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Phototunable Viscoelasticity in Hydrogels Through Thioester Exchange

  • Biomaterials - Engineering Cell Behavior
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Abstract

Mechanical cues are delivered to resident cells by the extracellular matrix and play an important role in directing cell processes, ranging from embryonic development and cancer metastasis to stem cell differentiation. Recently, cellular responses to viscoelastic and elastic mechanical cues have been studied; however, questions remain as to how cells identify and transduce these cues differently. We present a synthetic cell culture substrate with viscoelastic properties based on thioester exchange chemistry that can be modulated in situ with the photoinitiated thiol-ene ‘click’ reaction. With this method, stress relaxation in thioester hydrogels with an average relaxation time of 740,000 s can be switched off in the presence of cells without change to the elastic modulus. NIH 3T3 fibroblasts, cultured for 48 h on viscoelastic compared to elastic thioester substrates, displayed increased cell area (660–560 μm2) and increased nuclear to cytoplasmic YAP/TAZ ratios (2.4 to 2.2) when cultured on elastic compared to viscoelastic hydrogels, respectively. Next, when the viscoelasticity was switched off after 24 h, the fibroblasts responded to this change and exhibited an average cell area of 540 μm2, and nuclear to cytoplasmic YAP/TAZ ratio of 2.1, approaching that of the control elastic gels. Phototunable viscoelastic thioester hydrogels provide a tunable materials system to investigate time-dependent cellular responses to viscoelasticity and should prove useful for understanding the dynamics of mechanoresponsive cellular pathways.

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Abbreviations

ECM:

Extracellular matrix

hMSC:

Human mesenchymal stem cell

YAP:

Yes-associated protein

TAZ:

Transcriptional co-activator with PDZ binding motif

DMEM:

Dulbecco’s modified Eagle’s media

NB COOH:

5-Norbornene-2-carboxylic acid (Norbornene COOH)

PBS:

Phosphate buffered saline

FBS:

Fetal bovine serum

kDa:

Kilodalton

PEG:

Poly(ethylene glycol)

TENB:

Thioester Norbornene

LAP:

Phenyl-2,4,6-trimethylbenzoylphosphinate

PFA:

Paraformaldehyde

BSA:

Bovine serum albumin

HATU:

N-[(Dimethylamino)-1H-1,2,3-triazolo-[4,5-b]pyridin-1-ylmethylene]-N-methylmethanaminium hexafluorophosphate N-oxide

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Acknowledgments

This work was supported by a grant from the National Institutes of Health (DE016523), and BJC also gratefully acknowledges support via a GAANN fellowship from the Department of Education. The authors would also like to gratefully acknowledge Dr. Kemal Arda Günay and Francis Yavitt for thoughtful conversation and critical reviews in the preparation of this manuscript. The authors do not have any conflicts of interest to declare.

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Correspondence to Kristi S. Anseth.

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Carberry, B.J., Rao, V.V. & Anseth, K.S. Phototunable Viscoelasticity in Hydrogels Through Thioester Exchange. Ann Biomed Eng 48, 2053–2063 (2020). https://doi.org/10.1007/s10439-020-02460-w

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  • DOI: https://doi.org/10.1007/s10439-020-02460-w

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