Spatiotemporal Modification of Stimuli-Responsive Hyaluronic Acid/Poly(N-isopropylacrylamide) Hydrogels

Abstract

Current methods to spatiotemporally modify stimuli response in hydrogels are typically subtractive and lead to a decrease in response. To increase the breadth of hydrogel applications and biomedical systems, new formulations are needed that can introduce and increase stimuli response spatiotemporally in hydrogels. In this work, the light induced thiol-norbornene click chemistry reaction was used to modify the stimuli response of robust hyaluronic acid hydrogels through an additive process in spatiotemporal fashion, overcoming this limitation. These stimuli responsive hydrogels were made from norbornene functionalized hyaluronic acid (NorHA) crosslinked with thermo-responsive dithiol-terminated poly(N-isopropylacrylamide) (DTPN).Varying crosslinker molecular weight and gelation conditions led to a range of compression modulus (5 to 54 kPa) and mass loss (9 to 33%) upon heating to 37 °C while retaining a majority NorHA in the hydrogel. The thermo-response of these hydrogels could not only be controlled by the crosslink density, but also by heating to 55 °C to increase the dewatering of the hydrogels.The stimuli response of the hydrogels were temporally increased by introducing additional DTPN and UV-initiator to an original hydrogel with subsequent irradiation. This modification was extended to spatiotemporally changing the stimuli response by photopatterning DTPN into a NorHA hydrogel, yielding a hydrogel that changed shape and topology through heating.Furthermore, human mesenchymal stem cells could adhere and proliferate on the DTPN patterned surface, demonstrating that the materials could be used for studies where cells are present.

Synthesis and Spatiotemporal Modification of Biocompatible and Stimuli‐Responsive Carboxymethyl Cellulose Hydrogels Using Thiol‐Norbornene Chemistry

“…To measure the thermoresponse, the percentage of hydrogel mass (water) lost upon heating relative to 4 °C (ML) was measured at 37 and 55 °C for the two formulations (Figure b). ML values at 37 °C for T/NB of 0.2 and 0.5 were 10.8% and 39.6%, respectively, and significantly different (α = 0.05), confirming that DTPN content can control the thermoresponse in NorCMC in a manner similar to previous work with a norbornene‐functionalized hyaluronic acid …”

“…Furthermore, the properties of cross‐linker (stimuli responsiveness, enzymatic degradation, reactivity, etc.) can be imparted to the hydrogel by this cross‐linking process . In general, any molecule with at least two thiol groups could potentially be used to cross‐link NorCMC.…”

“…Subsequently, hydrogels were incubated at either 4, 37, or 55 °C in PBS for 24 h and massed after each temperature cycle ( W measured ) as described in ref. . The relative mass loss (ML) was calculated as defined in Equation …”

“…Photo‐cross‐linking through the radically induced thiol‐ene reaction has been an effective, fast, orthogonal, and biologically safe process to fabricate robust hydrogels from a variety of precursors . However, using the thiol‐ene reaction to create CMC hydrogels has not been extensively studied with only a few example of norbornene‐functionalized PEG reacting with a thiol‐functionalized CMC .…”

“…Moreover, modifications to stimuli response, molecule presentation, and physical properties should be possible in a spatiotemporal manner to mimic the dynamic nature of living systems . Previous work has demonstrated that photopatterning with the thiol‐norbornene reaction can spatiotemporally modify the stimuli response of hydrogels . For CMC hydrogels, similar reactions and processes should yield hydrogels that can address the complex and varied challenges for biomaterials.…”