creating alginate hydrogel microspheres using microfluidic electrospray for controlled drug release

Developing Sodium Alginate Hydrogel Microspheres for Biomedical Use

Drug delivery systems are a research hotspot in the field of bio-tissue engineering, aiming to improve drug delivery efficiency and efficacy and reduce adverse reactions and side effects1. Among these systems, hydrogel microspheres, characterized by good biocompatibility, tunable mechanical properties, and functional plasticity, are one of the most commonly used vehicles for drug loading and delivery2. They can be used for both slow and controlled release of drugs, provide good protective effects for drugs, avoid or minimize non-specific effects of drugs in other tissues, and target drug delivery to specific tissue structures3. Therefore, hydrogel microspheres have become a new and efficient drug delivery system, with research in this field gradually emerging4.
Hydrogel microspheres are typically synthesized from biodegradable materials, including polysaccharides, proteins, and natural polymers5. Among them, ALG is a biocompatible, biodegradable polysaccharide extracted from marine brown algae6. Its molecular chain contains free hydroxyl and carboxyl groups that can crosslink with most divalent or multivalent cations to form a water-insoluble hydrogel structure with a three-dimensional network5. The hydrogel microspheres formed by ALG can be converted into negatively charged polyelectrolytes in neutral and alkaline solutions. This repulsion between negative charges causes the microspheres to swell, allowing the release of the encapsulated active ingredient or drug. These properties have led to the consideration of ALG microspheres as promising drug carriers widely used for drug loading and controlled release7.
Various methods exist for the preparation of hydrogel microspheres. Traditional ALGMS preparation methods usually include the sol-gel method or the emulsion-sol method. These methods involve steps such as precipitation, co-precipitation, and gelation reactions to obtain the target microspheres8. In recent years, with the continuous development of microfluidic technology, the microfluidic electrospray method has gradually become an efficient and precise microsphere preparation method9. This method utilizes microfluidic technology to electrospray a polymer solution through a microfine nozzle to form micrometer-sized droplets and microspheres during the subsequent curing or cross-linking process10. Compared to the traditional method, microfluidic electrospray offers precise control of microsphere particle size and morphology by adjusting parameters such as solution flow rate, voltage, and fine nozzle size11. It also enables high-speed continuous preparation of microspheres, improving preparation efficiency and maintaining mild reaction conditions. In addition, ALGMS can be prepared to possess various functions, such as controlled-release drugs and loaded catalysts, enabling their easy application in various fields.
Here, we present a protocol for the preparation of ALG microspheres using the microfluidic electrospray method. The process involves passing an ALG solution through a microfluidic device and subjecting it to electrospray. The resulting droplets were collected in the solution containing different metal ions (Ca2+, Cu2+, Zn2+, and Fe3+) to initiate the cross-linking reaction. This reaction improves the stability and adhesion of the microspheres and endows them with different functionalities. This method is easy to perform, and the synthesized microspheres exhibit good size uniformity in their morphology. In addition, we investigated their antimicrobial properties, slow drug-release ability, and biocompatibility. This protocol will be useful for further drug development and production.

Author Spotlight: Advancing Therapeutics with Biocompatible Sodium Alginate Hydrogel Microspheres

Preparation of Cross-Linked Sodium Alginate Microspheres with Different Metal Ions Using the Microfluidic Electrospray Technology

Hydrogen microspheres are characterized by good compatibility, design flexibility, and high degree of customization. They have a broad application protector in biomedical fields such as therapeutic drug delivery and the construction of TC repair discoveries. In this study, we prepared hydrogen microspheres using a simple microfluidic device.Recently we have been trying to use hydrogen microspheres loaded with some small molecules from traditional Chinese medicine to promote all the healing. In this study, we found that zinc and copper ion cross-link the sodium alginate microspheres have good anti-microbial properties and thus copper ARGMS, and zinc ARGMS are suitable for the treatment of bacterial infectious diseases.

Creating Alginate Hydrogel Microspheres Using Microfluidic Electrospray for Controlled Drug Release

To begin, mix ALG with ultrapure water in a water bath, tempered at 50 degrees Celsius. Separately, prepare mass fraction with 5%solutions of calcium chloride, ferric chloride, zinc sulfate, and copper sulfate in ultrapure water. Pour each solution separately into a collecting dish.Place a glass capillary tube over a blowtorch flame to soften it and stretch it to various diameters. With a glass cutter, cut off the fine parts and gently polish the tip port with silicon carbide sandpaper. Connect the thick end of the capillary tube to a long tubing and the other end to a dispensing needle in a five-milliliter syringe.Attach the syringe to the microfluidic syringe pump and the capillary tubing at one end to the holder. Connect the red high-voltage end clip of the high-voltage power supply to the dispensing needle of the syringe and place the silver clip in the collection fluid. This configuration creates a simple microfluidic electrospray device.Place the collection dishes containing different metal ions directly under the capillary tube. Turn on the microfluidic syringe pump. Select fast forward to prime the tube with the ALG and set the flow rate to two milliliters per hour.Switch on the high-voltage power switch and turn the knob to set the voltage to five to seven kilovolts. Collect ALG microspheres cross-linked with different metal ions. After the formation of ALG hydrogel microspheres, transfer them to individual labeled 1.5-milliliter centrifuge tubes.The micrographs of ALG microspheres showed good sphericity, smooth surface, and uniform particle size distribution. Scanning electron microscopy showed that the microspheres were generally spherical with well-defined roundness.

creating-alginate-hydrogel-microspheres-using-microfluidic

Research

JoVE Journal

Bioengineering

Microspheres are micrometer-sized particles that can load and gradually release drugs via physical encapsulation or adsorption onto the surface and within polymers. In the field of biomedicine, hydrogel microspheres have been extensively studied for their application as drug carriers owing to their ability to reduce the frequency of drug administration, minimize side effects, and improve patient compliance. Sodium alginate (ALG) is a naturally occurring linear polysaccharide with three backbone glycosidic linkages. There are two auxiliary hydroxyl groups present in each of the moieties of the polymer, which have the characteristics of an alcohol hydroxyl moiety. The synthetic ALG units can undergo chemical cross-linking reactions with metal ions, forming a cross-linked network structure of polymer stacks, ultimately forming a hydrogel. Hydrogel microspheres can be prepared using a simple process involving the ionic cross-linking properties of ALG. In this study, we prepared ALG-based hydrogel microspheres (ALGMS) using a microfluidic electrodeposition strategy. The prepared hydrogel microspheres were uniformly sized and well-dispersed, owing to accurate control of the microfluidic electrospray flow. ALGMS cross-linked with different metal ions were prepared using a microfluidic electrospray technique combining microfluidic and high electric field, and its antimicrobial properties, slow drug release ability, and biocompatibility were investigated. This technology holds promise for application in advanced drug development and production.

The protocol describes the preparation of sodium alginate microspheres cross-linked with different metal ions using a microfluidic device for drug carrier design. The antimicrobial properties and slow drug release of these microspheres were also investigated.

Microspheres are micrometer-sized particles that can load and gradually release drugs via physical encapsulation or adsorption onto the surface and within ...

Biocompatibility Tests to Assess the Use of Sodium Alginate Hydrogel Microspheres for Drug Delivery

To begin, prepare zinc, calcium, copper, and ferric alginate hydrogel micro-spheres. For the antimicrobial performance test, add 10 milliliters of each of the two bacterial solutions into a 15 milliliter sterile centrifuge tube. Then incubate the cultures with 0.5 milliliters of hydrogel microspheres in a constant temperature shaker.Dilute each bacterial solution, 10 to the power of five times, with sterile water. Using sterile glass beads, evenly spread 200 microliters of bacterial solution on an LB solid medium. Place the plates in an incubator at 37 degrees Celsius for 12 hours to assess colony formation.Add one milligram per milliliter of bovine serum albumin or BSA suspension, to 500 microliters of each microsphere and incubate for 24 hours. Add each saturated sample to one milliliter PBS, and agitate for 15 minutes at 37 degrees Celsius with continuous shaking at 80 revolutions per minute. After aliquoting, replace the medium with a fresh one at one, three, six, 12, 24, 36, and 48 hours.Quantify the supernatant protein concentrations at specific times. Add the prepared ALG microspheres to PBS, and incubate them at 37 degrees Celsius for 24 hours. Obtain whole blood from healthy mice in anticoagulation tubes containing sodium citrate.After vortexing centrifuge the tube for 15 minutes at 1, 500 revolutions per minute to obtain red blood cells. After flushing the cells, prepare a 10%red blood cell solution with PBS, and add 20 microliters of blood cell solution to the microsphere experimental and control groups. Incubate the samples at 37 degrees Celsius for four hours, and centrifuge them at 1, 500 RPM for 15 minutes.After keeping the supernatant aside, photograph the red blood cells in each group following hemolysis. Finally, measure the absorbance values of the supernatants in each group and compute the hemolysis rate using the formula. Different microspheres exhibited antibacterial activity against staphylococcus aureus and escherichia coli with copper and zinc, ALG microspheres, showing the strongest antibacterial properties.The drug release assay revealed that the release rate of the iron microsphere was relatively faster than that of the other three ions. Biocompatibility assessment showed that the red blood cells in the suspension remained intact upon contact with different microspheres, indicating minimal hemolysis by the microspheres.