Jing Xia

Subtitle 1: Decoupling the effects of nanopore size and surface roughness on the attachment, spreading and differentiation of bone marrow-derived stem cells

The nanopore size and roughness of nanoporous surface are two critical variables in determining stem cell fate, but little is known about the contribution from each cue individually. To address this gap, we use two-dimensional nanoporous membranes with controlled nanopore size and roughness to culture bone marrow-derived mesenchymal stem cells (BMSCs), and study their behaviors such as attachment, spreading and differentiation, as shown in Figure 1. We find that increasing the roughness of nanoporous surface has no noticeable effect on cell attachment, and only slightly decreases cell spreading areas and inhibits osteogenic differentiation. However, BMSCs cultured on membranes with larger nanopores have significantly fewer attached cells and larger spreading areas. Moreover, these cells cultured on larger nanopores undergo enhanced osteogenic differentiation by expressing more alkaline phosphatase, osteocalcin, osteopontin, and secreting more collagen type I. These results suggest that although both nanopore size and roughness can affect BMSCs, nanopore size plays a more significant role than roughness in controlling BMSC behavior.



Figure 1. Representative scanning electron microscopy (SEM) image of cells cultured on 80 nm smooth membrane (left) and local zoom (right).

Subtitle 2: Design of electromagnetic tweezer for cellular mechanics studies

The mechanical properties of cell are very important for maintaining cellular integrity and fulfill their functions. However, there are only limited tools to investigate the mechanics of cells at submicron scale, such as atomic force microscope and optical tweezer, partially due to the limited force range available in each tool. Here, we develop an electromagnetic tweezer that can apply forces spanning several orders of magnitude, as shown in Figure 2. By controlling the electric current in the solenoid, the force can be varied from a few piconewton to hundreds nanonewton. This tool is further used to investigate the cell mechanics. By applied the magnetic force on the paramagnetic beads that’s attached on the cells, we can probe the mechanical properties of cells, as shown in Figure 3.


Figure 2. Setup of electromagnetic tweezer


Figure 3. Pulling a paramagnetic bead with electromagnetic tweezer

Contact: Jing Xia jxia01@fas.harvard.edu