The Feasibility of Using Pulsed-Vacuum in Stimulating Calcium-Alginate Hydrogel Balls

The effect of the pulsed-vacuum stimulation (PVS) on the external gelation process of calcium-alginate (Ca-Alg) hydrogel balls was studied. The process was conducted at four different working pressures (8, 35, 61, and 101 kPa) for three pulsed-vacuum cycles (one cycle consisted of three repetitions of 10 min of depressurization and 10 min of vacuum liberation). The diffusion coefficients (D) of calcium cations (Ca2+) gradually reduced over time and were significantly pronounced (p < 0.05) at the first three hours of the external gelation process. The rate of weight reduction (WR) and rate of volume shrinkage (Sv) varied directly according to the D value of Ca2+. A significant linear relationship between WR and Sv was observed for all working pressures (R2 > 0.91). An application of a pulsed vacuum at 8 kPa led to the highest weight reduction and shrinkage of Ca-Alg hydrogel samples compared to other working pressures, while 61 kPa seemed to be the best condition. Although all textural characteristics (hardness, breaking deformation, Young’s modulus, and rupture strength) did not directly variate by the level of working pressures, they were likely correlated with the levels of WR and Sv. Scanning electron micrographs (SEM) supported that the working pressure affected the characteristics of Ca-Alg hydrogel structure. Samples stimulated at a working pressure of 8 kPa showed higher deformation with heterogenous structure, large cavities, and looser layer when compared with those at 61 kPa. These results indicate the PVS is a promising technology that can be effectively applied in the external gelation process of Ca-Alg gel.

Effect of Process Conditions and Colloidal Properties of Cellulose Nanocrystals Suspensions on the Production of Hydrogel Beads

The influence of the physical, rheological, and process parameters on the cellulose nanocrystal (CNC) drops before and after external gelation in a CaCl2 solution was investigated. The dominant role of the CNC’s colloidal suspension properties, such as the viscous force, inertial, and surface tension forces in the fluid dynamics was quantitatively evaluated in the formation of drops and jellified beads. The similarity and difference between the behavior of carbohydrate polymers and rod-like crystallites such as CNC were enlightened. Pump-driven and centrifugally-driven external gelation approaches were followed to obtain CNC hydrogel beads with tunable size and regular shape. A superior morphological control—that is, a more regular shape and smaller dimension of the beads—were obtained by centrifugal force-driven gelation. These results suggest that even by using a simple set-up and a low-speed centrifuge device, the extrusion of a colloidal solution through a small nozzle under a centrifugal field is an efficient approach for the production of CNC hydrogel beads with good reproducibility, control over the bead morphology and size monodispersion.

Microfluidic on-chip Production of Alginate Hydrogels Using Double Co-flow Geometry

Microfluidic on-chip production of microgels employing external gelation has numerous biological and pharmaceutical applications, particularly for the encapsulation of delicate cargos, however, the on-chip production of microgels in microfluidic devices can be challenging due to problems such as clogging caused by accelerated progress in precursor solution viscosity. Here, we introduce a novel microfluidic design incorporating two consecutive co-flow geometries for microfluidic droplet generation. A shielding oil phase is employed to avoid emulsification and gelation stages from occurring simultaneously, thereby preventing clogging. The results revealed that the microfluidic device could generate highly monodispersed spherical droplets (coefficient of variation < 3%) with an average diameter in the range of 60–200 μm. Additionally, it was demonstrated that the device could appropriately create a shelter of the oil phase around the inner aqueous phase regardless of the droplet formation regime and flow conditions. The ability of the proposed microfluidic device in the generation of microgels was validated by producing alginate microgels utilizing an aqueous solution of calcium chloride as the continuous phase.

Microfluidic on-chip production of microgels using combined geometries

Microfluidic on-chip production of microgels using external gelation can serve numerous applications that involve encapsulation of sensitive cargos. Nevertheless, on-chip production of microgels in microfluidic devices can be challenging due to problems induced by the rapid increase in precursor solution viscosity like clogging. Here, a novel design incorporating a step, which includes a sudden increase in cross-sectional area, before a flow-focusing nozzle was proposed for microfluidic droplet generators. Besides, a shielding oil phase was utilized to avoid the occurrence of emulsification and gelation stages simultaneously. The step which was located before the flow-focusing nozzle facilitated the full shielding of the dispersed phase due to 3-dimensional fluid flow in this geometry. The results showed that the microfluidic device was capable of generating highly monodispersed spherical droplets (CV < 2% for step and CV < 5% for flow-focusing nozzle) with an average diameter in the range of 90–190 μm, both in step and flow-focusing nozzle. Moreover, it was proved that the device could adequately create a shelter for the dispersed phase regardless of the droplet formation locus. The ability of this microfluidic device in the production of microgels was validated by creating alginate microgels (with an average diameter of ~ 100 μm) through an external gelation process with on-chip calcium chloride emulsion in mineral oil.

Modified-release of encapsulated bioactive compounds from annatto seeds produced by optimized ionic gelation techniques

To compare the encapsulation of annatto extract by external gelation (EG) and internal gelation (IG) and to maximize process yield (% Y), two central composite designs were proposed. Calcium chloride (CaCl2) concentration (0.3–3.5%), alginate to gelling solution ratio (1:2–1:6); acetic acid (CH3COOH) concentration (0.2–5.0%) and alginate to gelling solution ratio (1:2–1:6) were taken as independent variables for EG and IG respectively. Release studies were conducted under different conditions; morphology, particle size, the encapsulation efficiency (EE), and release mechanism were evaluated under optimized conditions. The optimized EG conditions were 0.3% CaCl2 and 1:1.2 alginate to gelling solution ratio, whereas a 0.3% CH3COOH and 1:5 alginate to gelling solution ratio were optimized conditions for IG. When 20% extract was employed, the highest EE was achieved, and the largest release was obtained at a pH 6.5 buffer. The Peppas–Sahlin model presented the best fit to experimental data. Polyphenol release was driven by diffusion, whereas bixin showed anomalous release. These results are promising for application as modulated release agents in food matrices.

THE CONCEPTUAL DESIGN FOR LIQUID EFFLUENT TREATMENT OF UO2 KERNEL FABRICATION

THE CONCEPTUAL DESIGN FOR LIQUID EFFLUENT TREATMENT OF UO2 KERNEL FABRICATION. The pebble fuel for HTGR is prepared through fabrication of UO2 kernel, coated particle and spherical element fuel. In the fabrication of UO2 kernel by external gelation method, a multicomponent of liquid effluent is generated. Therefore, the liquid effluent is required to be treated for safety reason before disposed to waste storage. In this paper, the conceptual design for the liquid effluent treatment of UO2 kernel fabrication is performed with the simulation process using CHEMCAD software. CHEMCAD is a software that can be utilized for chemical process design. The results showed that the proposed conceptual design is able to separate valuable components: isopropyl alcohol (IPA) and tetrahydrofurfuryl alcohol (THFA). The flowrate of IPA product is 5.28 kg/h with purity of 0.99 in mass fraction and the flowrate of THFA product is 1.01 kg/h with purity of 0.99 in mass fraction.Keywords: liquid effluent, UO2 kernel, CHEMCAD, HTGR.