- Supported biomembranes

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	Biocompatible Materials » Project survey » Exploratory projects » Supported biomembranes

Background and description

Supported phospholipid bilayer (SPB) membranes have received growing interest during the last decade. One reason is their potential or proven value for applications in design of biosensors, coatings of medical implants, drug delivery, drug screening, catalytic interfaces and as biologically inert surfaces (Sackmann, E., Science, 1996. 271: p. 43-48. and Tampé, R., et al., H.C. Hoch, L.W. Jelinsi, and H.G. Craighead, Editors. 1996, Cambridge University Press: Cambridge. p.201-221.) A potentially very interesting application for the future is to use these membranes as supports for controlled stem cell growth and differentiation. A second reason, followed up in teh SSF programme BIOMICS is to use such layers - or intact vesicles - for biosensing platforms. A third reason for the interest in SPBs is that they are presenting a number of challenges of purely scientific nature, e.g., what are the mechanisms behind the autocatalytic and self-assembling processes involved in SPB formation? Functionalized membranes constitute interesting model systems for cell membranes and may provide a route to understand - or at least study - some aspects of cell-mediated processes such as cell-cell interaction, biological signal transduction and budding. During the past few years, many different types of supported membranes have been produced and characterized. The most promising technique to form bilayers is self-assembly from vesicles in solution.

Scientific results

AFM image of biomembrane patches on a solid support

The above questions have been addressed in this project (and in other related projects) over the past six years (see Publications ref 7.2:7 and references therein) by experimental and mathematical simulation methods. First the formation of bilayers from vesicles in solution was studied. Today a thorough –but not complete – understanding has been achieved of how an initially clean surface is converted to a completely bilayer covered surface (on e.g. a silica surface). The methods employed were QCM-D, SPR and AFM. AFM provides microscopic information (Postdoc. Michael Zäch 100% supported by the programme). The picture that emerged is: Vesicles (25-200 nm) that arrive at the surface are first adsorbed intact. When the coverage reaches a critical value, the vesicles rupture and fuse to bilayer patches. As more vesicles are added, they continue to rupture and fuse until a complete bilayer is covering the surface. This picture is corroborated by Monte Carlo simulations (ref. 7.2:1).

The above mapping was followed by measurements of protein adsorption and cell attachment/growth on these surfaces, showing a high degree of protein and cell resistance (partly within the Biomaterials consortium). Then SPBs were made active by incorporation of functional molecules such as biotin and membrane proteins (mainly within BIOMICS and Chalmers Bioscience initiative). The current activities are focused on two directions (in this programme and in a new FP6 EU STREP project “Nanocues”). The first direction is nanoscale patterning by AFM of surface patterns containing alternating areas of bilayers, intact vesicles and empty surface. Such patterning is very interesting for steered cell growth and sensing. This part of the project continues until the end of 2004 with remaining funding from this project. The second direction is binding of stem cell specific peptides (Dr. J. Gold) to the bilayers and studies of specific cell interaction with such functionalized bilayers (collaboration with Prof. Ernest Arenas, KI). This part will successively merge into the EU STREP project “Nanocues”.

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