Mechanical properties of the extracellular microenvironment are known to alter cellular behavior, such as spreading, proliferation or differentiation. Previous studies have primarily focused on studying the effect of matrix stiffness on cells using hydrogel substrates that exhibit purely elastic behavior. However, these studies have neglected a key property exhibited by the extracellular matrix (ECM) and various tissues; viscoelasticity and subsequent stress-relaxation. As muscle exhibits viscoelasticity, stress-relaxation could regulate myoblast behavior such as spreading and proliferation, but this has not been previously studied. In order to test the impact of stress relaxation on myoblasts, we created a set of two-dimensional RGD-modified alginate hydrogel substrates with varying initial elastic moduli and rates of relaxation. The spreading of myoblasts cultured on soft stress-relaxing substrates was found to be greater than cells on purely elastic substrates of the same initial elastic modulus. Additionally, the proliferation of myoblasts was greater on hydrogels that exhibited stress-relaxation, as compared to cells on elastic hydrogels of the same modulus. These findings highlight stress-relaxation as an important mechanical property in the design of a biomaterial system for the culture of myoblasts.
Several thousand metric tonnes of aquatic biomass are removed from water bodies every year, so that these waters can continue to be used for ship and boat traffic and for leisure activities. The mowed material is generally disposed off without any further use. Therefore, the crop properties of samples from 39 weed control measures all over Germany were examined to assess the suitability of aquatic plant biomass as a substrate for anaerobic digestion systems. Analysis of the crop samples consisted of the identification of plant species and the evaluation of sediment contents and concentrations of macroelements. The methane yield was determined for selected aquatic plants. Analysis revealed a carbon/nitrogen ratio (C/N) of between 10 and 20 in 74% of samples. The concentrations of nitrogen and phosphorous in the samples were comparable to grass silages. With regard to heavy metal concentrations, the threshold values for biowaste for nickel, zinc, and cadmium were exceeded in three samples. There were no significant seasonal differences in substrate characteristics and qualities. The specific methane yields of individual aquatic plants were between 142 and 372 LCH4/kg volatile solids (VS). The results of this study showed that aquatic macrophytes can be used as substrates in anaerobic digestion plants without any restrictions.
Background: As part of the maintenance of lakes and rivers, large quantities of aquatic biomass are produced every year. Neophytes, such as Elodea nuttallii, compete with native species and cause a disturbance to the ecosystem, which can manifest itself in the form of eutrophication. Aquatic macrophytes are not in competition with the production of food and animal feed and thus can be used in anaerobic digestion plants to replace a fraction of commonly used renewables such as maize or grass silage. Mixed silage of Elodea biomass with wheat straw was recently developed to allow for the conservation of mowed aquatic biomass. In this paper, the digestibility of this silage was tested in a long-term semi-continuous fermentation experiment with a duration of 212 days. Methods: A continous-stirred tank reactor with a working volume of 31 L was used for the semi-continuous fermentation experiment. The substrate Elodea-straw silage was supplied to the fermenter once a day. The samples of digestates were analyzed directly after sampling twice a week for total solids, volatile solids, VFA/TAC, NH 4 -N, acetate, propionate, butyrate, and water-solutle elements. The biogas composition was determined by means of gas chromatograph once a week.
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