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- ItemAutomatic Actin Filament Quantification and Cell Shape Modeling of Osteoblasts on Charged Ti Surfaces(Basel : MDPI, 2021) Gruening, Martina; Dawson, Jonathan E.; Voelkner, Christian; Neuber, Sven; Fricke, Katja; van Rienen, Ursula; Speller, Sylvia; Helm, Christiane A.; Nebe, J. BarbaraSurface charges at the cellโbiomaterial interface are known to determine cellular functions. Previous findings on cell signaling indicate that osteoblastic cells favor certain moderately positive surface charges, whereas highly positive charges are not tolerated. In this study, we aimed to gain deeper insights into the influence exerted by surface charges on the actin cytoskeleton and the cell shape. We analyzed surfaces with a negative, moderately positive, and highly positive zeta (ฮถ) potential: titanium (Ti), Ti with plasma polymerized allylamine (PPAAm), and Ti with a polydiallyldimethylammonium chloride (PDADMA) multilayer, respectively. We used the software FilaQuant for automatic actin filament quantification of osteoblastic MG-63s, analyzed the cell edge height with scanning ion conductance microscopy (SICM), and described the cellular shape via a mathematical vertex model. A significant enhancement of actin filament formation was achieved on moderately positive (+7 mV) compared with negative ฮถ-potentials (โ87 mV). A hampered cell spreading was reflected in a diminished actin filament number and length on highly positively charged surfaces (+50 mV). Mathematical simulations suggested that in these cells, cortical tension forces dominate the cellโsubstrate adhesion forces. Our findings present new insights into the impact of surface charges on the overall cell shape and even intracellular structures.
- ItemEnhancement of Intracellular Calcium Ion Mobilization by Moderately but Not Highly Positive Material Surface Charges(Lausanne : Frontiers Media, 2020) Gruening, Martina; Neuber, Sven; Nestler, Peter; Lehnfeld, Jutta; Dubs, Manuela; Fricke, Katja; Schnabelrauch, Matthias; Helm, Christiane A.; Mรผller, Rainer; Staehlke, Susanne; Nebe, J. BarbaraElectrostatic forces at the cell interface affect the nature of cell adhesion and function; but there is still limited knowledge about the impact of positive or negative surface charges on cell-material interactions in regenerative medicine. Titanium surfaces with a variety of zeta potentials between โ90 mV and +50 mV were generated by functionalizing them with amino polymers, extracellular matrix proteins/peptide motifs and polyelectrolyte multilayers. A significant enhancement of intracellular calcium mobilization was achieved on surfaces with a moderately positive (+1 to +10 mV) compared with a negative zeta potential (โ90 to โ3 mV). Dramatic losses of cell activity (membrane integrity, viability, proliferation, calcium mobilization) were observed on surfaces with a highly positive zeta potential (+50 mV). This systematic study indicates that cells do not prefer positive charges in general, merely moderately positive ones. The cell behavior of MG-63s could be correlated with the materialsโ zeta potential; but not with water contact angle or surface free energy. Our findings present new insights and provide an essential knowledge for future applications in dental and orthopedic surgery. ยฉ Copyright ยฉ 2020 Gruening, Neuber, Nestler, Lehnfeld, Dubs, Fricke, Schnabelrauch, Helm, Mรผller, Staehlke and Nebe.
- ItemProtective role of sphingomyelin in eye lens cell membrane model against oxidative stress(Basel : MDPI, 2021) Ravandeh, Mehdi; Coliva, Giulia; Kahlert, Heike; Azinfar, Amir; Helm, Christiane A.; Fedorova, Maria; Wende, KristianIn the eye lens cell membrane, the lipid composition changes during the aging process: the proportion of sphingomyelins (SM) increases, that of phosphatidylcholines decreases. To investigate the protective role of the SMs in the lens cell membrane against oxidative damage, analytical techniques such as electrochemistry, high-resolution mass spectrometry (HR-MS), and atomic force microscopy (AFM) were applied. Supported lipid bilayers (SLB) were prepared to mimic the lens cell membrane with different fractions of PLPC/SM (PLPC: 1-palmitoyl-2-linoleoylsn-glycero-3-phosphocholine). The SLBs were treated with cold physical plasma. A protective effect of 30% and 44% in the presence of 25%, and 75% SM in the bilayer was observed, respectively. PLPC and SM oxidation products were determined via HR-MS for SLBs after plasma treatment. The yield of fragments gradually decreased as the SM ratio increased. Topographic images obtained by AFM of PLPC-bilayers showed SLB degradation and pore formation after plasma treatment, no degradation was observed in PLPC/SM bilayers. The results of all techniques confirm the protective role of SM in the membrane against oxidative damage and support the idea that the SM content in lens cell membrane is increased during aging in the absence of effective antioxidant systems to protect the eye from oxidative damage and to prolong lens transparency.
- ItemInfluence of molecular weight of polycation polydimethyldiallylammonium and carbon nanotube content on electric conductivity of layer-by-layer films(Amsterdam [u.a.] : Elsevier, 2022) Neuber, Sven; Sill, Annekatrin; Efthimiopoulos, Ilias; Nestler, Peter; Fricke, Katja; Helm, Christiane A.For biological and engineering applications, nm-thin films with high electrical conductivity and tunable sheet resistance are desirable. Multilayers of polydimethyldiallylammonium chloride (PDADMA) with two different molecular weights (322 and 44.3 kDa) and oxidized carbon nanotubes (CNTs) were constructed using the layer-by-layer technique. The surface coverage of the CNTs was monitored with a selected visible near infrared absorption peak. Both the film thickness and the surface coverage of the CNTs increased linearly with the number of CNT/PDADMA bilayers deposited (film thickness up to 80 nm). Atomic force microscopy images showed a predominantly surface-parallel orientation of CNTs. Ohmic behavior with constant electrical conductivity of each CNT/PDADMA film and conductivity up to 4 ยท 103 S/m was found. A change in PDADMA molecular weight by almost a factor of ten has no effect on the film thickness and electrical conductivity, only the film/air roughness is reduced. However, increasing CNT concentration in the deposition dispersion from 0.15 up to 0.25 mg/ml results in an increased thickness of a CNT/PDADMA bilayer (by a factor of three). The increased bilayer thickness is accompanied by a decreased electrical conductivity (by a factor of four). The decreased conductivity is attributed to the increased monomer/CNT ratio.