Stepwise construction of dynamic microscale concentration gradients around hydrogel-encapsulated cells in a microfluidic perfusion culture device

Inside living organisms, concentration gradients dynamically change over time as biological processes progress. Therefore, methods to construct dynamic microscale concentration gradients in a spatially controlled manner are needed to provide more realistic research environments. Here, we report a novel method for the construction of dynamic microscale concentration gradients in a stepwise manner around cells in micropatterned hydrogel. In our method, cells are encapsulated in a photodegradable hydrogel formed inside a microfluidic perfusion culture device, and perfusion microchannels are then fabricated in the hydrogel by micropatterned photodegradation. The cells in the micropatterned hydrogel can then be cultured by perfusing culture medium through the fabricated microchannels. By using this method, we demonstrate the simultaneous construction of two dynamic concentration gradients, which allowed us to expose the cells encapsulated in the hydrogel to a dynamic microenvironment.


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Comments to the Author(s)
The authors conducted well designed investigation on the effect of the concentration gradient on the diffusive flux on encapsulated cells in micro-patterned hydrogel. In fact they succeeded to mimic the conditions in a real tissue. Of course this is not a scientific breakthrough as far as the first Fick's law is well known, but the contribution of the paper consists in building up of scaffold in which a real cells can be encapsulated and perfused by real patterned micro-channel. This opens a gate for many more detailed investigations of cultures of cells. I really kike the work and recommend its publication.

03-Apr-2020
Dear Dr Sugiura: Title: Stepwise construction of dynamic microscale concentration gradients around hydrogelencapsulated cells in a microfluidic perfusion culture device Manuscript ID: RSOS-200027 Thank you for your submission to Royal Society Open Science. The chemistry content of Royal Society Open Science is published in collaboration with the Royal Society of Chemistry.
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Reviewer: 2
Comments to the Author(s) This work reported a method of constructing chemical concentration gradients in photodegradable hydrogels for microfluidic cell culture. The major concerns from the reviewer are as follows: 1.
The authors repeatedly emphasized the importance and the construction of "dynamic concentration gradients". However, in the reviewer's opinion, the term "dynamic" used here may be inapposite.

2.
The cytocompatibility of both the hydrogel material and the fabrication process should be characterized.

3.
The authors should quantitatively characterize cell viability after perfusion cell culture.

4.
HepG2 cells were embedded in hydrogels when micropatterning two simultaneous concentration gradients, however, no cell biology results were given. 5.
The authors should demonstrate the importance of concentration gradient generated here for cell biology (not just cell survival).

Reviewer: 3
Comments to the Author(s) The authors conducted well designed investigation on the effect of the concentration gradient on the diffusive flux on encapsulated cells in micro-patterned hydrogel. In fact they succeeded to mimic the conditions in a real tissue. Of course this is not a scientific breakthrough as far as the first Fick's law is well known, but the contribution of the paper consists in building up of scaffold in which a real cells can be encapsulated and perfused by real patterned micro-channel. This opens a gate for many more detailed investigations of cultures of cells. I really kike the work and recommend its publication.

Comments to the Author(s)
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Dear Dr Sugiura: Title: Stepwise construction of dynamic microscale concentration gradients around hydrogelencapsulated cells in a microfluidic perfusion culture device Manuscript ID: RSOS-200027.R1 It is a pleasure to accept your manuscript in its current form for publication in Royal Society Open Science. The chemistry content of Royal Society Open Science is published in collaboration with the Royal Society of Chemistry.
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