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Recyclable Organocatalyzed Poly(Thiourethane) Covalent Adaptable Networks.

ABSTRACT: A new type of tetraphenylborate salts derived from highly basic and nucleophilic amines, namely 1,5-diazabicyclo[4.3.0]non-5-ene (DBN), 1,8-diazabicyclo(5.4.0)undec-7-ene (DBU) and triazabicyclodecene (TBD), was applied to the preparation of networked poly(thiourethane)s (PTUs), which showed a vitrimer-like behavior, with higher stress-relaxation rates than PTUs prepared by using dibutyl thin dilaurate (DBTDL) as the catalyst. The use of these salts, which release the amines when heated, instead of the pure amines, allows the formulation to be easily manipulated to prepare any type of samples. The materials prepared from stoichiometric mixtures of hexamethylene diisocyanate (HDI), trithiol (S3) and with a 10% of molar excess of isocyanate or thiol were characterized by FTIR, thermomechanical analysis, thermogravimetry, stress-relaxation tests and tensile tests, thus obtaining a complete thermal and mechanical characterization of the materials. The recycled materials obtained by grinding the original PTUs and hot-pressing the small pieces in the optimized time and temperature conditions were fully characterized by mechanical, thermomechanical and FTIR studies. This allowed us to confirm their recyclability, without appreciable changes in the network structure and performance. From several observations, the dissociative interchange trans-thiocarbamoylation mechanism was evidenced as the main responsible of the topological rearrangements at high temperature, resulting in a vitrimeric-like behavior.

SUBMITTER: Gamardella F

PROVIDER: S-EPMC7761908 | biostudies-literature | 2020 Dec

REPOSITORIES: biostudies-literature

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Recyclable Organocatalyzed Poly(Thiourethane) Covalent Adaptable Networks.

Gamardella Francesco F Muñoz Sara S De la Flor Silvia S Ramis Xavier X Serra Angels A

Polymers 20201204 12

A new type of tetraphenylborate salts derived from highly basic and nucleophilic amines, namely 1,5-diazabicyclo[4.3.0]non-5-ene (DBN), 1,8-diazabicyclo(5.4.0)undec-7-ene (DBU) and triazabicyclodecene (TBD), was applied to the preparation of networked poly(thiourethane)s (PTUs), which showed a vitrimer-like behavior, with higher stress-relaxation rates than PTUs prepared by using dibutyl thin dilaurate (DBTDL) as the catalyst. The use of these salts, which release the amines when heated, instead ...[more]

PMID: 33291704

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Project description:Cartilage tissue engineering strategies often rely on hydrogels with fixed covalent crosslinks for chondrocyte encapsulation, yet the resulting material properties are largely elastic and can impede matrix deposition. To address this limitation, hydrazone crosslinked poly(ethylene glycol) hydrogels were formulated to achieve tunable viscoelastic properties and to study how chondrocyte proliferation and matrix deposition vary with the time-dependent material properties of covalent adaptable networks. Hydrazone equilibrium differences were leveraged to produce average stress relaxation times from hours (4.01 × 103 s) to months (2.78 × 106 s) by varying the percentage of alkyl-hydrazone (aHz) and benzyl-hydrazone (bHz) crosslinks. Swelling behavior and degradation associated with adaptability were characterized to quantify temporal network changes that can influence the behavior of encapsulated chondrocytes. After four weeks, mass swelling ratios varied from 36 ± 3 to 17 ± 0.4 and polymer retention ranged from 46 ± 4% to 92 ± 5%, with higher aHz content leading to loss of network connectivity with time. Hydrogels were formulated near the Flory-Stockmayer bHz percolation threshold (17% bHz) to investigate chondrocyte response to distinct levels of covalent architecture adaptability. Four weeks post-encapsulation, formulations with average relaxation times of 3 days (2.6 × 105s) revealed increased cellularity and an interconnected articular cartilage-specific matrix. Chondrocytes embedded in this adaptable formulation (22% bHz) deposited 190 ± 30% more collagen and 140 ± 20% more sulfated glycosaminoglycans compared to the 100% bHz control, which constrained matrix deposition to pericellular space. Collectively, these findings indicate that incorporating highly adaptable aHz crosslinks enhanced regenerative outcomes. However, connected networks containing more stable bHz bonds were required to achieve the highest quality neocartilaginous tissue. STATEMENT OF SIGNIFICANCE: Covalently crosslinked hydrogels provide robust mechanical support for cartilage tissue engineering applications in articulating joints. However, these materials traditionally demonstrate purely elastic responses to deformation despite the dynamic viscoelastic properties of native cartilage tissue. Here, we present hydrazone poly(ethylene glycol) hydrogels with tunable viscoelastic properties and study covalent adaptable networks for cartilage tissue engineering. Using hydrazone equilibrium and Flory-Stockmayer theory we identified average relaxation times leading to enhanced regenerative outcomes and showed that extracellular matrix deposition was biphasic as a function of the hydrazone covalent adaptability. We also showed that the incorporation of highly adaptable covalent crosslinks could improve cellularity of neotissue, but that a percolating network of more stable bonds was required to maintain scaffold integrity and form the highest quality neocartilaginous tissue.

Dataset Information

Recyclable Organocatalyzed Poly(Thiourethane) Covalent Adaptable Networks.

Publications

Recyclable Organocatalyzed Poly(Thiourethane) Covalent Adaptable Networks.

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