# Response of Osteoblasts to Electric Field Line Patterns Emerging from Molecule Stripe Landscapes
Studies with MG-63 osteoblasts on homogeneous amine-terminated molecular layers revealed superior adhesion performance, i.e., the largest adhesion areas and the most vital intracellular Ca\({}^{2+}\) mobilization on plasma-polymerized polyallylamine and (3-Aminopropyl)triethoxysilane (APTES), in comparison to natively oxidized Ti surfaces [7]. Regarding morphological studies on cell adhesion to surfaces with molecular stripe patterns, the question arises whether topographic or biochemical cues dominate. Therefore, a decisive parameter is the height of the stripes, which is often not explicitly given. In case of few 10 nm high stripes, additionally to a preference for ECM materials, contact guidance can play a role. Most studies use ECM species for stripe patterns, where the cell adhesion behavior is governed by the strong affinity to anchor, even at large topographic heights. Though the situation is distinct from our study, where we aim to explore other types of mechanisms and use \"innocent molecular species\" for stripe patterns, we provide a brief summary of findings on stripe patterns with ECM species [21; 22; 23; 24; 25; 26; 27; 28]: Spindle shapes and alignment of fibroblasts inbetween fibronectin island rows have been observed [23]. The islands appear to be quite high, since only the template underneath has been prepared by microcontact printing. Similarly, 2 um fibronectin stripes with varying spacing gave rise to elongation and directional migration of fibroblasts in terms of contact guidance [25]. REF52 fibroblasts prefer adhesion on fibronectin stripes, inbetween non-adhesive Polyethylene glycol (PEG) stripes, particularly if the PEG stripe width exceeds 8 um[29]. Since the fibronectin is adsorbed to photolithographically prepared Au structures, these regions may protrude. Extremely high structures (pillars) lead to reduced adhesion area, in terms of formation of bridges and traction forces [27]. Muscle cells and murine myoblasts adhered to microprinted, assumingly flat, stripes of fibronectin or lamilin took the characteristic spindle shape and aligned [22; 28]. Human vena saphena cells, at large stripe distances, also adhere to fibronectin stripes and adopt a spindle shape [21]. Non-adhesive (hydrophobic) and adhesive stripes have been constituted by methyl termination and untreated regions of fused quartz, respectively, fabricated photo-lithographically [24]. The height differences should be in the region of the dimension of one methyl group, thus below one nanometer. Beyond 24 \(\upmu\)m stripe period a spindle shape and orientation have been observed with hamster (BHK) and canine (MDCK) kidney cells [24]. An interesting option is backfilling inbetween ECM stripes by other materials such as poly-l-lysine (PLL) or PLL-polyethylglycol [26]. PLL has positive charges, and the observation is that cells adhere to ECM stripes with the typical spindle shape and orientation. ECM protein species, such as collagen or fibronectin allow biochemical adhesion, i.e., expression of focal adhesion points, so that one may expect, that with these species any electric field effects or other physical cues are overruled. In electric DC fields live cells, with their negative \(\zeta\) potential, often migrate towards the cathode, thus in the direction of the electric field [30; 31]. Dead systems, such as lipid vesicles with negative \(\zeta\) potential, will drift opposite to the electric field \(\vec{E}\) (thus towards the anode). The speed of electrophoresis [32] is \(\vec{v}=\epsilon_{0}\epsilon\vec{v}\,\vec{E}/\eta\) with \(\epsilon_{0}\) denoting the permittivity of vacuum, \(\epsilon\) the relative permittivity of the medium, and \(\eta\) its viscosity. Thus, live cells most often move opposite to electrophoresis. Electrophoresis is a passive process, while cell migration is active. The directions of electroaxis may be related to the wound potential, which is negative.