Self-healing hydroxypropyl guar gum/poly (acrylamide-co-3-acrylamidophenyl boronic acid) composite hydrogels with yield phenomenon based on dynamic PBA ester bonds and H-bond

Development and characterization of polyethylene oxide and guar gum-based hydrogel; a detailed in-vitro analysis of degradation and drug release kinetics

Herein, we synthesized hydrogel films from crosslinked polyethylene oxide (PEO) and guar gum (GG) which can offer hydrophilicity, antibacterial efficacy, and neovascularization. This study focuses on synthesis and material/biological characterization of rosemary (RM) and citric acid (CA) loaded PEO/GG hydrogel films. Scanning Electron Microscopy images confirmed the porous structure of the developed hydrogel film matrix (PEO/GG) and the dispersion of RM and CA within it. This porous structure promotes moisture adsorption, cell attachment, proliferation, and tissue layer formation. Fourier Transform Infrared Spectroscopy (FTIR) further validated the crosslinking of the PEO/GG matrix, as confirmed by the appearance of C-O-C linkage in the FTIR spectrum. PEO/GG and PEO/GG/RM/CA revealed similar degradation and release kinetics in Dulbecco's Modified Eagle Medium, Simulated Body Fluid, and Phosphate Buffer Saline (degradation of ∼55 % and release of ∼60 % RM in 168 h.). The developed hydrogel film exhibited a zone of inhibition against Escherichia. coli (2 mm) and Staphylococcus. aureus (9 mm), which can be attributed to the presence of RM in the hydrogel film. Furthermore, incorporating CA in the hydrogel film promoted neovascularization, as confirmed by the Chorioallantoic Membrane Assay. The developed RM and CA-loaded PEO/GG-based hydrogel films offered suitable in-vitro properties that may aid in potential wound healing applications.

Hierarchical Macroporous Agarose Materials with Polyethyleneimine-Assisted Multiple Boronate Affinity Binding Sites for the Separation of Neomycin

Quantification of neomycin residues in food samples demands an efficient purification platform. Herein, hierarchical macroporous agarose monoliths with multiple boronate affinity sites were established for selective separation of neomycin. The silica core was synthesized by "one-step" Stöber procedures followed by modification with amino group and incorporation of polyethyleneimine. A versatile macroporous agarose monolith was prepared by emulsification strategies and functionalized with epoxy groups. After introducing polyethyleneimine-integrated silica nanoparticles onto the agarose monolith, fluorophenylboronic acids were immobilized. The physical and chemical characteristics of the composite monolith were analyzed systematically. After optimization, neomycin showed high binding ability of 23.69 mg/g, and the binding capacity can be manipulated by changing the pH and adding monosaccharides. The composite monolith was subsequently utilized to purify neomycin from the spiked model aquatic products followed by high-performance liquid chromatography analysis, which revealed a remarkable neomycin purification effect, indicating the great potential in the separation of neomycin from complicated aquatic products.

Tuning interfacial microstructure of alginate-based amphiphile by dynamic bonding for stabilizing Pickering emulsion

Polysaccharide-based soft colloidal particles mediated by the dynamic bonding-engineered interfacial self-assembly can regulate the properties of oil-water interfacial films, availing the stability of emulsions under a wide pH range. The amphiphilic phenylboronic alginate soft colloidal particles (Alg-PBA) were designed to stabilize pH-responsive Pickering emulsions (PEs). Combining stability analysis with quartz crystal microbalance and dissipation monitoring (QCM-D), the microstructure and viscoelasticity of Alg-PBA at the oil-water interface were determined. The results showed that PEs stabilized by Alg-PBA due to a thicker and stronger viscoelastic interface film induced by BO bonds and hydrogen bonds. The structure-function relationship of the Alg-PBA emulsifier driven by dynamic bonds was further elaborated at multiple scales by laser scanning microscopy (CLSM) and scanning electron microscopy (SEM). Meanwhile, the microstructure of aerogels templated by emulsion could be tuned by adjusting dynamic bonds, which provides a new idea for polysaccharide soft material engineering.

pH responsive cationic guar gum-borate self-healing hydrogels for muco-adhesion

We developed a new muco-adhesive hydrogel composed of cationic guar gum (CGG) and boric acid (BA). The CGG-BA precursor solution of 0.5-2% w/v concentration exhibited fluidity at low pH (3-5), while gelation occurred within 1 min at physiological pH (7-8) conditions. Scanning electron microscopy and Fourier-transform infrared spectroscopy results confirmed the change in physical and chemical behavior, respectively, with change in pH. The pH-responsive self-healing ability was analyzed through microscopy and rheology. CGG-BA hydrogels showed good self-healing property at pH 7.4. The in vitro biocompatibility test of the hydrogel studied using NIH3T3 and NHEK cells showed that it was non-toxic at concentrations of CGG-BA below 2% w/v. Ex vivo mucoadhesive tests confirmed the hydrogel's potential for use as a muco-adhesive. Burst pressure tests were conducted using pig esophageal mucosa and the results showed that at pH 7.4, 1% w/v CGG-BA self-healable hydrogel resisted about 8 ± 2 kPa pressure, comparable to that of Fibrin glue. This was higher than that at solution (pH 5) and brittle gel (pH 10) conditions. To confirm the good adhesive strength of the self-healable hydrogels, lap shear tests conducted, resulted in adhesive strengths measured in the range of 1.0 ± 0.5-2.0 ± 0.6 kPa, which was also comparable to fibrin glue control 1.8 ± 0.6 kPa. Hydrogel weight measurements showed that 40-80% gel lasted under physiological conditions for 10 h. The results suggest that CGG-BA hydrogel has potential as a pH responsive mucosal protectant biomaterial.

Cellulose nanocrystals boosted hydrophobic association in dual network polymer hydrogels as advanced flexible strain sensor for human motion detection

Conductive hydrogels attract the attention of researchers worldwide, especially in the field of flexible sensors like strain and pressure. These flexible materials have potential applications in the field of electronic skin, soft robotics, energy storage, and human motion detection. However, its practical application is limited due to low stretchability, high hysteresis energy, low conductivity, long-range strain sensitivity, and high response time. It's still a challenging job to endow all these properties in a single hydrogel network. In the present work, cellulose nano crystals (CNCs) reinforced hydrophobically associated gels were developed using APS as a source of radical polymerization, acrylamide and lauryl methacrylate were used as a monomer. CNCs reinforced the hydrophobically associated hydrogels through hydrogen bonding to retain the hydrogel's network structure. Hydrogels consist of dual crosslinking, which demonstrate exceptional mechanical performance (fracture stress and strain, toughness, and Young's modulus). The low hysteresis energy (10.9 kJm^-3) and high conductivity (22.97 mS/cm) make the hydrogels a strong candidate for strain sensors with high sensitivity (GF = 19.25 at 700% strain) and a fast response time of 200 ms. Cyclic performance was also investigated up to 300 continuous cycles. After 300 cycles, the hydrogels were still stable and no considerable change was observed. These hydrogels are capable of sensing different human motions like wrist, finger bending, and neck (up-down and straight and right/left motion of neck). The hydrogels also demonstrate changes in current in response to swallowing, different speaking words, and writing different alphabets. These results suggest that our prepared materials can sense different small and large human motions, and also could be used in any electronic device where strain sensing is required.

Influence of organoboron cross-linker and reservoir characteristics on filtration and reservoir residual of guar gum fracturing fluid in low-permeability shale gas reservoirs

To effectively reduce the filtration rate of water-based fracturing fluid and promote the pressure holding effect of fracturing fluid in underground unconventional reservoirs, an efficient and clean organic-boron cross-linker was synthesized with boric acid and low alcohols. The results obtained that the synthesized organoboron cross-linker exhibits better fluid loss performance to water-based fracturing fluid than the commercially available cross-linker. This organoboron cross-linker allowed decreasing filtration coefficient more than 0.74 × 10^-2 m³·min^1/2 as a result of the network structure formed by the organoboron cross-linker and guar gum molecule. However, commercially available cross-linker exhibits a relatively large filtered mass of water more than 1.33 × 10^-2 m³·min^1/2 at the same condition. Meanwhile, the cross-linked guar gum fracturing fluid can significantly improve the fluid loss property with the increase of cross-linker content and pressure, and an increased fluid filtration gradually was revealed with increasing the reservoir temperature and current speed. Moreover, the damage of shale reservoir caused by the prepared boron cross-linker was only 11%, which was lower than 18% of the commercial boron cross-linker under the same conditions.

Self-Healing Hydrogels: Development, Biomedical Applications, and Challenges

Polymeric hydrogels have drawn considerable attention as a biomedical material for their unique mechanical and chemical properties, which are very similar to natural tissues. Among the conventional hydrogel materials, self-healing hydrogels (SHH) are showing their promise in biomedical applications in tissue engineering, wound healing, and drug delivery. Additionally, their responses can be controlled via external stimuli (e.g., pH, temperature, pressure, or radiation). Identifying a suitable combination of viscous and elastic materials, lipophilicity and biocompatibility are crucial challenges in the development of SHH. Furthermore, the trade-off relation between the healing performance and the mechanical toughness also limits their real-time applications. Additionally, short-term and long-term effects of many SHH in the in vivo model are yet to be reported. This review will discuss the mechanism of various SHH, their recent advancements, and their challenges in tissue engineering, wound healing, and drug delivery.

Polydopamine constructed interfacial molecular bridge in nano-hydroxylapatite/polycaprolactone composite scaffold

Nano-hydroxylapatite (nano-HAP)/polycaprolactone (PCL) composite scaffold is proved to possess great potential for bone tissue engineering application since the biocompatibility of PCL and the osteoinduction ability of nano-HAP. However, the interfacial bonding between nano-HAP and PCL is weak by reason of the difference in thermodynamic properties. Herein, nano-HAP was modified by polydopamine (PDA) and then added to the PCL matrix to enhance their interface bonding in bone scaffold manufactured by selective laser sintering (SLS). The results indicated that PDA acted as an interfacial molecular bridge between PCL and nano-HAP. On one hand, the amino groups of PDA formed hydrogen bonding with the hydroxyl groups of nano-HAP, and on the other hand, the catechol groups of PDA formed hydrogen bonding with the ester groups of PCL. Compared with the HAP/PCL scaffolds, the tensile and compressive strength of the P-HAP/PCL scaffolds loading 12 wt% P-HAP were increased by 10% and 16%, respectively. Meanwhile, the scaffold possessed great bioactivity and cytocompatibility that could accelerate the formation of apatite layers and promote the cell adhesion, proliferation and differentiation.

A Radiolabeling Method for Precise Quantification of Polymers

Radiolabeling a protein, molecule, or polymer can provide accurate and precise quantification in biochemistry, biomaterials, pharmacology, and drug delivery research. Herein, we describe a method to ¹²⁵I label two different polymers for precise quantification in different applications. The surfaces of model contact lenses were modified with phenylboronic acid to bind and release the natural polymer, hyaluronic acid (HA); HA uptake and release were quantified by radiolabeling. In the second example, the in vivo distribution of a mucoadhesive micelle composed of the block copolymer of poly(lactide)-b-poly(methacrylic acid-co-acrylamidophenylboronic acid) was investigated. The presence of phenyl boronic acid groups (PBA), which bind to mucosal surfaces, was proposed to improve the retention of the micelle. ¹²⁵I labeling of polymers was examined for quantification of microgram amounts of HA present on a contact lens or to evaluate the enhanced retention of PBA micelles on mucosal surfaces in vivo. The introduction of phenol groups onto the polymers allowed for the labeling. HA was modified with phenol groups through a coupling reaction of its carboxylic acid with hydroxybenzylamine. Phenol functional block copolymer micelles with and without PBA were synthesized by including N-(4-hydroxyphenethyl)acrylamide during polymerization. The phenol groups of HA and the block copolymers were labeled with ¹²⁵I using a modified ICl labeling method. ¹²⁵I labeling enabled quantification of HA loading and release including the effect of varying amounts of PBA on the contact lens surfaces. Micelles made from ¹²⁵I-labeled block copolymers with and without PBA were administered intranasally to Brown Norway rats. The animals were sacrificed either immediately after or 4 h after their last nasal instillation, and the nasopharyngeal tissues were removed and quantified. Radioactivity measurements demonstrated that the presence of the PBA mucosal binding groups led to approximately four times higher retention. The HA and block copolymer ¹²⁵I labeling presented in this article demonstrates the utility of the method for quantification and tracking of microgram quantities of polymers in diverse applications.

Recent advances in dynamic covalent bond-based shape memory polymers

Dynamic covalent bond-based shape memory polymers (DCB-SMPs) are one of most important SMPs which have a wide potential application prospect. Different from common strong covalent bonds, DCBs own relatively weak bonding energy, similarly to the supramolecular interactions of noncovalent bonds, and can dynamically combine and dissociate these bonds. DCB-SMP solids, which can be designed to respond for different stimuli, can provide excellent self-healing, good reprocessability, and high mechanical performance, because DCBs can obtain dynamic cross-linking without sacrificing ultrahigh fixing rates. Furthermore, besides DCB-SMP solids, DCB-SMP hydrogels with responsiveness to various stimuli also have been developed recently, which have special biocompatible soft/wet states. Particularly, DCB-SMPs can be combined with emerging 3D-printing techniques to design various original shapes and subsequently complex shape recovery. This review has summarized recent research studies about SMPs based on various DCBs including DCB-SMP solids, DCB-SMP hydrogels, and the introduction of new 3D-printing techniques using them. Last but not least, the advantages/disadvantages of different DCB-SMPs have been analyzed via polymeric structures and the future development trends in this field have been predicted.

Connecting the Dynamics and Reactivity of Arylboronic Acids to Emergent and Stimuli-Responsive Material Properties

Over the past two decades, arylboronic acid-functionalized biomaterials have been used in a variety of sensing and stimuli-responsive scaffolds. Their diverse applications result from the diverse reactivity of arylboronic acids,...

Novel glucose-responsive nanoparticles based on p-hydroxyphenethyl anisate and 3-acrylamidophenylboronic acid reduce blood glucose and ameliorate diabetic nephropathy

An insulin delivery system that self-regulates blood sugar levels, mimicking the human pancreas, can improve hyperglycaemia. At present, a glucose-responsive insulin delivery system combining AAPBA with long-acting slow release biomaterials has been developed. However, the safety of sustained-release materials and the challenges of preventing diabetic complications remain. In this study, we developed a novel polymer slow release material using a plant extract—p-hydroxyphenylethyl anisate (HPA). After block copolymerisation with AAPBA, the prepared nanoparticles had good pH sensitivity, glucose sensitivity, insulin loading rate and stability under physiological conditions and had high biocompatibility. The analysis of streptozotocin-induced diabetic nephropathy (DN) mouse model showed that the insulin-loaded injection of nanoparticles stably regulated the blood glucose levels of DN mice within 48 ​h. Importantly, with the degradation of the slow release material HPA in vivo, the renal function improved, the inflammatory response reduced, and antioxidation levels in DN mice improved. This new type of nanoparticles provides a new idea for hypoglycaemic nano-drug delivery system and may have potential in the prevention and treatment of diabetic complications.

•

We established a new glucose-responsive intelligent system with HPA.

•

p(AAPBA-b-HPA) shows good pH and glucose sensitivity.

•

p(AAPBA-b-HPA) nanoparticles can slowly release HPA and insulin.

•

This system can be used to regulate blood glucose.

•

p(AAPBA-b-HPA) nanoparticles can aid in diabetic nephropathy prevention and treatment.

Self-Healing Mechanism and Conductivity of the Hydrogel Flexible Sensors: A Review

Sensors are devices that can capture changes in environmental parameters and convert them into electrical signals to output, which are widely used in all aspects of life. Flexible sensors, sensors made of flexible materials, not only overcome the limitations of the environment on detection devices but also expand the application of sensors in human health and biomedicine. Conductivity and flexibility are the most important parameters for flexible sensors, and hydrogels are currently considered to be an ideal matrix material due to their excellent flexibility and biocompatibility. In particular, compared with flexible sensors based on elastomers with a high modulus, the hydrogel sensor has better stretchability and can be tightly attached to the surface of objects. However, for hydrogel sensors, a poor mechanical lifetime is always an issue. To address this challenge, a self-healing hydrogel has been proposed. Currently, a large number of studies on the self-healing property have been performed, and numerous exciting results have been obtained, but there are few detailed reviews focusing on the self-healing mechanism and conductivity of hydrogel flexible sensors. This paper presents an overview of self-healing hydrogel flexible sensors, focusing on their self-healing mechanism and conductivity. Moreover, the advantages and disadvantages of different types of sensors have been summarized and discussed. Finally, the key issues and challenges for self-healing flexible sensors are also identified and discussed along with recommendations for the future.

A self-healing smart photonic crystal hydrogel sensor for glucose and related saccharides

A self-healing smart PhC hydrogel sensor that combines the optical property of photonic crystal and the dynamic regeneration property of boronate ester bond has been prepared for determination of glucose and related saccharides using Debye diffraction ring detection. The boronate ester bond formed through phenylboronic acid and dopamine endows the hydrogel network self-healing ability, and the tensile stress of the healing hydrogel can recover to 94.4%; this excellent self-healing property can effectively improve the reliability and lifetime of the hydrogel. Due to the high bonding capacity between 1,2- and 1,3-diol and phenylboronic acid, the hydrogel sensor has a good recognition ability for glucose and related saccharides. The reaction between the monosaccharides and the phenylboronic acid group makes the sensor swell and the diameter of the Debye diffraction ring decrease. The sensor shows good reuse and responsive ability for saccharides; the RSD of the recoverability assays is 4.3%. The determination range of the sensor to glucose is 0.5 to 12 mM. The sensor also has good response to glucose in urine, exhibiting potential application value in the preliminary screening of diabetes. Although the sensor has poor selectivity for specific monosaccharides, the process of measuring the Debye ring makes the determination no longer rely on expensive and complicated equipment and greatly simplifies the determining process and reduces the cost of determination, which shows a broad application prospect. The boronate ester bond formed through phenylboronic acid and dopamine results in the self-healing property of hydrogel network, which can effectively improve the reliability and lifetime of hydrogel. And due to the high bonding capacity between 1,2- and 1,3-diol and phenylboronic acid, the smart hydrogel sensor has a good recognition ability for glucose and related saccharides. The reaction between the monosaccharides and the phenylboronic acid group breaks the original boronate ester bond; this will lead to a decrease in cross-linking density of the PhC hydrogel sensor and further makes the sensor swell and the diameter of the Debye diffraction ring decrease.

Capillary forces drive buckling, plastic deformation, and break-up of 3D printed beams

Capillary forces acting at the interfaces of soft materials lead to deformations over the scale of the elastocapillary length. When surface stresses exceed a material's yield stress, a plastocapillary effect is expected to arise, resulting in yielding and plastic deformation. Here, we explore the interfacial instabilities of 3D-printed fluid and elastic beams embedded within viscoelastic fluids and elastic solid support materials. Interfacial instabilities are driven by the immiscibility between the paired phases or their solvents. We find that the stability of an embedded structure is predicted from the balance between the yield stress of the elastic solid, τ_y, the apparent interfacial tension between the materials, γ', and the radius of the beam, r, such that τ_y > γ'/r. When the capillary forces are sufficiently large, we observe yielding and failure of the 3D printed beams. Furthermore, we observe new coiling and buckling instabilities emerging when elastic beams are embedded within viscous fluid support materials. The coiling behavior appear analogous to elastic rope coiling whereas the buckling instability follows the scaling behavior predicted from Euler-Bernoulli beam theory.

Design of facile technology for the efficient removal of hydroxypropyl guar gum from fracturing fluid

With the increasing demand for energy, fracturing technology is widely used in oilfield operations over the last decades. Typically, fracturing fluids contain various additives such as cross linkers, thickeners and proppants, and so forth, which makes it possess the properties of considerably complicated components and difficult processing procedure. There are still some difficult points needing to be explored and resolved in the hydroxypropyl guar gum (HPG) removal process, e.g., high viscosity and removal of macromolecular organic compounds. Our works provided a facile and economical HPG removal technology for fracturing fluids by designing a series of processes including gel-breaking, coagulation and precipitation according to the diffusion double layer theory. After this treatment process, the fracturing fluid can meet the requirements of reinjection, and the whole process was environment friendly without secondary pollution characteristics. In this work, the fracturing fluid were characterized by scanning electron microscopy (SEM), Energy dispersive X-ray (EDX), X-ray diffraction (XRD) and Fourier transformed infrared (FTIR) spectroscopy technologies, etc. Further, the micro-stabilization and destabilization mechanisms of HPG in fracturing fluid were carefully investigated. This study maybe opens up new perspective for HPG removal technologies, exhibiting a low cost and strong applicability in both fundamental research and practical applications.

Locust bean gum/gellan gum double-network hydrogels with superior self-healing and pH-driven shape-memory properties

In this work, we prepared locust bean gum (LBG)/gellan gum (Gg) double network (DN) hydrogels based on pH-sensitive borate-ester bonds in the LBG network and hydrogen-bond-associated double-helix bundles in the Gg network by using two novel natural polysaccharide polymers. The DN hydrogels with optimized Gg and borax concentrations exhibit good mechanical properties (the fracture tensile stress is almost three times that of the LBG single network hydrogel). Because of their unique thermo- and pH-sensitive DN structure, the LBG/Gg DN hydrogels also show excellent self-healing, thermo-processability, and pH-driven shape memory properties. Such novel DN hydrogels demonstrate strong potentiality in many challenging applications such as biomedicine, soft robotics and other fields.