Covalent Binding of Maleic Anhydride Copolymer Monolayers to Polyacrylamide Hydrogels

FT-IR combined with oscillatory rheology: How to evaluate chemical structure of ester derivatives of MA-containing compatibilizers

Ester derivatives of experimental olefin-maleic anhydride copolymers synthesized at the University of Pannonia have been investigated by both classical and instrumental analytical methods that contribute to a deeper understanding of how that type of additives functions as compatibilizers for plastics and rubbers. Titration-based acid and saponification numbers have provided limited information about the chemical structure of the experimental copolymer compounds. A prompt, precise and low-cost method or combination of methods has been required to access to the ratio of the various derivatives not only straight after esterification but also for quality control during long-term storage considering the even stricter sustainability aspects either. Reproduction and scaling-up synthesises can be also followed by the combined measuring techniques of Fourier-transform infrared spectroscopy (FT-IR) and oscillatory rheometry. Structural changes occurred in the additives could be followed through monitoring their Ester Indices (EI) during the measurement, which can be connected also to the long-term properties. Experimental additives (AD) like AD-1 and AD-2 types with lower EI values of 21.5 % and 32.1 %, respectively, resulted in higher upper limits of the linear viscoelastic (LVE) range (15 % and 10 %). Conversely, the higher EI values of AD-3 and AD-4 led to significantly lower or even immeasurable upper limits of the LVE range. Additives with solid behaviour showed slight dependence on frequency above the crossover point that indicated strong connections disappearing.

Current strategies for ligand bioconjugation to poly(acrylamide) gels for 2D cell culture: Balancing chemo-selectivity, biofunctionality, and user-friendliness

Hydrogel biomaterials in combination with living cells are applied in cell biology, tissue engineering and regenerative medicine. In particular, poly(acrylamide) (PAM) hydrogels are frequently used in cell biology laboratories as soft substrates for 2D cell culture. These biomaterials present advantages such as the straightforward synthesis, regulable mechanical properties within physiological range of native soft tissues, the possibility to be biofunctionalized with ligands to support the culture of living cells, and their optical transparency that makes them compatible with microscopy methods. Due to the chemical inertness and protein repellant properties of PAM hydrogels, these materials alone do not support the adhesion of cells. Therefore, biofunctionalization of PAM gels is necessary to confer them bioactivity and to promote cell-material interactions. Herein, the current chemical strategies for the bioconjugation of ligands to PAM gels are reviewed. Different aspects of the existing bioconjugation methods such as chemo-selectivity and site-specificity of attachment, preservation of ligand’s functionality after binding, user-friendliness and cost are presented and compared. This work aims at guiding users in the choice of a strategy to biofunctionalize PAM gels with desired biochemical properties.

Actin stress fiber dynamics in laterally confined cells

Multiple cellular processes are affected by spatial constraints from the extracellular matrix and neighboring cells. In vitro experiments using defined micro-patterning allow for in-depth analysis and a better understanding of how these constraints impact cellular behavior and functioning. Herein we focused on the analysis of actin cytoskeleton dynamics as a major determinant of mechanotransduction mechanisms in cells. We seeded primary human umbilical vein endothelial cells onto stripe-like cell-adhesive micro-patterns with varying widths and then monitored and quantified the dynamic reorganization of actin stress fibers, including fiber velocities, orientation and density, within these live cells using the cell permeable F-actin marker SiR-actin. Although characteristic parameters describing the overall stress fiber architecture (average orientation and density) were nearly constant throughout the observation time interval of 60 min, we observed permanent transport and turnover of individual actin stress fibers. Stress fibers were more strongly oriented along stripe direction with decreasing stripe width, (5° on 20 μm patterns and 10° on 40 μm patterns), together with an overall narrowing of the distribution of fiber orientation. Fiber dynamics was characterized by a directed movement from the cell edges towards the cell center, where fiber dissolution frequently took place. By kymograph analysis, we found median fiber velocities in the range of 0.2 μm/min with a weak dependence on pattern width. Taken together, these data suggest that cell geometry determines actin fiber orientation, while it also affects actin fiber transport and turnover.