Enzyme cross-linked pectin microgel particles for use in foods

A New Approach for On-Chip Production of Biological Microgels Using Photochemical Cross-Linking

Photochemical cross-linking is a key step for manufacturing microgels in numerous applications, including drug delivery, tissue engineering, material production, and wound healing. Existing photochemical cross-linking techniques in microfluidic devices rely on UV curing, which can cause cell and DNA damage. We address this challenge by developing a microfluidic workflow for producing microgels using visible light-driven photochemical cross-linking of aqueous droplets dispersed in a continuous oil phase. We report a proof-of-concept to construct microgels from the protein Bovine Serum Albumin (BSA) with [Ru(bpy)3]2+ mediated cross-linking. By controlling the capillary number of the continuous and dispersed phases, the volumetric flow rate, and the photochemical reaction time within the microfluidic tubing, we demonstrate the construction of protein microgels with controllable and uniform dimensions. Our technique can, in principle, be applied to a wide range of different proteins with biological and responsive properties. This work therefore bridges the gap between hydrogel manufacturing using visible light and microfluidic microgel templating, facilitating numerous biomedical applications.

Synthetic and biopolymeric microgels: Review of similarities and difference in behaviour in bulk phases and at interfaces

This review discusses the current knowledge of interfacial and bulk interactions of biopolymeric microgels in relation to the well-established properties of synthetic microgels for applications as viscosity modifiers and Pickering stabilisers. We present a timeline showing the key milestones in designing microgels and their bulk/ interfacial performance. Poly(N-isopropylacrylamide) (pNIPAM) microgels have remained as the protagonist in the synthetic microgel domain whilst proteins or polysaccharides have been primarily used to fabricate biopolymeric microgels. Bulk properties of microgel dispersions are dominated by the volume fraction (ϕ) of the microgel particles, but ϕ is difficult to pinpoint, as addressed by many theoretical models. By evaluating recent experimental studies over the last five years, we find an increasing focus on the analysis of microgel elasticity as a key parameter in modulating their packing at the interfaces, within the provinces of both synthetic and biopolymeric systems. Production methods and physiochemical factors shown to influence microgel swelling in the aqueous phase can have a significant impact on their bulk as well as interfacial performance. Compared to synthetic microgels, biopolymer microgels show a greater tendency for polydispersity and aggregation and do not appear to have a core-corona structure. Comprehensive studies of biopolymeric microgels are still lacking, for example, to accurately determine their inter- and intra- particle interactions, whilst a wider variety of techniques need to be applied in order to allow comparisons to real systems of practical usage.

Physicochemical, structural and in vitro gastrointestinal tract release properties of ι-carrageenan/sodium caseinate synbiotic microgels produced by double-crosslinking with calcium ions and transglutaminase

The aim of this study was to develop ι-carrageenan (ιC)/sodium caseinate (NaCas) synbiotic microgels loading Lacticasebacillus paracasei produced by double-crosslinking with calcium ions and different concentrations (0, 5, 10, and 15 U/g protein) of transglutaminase (TGase). The synbiotic microgels were coated/filled with pectic oligosaccharide (POS). Field emission scanning electron microscope (FE-SEM) and X-ray diffraction (XRD) analyses indicated that L. paracasei was successfully microencapsulated in synbiotic microgels. In Fourier transform infrared (FT-IR) analysis, the new formation of covalent and ionic crosslinking was observed in double-crosslinked synbiotic microgels. The encapsulation efficiency of L. paracasei was significantly increased from 87.82 to 97.68 % by increasing the concentration of TGase from 0 to 15 U/g protein, respectively. After exposure to simulated gastric fluid for 2 h and simulated intestinal fluid for 4 h, the survival rate of L. paracasei was significantly increased as the concentration of TGase increased.

Fabrication, characterization and emulsifying properties of agarose microgel

Agarose microgels were prepared with bottom-up approach, and the emulsifying properties of agarose microgels were investigated. Physical properties of microgels are varied with agarose concentration, and further affect the emulsifying performance of microgels. Enhanced surface hydrophobicity index and decreased particle size of microgels was recorded with the increasing of agarose concentration, which was conducive to emulsifying properties of microgels. Improved interfacial adsorption of microgels was evidenced by Dynamic surface tension and SEM. However, microscopic morphology of microgel at O/W interface indicated that increasing agarose concentration could weaken the deformability of microgels. The influence of external conditions (pH and NaCl) on the physical properties of microgels were investigated, and their effects on the emulsion stability were evaluated. Compared with acidification, NaCl was appeared to be more destructive to emulsion stability. Results indicated acidification and NaCl could decrease surface hydrophobicity index of microgels, but there was differentiation in the variation of particle size. It was inferred that deformability of microgels could make contribution to the stability of emulsion. This study verified that microgelation was a feasible scheme to improve the interfacial properties of agarose, and the influence of agarose concentration, pH, and NaCl on the emulsifying performance of microgels was investigated.

Injectable Microporous Annealed Particle Hydrogel Based on Guest-Host-Interlinked Polyethylene Glycol Maleimide Microgels

Microporous annealed particle (MAP) hydrogels have emerged as a versatile biomaterial platform for regenerative medicine. MAP hydrogels have been used for the delivery of cells and organoids but often require annealing post injection by an external source. We engineered an injectable, self-annealing MAP hydrogel with reversible interparticle linkages based on guest-host functionalized polyethylene glycol maleimide (PEG-MAL) microgels. We evaluated the effect of guest-host linkages on different types of microgels fabricated by either batch emulsion or mechanical fragmentation methods. Batch emulsion generated small spherical microgels with controllable 10-100 μm diameters and mechanical fragmentation generated irregular microgels with larger diameters (100-200 μm). Spherical microgels (15 μm) showed self-healing behavior and completely recovered from high strain while fragmented microgels (133 μm) did not recover. Guest-host interactions significantly contributed to the mechanical properties of spherical microgels but had no effect on fragmented microgels. Spherical microgels were superior to the fragmented microgels for co-injection of immune cells and pancreatic islets due to their lower force of injection, demonstrating more homogeneously distributed cells and greater cell viability after injection. Based on these studies, the spherical guest-host MAP hydrogels provide a controllable, injectable scaffold for engineered microenvironments and cell delivery applications.