Scholarly Works, Macromolecules Innovation Institute (MII)

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Octopus-Inspired Adhesives with Switchable Attachment to Challenging Underwater Surfaces
Lee, Chanhong; Via, Austin C.; Heredia, Aldo; Adjei, Daniel A.; Bartlett, Michael D. (Wiley-VCH, 2024-10-09)
Adhesives that excel in wet or underwater environments are critical for applications ranging from healthcare and underwater robotics to infrastructure repair. However, achieving strong attachment and controlled release on difficult substrates, such as those that are curved, rough, or located in diverse fluid environments, remains a major challenge. Here, an octopus-inspired adhesive with strong attachment and rapid release in challenging underwater environments is presented. Inspired by the octopus’s infundibulum structure, a compliant, curved stalk, and an active deformable membrane for multi-surface adhesion are utilized. The stalk’s curved shape enhances conformal contact on large-scale curvatures and increases contact stress for adaptability to small-scale roughness. These synergistic mechanisms improve contact across multiple length scales, resulting in switching ratios of over 1000 within ≈30 ms with consistent attachment strength of over 60 kPa on diverse surfaces and conditions. These adhesives are demonstrated through the robust attachment and precise manipulation of rough underwater objects.
Polymer characterization by size-exclusion chromatography with multi-angle light scattering (SEC-MALS): a tutorial review
Matson, John B.; Steele, Anna Q.; Mase, Jonathan D.; Schulz, Michael D. (Royal Society Chemistry, 2024)
This tutorial review presents the theory and application of SEC-MALS with minimal equations and a focus on synthetic polymer characterization, serving as an entry point for polymer scientists who want to learn more about SEC-MALS. We discuss the principles of static light scattering, outline its capability to generate absolute weight-average molar mass values, and extend its application to SEC-MALS. Practical elements are emphasized, enabling researchers to appreciate how values for Mn, Mw, and Đ are determined in an SEC-MALS experiment and how experimental conditions and input values, such as the specific refractive index increment (dn/dc), influence the results. Several illustrative SEC-MALS experiments demonstrate the impact of separation quality on Mn (as opposed to Mw), the appearance of contaminants in SEC chromatograms from sample preparation, the influence of concentration on data quality, and how polymer topology affects molecular weight characterization in SEC. Finally, we address practical considerations, common issues, and persistent misconceptions.
High Modulus, Strut-like poly(ether ether ketone) Aerogels Produced from a Benign Solvent
Spiering, Glenn A.; Godshall, Garrett F.; Moore, Robert B. (MDPI, 2024-04-22)
Poly(ether ether ketone) (PEEK) was found to form gels in the benign solvent 1,3-diphenylacetone (DPA). Gelation of PEEK in DPA was found to form an interconnected, strut-like morphology composed of polymer axialites. To our knowledge, this is the first report of a strut-like morphology for PEEK aerogels. PEEK/DPA gels were prepared by first dissolving PEEK in DPA at 320 °C. Upon cooling to 50 °C, PEEK crystallizes and forms a gel in DPA. The PEEK/DPA phase diagram indicated that phase separation occurs by solid–liquid phase separation, implying that DPA is a good solvent for PEEK. The Flory–Huggins interaction parameter, calculated as χ₁₂ = 0.093 for the PEEK/DPA system, confirmed that DPA is a good solvent for PEEK. PEEK aerogels were prepared by solvent exchanging DPA to water then freeze-drying. PEEK aerogels were found to have densities between 0.09 and 0.25 g/cm³, porosities between 80 and 93%, and surface areas between 200 and 225 m²/g, depending on the initial gel concentration. Using nitrogen adsorption analyses, PEEK aerogels were found to be mesoporous adsorbents, with mesopore sizes of about 8 nm, which formed between stacks of platelike crystalline lamellae. Scanning electron microscopy and X-ray scattering were utilized to elucidate the hierarchical structure of the PEEK aerogels. Morphological analysis found that the PEEK/DPA gels were composed of a highly nucleated network of PEEK axialites (i.e., aggregates of stacked crystalline lamellae). The highly connected axialite network imparted robust mechanical properties on PEEK aerogels, which were found to densify less upon freeze-drying than globular PEEK aerogel counterparts gelled from dichloroacetic acid (DCA) or 4-chlorphenol (4CP). PEEK aerogels formed from DPA were also found to have a modulus–density scaling that was far more efficient in supporting loads than the poorly connected aerogels formed from PEEK/DCA or PEEK/4CP solutions. The strut-like morphology in these new PEEK aerogels also significantly improved the modulus to a degree that is comparable to high-performance crosslinked aerogels based on polyimide and polyurea of comparable densities.
Additive Manufacturing of Poly(phenylene Sulfide) Aerogels via Simultaneous Material Extrusion and Thermally Induced Phase Separation
Godshall, Garrett F.; Rau, Daniel A.; Williams, Christopher B.; Moore, Robert B. (Wiley-VCH GmbH, 2023-11)
Additive manufacturing (AM) of aerogels increases the achievable geometric complexity, and affords fabrication of hierarchically porous structures. In this work, a custom heated material extrusion (MEX) device prints aerogels of poly(phenylene sulfide) (PPS), an engineering thermoplastic, via in situ thermally induced phase separation (TIPS). First, pre-prepared solid gel inks are dissolved at high temperatures in the heated extruder barrel to form a homogeneous polymer solution. Solutions are then extruded onto a room-temperature substrate, where printed roads maintain their bead shape and rapidly solidify via TIPS, thus enabling layer-wise MEX AM. Printed gels are converted to aerogels via postprocessing solvent exchange and freeze-drying. This work explores the effect of ink composition on printed aerogel morphology and thermomechanical properties. Scanning electron microscopy micrographs reveal complex hierarchical microstructures that are compositionally dependent. Printed aerogels demonstrate tailorable porosities (50.0–74.8%) and densities (0.345–0.684 g cm⁻³), which align well with cast aerogel analogs. Differential scanning calorimetry thermograms indicate printed aerogels are highly crystalline (≈43%), suggesting that printing does not inhibit the solidification process occurring during TIPS (polymer crystallization). Uniaxial compression testing reveals that compositionally dependent microstructure governs aerogel mechanical behavior, with compressive moduli ranging from 33.0 to 106.5 MPa.
Molecular modeling of Poly(methyl methacrylate-block-acrylonitrile) as Precursors of Porous Carbon Fibers
Hao, Xi; Serrano, Joel; Liu, Guoliang; Cheng, Shengfeng (2023-04-22)
Inducing stratification of colloidal mixtures with a mixed binary solvent
Liu, Binghan; Grest, Gary S.; Cheng, Shengfeng (Royal Society of Chemistry, 2023-12-06)
Molecular dynamics simulations are used to demonstrate that a binary solvent can be used to stratify colloidal mixtures when the suspension is rapidly dried. The solvent consists of two components, one more volatile than the other. When evaporated at high rates, the more volatile component becomes depleted near the evaporation front and develops a negative concentration gradient from the bulk of the mixture to the liquid-vapor interface while the less volatile solvent is enriched in the same region and exhibit a positive concentration gradient. Such gradients can be used to drive a binary mixture of colloidal particles to stratify if one is preferentially attracted to the more volatile solvent and the other to the less volatile solvent. During solvent evaporation, the fraction of colloidal particles preferentially attracted to the less volatile solvent is enhanced at the evaporation front, whereas the colloidal particles having stronger attractions with the more volatile solvent are driven away from the interfacial region. As a result, the colloidal particles show a stratified distribution after drying, even if the two colloids have the same size.
Diffusiophoresis as a physical mechanism underlying small-on-top stratification in evaporating bidisperse nanoparticle suspensions
Liu, Binghan; Grest, Gary; Cheng, Shengfeng (2023-05-17)
Operando characterization and regulation of metal dissolution and redeposition dynamics near battery electrode surface
Zhang, Yuxin; Hu, Anyang; Xia, Dawei; Hwang, Sooyeon; Sainio, Sami; Nordlund, Dennis; Michel, F. Marc; Moore, Robert B.; Li, Luxi; Lin, Feng (Nature Portfolio, 2023-07)
Mn dissolution has been a long-standing, ubiquitous issue that negatively impacts the performance of Mn-based battery materials. Mn dissolution involves complex chemical and structural transformations at the electrode–electrolyte interface. The continuously evolving electrode–electrolyte interface has posed great challenges for characterizing the dynamic interfacial process and quantitatively establishing the correlation with battery performance. In this study, we visualize and quantify the temporally and spatially resolved Mn dissolution/redeposition (D/R) dynamics of electrochemically operating Mn-containing cathodes. The particle-level and electrode-level analyses reveal that the D/R dynamics is associated with distinct interfacial degradation mechanisms at different states of charge. Our results statistically differentiate the contributions of surface reconstruction and Jahn–Teller distortion to the Mn dissolution at different operating voltages. Introducing sulfonated polymers (Nafion) into composite electrodes can modulate the D/R dynamics by trapping the dissolved Mn species and rapidly establishing local Mn D/R equilibrium. This work represents an inaugural effort to pinpoint the chemical and structural transformations responsible for Mn dissolution via an operando synchrotron study and develops an effective method to regulate Mn interfacial dynamics for improving battery performance.
Uncorrelated Lithium-Ion Hopping in a Dynamic Solvent-Anion Network
Yu, Deyang; Troya, Diego; Korovich, Andrew G.; Bostwick, Joshua E.; Colby, Ralph H.; Madsen, Louis A. (American Chemical Society, 2023-03)
Lithium batteries rely crucially on fast charge and mass transport of Li+ in the electrolyte. For liquid and polymer electrolytes with added lithium salts, Li+ couples to the counter-anion to form ionic clusters that produce inefficient Li+ transport and lead to Li dendrite formation. Quantification of Li+ transport in glycerol-salt electrolytes via NMR experiments and MD simulations reveals a surprising Li+-hopping mechanism. The Li+ transference number, measured by ion-specific electrophoretic NMR, can reach 0.7, and Li+ diffusion does not correlate with nearby ion motions, even at high salt concentration. Glycerol's high density of hydroxyl groups increases ion dissociation and slows anion diffusion, while the close proximity of hydroxyls and anions lowers local energy barriers, facilitating Li+ hopping. This system represents a bridge between liquid and inorganic solid electrolytes, thus motivating new molecular designs for liquid and polymer electrolytes to enable the uncorrelated Li+-hopping transport needed for fast-charging and all-solid-state batteries.
Enzyme-Triggered Chemodynamic Therapy via a Peptide-H2S Donor Conjugate with Complexed Fe2+
Zhu, Yumeng; Archer, William R.; Morales, Katlyn F.; Schulz, Michael D.; Wang, Yin; Matson, John B. (Wiley-V C H Verlag, 2023-04)
Inducing high levels of reactive oxygen species (ROS) inside tumor cells is a cancer therapy method termed chemodynamic therapy (CDT). Relying on delivery of Fenton reaction promoters such as Fe2+, CDT takes advantage of overproduced ROS in the tumor microenvironment. We developed a peptide-H2S donor conjugate, complexed with Fe2+, termed AAN-PTC-Fe2+. The AAN tripeptide was specifically cleaved by legumain, an enzyme overexpressed in glioma cells, to release carbonyl sulfide (COS). Hydrolysis of COS by carbonic anhydrase formed H2S, an inhibitor of catalase, an enzyme that detoxifies H2O2. Fe2+ and H2S together increased intracellular ROS levels and decreased viability in C6 glioma cells compared with controls lacking either Fe2+, the AAN sequence, or the ability to generate H2S. AAN-PTC-Fe2+ performed better than temezolimide while exhibiting no cytotoxicity toward H9C2 cardiomyocytes. This study provides an H2S-amplified, enzyme-responsive platform for synergistic cancer treatment.
Supramolecular Peptide Nanostructures Regulate Catalytic Efficiency and Selectivity
Li, Zhao; Joshi, Soumil Y.; Wang, Yin; Deshmukh, Sanket A.; Matson, John B. (Wiley-V C H, 2023-05)
We report three constitutionally isomeric tetrapeptides, each comprising one glutamic acid (E) residue, one histidine (H) residue, and two lysine (K-S) residues functionalized with side-chain hydrophobic S-aroylthiooxime (SATO) groups. Depending on the order of amino acids, these amphiphilic peptides self-assembled in aqueous solution into different nanostructures:nanoribbons, a mixture of nanotoroids and nanoribbons, or nanocoils. Each nanostructure catalyzed hydrolysis of a model substrate, with the nanocoils exhibiting the greatest rate enhancement and the highest enzymatic efficiency. Coarse-grained molecular dynamics simulations, analyzed with unsupervised machine learning, revealed clusters of H residues in hydrophobic pockets along the outer edge of the nanocoils, providing insight for the observed catalytic rate enhancement. Finally, all three supramolecular nanostructures catalyzed hydrolysis of the l-substrate only when a pair of enantiomeric Boc-l/d-Phe-ONp substrates were tested. This study highlights how subtle molecular-level changes can influence supramolecular nanostructures, and ultimately affect catalytic efficiency.
Facile Implementation of Antimicrobial Coatings through Adhesive Films (Wraps) Demonstrated with Cuprous Oxide Coatings
Behzadinasab, Saeed; Williams, Myra D.; Falkinham, Joseph O.; Ducker, William A. (MDPI, 2023-05-17)
Antimicrobial coatings have a finite lifetime because of wear, depletion of the active ingredient, or surface contamination that produces a barrier between the pathogen and the active ingredient. The limited lifetime means that facile replacement is important. Here, we describe a generic method for rapidly applying and reapplying antimicrobial coatings to common-touch surfaces. The method is to deposit an antimicrobial coating on a generic adhesive film (wrap), and then to attach that modified wrap to the common-touch surface. In this scenario, the adhesion of the wrap and antimicrobial efficacy are separated and can be optimized independently. We demonstrate the fabrication of two antimicrobial wraps, both using cuprous oxide (Cu₂O) as the active ingredient. The first uses polyurethane (PU) as the polymeric binder and the second uses polydopamine (PDA). Our antimicrobial PU/Cu₂O and PDA/Cu₂O wraps, respectively, kill >99.98% and >99.82% of the human pathogen, P. aeruginosa, in only 10 min, and each of them kill >99.99% of the bacterium in 20 min. These antimicrobial wraps can be removed and replaced on the same object in <1 min with no tools. Wraps are already frequently used by consumers to coat drawers or cars for aesthetic or protective purposes.
Fluorescent detection of hydrogen sulfide (H2S) through the formation of pyrene excimers enhances H2S quantification in biochemical systems
Pose, Manuela; Dillon, Kearsley M.; Denicola, Ana; Alvarez, Beatriz; Matson, John B.; Moeller, Matias N.; Cuevasanta, Ernesto (Elsevier, 2022-10)
Hydrogen sulfide (H2S) is produced endogenously by several enzymatic pathways and modulates physiological functions in mammals. Quantification of H2S in biochemical systems re-mains challenging because of the presence of interferents with similar reactivity, particularly thiols. Herein, we present a new quantification method based on the formation of pyrene exci-mers in solution. We synthesized the probe 2-(maleimido)ethyl 4-pyrenylbutanoate (MEPB) and determined that MEPB reacted with H2S in a two-step reaction to yield the thioether-linked dimer (MEPB)2S, which formed excimers upon excita-tion, with a broad peak of fluorescence emission centered at 480 nm. In contrast, we found that the products formed with thiols showed peaks at 378 and 398 nm. The difference in emission between the products prevented the interference. Furthermore, we showed that the excimer fluorescence signal yielded a linear response to H2S, with a limit of detection of 54 nM in a fluorometer. Our quantification method with MEPB was successfully applied to follow the reaction of H2S with glutathione disulfide and to quantify the production of H2S from cysteine by Escherichia coli. In conclusion, this method represents an addition to the toolkit of biochemists to quantify H2S specifically and sensitively in biochemical systems.
Terminology for chain polymerization (IUPAC Recommendations 2021)
Fellows, Christopher M.; Jones, Richard G.; Keddie, Daniel J.; Luscombe, Christine K.; Matson, John B.; Matyjaszewski, Krzysztof; Merna, Jan; Moad, Graeme; Nakano, Tamaki; Penczek, Stanislaw; Russell, Gregory T.; Topham, Paul D. (Walter De Gruyter, 2022-09)
Chain polymerizations are defined as chain reactions where the propagation steps occur by reaction between monomer(s) and active site(s) on the polymer chains with regeneration of the active site(s) at each step. Many forms of chain polymerization can be distinguished according to the mechanism of the propagation step (e.g., cyclopolymerization - when rings are formed, condensative chain polymerization - when propagation is a condensation reaction, group-transfer polymerization, polyinsertion, ring-opening polymerization - when rings are opened), whether they involve a termination step or not (e.g., living polymerization - when termination is absent, reversible-deactivation polymerization), whether a transfer step is involved (e.g., degenerative-transfer polymerization), and the type of chain carrier or active site (e.g., radical, ion, electrophile, nucleophile, coordination complex). The objective of this document is to provide a language for describing chain polymerizations that is both readily understandable and self-consistent, and which covers recent developments in this rapidly evolving field.
Customized blends of polypropylene for extrusion based additive manufacturing
Das, Arit; Shanmugham, Nishanth; Bortner, Michael J. (Wiley, 2022-11)
Filament-based material extrusion (MatEx) additive manufacturing has garnered great interest due to its simplicity, customizability, and cost-effectiveness. However, MatEx of semicrystalline polymers is still largely relegated to prototyping applications. Major issues involving volumetric shrinkage and warpage of the printed parts must be addressed in order to employ them for printing functional parts. Moreover, the crystallization behavior and rheology of the polymer are dependent on the MatEx processing conditions. In the current work, the printability of blends of isotactic polypropylene with a soft, low crystallinity propylene based homopolymer is evaluated. Addition of the homopolymer resulted in an increase in the crystallization window of the blends by similar to 6 degrees C that had a profound impact on the interlayer adhesion and residual stress state. The shear-dependent melt flow behavior inside the printing nozzle as well as the interlayer chain diffusion and interlayer welding on the print bed were investigated. Rheological characterizations also indicate sufficient dispersion and miscibility of the homopolymer in the neat polypropylene matrix. The incorporation of the homopolymer as an additive significantly improved the dimensional accuracy of the printed parts through better dissipation of the entrapped residual stresses during MatEx. Moreover, the degree of mechanical anisotropy of the parts was significantly lower than that obtained using many 3D printable grade polymers. The findings from this study can be leveraged in toolpath planning, process parameter optimization, and new feedstock development, highlighting current limitations as well as providing valuable insights into necessary processing modifications in order to enable MatEx of next generation semicrystalline polymers.
Multi-axis alignment of Rod-like cellulose nanocrystals in drying droplets
Pritchard, Cailean Q.; Navarro, Fernando; Roman, Maren; Bortner, Michael J. (Elsevier, 2021-12)
Hypothesis: Radial capillary flow in evaporating droplets carry suspended nanoparticles to its periphery where they are deposited and form a coffee-ring. Rod-like nanoparticles seeking to minimize their capillary energy will align with their long-axis parallel to the contact line. Particles exhibiting electrostatic repulsion, such as cellulose nanocrystals (CNCs), establish a competition between capillary flow-induced impingement against a growing coffee-ring and entropic minimization leading to enhanced particle mobility. Therefore, balancing these effects by manipulating the local particle concentration in drying droplets should result in deposition with a controlled orientation of CNCs. Experiments: The dynamic local order in aqueous suspensions of CNCs in evaporating sessile droplets was investigated through time-resolved polarized light microscopy. The spatial distribution of alignment in deposited CNCs was explored as a function of nanoparticle concentration, droplet volume, initial degree of anisotropy, and substrate hydrophobicity. Computational analysis of the rotational Péclet number during evaporation was also investigated to evaluate any effects of shear-induced alignment. Findings: Multiple modes of orientation were identified suggesting local control over CNC orientation and subsequent properties can be attained via droplet-based patterning methods. Specifically, high local particle concentrations led to tangential alignment and lower local particle concentrations resulted in new evidence for radial alignment near the center of dried droplets.
Molecular Weight Distribution of Branched Polymers: Comparison between Monte Carlo Simulation and Flory-Stockmayer Theory
Wen, Chengyuan; Odle, Roy; Cheng, Shengfeng (MDPI, 2023-04-04)
It is challenging to predict the molecular weight distribution (MWD) for a polymer with a branched architecture, though such information will significantly benefit the design and development of branched polymers with desired properties and functions. A Monte Carlo (MC) simulation method based on the Gillespie algorithm is developed to quickly compute the MWD of branched polymers formed through step-growth polymerization, with a branched polyetherimide from two backbone monomers (4,4′-bisphenol A dianhydride and m-phenylenediamine), a chain terminator (phthalic anhydride), and a branching agent (tris[4-(4-aminophenoxy)phenyl] ethane) as an example. This polymerization involves four reactions that can be all reduced to a condensation reaction between an amine group and a carboxylic anhydride group. A comparison between the MC simulation results and the predictions of the Flory-Stockmayer theory on MWD shows that the rates of the reactions are determined by the concentrations of the functional groups on the monomers involved in each reaction. It further shows that the Flory-Stockmayer theory predicts MWD well for systems below the gel point but starts to fail for systems around or above the gel point. However, for all the systems, the MC method can be used to reliably predict MWD no matter if they are below or above the gel point. Even for a macroscopic system, a converging distribution can be quickly obtained through MC simulations on a system of only a few hundred to a few thousand monomers that have the same molar ratios as in the macroscopic system.
Encapsulation of PI3K Inhibitor LY294002 within Polymer Nanoparticles Using Ion Pairing Flash Nanoprecipitation
Fergusson, Austin D.; Zhang, Rui; Riffle, Judy S.; Davis, Richey M. (MDPI, 2023-04-06)
Flash nanoprecipitation (FNP) is a turbulent mixing process capable of reproducibly producing polymer nanoparticles loaded with active pharmaceutical ingredients (APIs). The nanoparticles produced with this method consist of a hydrophobic core surrounded by a hydrophilic corona. FNP produces nanoparticles with very high loading levels of nonionic hydrophobic APIs. However, hydrophobic compounds with ionizable groups are not as efficiently incorporated. To overcome this, ion pairing agents (IPs) can be incorporated into the FNP formulation to produce highly hydrophobic drug salts that efficiently precipitate during mixing. We demonstrate the encapsulation of the PI3K inhibitor, LY294002, within poly(ethylene glycol)-b-poly(D,L lactic acid) nanoparticles. We investigated how incorporating two hydrophobic IPs (palmitic acid (PA) and hexadecylphosphonic acid (HDPA)) during the FNP process affected the LY294002 loading and size of the resulting nanoparticles. The effect of organic solvent choice on the synthesis process was also examined. While the presence of either hydrophobic IP effectively increased the encapsulation of LY294002 during FNP, HDPA resulted in well-defined colloidally stable particles, while the PA resulted in ill-defined aggregates. The incorporation of hydrophobic IPs with FNP opens the door for the intravenous administration of APIs that were previously deemed unusable due to their hydrophobic nature.
N-thiocarboxyanhydrides, amino acid-derived enzyme-activated H2S donors, enhance sperm mitochondrial activity in presence and absence of oxidative stress
Pintus, Eliana; Chinn, Abigail F.; Kadlec, Martin; García-Vázquez, Francisco A.; Novy, Pavel; Matson, John B.; Ros-Santaella, José L. (2023-02-16)
Background Hydrogen sulfide (H2S) donors are crucial tools not only for understanding the role of H2S in cellular function but also as promising therapeutic agents for oxidative stress-related diseases. This study aimed to explore the effect of amino acid-derived N-thiocarboxyanhydrides (NTAs), which release physiological H2S levels in the presence of carbonic anhydrase, on porcine sperm function during short-term incubation with and without induced oxidative stress. For this purpose, we employed two H2S-releasing NTAs with release half-lives (t1/2) in the range of hours that derived from the amino acids glycine (Gly-NTA) or leucine (Leu-NTA). Because carbonic anhydrase is crucial for H2S release from NTAs, we first measured the activity of this enzyme in the porcine ejaculate. Then, we tested the effect of Gly- and Leu-NTAs at 10 and 1 nM on sperm mitochondrial activity, plasma membrane integrity, acrosomal status, motility, motile subpopulations, and redox balance during short-term incubation at 38 °C with and without a reactive oxygen species (ROS)-generating system. Results Our results show that carbonic anhydrase is found both in spermatozoa and seminal plasma, with activity notably higher in the latter. Both Gly- and Leu-NTAs did not exert any noxious effects, but they enhanced sperm mitochondrial activity in the presence and absence of oxidative stress. Moreover, NTAs (except for Leu-NTA 10 nM) tended to preserve the sperm redox balance against the injuries provoked by oxidative stress, which provide further support to the antioxidant effect of H2S on sperm function. Both compounds also increased progressive motility over short-term incubation, which may translate into prolonged sperm survival. Conclusions The presence of carbonic anhydrase activity in mammalian spermatozoa makes NTAs promising molecules to investigate the role of H2S in sperm biology. For the first time, beneficial effects of NTAs on mitochondrial activity have been found in mammalian cells in the presence and absence of oxidative stress. NTAs are interesting compounds to investigate the role of H2S in sperm mitochondria-dependent events and to develop H2S-related therapeutic protocols against oxidative stress in assisted reproductive technologies.
Effects of Chitosan Molecular Weight and Degree of Deacetylation on Chitosan-Cellulose Nanocrystal Complexes and Their Formation
Wang, Hezhong; Roman, Maren (MDPI, 2023-01-31)
This study was conducted to determine the effects of chitosan molecular weight and degree of deacetylation (DD) on chitosan–cellulose nanocrystal (CNC) polyelectrolyte–macroion complexes (PMCs) and their formation. Chitosan samples with three different molecular weights (81, 3 · 10³, 6 · 10³ kDa) and four different DDs (77, 80, 85, 89%) were used. The effects on PMC formation were determined by turbidimetric titration. An effect of the molecular weight of chitosan was not observed in turbidimetric titrations. Turbidity levels were higher for CNCs with lower sulfate group density and larger hydrodynamic diameter than for CNCs with higher sulfate group density and smaller hydrodynamic diameter. Conversely, turbidity levels were higher for chitosans with higher DD (higher charge density) than for chitosans with lower DD (lower charge density). PMC particles from chitosans with different molecular weights were characterized by scanning electron microscopy, laser Doppler electrophoresis, and dynamic light scattering. PMCs from high-molecular-weight chitosan were more spherical and those from medium-molecular-weight chitosan had a slightly larger hydrodynamic diameter than PMCs from the respective other two chitosans. The molecular weight of the chitosan was concluded to have no effect on the formation of chitosan–CNC PMC particles and only a minor effect on the shape and size of the particles. The higher turbidity levels for CNCs with lower sulfate group density and larger hydrodynamic diameter and for chitosans with higher DD were attributed to a larger number of CNCs being required for charge compensation.

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