The authors report on the characterization of the charge formation at supported bilayer lipid membranes (sBLMs) prepared from the zwitterionic lipid 1,2-dioleoyl-sn-glycero-3-phosphatidylcholine on planar silicon dioxide substrates. The charging of the sBLMs was studied in KCl solutions of different ionic strengths between 0.1 and 10 mM by streaming current measurements. In addition, attenuated total reflection Fourier transform infrared spectroscopy and fluorescence microscopy were applied to determine the lipid concentration in the membrane and to study the influence of the harsh conditions (pH 9-2, shear forces) during the electrokinetic measurements on the membrane stability and the lipid diffusion coefficient. The sBLMs were found to be extremely stable. Isoelectric points of about 4 revealed that unsymmetrical adsorption of hydroxide and hydronium ions determined the charging of the outer leaflet of the membrane in the investigated pH range. The diffusion coefficients were found to be rather independent on the ionic strength at neutral and alkaline pH. However, significantly decreased lipid diffusion at pH<4 indicated a charge-induced transition of the fluidic bilayer into a gel/ordered-phase bilayer.

Materials capable of directing cell fate by providing spatially-graded mechanical and biomolecular cues are critically important in the reconstitution of living matter. Herein, we report a multi-component inkjet bioprinting method that allows for spatially varying composition and network properties in cell-instructive glycosaminoglycan (GAG)-based biohybrid and pure poly(ethylene glycol) hydrogels with unprecedented (50 μ m) resolution. The principle relies on the covalent crosslinking of different polymeric precursors through a very rapid bio-orthogonal Michael type addition scheme adjusted in ways to occur during the fusion of bio-ink droplets prior to and upon contact with the target. Exemplary data show that chemotactic molecular gradients produced by this approach within printed GAG-gels of defined zonal architecture can effectively direct migratory activity and morphogenesis of embedded human bone-marrow derived mesenchymal stem cells. The introduced methodology is expected to enable a new, holistic level of control over reductionistic tissue and organoid models.

Incorporation of sulfated glycosaminoglycans (GAGs) into cell‐instructive polymer networks is shown to be instrumental in controlling the diffusivity and activity of growth factors. However, a subtle balance between local retention and release of the factors is needed to effectively direct cell fate decisions. To quantitatively unravel material characteristics governing these key features, the GAG content and the GAG sulfation pattern of star‐shaped poly(ethylene glycol) (starPEG)–GAG hydrogels are herein tuned to control the local availability and bioactivity of GAG‐affine vascular endothelial growth factor (VEGF165). Hydrogels containing varying concentrations of heparin or heparin derivatives with different sulfation pattern are prepared and thoroughly characterized for swelling, mechanical properties, and growth factor transport. Mathematical models are developed to predict the local concentration and spatial distribution of free and bound VEGF165 within the gel matrices. The results of simulation and experimental studies concordantly reveal how the GAG concentration and sulfation pattern determine the local availability of VEGF165 within the cell‐instructive hydrogels and how the factor—in interplay with cell‐instructive gel properties—determines the formation and spatial organization of capillary networks of embedded human vascular endothelial cells. Taken together, this study exemplifies how mathematical modeling and rational hydrogel design can be combined to pave the way for precision tissue engineering.

We systematically applied microslit electrokinetic experiments to explore the role of various electrolytes (KCl, CaCl₂, K₂SO₄ and LaCl₃) in the pH dependent charging of nonpolar poly(tetrafluoroethylene-co-2,2-bistrifluoromethyl-4,5-difluoro-1,3-dioxole) (Teflon® AF) thin films. The results impressively reveal the dominating role of hydroxide and hydronium ions for the charging of water/hydrophobic wall interfaces even in the presence multivalent electrolyte ions. In any system the charging primarily reflected the preferential adsorption of hydroxide over hydronium ions while the electrolyte ions were concluded to determine the magnitude of the surface charge according to their hydration characteristics.