Biomimicry on a dish

This lecture mainly spoke about some of the newer developments in cell culture technology. Let's see what the future has to offer!

Lab on a chip

Efforts are being made to simulate organs using other materials (rather than having to operate on unfortunate animals or humans). In this lecture, we looked at the lung on a chip, though there are other organs on chips that are being developed too. The "lung on a chip" consists of a main chamber with two side chambers. The side chambers are connected to vacuums, allowing them to contract and expand, stretching the middle chamber in the process. The middle chamber is divided in half by a porous membrane with cells cultured on either side- one side, simulating the lung, is coated with alveolar epithelial cells, and the other side, simulating the blood vessel, is coated with endothelial cells. The area simulating the blood vessel is filled with a viscous fluid and the area simulating the alveoli is filled with air. Processes such as immune cell migration (through the porous membrane) have been simulated on these "lungs on a chip."

Biomechanical mimicry

In these lectures, we've been talking a lot about how mechanical stimuli (such as tissue stiffness) affect cell behaviour. Therefore, we need to try and mimic these mechanical forces in vitro. These mechanical forces can include stiffness (as already repeated ad nauseum), pattern alignment (as mentioned here, shape can affect cell differentiation) and other dynamic forces (such as cyclic stretching and relaxation, microfluidic systems etc.).

Protein patterns

ECM proteins can be "patterned" onto a hydrogel by literally stamping them on. Cells can only adhere to ECM proteins (and not directly to the hydrogel- if you don't trust me on this one, you can also guarantee specific binding by "blocking" with pluronic F127). Therefore, such patterning limits the area where cells can grow, which may affect their behaviour.

Stiffness (and stiffness patterns)

Chances are, cells in vivo are introduced to a variety of different stiffnesses. This can be explored in vitro by using a step gradient (where you have alternating lines of stiff vs. soft) or a linear gradient (gel gradually changes from soft to stiff).

I've already mentioned a step gradient hydrogel (zebraxis) here. Step gradient hydrogels, like zebraxis, can be created by using a photomask during UV polymerisation of the hydrogel. A more recent invention is a glass slide of sorts that comes in two halves. Each half has "teeth" that mesh with the "teeth" of the other half. A different hydrogel can be created on each half, and the two halves can be interlocked or moved apart at will. This might allow us to view the effect of direct contact between cells of two different stiffnesses, or paracrine signalling between cells of the different stiffnesses. Yet another invention is that of "digital stiffness writing," which uses a special heat-sensitive gel filled with gold nanorods. When a laser hits the gold nanorods, they vibrate, producing heat. This heat then causes further polymerisation (and an increase in stiffness) in the area touched by the laser.

Formation of linear hydrogels has traditionally used a gradient photomask. Unfortunately, the gradient photomask method has poor reproducibility, and can be very expensive. Therefore, our lecturer came up with an easier way to make a gradient hydrogel. I'm not 100% certain on the method (I did my research placement with him, but I'll admit right now that my participation in that placement has been very casual at best), but I'm fairly sure that it entails making a wedge-shaped hydrogel in a square-shaped well and then pouring another hydrogel mix on top.

Dynamic systems

Moving ahead, we are looking at new ways to culture cells that take a range of other factors into account. For example, the beating bioreactor uses a magnet that turns off and on in order to relax and stretch the gel, respectively. This simulates other tissues that stretch and relax periodically (such as the heart).

And I think that's it...? Or not- there's an extra mechanobiology lecture on LMS, which I should watch at some point. So maybe this isn't the last PHYL3001 post after all...!