Application note: Hydrogels

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Introduction

Hydrogels are three-dimensional, hydrophilic, polymeric networks capable of absorbing large amounts of water or biological fluids. Due to their high water content, porosity and soft consistency, they closely simulate natural living tissue, more than any other class of synthetic biomaterials. Hydrogels may be chemically stable or they may degrade and eventually disintegrate and dissolve [N.A. Peppas, P. Bures, W. Leobandung, H. Ichikawa, Eur J Pharm Biopharm, 50 (2000), pp. 27-46]. Because they closely simulate natural living tissue hydrogel particles are widely used in cell sorting, tissue engineering and drug delivery for sustained release.

To produce hydrogel microparticles using microfluidics, different methods can be used. In this application note polyacrylamide hydrogels where produced using addition polymerization, through a chemical reaction of monomers started by a free radical and supported by a catalyst. Other possible methods to initiate hydrogel polymerisation:

  • Chemical catalysts
  • UV-radiation
  • Free radicals
  • Heat

A schematic overview of the polymerization reaction in a microfluidic device can be seen in figure 1.

Figure 1: Schematic overview of the polymerisation of polyacrylamide gels in the MicroSpere Creator .

Method and materials

How it works

Polyacrylamide gels are formed by copolymerisation of acrylamide and bis-acrylamide (“bis,” N,N'- methylene-bis- acrylamide). The reaction is a vinyl addition polymerisation initiated by a free radical-generating system (Polymerisation is initiated by ammonium persulfate and TEMED (tetramethylethylenediamine): TEMED accelerates the rate of formation of free radicals from persulfate and these in turn catalyze polymerisation. The persulfate free radicals convert acrylamide monomers to free radicals which react with unactivated monomers to begin the polymerization chain reaction The elongating polymer chains are randomly crosslinked by bis-acrylamide, resulting in a gel with a characteristic porosity which depends on the polymerization conditions and monomer concentrations [Menter, P. Acrylamide Polymerization—A Practical Approach. Bio-Rad Tech Note 156(2000)]. at

Figure 2: Schematic overview of the polymerisation of polyacrylamide gels.

Production steps

To produce hydrogels in the MicroSphere Creator the following items are needed:

  • Hydrophobic chip
  • Mixture for the dispersed phase with:
    -Water
    -Monomers
    -Crosslinkers
  • Mixture for the continuous phase with:
    -Oil
    -Surfactant
    -Catalyst
  • Fume extractor
  • Water bath

Protocol for preparing the "dispersed" phase

To prepare the dispersed phase the following chemicals where used:

  • Acrylamide/bis-acrylamide
  • Ammonium persulfate, APS.
  • DI Water or Ultrapure Water

Steps used:

  1. All work with these substances must be conducted in the fume extractor.
  2. Weigh the APS and transfer to the tube.
  3. Fill the tube with water
  4. Add Acrylamide/bis-acrylamide
  5. Cover the tube with aluminum foil to avoid the contact with the light
  6. Bring the gel solution to room temperature in a water bath

Protocol for preparing the "continuous" phase

To prepare the continuous phase the following chemicals where used:

  • Fluorinert FC-40
  • Tetramethylethylenediamine
  • Fluorsurfactant

Steps used:

  1. All work with these substances must be conducted in the fume extractor.
  2. Add Fluorinert FC-40
  3. Add Tetramethylethylenediamine
  4. Add Fluorosurfactant

Production in the MicroSphere Creator

The prepared 'dispersed' and 'continuous' phase were inserted in the MicroSphere Creator. Using the provided software the pressure regulated system can be started and the hydrogel droplets can be produced.

Figure 3: Droplet generation inside the MicroSphere Creator.

Results

Two samples were produced using the MicroSphere Creator. The created hydrogel particles where analysed after production. The results can be seen below.

Sample 1

Figure 4: MicroScope image of hydrogel particles from sample 1.
Figure 5: Size distribution of hydrogel particles from sample 1.

Count Statistics

  • Count: 1357                        •    Dn10: 20.3 μm                            •    Concentrations: 2.5 x 10^6 MB/mL
  • Mode: 24.3 μm                 •    Dn50: 24.1 μm                            •    PDI: 0.17
  • Mean: 23.2 μm                  •    Dn90: 25.3 μm           

Sample 2

Figure 6: MicroScope image of hydrogel particles from sample 2.
Figure 5: Size distribution of hydrogel particles from sample 2.

Count Statistics

  • Count: 3607                        •    Dn10: 17.2 μm                            •    Concentrations: 3.9 x 10^6 MB/mL
  • Mode: 22.5 μm                 •    Dn50: 22.7 μm                            •    PDI: 0.19
  • Mean: 22.3 μm                  •    Dn90: 26.4 μm           

If your have any questions regarding hydrogel production and/or the MicroSphere Creator, don't hesitate to contact us. Our team of experts are available to help.

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