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Mammalian cell morphology has been linked to the viscoelastic properties of the adhesion substrate, which is particularly relevant in biological processes such as wound repair and embryonic development where cell spreading and migration are critical. Plastic deformation, degradation, and relaxation of stress are typically coupled in biomaterial systems used to explore these effects, making it unclear which variable drives cell behavior. Here we present a nondegradable polymer architecture that specifically decouples irreversible creep from stress relaxation and modulus. We demonstrate that network plasticity independently controls mesenchymal stem cell spreading through a biphasic relationship dependent on cell-intrinsic forces, and this relationship can be shifted by inhibiting actomyosin contractility. Kinetic Monte Carlo simulations also show strong correlation with experimental cell spreading data as a function of the extracellular matrix (ECM) plasticity. Furthermore, plasticity regulates many ECM adhesion and remodeling genes. Altogether, these findings confirm a key role for matrix plasticity in stem cell biophysics, and we anticipate this will have ramifications in the design of biomaterials to enhance therapeutic applications of stem cells.

Myelofibrosis (MF) is a progressive, myeloid malignancy characterized by deposition of collagen and reticulin fibers in the bone marrow (BM). Previous studies have shown that monocytosis is associated with poor prognosis in MF, highlighting a potential pathogenic role for monocytes in MF. Although many studies have addressed the role of cell-intrinsic and soluble extracellular factors in MF development, it is currently unknown if mechanical properties of fibrotic BM contribute to aberrant differentiation of myeloid cells and of monocytes in particular. We first defined the stiffness and viscoelastic properties of healthy and fibrotic BM. Stiffness is defined as the resistance of a matrix to deformation, while viscoelasticity is the rate of dissipation of an applied stress over time. Independent of stiffness, an applied stress relaxes rapidly in a more viscous, liquid-like matrix, whereas in a more elastic, solid-like material, stress relaxes slowly. We next generated a cohort of fibrotic and non-fibrotic mice by transplanting retrovirally transduced JAK2V617F or empty vector (EV) control hematopoietic stem and progenitor cells (HSPCs) into lethally irradiated recipients. Femurs from these mice were harvested seven months post-transplant, as well as from age- and sex-matched healthy primary mice. Nanoindentation was performed to measure BM stiffness and viscoelasticity. Fibrotic BM showed higher stiffness, as well as trending higher elastic, solid-like properties, compared to BM of control mice. We then aimed to study the effect of matrix stiffness and viscoelasticity on monocytes. Human BM-derived monocytes were encapsulated in stiff, viscous or stiff, elastic hydrogels and cultured in the presence of GM-CSF, IL-4, and PGE2 for 3 days, followed by nanoString and flow cytometry analyses. Cells in elastic gels upregulated gene sets associated with co-stimulatory molecules and cytokine receptor signaling, MHC class II antigen presentation, and regulation of extracellular matrix (ECM), compared to cells in viscous gels of the same stiffness. The fraction of dendritic cells (DCs) was significantly upregulated, as indicated by double-positive CD11c+CD1c+ (40.9% viscous vs 69.5% elastic of CD11b+HLA-DR+ cells) and CD80+ cells (20.9% viscous vs 62.7% elastic of CD11b+HLA-DR+ cells), and surface expression of HLA-DR (gMFI 2587 viscous vs 6334 elastic). Consistent with these findings, the fraction of pro-fibrotic SLAMF7+ cells (4.2% viscous vs 17.3% elastic) were also significantly higher in elastic gels. Together, these data suggest that stiff, elastic ECM drives pro-inflammatory polarization and differentiation of monocytes into antigen-presenting cells. Next, we examined the role of the cytoskeleton on human monocyte differentiation. Cortical F-actin was significantly upregulated in cells in stiff, elastic gels compared to viscous gels. Cells were exposed to a highly selective small molecular inhibitor of the γ-isoform of PI3K. Treatment with the PI3Ky inhibitor significantly reduced F-actin staining of cells in elastic gels, upregulated immature monocyte markers, reduced surface expression of HLA-DR, and downregulated the cytokines IL6, IL8, CCL4, which have previously been associated with disease progression in myelofibrosis. In line with the above human ex vivo data, BM isolated from fibrotic mice (described above) showed skewing towards Ly6G-Ly6C+ monocytes (a population enriched for inflammatory monocytes) within the CD11b myeloid compartment compared to control transplanted mice or to non-fibrotic mice that were transplanted with endogenously expressing Jak2V617F cells. Additionally, the percentage of conventional DCs (cDCs) was increased in fibrotic Jak2V617F mice compared to control mice. Importantly, 16 day in vivo treatment with the PI3Ky inhibitor significantly reduced the fraction of Ly6G-Ly6C+ monocytes within the CD11b compartment as well as the fraction of cDCs, compared to vehicle-treated Jak2V617F mice. In summary, fibrotic BM is stiffer and more elastic than normal BM. Our studies show that a stiff, elastic BM environment drives monocytes towards a more pro-inflammatory state which can in part be suppressed by PI3K-γ inhibition. Our results have relevance for human MF by demonstrating that a fibrotic BM niche is not just a consequence of chronic inflammation but is also inflammation-promoting. KHV and AEM contributed equally to this work. Disclosures Pozdnyakova: Scopio Labs: Consultancy. Mullally: Janssen, PharmaEssentia, Constellation and Relay Therapeutics: Consultancy. Wucherpfennig: Novartis: Research Funding; Nextechinvest: Membership on an entity's Board of Directors or advisory committees; Immunitas Therapeutics: Current holder of individual stocks in a privately-held company; TScan Therapeutics: Membership on an entity's Board of Directors or advisory committees; TCR2 Therapeutics: Membership on an entity's Board of Directors or advisory committees; SQZ Biotech: Membership on an entity's Board of Directors or advisory committees. Mooney: Novartis: Patents & Royalties: Licensed IP, Research Funding; Sirenex: Patents & Royalties: Licensed IP; Samyang Corp: Membership on an entity's Board of Directors or advisory committees; IVIVA: Membership on an entity's Board of Directors or advisory committees; Attivare: Current holder of individual stocks in a privately-held company, Membership on an entity's Board of Directors or advisory committees; Revela: Membership on an entity's Board of Directors or advisory committees; Amend Surgical: Patents & Royalties: Licensed IP; Lyell: Current equity holder in publicly-traded company, Patents & Royalties.

The majority of current pH-triggered release systems is designed to respond to either low or high pH. Encapsulants based on polyampholytes are an example of materials that can respond to both acidic and basic pH. However, polyampholyte-based encapsulants generally possess a low loading capacity and have difficulty retaining their small-molecule cargo. The current work utilizes interfacial polymerization between polyamines and a pyromellitic diester diacid chloride to form high capacity "liquid core-shell" polyamide microcapsules that are stable in a dry or nonpolar environment but undergo steady, controlled release at pH 7.4 and accelerated release at pH 5 and pH 10. The rate of release can be tuned by adjusting the amine cross-linker feed ratio, which varies the degree of cross-linking in the polymer shell. The thin-shell microcapsule exhibited suitable barrier properties and tunable dual acid/base-triggered release, with applications in a wide range of pH environments.

Wound infections cause inflammation, tissue damage, and delayed healing that can lead to invasive infection and even death. The efficacy of systemic antibiotics is limited due to poor tissue penetration that is especially a problem in burn and blast wounds where the microcirculation is disrupted. Topical administration of antimicrobials is an attractive approach because it prevents infection and avoids systemic toxicity, while hydrogels are an appealing vehicle for topical drug delivery. They are easy to apply to the wound site by being injectable, the drug release properties can be controlled, and their many characteristics, such as biodegradation, mechanical strength, and chemical and biological response to stimuli can be tailored. Hydrogels also create a moist wound environment that is beneficial for healing. The purpose of this study was to formulate an agarose hydrogel that contains high concentrations of minocycline or gentamicin and study its characteristics. Subsequently, the minocycline agarose hydrogel was tested in a porcine burn model and its effect as a prophylactic treatment was studied. The results demonstrated that 0.5% agarose in water was the optimal concentration in terms of viscosity and pH. Bench testing at room temperature demonstrated that both antibiotics remained stable in the hydrogel for at least 7 days and both antibiotics demonstrated sustained release over the time of the experiment. The porcine burn experiment showed that prophylactic treatment with the agarose minocycline hydrogel decreased the burn depth and reduced the number of bacteria as efficiently as the commonly used silver sulfadiazine cream.

Versatile and readily available battery materials compatible with a range of electrode configurations and cell designs are desirable for renewable energy storage. Here we report a promising class of materials based on redox active colloids (RACs) that are inherently modular in their design and overcome challenges faced by small-molecule organic materials for battery applications, such as crossover and chemical/morphological stability. RACs are cross-linked polymer spheres, synthesized with uniform diameters between 80 and 800 nm, and exhibit reversible redox activity as single particles, as monolayer films, and in the form of flowable dispersions. Viologen-based RACs display reversible cycling, accessing up to 99% of their capacity and 99 ± 1% Coulombic efficiency over 50 cycles by bulk electrolysis owing to efficient, long-distance intraparticle charge transfer. Ferrocene-based RACs paired with viologen-based RACs cycled efficiently in a nonaqueous redox flow battery employing a simple size-selective separator, thus demonstrating a possible application that benefits from their colloidal dimensions. The unprecedented versatility in RAC synthetic and electrochemical design opens new avenues for energy storage.

We recently reported cationic cyclopolymerization of o-vinylbenzaldehydes initiated by boron trifluoride to generate acid-sensitive poly(o-(α-alkyl)vinylbenzaldehyde). Herein we report preparation of core–shell microcapsules (μCs) using flow-focusing microfluidic techniques with shells composed of poly(o-(α-methyl)vinylbenzaldehyde) (PMVB) that release their payload in response to dilute aqueous acid solution. Release profiles of encapsulated fluorescein isothiocyanate-labeled dextran from μCs are controlled by varying the proton concentration and shell-wall thickness. SEM studies indicate that the system’s unique reversible release mechanism involves porosity changes in the shell wall due to microcrack formation.

Ring-opening metathesis polymerization (ROMP) was used to synthesize hydrogels via copolymerization of a diamine monomer 3 and a novel cross-linker 5 using Grubbs' third generation catalyst as initiator. Reactions were performed at two different monomer concentrations and at various initial molar ratios of cross-linker to initiator. At low monomer concentration, gelation occurred at initial cross-linker to initiator ratios of 1.5 and greater, which decreased to values of 1.05 and greater when increasing the monomer concentration. This result is in agreement with the Flory–Stockmayer theory. The gel yield and swelling properties were also found to be dependent on the cross-linker to initiator molar ratios. GPC data of the sol fractions showed quantitative consumption of both the monomer and the cross-linker. The molecular weight of the sol fraction was independent of the initiator concentration at constant cross-linker concentration of 2.5 mol%. Gels were found to swell up to 72 times their weight in 0.9% NaCl solution.

A new approach toward the fabrication of oriented, suspended fibers from the melting of free-standing polymer thin films is presented. Thin films (between 35 and 120 nm) cast via flow coating are melted atop lithographically patterned arrays of pillars to form suspended fibers (from ∼2 to 3 μm in diameter) between pillars. The effects of film thickness and pillar spacing on fiber diameter and yield are probed in a combinatorial fashion. A novel image analysis technique for the acquisition of fiber diameter across the multivariable parameter space is also outlined. This thin film melting approach details a new technique toward the fabrication of oriented, suspended micro and nanofiber networks with specific point to point connections in desired architectures.