Fast Gelation Process Research Articles

Fast fabrication of “all-in-one” injectable hydrogels as antibiotic alternatives for enhanced bacterial inhibition and accelerating wound healing

Skin wound infection has become a notable medical threat. Herein, the polysaccharide-based injectable hydrogels with multifunctionality were developed by a simple and fast gelation process not only to inactivate bacteria but also to accelerate bacteria-infected wound healing. Sodium nitroprusside (SNP) loaded PCN-224 nanoparticles were introduced into the polymer matrix formed by the dynamic and reversible coordinate bonds between Ag+ with carboxyl and amino or hydroxyl groups on carboxymethyl chitosan (CMCS), hydrogen bonds and electrostatic interactions in the polymer to fabricate SNP@PCN@Gel hydrogels. SNP@PCN@Gel displayed interconnected porous structure, excellent self-healing capacity, low cytotoxicity, good blood compatibility, and robust antibacterial activity. SNP@PCN@Gel could produce reactive oxygen species (ROS) and NO along with Fe2+, and showed long-term sustained release of Ag+, thereby effectively killing bacteria by synergistic photothermal (hyperthermia), photodynamic (ROS), chemodynamic (Fenton reaction), gas (NO) and ion (Ag+ and -NH3+ in CMCS) therapy. Remarkably, the hydrogels significantly promoted granulation tissue formation, reepithelization, collagen deposition and angiogenesis as well as wound contraction in bacteria-infected wound healing. Taken together, the strategy represented a general method to engineer the unprecedented photoactivatable “all-in-one” hydrogels with enhanced antibacterial activity and paved a new way for development of antibiotic alternatives and wound dressing.Graphical abstract

Hyaluronic acid hydrogels with excellent self-healing capacity and photo-enhanced mechanical properties for wound healing

A continuously stable moist healing environment is immensely beneficial for wound healing, which can be availably achieved by providing an in situ hydrogel with enough strength resembling skin tissue and self-healing ability. Herein, through a dual-crosslinking strategy, hyaluronic acid-based hydrogels with excellent self-healing capacity and enhanced mechanical properties are fabricated via the acylhydrazone linkages and subsequent photocrosslinking based on hydrazide-modified sodium hyaluronate and aldehyde-modified maleic sodium hyaluronate. The hydrogels demonstrate the fast gelation process (< 1 min), the controlled swelling behaviors, and the good biocompatibility. Notably, they possess enhanced mechanical strength similar to the human dermis (∼ 2.2 kPa). Also, they can self-heal rapidly with a self-healing efficiency of ∼90 % at 6 h. Based on this, the hyaluronic acid-based hydrogels, without any biological factors involved, can facilitate the full-thickness skin wound reconstruction process by accelerating the three phases of the wound repair, including reducing wound inflammation in the inflammatory phase, promoting angiogenesis in the proliferative phase, and promoting the deposition and reconstruction of collagen in the remodeling phase. The produced hyaluronic acid hydrogel can serve as an ideal candidate for wound healing.

Preparation of Hemicellulose Nanoparticle-Containing Ionic Hydrogels with High Strength, Self-Healing, and UV Resistance and Their Applications as Strain Sensors and Asymmetric Pressure Sensors.

Smart functional fillers can significantly enhance the comprehensive properties of ionic hydrogels, such as their mechanical properties, which are key features of hydrogels in wearable sensor applications. As a plant-derived natural polymer, hemicellulose can serve as smart functional fillers. In this study, tannic acid-modified hemicellulose nanoparticles (TA@HC) and Fe3+ were used in the preparation of PAA/TA@HC/Fe3+ hydrogels. The addition of TA@HC and Fe3+ in the sodium persulfate (SPS) and acrylic acid (AA) polymerization system resulted in a fast gelation process that was completed within a short time (as short as 30 s) at room temperature. The catechol-rich TA and Fe3+ system allows for quick activation of SPS to produce free radicals, generating abundant hydroxyl groups in a short period of time, which was responsible for the fast gelation. Furthermore, due to the TA@HC effect and the dynamic catechol (TA)-Fe3+ redox system, the PAA/TA@HC/Fe3+ hydrogel exhibited excellent mechanical properties with an exceptionally high strain (as high as 5600%), adhesiveness, rapid and efficient self-healing ability, and reproducible self-adhesion onto various substrates. More importantly, asymmetric adhesive PAA/TA@HC/Fe3+ hydrogels were prepared by selective Fe3+ coating of the upper hydrogel surface to render the top surface nonadhesive so that the same hydrogel with different adhesiveness between the upper and bottom surfaces was obtained. The asymmetric adhesive hydrogel design permits the adhesive side to fit comfortably to the skin and the nonadhesive side showing anti-interference against various different pollutant materials, accurately serving as a pressure sensor.

FeSe and Fe3Se4 encapsulated in mesoporous carbon for flexible solid-state supercapacitor

Metal selenides have been developed as promising alternatives of metal oxides in energy storage field due to their high conductivity and low bandgap. However, the synthesis of selenides usually suffers from the low melting point and strong volatility of selenium at temperatures higher than 217 ℃. Herein, a facile strategy was developed to prepare iron selenides using a template of Se-contained MOF gel, which could in situ immobilize Se powder due to the fast gelation process, resulting a porous, uniform and tight precursor. By adjusting the mole ratio of Fe and Se in the precursor, FeSe@C and Fe3Se4@C were controllably synthesized with rich mesopores and excellent carbon-encapsulation structure. The kinetics analysis indicates that these unique structures are beneficial for improving electrode kinetics, charge/ion-transfer resistance and electrochemical stability. FeSe@C and Fe3Se4@C exhibit significant capacitances (611.0F g−1 and 569.0F g−1 at 1 A g−1), and excellent cycling properties (94.22% and 93.28% retention after 2000 charge–discharge cycles at 5 A g−1). When estimated in practical application, the flexible solid-state symmetric supercapacitor of FeSe@C//Fe3Se4@C delivers a high Csp of 160.1F g−1, the superior energy density of 32.1 W h kg−1 and a high specific power density of 5998 W kg−1 with 89.5% capacitance retention after 5000 cycles, and the outstanding flexibility.

In Situ Forming and Reversibly Cross-Linkable Hydrogels Based on Copolypept(o)ides and Polysaccharides.

The emerging tide of hydrogels in biomedical fields drives them to possess good biocompatibility, tunable mechanical properties, and fast gelation process. Herein, a composite hydrogel containing copolypept(o)ides and functional polysaccharides was constructed through dynamic acylhydrazone linkages. First, a series of peptide-peptoid copolymers were synthesized by ring-opening polymerization of sarcosine (Sar) and l-glutamic acid γ-benzyl ester (BLG) N-carboxyanhydrides (NCAs). The benzyl groups of BLG units were substituted with hydrazide groups through ester-amide exchange aminolysis reaction. The statistical copolymer of poly(sarcosine-co-glutamate-hydrazide) (P(Sar-co-GH)) was chosen as an optimized precursor due to its excellent water solubility and gel-forming ability with aldehyde-modified sodium alginate (OSA). Moreover, cellulose nanocrystals (CNCs) were prepared as nanofillers to reinforce the P(Sar-co-GH)-OSA hydrogel. We demonstrated that the copolymer sequences and composition contents made a difference to the properties of the formed hydrogels by variation of the cross-linking density. The dynamic acylhydrazone bonds endowed hydrogels with pH responsiveness and reversible networks. The NIH/3T3 cells encapsulated in the hydrogels maintained high viability and proliferation abilities, indicating that the nanocomposite hydrogels could be explored to fabricate a customized responsive drug delivery system or cell scaffolds for tissue engineering.

Comparison of Bioorthogonally Cross-Linked Hydrogels for in Situ Cell Encapsulation.

Hydrogels are water-saturated polymer networks and extensively used in drug delivery, tissue repair engineering, and cell cultures. For encapsulation of drugs or cells, the possibility to form hydrogels in situ is very much desired. This can be achieved in numerous ways, including use of bioorthogonal chemistry to create polymer networks. Here we report a set of bioorthogonally clickable polymers that was designed with the aim to find a combination that could rapidly encapsulate cells in a three-dimensional manner to improve the preparation of hydrogels as tissue mimics. To this end, tetrazine (Tet), trans-cyclooctene (TCO), azide (N3), dibenzocyclooctyne (DBCO), bicyclo[6.1.0]nonyne (BCN), 3,4-dihydroxyphenylacetic acid (DHPA), and norbornene (Norb) were grafted to four-armed poly(ethylene)glycol (star-PEG) polymers of 10 kDa. Inverted vial tests and rheology demonstrated that hydrogels formed within seconds from combinations of TCO-Tet, BCN-DHPA, and BCN-Tet. Hydrogels from DBCO-N3, DBCO-DHPA, and BCN-N3 formed in the range of minutes, whereas the Norb-Tet ligation required multiple hours to form a gel. After this comparison, we chose to prepare hydrogels via DBCO-N3 and BCN-N3 and employed them for human mesenchymal stem cell (HMSC) cultures for a period of 5 days. We additionally incorporated RGDS and MMP cleavable peptide (MMPcp) motifs in these gels to stimulate cell adhesion and add degradability. Both DBCO and BCN gel systems including the functional peptide motifs allowed HMSCs to be viable and spread in 5 days. The DBCO-based hydrogel could trap cells at different depths due to its fast gelation process, while the slower gelation of the BCN-based hydrogel led to cell sedimentation.

Time-Resolved Mechanical Spectroscopy of Soft Materials via Optimally Windowed Chirps

The ability to measure the bulk dynamic behavior of soft materials with combined time- and frequency-resolution is instrumental for improving our fundamental understanding of connections between the microstructural dynamics and the macroscopic mechanical response. Current state-of-the-art techniques are often limited by a compromise between resolution in the time and frequency domain, mainly due to the use of elementary input signals that have not been designed for fast time-evolving systems such as materials undergoing gelation, curing or self-healing. In this work, we develop an optimized and robust excitation signal for time-resolved mechanical spectroscopy through the introduction of joint frequency- and amplitude-modulated exponential chirps. Inspired by the biosonar signals of bats and dolphins, we optimize the signal profile to maximize the signal-to-noise ratio while minimizing spectral leakage with a carefully-designed modulation of the envelope of the chirp. A combined experimental and numerical investigation reveals that there exists an optimal range of window profiles that minimizes the error with respect to standard single frequency sweep methods. The minimum error is set by the noise floor of the instrument, suggesting that the accuracy of an optimally windowed chirp signal is directly comparable to that achievable with a standard frequency sweep, while the acquisition time can be reduced by up to two orders of magnitude, for comparable spectral content. Finally, we demonstrate the ability of this optimized signal to provide time- and frequency-resolved rheometric data by studying the fast gelation process of an acid-induced protein gel. The use of optimally windowed chirps enables a robust rheological characterization of a wide range of soft materials undergoing rapid mutation and has the potential to become an invaluable tool for researchers across different disciplines.

Structural, microrheological and kinetic properties of a ternary silica-Pluronic F127-starch thermosensitive system

HypothesisThe sol-gel transition in aqueous suspensions consisting of silica particles and thermosensitive polymer is controlled by inter-particle forces and solution properties of the polymer. Addition of a second non-thermosensitive polymer may affect the transition. The purpose of this work was to characterize the kinetics of the sol-gel transition and to understand the effects of a second non-thermosensitive polymer on the microstructure, using a combination of classical rheology and microrheology. ExperimentsClassical rotational rheology as well as two microrheology methods, Multiple Particle Tracking (MPT) and Diffusing Wave Spectroscopy (DWS), were used to investigate the sol-gel transition of a ternary silica-Pluronic F127-starch thermosensitive system. FindingsClassical rheometry and DWS indicated sol-gel transition temperature ∼25 °C at 1 wt% Pluronic, independently of the concentration of the other components. DWS showed a fast gelation process, less than two minutes for all samples, beside a second slow kinetic process. In the gel state, MPT indicated micro-structural and micro-viscoelastic differences compared to rotational rheology. This was explained by formation of an elastic matrix of silica and polymers in combination with assembly of silica particles in large macroporous agglomerates. Presence of starch led to breakdown of the macroporous network, leaving the homogeneous elastic network left.

A Facile and Fast Gelation Process to Prepare Highly Spherical Millimeter‐Sized Silica Aerogel Beads

Millimeter‐sized silica aerogel beads were successfully prepared by a facile fast gelation process, in which silica sol beads were generated by extruding preformed silica sol through multiple nozzles into oil phase and then transformed into silica alcogel beads, followed by supercritical drying. The transition process from the silica sol to the silica alcogel beads was finished at a 97.6% conversion rate. The resultant silica aerogel beads have an average diameter of ~1.5 mm with a good sphericity, and an average pore size of ~12 nm with topical porous three‐dimensional network structures.

Preparation of Silica–Alumina Hollow Spheres with a Single Surface Hole by Co-axial Microchannel

Si/Al composite hollow spheres with a surface hole were prepared with the co-axial microchannel in a one-step method. It is easy to use the technique for size control and continuous operation. At Si/Al ratio between 4 and 5, a hole forms on the surface, due to the fast gelation process and high viscosity of the sol. Scanning electron microscopy, nitrogen adsorption–desorption isotherms, and mercury intrusion method are used to characterize the samples. The hole size is 40–150μm and the particle size is 450–600μm. The size can be adjusted by the flow rate of the oil phase.

Injectable and Biodegradable Supramolecular Hydrogels by Inclusion Complexation between Poly(organophosphazenes) and α-Cyclodextrin

Biodegradable poly(organophosphazenes) containing side chains of various oligo(ethylene glycol) methyl ethers (mPEGs) and glycine ethyl ester units were synthesized and characterized. Novel supramolecular-structured hydrogel systems based on the inclusion complex between the mPEG grafted polyphosphazenes and α-cyclodextrin were prepared in aqueous media. The gelation time depended on the length of the mPEG side chains, the molar ratio between mPEG repeat units and α-cyclodextrin, and the concentration of the polymeric gel precursors. The rheological measurements of the supramolecular hydrogels indicate a fast gelation process and flowable character under a large strain. The hydrogel systems demonstrate unique structure-related reversible gel–sol transition properties at a certain temperature due to the reversible supramolecular assembly. The formation of a channel-type inclusion complex induced gelation mechanism was studied by DSC, TGA, 13C CP/MAS NMR, and X-ray diffraction techniques. The strong potenti...

Evidence for Kinetic Nucleation in Helical Nanofiber Formation Directed by Chiral Solvent for a Perylene Bisimide Organogelator

The self-assembly behavior of an achiral perylene bisimide (PBI) organogelator that bears two 3,4,5-tridodecyloxybenzoylaminoethyl substituents at the imide positions has been investigated in chiral solvents (R)- and (S)-limonene in great detail by circular dichroism (CD) spectroscopy and atomic force microscopy (AFM). CD spectroscopic studies on dilute solutions revealed a preferential population of one-handed helical assemblies in chiral solvent with an enantiomeric excess close to 100 %, whereas AFM images of more than 100 nanofibers of the organogel obtained from more concentrated solutions were found to consist of both handed helices with an enantiomeric excess of only 20 %. This discrepancy is attributed to the fast gelation process at high dye concentration that evidently proceeds through non-equilibrated nuclei in a kinetic rather than thermodynamic self-assembly process. Under these conditions the chiral induction from the homochiral solvent may not be adequate in effectively populating only one-handed helices.

Production of low-density sodium silicate-based hydrophobic silica aerogel beads by a novel fast gelation process and ambient pressure drying process

We report a method to synthesize low-density transparent mesoporous silica aerogel beads by ambient pressure drying (APD). The beads were prepared by acid–base sol–gel polymerization of sodium silicate in aqueous ammonia solution via the ball dropping method (BDM). To minimize shrinkage during drying, wet silica beads were initially prepared; their surfaces were then modified using trimethylchlorosilane (TMCS) via simultaneous solvent exchange and surface modification. The effects of the volume percentage (%V) of TMCS on the physical and textural properties of the beads were investigated. The specific surface area and cumulative pore volume of the silica aerogel beads increased with an increase in the %V of TMCS. Silica aerogel beads with low packing bed density (0.081 g/cm 3), high surface area (917 m 2/g), and large cumulative pore volume (2.8 cm 3/g) was obtained when 10%V TMCS was used. Properties of the final product were examined by FE-SEM, TEM, BET, and TG–DT analyses. Surface chemical modifications were confirmed by FTIR spectroscopy. The hydrophobic silica aerogel beads were thermally stable up to 411 °C. We discuss our results and compare our findings for modified versus unmodified silica beads.

Preparation of molecularly imprinted polymers via atom transfer radical “bulk” polymerization

AbstractThe first application of atom transfer radical “bulk” polymerization (ATRBP) in molecular imprinting is described, which provides molecularly imprinted polymers (MIPs) with obvious imprinting effects towards the template, very fast binding kinetics, and an appreciable selectivity over structurally related compounds. In comparison with the MIP prepared via the normally used traditional “bulk” free radical polymerization (BFRP), the MIPs obtained via ATRBP showed somewhat lower binding capacities and apparent maximum numbers Nmax for high‐affinity sites as well as quite similar binding association constants Ka for high‐affinity sites and high‐affinity site densities, in contrast with the previous reports (e.g., nitroxide/iniferter‐mediated “bulk” polymerization provided MIPs with improved properties). This is tentatively ascribed to the occurrence of rather fast gelation process in ATRBP, which greatly restricted the mobility of the chemical species, leading to a heavily interrupted equilibrium between dormant species and active radicals and heterogeneous polymer networks. In addition, the general applicability of ATRBP was also confirmed by preparing MIPs for different templates. This work clearly demonstrates that applying controlled radical polymerizations (CRPs) in molecular imprinting not always benefits the binding properties of the resultant MIPs, which is of significant importance for the rational use of CRPs in generating MIPs with improved properties. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 532–541, 2010

Pyrene derived functionalized low molecular weight organic gelators and gels

Pyrene derived binary functionalized low molecular weight organic gelators (FLMOGs) and gels thereof in selected organic solvents were synthesized and characterized. The functionality refers to a functional group that does not take part in formation of the supramolecular gel network, but remains free and available for other purposes, such as to bind nanoparticles or other molecules into the gel structure. Functional groups were observed to disturb gel formation strongly, if they interact with each other within the same supramolecule due to the formation of competitive structures. Preventing such interactions restored the original gel properties. A gel with weaker supramolecular bonding than the binding between the functional groups was successfully made by separating the functional groups by distance. The π–π-interaction was found to be of negligible significance to the supramolecular binding energy, but probably essential to align the molecules to a one-dimensional chain and bring them into the range of van der Waals forces mainly responsible for the binding in this system. Solvent was observed to increase the binding energy of the supramolecule. All molecules were characterized by spectroscopic techniques and elemental analysis. Selected gels were characterized with rheometry, scanning electron microscopy, UV- and fluorescence spectroscopy. Gelation kinetics and hysteresis were measured by UV-spectroscopy and a fast gelation process was observed for all the gelators studied. The melting enthalpies were measured by DSC and calculated theoretically by PM3 level of theory.

An example of integrative chemistry: Combined gelation of boehmite and sodium alginate for the formation of porous beads

We describe in the present report how the production of millimetric beads containing porous aluminum oxihydroxide (boehmite) can be obtained easily by taking advantage of the fast gelation process of sodium alginate by ion exchange. The combination of two gelation mechanisms led us to the preparation of objects that can be more easily manipulated than powder and still exhibit the porous properties of this latter, with similar surface area. This pathway can be extended to various systems and it constitutes an additional example of a recent concept called “integrative chemistry” [R. Backov, Soft Matter 2 (2006) 452–464].

Highly porous SiH containing hybrids prepared by a novel process: rapid gelation of hydrogensilsesquioxane under ambient pressure

A novel fast gelation route for the preparation of highly porous materials is described. Commercially available hydrogensilsesquioxane was used as the precursor in this approach, leading through a simple, single step process to gels, within minutes. This novel approach relied on increase of wet gel pore radius ( r p) to reduce the capillary pressure upon drying. The increment of r p was achieved by the evolution of hydrogen gas during the gelation step, which was triggered by the use of activating agents. NH 4OH, formamide, and polyethylene glycol were used as activating agents for this purpose. The resulting porosity in fast gelation derived porous materials was much broader than those in the conventional aerogels, with macropores up to several hundred nm, along with mesopores. Systematic studies of this novel fast gelation process were carried out through careful variation of the experimental conditions to gain control in the mesopore region. NH 4OH was unable to control the amount of SiH conversion into SiOH during the fast gelation process, trace amount of NH 4OH (0.036%) was sufficient to convert all of the SiH functions. The resulting porous materials derived by this activating agent showed a broad distribution covering the entire mesopore region. Polyethylene glycol and formamide showed better control over SiH to SiOH conversion, with a higher amount of activating agents giving higher conversions. Similar trends of both activating agents level onto total pore volume in the resulting porous materials were observed through the porosity evaluations, with the mid range concentration leading to the highest total pore volume. Mesopores with a narrow size distribution between 30 and 50 Å were observed in porous materials generated by the lower concentration in both series.