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Hydrogels with dynamically tunable crosslinking are invaluable for directing stem cell fate and mimicking a stiffening matrix during fibrosis or tumor development. The increases in matrix stiffness during tissue development are often accompanied by the accumulation of extracellular matrices (e.g., collagen, hyaluronic acid (HA)), a phenomenon that has received little attention in the development of dynamic hydrogels. In this contribution, we present a gelatin-based cell-laden hydrogel system capable of being dynamically stiffened while accumulating HA, a key glycosaminoglycans (GAG) increasingly deposited by stromal cells during tumor progression. Central to this strategy is the synthesis of a dually-modified gelatin macromer – gelatin-norbornene-carbohydrazide (GelNB-CH), which is susceptible to both thiol-norbornene photopolymerization and hydrazone click chemistry. We demonstrate that the crosslinking density of cell-laden thiol-norbornene hydrogels can be dynamically tuned via simple incubation with aldehyde-bearing macromers (e.g., oxidized dextran (oDex) or oHA). The GelNB-CH hydrogel system is highly cytocompatible, as demonstrated by in situ encapsulation of pancreatic cancer cells (PCC) and cancer-associated fibroblasts (CAF). This unique dynamic stiffening scheme provides a platform to study tandem accumulation of HA and elevation in matrix stiffness in the pancreatic tumor microenvironment. Statement of significance Hydrogels permitting on-demand and secondary crosslinking are ideal for mimicking a stiffening tumor microenvironment (TME). However, none of the current dynamic hydrogels account for both stiffening and accumulation of hyaluronic acid (HA), a major extracellular matrix component increasingly deposited in tumor stromal tissues, including pancreatic ductal adenocarcinoma (PDAC). The current work addresses this gap by developing a dynamic hydrogel system capable of simultaneously increasing stiffness and HA accumulation. This is achieved by a new gelatin macromer permitting sequential thiol-norbornene (for primary network crosslinking) and hydrazone click chemistry (for bioinert or biomimetic stiffening with oxidized dextran (oDex) or oHA, respectively). The results of this study provide new insights into how dynamically changing physicochemical matrix properties guide cancer cell fate processes.

Hyperkalemia is a potentially life-threatening electrolyte abnormality in both children and adults. In the setting of elevated serum potassium concentrations, cardiac conduction disturbances and cardiac arrest may occur. In the pediatric intensive care unit (PICU) setting, the differential diagnosis of hyperkalemia may be extensive including increased potassium intake or administration, increased endogenous production, decreased renal excretion, and intracellular to extracellular shifts related to changes in acid-base status. We present a 4-month-old infant who developed hyperkalemia during the recovery phase of her PICU course for respiratory failure. A thorough investigation demonstrated that the hyperkalemia was most likely the result of the commonly used antibiotic, trimethoprim-sulfamethoxazole (Bactrim®). Potential etiologies of hyperkalemia in the PICU patient are discussed and previous reports of hyperkalemia associated with trimethoprim-sulfamethoxazole presented.

Xeno-free and chemically-defined poly(ethylene glycol) (PEG)-based hydrogels are increasingly used for in vitro culture and differentiation of induced pluripotent stem cells (iPSCs). These synthetic matrices provide highly tunable gelation kinetics and adaptable material properties that are crucial for guiding stem cell fate processes. In this work, we integrated sequential norbornene-click chemistries for forming synthetic and dynamically tunable PEG-peptide hydrogels to promote human iPSCs culture and differentiation. Specifically, iPSCs were photo-encapsulated in xeno-free thiol-norbornene hydrogels crosslinked by multi-arm PEG-norbornene (PEG-NB) and protease-labile peptide crosslinkers. These matrices were used to evaluate growth of iPSCs under the influence of matrix degradability, adhesion ligands, cell density, and ROCK inhibition. We further employed tetrazine-norbornene (Tz-NB) inverse electron demand Diels-Alder (iEDDA) reaction to dynamically stiffen these cell-laden hydrogels. Fast reactive Tz and its more stable derivative methyltetrazine (mTz) were tethered to multi-arm PEG, yielding mono-functionalized PEG-Tz and PEG-mTz, as well as dual-functionalized PEG-Tz/mTz that readily reacted with PEG-NB to form additional crosslinks in the cell-laden hydrogels. The versatility of this stiffening approach was demonstrated with different Tz-modified macromers (e.g., hyaluronic acid-Tz and heparin-Tz) or by intermittent incubation of PEG-Tz for temporally regulated stiffening. Finally, the Tz-NB-mediated dynamic stiffening was explored for 4D culture and definitive endoderm differentiation of human iPSCs. Overall, this dynamic hydrogel platform affords exquisite controls of hydrogel crosslinking for serving as a xeno-free and dynamic stem cell niche.