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1. Moduli of Mussel‐Inspired, Metal‐Coordinated Hydrogels Comprising Four‐, Six‐, and Eight‐Arm Polymers

   https://doi.org/10.1002/macp.202300102  

   Darby, Daniel R. ; Stephens, Lauren F. ; Chwatko, Malgorzata ; Pham, Jonathan T. ( August 2023 , Macromolecular Chemistry and Physics)

   Metal‐coordinated hydrogels can form a percolated network with transient bonds due to metal ions‐functional group coordination. Each metal ion can link with more than one ligand, leading to intricate speciation of bonding modes. While the mechanics of transient gels made with four‐arm polymers are often studied, less is known about how increasing the number of arms affects the modulus. Using shear rheology, the modulus of hydrogels prepared from four‐, six‐, and eight‐armed poly(ethylene glycols), functionalized with histidine ligands that complex with nickel (II) ions is measured. These gels have matched polymer wt.% and varied pH to compare their moduli. It is considered whether the modulus can be described by established polymer network models by calculating the speciation of metal‐coordinated cross‐links and then incorporating it into a phantom network prediction. This study finds that 1) increasing the number of polymer arms increases the modulus, 2) the phantom network allows reasonable modulus approximation for four‐arm and six‐arm gels, and 3) the modulus of eight‐arm gels exceeds the phantom network prediction. Since polymer cores act as chemical cross‐links and metal‐coordinated cross‐links form network strands, it is possible that increasing the number of metal‐coordinated linkages per molecule reinforces the chemical cross‐link at the polymer core.

    

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2. Soft interactions and volume exclusion by polymeric crowders can stabilize or destabilize transient structure in disordered proteins depending on polymer concentration

   https://doi.org/10.1002/prot.25307  

   Rusinga, Farai I. ; Weis, David D. ( May 2017 , Proteins: Structure, Function, and Bioinformatics)

   The effects of macromolecular crowding on the transient structure of intrinsically disordered proteins is not well‐understood. Crowding by biological molecules inside cells could modulate transient structure and alter IDP function. Volume exclusion theory and observations of structured proteins suggest that IDP transient structure would be stabilized by macromolecular crowding. Amide hydrogen exchange (HX) of IDPs in highly concentrated polymer solutions would provide valuable insights into IDP transient structure under crowded conditions. Here, we have used mass spectrometry to measure HX by a transiently helical random coil domain of the activator of thyroid and retinoid receptor (ACTR) in solutions containing 300 g L⁻¹and 400 g L⁻¹of Ficoll, a synthetic polysaccharide, using a recently‐developed strong cation exchange‐based cleanup method [Rusinga, et al., Anal Chem 2017;89:1275–1282]. Transiently helical regions of ACTR exchanged faster in 300 g L⁻¹Ficoll than in dilute buffer. In contrast, one transient helix exchanged more slowly in 400 g L⁻¹Ficoll. Nonspecific interactions destabilize ACTR helicity in 300 g L⁻¹Ficoll because ACTR engages with the Ficoll polymer mesh. In contrast, 400 g L⁻¹Ficoll is a semi‐dilute solution where ACTR cannot engage the Ficoll mesh. At this higher concentration, volume exclusion stabilizes ACTR helicity because ACTR is compacted in interstitial spaces between Ficoll molecules. Our results suggest that the interplay between nonspecific interactions and volume exclusion in different cellular compartments could modulate IDP function by altering the stability of IDP transient structures. Proteins 2017; 85:1468–1479. © 2017 Wiley Periodicals, Inc.

    

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3. Decoupling the Ionic Conductivity and Elastic Modulus of Gel Electrolytes: Fully Zwitterionic Copolymer Scaffolds in Lithium Salt/Ionic Liquid Solutions

   https://doi.org/10.1002/aenm.201801646  

   D'Angelo, Anthony J. ; Panzer, Matthew J. ( July 2018 , Advanced Energy Materials)

   A critical barrier to overcome in the development of solid‐state electrolytes for lithium batteries is the trade‐off between sacrificing ionic conductivity for enhancement of mechanical stiffness. Here, a physically cross‐linked, polymer‐supported gel electrolyte consisting of a lithium salt/ionic liquid solution featuring a fully zwitterionic (ZI) copolymer network is introduced for rechargeable lithium‐based batteries. The ZI scaffold is synthesized using a 3:1 molar ratio of 2‐methacryloyloxyethyl phosphorylcholine and sulfobetaine vinylimidazole, and the total polymer content is varied between 1.1 and 12.5 wt%. Room‐temperature ionic conductivity values comparable to the base liquid electrolyte (≈1 mS cm⁻¹) are achieved in ZI copolymer‐supported gels that display compressive elastic moduli as large as 14.3 MPa due to ZI dipole–dipole cross‐links. Spectroscopic characterization suggests a change in the Li⁺coordination shell upon addition of the zwitterions, indicative of strong Li⁺···ZI group interactions. Li⁺transference number measurements reveal an increase in Li⁺conductivity within a ZI gel electrolyte (nearly doubles). ZI gels display enhanced stability against Li metal, dendrite suppression, and suitable charge–discharge performance in a graphite|lithium nickel cobalt manganese oxide cell. Fully ZI polymer networks in nonvolatile, ionic liquid‐based electrolytes represent a promising approach toward realizing highly conductive, mechanically rigid gels for lithium battery technologies.

    

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4. Reproducible and controlled peptide functionalization of polymeric nanoparticles

   https://doi.org/10.3389/fbiom.2022.1003172  

   Chandrasiri, Indika ; Liu, Yuxuan ; Adjei-Sowah, Emmanuela ; Xiao, Baixue ; Benoit, Danielle S. ( October 2022 , Frontiers in Biomaterials Science)

   Polymeric nanoparticles containing multiple amines and carboxylates have been frequently used in drug delivery research. Reproducible and controlled conjugation among these multifunctional biomaterials is necessary to achieve efficient drug delivery platforms. However, multiple functional groups increase the risk of unintended intramolecular/intermolecular reactions during conjugation. Herein, conjugation approaches and possible undesired reactions between multi-amine functionalized peptides, multi-carboxylate functionalized polymers, and anhydride-containing polymers [Poly(styrene-alt-maleic anhydride)-b-poly(styrene)] were investigated under different conjugation strategies (carbodiimide chemistry, anhydride ring-opening via nucleophilic addition elimination). Muti-amine peptides led to extensive crosslinking between polymers regardless of the conjugation chemistry. Results also indicate that conventional peptide quantification methods (i.e., o-phthalaldehyde assay, bicinchoninic acid assay) are unreliable. Gel permeation chromatography (GPC) provided more accurate qualitative and quantitative evidence for intermolecular crosslinking. Crosslinking densities were correlated with higher feed ratios of multifunctional peptides and carbodiimide coupling reagents. Selectively protected peptides (Lys-Alloc) exhibited no crosslinking and yielded peptide-polymer conjugates with controlled dispersity and molecular weight. Furthermore, anhydride ring-opening (ARO) nucleophilic addition elimination was successfully introduced as a facile yet robust peptide conjugation approach for cyclic anhydride-containing polymers.

    

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5. Temperature‐dependent structure and compressive mechanical behavior of alginate/polyethylene oxide–poly(propylene oxide)–poly(ethylene oxide) hydrogels

   https://doi.org/10.1002/jbm.b.34437  

   Quah, Suan P. ; Nykypanchuk, Dmytro ; Bhatia, Surita R. ( June 2019 , Journal of Biomedical Materials Research Part B: Applied Biomaterials)

   We report the structural and mechanical behavior of multicomponent hydrogels comprising the commercial poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) block copolymer F127 and alginate. Previous studies on this system have shown thermoreversible behavior in shear rheology. Here we explore the properties of these materials under compression and large deformations, relevant to applications such as wound dressings that require mechanical robustness. For gels with lower F127 concentration, we find that the stiffness of the gels can be ascribed to the alginate network, and that the Young's modulus and fracture stress do not strongly depend on temperatures. However, for gels with an F127 concentration of 30 wt %, the Young's modulus is enhanced at higher temperatures. Under large deformations, the fracture stress and fracture strain of the materials can be independently varied using the alginate and F127 concentrations, respectively; without the trade‐off in these properties that is often observed in rigid polymer networks. Small‐angle X‐ray scattering shows a power‐law dependence scattering intensity onqarising from the alginate network and scattering peaks consistent with rearranging micelles. For gels with lower F127 concentrations, we find a disordered–body‐centered cubic (BCC)‐face‐centered cubic (FCC) progression of states with temperature, and a BCC/FCC mixture for gels with higher F127 concentrations.

    

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