Fractal Structure of Hydrogels Modulates Stem Cell Behavior

Fractal dimension (<i>D</i>_f) is an index to describe the irregular continuous structure by quantifying the complexity. The concept of fractals has been employed to describe the complicated structure of polymer gel and human tissue. This study examined the effect of <i>D</i>_f on cell proliferation and stem cell differentiation in six polymer hydrogels with <i>D</i>_f ranging from 1.2 to 2.1. It was observed that fibroblasts and mesenchymal stem cells (MSCs) grew faster in hydrogels with higher <i>D</i>_f. Moreover, hydrogels with a fractal structure of <i>D</i>_f ≤ 1.4, ≥1.6, and ≥1.8 promoted the neural, osteogenic, and chondrogenic differentiation of MSCs, respectively. The fractal structure of gel can modulate cell proliferation and fate, which provides an insight into designing the appropriate fractal and molecular structure of polymer hydrogel for biomedical applications

Biodegradable Water-Based Polyurethane Shape Memory Elastomers for Bone Tissue Engineering

Shape memory polymers (SMPs) are polymers with the shape memory effect. The biodegradable SMPs are candidate materials for making biomedical devices and scaffolds for tissue engineering. Superparamagnetic iron oxide nanoparticles (SPIO NPs) have recently been reported to promote the osteogenic induction of human mesenchymal stem cells (hMSCs). In this study, we synthesized water-based biodegradable shape memory polyurethane (PU) as the main component of the 3D printing ink for fabricating bone scaffolds. The 3D printing ink contained 500 ppm of SPIO NPs to promote osteogenic induction and shape fixity, and it also contained polyethylene oxide (PEO) or gelatin for the improvement of printability. Scaffolds were printed by the microextrusion-based low-temperature fuse deposition manufacturing (LFDM) platform. Both PU–PEO and PU–gelatin ink showed excellent printability. Shape memory properties were evaluated in 50 °C air and 37 °C water. PU–PEO scaffolds showed better shape fixity and recovery than PU–gelatin scaffolds, while the shape memory properties in water were better than those in air. hMSCs were seeded for evaluation of bone regeneration. The proliferation of the hMSCs in PU/gelatin and PU/gelatin/SPIO scaffolds was greater than that in PU/PEO and PU/PEO/SPIO scaffolds, confirming the better compatibility of gelatin vs PEO as the viscosity enhancer of the ink. The gradual release of SPIO NPs from the scaffolds promoted the osteogenesis of seeded hMSCs. With SPIO in the scaffolds, the osteogenesis increased 2.7 times for PU/PEO and 1.5 times for PU/gelatin scaffolds based on the collagen content. Meanwhile, SPIO release from PU/PEO/SPIO scaffolds was faster than that from PU/gelatin/SPIO scaffolds at 14 days, consistent with the better osteogenesis observed in PU/PEO/SPIO scaffolds. We concluded that 3D printed PU scaffolds with shape memory properties, biodegradability, and osteogenic effect may be employed to the minimally invasive surgical procedures as customized-bone substitutes for bone tissue engineering

Functionalized Nanoporous Gyroid SiO₂ with Double-Stimuli-Responsive Properties as Environment-Selective Delivery Systems

Herein, we aim to fabricate nanoporous gyroid SiO₂ from templated sol–gel reaction using degradable block copolymer with gyroid-forming nanostructure as a template and then to functionalize the nanoporous materials using “smart” polymer, poly­(2-(dimethylamino)­ethyl methacrylate) (PDMAEMA), brushes via the “grafting from” method to give double-stimuli-responsive properties. By taking advantage of the responses to environmental stimuli, both thermal and pH, the pore features can be well-defined by the stretching and recoiling of PDMAEMA brushes because of their adjustable chain conformations with reversible character. The responsive properties with respect to environmental stimuli can be successfully traced by temperature-resolved small-angle X-ray scattering (SAXS) in aqueous environment. Owing to the high specific surface area and porosity, 3D pore network, biocompatibility, and environmental responses, the functionalized nanoporous gyroid SiO₂ is further demonstrated as a stimuli-responsive controlled release system

Supramolecular Nanostructure Formation of Coassembled Amyloid Inspired Peptides

Characterization of amyloid-like aggregates through converging approaches can yield deeper understanding of their complex self-assembly mechanisms and the nature of their strong mechanical stability, which may in turn contribute to the design of novel supramolecular peptide nanostructures as functional materials. In this study, we investigated the coassembly kinetics of oppositely charged short amyloid-inspired peptides (AIPs) into supramolecular nanostructures by using confocal fluorescence imaging of thioflavin T binding, turbidity assay and in situ small-angle X-ray scattering (SAXS) analysis. We showed that coassembly kinetics of the AIP nanostructures were consistent with nucleation-dependent amyloid-like aggregation, and aggregation behavior of the AIPs was affected by the initial monomer concentration and sonication. Moreover, SAXS analysis was performed to gain structural information on the size, shape, electron density, and internal organization of the coassembled AIP nanostructures. The scattering data of the coassembled AIP nanostructures were best fitted into to a combination of polydisperse core–shell cylinder (PCSC) and decoupling flexible cylinder (FCPR) models, and the structural parameters were estimated based on the fitting results of the scattering data. The stability of the coassembled AIP nanostructures in both fiber organization and bulk viscoelastic properties was also revealed via temperature-dependent SAXS analysis and oscillatory rheology measurements, respectively

Nanoarchitectonics of Nanocellulose Filament Electrodes by Femtosecond Pulse Laser Deposition of ZnO and <i>In Situ</i> Conjugation of Conductive Polymers

Electroactive filament electrodes were synthesized by wet-spinning of cellulose nanofibrils (CNF) followed by femtosecond pulse laser deposition of ZnO (CNF@ZnO). A layer of conducting conjugated polymers was further adsorbed by in situ polymerization of either pyrrole or aniline, yielding systems optimized for electron conduction. The resultant hybrid filaments were thoroughly characterized by imaging, spectroscopy, electrochemical impedance, and small- and wide-angle X-ray scattering. For the filaments using polyaniline, the measured conductivity was a result of the synergy between the inorganic and organic layers, while the contribution was additive in the case of the systems containing polypyrrole. This observation is rationalized by the occurrence of charge transfer between ZnO and polyaniline but not that with polypyrrole. The introduced conductive hybrid filaments displayed a performance that competes with that of metallic counterparts, offering great promise for next-generation filament electrodes based on renewable nanocellulose

Synthesis of Thermoresponsive Amphiphilic Polyurethane Gel as a New Cell Printing Material near Body Temperature

Waterborne polyurethane (PU) based on poly­(ε-caprolactone) (PCL) diol and a second oligodiol containing amphiphilic blocks was synthesized in this study. The microstructure was characterized by dynamic light scattering (DLS), small-angle X-ray scattering (SAXS), and rheological measurement of the PU dispersion. The surface hydrophilicity measurement, infrared spectroscopy, wide-angle X-ray diffraction, mechanical and thermal analyses were conducted in solid state. It was observed that the presence of a small amount of amphiphilic blocks in the soft segment resulted in significant changes in microstructure. When 90 mol % PCL diol and 10 mol % amphiphilic blocks of poly­(l-lactide)–poly­(ethylene oxide) (PLLA–PEO) diol were used as the soft segment, the synthesized PU had a water contact angle of ∼24° and degree of crystallinity of ∼14%. The dispersion had a low viscosity below room temperature. As the temperature was raised to body temperature (37 °C), the dispersion rapidly (∼170 s) underwent sol–gel transition with excellent gel modulus (<i>G</i>′ ≈ 6.5 kPa) in 20 min. PU dispersions with a solid content of 25–30% could be easily mixed with cells in sol state, extruded by a 3D printer, and deposited layer by layer as a gel. Cells remained alive and proliferating in the printed hydrogel scaffold. We expect that the development of novel thermoresponsive PU system can be used as smart injectable hydrogel and applied as a new type of bio-3D printing ink

Synthesis of Thermoresponsive Amphiphilic Polyurethane Gel as a New Cell Printing Material near Body Temperature

Waterborne polyurethane (PU) based on poly­(ε-caprolactone) (PCL) diol and a second oligodiol containing amphiphilic blocks was synthesized in this study. The microstructure was characterized by dynamic light scattering (DLS), small-angle X-ray scattering (SAXS), and rheological measurement of the PU dispersion. The surface hydrophilicity measurement, infrared spectroscopy, wide-angle X-ray diffraction, mechanical and thermal analyses were conducted in solid state. It was observed that the presence of a small amount of amphiphilic blocks in the soft segment resulted in significant changes in microstructure. When 90 mol % PCL diol and 10 mol % amphiphilic blocks of poly­(l-lactide)–poly­(ethylene oxide) (PLLA–PEO) diol were used as the soft segment, the synthesized PU had a water contact angle of ∼24° and degree of crystallinity of ∼14%. The dispersion had a low viscosity below room temperature. As the temperature was raised to body temperature (37 °C), the dispersion rapidly (∼170 s) underwent sol–gel transition with excellent gel modulus (<i>G</i>′ ≈ 6.5 kPa) in 20 min. PU dispersions with a solid content of 25–30% could be easily mixed with cells in sol state, extruded by a 3D printer, and deposited layer by layer as a gel. Cells remained alive and proliferating in the printed hydrogel scaffold. We expect that the development of novel thermoresponsive PU system can be used as smart injectable hydrogel and applied as a new type of bio-3D printing ink

Homology Modeling and Molecular Dynamics Simulation Combined with X‑ray Solution Scattering Defining Protein Structures of Thromboxane and Prostacyclin Synthases

A combination of molecular dynamics (MD) simulations and X-ray scattering (SAXS) has emerged as the approach of choice for studying protein structures and dynamics in solution. This approach has potential applications for membrane proteins that neither are soluble nor form crystals easily. We explore the water-coupled dynamic structures of thromboxane synthase (TXAS) and prostacyclin synthase (PGIS) from scanning HPLC–SAXS measurements combined with MD ensemble analyses. Both proteins are heme-containing enzymes in the cytochrome P450 family, known as prostaglandin H₂ (PGH₂) isomerase, with counter-functions in regulation of platelet aggregation. Currently, the X-ray crystallographic structures of PGIS are available, but those for TXAS are not. The use of homology modeling of the TXAS structure with ns−μs explicit water solvation MD simulations allows much more accurate estimation of the configuration space with loop motion and origin of the protein behaviors in solution. In contrast to the stability of the conserved PGIS structure in solution, the pronounced TXAS flexibility has been revealed to have unstructured loop regions in connection with the characteristic P450 structural elements. The MD-derived and experimental-solution SAXS results are in excellent agreement. The significant protein internal motions, whole-molecule structures, and potential problems with protein folding, crystallization, and functionality are examined

Tracing the Surfactant-Mediated Nucleation, Growth, and Superpacking of Gold Supercrystals Using Time and Spatially Resolved X‑ray Scattering

The nucleation and growth process of gold supercrystals in a surfactant diffusion approach is followed by simultaneous small- and wide-angle X-ray scattering (SAXS/WAXS), supplemented with scanning electron microscopy. The results indicate that supercrystal nucleation can be activated efficiently upon placing a concentrated surfactant solution of a nematic phase on top of a gold nanocrystal solution droplet trapped in the middle of a vertically oriented capillary tube. Supercrystal nuclei comprised of tens of gold nanocubes are observed nearly instantaneously in the broadened liquid–liquid interface zone of a steep gradient of surfactant concentration, revealing a diffusion-kinetics-controlled nucleation process. Once formed, the nuclei can sediment into the naoncrystal zone below, and grow efficiently into cubic or tetragonal supercrystals of ∼1 μm size within ∼100 min. Supercrystals matured during sedimentation in the capillary can accumulate and face-to-face align at the bottom liquid–air interface of the nanocrystal droplet. This is followed by superpacking of the supercrystals into highly oriented hierarchical sheets, with a huge number of gold nanocubes aligned for largely coherent crystallographic orientations

Directing the Interfacial Morphology of Hierarchical Structures of Dendron-Jacketed Block Copolymers via Liquid Crystalline Phases

Interfacial morphologies of hierarchically phase-separated domains in supramolecular dendron-jacketed block copolymers (DJBCP) are directed via liquid-crystalline (LC) phases of the dendronized blocks. The DJBCP is formed with a dendron 4′-(3,4,5-trioctyloxybenzoyloxy)­benzoic acid (TOB), selectively incorporated into the P4VP block of poly­(styrene)-<i>block</i>-poly­(4-vinylpyridine) (PS-<i>b</i>-P4VP). Revealed from small- and wide-angle X-ray scattering as well as transmission electron microscopy, the hexagonally packed columnar LC phase (HEX_col) of the dendronized blocks P4VP­(TOB) can substantially decrease the curvature of the intermaterial dividing surfaces (IMDS) of the DJBCP. Consequently formed are hierarchically structured DJBCP with hexagonally packed hexagon PS cylinders. As the locally two-dimensionally (2D)-ordered HEX_col phase reduces to 1D ordered smectic (Sm) phase with weakened LC packing strength, the planar IMDS of the DJBCP relaxes into curved IMDS for circular PS cylinders. IMDS flattening effect imposed by the columnar LC phase is further strengthened via a triblock DJBCP of P4VP­(TOB)_<i>x</i>-<i>b</i>-PS-<i>b</i>-P4VP­(TOB)_<i>x</i>, leading to a highly oriented honeycomb structure with an ordering length up to sub-millimeter. The LC-controlled IMDS morphology of the DJBCP might facilitate fabrication of templates toward nanoperiodic arrays with sharp channel edges for lithography applications