3D Bioprinting and Biofabrication

Question 1

    The stimulus waveform is approximately that of a square pulse of 5V amplitude. Describe what happens to the stimulus waveform with the bioreactor attached

  1. When the bioreactor is attached, the voltage of the stimulus waveform is reduced to between 1.5-3V from 5V.

    2. Assuming there is a single impedance value for a single bioreactor can you think of an explanation for why the stimulus waveform might be distorted when connected to the load?

  2. Since impedance is given by V/I (voltage/current), the current rating of the stimulation device must be too low. In this case, a custom stimulator may need to be built in order to increase the current.

    3. How might you expect the pink waveform to change if several of the same bioreactors were to be attached in parallel to this stimulator?

  3. The voltage would decrease the amplitude of the waveform even further because the total resistance would increase.

    4. What recommendation for modifying the stimulator would you make to solve this problem?

  4. A custom stimulator can be created with an amplifier which would increase the current rating.

Question 3


The text describes how to design custom bioreactors to efficiently grow tissues. The parameters mentioned include void volume (empty space/porosity), fluid velocity, and channel geometry (designed cylindrically). As the tissue grows over time, the void volume should decrease as the space is filled. Consequently, fluid velocity may also decrease. The bioreactor should maintain the same levels of shear stress that bone tissue requires to grow.


One of the biggest challenges with bioreactors is that the fluid velocity and cell growth may not remain consistent across the tissue as it grows in size. The paper mentions that the growth and fluid velocity is the highest at the edges where new cells are proliferating. The central tissue may experience toxicity and cell death due to density issues. The best chance for success would be to even out the gradient of flow rate throughout the tissue.

DIY Expiriment

I used a frozen banana and allowed it to sit in a mixture of detergent and water for 5 days. Unfortunately, I did not notice a change in the color. It seems that either 5 days was not long enough for the banana to decellularize, or perhaps I did not freeze it for long enough/at cold enough temperatures. Here is a picture of the banana on Day 5.