Product Description

Extralink® (PEGDA, polyethylene glycol diacrylate) 0.5mL vials contain 5mg of diacrylated PEG and 2.5 mL vials contain 25 mg. Vials are blanketed by nitrogen and under a slight vacuum.

Extralink® is polyethylene diacrylate (PEGDA) with a molecular weight of 3500 Da. It is a thiol-reactive crosslinker that convalently reacts with the thiol groups in Glycosil®, Heprasil® and Gelin-S® to form viscoelastic hydrogels. Extralink® vials are >80% acrylated and supplied as the crosslinking component in all HyStem® hydrogel kits.

Extralink® vials are paired with HyStem-C and HyStem–HP kits while Extralink-Lite vials are paired with HyStem hydrogel kits to provide comparable experiences despite the different HA concentrations.

Extralink® is used to chemically crosslink Glycosil (or Heprasil) and Gelin-S in Hystem-C and HyStem-HP kits. The gelation time ranges from as short as 5 minutes to as long as a couple of hours, depending upon the amount of Extralink used and the concentration/dilution of the Glycosil, Gelin-S and/or Heprasil.

Similarly, Extralink-Lite is used in place of Extralink for applications where Gelin-S is not included. The higher relative concentration of Glycosil requires less crosslinker to emulate the gelation time and stiffness of HyStem-C and HyStem-HP.



Extralink: Store Extralink in the original vial unopened at -20°C for up to one year. Reconstituted Extralink solutions can be stored at -20 °C for ~ one month.

Note: It is recommended to reconstitute each vial in its entirety.

Directions for Use

When reconstituted, it will be in 1x phosphate buffered saline (PBS) buffer pH ~7.4. The amount of DG Water used for dissolution depends on the vial.

Extralink should be prepared in the following manner:

  1. Allow the Extralink® vial to come to room temperature.
  2. Under aseptic conditions, using a syringe and needle, add to the vial the amount of DG Water indicated on the label.
  3. Invert several times to dissolve.
  4. Extralink is used to chemically crosslink hydrogels made from Glycosil® or Heprasil® and Gelin-S®. Extralink does not form a hydrogel on its own.
  5. Typically, Extralink is used in a 4:1 volume ratio with Glycosil®, Heprasil®, and Gelin-S, as follows:
    • 0.25 mL Extralink® is crosslinked with 0.5 mL Glycosil® + 0.5 mL Gelin-S
    • 0.25 mL Extralink® is crosslinked with 0.5 mL Heprasil® + 0.5 mL Gelin-S
  1. Note the gelation time varies depending upon the amount of Extralink®, the amount of Glycosil®, or Heprasil®, and the amount of Gelin-S used. Hydrogels that include Gelin-S will typically have longer gelation times than those made only with Glycosil®, or Heprasil®.
  2. Note: Gelin-S will not form a hydrogel when mixed with Extralink®.

Note: Hydrogels made using only Extralink® and Glycosil® or Heprasil® will not support cell attachment.

Product Q & A

Globular particles less than 75 kDa should be able to freely diffuse through a HyStem hydrogel.

When reconstituted using DG water, the pH of each HyStem component will be approximately 7.4-7.6.

One year from the date of receipt, if stored properly.

Any sterile, deionized, degassed water can be substituted for reconstitution. However, in order to ensure accurate and predictable dissolution and gelation times, our DG Water is highly recommended, as it is degassed, blanketed in argon, and has undergone validation testing with each HyStem component.

Gelin-S provides cellular attachment sites when incorporated in the hydrogel. Gelin-S is thiol-modified, denatured collagen I, derived from either bovine or porcine sources. Gelin-S is included in all HyStem-C and HyStem-HP kits.

Gelin-S has been thiol-modified in the same manner as the hyaluronan in Glycosil (or Heprasil), so that it covalently crosslinks with the Extralink in the HyStem hydrogels.

Yes. Peptides that contain a cysteine residue can be used. The cysteine residue must be present for the peptide to be covalently bonded to the hydrogel substrate.

Yes. ECM proteins, such as laminin, collagen, fibronectin, or vitronectin can be non-covalently incorporated into the hydrogel prior to crosslinking.

HyStem hydrogels and sponges differ in hydration and homogeneity. HyStem sponges are typically polymerized hydrogels that are subsequently freeze-dried. The resulting sponge is a fibrous, mesh network with pores and niches that enable cells to infiltrate and adhere. A true HyStem hydrogel is an encapsulating liquid that polymerizes around suspended cells in culture.

No. The compliance of the hydrogels is set by the amount of Extralink crosslinker added, the concentration of Glycosil (or Heprasil) and Gelin-S used, and the ratio of Glycosil (or Heprasil) to Gelin-S. Once this chemical structure of the hydrogel is fixed, it is not altered by prolonged exposure to cell culture medium.

HyStem sponges can be terminally sterilized by E-beam. HyStem hydrogels have not yet been validated for use with E-beam sterilization methods. HyStem hydrogels are not terminally sterilized by gamma irradiation.

Gelation time is affected by multiple aspects of the gel’s composition.

One way to change the gelation time of a hydrogel is to vary the amount of crosslinker used. Gels with a lower amount of Extralink crosslinker will have a longer gelation time than those with a higher amount of crosslinker. Changing the amount of crosslinker will produce slight changes in gelation time.

Gelation time can be dramatically changed by varying the Glycosil (or Heprasil) and Gelin-S concentrations. Concentrated solutions of Glycosil (or Heprasil) and Gelin-S will create a solution with a much shorter gelation time. This can easily be done by reconstituting the components in a smaller volume of DG Water. Alternatively, diluting these components in larger volumes of DG Water will dramatically increase the total time to form the hydrogel.

HyStem Hydrogels are virtually transparent and should not interfere with microscopy.

HyStem hydrogels may generate mild inflammation as part of the body’s natural healing process in response to injury. HyStem hydrogels do not trigger immune response when used in vivo. (These products are not for human use)

HyStem is degraded in vivo by matrix metalloproteinases (collagenases) and hyaluronidases.

Trypsin, Dipase, collagenase, and hyaluronidase have been used to help detach cells from the surface or from within HyStem hydrogels.

In general, the pore size for HyStem-C and HyStem-HP hydrogels is ~17 nm. 

Product Certificate of Analysis

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Safety and Documentation

Certificate of Origin

Safety Data Sheet

Product Disclaimer

This product is for R&D use only and is not intended for human or other uses. Please consult the Material Safety Data Sheet for information regarding hazards and safe handling practices.