Water-Dependent Blending of Pectin Films: The Mechanics of Conjoined Biopolymers

Pectin Hydrogels as Structural Platform for Antibacterial Drug Delivery

Hydrogels are hydrophilic 3-dimensional networks characterized by the retention of a large amount of water. Because of their water component, hydrogels are a promising method for targeted drug delivery. The water component, or "free volume", is a potential vehicle for protein drugs. A particularly intriguing hydrogel is pectin. In addition to a generous free volume, pectin has structural characteristics that facilitate hydrogel binding to the glycocalyceal surface of visceral organs. To test drug function and pectin integrity after loading, we compared pectin films from four distinct plant sources: lemon, potato, soybean, and sugar beet. The pectin films were tested for their micromechanical properties and intrinsic antibacterial activity. Lemon pectin films demonstrated the greatest cohesion at 30% water content. Moreover, modest growth inhibition was observed with lemon pectin (p < 0.05). No effective inhibition was observed with soybean, potato, or sugar beet films (p > 0.05). In contrast, lemon pectin films embedded with carbenicillin, chloramphenicol, or kanamycin demonstrated significant bacterial growth inhibition (p < 0.05). The antibacterial activity was similar when the antibiotics were embedded in inert filter disks or pectin disks (p > 0.05). We conclude that lemon pectin films represent a promising structural platform for antibacterial drug delivery.

Biomechanics of a Plant-Derived Sealant for Corneal Injuries

Purpose

The corneal epithelium has a glycocalyx composed of membrane-associated glycoproteins, mucins, and galactin-3. Similar to the glycocalyx in visceral tissues, the corneal glycocalyx functions to limit fluid loss and minimize frictional forces. Recently, the plant-derived heteropolysaccharide pectin has been shown to physically entangle with the visceral organ glycocalyx. The ability of pectin to entangle with the corneal epithelium is unknown.

Methods

To explore the potential role of pectin as a corneal bioadhesive, we assessed the adhesive characteristics of pectin films in a bovine globe model.

Results

Pectin film was flexible, translucent, and low profile (80 µm thick). Molded in tape form, pectin films were significantly more adherent to the bovine cornea than control biopolymers of nanocellulose fibers, sodium hyaluronate, and carboxymethyl cellulose (P < 0.05). Adhesion strength was near maximal within seconds of contact. Compatible with wound closure under tension, the relative adhesion strength was greatest at a peel angle less than 45 degrees. The corneal incisions sealed with pectin film were resistant to anterior chamber pressure fluctuations ranging from negative 51.3 ± 8.9 mm Hg to positive 214 ± 68.6 mm Hg. Consistent with these findings, scanning electron microscopy demonstrated a low-profile film densely adherent to the bovine cornea. Finally, the adhesion of the pectin films facilitated the en face harvest of the corneal epithelium without physical dissection or enzymatic digestion.

Conclusions

We conclude that pectin films strongly adhere to the corneal glycocalyx.

Translational Relevance

The plant-derived pectin biopolymer provides potential utility for corneal wound healing as well as targeted drug delivery.

Optical and Mechanical Properties of Self-Repairing Pectin Biopolymers

Pectin’s unique physicochemical properties have been linked to a variety of reparative and regenerative processes in nature. To investigate the effect of water on pectin repair, we used a 5 mm stainless-steel uniaxial load to fracture glass phase pectin films. The fractured gel phase films were placed on a 1.5–1.8 mm thick layer of water and incubated for 8 h at room temperature and ambient humidity. There was no immersion or agitation. The repaired pectin film was subsequently assessed for its optical and mechanical properties. Light microscopy demonstrated repair of the detectable fracture area and restoration of the films’ optical properties. The burst strength of the repaired film declined to 55% of the original film. However, its resilience was restored to 87% of the original film. Finally, a comparison of the initial and post-repair fracture patterns demonstrated no recurrent fissures in the repaired glass phase films. The water-induced repair of the pectin film was superior to the optical and mechanical properties of the repaired films composed of nanocellulose fibers, sodium hyaluronate, and oxidized cellulose. We conclude that the unique physicochemical properties of pectin facilitate the water-induced self-repair of fractured pectin films.

Progress and challenges in sorghum biotechnology, a multipurpose feedstock for the bioeconomy

Sorghum [Sorghum bicolor (L.) Moench] is the fifth most important cereal crop globally by harvested area and production. Its drought and heat tolerance allow high yields with minimal input. It is a promising biomass crop for the production of biofuels and bioproducts. In addition, as an annual diploid with a relatively small genome compared with other C4 grasses, and excellent germplasm diversity, sorghum is an excellent research species for other C4 crops such as maize. As a result, an increasing number of researchers are looking to test the transferability of findings from other organisms such as Arabidopsis thaliana and Brachypodium distachyon to sorghum, as well as to engineer new biomass sorghum varieties. Here, we provide an overview of sorghum as a multipurpose feedstock crop which can support the growing bioeconomy, and as a monocot research model system. We review what makes sorghum such a successful crop and identify some key traits for future improvement. We assess recent progress in sorghum transformation and highlight how transformation limitations still restrict its widespread adoption. Finally, we summarize available sorghum genetic, genomic, and bioinformatics resources. This review is intended for researchers new to sorghum research, as well as those wishing to include non-food and forage applications in their research.

Functional Adhesion of Pectin Biopolymers to the Lung Visceral Pleura

Pleural injuries and the associated "air leak" are the most common complications after pulmonary surgery. Air leaks are the primary reason for prolonged chest tube use and increased hospital length of stay. Pectin, a plant-derived heteropolysaccharide, has been shown to be an air-tight sealant of pulmonary air leaks. Here, we investigate the morphologic and mechanical properties of pectin adhesion to the visceral pleural surface of the lung. After the application of high-methoxyl citrus pectin films to the murine lung, we used scanning electron microscopy to demonstrate intimate binding to the lung surface. To quantitatively assess pectin adhesion to the pleural surface, we used a custom adhesion test with force, distance, and time recordings. These assays demonstrated that pectin-glycocalyceal tensile adhesive strength was greater than nanocellulose fiber films or pressure-sensitive adhesives (p < 0.001). Simultaneous videomicroscopy recordings demonstrated that pectin-glycocalyceal adhesion was also stronger than the submesothelial connective tissue as avulsed surface remnants were visualized on the separated pectin films. Finally, pleural abrasion and hyaluronidase enzyme digestion confirmed that pectin binding was dependent on the pleural glycocalyx (p < 0.001). The results indicate that high methoxyl citrus pectin is a promising sealant for the treatment of pleural lung injuries.

Biomaterial-Assisted Anastomotic Healing: Serosal Adhesion of Pectin Films

Anastomotic leakage is a frequent complication of intestinal surgery and a major source of surgical morbidity. The timing of anastomotic failures suggests that leaks are the result of inadequate mechanical support during the vulnerable phase of wound healing. To identify a biomaterial with physical and mechanical properties appropriate for assisted anastomotic healing, we studied the adhesive properties of the plant-derived structural heteropolysaccharide called pectin. Specifically, we examined high methoxyl citrus pectin films at water contents between 17-24% for their adhesivity to ex vivo porcine small bowel serosa. In assays of tensile adhesion strength, pectin demonstrated significantly greater adhesivity to the serosa than either nanocellulose fiber (NCF) films or pressure sensitive adhesives (PSA) (p < 0.001). Similarly, in assays of shear resistance, pectin demonstrated significantly greater adhesivity to the serosa than either NCF films or PSA (p < 0.001). Finally, the pectin films were capable of effectively sealing linear enterotomies in a bowel simulacrum as well as an ex vivo bowel segment. We conclude that pectin is a biomaterial with physical and adhesive properties capable of facilitating anastomotic healing after intestinal surgery.

Visualizing pectin polymer-polymer entanglement produced by interfacial water movement

In this report, we investigated the physical conditions for creating pectin polymer-polymer (homopolymer) entanglement. The potential role of water movement in creating pectin entanglement was investigated by placing water droplets-equivalent to the water content of two gel phase films-between two glass phase films and compressing the films at variable probe velocities. Slow probe velocity (0.5 mm/sec) demonstrated no significant debonding. Corresponding videomicroscopy demonstrated an occasional water bridge, but no evidence of stranding or polymer entanglement. In contrast, fast probe velocity (5 mm/sec) resulted in 1) an increase in peak adhesion strength, 2) a progressive debonding curve, and 3) increased work of cohesion (p < .001). Corresponding videomicroscopy demonstrated pectin stranding and delamination between pectin films. Scanning electron microscopy images obtained during pectin debonding provided additional evidence of both stranding and delamination. We conclude that water movement can supply the motive force for the rapid chain entanglement between pectin films.