© 1999 Robert A. Freitas Jr. All Rights Reserved.

Robert A. Freitas Jr., Nanomedicine, Volume I: Basic Capabilities, Landes Bioscience, Georgetown, TX, 1999

9.4.5.1 Transmembrane Brachiation

One simple approach to cytopenetration is to insert a narrow manipulator arm through the plasma membrane, perhaps assisted by a wall-breaching tool tip analogous to the T4 lysozyme enzyme that opens a hole in bacterial cell peptidoglycan walls,^3150-3152 or the T4 DNA-injection system that is specifically designed for lipid bilayer penetration.^1179,1180 The terminus of the manipulator firmly attaches to an actin or microtubular fixed component of the interior cytoskeleton, then retracts, towing the nanorobot through the lipid bilayer surface. Metamorphic reshaping of the nanorobot aspect minimizes the total number of noncovalent lipid bilayer bonds that must be disturbed during transit. Cell surfaces tolerate forces up to ~1 nN per 100 nm² before breaking, so a ~1 nN arm tip smaller than 100 nm² in cross section should be able to push itself through the cellular plasma membrane and into the interior of the cell. As a very crude estimate of the penetration energy required, taking the membranolytic limit as 3 x 10⁶ N/m², then a 1-micron long, 1-nm wide tear can be opened up by applying ~3000 pN of force through a distance of ~10 nm (typical plasma membrane thickness) costing ~30,000 zJ of energy, a ~0.003 pW power demand during a ~10 millisec transit time at a ~100 micron/sec transit speed. It may also be possible to reduce entry forces by inducing lipid bilayer membrane demixing using a tangentially-applied electric field.¹⁶¹³

Last updated on 21 February 2003