Measurements of Young’s moduli are mostly evaluated using strong assumptions, such as sample homogeneity and isotropy. At the same time, descriptions of measurement parameters often lack detailed specifications. Many of these assumptions are, for soft hydrogels especially, not completely valid and the complexity of hydrogel microindentation demands more sophisticated experimental procedures in order to describe their elastic properties more accurately. We created an algorithm that automates indentation data analysis as a basis for the evaluation of large data sets with consideration of the influence of indentation depth on the measured Young’s modulus. The algorithm automatically determines the Young’s modulus in indentation regions where it becomes independent of the indentation depth and furthermore minimizes the error from fitting an elastic model to the data. This approach is independent of the chosen elastic fitting model and indentation device. With this, we are able to evaluate large amounts of indentation curves recorded on many different sample positions and can therefore apply statistical methods to overcome deviations due to sample inhomogeneities. To prove the applicability of our algorithm, we carried out a systematic analysis of how the indentation speed, indenter size and sample thickness affect the determination of Young’s modulus from atomic force microscope (AFM) indentation curves on polyacrylamide (PAAm) samples. We chose the Hertz model as the elastic fitting model for this proof of principle of our algorithm and found that all of these parameters influence the measured Young’s moduli to a certain extent. Hence, it is essential to clearly state the experimental parameters used in microindentation experiments to ensure reproducibility and comparability of data.
Organotypic tissue cultures are highly promising for performing in vivo type studies in vitro. Currently, however, very limited survival times of only a few days for adult tissue often severely limit their application. Here, superhydrophilic nanostructured substrates with ideal material properties ensure tissue adhesion, essential for organotypic culture, while migration of single cells out of the tissue is hampered. Tuning substrate properties, for the first time, adult neuronal tissue could be cultured for 14 days with no indications of degeneration.
Porous
hydrogel scaffolds are ideal candidates for mimicking cellular
microenvironments, regarding both structural and mechanical aspects.
We present a novel strategy to use uniquely designed ceramic networks
as templates for generating hydrogels with a network of interconnected
pores in the form of microchannels. The advantages of this new approach
are the high and guaranteed interconnectivity of the microchannels,
as well as the possibility to produce channels with diameters smaller
than 7 μm. Neither of these assets can be ensured with other
established techniques. Experiments using the polyacrylamide substrates
produced with our approach have shown that the migration of human
pathogenic
Acanthamoeba castellanii
trophozoites
is manipulated by the microchannel structure in the hydrogels. The
parasites can even be captured inside the microchannel network and
removed from their incubation medium by the porous polyacrylamide,
indicating the huge potential of our new technique for medical, pharmaceutical,
and tissue engineering applications.
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