Tunable Rheological Properties Research Articles

Smart viscoelastic anion polyelectrolyte fluids “crosslinked” by CO2

Smart fluids with tunable rheological properties show a wide range of applications in various areas, so they have attracted intense interest. Recently, the viscoelastic fluids with tunable rheological properties, particularly the CO2-triggered smart fluids, have become a popular topic because such reversible change in viscoelasticity conferring them new functions and expanding their applications. Additionally, anioinc polymers can be crosslinked to impart fluids significantly improved rheological properties. Herein, Sodium polyacrylate (NaPAA) and 2,4,6-tris(dimethylaminomethyl)phenol (TAP) are employed to prepare aqueous fluid. The solution properties of the fluid with and without CO2 are examined by steady and dynamical rheology. The effects of NaCl concentration and the ratio of NaPAA/TAP on the rheologies are studied and the interactions between TAP and NaPAA in the absence and presence of CO2 are investigated using pH titration, 1H NMR and cryo-TEM technology. CO2 is able to reversibly change the rheological properties of the fluid via protonating and deprotonating TAP, imparting it smart response. In the absence of NaCl, the introduction of the CO2 reduces the viscosity and elasticity of the fluid as the produced quaternary ammonium salts largely screen the electrostatic repulsions of NaPAA chains. However, in the presence of NaCl, the addition of CO2 greatly enhances the viscoelasticity of the fluid because the protonated TAP strongly interacts with NaPAA forming three-dimensional networks.

An injectable and antifouling self-fused supramolecular hydrogel for preventing postoperative and recurrent adhesions

Abdominal adhesions is a type of serious complication of abdominal surgery. Existing barrier hydrogels are severely limited in the prevention of adhesions due to their poor controllability and long retention time in vivo. Here, we fabricate a supramolecular hydrogel (PNAGA-PHPMA) by copolymerization of N-acryloyl glycinamide (NAGA), a hydrogen bonding monomer, and highly hydrophilic N-(2-hydroxypropyl) methacrylamide (HPMA). The injectable PNAGA-PHPMA hydrogel cross-linked by reversible hydrogen bonds exhibits tunable rheological properties, preferable self-fused ability governed by H-bonds, excellent antifouling capability, and on-demand retention time in vivo. Squeezed out of a syringe to the abdominal cavity, the fragmented gel piece self-fused into an intact hydrogel, thus demonstrating an efficient inhibitory effect on postoperative abdominal adhesions and recurrent adhesions after adhesiolysis. The molecular mechanism studies reveal that the hydrogel significantly downregulates fibrosis-related cytokines (TGF-β1 and Fibrinogen) and pro-inflammatory cytokines (TNF-α and IL-6), regulates the fibrinolytic system balance (t-PA and PAI-1), and inhibits the activity of Erk1/2 and p38 kinase in the mitogen-activated protein kinase (MAPK) signaling pathway, thereby showing an excellent anti-fibrotic and anti-inflammatory effect. This injectable and antifouling self-fused supramolecular hydrogel has a profound clinical significance for the prevention of postoperative adhesions and recurrent adhesions.

Preliminary Insights into Electro-Sensitive Ecolubricants: A Comparative Analysis Based on Nanocelluloses and Nanosilicates in Castor Oil

The newest generation of lubricants needs to adapt to stricter environmental policies. Simple and sustainable formulations with tunable rheological properties under the action of electric potentials may be the key. The present research explored the feasibility of producing electro-sensitive ecolubricants based on nanocellulose (crystalline and fibrillar) or nanoclay (Cloisite 15A montmorillonite and halloysite nanotubes) dispersions in castor oil, at concentrations that ranged from 2 to 6 wt.%. Broadband dielectric spectroscopy (BDS) measurements allowed for a first estimate on the electro-responsive potential of the nanofluids. The nanocelluloses and the montmorillonite suspensions presented a relaxation event in the dielectric loss, ε″, centered at ca. 2–4 kHz, which is related to interfacial polarization. Moreover, their actual electro-rheological (ER) effect under high electric potentials up to 4 kV/mm was assessed by determining the magnitude of the yield stress from steady flow curves at 25 °C. It was found that the nanocelluloses and the montmorillonite showed an enhancement of three orders of magnitude in their yield stress values at 4 kV/m. This enhancement was much greater than in the halloysite nanoclay, which did not exhibit any polarization). This is the starting point for the development of environmentally friendly ER lubricating fluids, based on nanocellulose and montmorillonites (layered nanosilicates), which might assist in reducing the friction and wear through the application of controlled electric fields.

Biocompatible and self-recoverable succinoglycan dialdehyde-crosslinked alginate hydrogels for pH-controlled drug delivery

We fabricated polysaccharide-based hydrogels, which are biocompatible, self-recoverable and pH-sensitive. Succinoglycan dialdehyde (SGDA) was first synthesized from bacterial succinoglycan directly isolated from Sinorhizobium meliloti and then hydrazine-functionalized alginate (HZ-Alg) was prepared to form SGDA-crosslinked alginate hydrogels (SGDA/HZ-Alg) without any catalyst. Due to structural characteristics of SGDA, SGDA/HZ-Alg were effectively obtained in a short time even at low concentrations (0.94–1.57 wt%) where they exhibited self-recoverable and tunable rheological properties corresponding to efficiency of recovery from 93.2%–97.9%. Moreover, SGDA/HZ-Alg showed the pH-responsive degradation as well as pH-controlled release behavior for 5-fluorouracil. 5-Fluorouracil was released approximately 98 % at pH 2.0 within 12 h, but not completely released even after 24 h at pH 7.4. The WST-8 assay results also demonstrated that SGDA/HZ-Alg did not show any cytotoxicity against HEK-293 cells. Since the suggested hydrogels are biocompatible, rheologically self-recoverable and tunable, and pH-controllable, they would be potential biomaterials for the hydrogel-based drug delivery systems.

Rheological Properties of İnjectable Hyaluronic Acid Hydrogels for Soft Tissue Engineering Applications

Hydrogels are cross-linked three-dimensional (3D) polymeric network, which can hold the water within its porous structure. They have recently been used in various biomedical applications. In this study, injectable hyaluronic acid (HA) hydrogels were prepared using different concentrations of 1,4-butanediol diglycidyl ether (BDDE) as a crosslinker (1-5% w/w) and investigated their rheological, swelling and injectability properties. The results demonstrated that the rheological characteristics of hydrogels enhanced with increasing crosslinker concentration. The elastic modulus of the hydrogels ranged from 280 Pa to 990 Pa, while the complex viscosities were found between 42 Pa.s and 190 Pa.s at an oscillation frequency of 1 Hz. These results clearly suggest that the injectable HA hydrogels are a potential candidate for various soft tissue engineering applications due to their highly tunable rheological properties.

Semi-quantitative Analysis of the UV-responsive Behavior of Anisotropic Phase Constructed by Gemini Surfactant 12-3-12·2Br− and trans-ortho-Methoxycinnamate

Photo-responsive materials with adjustable self-assembly morphologies and tunable rheological properties have attracted widespread interests of researchers in recent years because of their potential applications in controlled release, microfluidics, sensors, and so forth. In this paper, a series of UV-sensitive anisotropic fluids were prepared by combining trans-ortho-methoxycinnamate (trans-OMCA, in its salts form) and cationic Gemini surfactant propanediyl-α, ω-bis (N-dodecyl-N, N-dimethylammonium bromide) (12-3-12·2Br−) based on the research of self-assembly behaviors of the mixed system. The photo-responsive behaviors of anisotropic fluid formed in 12-3-12·2Br−/trans-OMCA/H2O system including macroscopic phase transition, microstructure transformation, rheological property, molecular interaction and isomerization degree of trans-OMCA were investigated by various techniques including UV-vis spectrum, rheology measurement, 1H NMR and 2D NOESY spectrum, transmission electron microscopy (TEM), polarized optical microscopy (POM), and dynamic light scattering (DLS). It is proved that upon exposure to UV-light, ortho-methoxycinnamate (OMCA) undergoes a photo-isomerization from trans form to cis form, which results in geometry transitions of the 12-3-12·2Br−/OMCA aggregates accompanied by a continuous phase separation and combination macroscopically; both proportion and concentration of OMCA in anisotropic solution have great influences on the photo-responsive behaviors of the system including the durations of UV irradiation and isomerization degrees of OMCA at the phase transition points. The photo-responsiveness of this smart fluids and the quantitative analysis are expected to provide reference for academic research or practical application in the fields of biomedicine, soft matters, food engineering and sunscreen.

Self-Healing and Moldable Poly(2-isopropenyl-2-oxazoline) Supramolecular Hydrogels Based on a Transient Metal Coordination Network

Materials that are capable of autonomous healing upon damage is the focus of many research groups because of the numerous potential applications of these materials, such as coatings, actuators for robotic applications, and wound healing. Although significant progress in the area has been achieved, the synthesis and large-scale applications of self-healing and moldable materials continue to be challenging. The present study highlights the use of poly(2-isopropenyl-2-oxazoline) partially modified with 2,2':6',2 ''-terpyridine-4'-carboxylic acid (TPy) for the synthesis of self-healing and moldable metallo-supramolecular hydrogels by metal coordination. The hydrogelation was triggered by the addition of divalent transition metal ions (e.g., Fe2+, Ni2+, Co2+, and Zn2+). Using this approach, metallo-supramolecular hydrogels with tunable rheological properties could be obtained, while evidencing the correlation between the hydrogel mechanical properties and the binding strength and kinetic lability of the supramolecular cross-linking motifs. The resulting hydrogels exhibited rapid self-healing properties at room temperature as confirmed by rheological measurements. Moreover, hydrogels cross-linked with Co2+ and Zn2+ showed a gel-sol transition, indicative of the higher kinetic lability of their complexes. The hydrogels exhibited fast and excellent repeatable autonomic healing capacity even at higher cross-linking density, making them useful as autonomously repairing materials and coatings. Compared to the conventional metallo-hydrogels, the herein developed hydrogels can be molded into a variety of complex geometrical shapes, which could be potentially applied in various areas from soft robotics to dynamic self-healing coatings.

Threading-Induced Dynamical Transition in Tadpole-Shaped Polymers.

The relationship between polymer topology and bulk rheology remains a key question in soft matter physics. Architecture-specific constraints (or threadings) are thought to control the dynamics of ring polymers in ring–linear blends, which thus affects the viscosity to range between that of the pure rings and a value larger, but still comparable to, that of the pure linear melt. Here we consider qualitatively different systems of linear and ring polymers, fused together in “chimeric” architectures. The simplest example of this family is a “tadpole”-shaped polymer, a single ring fused to the end of a single linear chain. We show that polymers with this architecture display a threading-induced dynamical transition that substantially slows chain relaxation. Our findings shed light on how threadings control dynamics and may inform design principles for chimeric polymers with topologically tunable bulk rheological properties.

Injectable in situ forming kartogenin-loaded chitosan hydrogel with tunable rheological properties for cartilage tissue engineering

Limited regeneration capacity of cartilage can be addressed by tissue engineering approaches including localized delivery of bioactive agents using biomaterials. Although chitosan hydrogels have been considered as appropriate candidates for these purposes, however, their poor mechanical properties limit their real applications. Here, we develop in situ forming chitosan hydrogels with enhanced shear modulus by chemical modification of chitosan using N-(β-maleimidopropyloxy) succinimide ester (BMPS). Moreover, we utilize β-Glycerophosphate (β-GP) in the hydrogels for achieving thermosensitivity. We investigate the effects of BMPS, β-GP and chitosan concentration on rheological and swelling properties of the hydrogels. Accordingly, we generate significant statistical models by response surface method to predict these properties. These models provide us beneficial tools to tune the hydrogel properties depending on the cartilage defect location and properties. Finally, we incorporate a recently discovered small biomolecule, kartogenin (KGN), for promoting chondrogenesis of stem cells into the optimized hydrogel. The hydrogel’s shear modulus is 78 ± 5 kPa which covers a wide range of human articular cartilage shear modulus (50–250 kPa). It can be injected to the defects non-invasively at room temperature which gels at 37 °C within minutes. Additionally, it provides a sustained KGN release for ∼40 days that may eliminate the need of multiple injections. In vitro chondrogenic results confirm enhanced chondrogenic differentiation of human adipose mesenchymal stem cells (hAMSCs) treated with KGN-loaded hydrogel, compared to pure KGN. Based on the enhanced hydrogel shear modulus, injectability, gelation behavior, long-term drug release and in vitro results, this thermosensitive hydrogel looks promising for cartilage tissue engineering.

Chitosan/PAMAM/Hydroxyapatite Engineered Drug Release Hydrogels with Tunable Rheological Properties.

In this paper, a new formulation of biodegradable and bioresorbable chitosan-based hydrogel for controlled drug release was investigated. A chitosan–dendrimer–hydroxyapatite hydrogel, obtained by covalently grafting chitosan powder with an hyperbranched PAMAM dendrimer followed by in-situ precipitation of hydroxyapatite and gelification, was synthesized and characterized by FTIR, NMR, TGA, XRD and rheological studies. The hydrogels have been also doped with an anti-inflammatory drug (ketoprofen) in order to investigate their drug release properties. Chemical and chemical-physical characterizations confirmed the successful covalent functionalization of chitosan with PAMAM and the synthesis of nanostructured hydroxyapatite. The developed hydrogel made it possible to obtain an innovative system with tunable rheological and drug-releasing properties relative to the well-known formulation containing chitosan and hydroxyapatite powder. The developed hydrogel showed different rheological and drug-releasing properties of chitosan matrix mixed with hydroxyapatite as a function of dendrimer molecular weight; therefore, the chitosan–dendrimer–hydroxyapatite hydrogel can couple the well-known osteoconductive properties of hydroxyapatite with the drug-release behavior and good processability of chitosan–dendrimer hydrogels, opening new approaches in the field of tissue engineering based on biopolymeric scaffolds.

Chitosan-stabilized emulsion gels via pH-induced droplet flocculation

The formation and stabilization of Pickering-type emulsion gels at low oil fractions (φ) remains a challenge. This work reports on the fabrication of emulsion gels solely stabilized by chitosan at φ values as low as 0.2 via pH adjustment and storage time. We show that slight adjustments in pH in a narrow window from 6.4 to 7.0 (near the pKa of chitosan) can effectively tune the gelation properties of chitosan through control of surface charge and floc size. Upon storage of 2 or more days, oil droplets coated with these aggregated chitosan particles flocculate to form and strengthen self-supporting emulsion gels. The increase in pH not only promotes the formation of networked chitosan particles in the continuous phase but also leads to an increase in inter-droplet interactions, resulting in an enhancement in emulsion gel strength. Increasing φ from 0.2 to 0.75 results in more rapid emulsion gel formation with a higher elastic modulus. The present findings demonstrate the effectiveness of pH-tailored chitosan particles in generating and stabilizing O/W emulsion gels with tunable microstructure and rheological properties.

TEMPO-Nanocellulose/Ca2+ Hydrogels: Ibuprofen Drug Diffusion and In Vitro Cytocompatibility.

Stable hydrogels with tunable rheological properties were prepared by adding Ca2+ ions to aqueous dispersions of 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO)-oxidized and ultra-sonicated cellulose nanofibers (TOUS-CNFs). The gelation occurred by interaction among polyvalent cations and the carboxylic units introduced on TOUS-CNFs during the oxidation process. Both dynamic viscosity values and pseudoplastic rheological behaviour increased by increasing the Ca2+ concentration, confirming the cross-linking action of the bivalent cation. The hydrogels were proved to be suitable controlled release systems by measuring the diffusion coefficient of a drug model (ibuprofen, IB) by high-resolution magic angle spinning (HR-MAS) nuclear magnetic resonance (NMR) spectroscopy. IB was used both as free molecule and as a 1:1 pre-formed complex with β-cyclodextrin (IB/β-CD), showing in this latter case a lower diffusion coefficient. Finally, the cytocompatibility of the TOUS-CNFs/Ca2+ hydrogels was demonstrated in vitro by indirect and direct tests conducted on a L929 murine fibroblast cell line, achieving a percentage number of viable cells after 7 days higher than 70%.

A Fe3+-crosslinked pyrogallol-tethered gelatin adhesive hydrogel with antibacterial activity for wound healing.

In this work, a tunicate-inspired gelatin-based hydrogel is prepared by simply mixing 2,3,4-trihydroxybenzaldehyde (THB)-tethered gelatin solution with a small amount of Fe3+ ions via the Schiff-base reaction and simultaneous formation of hexavalent Fe-complexes. The resulting hydrogel (termed GelTHB-Fe) exhibits not only tunable gelation time, rheological properties and self-healing ability by adjusting the composition, but also robust adhesion to a variety of materials, with an average adhesion strength of 136.7 kPa, 147.3 kPa, 153.7 kPa, 92.9 kPa, and 56.5 kPa to PMMA, iron, ceramics, glass and pigskin, respectively. Intriguingly, the pyrogallol moieties impart an antibacterial activity to the GelTHB-Fe hydrogel, which is shown to reduce infection and promote wound healing in a diabetic rat model. This GelTHB-Fe hydrogel holds great potential as a promising tissue adhesive.

Methacrylated Hyaluronic Acid–Based Hydrogels Maintain Stemness in Human Dental Pulp Stem Cells

2-Aminoethyl methacrylate (AEMA)–modified hyaluronic acid (HA) hydrogels with tunable swelling, degradation, and rheological properties were developed to maintain the native spherical and stemness of human dental pulp stem cells (DPSCs). Two molecular weights (MW) of HA, 18 and 270 kDa, and 25% degree of AEMA substitution were used to synthesize the HA macromers and hydrogels. The HA macromers were characterized by 1H NMR, and the AEMA-HA hydrogels were synthesized by UV polymerization. The swelling, hydrolytic degradation, and rheological properties of the hydrogels strongly depended on the MW of HA. The degradation rate decreased and the storage modulus increased with the increase in the MW of HA. The storage modulus of the hydrogels decreased with degradation of the hydrogels. The hydrogels were not cytotoxic to DPSCs evidenced by MTT assay, Hoechst 33342 live cell staining, and propidium iodide dead cell staining. The hydrogels maintained the native spherical morphology and stemness of DPSCs when the hydrogels’ storage moduli were in the ranges of 486–681 Pa. In contrast, DPSCs grown on 2D cell culture substrates showed a flat and elongated shape and could not maintain their native spherical shape. The hydrogels increased the expression of the stemness including NANOG and SOX2 of DPSCs (3 and 24 folds, respectively) when their storage modulus was 681.41 ± 92.81 Pa in comparison with DPSCs grown on 2D cell culture plates. The designed AEMA-HA hydrogels mimic the in vivo 3D environment to grow DPSCs. Thus, they appear to have great potential for clinical applications in regenerative medicine and other therapeutic remedies after further optimization in the future. Regenerative medicine is a translational approach that offers the possibility to replace or heal the diseased or damaged tissues caused by trauma, age, infection, cancer, or inherited defects. Such reinstatement of the functionality or healing of the damaged cells or tissues often includes the combination of numerous strategies including the use of biomaterials/scaffolds, stem cells, growth factors, and small molecules. In this study, we used hyaluronic acid (HA), a naturally occurring polysaccharide biopolymer commonly found in the extracellular matrix of connective tissues, to synthesize 3D hydrogel scaffolds for growing human dental pulp stem cells (DPSCs). We evaluated the effects of the molecular weight of HA, and the swelling, degradation, and rheological properties of the hydrogels on maintaining the native spherical and stemness of DPSCs for future therapeutic applications including regenerative medicine.

Dual Crosslinked Gelatin Methacryloyl Hydrogels for Photolithography and 3D Printing.

Gelatin methacryloyl (GelMA) hydrogels have been used in tissue engineering and regenerative medicine because of their biocompatibility, photopatternability, printability, and tunable mechanical and rheological properties. However, low mechanical strength limits their applications in controlled drug release, non-viral gene therapy, and tissue and disease modeling. In this work, a dual crosslinking method for GelMA is introduced. First, photolithography was used to pattern the gels through the crosslinking of methacrylate incorporated amine groups of GelMA. Second, a microbial transglutaminase (mTGase) solution was introduced in order to enzymatically crosslink the photopatterned gels by initiating a chemical reaction between the glutamine and lysine groups of the GelMA hydrogel. The results showed that dual crosslinking improved the stiffness and rheological properties of the hydrogels without affecting cell viability, when compared to single crosslinking with either ultraviolet (UV) exposure or mTGase treatment. Our results also demonstrate that when treated with mTGase, hydrogels show decreased swelling properties and better preservation of photolithographically patterned shapes. Similar effects were observed when three dimensional (3D) printed and photocrosslinked substrates were treated with mTGase. Such dual crosslinking methods can be used to improve the mechanical properties and pattern fidelity of GelMA gels, as well as dynamic control of the stiffness of tissue engineered constructs.

Injectable in situ dual-crosslinking hyaluronic acid and sodium alginate based hydrogels for drug release

A series of injectable in situ dual-crosslinking hydrogels (HA/ALG) based on oxidized sodium alginate (oxi-ALG) and hyaluronic acid modified with thiol and hydrazide (HA-SH/CDH) were prepared via hydrazone bonds and disulfide bonds. The chemical structures, morphologies, rheological properties, gelling time, swelling ratio, degradation rate and drug release behavior of hydrogels were investigated. HA/ALG hydrogels exhibited tunable gelling time, rheological properties, swelling ratio and degradation rate with varying precursor concentrations. The gelling time of HA/ALG hydrogels ranged from 157 s to 955 s, the values of yield stress of HA2/ALG2, HA3/ALG3 and HA4/ALG4 hydrogels were 1724, 4349 and 5306 Pa, and the degradation percentage of HA2/ALG2, HA3/ALG3 and HA4/ALG4 hydrogels were about 64%, 51% and 42% after incubating 35 days, respectively. Bovine serum albumin (BSA) was used as a model drug to investigate the drug controlled release properties, and the in vitro cumulative release percentage of BSA from HA2/ALG2, HA3/ALG3 and HA4/ALG4 drug-loaded hydrogels were about 79%, 72% and 69% after 20 days. The series of injectable in situ dual-crosslinking HA/ALG hydrogels could be an attractive candidate for drug delivery system, tissue engineering and regenerative medicine.

Colloidal Materials for 3D Printing.

In recent years, 3D printing has led to a disruptive manufacturing revolution that allows complex architected materials and structures to be created by directly joining sequential layers into designed 3D components. However, customized feedstocks for specific 3D printing techniques and applications are limited or nonexistent, which greatly impedes the production of desired structural or functional materials. Colloids, with their stable biphasic nature, have tremendous potential to satisfy the requirements of various 3D printing methods owing to their tunable electrical, optical, mechanical, and rheological properties. This enables materials delivery and assembly across the multiple length scales required for multifunctionality. Here, a state-of-the-art review on advanced colloidal processing strategies for 3D printing of organic, ceramic, metallic, and carbonaceous materials is provided. It is believed that the concomitant innovations in colloid design and 3D printing will provide numerous possibilities for the fabrication of new constructs unobtainable using traditional methods, which will significantly broaden their applications.

Characterization of Orange Oil Powders and Oleogels Fabricated from Emulsion Templates Stabilized Solely by a Natural Triterpene Saponin.

A new facile route was reported to use the natural triterpene Quillaja saponin (QS)-stabilized orange emulsions as a template for the development of flavor oil powders and oleogels achieved by the tunable oil fraction and drying mode. A fibrosis network interfacial film from self-assembly of QS at the oil-water interface possibility contributed to the fabrication of stable emulsion precursors and subsequent oil powder and oleogels by packing oil droplets in the network structure. An oil powder containing as high as 93 wt % orange oil was obtained by spray drying, showing excellent stability, flowability, and reconstitution ability. Upon the medium water removal rate of freeze drying, porous structured solid products followed by oleogels by a simple shearing can be formed. Upon oven drying, a translucent oleogel with high oil loading of 98.2 wt % was obtained from the high internal phase emulsion template. The resulting oleogels showed tunable rheological and texture properties, thixotropic recovery by modulating the oil fraction and water evaporation rate, and reversibility to reconstituted emulsions. Structuring liquid oil into solid materials by simply drying the continuous water from solely QS-based emulsions is very encouraging and provides new insights into various functional applications in the fields of foods, pharmaceuticals, cosmetics, and agriculture.

One- and two-photon responsive injectable nano-bundle biomaterials from co-assembled lipopeptides for controlling molecular diffusion.

An injectable biomaterial has been prepared through co-assembly of lipopeptides C4-Bhc-Glu-Glu-NH2 and C14-Phe-Lys-Lys-NH2. This biomaterial contained a large number of nanofibre bundles (nano-bundles, NBs) of lipopeptide co-assemblies and performed like hydrogels. The morphologies of the NBs were observed by transmission electron microscopy (TEM) and atomic force microscopy (AFM). The rheological properties were investigated with a rheometer. Excitingly, the NB biomaterials exhibited shear thinning and self-healing properties, and could be used as injectable biomaterials. The coumarin group in the lipopeptides endowed the NB biomaterials with both ultraviolet (UV, a one photon process) and near-infrared (NIR) light (a two photon process) responsiveness. A small molecule (Doxorubicin, DOX) and a large molecule (bovine serum albumin, BSA) were used as model drugs, and both of them could be encapsulated in the NB biomaterials and could also be released sustainably or explosively under different conditions (with or without one- and two-photon irradiation). DOX and BSA have different release behaviors because of the NBs. Cell assays showed that the co-assembled NB biomaterials exhibited low cytotoxicity to normal cells. However, when DOX was loaded, the NB biomaterials could kill HeLa cells sustainably. Under UV and NIR irradiation, HeLa cells could be killed rapidly because of the burst release of DOX. The co-assembled supramolecular NB biomaterials with dual-responsiveness, tunable rheological properties and multi-drug encapsulating ability might have potential in biomedical engineering.

Thermosensitive supramolecular and colloidal hydrogels via self-assembly modulated by hydrophobized cellulose nanocrystals

Utilization of reversible non-covalent interactions is a versatile design strategy for the development of stimuli responsive soft materials. In this study, hydrophobic interactions were harnessed to assemble water-soluble macromolecules and nanoparticles into a transient hybrid network forming thermosensitive hydrogels with tunable rheological properties. Hybrid hydrogels were built of biopolymer derived components: cellulose nanocrystals (CNCs), nanoparticles of high aspect ratio, and hydroxypropyl methylcellulose (HPMC). To enable polymer/CNC assembly via hydrophobic interactions, the surface of highly hydrophilic CNCs was modified by binding octyl moieties (octyl-CNCs). The amphiphilicity of octyl-CNCs was confirmed by surface tension measurements. The molecular and particulate amphiphiles assemble into hybrid networks, which result in stiffer and stronger hydrogels compared to HPMC hydrogels and hydrogels reinforced with hydrophilic CNCs. Hybrid hydrogels retain the ability of HPMC hydrogels to flow under applied shear stress. However, significantly higher viscosity was achieved for HPMC/octyl-CNCs compared with HPMC/CNCs hydrogels. The inherent thermal response of rheological properties of HPMC hydrogels was further amplified in combination with octyl-CNCs due to temperature-induced polymer/nanoparticle association via hydrophobic interactions. Saturation transfer difference NMR spectroscopy demonstrated the growth of network-bound water with an increase in temperature, which correlates with the increase of stiffness and viscosity of hydrogels upon heating. Rheological properties of these hybrid hydrogels are defined by the content of the soluble polymer and the CNCs, and it is shown that they can be finely adjusted for a required application.Graphical abstract