Pyro-Electrification of Freestanding Polymer Sheets: A New Tool for Cation-Free Manipulation of Cell Adhesion in vitro

Abstract

Localized electric fields have become, in recent years, a source of inspiration to researchers and laboratories thanks to a huge amount of applications derived from it, including positioning of microparticles as building blocks for electrical, optical, and magnetic devices. The possibility of producing polymeric materials with surface charge thus opens new perspectives for applications where process simplicity and cost-effectiveness of flexible electronics are of fundamental importance. In particular, the influence of surface charges is widely studied and is a critical issue especially when new materials and functional technologies are introduced. Here, we report a voltage-free pyro-electrification (PE) process able to induce a permanent dipole orientation into polymer sheets under both mono- and bipolar distribution. The technique makes use of the pyroelectric effect for generating electric potentials on the order of kilovolts by an easy-to-accomplish thermal treatment of ferroelectric lithium niobate (LN) crystals. The PE allows us to avoid the expensive and time-consuming fabrication of high-power electrical circuits, as occurs in traditional generator-based techniques. Since the technique is fully compatible with spin-coating-based procedures, the pyro-electrified polymer sheets are easily peeled off the surface of the LN crystal after PE completion, thus providing highly stable and freestanding charged sheets. We show the reliability of the technique for different polymers and for different applications ranging from live cell patterning to biofilm formation tests for bacteria linked to food-processing environments.

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“…According to the pyroelectric effect, this phenomenon is associated with a high electric field that originates from the surface of the crystal [12][13][14]. This electric field can be used for a wide range of applications from biological to soft matter manipulation [15][16][17][18][19]. In this case, the generated electric field is used for dividing the mother drop (which faces the field) into many small micro-drops that will be accumulated in a single site of micrometre size on the reaction support generating what we call drop-split-and-stack (DSS).…”

Detecting Collagen Molecules at Picogram Level through Electric Field-Induced Accumulation

“…When the crystal is stimulated through a temperature variation, a surface charge density α = p i ∆T appears locally due to uncompensated charges and a high electric field (E NL~1 0 7 V/m) is generated on the surface of the LN crystal. Recently, we demonstrated for the first time the possibility of using the pyroelectric effect for a wide variety of applications, ranging from biological to soft matter manipulation application [36][37][38][39][40].…”

Quantitative determination of rapid biomass formation on pyro-electrified polymer sheets

“…Recently, we presented a simple and voltage-free methodology called pyro-electrification (PE) for inducing a positive permanent charge in polymeric freestanding sheets, through the pyroelectric effect in lithium niobate (LN) crystals. These sheets can promote the adhesion of both eukaryotic and prokaryotic cells [ [24] , [25] , [26] , [27] , [28] ] onto otherwise cytophobic surfaces. Such approach is innovative as it is based on a physical phenomenon that avoids chemical treatments of the surfaces.…”

“…Here a further characterization is presented for this innovative methodology. Considering the peculiar rapidity of biofilm growth on the BET-carrier [ 24 , 28 ], we focused our attention on the first stages of biofilm formation by performing an accurate quantitative evaluation of the biofilm mass by a crystal violet (CV) assay. The biofilm mass adhering on the BET-carrier in the first hours of incubation was determined through optical density (OD) measurements and the viability of the adhering bacteria was evaluated by standard staining procedures.…”