Determining the Time Window for Dynamic Nanowire Cell Penetration Processes

Abstract

Nanowire (NW) arrays offer opportunities for parallel, nondestructive intracellular access for biomolecule delivery, intracellular recording, and sensing. Spontaneous cell membrane penetration by vertical nanowires is essential for these applications, yet the time- and geometry-dependent penetration process is still poorly understood. In this work, the dynamic NW-cell interface during cell spreading was examined through experimental cell penetration measurements combined with two mechanical models based on substrate adhesion force or cell traction forces. Penetration was determined by comparing the induced tension at a series of given membrane configurations to the critical membrane failure tension. The adhesion model predicts that penetration occurs within a finite window shortly after initial cell contact and adhesion, while the traction model predicts increasing penetration over a longer period. NW penetration rates determined from a cobalt ion delivery assay are compared to the predicted results from the two models. In addition, the effects of NW geometry and cell properties are systematically evaluated to identify the key factors for penetration.

Mechanical Criterion for the Rupture of a Cell Membrane under Compression

“…2 to estimate S contact leads to a critical stress of~8 kPa, it is probably more accurate to estimate the contact area as that of a spherical cap, S contact2 pR 2 , leading to a larger stress of~50 kPa. In another study using nanoneedle geometries, Xie et al (46,47) investigated the penetration of nanowires fixed to a substrate into cells that adhere to this substrate. They used a cell membrane rupture criterion based on activation energy theory and leading to a critical membrane tension to be reached before rupture (42,44).…”

High‐Aspect‐Ratio Nanostructured Surfaces as Biological Metamaterials

“…Throughout the literature, interactions are variously described as penetrating, piercing, perturbing, impaling, indenting, and mechanically disrupting the cell membrane, which reflects in part the lack of consensus over what is happening. In particular, many reports question whether the cell membrane is spontaneously penetrated by nanostructures, and this topic has been presented as a source of contention within the field. In this context, spontaneous penetration refers to a high‐aspect‐ratio nanostructure piercing the membrane of a cell that has been seeded onto a surface (with minimal applied external force).…”

Cellular Deformations Induced by Conical Silicon Nanowire Arrays Facilitate Gene Delivery

“…Despite successful delivery of a broad variety of biomolecules into diverse cell types, the exact mechanism of whether and how the NW arrays can mechanically pierce cellular membranes and/or the nucleus is still not well understood, and has been the subject of an ongoing debate for almost a decade . Various reports have demonstrated that NW‐mediated intracellular delivery often relies on mechanical penetration, which can be maximized by manipulating a combination of key parameters, such as application of external force, interfacing approaches,13f,25 cellular adhesion force,9a,26 NW geometry (density, length, and diameter),17b,27 surface functionalization, and interfacing time . For example, effective delivery of biomolecules (plasmid DNAs, siRNAs, and proteins) into smaller immune cells that grow in suspension requires the use of longer (2−3 µm), sharper (diameter < 150 nm), and denser (0.3−1.0 NWs µm −2 ) NWs, whereas slightly shorter and less dense NWs are more suitable for larger adherent cells 17b.…”

“…For example, effective delivery of biomolecules (plasmid DNAs, siRNAs, and proteins) into smaller immune cells that grow in suspension requires the use of longer (2−3 µm), sharper (diameter < 150 nm), and denser (0.3−1.0 NWs µm −2 ) NWs, whereas slightly shorter and less dense NWs are more suitable for larger adherent cells 17b. Arguing against NW‐mediated direct penetration, some work has posited that the majority of NWs fail to gain a stable access to the cell interior spontaneously,10a,29,30 and others have suggested that endocytosis could be one of the prevalent mechanisms behind NW‐mediated intracellular delivery 23a. In particular, recent studies have shown evidence that vertical nanostructures induce well‐defined membrane curvatures, stimulating clathrin‐mediated endocytosis (CME) and caveolae‐mediated endocytosis (CavME) 23a,31.…”