Fusion of biomimetic stealth probes into lipid bilayer cores

Abstract

Many biomaterials are designed to regulate the interactions between artificial and natural surfaces. However, when materials are inserted through the cell membrane itself the interface formed between the interior edge of the membrane and the material surface is not well understood and poorly controlled. Here we demonstrate that by replicating the nanometer-scale hydrophilichydrophobic-hydrophilic architecture of transmembrane proteins, artificial "stealth" probes spontaneously insert and anchor within the lipid bilayer core, forming a high-strength interface. These nanometer-scale hydrophobic bands are readily fabricated on metallic probes by functionalizing the exposed sidewall of an ultrathin evaporated Au metal layer rather than by lithography. Penetration and adhesion forces for butanethiol and dodecanethiol functionalized probes were directly measured using atomic force microscopy (AFM) on thick stacks of lipid bilayers to eliminate substrate effects. The penetration dynamics were starkly different for hydrophobic versus hydrophilic probes. Both 5-and 10 nm thick hydrophobically functionalized probes naturally resided within the lipid core, while hydrophilic probes remained in the aqueous region. Surprisingly, the barrier to probe penetration with short butanethiol chains (E o;5 nm ¼ 21.8k b T , E o;10 nm ¼ 15.3k b T ) was dramatically higher than longer dodecanethiol chains (E o;5 nm ¼ 14.0k b T , E o;10 nm ¼ 10.9k b T ), indicating that molecular mobility and orientation also play a role in addition to hydrophobicity in determining interface stability. These results highlight a new strategy for designing artificial cell interfaces that can nondestructively penetrate the lipid bilayer.atomic force microscopy | biophysics | membranes | proteins

Molecular Structure Influences the Stability of Membrane Penetrating Biointerfaces.

“…10 The results presented here also indicate a dependence on molecule size and microscopic geometry. If the magnitude of van der Waals bonding was the sole component contributing to interface stability, it is thought that tert-dodecanethiol and cis-9-octadecene-1-thiol would both display stronger interfaces than the alkanethiol series.…”

“…10,11 These devices rely on exposing the edge of an embedded Au layer, which is sandwiched between metal layers that possess a hydrophilic oxide (e.g. Cr, Ti).…”

“…10 AFM cantilevers with a Cr/Au/Cr stack located at the tip were fabricated using a combination of metal deposition and focused ion beam (FIB) milling. This procedure, which is described in detail elsewhere, 10,11 results in cantilevers with ~200nm posts at the tip that contain a 5nm Au band (Fig. 1b,d).…”

“…However, this observation should not be used to overlook the importance of the molecular scale configuration; previous work has shown that hydrophobicity drives spontaneous insertion into the bilayer core. 10 Once integrated inside the bilayer, though, other molecular properties seem to determine the interfacial strength. The results presented here suggest monolayer crystallinity and molecular size (properties that influence the intermolecular interactions at the probe-bilayer interface) all contribute to the overall interfacial strength.…”

Continuum model of mechanical interactions between biological cells and artificial nanostructures

“…However, an increased understanding of the interactions between cell membranes and probe surfaces is essential for the development of membrane-fusing "stealth" nanostructures with heterogeneously functionalized sidewalls. 25 The cell is treated as a nonadherent elastic body which deforms on contact with the cylindrical probe. This is a crucial distinction from the scenario considered by Sen et al,26 where the cell is strongly fixed on a substrate and contacted by an external probe from solution, modeled by holding the cell footprint constant.…”