Highly ordered biobased scaffolds: From liquid to solid foams – A short review

Sebastien Andrieux

In an article published by Sébastien Andrieux, Wiebke Drenckhan, Cosima Stubenrauch in the journal “Polymer”, the authors show that microfluidics liquid foam templating can be used to produce biobased highly monodisperse chitosan foams. The demonstrated system employs a fine and smooth control of the two-phase flow rates to accurately tune the bubble size generation, with diameters ranging from 200 to 800 µm. Solid chitosan foams can be obtained by freeze-drying the resulting highly ordered chitosan liquid foams.

ABSTRACT

Polymer foams are widely employed materials due to their versatile properties (thermal and acoustic insulation, mechanical dampling, fluid transport, etc.). This work offers a microfluidics liquid foam templating route that generates biobased monodisperse chitosan foams from aqueous chitosan solutions, stabilized via a biobased sugar surfactant. Microfluidics allows to generate bubble sizes ranging from 200 to 800 µm. The high level of monodispersity results in the formation of highly ordered liquid foams, as well as well-controlled structures of bioscaffold for tissue engineering application.  

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Fig 1. Bubble diameter evolution per set of gas and liquid pressures applied via pressure-driven flow controller.

Fig 1. Bubble diameter evolution per set of gas and liquid pressures applied via a pressure-driven flow controller. Courtesy of Sébastien Andrieux.

INTRODUCTION TO LIQUID FOAM TEMPLATING

Foams are gas bubbles dispersed in a liquid (aqueous foams) or in a solid matrix (polymer foams). Polymer foams are used in a wide range of applications due to their light weight and a high specific surface area compared to other materials. Solid foams, like other porous materials, can serve as an open-cell scaffold for tissue engineering [1]. For such a material, the pore size and polydispersity are key parameters in cell colonization [2-4]. The optimal pore size is dependent upon the kind of cell cultivated. Therefore, there is a clear need for techniques enabling an effective tuning of the scaffold pore size. Here, liquid foam templating based on the translation of a liquid template into a solidified version of its initial liquid structure, is employed to tailor the resulting porous solid foam morphology [5].

AIM & OBJECTIVES

  • To tune precisely and finely the liquid foam structure via microfluidics.
  • To retain the structure of the liquid template throughout the solidification process.
  • To generate fully biobased and highly ordered solid foams.
Set-up for liquid foam templating.

Fig. 2 Set-up for liquid foam templating. Available here from PhD Thesis of Sébastien Andrieux.

Video 1: Courtesy of Sébastien Andrieux – Steady microfluidics bubbling for liquid foam templating obtained with OB1 Mk2 Elveflow pressure-driven flow controller.

Video 2: Courtesy of Sébastien Andrieux – Oscillating microfluidics bubbling for liquid foam templating obtained with OB1 Mk2 Elveflow pressure-driven flow controller.

Pictures of Chitosan foams.

Fig. 3 Pictures of Chitosan foams. Courtesy of Sébastien Andrieux.

KEY FINDINGS

This work introduces a new route towards tailoring effectively with microfluidics the generation of fully biobased and highly ordered solid foams via liquid foam templating. The foam was generated within the microfluidic devices by co-injection of nitrogen and foaming solution containing both Chitosan and Genipin (biobased polymer and cross-linker respectively).

Both COC (Cyclic Olefin Copolymer) and glass flow-focusing chips were employed to generate bubble diameters ranging from 200 to 800 µm via microfluidics bubbling as represented in Fig 1.

The fluids flow rates were controlled with Elveflow’s OB1 pressure-driven flow controller connected to a nitrogen tank as illustrated in Fig.2 and video 1 and 2.

The liquid foam was collected in a polystyrene Petri dish and cross-linked at 40°C for 2 hours. The resulting foam was further solidified and dried either via freeze-drying or by placing it at 60°C for 18 hours.

The author produced both highly monodisperse liquid and resulting solid foams with a polydispersity index varying from 2.9% up to 3.5% as described in Fig 3 and Fig 4.

Taken together, these findings suggest that microfluidics is a powerful tool to produce monodisperse foams with fine tuning of bubble sizes. Here, this method was used to generated highly ordered biobased scaffold.

Interestingly, another paper published in Langmuir Journal by Andrieux et al. (2017) shows that the polydispersity of the foam can be tuned similarly by sequentially applying changes in the gas pressure for a fixed liquid flow rate as performed in video 2.

If you’re interested in reproducing what Sébastien Andrieux achieved in his work, feel free to contact our team of experts for additional information about the OB1 pressure-driven flow controller for fine tuning of your fluid flow!

Pictures of Chitosan foams and Polydispersity Index evolution

Fig. 4 Pictures of Chitosan foams and Polydispersity Index evolution. Courtesy of Sébastien Andrieux.

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REFERENCES TO LIQUID FOAM TEMPLATING

[1] A. Barbetta, A. Gumiero, R. Pecci, R. Bedini, M. Dentini, Biomacromolecules 10 (12) (2009) 3188-3192.

[2] A. Barbetta, G. Rizzitelli, R. Bedini, R. Pecci, M. Dentini, Soft Matter 6 (8) (2010) 1792-1795.

[3] K.-Y. Chung, N.C. Mishra, C.-C. Wang, F.-H. Lin, K.-H. Lin, Biomicrofluidics 3 (2009), 022403.

[4] M. Costantini, C. Colosi, J. Guzowski, A. Barbetta, J. Jaroszewicz,W. Swieszkowski, M. Dentini, P. Garstecki, J. Mater. Chem. B 2 (16) (2004) 2290-2300.

[5] S. Andrieux, A. Quell, C. Stubenrauch, W. Drenckhan, J. advances in Colloid and Interface Science (256) (2018) 276-290.