Glucose‐Triggered Insulin Release from Fe 3+ ‐Cross‐linked Alginate Hydrogel: Experimental Study and Theoretical Modeling

Dual Cross-Linked Stimuli-Responsive Alginate-Based Hydrogels

Sodium alginate with different molecular weights (55, 170, and 320 kg mol-1) were chemically modified by grafting methacrylic moieties onto the hydroxyl groups of the alginate backbone. The methacrylation was optimized to obtain different degrees of modification. Chemically cross-linked hydrogels were obtained following UV-light irradiation in the presence of a photoinitiator. The swelling behavior and the mechanical properties were observed to depend on both the degree of methacrylation and the alginate molecular weight. Due to the chain entanglement present in high-viscosity sodium alginate, lower degrees of modification were required to tune the hydrogel properties. Moreover, in the presence of Ca2+, secondary cross-linking was introduced by the coordination of the alginate guluronate moieties with the Ca2+ ions. The addition of this secondary cross-linking caused fast volume shrinkage and a reinforcement of the mechanical properties. The secondary cross-linking was reversible, and the hydrogels regained their original shape for at least three cycles. Additionally, the dual cross-linked network can be used to induce adhesion between hydrogels and serve as a building block for self-folding actuators.

Zinc insulin hexamer loaded alginate zinc hydrogel: preparation, characterization and in vivo hypoglycemic ability

Alginate zinc hydrogel loaded with zinc insulin hexamer was prepared and characterized for oral insulin administration. The hydrogel was fabricated by dripping zinc insulin hexamer into sodium alginate solution and followed by crosslinking by zinc chloride. SEM image reveals the zinc insulin hexamer was integrated into the matrix of hydrogel. Zinc insulin hexamer loaded hydrogel shows no obvious cytotoxicity to both HT29 and Caco-2 cells. The developed hydrogel retards the burst release of insulin in simulated gastric fluid but promotes the release when in simulated intestinal fluid. In the diabetic mice, zinc insulin hexamer loaded alginate hydrogel demonstrates significant and prolonged hypoglycemic effect.

Enhanced postoperative cancer therapy by iron-based hydrogels

Surgical resection is a widely used method for the treatment of solid tumor cancers. However, the inhibition of tumor recurrence and metastasis are the main challenges of postoperative tumor therapy. Traditional intravenous or oral administration have poor chemotherapeutics bioavailability and undesirable systemic toxicity. Polymeric hydrogels with a three-dimensional network structure enable on-site delivery and controlled release of therapeutic drugs with reduced systemic toxicity and have been widely developed for postoperative adjuvant tumor therapy. Among them, because of the simple synthesis, good biocompatibility, biodegradability, injectability, and multifunctionality, iron-based hydrogels have received extensive attention. This review has summarized the general synthesis methods and construction principles of iron-based hydrogels, highlighted the latest progress of iron-based hydrogels in postoperative tumor therapy, including chemotherapy, photothermal therapy, photodynamic therapy, chemo-dynamic therapy, and magnetothermal-chemical combined therapy, etc. In addition, the challenges towards clinical application of iron-based hydrogels have also been discussed. This review is expected to show researchers broad perspectives of novel postoperative tumor therapy strategy and provide new ideas in the design and application of novel iron-based hydrogels to advance this sub field in cancer nanomedicine.

A dual crosslinked hydrogel-mediated integrated peptides and BMSC therapy for myocardial regeneration

The efficacy of myocardial regeneration strategies for myocardial infarction (MI) is significantly compromised by the complex structure and microenvironment of the myocardium. Although tissue engineering strategies based on cell therapy and/or pro-angiogenesis can somewhat improve cardiac function, the lack of proper myocardial materials that can withstand sustained deformability and adaptable mechanical properties severely affects myocardial wall integrity, systolic-diastolic cycles, and regeneration. Herein, we developed an integrated single "all-in-one" in situ dual crosslinking conductive hydrogel with favorable treatment properties termed as MaHA/B-G-SH/Fe³⁺ by ionic interactions and chemical covalency based on modified hyaluronic acid (HA), gelatin (G), and Fe³⁺. The resulting dual crosslinking dynamic hydrogel not only provides self-healing and mechanical properties adapted to the myocardial systolic-diastolic cycle with simultaneous electrical signal transmission to fibrous islands and normal tissue, but also leads to significant increase of the myocardial wall thickness very close to that of normal myocardium upon one single injection with complete degradation within 28 days. Notably, the hydrogel covalently conjugated with a tailored peptide sequence of GGR-KLT and encapsulated with bone mesenchymal stem cells (BMSCs) was further used for in situ injection in a rat MI model, which exhibited (i) efficient inhibition of excessive matrix degradation dependent on early MMP-2 expression, (ii) triggered on-demand release of KLT for at least 14 days and significant promotion of angiogenesis, and (iii) synergistic BMSCs considerably enhanced myocardial regeneration within 28 days. Taken together, the dual crosslinking conductive hydrogel-mediated synergistic peptide and cell therapy provides comprehensive recovery and regeneration of the structure and function of the injured myocardium, thus demonstrating great potential for clinical translations.

Alginate-Based Smart Materials and Their Application: Recent Advances and Perspectives

Nature produces materials using available molecular building blocks following a bottom-up approach. These materials are formed with great precision and flexibility in a controlled manner. This approach offers the inspiration for manufacturing new artificial materials and devices. Synthetic artificial materials can find many important applications ranging from personalized therapeutics to solutions for environmental problems. Among these materials, responsive synthetic materials are capable of changing their structure and/or properties in response to external stimuli, and hence are termed "smart" materials. Herein, this review focuses on alginate-based smart materials and their stimuli-responsive preparation, fragmentation, and applications in diverse fields from drug delivery and tissue engineering to water purification and environmental remediation. In the first part of this report, we review stimuli-induced preparation of alginate-based materials. Stimuli-triggered decomposition of alginate materials in a controlled fashion is documented in the second part, followed by the application of smart alginate materials in diverse fields. Because of their biocompatibility, easy accessibility, and simple techniques of material formation, alginates can provide solutions for several present and future problems of humankind. However, new research is needed for novel alginate-based materials with new functionalities and well-defined properties for targeted applications.

Improved hemostatic effects by Fe3+ modified biomimetic PLLA cotton-like mat via sodium alginate grafted with dopamine

The development of an excellent, bioabsorbable hemostatic material for deep wound remains a challenge. In this work, a biodegradable cotton-like biomimetic fibrous mat of poly (l-lactic acid) (PLLA) was made by melt spinning. Subsequently, SD composite was prepared by cross-linking sodium alginate (SA) with dopamine (DA). It was immobilized on the fibre surface, which inspired by mussel byssus. Finally, Fe3+ was loaded onto the 0.5SD/PLLA composite by chelation with the carboxyl of alginate and phenolic hydroxy of dopamine. The haemostasis experiment found that the hemostatic time 47 s in vitro. However, the bleeding volume was 0.097 g and hemostatic time was 23 s when 20Fe3+-0.5SD/PLLA was applied in the haemostasis of the rat liver. As a result of its robust hydrophilicity and bouffant cotton-like structure, it could absorb a large water from blood, which could concentrate the component of blood and reduce the clotting time. Furthermore, the addition of Fe3+ in the 0.5SD/PLLA had a significant effect on improve hemostatic property. It also displayed excellent antibacterial property for Escherichia coli and Staphylococcus aureus. Notably, it possesses superior hemocompatibility, cytocompatibility and histocompatibility. Hence, 20Fe3+-0.5SD/PLLA has high potential application in haemostasis for clinical settings due to its outstanding properties.

How does counter-cation substitution influence inter- and intramolecular hydrogen bonding and electrospinnability of alginates

Despite numerous applications of nanofibrous alginate (Alg) mat, its facile fabrication via electrospinning is still challenging. The low alginate content compared to the carrier polymer and existence of impurities are the main drawbacks of existing approaches. The purpose of this research is both to study and improve alginate electrospinnability by focusing on the effect of inter- and intramolecular hydrogen bonding. Based on hard and soft acids and bases (HSAB) theory, the Na⁺ cations (carboxylate counter-cation) were substituted with a harder acid, Li⁺ cation, to increase the strength of ionic interaction and decrease the density of hydrogen bonding. Viscosity and electrical conductivity measurements as well as FTIR and ¹H NMR revealed a lower intramolecular hydrogen bonding density in Li-Alg. SEM images showed improvement of alginate electrospinnability for Li-Alg compared to the salts of Na-Alg and K-Alg. This study sheds more light on underlying reasons hindering alginate electrospinning and introduces a simple method for fabrication of nanofibers with high alginate content.

Natural Polymer-based Stimuli-responsive Hydrogels

The abilities of intelligent polymer hydrogels to change their structure and volume phase in response to external stimuli have provided new possibilities for various advanced technologies and great research and application potentials in the medical field. The natural polymer-based hydrogels have the advantages of environment-friendliness, rich sources and good biocompatibility. Based on their responsiveness to external stimuli, the natural polymer-based hydrogels can be classified into the temperature-responsive hydrogel, pH-responsive hydrogel, light-responsive hydrogel, electricresponsive hydrogel, redox-responsive hydrogel, enzyme-responsive hydrogel, magnetic-responsive hydrogel, multi-responsive hydrogel, etc. In this review, we have compiled some recent studies on natural polymer-based stimuli-responsive hydrogels, especially the hydrogels prepared from polysaccharides. The preparation methods, properties and applications of these hydrogels in the medical field are highlighted.

Not-XOR (NXOR) Logic Gate Realized with Enzyme-Catalyzed Reactions: Optical and Electrochemical Signal Transduction

The studied enzyme-based biocatalytic system mimics NXOR Boolean logic gate, which is a logical operator that corresponds to equality in Boolean algebra. It gives the functional value true (1) if both functional arguments (input signals) have the same logical value (0,0 or 1,1), and false (0) if they are different (0,1 or 1,0). The output signal producing reaction is catalyzed by pyrroloquinoline quinone-dependent glucose dehydrogenase (PQQ-GDH), which is inhibited at acidic and basic pH values. Two other reactions catalyzed by esterase and urease produce acetic acid and ammonium hydroxide, respectively, shifting solution pH from the optimum pH for PQQ-GDH to acidic and basic values (1,0 and 0,1 input combinations, respectively), thus switching the enzyme activity off (output 0). When the input signals are not applied (0,0 combination) or both applied compensating each other (1,1 combination) the optimum pH is preserved, thus keeping PQQ-GDH running at the high rate (output 1). The biocatalytic cascade mimicking the NXOR gate was characterized optically and electrochemically. In the electrochemical experiments the PQQ-GDH enzyme communicated electronically with a conducting electrode support, thus resulting in the electrocatalytic current when signal combinations 0,0 and 1,1 were applied. The logic gate operation, when it was realized electrochemically, was also extended to the biomolecular release controlled by the gate. The release system included two electrodes, one performing the NXOR gate and another one activated for the release upon electrochemically stimulated alginate hydrogel dissolution. The studied system represents a general approach to the biocatalytic realization of the NXOR logic gate, which can be included in different catalytic cascades mimicking operation of concatenated gates in sophisticated logic circuitries.

Alginate Nanoparticles for Drug Delivery and Targeting

Nanotechnology refers to the control, manipulation, study and manufacture of structures and devices at the nanometer size range. The small size, customized surface, improved solubility and multi-functionality of nanoparticles will continue to create new biomedical applications, as nanoparticles allow to dominate stability, solubility and bioavailability, as well controlled release of drugs. The type of a nanoparticle, and its related chemical, physical and morphological properties influence its interaction with living cells, as well as determine the route of clearance and possible toxic effects. This field requires cross-disciplinary research and gives opportunities to design and develop multifunctional devices, which allow the diagnosis and treatment of devastating diseases. Over the past few decades, biodegradable polymers have been studied for the fabrication of drug delivery systems. There was extensive development of biodegradable polymeric nanoparticles for drug delivery and tissue engineering, in view of their applications in controlling the release of drugs, stabilizing labile molecules from degradation and site-specific drug targeting. The primary aim is to reduce dosing frequency and prolong the therapeutic outcomes. For this purpose, inert excipients should be selected, being biopolymers, e.g. sodium alginate, commonly used in controlled drug delivery. Nanoparticles composed of alginate (known as anionic polysaccharide widely distributed in the cell walls of brown algae which, when in contact with water, forms a viscous gum) have emerged as one of the most extensively characterized biomaterials used for drug delivery and targeting a set of administration routes. Their advantages include not only the versatile physicochemical properties, which allow chemical modifications for site-specific targeting but also their biocompatibility and biodegradation profiles, as well as mucoadhesiveness. Furthermore, mechanical strength, gelation, and cell affinity can be modulated by combining alginate nanoparticles with other polymers, surface tailoring using specific targeting moieties and by chemical or physical cross-linking. However, for every physicochemical modification in the macromolecule/ nanoparticles, a new toxicological profile may be obtained. In this paper, the different aspects related to the use of alginate nanoparticles for drug delivery and targeting have been revised, as well as how their toxicological profile will determine the therapeutic outcome of the drug delivery system.

Glucose Oxidase-Based Glucose-Sensitive Drug Delivery for Diabetes Treatment

The glucose-sensitive drug delivery systems based on glucose oxidase (GOD), which exhibit highly promising applications in diabetes therapy, have attracted much more interest in recent years. The self-regulated drug delivery systems regulate drug release by glucose concentration automatically and continuously to control the blood glucose level (BGL) in normoglycemic state. This review covers the recent advances at the developments of GOD-based glucose-sensitive drug delivery systems and their in vivo applications for diabetes treatment. The applications of GOD-immobilized platforms, such as self-assembly layer-by-layer (LbL) films and polymer vesicles, cross-linking hydrogels and microgels, hybrid mesoporous silica nanoparticles, and microdevices fabricated with insulin reservoirs have been surveyed. The glucose-sensitive drug delivery systems based on GOD are expected to be a typical candidate for smart platforms for potential applications in diabetes therapy.