Gellan microgels produced in planar microfluidic devices

Starch can act differently when combined with alginate or gellan gum to form hydrogels

Microgels were tailored by combining starches from different sources (corn, potato or phosphated) and anionic polysaccharides (gellan gum or alginate) using ionic gelation. Rheological analysis pointed out a lower consistency index for alginate-based solutions compared to the gellan-based ones and, therefore, this favored the formation of smaller droplets during the atomization process (58.74 ± 1.72 µm vs. 101.38 ± 2.71 µm). Additionally, it was noticed that the starch granule size isdirectly related to the diameter of the particle formed, both for gellan and alginate systems. The combination between starches and anionic gums still promoted an increase in the water holding capacity, probably due to the presence of additional hydrophilic groups from starch. According to the mechanical properties, starch acts differently when combined with alginate or gellan gum, considering it strengthened the biopolymeric network for the alginate-based gels increasing the stress at rupture values (except for potato starch), while it decreasedthe hardness and elasticity for gellan-based gels. Microparticles based on gellan and alginate showed high anthocyanin encapsulation efficiency (EE ≥ 80%) in all systems. In these cases, the addition of starch did not contribute to increasing this property, even though starch granules filled the gel pores. The high EE showed that the studied systems allow the encapsulation of anthocyanin and suggest possible encapsulation of other hydrophilic bioactive compounds, considering the best type of starch for each application.

Droplet-Based Microfluidics as a Platform to Design Food-Grade Delivery Systems Based on the Entrapped Compound Type

Microfluidic technology has emerged as a powerful tool for several applications, including chemistry, physics, biology, and engineering. Due to the laminar regime, droplet-based microfluidics enable the development of diverse delivery systems based on food-grade emulsions, such as multiple emulsions, microgels, microcapsules, solid lipid microparticles, and giant liposomes. Additionally, by precisely manipulating fluids on the low-energy-demand micrometer scale, it becomes possible to control the size, shape, and dispersity of generated droplets, which makes microfluidic emulsification an excellent approach for tailoring delivery system properties based on the nature of the entrapped compounds. Thus, this review points out the most current advances in droplet-based microfluidic processes, which successfully use food-grade emulsions to develop simple and complex delivery systems. In this context, we summarized the principles of droplet-based microfluidics, introducing the most common microdevice geometries, the materials used in the manufacture, and the forces involved in the different droplet-generation processes into the microchannels. Subsequently, the encapsulated compound type, classified as lipophilic or hydrophilic functional compounds, was used as a starting point to present current advances in delivery systems using food-grade emulsions and their assembly using microfluidic technologies. Finally, we discuss the limitations and perspectives of scale-up in droplet-based microfluidic approaches, including the challenges that have limited the transition of microfluidic processes from the lab-scale to the industrial-scale.

Progress and opportunities in Gellan gum-based materials: A review of preparation, characterization and emerging applications

Gellan gum, a microbial exopolysaccharide, is biodegradable and has potential to fill several key roles in many fields from food to pharmacy, biomedicine and tissue engineering. In order to improve the physicochemical and biological properties of gellan gum, some researchers take advantage of numerous hydroxyl groups and the free carboxyl present in each repeating unit. As a result, design and development of gellan-based materials have advanced significantly. The goal of this review is to provide a summary of the most recent, high-quality research trends that have used gellan gum as a polymeric component in the design of numerous cutting-edge materials with applications in various fields.

Research progress of water-in-oil emulsion gelated with internal aqueous phase: gel factors, gel mechanism, application fields, and future direction of development

The W/O emulsion is a promising system. Its special structure can keep the sensory properties of fat while reducing the fat content. Improving the stability and physical properties of W/O emulsions is generally oriented toward outer oil-phase modified oil gels and inner water-phase modified inner hydrogels. In this paper, the research progress of internal aqueous gel was reviewed, and some gel factors suitable for internal aqueous gel and the gel mechanism of main gel factors were discussed. The advantages of this internal aqueous gel emulsion system allow its use in the field of fat substitutes and encapsulating substances. Finally, some shortcomings and possible research directions in the future were proposed, which would provide a theoretical basis for the further development of internal water-phase gelled W/O emulsion in the future.

Fabrication of monodisperse alginate microgel beads by microfluidic picoinjection: a chelate free approach

Micron-sized alginate hydrogel beads are extensively employed as an encapsulation medium for biochemical and biomedical applications. Here we report on the microfluidic assisted fabrication of calcium alginate (Ca-alginate) beads by on-chip picoinjection of aqueous calcium chloride (CaCl2) in emulsified aqueous sodium alginate (Na-alginate) droplets or by picoinjection of Na-alginate solution in emulsified aqueous CaCl2 droplets. There is no added chelator to reduce the Ca activity in either of the two strategies. The two fabrication strategies are implemented using a flow-focusing and picoinjection modules in a single PDMS chip. Aqueous alginate solution was emulsified and infused with CaCl2 solution as the squeezed droplet pass the picoinjection channel; consequently, monodisperse, spherical, and structurally homogeneous Ca-alginate beads were obtained. Monodisperse alginate microgel populations with a mean diameter in the range of 8 to 28 μm and standard deviation less than 1 μm were successfully generated using microfluidic channels with various dimensions and controlling the flow parameters. Monodisperse but also non-spherical particles with diameters 6 to 15 μm were also fabricated when picoinjecting Na-alginate solution in emulsified aqueous CaCl2 droplets. The Ca-alginate microbeads fabricated with tailormade size in the range from sub-cellular and upwards were in both strategies realized without any use of chelators or change in pH conditions, which is considered a significant advantage for further exploitation as encapsulation process for improved enzymatic activity and cell viability.

Red beet extract usage in gelatin/gellan based gummy candy formulation introducing Salix aegyptiaca distillate as a flavouring agent

Nowadays, the functionalization of food products using natural health-promoting additives is of great interest. Betalains are the natural pigments of red beets and are known for their health-promoting characteristics. The aim of this study was to evaluate gummy candies formulated with red beet extract (0.1 or 0.3%) as the coloring agent, Salix aegyptiaca distillate as the flavoring agent, and gellan gum (0.5 or 1.5%) as the gelling co-agent. The prepared gummy candy samples were assessed via texture profile analysis, DPPH assay, sensory evaluation, and color analysis. The results revealed that hardness (~ 60 N) improved and gumminess (~ 15 N) decreased with an increment in gellan gum content in the gummy candy formulation. Statistical analysis indicated that by addition of red beet extract, the radical scavenging capacity of the samples increased (50%) significantly (p < 0.05). Furthermore, gellan gum usage lead to the generation of a glossy red color and enhanced the lightness of the samples in comparison with gelatin-based gummy candies. About sensory evaluation, the panelists confirmed that usage of Salix aegyptiaca improved the sensory characteristics of the gummy candy (overall acceptance from 7.4 to 8.2; out of 9). Our findings suggest that gellan gum (as a highly transparent, acid-resistant, gel-forming gum), red beet extract (as an acid-stabilized natural color), and Salix aegyptiaca distillate have immense potential in the food industry for use as structuring, coloring, and flavoring agents, respectively.

Core-Shell Encapsulation of Lipophilic Substance in Jelly Fig (Ficus awkeotsang Makino) Polysaccharides Using an Inexpensive Acrylic-Based Millifluidic Device

The polysaccharides extracted from the achenes of jelly fig, Ficus awkeotsang Makino, were mainly composed of low methyl pectin and used as a novel shell material for encapsulating lipophilic bioactives in the core of microcapsule. The polysaccharide microcapsules with oil core were prepared using a novel acrylic-based millifluidic device developed in this study. To investigate the physiochemical properties of and find the suitable formula of polysaccharide shells, the films casted with jelly fig polysaccharide were thoroughly characterized. For the preparation of microcapsules, the millifluidic device was optimized by controlling the flow rate to obtain uniform spherical shape with a core diameter of 1.4-1.9 mm and the outer diameter of 2.1-2.8 mm. The encapsulation efficiency was around 90%, and the microcapsules displayed a clear boundary between the polysaccharide shell and oil core. Encapsulation of curcumin in the microcapsules was prepared to test the applicability of the device and processes developed in this study, and the results showed that the microencapsulation could enhance the stability of curcumin against external environment. Overall, the results suggested that the jelly fig polysaccharides and the developed millifluidic device can be useful for the preparation of core-shell microcapsules for encapsulation of lipophilic bioactives.

Microporous drug-eluting large silk particles through cryo-granulation

A facile method for the preparation of large, microporous, drug-loaded particles is presented. High shear bollus injections of silk with cross-linker and drug colloids into super-cooled hexane were utilized to trigger phase separation of silk droplets, followed by immediate freezing at -60°C. A subsequent -20°C freeze-thaw of the frozen droplets resulted in self-assembly (crystallization) of the silk. The silk particles developed an internal interconnected microporous morphology with 0.1-10 µm in diameter pores. The silk particles ranged in diameter from 100 to 1,300 µm, with particle mean diameter and polydispersity controlled by the starting concentration of the cross-linking agent and silk, the rheology of the reaction mixture, and the injection pressure (80 - 300kPa). Cryogranulation provided a one-step process to produce microporous meso-scale silk particles with encapsulated drugs, such as doxorubicin chloride (DoxR), tobramycin sulfate (TS), kanamycin sulfate (KS) or gentamicin sulfate (GS). Almost 100% drug encapsulation efficiency was achieved in the process, and subsequent release profiles depended on the starting concentration of both the drug, silk, and pH of the elution medium. Kirby-Bauer tests and bioluminescent imaging confirmed the retention of anti-bacterial potency of the antibiotics pre-encapsulated in the cryo-particles, and macroparticles cytocompatibility towards human fibroblast and kidney cells.

3D-printed air-blast microfluidic nozzles for preparing calcium alginate microparticles

Uniform calcium alginate microparticles were prepared through 3D-printed coaxial air-blast microfluidic nozzles.