterials') and biological media. Of particular interest is how the thickness of such coatings plays a role in mediating protein adsorption. The motivation for this study are reported observations that ultrathin coatings affect bio-interface interactions, but it is not understood how the presence of an ultrathin coating affects the nature and range of the interfacial forces involved in bio-interface interactions, such as the adsorption of proteins on the surface of biomaterials. It is also not clear what coating thickness is required to shield the underlying material from exerting an influence.
The hypothesis of this study is that analysis of interfacial forces emanating from materials coated with ultrathin coatings of varying compositions and thickness will provide the necessary fundamental understanding for the rational design of coatings for the optimal control of such bio-interactions. The fundamental understanding acquired in this project is expected to provide a basis for the rational design of improved biomedical devices.
Modern biotechnology, health care devices, and bio-diagnostic assay technologies require synthetic polymeric or ceramic materials that need to meet a number of requirements such as strength or flexibility. The most important requirement, however, is that the material possesses appropriate surface properties. The reason for this is that biological molecules encounter the surface of biomaterials, and the chemical composition and properties of material surfaces determine the consequences of the interfacial encounter between a biological molecule and the material surface. It is well known in the biomaterials literature that immediately after a material contacts a biological environment
- be it for instance a protein solution in a vial, or blood or soft tissue when an implant is used in human medicine - various proteins reach the surface of the synthetic material and interact with it. These interfacial interactions lead to some of the proteins sticking irreversibly to the surface; other proteins desorb again. Adsorbed and denatured proteins then cause further biological reactions that can have various, usually adverse, biological consequences. Biological media contain various proteins which compete for adsorption onto surfaces.
It has been observed that coatings can markedly affect the adsorbed amounts of proteins on synthetic biomaterials and the balance between competing proteins. Often the material underneath the coating produces adverse biological effects that must be shielded by the coating. What minimum coating thickness is needed to shield the bulk material, and why? Adsorbing proteins react to interfacial forces that emanate from the biomaterial, and thus the analysis and interpretation of interfacial forces may yield understanding of why proteins react in the observed ways. Polymeric coatings are dielectric in nature, and hence the bio-interfacial responses will be correlated with dielectric properties, which also play a role in other interesting areas such as electrowetting.
Aims and Significance: The principal aim of this project is to acquire a fundamental understanding of interfacial forces that emanate from solids that comprise an ultrathin coating on a solid bulk material ("substrate"), and how these forces affect competitive protein adsorption. Below a minimal thickness, the coating will not fully shield interfacial forces emanating from the substrate, and the interfacial forces, and the observed interfacial properties such as wetting and protein adsorption, will be governed by a superposition of contributions from the substrate and the coating. At present no information at all is available on this. Moreover, the minimal thickness required to fully shield a substrate will depend on the dielectric properties of the coating. Conversely, an understanding of additive interfacial effects from substrates and coatings may enable us to balance interfacial forces for optimal interfacial interactions. Thus, by understanding such interactions, one may be able to establish design "rules" for optimal coatings for various interfacial applications, such as in biotechnology. Such rationally designed, novel coatings are expected to open up a range of applications in diverse industries. This project will focus on the correlations between these forces and bio-interfacial properties, studied by protein adsorption.
Such research is necessarily inter-disciplinary, and the student will acquire skills and understanding of materials science, coatings and surface science, and protein biochemistry. This will equip him/her well for future employment in areas where coatings and interfaces are utilized..
Methodology: Several chemically different coatings will be fabricated by plasma polymerization on selected substrates. These coatings will be subjected to detailed analysis by surface characterization techniques such as XPS, AFM and ToF-SSIMS. Using a colloid-probe AFM method, interfacial forces will be measured as a function of coating composition and thickness. Streaming potential measurements as a function of pH, and experiments involving the competitive adsorption of proteins will also be performed. The observed interfacial forces will be interpreted within the framework of DLVO theory and correlated with protein adsorption patterns.
References
1) JC Vickerman, Ed., Surface Analysis - The Principal Techniques, John Wiley & Sons, Chichester, 1997.
2) GP Lopez et al., J Biomed Mater Res. 26: 415-439 (1992).
3) WA Ducker et al., Nature 353: 239-241 (1991).
