Using the Reference Shrinkage Curve to Estimate the Corrected Crack Volume of a Soil Layer
To estimate the correct soil crack volume based on the shrinkage geometry factor, in addition to measurements with core samples, one also needs to know the shrinkage curve of the soil matrix without cracks. For such a curve one can use the soil reference shrinkage curve that is only stipulated by intraaggregate clay shrinkage without interaggregate cracking. The objective of this work is to illustrate such use of the reference shrinkage curve and, in addition, to argue the necessity to correct the usual estimates of the shrinkage geometry factor in order to correctly estimate the soil crack vol- ume. The illustration is based on available data and reference shrinkage curves for eight soils.
Linking Soil Shrinkage Behavior and Cracking in Two Paddy Soils as Affected by Wetting and Drying Cycles
Soil cracks develop in paddy soils during wetting and drying (WD) cycles. Although changes in soil structure related to cracking have often been described as soil shrinkage, the relationship between soil shrinkage and cracking remains unclear. The objectives of this study were to investigate how WD cycles affect soil shrinkage and cracking and to establish a link between soil shrinkage in the laboratory and cracking in the field. Two paddy fields (one young paddy field and one old paddy field) were subjected to multiple WD cycles during rice growth. Soil cracks were photographed in the field, and the area density (Dc), compactness of cracks (CP), and equivalent width (EW) of the cracks were analyzed. The shrinkage curves of soil cores that were sampled in the two paddy fields were determined after they were subjected to various laboratory-based simulated WD cycles (including variations in intensity, frequency, and sequence). To estimate soil cracking, three parameterizations based on the shrinkage curves of the soil cores treated with non-predrying (Parameterization A), slight drying (Parameterization B), and intense drying (Parameterization C) were established. The YPF soil presented greater Dc and CP than the OPF soil (P < 0.05), whereas the OPF soil exhibited greater EW and coefficient of linear extensibility (P < 0.05). Area density was not only affected by the current soil water content or by the previous drying history. As the number of WD cycles increased, equivalent width generally increased, whereas CP decreased. The intensity of the WD cycles affected shrinkage more than the frequency or sequence. The fitted geometry factor, rₛ, decreased from Parameterization A to Parameterization C for both soils. The Dc values were more accurately estimated by using soil shrinkage curves that included the intensity of the WD cycles. Our results demonstrate that the soil shrinkage curve associated with rₛ can better predict cracking when the effects of WD cycles are considered.
Engineering bio-inks for 3D bioprinting cell mechanical microenvironment
Three-dimensional (3D) bioprinting has become a promising approach to construct­ing functional biomimetic tissues for tissue engineering and regenerative medicine. In 3D bioprinting, bio-inks are essential for the construction of cell microenviron­ment, thus affecting the biomimetic design and regenerative efficiency. Mechanical properties are one of the essential aspects of microenvironment, which can be char­acterized by matrix stiffness, viscoelasticity, topography, and dynamic mechanical stimulation. With the recent advances in functional biomaterials, various engineered bio-inks have realized the possibility of engineering cell mechanical microenviron­ment in vivo. In this review, we summarize the critical mechanical cues of cell micro­environments, review the engineered bio-inks while focusing on the selection princi­ples for constructing cell mechanical microenvironments, and discuss the challenges facing this field and the possible solutions for them.