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.

Pectin based biologic Velcro effectively seals traumatic solid organ and small bowel injuries.

INTRODUCTION: Injuries to the liver and small bowel are common in multiple injuries. While there are currently a variety of accepted damage-control techniques to expeditiously manage such injuries, morbidity and mortality remain high. Pectin polymers have previously been shown to effectively seal visceral organ injuries ex vivo through physiochemical entanglement with the glycocalyx. We sought to compare the standard of care for the management of penetrating liver and small bowel injuries with a pectin-based bioadhesive patch in a live animal model. METHODS: Fifteen adult male swine underwent a laparotomy with standardized laceration to the liver. Animals were randomized to one of three treatment arms: packing with laparotomy pads (n = 5), suture repair (n = 5), or pectin patch repair (n = 5). Following 2 hours of observation, fluid was evacuated from the abdominal cavity and weighed. Next, a full-thickness small bowel injury was created, and animals were randomized to either a sutured repair (n = 7) or pectin patch repair (n = 8). The segment of bowel was then pressurized with saline, and the burst pressure was recorded. RESULTS: All animals survived the protocol to completion. There were no clinically significant differences between groups regarding baseline vitals or laboratory studies. On one-way analysis of variance, there was a statistically significant difference between groups regarding blood loss after liver repair (26 mL suture vs. 33 mL pectin vs. 142 mL packing, p < 0.01). On post hoc analysis, there was no statistically significant difference between suture and pectin ( p = 0.9). After repair, small bowel burst pressures were similar between pectin and suture repair (234 vs. 224 mm Hg, p = 0.7). CONCLUSION: Pectin-based bioadhesive patches performed similarly to the standard of care for the management of liver lacerations and full-thickness bowel injuries. Further testing is warranted to assess the biodurability of a pectin patch repair, as it may offer a simple option to effectively temporize traumatic intra-abdominal injuries.

Bioadhesive patch as a parenchymal sparing treatment of acute traumatic pulmonary air leaks.

INTRODUCTION: Traumatic pulmonary injuries are common in chest trauma. Persistent air leaks occur in up to 46% of patients depending on injury severity. Prolonged leaks are associated with increased morbidity and cost. Prior work from our first-generation pectin patches successfully sealed pulmonary leaks in a cadaveric swine model. We now test the next-generation pectin patch against wedge resection in the management of air leaks in anesthetized swine. METHODS: A continuous air leak of 10% to 20% percent was created to the anterior surface of the lung in intubated and sedated swine. Animals were treated with a two-ply pectin patch or stapled wedge resection (SW). Tidal volumes (TVs) were recorded preinjury and postinjury. Following repair, TVs were recorded, a chest tube was placed, and animals were observed for presence air leak at closure and for an additional 90 minutes while on positive pressure ventilation. Mann-Whitney U test and Fisher's exact test used to compare continuous and categorical data between groups. RESULTS: Thirty-one animals underwent either SW (15) or pectin patch repair (PPR, 16). Baseline characteristics were similar between animals excepting baseline TV (SW, 10.3 mL/kg vs. PPR, 10.9 mL/kg; p = 0.03). There was no difference between groups for severity of injury based on percent of TV loss (SW, 15% vs. PPR, 14%; p = 0.5). There was no difference in TV between groups following repair (SW, 10.2 mL/kg vs. PPR, 10.2 mL/kg; p = 1) or at the end of observation (SW, 9.8 mL/kg vs. PPR, 10.2 mL/kg; p = 0.4). One-chamber intermittent air leaks were observed in three of the PPR animals, versus one in the SW group ( p = 0.6). CONCLUSION: Pectin patches effectively sealed the lung following injury and were noninferior when compared with wedge resection for the management of acute traumatic air leaks. Pectin patches may offer a parenchymal sparing option for managing such injuries, although studies evaluating biodurability are needed.

Improved outcomes utilizing a novel pectin-based pleural sealant following acute lung injury.

BACKGROUND: Persistent air leaks after thoracic trauma are associated with significant morbidity. To evaluate a novel pectin sealant in a swine model of traumatic air leaks, we compared a pectin biopolymer with standard surgical and fibrin-based interventions. METHODS: A standardized lung injury was created in male Yorkshire swine. Interventions were randomized to stapled wedge resection (n = 5), topical fibrin glue (n = 5), fibrin patch (n = 5), and a pectin sealant (n = 6). Baseline, preintervention and postintervention tidal volumes (TV) were recorded. Early success was defined as the return to near-normal TV (>95% of baseline). Late success was defined as no detectable air leak in the chest tube after chest closure. RESULTS: There were no differences in injury severity between groups (mean TV loss, 62 ± 17 mL, p = 0.2). Early success was appreciated in 100% (n = 6) of the pectin interventions which was significantly better than the fibrin sealant (20%, n = 1), fibrin patch (20%, n = 1), and stapled groups (80%, n = 4, p = 0.01). The percent of return to baseline TV after sealant intervention was significantly increased in the pectin (98%) and staple arms (97%) compared with the fibrin sealant (91%) and fibrin patch arms (90%) (p = 0.02; p = 0.03). Late success was also improved with the pectin sealant: no air leak was detected in 83% of the pectin group compared with 40% in the stapled group (p = 0.008)-90% of the fibrin-based interventions resulted in continuous air leaks (p = 0.001). CONCLUSION: Pectin-based bioadhesives effectively seal traumatic air leaks upon application in a porcine model. Further testing is warranted as they may provide a superior parenchymal-sparing treatment option for traumatic air leaks.

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

Biodegradable pectin polymers have been recommended for a variety of biomedical applications, ranging from the delivery of oral drugs to the repair of injured visceral organs. A promising approach to regulate pectin biostability is the blending of pectin films. To investigate the development of conjoined films, we examined the physical properties of high-methoxyl pectin polymer-polymer (homopolymer) interactions at the adhesive interface. Pectin polymers were tested in glass phase (10-13% w/w water content) and gel phase (38-41% w/w water content). The tensile strength of polymer-polymer adhesion was measured after variable development time and compressive force. Regardless of pretest parameters, the adhesive strength of two glass phase films was negligible. In contrast, adhesion testing of two gel phase films resulted in significant tensile adhesion strength (p < 0.01). Adhesion was also observed between glass phase and gel phase films-likely reflecting the diffusion of water from the gel phase to the glass phase films. In studies of the interaction between two gel phase films, the polymer-polymer adhesive strength increased linearly with increasing compressive force (range 10-80 N) (R2 = 0.956). In contrast, adhesive strength increased logarithmically with time (range 10-10,000 s) (R2 = 0.913); most of the adhesive strength was observed within minutes of contact. Fracture mechanics demonstrated that the adhesion of two gel phase films resulted in a conjoined film with distinctive physical properties including increased extensibility, decreased stiffness and a 30% increase in the work of cohesion relative to native polymers (p < 0.01). Scanning electron microscopy of the conjoined films demonstrated cross-grain adhesion at the interface between the adhesive homopolymers. These structural and functional data suggest that blended pectin films have emergent physical properties resulting from the cross-grain intermingling of interfacial pectin chains.

Pectin biopolymer mechanics and microstructure associated with polysaccharide phase transitions.

Polysaccharide polymers like pectin can demonstrate striking and reversible changes in their physical properties depending upon relatively small changes in water content. Recent interest in using pectin polysaccharides as mesothelial sealants suggests that water content, rather than nonphysiologic changes in temperature, may be a practical approach to optimize the physical properties of the pectin biopolymers. Here, we used humidified environments to manipulate the water content of dispersed solution of pectins with a high degree of methyl esterification (high-methoxyl pectin; HMP). The gel phase transition was identified by a nonlinear increase in compression resistance at a water content of 50% (w/w). The gel phase was associated with a punched-out fracture pattern and scanning electron microscopy (SEM) images that revealed a cribiform (Swiss cheese-like) pectin microstructure. The glass phase transition was identified by a marked increase in resilience and stiffness. The glass phase was associated with a star-burst fracture pattern and SEM images that demonstrated a homogeneous pectin microstructure. In contrast, the burst strength of the pectin films was largely independent of water content over a range from 5 to 30% (w/w). These observations indicate the potential to use water content in the selective regulation of the physical properties of HMP biopolymers.

Analysis of pectin biopolymer phase states using acoustic emissions.

Acoustic emissions are stress or elastic waves produced by a material under external load. Since acoustic emissions are generated from within and transmitted through the substance, the acoustic signature provides insights into the physical and mechanical properties of the material. In this report, we used a constant velocity probe with force and acoustic emission monitoring to investigate the properties of glass phase and gel phase pectin films. In the gel phase films, a constant velocity uniaxial load produced periodic premonitory acoustic emissions with coincident force variations (saw-tooth pattern). SEM images of the gel phase microarchitecture indicated the presence of slip planes. In contrast, the glass phase films demonstrated early acoustic emissions, but effectively no force or acoustic evidence of periodic or premonitory emissions. Microstructural imaging of the glass phase films indicated the presence of early microcracks as well as dense polymerization of the pectin (without evidence of slip planes). We conclude that the water content in the pectin films contributes to not only the physical properties of the films, but also the stick-slip motion observed with constant uniaxial load. Further, acoustic emissions provide a sensitive and practical measure of this mechanical behavior.

The Effect of Calcium on the Cohesive Strength and Flexural Properties of Low-Methoxyl Pectin Biopolymers.

Abstract: Pectin binds the mesothelial glycocalyx of visceral organs, suggesting its potential role as a mesothelial sealant. To assess the mechanical properties of pectin films, we compared pectin films with a less than 50% degree of methyl esterification (low-methoxyl pectin, LMP) to films with greater than 50% methyl esterification (high-methoxyl pectin, HMP). LMP and HMP polymers were prepared by step-wise dissolution and high-shear mixing. Both LMP and HMP films demonstrated a comparable clear appearance. Fracture mechanics demonstrated that the LMP films had a lower burst strength than HMP films at a variety of calcium concentrations and hydration states. The water content also influenced the extensibility of the LMP films with increased extensibility (probe distance) with an increasing water content. Similar to the burst strength, the extensibility of the LMP films was less than that of HMP films. Flexural properties, demonstrated with the 3-point bend test, showed that the force required to displace the LMP films increased with an increased calcium concentration (p < 0.01). Toughness, here reflecting deformability (ductility), was variable, but increased with an increased calcium concentration. Similarly, titrations of calcium concentrations demonstrated LMP films with a decreased cohesive strength and increased stiffness. We conclude that LMP films, particularly with the addition of calcium up to 10 mM concentrations, demonstrate lower strength and toughness than comparable HMP films. These physical properties suggest that HMP has superior physical properties to LMP for selected biomedical applications.

Structural heteropolysaccharides as air-tight sealants of the human pleura.

Pulmonary "air leaks," typically the result of pleural injury caused by lung surgery or chest trauma, result in the accumulation of air in the pleural space (pneumothorax). Air leaks are a major source of morbidity and prolonged hospitalization after pulmonary surgery. Previous work has demonstrated structural heteropolysaccharide (pectin) binding to the mouse pleural glycocalyx. The similar lectin-binding characteristics and ultrastructural features of the human and mouse pleural glycocalyx suggested the potential application of these polymers in humans. To investigate the utility of pectin-based polymers, we developed a simulacrum using freshly obtained human pleura. Pressure-decay leak testing was performed with an inflation maneuver that involved a 3 s ramp to a 3 s plateau pressure; the inflation was completely abrogated after needle perforation of the pleura. Using nonbiologic materials, pressure-decay leak testing demonstrated an exponential decay with a plateau phase in materials with a Young's modulus less than 5. In human pleural testing, the simulacrum was used to test the sealant function of four mixtures of pectin-based polymers. A 50% high-methoxyl pectin and 50% carboxymethylcellulose mixture demonstrated no sealant failures at transpleural pressures of 60 cmH2 O. In contrast, pectin mixtures containing 50% low-methoxyl pectin, 50% amidated low-methoxyl pectins, or 100% carboxymethylcellulose demonstrated frequent sealant failures at transpleural pressures of 40-50 cmH2 O (p < 0.001). Inhibition of sealant adhesion with enzyme treatment, dessication and 4°C cooling suggested an adhesion mechanism dependent upon polysaccharide interpenetration. We conclude that pectin-based heteropolysaccharides are a promising air-tight sealant of human pleural injuries. © 2018 Wiley Periodicals, Inc. J. Biomed. Mater. Res. Part B, 2018. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 799-806, 2019.

Functional Mechanics of a Pectin-Based Pleural Sealant after Lung Injury.

Pleural injury and associated air leaks are a major influence on patient morbidity and healthcare costs after lung surgery. Pectin, a plant-derived heteropolysaccharide, has recently demonstrated potential as an adhesive binding to the glycocalyx of visceral mesothelium. Since bioadhesion is a process likely involving the interpenetration of the pectin-based polymer with the glycocalyx, we predicted that the pectin-based polymer may also be an effective sealant for pleural injury. To explore the potential role of an equal (weight%) mixture of high-methoxyl pectin and carboxymethylcellulose as a pleural sealant, we compared the yield strength of the pectin-based polymer to commonly available surgical products. The pectin-based polymer demonstrated significantly greater adhesion to the lung pleura than the comparison products (p < 0.001). In a 25 g needle-induced lung injury model, pleural injury resulted in an air leak and a loss of airway pressures. After application of the pectin-based polymer, there was a restoration of airway pressure and no measurable air leak. Despite the application of large sheets (50 mm2) of the pectin-based polymer, multifrequency lung impedance studies demonstrated no significant increase in tissue damping (G) or hysteresivity (η)(p > 0.05). In 7-day survival experiments, the application of the pectin-based polymer after pleural injury was associated with no observable toxicity, 100% survival (N = 5), and restored lung function. We conclude that this pectin-based polymer is a strong and nontoxic bioadhesive with the potential for clinical application in the treatment of pleural injuries.

Structural Heteropolysaccharide Adhesion to the Glycocalyx of Visceral Mesothelium.

Bioadhesives are biopolymers with potential applications in wound healing, drug delivery, and tissue engineering. Pectin, a plant-based heteropolysaccharide, has recently demonstrated potential as a mucoadhesive in the gut. Since mucoadhesion is a process likely involving the interpenetration of the pectin polymer with mucin chains, we hypothesized that pectin may also be effective at targeting the glycocalyx of the visceral mesothelium. To explore the potential role of pectin as a mesothelial bioadhesive, we studied the interaction of various pectin formulations with the mesothelium of the lung, liver, bowel, and heart. Tensile strength, peel strength, and shear resistance of the bioadhesive-mesothelial interaction were measured by load/displacement measurements. In both high-methoxyl pectins (HMP) and low-methoxyl pectins, bioadhesion was greatest with an equal weight % formulation with carboxymethylcellulose (CMC). The tensile strength of the high-methoxyl pectin was consistently greater than low-methoxyl or amidated low-methoxyl formulations (p < 0.05). Consistent with a mechanism of polymer-glycocalyx interpenetration, the HMP adhesion to tissue mesothelium was reversed with hydration and limited by enzyme treatment (hyaluronidase, pronase, and neuraminidase). Peel and shear forces applied to the lung/pectin adhesion resulted in a near-interface structural failure and the efficient isolation of intact en face pleural mesothelium. These data indicate that HMP, in an equal weight % mixture with CMC, is a promising mesothelial bioadhesive for use in experimental and therapeutic applications.

Outcomes and cost-effectiveness of alternative staging strategies for non-small-cell lung cancer.

PURPOSE: To identify the optimal strategy for staging the mediastinum of patients with known non-small-cell lung cancer (NSCLC), stratified by tumor (T) classification. METHODS: We used a decision-analytic model to compare the health outcomes and cost-effectiveness of three staging strategies: (1) chest computed tomography alone, (2) selective mediastinoscopy, and (3) routine mediastinoscopy. The overall effectiveness and cost of each strategy was a function of the proportion of patients accurately staged and the risks, benefits, and costs of the diagnostic tests and treatments used. Probability estimates and costs were derived from primary data and the literature. We adopted a societal perspective and calculated incremental cost-effectiveness ratios (ICERs) as cost per quality-adjusted life year (QALY) gained. RESULTS: Both mediastinoscopy strategies correctly identified more patients with mediastinal involvement (N2/N3 disease) and assigned them to multimodal regimens. Routine mediastinoscopy maximized quality-adjusted life expectancy in all patients, irrespective of T classification, and this result was robust to varying the model estimates over their reported ranges. In T1 patients, selective mediastinoscopy cost $24,500 per QALY gained, compared with $78,800 per QALY gained for routine mediastinoscopy. In T2 and T3 patients, the ICER of routine mediastinoscopy was more favorable ($42,800 and $53,400 per QALY gained, respectively). CONCLUSION: Routine mediastinoscopy maximizes quality-adjusted life expectancy in patients with known NSCLC, and its ICER compares favorably with other currently accepted medical technologies. The survival benefit and cost-effectiveness of this strategy are greater in patients with T2 and T3 tumors and are likely to improve with advances in multimodal therapy.