Glioblastoma (GBM) is the most malignant and highly aggressive brain tumor. In this study, four types of typical GBM cell lines (LN229, SNB19, U87, U251) were cultured in a microfabricated 3-D model to study their in vitro behaviors. The 3-D in vitro model provides hollow micro-chamber arrays containing a natural collagen interface and thus allows the GBM cells to grow in the 3-D chambers. The GBM cells in this model showed specific properties on the aspects of cell morphology, proliferation, migration, and invasion, some of which were rarely observed before. Furthermore, how the cells invaded into the surrounding ECM and the corresponding specific invasion patterns were observed in details, implying that the four types of cells have different features during their development in cancer. This complex in vitro model, if applied to patient derived cells, possesses the potential of becoming a clinically relevant predictive model.

Lipid membrane with freely exposed edge is regarded as smooth surface with curved boundary. Exterior differential forms are introduced to describe the surface and the boundary curve. The total free energy is defined as the sum of Helfrich’s free energy and the surface and line tension energy. The equilibrium equation and boundary conditions of the membrane are derived by taking the variation of the total free energy. These equations can also be applied to the membrane with several freely exposed edges. Analytical and numerical solutions to these equations are obtained under the axisymmetric condition. The numerical results can be used to explain recent experimental results obtained by Saitoh et al. [Proc. Natl. Acad. Sci. 95, 1026 (1998)].

A 3-D microfluidic system consisting of microchamber arrays embedded in a collagen hydrogel with tuneable biochemical gradients that mimics the tumour microenvironment of mammary glands was constructed for the investigation on the interactions between invasive breast cancer cells and stromal cells. The hollow microchambers in collagen provide a very similar 3-D environment to that in vivo that regulates collective cellular dynamics and behaviour, while the microfluidic channels surrounding the collagen microchamber arrays allow one to impose complex concentration gradients of specific biological molecules or drugs. We found that breast epithelial cells (MCF-10A) seeded in the microchambers formed lumen-like structures similar to those in epithelial layers. When MCF-10A cells were co-cultured with invasive breast cancer cells (MDA-MB-231), the formation of lumen-like structures in the microchambers was inhibited, indicating the capability of cancer cells to disrupt the structures formed by surrounding cells for further invasion and metastasis. Subsequent mechanism studies showed that down regulation of E-cad expression due to MMPs produced by the cancer cells plays a dominant role in determining the cellular behaviour. Our microfluidic system offers a robust platform for high throughput studies that aim to understand combinatorial effects of multiple biochemical and microenvironmental factors.

Parallel Tempering Simulation on Generalized Canonical Ensemble - Volume 12 Issue 5 - Shun Xu, Xin Zhou, Zhong-Can Ou-Yang

Cell membranes contain a variety of biomolecules, especially various kinds of lipids and proteins, which constantly change with fluidity and environmental stimuli. Though Helfrich curvature elastic energy has successfully explained many phenomena for single-component membranes, a new theoretical framework for multicomponent membranes is still a challenge. In this work, we propose a generalized Helfrich free-energy functional describe equilibrium shapes and phase behaviors related to membrane heterogeneity via curvature-component coupling within a unified framework. For multicomponent membranes, a new but important Laplace–Beltrami operator is derived from the variational calculation on the integral of Gaussian curvature and applied to explain the spontaneous nanotube formation of an asymmetric glycolipid vesicle. Therefore, our general mathematical framework shows predictive capabilities beyond the existing multicomponent membrane models. A set of new curvature-component coupling Euler-Lagrange equations has been derived for global vesicle shapes associated with the composition redistribution of multicomponent membranes for the first time and specified into several typical geometric shapes. The equilibrium radii of isotonic vesicles for both spherical and cylindrical geometries are calculated. The analytical solution for isotonic vesicles reveals that membrane stability requires distinct bending rigidities among components ($k_{\mathrm{A}}\ne k_{\mathrm{B}}$, ${\overline{k}}_{\mathrm{A}}\ne {\overline{k}}_{\mathrm{B}}$) whose bending rigidities are linearly related, which is consistent with experimental observations of coexisting lipid domains. Furthermore, we elucidate the biophysical implications of the derived shape equations, linking them to experimentally observed membrane remodeling processes. Our new free-energy framework provides a baseline for more detailed microscopic membrane models.