Self-spreading

By taking advantage of this aspect, we can transport and manipulate any collection of molecules in the lipid bilayer, irrespective of their charge. By constructing a micro-channel on the substrate, we can control the direction of the self-spreading. Furukawa et al. fabricated photo-lithographic micro-channels with a width of 1-20 tm [50]. 

Figure 13.5 (a) Fluorescence micrograph of the self-spreading lipid bilayer doped with a dye molecule. The lipid bilayer spread on an oxidized silicon wafer from a deposited lipid aggregate illustrated on the left, (b) A schematic drawing of the selfspreading lipid bilayer from the lipid aggregate. Adapted from Ref [48] with permission. 

Figure 13.6 (a) Confocal micrograph of a circularly self-spreading lipid monolayer. A rhodamine-labeled lipid is doped to visualize the spreading behavior, (b) A schematic illustration of the front edge of the self-spreading lipid monolayer [51]. 

In addition to the self-spreading lipid bilayer, it was also found that a lipid mono-layer showed similar spreading behavior on a hydrophobic surface (Figure 13.6) [51]. By fabricating an appropriate hydrophobic surface pattern, the spreading area and direction can be easily controlled. For both the self-spreading bilayer and monolayer, non-biased molecular transportation is an important key concept for the next generation of microfiuidic devices. 

Figure 13.7 (a) The self-spreading distance and (b) velocity of egg-PC lipid bilayer in NaCI aqueous solutions with different concentrations, (x) 100mM, (0) 10mM, and ( ) 1 mM. Adapted from Ref [53] with permission. 

This result demonstrates that the self-spreading dynamics are controllable by tuning the bilayer-substrate interactions. The above-mentioned electrolyte dependence is an example of this fact. Considering that there are many parameters that alter the bilayer-substrate interaction, a diverse approach can be proposed. For example, Nissen et al. investigated the spreading dynamics on the substrate coated with polymetic materials [48]. They found that insertion of a hydrophilic and inert polymer layer under the self-spreading lipid bilayer strongly attenuated the bilayer-substrate interaction. 

Of course, other physical and chemical conditions also affect the self-spreading dynamics. Figure 13.9 shows the dependences of P on the temperature and lipid... 

This fact strongly suggests that it is not sufficient to consider only the bilayer-substrate interaction for a comprehensive understanding of the self-spreading dynamics. 

By comparing the structures of DM PC and DMTAP, it is clear that the structure of the head group is different and that DMTAP has a smaller head group. Thus, addition of DMTAP disturbs the formation of a thermodynamically stable bilayer structure. This energy cost reduces the self-spreading driving energy, which could be one of the reasons why the addition of DMTAP led to a decrease in p. 

In addition to the spreading dynamics, the stacking structure of the self-spreading lipid bilayer is also controllable via the NaCl concentration [54, 55]. Further experimental and theoretical investigations regarding the control of self-spreading are required before we will be able to easily control the self-spreading behavior in microfluidic devices. 

Molecular Manipulation on the Self-Spreading Lipid Bilayer... 

The most intriguing aspect of the self-spreading lipid bilayer is that any molecule in the bilayer can be transported without any external bias. The unique characteristic of the spreading layer offers the chance to manipulate molecules without applying any external biases. This concept leads to a completely non-biased molecular manipulation system in a microfluidic device. For this purpose, the use of nano-space, which occasionally offers the possibility of controlling molecular diffusion dynamics, would be a promising approach. 

Furukawa, K, Nakashima, H.. Kashimura, Y. and Torimitsu, K (2006) MicroChannel device using self-spreading lipid bilayer as molecule carrier. Lab on a Chip, 6, 1001-1006. 

Nabika, H., Takimoto, B., lijima, N. and Murakoshi, K (2008) Observation of self spreading lipid bilayer on hydrophilic surface with a periodic array of metallic nano-gate. Electrochim. Acta, 53, 6278-6283. 

Elferink, M.G., Schleper, C., and Zillig, W. (1996) Transformation of the extremely thermoacidophilic archaeon Sulfolobus solfataricus via a self-spreading vector. EEMS Microbiol Lett, 137, 31-35. 

As can be seen from Fig. 7.43, the average value of micro-stress decrease when temperature increasing after 10 min rapid decrease of stress, it basically unchanged later. The rate of increase of particle size distribution at low temperatures is small from wide to narrow, representing the self-spread movement on the edge of nanocrystalline Fe particle is relatively slow, and the crystal growth activation energy is about 100 kJ mol F... 

At high-temperature, initial growth of particle is rapid, the particle size distribution has become very wide, the crystal growth activation energy increases to 175kJ mol" which mean nano-iron crystal strengthens its self-spread ability at the edge of coarse particles. 

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