We report on recent advances in the fabrication of three‐dimensional (3D) scaffolds for tissue engineering and regenerative medicine constructs using a two‐photon polymerization technique (2PP). 2PP is a novel CAD/CAM technology allowing the fabrication of any computer‐designed 3D structure from a photosensitive polymeric material. The flexibility of this technology and the ability to precisely define 3D construct geometry allows issues associated with vascularization and patient‐specific tissue fabrication to be directly addressed. The fabrication of reproducible scaffold structures by 2PP is important for systematic studies of cellular processes and better understanding of in vitro tissue formation. In this study, 2PP was applied for the generation of 3D scaffold‐like structures, using the photosensitive organic–inorganic hybrid polymer ORMOCER^® (ORganically MOdified CERamics) and epoxy‐based SU8 materials. By comparing the proliferation rates of cells grown on flat material surfaces and under control conditions, it was demonstrated that ORMOCER^® and SU8 are not cytotoxic. Additional tests show that the DNA strand breaking of GFSHR‐17 granulosa cells was not affected by the presence of ORMOCER^®. Furthermore, gap junction conductance measurements revealed that ORMOCER^® did not alter the formation of cell–cell junctions, critical for functional tissue growth. The possibilities of seeding 3D structures with cells were analysed. These studies demonstrate the great potential of 2PP technique for the manufacturing of scaffolds with controlled topology and properties. Copyright © 2008 John Wiley & Sons, Ltd.

Activity-dependent synaptic plasticity is critical for learning and memory. Considerable attention has been paid to mechanisms that increase or decrease synaptic efficacy, referred to as long-term potentiation (LTP) and long-term depression (LTD), respectively. It is becoming apparent that synaptic activity also modulates the ability to elicit subsequent synaptic changes. We provide direct experimental evidence that this modulation is attributable, at least in part, to variations in the level of postsynaptic depolarization required for inducing plasticity. In slices from adult hippocampal CA1, a brief pairing protocol known to produce LTP can also induce LTD. The voltage–response function for the induction of LTD and LTP in naive synapses exhibits three parts: at a postsynaptic membrane potential during pairing (V_m) ≤ −40 mV, no synaptic modification is obtained; atV_mbetween −40 and −20 mV, LTD is induced; and, finally, atV_m> −20 mV, LTP is generated. This function varies with initial synaptic efficacy. In depressed synapses, Θ⁻, theV_mabove which LTD is generated, is shifted toward more depolarizedV_msand Θ⁺, the LTD–LTP crossover point or, equivalently, theV_mabove which LTP is induced, toward more polarizedV_ms. Conversely in potentiated synapses, Θ⁻is shifted toward more polarizedV_ms. Therefore synaptic activity changes synaptic efficacy and accordingly adjusts the voltages for eliciting subsequent synaptic modifications. The concomitant shifts in the voltages for inducing LTD and LTP in opposite directions promote synaptic potentiation and inhibit synaptic depression in depressed synapses and vice versa in potentiated synapses.

Two-photon polymerization technique was applied to generate three-dimensional (3D) scaffold-like structures using the photosensitive organic—inorganic hybrid polymer ORMOCER^®. The structures were studied with respect to potential applications as scaffold for tissue engineering. Cell counting and comet assay, respectively, demonstrated that doubling time and DNA strand breaks of CHO cells, GFSHR-17 granulosa cells, GM-7373 endothelial cells, and SH-SY5Y neuroblastoma cells were not affected by ORMOCER^®. ORMOCER^® related alteration of formation of tissue specific cell-to-cell adhesions like gap junctions was ruled out by double whole-cell patch-clamp technique. Additionally, growth of cells on the vertical surfaces of 3D structures composed of ORMOCER^® is shown.

Tumour-treating fields (TTFields) use alternating electric fields which interfere with dividing cells, thereby reducing tumour growth. Previous reports suggest that electrical forces on cell structure proteins interfered with the chromosome separation during mitosis and induced apoptosis. In the present report we evaluate electromagnetic exposure of cells in telophase/cytokinesis in order to further analyse the mechanism of action on cells. We performed numerical electromagnetic simulations to analyse the field distribution in a cell during different mitotic phases. Based thereon, we developed an electric lumped element model of the mitotic cell. Both the electromagnetic simulation and the lumped element model predict a local increase of the specific absorption rate (SAR) as a measure of the electromagnetically induced power absorption density at the mitotic furrow which may help to explain the anti-proliferative effect. In accordance with other reports, cell culture experiments confirmed that TTFields reduce the proliferation of different glioma cell lines in a field strength- and frequency-dependent manner. Furthermore, we found an additional dependence on the commutation time of the electrical fields. The report gives new insights into TTFields’ anti-proliferative effect on tumours, which could help to improve future TTFields application systems.