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. Author manuscript; available in PMC: 2017 Apr 1.
Published in final edited form as: Acta Biomater. 2015 Oct 20;34:60–72. doi: 10.1016/j.actbio.2015.10.030

Fig. 8.

Fig. 8

Molecules included in PEG hydrogels. (a) The hydrogels are composed of (i) 8-arm PEG molecules, with each arm functionalized with a norbornene molecule; (ii) Di-thiolated PEG crosslinking molecules bridge multiple 8-arm PEG molecules together into an ordered polymer network. A di-thiolated PEG molecule acts as an inert crosslinking molecule that is not cell-degradable; (iii) In bioactive hydrogels, PEG molecules are decorated with CRGDS adhesion peptide or CRDGS scrambled peptide to modulate cell adhesion to the hydrogel; (iv) Di-thiolated matrix metalloproteinase (MMP) labile crosslinking peptides enable cell-driven hydrogel degradation. (b) “Background” hydrogels are void of cell adhesion molecules and are not subject to cell-driven degradation (top). “Hydrogel spots” modulate cell behavior through covalently attached adhesion molecules and are biodegradable via MMP activity (bottom). (c) Schematic representation of hydrogel array fabrication. (1) Separate hydrogel spot solutions containing various ratios of CRGDS adhesion peptide (red circles) and a scrambled CRDGS non-functional peptide (blue circles) are pipetted into wells of a PDMS stencil. Total pendant peptide concentration is fixed at 2 mM in all solutions. (2) The hydrogel spots are crosslinked in the stencil using UV light. (3) A crosslinked 1-mm thick “background” hydrogel slab is laid on top of the crosslinked bioactive hydrogel spots. A thin layer of background hydrogel solution is added to the slab to anchor the cured spots to the background. (4) The hydrogel spots are anchored to the background after treatment with UV light. (5) The completed hydrogel array is removed from the stencil. Red boxes highlight the raised spots in the schematic and side view images of the arrays. (Figure from Ref. [56] with permission.). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)