Carboxymethylpachymaran-zein coated plant microcapsules-based β-galactosidase encapsulation system for long-term effective delivery

Development of a tomato xylem-mimicking microfluidic system to study Ralstonia pseudosolanacearum biofilm formation

The bacterial wilt pathogen Ralstonia pseudosolanacearum (Rps) colonizes plant xylem vessels and blocks the flow of xylem sap by its biofilm (comprising of bacterial cells and extracellular material), resulting in devastating wilt disease across many economically important host plants including tomatoes. The technical challenges of imaging the xylem environment, along with the use of artificial cell culture plates and media in existing in vitro systems, limit the understanding of Rps biofilm formation and its infection dynamics. In this study, we designed and built a microfluidic system that mimicked the physical and chemical conditions of the tomato xylem vessels, and allowed us to dissect Rps responses to different xylem-like conditions. The system, incorporating functional surface coatings of carboxymethyl cellulose-dopamine, provided a bioactive environment that significantly enhanced Rps attachment and biofilm formation in the presence of tomato xylem sap. Using computational approaches, we confirmed that Rps experienced linear increasing drag forces in xylem-mimicking channels at higher flow rates. Consistently, attachment and biofilm assays conducted in our microfluidic system revealed that both seeding time and flow rates were critical for bacterial adhesion to surface and biofilm formation inside the channels. These findings provided insights into the Rps attachment and biofilm formation processes, contributing to a better understanding of plant-pathogen interactions during wilt disease development.

Advances in protein-based microcapsules and their applications: A review

Due to their excellent emulsification, biocompatibility, and biological activity, proteins are widely used as microcapsule wall materials for encapsulating drugs, natural bioactive substances, essential oils, probiotics, etc. In this review, we summarize the protein-based microcapsules, discussing the types of proteins utilized in microcapsule wall materials, the preparation process, and the main factors that influence their properties. Additionally, we conclude with examples of the vital role of protein-based microcapsules in advancing the food industry from primary processing to deep processing and their potential applications in the biomedical, chemical, and textile industries. However, the low stability and controllability of protein wall materials lead to degraded performance and quality of microcapsules. Protein complexes with polysaccharides or modifications to proteins are often used to improve the thermal instability, pH sensitivity, encapsulation efficiency and antioxidant capacity of microcapsules. In addition, factors such as wall material composition, wall material ratio, the ratio of core to wall material, pH, and preparation method all play critical roles in the preparation and performance of microcapsules. The application area and scope of protein-based microcapsules can be further expanded by optimizing the preparation process and studying the microcapsule release mechanism and control strategy.

Biobased Spore Microcapsules for Asphalt Self-Healing

Asphalt pavements and bituminous composites are majorly damaged by bitumen aging and fatigue cracking by traffic load. To add, maintenance and reparation of asphalt pavements is expensive and also releases significant amounts of greenhouse gases. These issues can be mitigated by promoting asphalt self-healing mechanisms with encapsulated rejuvenators. The ability of the required microcapsules to be resilient against high temperatures, oxidation, and mechanical stress is essential to promote such self-healing behavior without compromising the field performance of the asphalt pavement. This work proposes, for the first time, the use of extremely resistant biobased spores for the encapsulation of recycled oil-based rejuvenators to produce more resilient self-healing pavements. Spore encapsulants were obtained from natural spores (Lycopodium clavatum) by applying different chemical treatments, which enabled the selection of the best morphologically intact and clean spore encapsulant. The physical, morphological, and physicochemical changes were examined using fluorescence images, ATR-FTIR, SEM, size distribution, XRD, TGA and DSC analyses. Sunflower oil was used as the encapsulated rejuvenator with an optimal sol colloidal mixture for sporopollenin-oil of 1:5 (gram-to-gram). Vacuum, passive, and centrifugal encapsulation techniques were tested for loading the rejuvenator inside the clean spores and for selecting the best encapsulation technology. The encapsulation efficiency and the profiles of the accelerated release of the rejuvenator from the loaded spores over time were studied, and these processes were visualized with optical and inverted fluorescence microscopy. Vacuum encapsulation was identified as the best loading technique with an encapsulation efficiency of 93.02 ± 3.71%. The rejuvenator was successfully encapsulated into the clean spores, as observed by optical and SEM morphologies. In agreement with the TGA and DSC, the microcapsules were stable up to 204 °C. Finally, a self-healing test was conducted through fluorescence tests to demonstrate how these biobased spore microcapsules completely heal a crack into an aged bitumen sample in 50 min.

Role of Sporopollenin Shell Interfacial Properties in Protein Adsorption

Sporopollenin shells isolated from natural pollen grains have received attention in translational and applied research in diverse fields of drug delivery, vaccine delivery, and wastewater remediation. However, little is known about the sporopollenin shell's potential as an adsorbent. Herein, we have isolated sporopollenin shells from four structurally diverse pollen species, black walnut, marsh elder, mugwort, and silver birch, to study protein adsorption onto sporopollenin shells. We investigated three major interfacial properties, surface area, surface functional groups, and surface charge, to elucidate the mechanism of protein adsorption onto sporopollenin shells. We showed that sporopollenin shells have a moderate specific surface area (<12 m²/g). Phosphoric acid and potassium hydroxide treatments that were used to isolate sporopollenin shells from natural pollen grains also result in the functionalization of sporopollenin shell surfaces with ionizable groups of carboxylic acid and carboxylate salt. As a result, sporopollenin shells exhibit a negative ζ potential in the range of -75 to -82 mV at pH 10 when dispersed in water. The ζ potentials of sporopollenin shells remain negative in the pH range of 2.5-11, with the absolute value of ζ potential showing a decrease with the decrease in pH. The negative surface charge promotes the adsorption of protein onto the sporopollenin shell via electrostatic interaction. Despite having a moderate surface area, sporopollenin shells adsorb a significant amount of lysozyme (145-340 μg lysozyme per mg of sporopollenin shells). Lysozyme adsorption onto sporopollenin shells alters the surface, and the surface charge becomes positive at acidic pH. Overall, this study demonstrates the potential of sporopollenin shells to adsorb proteins, highlights the critical role of sporopollenin shell's interfacial properties in protein adsorption, and identifies the mechanism of protein adsorption on sporopollenin shells.

Tuning of Molecular Interactions between Zein and Tannic Acid to Modify Sunflower Sporopollenin Exine Capsules: Enhanced Stability and Targeted Delivery of Bioactive Macromolecules

There are multiple obstacles for the storage and digestion of orally administered bioactive macromolecules. This study developed a low-cost and sustained-release delivery system (sporopollenin exine capsules with zein/tannic acid modification) of proteins with excellent storage stability, and at the same time provided insights into the sustained-release mechanism through exploring the interaction between zein and tannic acid (TA). β-Galactosidase (β-Gal) was utilized as a model protein and loaded into sporopollenin exine capsules (SECs), which were then coated with the zein/TA system. Under the optimized zein/TA conditions, the zein/TA system showed better performance than the zein alone system in the sustained release of β-Gal, with the residual activity of about 70.26% after 24 h of simulated digestion. Evaluation of the storage stability demonstrated a β-Gal residual activity of nearly 90% for 28 days at 25 °C. Additionally, FTIR analysis demonstrated that the stability of the zein/TA system depends on both hydrogen bonding and certain covalent bonding through the Schiff-base reaction, and the sustained release is regulated by the bonding strength.

Designable Carboxymethylpachymaran/Metal Ion Architecture on Sunflower Sporopollenin Exine Capsules as Delivery Vehicles for Bioactive Macromolecules

There are multiple obstacles in the gastrointestinal tract (GIT) for oral administration of bioactive macromolecules. Here, we engineered an oral delivery vehicle (sporopollenin exine capsules with carboxymethylpachymaran (CMP)/metal ion modification) with targeted release based on food-grade ingredients and processing operations. Then, the interaction and binding mechanisms between CMP and metal ions in the vehicle were investigated. By using β-galactosidase (β-Gal) as a model protein, the systems were characterized for the surface morphology and monitored by the in vitro release profile of β-Gal. Notably, the CMP/metal ion systems not only markedly decreased the CMP dosage but also achieved a valid long-term release compared with the previously reported CMP system. Among all the systems, the CMP/3% AlCl₃ system showed the best ability to control the release with the maximum residual activity of β-Gal at nearly 72% after 24 h of treatment. Subsequently, the interaction mechanism between CMP and metal ions within the system was characterized by the perspectives of microstructure, rheological properties, and spectroscopy characteristics. The results indicated that the low pH conditions are conducive to the further cross-linking of CMP and metal ions, resulting in a high gel strength and thus a dense structure, which can impact the controlled release of β-Gal in the GIT. Overall, the system may be utilized in the administration of medical and functional foods, specifically for the delivery of bioactive proteins via the oral route.