The combined use of natural ECM components and synthetic materials offers an attractive alternative to fabricate hydrogel-based tissue engineering scaffolds to study cell-matrix interactions in three-dimensions (3D). A facile method was developed to modify gelatin with cysteine via a bifunctional PEG linker, thus introducing free thiol groups to gelatin chains. A covalently crosslinked gelatin hydrogel was fabricated using thiolated gelatin and poly(ethylene glycol) diacrylate (PEGdA) via thiol-ene reaction. Unmodified gelatin was physically incorporated in a PEGdA-only matrix for comparison. We sought to understand the effect of crosslinking modality on hydrogel physicochemical properties and the impact on 3D cell entrapment. Compared to physically incorporated gelatin hydrogels, covalently crosslinked gelatin hydrogels displayed higher maximum weight swelling ratio (Qmax), higher water content, significantly lower cumulative gelatin dissolution up to 7 days, and lower gel stiffness. Furthermore, fibroblasts encapsulated within covalently crosslinked gelatin hydrogels showed extensive cytoplasmic spreading and the formation of cellular networks over 28 days. In contrast, fibroblasts encapsulated in the physically incorporated gelatin hydrogels remained spheroidal. Hence, crosslinking ECM protein with synthetic matrix creates a stable scaffold with tunable mechanical properties and with long-term cell anchorage points, thus supporting cell attachment and growth in the 3D environment.
When measuring rheological properties in oscillatory shear flow, one worries about experimental error due to the temperature rise in the sample that is caused by viscous heating. For polymeric liquids, for example, this temperature rise causes the measured values of the components of the complex viscosity to be systematically low. For such linear viscoelastic property measurements, we use an analytical solution by Ding et al. [J. Non-Newtonian Fluid Mech. 86, 359 (1999)10.1016/S0377-0257(99)00004-X] to estimate the temperature rise. However, for large-amplitude oscillatory shear flow, no such analytical solution is available. Here we derive an analytical solution for the temperature rise in a corotational Maxwell fluid (a model with just two parameters: η0 and λ) subject to large-amplitude oscillatory shear flow. This result can then be generalized to a superposition of corotational Maxwell models for a quantitative estimate of the temperature rise. We chose the corotational Maxwell model because, when generalized for multiple relaxation times, it gives an accurate prediction for molten plastics in large-amplitude oscillatory shear flow. We identify three relevant pairs of thermal boundary conditions: (i) both plates isothermal, (ii) with heat loss by convection from both plates, and (iii) one plate isothermal, the other with heat loss by convection. We find that the time-averaged viscous heating increases as an even power series of the dimensionless shear rate amplitude (Weissenberg number), and that it decreases with the dimensionless imposed frequency (Deborah number). We distinguish between the dimensionless time-averaged temperature rise, $\bar \Theta $Θ¯, and the oscillating part, $\tilde \Theta $Θ̃, where $\Theta \equiv \bar \Theta + \tilde \Theta $Θ≡Θ¯+Θ̃. We solve analytically for the $\bar \Theta $Θ¯ profile through the sample thickness for all three pairs of thermal boundary conditions. For the worst case, two adiabatic walls, we derive an expression for the oscillating part of the temperature rise, $\tilde \Theta $Θ̃. We find this $\tilde \Theta $Θ̃ to be a Fourier series of even harmonics whose contribution to the temperature rise can be as important as $\bar \Theta $Θ¯. If both plates are adiabatic, then the sample temperature rises without bound. Otherwise, it does not.
In thermoforming, flat sheets of plastics are transformed into complex shapes by first softening the sheet, and then by shaping it. While softening, the sheet can extend under its own weight, making it concave. Called sag, this affects how each element of the sheet surface views the heater bank. This can worsen the variations in the heat flux distribution across the sheet. It can also cause the heat flux over and under each element on the sheet to differ. The resulting temperature gradients, either across the sheet or through its thickness, can complicate processability. To suppress sag, practitioners stretch the sheet laterally, using cambered transfer rails to keep the sheet taut. In this article, we model sag analytically, using transport phenomena in cylindrical coordinates, for a thin wide rectangular Newtonian isothermal sheet. We uncover a universal dimensionless relation between sag and time, and a useful dimensionless group that we call sagability. We find that the middle of the sagging sheet, unsuppressed, descends, to leading order, with the cube root of time, and our experiments confirm this. Also, we discover that at a particular time the sag increases rapidly without bound, and we call this phenomenon sag runaway. POLYM. ENG. SCI., 50:2060–2068, 2010. © 2010 Society of Plastics Engineers
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.