Sealing effect of rapidly curable gelatin-poly (L-glutamic acid) hydrogel glue on lung air leak

Poly (γ) glutamic acid: a unique microbial biopolymer with diverse commercial applicability

Microbial biopolymers have emerged as promising solutions for environmental pollution-related human health issues. Poly-γ-glutamic acid (γ-PGA), a natural anionic polymeric compound, is composed of highly viscous homo-polyamide of D and L-glutamic acid units. The extracellular water solubility of PGA biopolymer facilitates its complete biodegradation and makes it safe for humans. The unique properties have enabled its applications in healthcare, pharmaceuticals, water treatment, foods, and other domains. It is applied as a thickener, taste-masking agent, stabilizer, texture modifier, moisturizer, bitterness-reducing agent, probiotics cryoprotectant, and protein crystallization agent in food industries. γ-PGA is employed as a biological adhesive, drug carrier, and non-viral vector for safe gene delivery in tissue engineering, pharmaceuticals, and medicine. It is also used as a moisturizer to improve the quality of hair care and skincare cosmetic products. In agriculture, it serves as an ideal stabilizer, environment-friendly fertilizer synergist, plant-growth promoter, metal biosorbent in soil washing, and animal feed additive to reduce body fat and enhance egg-shell strength.

3D in vitro hydrogel models to study the human lung extracellular matrix and fibroblast function

The pulmonary extracellular matrix (ECM) is a macromolecular structure that provides mechanical support, stability and elastic recoil for different pulmonary cells including the lung fibroblasts. The ECM plays an important role in lung development, remodeling, repair, and the maintenance of tissue homeostasis. Biomechanical and biochemical signals produced by the ECM regulate the phenotype and function of various cells including fibroblasts in the lungs. Fibroblasts are important lung structural cells responsible for the production and repair of different ECM proteins (e.g., collagen and fibronectin). During lung injury and in chronic lung diseases such as asthma, idiopathic pulmonary fibrosis (IPF) and chronic obstructive pulmonary disease (COPD), an abnormal feedback between fibroblasts and the altered ECM disrupts tissue homeostasis and leads to a vicious cycle of fibrotic changes resulting in tissue remodeling. In line with this, using 3D hydrogel culture models with embedded lung fibroblasts have enabled the assessment of the various mechanisms involved in driving defective (fibrotic) fibroblast function in the lung's 3D ECM environment. In this review, we provide a summary of various studies that used these 3D hydrogel models to assess the regulation of the ECM on lung fibroblast phenotype and function in altered lung ECM homeostasis in health and in chronic respiratory disease.

Optimization of fermentation conditions, purification and rheological properties of poly (γ-glutamic acid) produced by Bacillus subtilis 1006-3

This study aimed to investigate the optimal fermentation condition, purification and rheological properties of extracellular polymers produced by Bacillus subtilis 1006-3. An optimum temperature of 30.2 °C, inoculation amount of 6.1%, and pH of 8.2 were determined via Response Surface Methodology. The result of amino acid analysis and gel electrophoresis indicated that the obtained polymer contained only glutamic acid, with a wide molecular weight range. This polymer was finally determined as γ-PGA by infrared spectroscopy. The γ-PGA solution displayed a behavior of pseudoplastic non-Newtonian fluid with shear thinning properties, which can be described by the Ostward-de Waele power law model. The apparent viscosity of γ-PGA solution increased with the increase in its concentration from 1% to 10%. The deviation in pH from neutral value, and the addition of NaCl or MgCl₂ can reduce the apparent viscosity of γ-PGA solution, and it was more sensitive to Mg²⁺ than to Na⁺ addition. At the concentration of 4, 6, and 8%, γ-PGA solution showed predominantly viscous response in the range of 0.1-100 rad/s angular frequency (G″>G'). These results indicated the potential application of the γ-PGA as a thickening agent.

Engineering Tough, Injectable, Naturally Derived, Bioadhesive Composite Hydrogels

Engineering mechanically robust bioadhesive hydrogels that can withstand large strains may open new opportunities for the sutureless sealing of highly stretchable tissues. While typical chemical modifications of hydrogels, such as increasing the functional group density of crosslinkable moieties and blending them with other polymers or nanomaterials have resulted in improved mechanical stiffness, the modified hydrogels have often exhibited increased brittleness resulting in deteriorated sealing capabilities under large strains. Furthermore, highly elastic hydrogels, such as tropoelastin derivatives are highly expensive. Here, gelatin methacryloyl (GelMA) is hybridized with methacrylate-modified alginate (AlgMA) to enable ion-induced reversible crosslinking that can dissipate energy under strain. The hybrid hydrogels provide a photocrosslinkable, injectable, and bioadhesive platform with an excellent toughness that can be tailored using divalent cations, such as calcium. This class of hybrid biopolymers with more than 600% improved toughness compared to GelMA may set the stage for durable, mechanically resilient, and cost-effective tissue sealants. This strategy to increase the toughness of hydrogels may be extended to other crosslinkable polymers with similarly reactive moieties.

Pulmonary pathologic alterations associated with biopsy inserted hydrogel plugs

The prevention of pneumothorax after percutaneous lung biopsy is a major patient safety concern. The insertion of hydrogel plugs into biopsy sites to mitigate this complication is a new intervention. The histology of the plug has not been previously reported, and in this study the histologic reaction is reported in 13 cases. The hydrogel plug forms a spherical basophilic matrix pool with an adjacent foreign body giant cell reaction and patchy eosinophilia. No extension to the pleural surface is present. The potential diagnostic errors related to the presence of the plug are discussed.

Deciphering metabolic responses of biosurfactant lichenysin on biosynthesis of poly-γ-glutamic acid

Poly-γ-glutamic acid (γ-PGA) is an extracellularly produced biodegradable polymer, which has been widely used as agricultural fertilizer, mineral fortifier, cosmetic moisturizer, and drug carrier. This study firstly discovered that lichenysin, as a biosurfactant, showed the capability to enhance γ-PGA production in Bacillus licheniformis. The exogenous addition of lichenysin improved the γ-PGA yield up to 17.9% and 21.9%, respectively, in the native strain B. licheniformis WX-02 and the lichenysin-deficient strain B. licheniformis WX02-ΔlchAC. The capability of intracellular biosynthesis of lichenysin was positively correlated with γ-PGA production. The yield of γ-PGA increased by 25.1% in the lichenysin-enhanced strain B. licheniformis WX02-Psrflch and decreased by 12.2% in the lichenysin-deficient strain WX02-ΔlchAC. Analysis of key enzyme activities and gene expression in the TCA cycle, precursor glutamate synthesis, and γ-PGA synthesis pathway revealed that the existence of lichenysin led to increased γ-PGA via shifting the carbon flux in the TCA cycle towards glutamate and γ-PGA biosynthetic pathways, minimizing by-product formation, and facilitating the uptake of extracellular substrates and the polymerization of glutamate to γ-PGA. Insight into the mechanisms of enhanced production of γ-PGA by lichenysin would define the essential parameters involved in γ-PGA biosynthesis and provide the basis for large-scale production of γ-PGA.

Poly-γ-glutamic Acid Synthesis, Gene Regulation, Phylogenetic Relationships, and Role in Fermentation

Poly-γ-glutamic acid (γ-PGA) is a biodegradable biopolymer produced by several bacteria, including Bacillus subtilis and other Bacillus species; it has good biocompatibility, is non-toxic, and has various potential biological applications in the food, pharmaceutical, cosmetic, and other industries. In this review, we have described the mechanisms of γ-PGA synthesis and gene regulation, its role in fermentation, and the phylogenetic relationships among various pgsBCAE, a biosynthesis gene cluster of γ-PGA, and pgdS, a degradation gene of γ-PGA. We also discuss potential applications of γ-PGA and highlight the established genetic recombinant bacterial strains that produce high levels of γ-PGA, which can be useful for large-scale γ-PGA production.

Enhanced sealing strength of a hydrophobically-modified Alaska pollock gelatin-based sealant

A novel tissue sealant composed of hydrophobically-modified Alaska pollock gelatin and polyethylene glycol-based crosslinker showed higher sealing effect than commercially available tissue sealant.

Microbial synthesis of poly-γ-glutamic acid: current progress, challenges, and future perspectives

Poly-γ-glutamic acid (γ-PGA) is a naturally occurring biopolymer made from repeating units of l-glutamic acid, d-glutamic acid, or both. Since some bacteria are capable of vigorous γ-PGA biosynthesis from renewable biomass, γ-PGA is considered a promising bio-based chemical and is already widely used in the food, medical, and wastewater industries due to its biodegradable, non-toxic, and non-immunogenic properties. In this review, we consider the properties, biosynthetic pathway, production strategies, and applications of γ-PGA. Microbial biosynthesis of γ-PGA and the molecular mechanisms regulating production are covered in particular detail. Genetic engineering and optimization of the growth medium, process control, and downstream processing have proved to be effective strategies for lowering the cost of production, as well as manipulating the molecular mass and conformational/enantiomeric properties that facilitate screening of competitive γ-PGA producers. Finally, future prospects of microbial γ-PGA production are discussed in light of recent progress, challenges, and trends in this field.

Poly-γ-glutamic acid: production, properties and applications

Poly-γ-glutamic acid (γ-PGA) is a naturally occurring biopolymer made up of repeating units of l-glutamic acid, d-glutamic acid or both. γ-PGA can exhibit different properties (conformational states, enantiomeric properties and molecular mass). Owing to its biodegradable, non-toxic and non-immunogenic properties, it has been used successfully in the food, medical and wastewater industries. Amongst other novel applications, it has the potential to be used for protein crystallization, as a soft tissue adhesive and a non-viral vector for safe gene delivery. This review focuses on the production, properties and applications of γ-PGA. Each application of γ-PGA utilizes specific properties attributed to various forms of γ-PGA. As a result of its growing applications, more strains of bacteria need to be investigated for γ-PGA production to obtain high yields of γ-PGA with different properties. Many medical applications (especially drug delivery) have exploited α-PGA. As γ-PGA is essentially different from α-PGA (i.e. it does not involve a chemical modification step and is not susceptible to proteases), it could be better utilized for such medical applications. Optimization of γ-PGA with respect to cost of production, molecular mass and conformational/enantiomeric properties is a major step in making its application practical. Analyses of γ-PGA production and knowledge of the enzymes and genes involved in γ-PGA production will not only help increase productivity whilst reducing the cost of production, but also help to understand the mechanism by which γ-PGA is effective in numerous applications.

Reduction of intraoperative air leaks with Progel in pulmonary resection: a comprehensive review

Intraoperative alveolar air leaks (IOALs) occur in 75% of patients during pulmonary resection. Despite routine use of sutures and stapling devices, they remain a significant problem in the daily practice of thoracic surgery. Air leaks that persist beyond postoperative day 5 often result in increased costs and complications. Several large meta-analyses have determined that sealants as a class reduce postoperative air leak duration and time to chest drain removal, but these results did not necessarily correlate with a reduction in length of postoperative hospital stay. These analyses grouped surgical sealants together of necessity, but differences in efficacy may exist due to the differing product characteristics, study protocols, surgical procedures, and study endpoints. Progel, currently the only pleural surgical sealant FDA-approved for use in lung resection, has demonstrated efficacy and safety in two controlled clinical studies and superiority over standard air leak closure methods in reducing IOALs and length of hospital stay. This paper will review these findings and report on real-world experience with this recently approved pleural sealant.

Bioadhesion and biocompatibility evaluations of gelatin and polyacrylic acid as a crosslinked hydrogel in vitro

This study describes the potentiality of crosslinked hydrogels comprised of gelatin and polyacrylic acid (CHGP) as a biological glue for soft tissues and compares its bonding strength with that of fibrin glue. Water-soluble carbodimide (WSC) was used to crosslink the mixture of gelatin and polyacrylic acid (PAA). An addition of PAA to gelatin increases bonding strength and reduces the gelation time and WSC concentration. Increasing the gelatin, WSC and PAA concentration increases the bonding strength. There is a critical concentration to have a maximum bonding strength. The cured hydrogel exhibited sufficient adhesion to mouse skin with a higher bonding strength than fibrin glue. The in vitro test has been done for evaluating CHGP toxicity.

Sealing effects of cross-linked gelatin

Surgical sealants form gel when applied to tissues. Currently, fibrin sealant has been successfully used in many surgical fields, but it has several disadvantages, including possible virus transmission, low adhesive strength, and high cost. In this study, gelatin and glutaraldehyde (GA) solutions were chosen to demonstrate the effectiveness of cross-linked gelatin gel as sealant and barrier, both of which have long been used in medical applications. It was found that the gelatin gel prepared from 26 wt% gelatin and 1 wt% GA solutions exhibited bonding strength almost three times higher than that of fibrin glue. The bonding strength increased with the increasing gelatin and GA concentrations. When a needle hole on PTFE vascular grafts was sealed with the gelatin gel, the water-resistant pressure significantly increased upon rubbing and was twice higher than that of fibrin glue. The cytotoxicity of gelatin gel was found to be much lower than that of albumin glue prepared at the same composition as commercially available BioGlue®. The gelatin gel was found to be also effective as barrier to prevent adhesion in a rat cecum abrasion model.

Poly (glutamic acid)--an emerging biopolymer of commercial interest

Poly (γ-glutamic acid) (PGA) is water-soluble, anionic, biodegradable, and edible biopolymer produced by Bacillus subtilis. It has multifarious potential applications in foods, pharmaceuticals, healthcare, water treatment and other fields. The production of PGA has already been established on the industrial scale. Various studies regarding the fermentative production, downstream processing and characterization of PGA have been reported in the literature. This review provides updated information on fermentative production of PGA by various bacterial strains and effect of fermentation conditions and media component on production of PGA in submerged as well as solid state fermentation. Information on the application of genetic engineering for enhancement of yield of PGA, kinetic studies for production of PGA in submerged fermentation and recovery and purification of PGA is included. An attempt has also been made to review the current and potential applications of PGA. This review may contribute to further development of this commercially and academically interesting biopolymer.

Oligomer adsorption on dry and wet collagen surfaces

The development of new biodegradable polymeric tissue adhesives has been almost stagnant for the past 10 years, primarily due to the inability to overcome the problem of inadequate adhesion properties. Efforts at the synthesis and modification of chemical structures by incorporating functional groups have proven futile. This study proposes using simulation as a preliminary move to obtain a better understanding of adsorption behavior on biological tissues. It is hoped that this understanding will subsequently serve as a guide for better polymer design and synthesis. Adsorption under both dry and wet conditions were simulated applying classical molecular mechanics and dynamics (MM/MD) because of their relevancy and efficiency. Twelve types of oligomers and a model collagen surface were constructed, followed by structural optimization and equilibration treatments. The COMPASS force field was used to describe the molecular potential energy surfaces. One strand of the oligomer was then located on top of the collagen surface and their interactions at equilibrium, in terms of van der Waals (vdW) and electrostatic energies, monitored over time. For the wet environment a thick water layer was constructed and placed on top of the oligomer and collagen surface. The results showed that the vdW component dominated physical adsorption for all oligomers, under both dry and wet conditions. This implies that interactions of polymers with tissue surfaces are inherently weak. Functional groups on oligomers could improve adhesion via electrostatic interaction. This interaction is, however, screened off in a wet environment, resulting in a reduction in the adsorption energy for all molecules studied. Of all the oligomers studied, poly(glycine) showed the strongest adsorption to collagen in both dry and wet conditions. Therefore, it is proposed to include the functional groups present in poly(glycine) in future tissue adhesive systems.

Surgical sealant for preventing air leaks after pulmonary resections in patients with lung cancer

BACKGROUND

Postoperative air leak is a frequent complication after pulmonary resection for lung cancer. It may cause serious complications, such as empyema, or prolong the need for chest tube and hospitalization. Different types of surgical sealants have been developed to prevent or to reduce postoperative air leaks. A systematic review was therefore undertaken to evaluate the evidence on their effectiveness.

OBJECTIVES

To evaluate the effectiveness of surgical sealants in preventing or reducing postoperative air leaks after pulmonary resection for lung cancer.

SEARCH STRATEGY

We searched the electronic databases MEDLINE (1966 to September 2008), EMBASE (1974 to September 2008), and the Cochrane Central Register of Controlled Trials (CENTRAL)(The Cochrane Library, Issue 3, 2008) and listed references. We hand searched conference proceedings to identify published and unpublished trials.

SELECTION CRITERIA

We included randomized controlled clinical trials in which standard closure techniques plus a sealant were compared with the same intervention with no use of any sealant in patients undergoing elective pulmonary resection provided that a large proportion of the patients studied had undergone pulmonary resection for lung cancer.

DATA COLLECTION AND ANALYSIS

Four reviewers independently selected the trials to be included in the review, assessed methodological quality of each trial and extracted data using a standardized form. Because of several limitations, narrative synthesis was used at this stage.

MAIN RESULTS

Sixteen trials, with 1642 randomized patients in total were included. In thirteen trials there were differences between treatment and control patients in reducing postoperative air leaks. This reduction proved to be significant in six trials. Three trials showed a significant reduction in time to chest drain removal in the treatment group. In two trials, the percentage of patients with persistent air leak was significantly smaller in the treatment group. Finally, three trials including 352 patients showed a statistically significant reduction in length of hospital stay.

AUTHORS' CONCLUSIONS

Surgical sealants reduce postoperative air leaks and time to chest drain removal but this reduction is not always associated with a reduction in length of postoperative hospital stay. Therefore, systematic use of surgical sealants with the objective of reducing hospital stay cannot be recommended at the moment. More and larger randomized controlled clinical trials are needed.

Production of Poly-γ-Glutamate (PGA) Biopolymer by Batch and Semicontinuous Cultures of Immobilized Bacilluslicheniformis strain-R

Production of Polyglutamate (PGA) biopolymer by immobilized Bacillus licheniformis strain-R was intensively investigated. Preliminary experiments were carried out to address the most suitable immobilization methodology. Entrapment of Bacillus cells in alginate-agar led optimal PGA production (36.75 g/l), with 1.32-and 2.18-fold increase in comparison with alginate-or K-carrageenan-immobilized cells, respectively. During semicontinuous cultivation of agar-alginate gel-cell mixture, production of PGA by 10 ml mixture was increased from 2(nd) to 3(rd) run whereas, increased till the 4(th) run using 15ml mixture. Adsorption was the most suitable immobilization technique for production of PGA and the sponge cubes was the preferred matrix recording 43.2 g/l of PGA with the highest cell adsorption. Furthermore, no PGA was detected when B. licheniformis cells were adsorbed on wood and pumice. Although luffa pulp-adsorbed cells recorded the highest PGA production (50.4 g/l), cell adsorption was the lowest. Semicontinuous cultivation of B. licheniformis cells adsorbed on sponge led to increase of PGA production till the 3(rd) run and reached 55.5 g/l then slightly decreased in the 4(th) run. The successful use of fixed-bed bioreactor for semicontinuous cultivation of B. licheniformis cells held on sponge cubes (3 runs, 96 hours/run) provides insight for the potential biotechnological production of PGA by immobilized cells.

The dynamics and clinical significance of alpha 2 plasmin inhibitor-plasmin complex and thrombin-antithrombin complex in postoperative pleural effusion following a pulmonary lobectomy

PURPOSE

The overall incidence of postoperative alveolar air leakage (AAL) remains high; however, the mechanism regarding how to adequately heal such postoperative AAL remains to be elucidated. The aim of this study was to determine any correlations between the activity of the fibrinolytic and coagulation system in the postoperative pleural effusion and appearance or disappearance of postoperative AAL.

METHODS

This study prospectively investigated 25 patients who underwent a pulmonary lobectomy from July 2005 to March 2006. Pleural effusion was collected through the chest tube. Alpha 2 plasmin inhibitor-plasmin complex (PIC), as a fibrinolytic marker, and thrombin-antithrombin complex (TAT), as a coagulation marker, were measured.

RESULTS

The activity of the coagulation system was higher than that of the fibrinolytic system. The concentration of TAT tended to increase (3rd vs 4th postoperative day [POD], P = 0.0907). The mean time of appearance and disappearance of postoperative AAL was 1.4 days and 3.2 days, respectively. The patients with postoperative AAL had a TAT level significantly below the average on the 3rd POD in comparison to the patients without postoperative AAL (P = 0.0163). Moreover, the concentration of TAT in patients with postoperative AAL was significantly lower than that in patients without postoperative AAL (1824.0 +/- 137.3 ng/ml vs 3444.0 +/- 287.6 ng/ml, P = 0.0113) on the 3rd POD. On the 4th POD, the concentration of TAT was almost same and there was no significance (P = 0.6759).

CONCLUSIONS

This study demonstrated for the first time the course of the fibrinolytic and coagulation activity in the pleural effusion after a pulmonary lobectomy, and showed that the delayed activity of the coagulation system is associated with the appearance of the postoperative AAL.

A novel approach for repairing of intestinal fistula using chitosan hydrogel

Intestinal fistula is associated with high morbidity and difficult to manage. Many fistulas require surgical treatment, which usually consists of segmental resection. In this study, using a rat model, the effectiveness of chitosan hydrogel as an intestinal fistula repair agent was investigated. Twenty rats underwent laparotomy under general anesthesia. The antimesentric portion of the cecum was incised (1 cm) and sutured to the abdominal wall. Chitosan hydrogel was applied daily to the fistula until it was completely closed. Blood samples taken from all animals were analyzed. After sacrifice, the cecum was removed and histopathologic investigation was performed. Spontaneous closure of the intestinal fistula was observed in all animals for both the control and chitosan hydrogel groups. Healing in the chitosan hydrogel group healing was faster than that in the control group. Blood analysis revealed significant differences between the chitosan hydrogel and control groups with regard to the total protein, albumin, total cholesterol and HDL before the surgery versus that on the day of sacrifice. Pathologic investigation also showed greater healing in the chitosan hydrogel group than the control group. This preliminary study showed the potential of chitosan hydrogel for repair of intestinal fistula. However further studies must be performed before we can approve testing chitosan hydrogel for intestinal fistula repair in humans.

Interaction force measurements for the design of tissue adhesives

Synthesis of tissue adhesives had been carried out in various laboratories in the past decades but the development is currently stalled. One of the key reasons, it is believed, is that researchers have not fully understood and resolved the role of the functional groups that are responsible for good adhesion to biological tissues. Further progress in synthesis is significantly hindered without this fundamental understanding. With this aim in mind, atomic force microscopy (AFM) has been exploited in this work to study the interactions between functional groups that are common to biological tissues. In this work, the AFM tip and substrates were functionalized and used to measure the non-specific interaction among these common functional groups. The ultimate aim of the study is to calculate the interaction force between a single pair of functional groups. A novel calculation method based on the AFM data and probe geometry is presented. The results provide insights into the strength of the bond between different functional groups and the could serve as a guide in selecting the appropriate functional groups in tissue adhesive synthesis. This method could be further applied to studies involving interfaces of biomedical devices where intermolecular interactions are of concern.

Development of new biodegradable hydrogel glue for preventing alveolar air leakage

OBJECTIVE

Air leakage is a frequent complication during lung surgery. A new hydrogel glue was created by mixing aldehyded dextran and epsilon-poly(l-lysine), and its feasibility as a surgical sealant was evaluated in comparison with that of conventional fibrin glue.

METHODS

Bursting pressure after application of each glue to 30 x 30-mm pleuroparenchymal defects was evaluated in two groups of 14 beagle dogs. Biodegradability and histotoxicity of the glues were evaluated in another 6 dogs with 15-mm circular pleuroparenchymal defects. Adhesions, infections, and histologic changes were observed on scheduled days for 6 months.

RESULTS

The mean bursting pressure after application was 38.4 +/- 4.6 cm H2O for the new glue and 32.1 +/- 4.5 cm H2O for fibrin glue (P = .02), the former providing more effective sealing of pulmonary air leakage than the latter. Macroscopically, no adhesions or infections were observed in areas of glue application. About 90% of the new glue degraded within 3 months, but complete disappearance was not observed by 6 months. On the other hand, the fibrin glue was replaced by white pleural tissue at 4 weeks. Histologically, the new glue was covered by one layer of mesothelial cells at 2 weeks and completely covered by thick fibrous tissue at 4 weeks. Inflammatory reaction was minimal around the residual glue after 3 months. Although the new glue degraded more slowly than did the fibrin glue, the biocompatibility of the new glue was sufficient for clinical use.

CONCLUSION

Our new hydrogel glue demonstrates a strong sealing effect, with good biocompatibility, and has potential usefulness as an adhesive in lung surgery.

Creation of a uniform pleural defect model for the study of lung sealants

OBJECTIVE

Animal models are indispensable for the development of new therapeutic methods for the closure of alveolar air leakage. However, it is difficult to create a uniform pleural defect model. The purpose of this study was to establish an appropriate animal model for assessing the efficacy and histotoxicity of synthetic sealants for lung surgery.

METHODS

Nine beagle dogs were used to evaluate the pleural defect model in comparison with conventional resection procedures. A donut-shaped silicon ring with an inner diameter of 15 mm was placed on the pleura, and 0.1 mL of cyanoacrylate was dropped into the ring. A pleural defect was created by sliding a microtome blade just beneath the polymerized cyanoacrylate. Hemostasis was performed by pressure with a sponge.

RESULTS

Morphologically, round areas of the pleura were uniformly resected with our procedure. The resected tissue consisted of pleura and thin underlying lung parenchyma. Among the results from 3 surgeons, there were no significant differences in the mean time required for hemostasis (P = .69), the mean thickness of the resected tissue (P = .13), and the mean amount of air leakage from the resected area (P = .19). No penetration of cyanoacrylate into the lung parenchyma was evidenced by immunofluorescence microscopy. Histologically, when the pleura was resected without using cyanoacrylate, a thick fibrocellular layer extended to the lung parenchyma. Furthermore, severe fibrosis was observed when electrocautery was used for hemostasis. However, when the pleura was resected using cyanoacrylate, the normal alveolar structure was preserved.

CONCLUSIONS

Our uniform pleural defect model using cyanoacrylate may be feasible for the evaluation of synthetic sealants for alveolar air leakage.

Glutamine Administration Enhances the Healing of Lung Parenchymal Injuries and Reduces Air Leakage in Rats

Beneficial effects of glutamine on wound healing are well known. Parenchymal injuries in the lung cause air leakage that resolves with wound healing. We aimed to determine the effect of glutamine on the healing of lung injuries. Wistar albino female rats were randomized in three groups. One group (control, n = 7) received intraperitoneal injection of 0.9% sodium chloride (1.5 ml /day), while other group (GLN, n = 7) received glutamine (1.5 g/kg/day), beginning two days prior to the operation for total four days. After thoracotomy, a lung parenchymal lesion was made with a scalpel in the right upper lobe. Only thoracotomy was performed to sham group (n = 4). Air leakage was observed in the isolated lungs of control group, but not GLN and sham groups, at 5 cm H(2)O of positive airway pressure (p < 0.001). The threshold of positive airway pressure for air leakage was 4.85 +/- 0.37 and 19.42 +/- 4.54 cm H(2)O for control and GLN groups, respectively (p < 0.001). For measurement of collagen content in the healing parenchyma, digital images were processed to calculate the stained area percentage (SAP). SAP for immature collagen, a marker for wound healing, was 0.36 +/- 0.18% and 1.48 +/- 0.83% (p = 0.02) in control and GLN groups, respectively, but no significant difference was noted in SAP for mature collagen. The grade of inflammation was not significantly different between control and GLN groups. We conclude that glutamine enhances lung parenchymal healing by increasing immature collagen secretion.

Preparation of γ-PGA/chitosan composite tissue engineering matrices

Gamma-poly(glutamic acid) (gamma-PGA), a hydrophilic and biodegradable polymer, was chosen to modify chitosan matrices to produce a gamma-PGA/chitosan composite biomaterial. Three types of both dense and porous composite matrices containing different amounts of gamma-PGA were fabricated. Chitosan and gamma-PGA matrices were also prepared as controls. Fluorescence staining indicated that chitosan and gamma-PGA were evenly distributed in the composite matrices. SEM micrographs showed that an interconnected porous structure with a pore size of 30-100 microm was present in all porous matrices except the gamma-PGA ones. By increasing the percentage of gamma-PGA from 0% to 20%, the swelling ratio of the matrices was enhanced from 1.6 to 3.2. Similarly, the contact angle of the matrices decreased from 113 degrees to 94 degrees . These data suggested that the surface hydrophilicity, water absorption rate, and swelling ratio were improved by adding gamma-PGA to the matrices. Additionally, the mechanical strength of the porous gamma-PGA/chitosan matrices was about 25-50%, higher than that of the unmodified chitosan matrices. The composite matrices were also examined and found to be an appropriate environment for cell attachment and proliferation. The cell density on the 20% gamma-PGA-modified matrices was almost triple that on the unmodified chitosan matrices on day 5. In summary, the gamma-PGA/chitosan composite matrices, due to their better hydrophilic, cytocompatible, and mechanical properties, are very promising biomaterials for tissue engineering applications.

Surgical sealant for preventing air leaks after pulmonary resections in patients with lung cancer

BACKGROUND

Postoperative air leak is a frequent complication after pulmonary resection for lung cancer. It may cause serious complications, such as empyema, or prolong the need for chest tube and hospitalisation. Surgical sealants of different types have been developed to prevent or to reduce postoperative air leaks. A systematic review was therefore undertaken to evaluate the evidence on their effectiveness.

OBJECTIVES

To evaluate the effectiveness of surgical sealants in preventing or in reducing postoperative air leaks after pulmonary resection for lung cancer.

SEARCH STRATEGY

The electronic databases MEDLINE (1966 to 2004), EMBASE (1974 to 2004), Cancerlit (1993 to 2004), the Cochrane Central Register of Controlled Trials (The Cochrane Library, Issue 3/2004) and listed references were searched, and handsearching of conference proceedings was conducted to identify published and unpublished trials.

SELECTION CRITERIA

Randomised controlled clinical trials were included in which standard closure techniques plus a sealant were compared with the same intervention with no use of any sealant in patients undergoing elective pulmonary resection provided that a large proportion of the patients included in the studies had undergone pulmonary resection for lung cancer.

DATA COLLECTION AND ANALYSIS

Three reviewers independently selected the trials to be included in the review, assessed methodological quality of each trial and extracted data using a standardised form. Because of several limitations, narrative synthesis was used at this stage.

MAIN RESULTS

Twelve trials, with 1097 patients in total, were included. In eight trials there was a statistically significant difference between treatment and control patients in reducing postoperative air leaks. However this reduction only proved a significant reduction of hospital stay in one trial. Only in one trial reduction of time of chest drain removal and reduction of percentage of patient with persistent air leak were significantly smaller in the treatment group.

AUTHORS' CONCLUSIONS

Although surgical sealants seem to reduce postoperative air leaks, length of hospitalisation is not affected and infectious complications may be increased. Therefore, systematic use of surgical sealants in clinical practice cannot be recommended at the moment. More randomised controlled clinical trials are needed.

Use of a novel absorbable hydrogel for augmentation of dural repair: results of a preliminary clinical study

OBJECTIVE

To evaluate the safety and performance of a synthetic dural sealant as an adjunct to standard surgical dural repair techniques to prevent cerebrospinal fluid (CSF) leakage.

METHODS

This study was designed as a prospective, nonrandomized, single-center clinical trial. The dural sealant is a synthetic absorbable hydrogel. Consecutive series of patients scheduled for elective cranial and intradural spinal surgery were included until a total of 50 applications were achieved. It was used primarily as an adjunct to ensure watertight dural closure. The end point was defined as no leak with the Valsalva maneuver after dural sealant application. The patients were followed up for 3 months after surgery to check for CSF leakage, standard laboratory and neurological examinations, and possible adverse advents.

RESULTS

Of the 49 patients, 46 were included and treated with the dural sealant because of spontaneous leak (n = 34; 69%) or leak after the Valsalva maneuver (n = 12; 25%). There was no leak in the other patients (n = 3; 6%). After application of the dural sealant, there was no leak in all 46 patients (100%). Of the 46 patients included, there was one case of overt CSF leak. One patient had a pseudomeningocele. There were no adverse events other than those related to the disease or to the surgical procedure itself.

CONCLUSION

The dural sealant, a synthetic absorbable hydrogel, is a useful adjunct to achieve watertight dural closure. Application resulted in 100% closure of intraoperative CSF leaks. There are no evident adverse effects.

Toward optimal tissue sealants for neurosurgery: use of a novel hydrogel sealant in a canine durotomy repair model

OBJECTIVE

Watertight dural repairs are difficult to achieve, and cerebrospinal fluid leakage causes complications and extends hospital stays. Therefore, a novel synthetic hydrogel film was evaluated as an adjunct to dural closure in a canine model.

METHODS

The self-polymerizing, absorbable, and biocompatible hydrogel was sprayed onto tissue and formed a flexible, adherent sealant. A 2-cm incision of cranial dura and arachnoid was created in 26 adult dogs and loosely repaired. Hydrogel was applied over the 2-mm dural gap in 13 dogs; 13 control dogs received no hydrogel application.

RESULTS

All dogs remained neurologically intact. Valsalva tests conducted at 1, 4, 7, and 56 days were associated with mean leakage pressures (+/- standard error of the mean) of 5 +/- 0, 5 +/- 0, 7 +/- 2, and 13 +/- 8 cm H(2)O in the controls and of 53 +/- 2, 37 +/- 11, 42 +/- 6, and 48 +/- 4 in the treated animals (P = 0.001, 0.053, 0.010, 0.035, respectively, at each time point; one-tailed t test). Histopathological analysis revealed minimal changes.

CONCLUSION

The hydrogel-treated animals exhibited normal progression of dural healing, no dural adhesions, and no underlying effects on the brain. Although dural healing progressed normally, the control animals displayed marked peridural adhesions. The results of this in vivo study suggest that hydrogels, such as that used here, may significantly decrease cerebrospinal fluid leakage, thereby increasing the safety and effectiveness of dural closure in patients and facilitating surgical reexploration.

Production and mass transfer characteristics of non-Newtonian biopolymers for biomedical applications

The market for microbial biopolymers is currently expanding to include several emerging biomedical applications. Specifically, these applications are drug delivery and wound healing. A fundamental understanding of the key fermentation parameters is necessary in order to optimize the production of these biopolymers. Considering that most microbial biopolymer systems exhibit non-Newtonian rheology, oxygen mass transfer can be an important parameter to optimize and control. In this article, we present a critical review of recent advances in rheological and mass transfer characteristics of selected biopolymers of commercial interest in biomedical applications.

Rheology, oxygen transfer, and molecular weight characteristics of poly(glutamic acid) fermentation by Bacillus subtilis

Poly(glutamic acid) (PGA) is a water-soluble, biodegradable biopolymer that is produced by microbial fermentation. Recent research has shown that PGA can be used in drug delivery applications for the controlled release of paclitaxel (Taxol) in cancer treatment. A fundamental understanding of the key fermentation parameters is necessary to optimize the production and molecular weight characteristics of poly(glutamic acid) by Bacillus subtilis for paclitaxel and other applications of pharmaceuticals for controlled release. Because of its high molecular weight, PGA fermentation broths exhibit non-Newtonian rheology. In this article we present experimental results on the batch fermentation kinetics of PGA production, mass transfer of oxygen, specific oxygen uptake rate, broth rheology, and molecular weight characterization of the PGA biopolymer.

Fibrin glue in pulmonary resection: a prospective, randomized, blinded study

BACKGROUND

In contrast to the rare large-airway bronchopleural fistulas after lung resection, peripheral or alveolar air leaks (AAL) are very common, often prolong hospital stay, increase utilization of resources, and on occasion result in significant morbidity. Various adjuncts have been used in attempts to reduce AAL. One of these, the topical application of fibrin glue, has to date failed to demonstrate efficacy in small clinical trials. This study reexamines the role of fibrin glue in routine lobar and wedge pulmonary resections.

METHODS

Of 113 patients enrolled, 13 became ineligible because of intraoperative findings. The remaining 100 patients were randomly assigned to one of two groups at the conclusion of lung resection, regardless of the presence or absence of identifiable air leak. The control group received no additional intervention. The experimental group underwent application of 5 mL of fibrin glue delivered by a pressurized, aerosolized spraying mechanism. Postoperatively a blinded clinical observer recorded outcomes including the incidence and duration of AAL, prolonged AAL (PAAL), the volume of pleural drainage, the time to tube removal, and the postoperative length of stay (LOS), as well as any complications related to treatment.

RESULTS

Both groups were comparable with regard to demographics, diagnoses, and procedures. Statistically significant reductions were found in the experimental group in the overall incidence of AAL (34% versus 68%, p = 0.001), mean duration of AAL (1.1 versus 3.1 days, p = 0.005), mean time to chest tube removal (3.5 versus 5.0 days, p = 0.02), and the incidence of PAAL (2% versus 16%, p = 0.015). There was no significant difference in the volume of chest tube drainage or LOS (4.6 days glue and 4.9 days control, p = 0.318). There were no complications related to the use of fibrin glue.

CONCLUSIONS

Aerosolized fibrin glue appears to be safe and effective in reducing AAL. The overall incidence of AAL was reduced by 50% and PAAL occurred in only 1 treated patient (2% versus the usually reported 15%). Further studies with this and other methods are required to delineate routine versus selective use, to compare methods, and clarify cost benefit.

Predictors of alveolar air leaks

Persistent air leaks are caused by the failure of the postoperative lung to achieve a configuration that is physiologically amenable to healing. The raw pulmonary surface caused by the dissection of the fissure often is separated from the pleura, and the air leak fails to close. Additionally, higher air flow thorough an alveolar-pleural fistula seems to keep the fistula open. Other factors that interfere with wound healing, such as steroid use, diabetes, or malnutrition, can result in persistence of the leak. A thoracic surgeon can minimize the incidence of air leak through meticulous surgical technique and can identify patients in whom the balance of risks (Table 1) and benefits warrant operative intervention based on an understanding of the underlying pathophysiology.

Poly(glutamic acid) for biomedical applications

Paclitaxel is a widely used anti-cancer agent. Conjugates of paclitaxel with poly(glutamic acid) have shown great promise in preclinical trials, and clinical trials are now underway. Preclinical data suggest that more paclitaxel is preferentially delivered to tumor sites vs. nonconjugated paclitaxel. When poly(glutamic acid) is conjugated to other families of cancer drugs, similar improvements in effectiveness and reduced toxicity are observed. Optimization of poly(glutamic acid) for use in drug delivery applications is a key step in making this technology viable.

In vivo evaluation of a new sealant material on a rat lung air leak model

The ability of an albumin-based hydrogel sealant (ABHS) to prevent air leakage through the suture line after pulmonary surgery was evaluated by comparison with that of a fibrin glue (FG). As an air-leak model, a rat lung was used in which a standard incision was made and the burst pressure for ABHS and FG was measured. The average burst pressures at time 0 for the FG and ABHS groups were 30.8+/-15.2 and 77.5 +/-19.1 mmHg, respectively. At Day 3, the value of ABHS (76.3 +/- 15.8 mmHg) was still significantly higher (P<0.05) than that of FG (60.0 +/- 21.9 mmHg). At Day 7, no statistical difference was observed between the FG group(71.2 +/- 18.6 mmHg) and the ABHS group(88.8 +/- 11.7 mmHg). Histological examination of the incision at Day 14 revealed that neither sealant was not visible at the incision site, and there was no evidence of adverse tissue reaction. It was concluded that ABHS had good sealing properties and is an alternative to FG for air leakage treatment in pulmonary surgery.

Suction vs water seal after pulmonary resection: a randomized prospective study

STUDY OBJECTIVE

To evaluate whether suction or water seal is superior in the management of chest tubes after pulmonary resection.

DESIGN

A prospective, randomized, controlled trial. After an initial, brief period of suction, patients were randomized to water seal or - 20 cm H(2)O suction.

SETTING

University hospital.

PATIENTS

Sixty-eight patients who underwent wedge resection, segmentectomy, or lobectomy were included in the study. Those patients who underwent reoperative surgery or lung volume reduction surgery were excluded.

RESULTS

There were 34 patients in each group. The two groups were evenly matched for age, sex, operation performed, severity of lung disease, and nutritional status. Fifteen patients in each group (44%) had an air leak at the completion of surgery. The duration of the air leak was shorter in the water seal group than in the suction group (mean +/- SEM, 1.50 +/- 0.32 days vs 3.27 +/- 0.80 days, respectively; p = 0.05). The mean times to removal of chest tubes were 3.33 +/- 0.35 days in the water seal group and 5.47 +/- 0.98 days in the suction group (p = 0.06). The length of stapled parenchyma was measured for each patient and averaged 24.9 cm for the water seal group and 18.5 cm for the suction group (p = 0.18). When corrected for the length of staple lines, the duration of air leaks and days with chest tube were dramatically lower in the water seal group (p = 0.02 and p = 0.02, respectively).

CONCLUSION

Placing chest tubes on water seal after a brief period of suction after pulmonary resection shortens the duration of the air leak and likely decreases the time that the chest tubes remain in place. Adoption of this practice may result in lower morbidity and lower hospital costs.