Browsing by Author "Dimmitt, Nathan H."

Now showing 1 - 4 of 4
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    Dynamic Click Hydrogels for Xeno-Free Culture of Induced Pluripotent Stem Cells
    (Wiley, 2020-11) Arkenberg, Matthew R.; Dimmitt, Nathan H.; Johnson, Hunter C.; Koehler, Karl R.; Lin, Chien-Chi; Biomedical Engineering, School of Engineering and Technology
    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.
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    Hydrolytically Degradable PEG-Based Inverse Electron Demand Diels-Alder Click Hydrogels
    (American Chemical Society, 2022) Dimmitt, Nathan H.; Arkenberg, Matthew R.; de Lima Perini, Mariana Moraes; Li, Jiliang; Lin, Chien-Chi; Biomedical Engineering, School of Engineering and Technology
    Hydrogels cross-linked by inverse electron demand Diels-Alder (iEDDA) click chemistry are increasingly used in biomedical applications. With a few exceptions in naturally derived and chemically modified macromers, iEDDA click hydrogels exhibit long-term hydrolytic stability, and no synthetic iEDDA click hydrogels can undergo accelerated and tunable hydrolytic degradation. We have previously reported a novel method for synthesizing norbornene (NB)-functionalized multiarm poly(ethylene glycol) (PEG), where carbic anhydride (CA) was used to replace 5-norbornene-2-carboxylic acid. The new PEGNBCA-based thiol-norbornene hydrogels exhibited unexpected fast yet highly tunable hydrolytic degradation. In this contribution, we leveraged the new PEGNBCA macromer for forming iEDDA click hydrogels with [methyl]tetrazine ([m]Tz)-modified macromers, leading to the first group of synthetic iEDDA click hydrogels with highly tunable hydrolytic degradation kinetics. We further exploited Tz and mTz dual conjugation to achieve tunable hydrolytic degradation with an in vitro degradation time ranging from 2 weeks to 3 months. Finally, we demonstrated the excellent in vitro cytocompatibility and in vivo biocompatibility of the new injectable PEGNBCA-based iEDDA click cross-linked hydrogels.
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    Injectable Acylhydrazone-Linked RAFT Polymer Hydrogels for Sustained Protein Release and Cell Encapsulation
    (Wiley, 2022) Lin, Fang-Yi; Dimmitt, Nathan H.; Moraes de Lima Perini, Mariana; Li, Jiliang; Lin, Chien-Chi; Biomedical Engineering, School of Engineering and Technology
    A new class of temperature responsive polymer, termed PADO, is synthesized by reversible addition-fragmentation chain-transfer (RAFT) polymerization. Synthesized from copolymerization of diacetone acrylamide (DAAM), di(ethylene glycol) ethyl ether acrylate (DEGA), and oligo(ethylene glycol) methyl ether acrylate (OEGA), PADO polymer phase separates at temperature above its LCST (36°C to 42°C) due to enhanced hydrophobic interactions between the short ethylene glycol side chains. Solution of PADO polymers exhibited injectable shear-thinning properties and reached sol-gel transition rapidly (< 5 min) at 37°C. When the ketone moieties on DAAM were linked by adipic acid dihydrazdie (ADH), PADO polymers formed crosslinked and injectable acylhydrazone hydrogels, which were hydrolytically degradable at a mild acidic environment owing to the pH sensitive acylhydrazone bonds. The pH-responsive degradation kinetics could be controlled by tuning polymer contents and ketone/hydrazide ratio. Importantly, the injectable PADO hydrogels were highly cytocompatible and could be easily formulated for pH-responsive sustained protein delivery.
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    Osteosarcoma-enriched transcripts paradoxically generate osteosarcoma-suppressing extracellular proteins
    (eLife Sciences, 2023-03-21) Li, Kexin; Huo, Qingji; Dimmitt, Nathan H.; Qu, Guofan; Bao, Junjie; Pandya, Pankita H.; Saadatzadeh, M. Reza; Bijangi-Vishehsaraei, Khadijeh; Kacena, Melissa A.; Pollok, Karen E.; Lin, Chien-Chi; Li, Bai-Yan; Yokota, Hiroki; Biomedical Engineering, School of Engineering and Technology
    Osteosarcoma (OS) is the common primary bone cancer that affects mostly children and young adults. To augment the standard-of-care chemotherapy, we examined the possibility of protein-based therapy using mesenchymal stem cells (MSCs)-derived proteomes and OS-elevated proteins. While a conditioned medium (CM), collected from MSCs, did not present tumor-suppressing ability, the activation of PKA converted MSCs into induced tumor-suppressing cells (iTSCs). In a mouse model, the direct and hydrogel-assisted administration of CM inhibited tumor-induced bone destruction, and its effect was additive with cisplatin. CM was enriched with proteins such as calreticulin, which acted as an extracellular tumor suppressor by interacting with CD47. Notably, the level of CALR transcripts was elevated in OS tissues, together with other tumor-suppressing proteins, including histone H4, and PCOLCE. PCOLCE acted as an extracellular tumor-suppressing protein by interacting with amyloid precursor protein, a prognostic OS marker with poor survival. The results supported the possibility of employing a paradoxical strategy of utilizing OS transcriptomes for the treatment of OS.