skip to main content


Title: Orthogonal click reactions enable the synthesis of ECM-mimetic PEG hydrogels without multi-arm precursors
Click chemistry reactions have become an important tool for synthesizing user-defined hydrogels consisting of poly(ethylene glycol) (PEG) and bioactive peptides for tissue engineering. However, because click crosslinking proceeds via a step-growth mechanism, multi-arm telechelic precursors are required, which has some disadvantages. Here, we report for the first time that this requirement can be circumvented to create PEG–peptide hydrogels solely from linear precursors through the use of two orthogonal click reactions, the thiol–maleimide Michael addition and thiol–norbornene click reaction. The rapid kinetics of both click reactions allowed for quick formation of norbornene-functionalized PEG–peptide block copolymers via Michael addition, which were subsequently photocrosslinked into hydrogels with a dithiol linker. Characterization and in vitro testing demonstrated that the hydrogels have highly tunable physicochemical properties and excellent cytocompatibility. In addition, stoichiometric control over the crosslinking reaction can be leveraged to leave unreacted norbornene groups in the hydrogel for subsequent hydrogel functionalization via bioorthogonal inverse-electron demand Diels–Alder click reactions with s -tetrazines. After selectively capping norbornene groups in a user-defined region with cysteine, this feature was leveraged for protein patterning. Collectively, these results demonstrate that our novel chemical strategy is a simple and versatile approach to the development of hydrogels for tissue engineering that could be useful for a variety of applications.  more » « less
Award ID(s):
1634858
NSF-PAR ID:
10101529
Author(s) / Creator(s):
; ; ;
Date Published:
Journal Name:
Journal of Materials Chemistry B
Volume:
6
Issue:
30
ISSN:
2050-750X
Page Range / eLocation ID:
4929 to 4936
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. Abstract

    Xeno‐free, chemically defined poly(ethylene glycol) (PEG)‐based hydrogels are being increasingly used for in vitro culture and differentiation of human induced pluripotent stem cells (hiPSCs). These synthetic matrices provide tunable gelation and adaptable material properties crucial for guiding stem cell fate. Here, sequential norbornene‐click chemistries are integrated to form synthetic, dynamically tunable PEG–peptide hydrogels for hiPSCs culture and differentiation. Specifically, hiPSCs are photoencapsulated in thiol–norbornene hydrogels crosslinked by multiarm PEG–norbornene (PEG–NB) and proteaselabile crosslinkers. These matrices are used to evaluate hiPSC growth under the influence of extracellular matrix properties. Tetrazine–norbornene (Tz–NB) click reaction is then employed to dynamically stiffen the cell‐laden hydrogels. Fast reactive Tz and its stable derivative methyltetrazine (mTz) are tethered to multiarm PEG, yielding mono‐functionalized PEG‐Tz, PEG‐mTz, and dualfunctionalized PEG‐Tz/mTz that react with PEG–NB to form additional crosslinks in the cell‐laden hydrogels. The versatility of Tz‐NB stiffening is demonstrated with different Tz‐modified macromers or by intermittent incubation of PEG‐Tz for temporal stiffening. Finally, the Tz–NB‐mediated dynamic stiffening is explored for 4D culture and definitive endoderm differentiation of hiPSCs. Overall, this dynamic hydrogel platform affords exquisite controls of hydrogel crosslinking for serving as a xeno‐free and dynamic stem cell niche.

     
    more » « less
  2. Abstract

    Electrospinning has been used to create scaffolds with tunable micro/nano architecture, stiffness, and porosity to mimic native extracellular matrix. This study investigated the effects of electrospinning parameters and hydrogel formulation (solvent and crosslinker type) on the architecture and properties of fibrous poly(ethylene glycol) (PEG) hydrogels formed from a photoclick thiol‐norbornene reaction. Fibrous hydrogels were prepared using hydrogel precursors (four‐arm PEG norbornene and multi‐thiol crosslinker), sacrificial poly(ethylene oxide) (PEO, 400 kDa), and photoinitiator (I2959) in either 2,2‐triflouroethanol (TFE) or water. Three thiol crosslinkers‐ 2,2′‐(ethylenedioxy)diethanethiol (EDT), pentaerythritol tetrakis(3mercaptopropionate) (PTMP), and PEG dithiol (PEGDT)‐ were investigated. Fibrous PEG networks with uniform fibers were produced at applied voltages of 10 or 12 kV for TFE and 16 kV for water. Fiber diameters of electrospun hydrogels were largely affected by the solvent when combined with PEO concentration and ranged from 0.5 to 3.5 mm in dry state. While the effect of crosslinker type on fiber diameter, morphology, and porosity of the fibrous hydrogel was minimal, it did modulate its shear modulus. To this end, this study provides the groundwork for selecting processing parameters to achieve desired properties of fibrous PEG thiol‐norbornene hydrogels for intended tissue engineering applications ranging from neural, cardiovascular to musculoskeletal.

     
    more » « less
  3. Abstract

    Hydrogels are promising scaffolds for adipose tissue regeneration. Currently, the incorporation of bioactive molecules in hydrogel system is used, which can increase the cell proliferation rate or improve adipogenic differentiation performance of stromal stem cells but often suffers from high expense or cytotoxicity because of light/thermal curing used for polymerization. In this study, decellularized adipose tissue is incorporated, at varying concentrations, with a thiol‐acrylate fraction that is then polymerized to produce hydrogels via a Michael addition reaction. The results reveal that the major component of isolated adipose‐derived extracellular matrix (ECM) is Collagen I. Mechanical properties of ECM polyethylene glycol (PEG) are not negatively affected by the incorporation of ECM. Additionally, human adipose‐derived stem cells (hASCs) are encapsulated in ECM PEG hydrogel with ECM concentrations varying from 0% to 1%. The results indicate that hASCs maintained the highest viability and proliferation rate in 1% ECM PEG hydrogel with most lipids formation when cultured in adipogenic conditions. Furthermore, more adipose regeneration is observed in 1% ECM group with in vivo study by Day 14 compared to other ECM PEG hydrogels with lower ECM content. Taken together, these findings suggest the ECM PEG hydrogel is a promising substitute for adipose tissue regeneration applications.

     
    more » « less
  4. null (Ed.)
    The fabrication of hydrogel materials has gained increased attention for a broad range of biomedical and biotechnological applications. However, one longstanding challenge in the field is to develop hydrogels that can be easily processed into the desired form factor, while achieving the necessary final physical and biochemical properties. Herein, we report a shear-thinning hydrogel ink that can be photo-cured to create a stretchable, suturable hydrogel whose polymer network is formed via the combination of thiol-Michael addition and radical polymerization. A shear-thinning hydrogel based on bis-methacrylated Pluronic® F-127 was modified with varying equivalents of 2,2′-(ethylenedioxy)diethanethiol (EDT) as an additive. We observed that aging the hydrogel over time prior to extrusion allowed the relatively slow thiol-Michael addition to occur (between thiol and methacrylate) prior to UV initiated photopolymerization of the methacrylates. The viscoelastic properties of these hydrogels could be tuned based on the amount of EDT added, and the aging time of the hydrogel formulation. The changes to the physical properties of the hydrogels were attributed to the increased chain length between network junctions that resulted from the thiol-Michael addition reactions. The optimized hydrogel composition was then extruded from a coaxial nozzle to produce hydrogel tubes that, after curing, were resistant to tearing and were suturable. These extrudable synthetic hydrogels with tunable viscoelastic properties are promising for tissue engineering applications and as surgical training models for human vasculature. 
    more » « less
  5. Three-dimensional (3D) bioprinting is important in the development of complex tissue structures for tissue engineering and regenerative medicine. However, the materials used for bioprinting, referred to as bioinks, must have a balance between a high viscosity for rapid solidification after extrusion and low shear force for cytocompatibility, which is difficult to achieve. Here, a novel bioink consisting of poly(ethylene glycol) (PEG) microgels prepared via off-stoichiometry thiol–ene click chemistry is introduced. Importantly, the microgel bioink is easily extruded, exhibits excellent stability after printing due to interparticle adhesion forces, and can be photochemically annealed with a second thiol–ene click reaction to confer long-term stability to printed constructs. The modularity of the bioink is also an advantage, as the PEG microgels have highly tunable physicochemical properties. The low force required for extrusion and cytocompatibility of the thiol–ene annealing reaction also permit cell incorporation during printing with high viability, and cells are able to spread and proliferate in the interstitial spaces between the microgels after the constructs have been annealed. Overall, these results indicate that our microgel bioink is a promising and versatile platform that could be leveraged for bioprinting and regenerative manufacturing. 
    more » « less