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

Composition, host responses and clinical applications of bioadhesives

Bioadhesives are medical devices used to join or seal tissues that have been injured or incised. They have been classified into tissue adhesives, sealants, and hemostatic agents. Bioadhesives such as FloSeal®, CoSeal®, BioGlue®, Evicel®, Tisseel®, Progel™ PALS, and TissuGlu® have been commercialized and used in clinical setting. They can be formulated with natural or synthetic components or a combination of both including albumin, glutaraldehyde, chitosan, cyanoacrylate, fibrin and thrombin, gelatin, polyethylene glycol (PEG), along with urethanes. Each formulation has intrinsic properties and has been developed and validated for a specific application. This review article briefs the mechanisms by which bioadhesives forms adhesion to tissues and highlights the correlation between bioadhesives composition and their potential host responses. Furthermore, clinical applications of bioadhesives and their application-driven requirements are outlined.

A Bi-Layer Hydrogel Cardiac Patch Made of Recombinant Functional Proteins

The development of minimally invasive cardiac patches, either as hemostatic dressing or treating myocardial infarction, is of clinical significance but remains a major challenge. Designing such patches often requires simultaneous consideration of several material attributes, including bioabsorption, non-toxicity, matching the mechanic properties of heart tissues, and working efficiently in wet and dynamic environments. Using genetically engineered multi-domain proteins, a printed bi-layer proteinaceous hydrogel patch for heart failure treatments is reported. The intrinsic self-healing nature of hydrogel materials physically enables seamless interfacial integration of two disparate hydrogel layers and functionally endows the cardiac patches with the combinatorial advantages of each layer. Leveraging the biocompatibility, structural stability, and tunable drug release properties of the bi-layer hydrogel, promising effects of hemostasis, fibrosis reduction, and heart function recovery on mice is demonstrated with two myocardium damage models. Moreover, this proteinaceous patch is proved biodegradable in vivo without any additive inflammations. In conclusion, this work introduces a promising new type of minimally invasive patch based on genetically modified double-layer protein gel for treating heart-related injuries or diseases.

Elucidating the degradation mechanism of a self-degradable dextran-based medical adhesive

We developed a self-degradable medical adhesive, LYDEX, consisting of periodate-oxidized aldehyde-functionalized dextran (AD) and succinic anhydride-treated ε-poly-l-lysine (SAPL). After gelation and adhesion of LYDEX by Schiff base bond formation between the AD aldehyde groups and SAPL amino groups, molecular degradation associated with the Maillard reaction is initiated, but the detailed degradation mechanism remains unknown. Herein, we elucidated the degradation mechanism of LYDEX by analyzing the main degradation products under typical solution conditions in vitro. The degradation of the LYDEX gel with a sodium periodate/dextran content of 2.5/20 was observed using gel permeation chromatography and infrared and ¹H NMR spectroscopy. The AD ratio in the AD-SAPL mixture increased as the molecular weight decreased with the degradation time. This discovery of LYDEX self-degradability is useful for clarifying other polysaccharide hydrogel degradation mechanisms, and valuable for the use of LYDEX in medical applications, such as hemostatic or sealant materials.

Bio-inspired green light crosslinked alginate-heparin hydrogels support HUVEC tube formation

Alginate is a polysaccharide which forms hydrogels via ionic and/or covalent crosslinking. The goal was to develop a material with suitable, physiologically relevant mechanical properties and biological impact for use in wound treatment. To determine if the novel material can initiate tube formation on its own, without the dependance on the addition of growth factors, heparin and/or arginyl-glycyl-aspartic acid (RGD) was covalently conjugated onto the alginate backbone. Herein, cell adhesion motifs and bioactive functional groups were incorporated covalently within alginate hydrogels to study the: 1) impact of crosslinked heparin on tubular network formation, 2) impact of RGD conjugation, and the 3) biological effect of vascular endothelial growth factor (VEGF) loading on cellular response. We investigated the structure-properties-function relationship and determined the viscoelastic and burst properties of the hydrogels most applicable for use as a healing cell and tissue adhesive material. Methacrylation of alginate and heparin hydroxyl groups respectively enabled free-radical covalent inter- and intra-molecular photo-crosslinking when exposed to visible green light in the presence of photo-initiators; the shear moduli indicate mechanical properties comparable to clinical standards. RGD was conjugated via carbodiimide chemistry at the alginate carboxyl groups. The adhesive and mechanical properties of alginate and alginate-heparin hydrogels were determined via burst pressure testing and rheology. Higher burst pressure and material failure at rupture imply physical tissue adhesion, advantageous for a tissue sealant healing material. After hydrogel formation, human umbilical vein endothelial cells (HUVECs) were seeded onto the alginate-based hydrogels; cytotoxicity, total protein content, and tubular network formation were assessed. Burst pressure results indicate that the cell responsive hydrogels adhere to collagen substrates and exhibit increased strength under high pressures. Furthermore, the results show that the green light crosslinked alginate-heparin maintained cell adhesion and promoted tubular formation.

Strontium ions protect hearts against myocardial ischemia/reperfusion injury

Timely restoration of blood supply following myocardial infarction is critical to save the infarcted myocardium, while reperfusion would cause additional damage. Strontium ions have been shown to promote angiogenesis, but it is unknown whether they can save the damaged myocardium. We report that myocardial ischemia/reperfusion (I/R)-induced functional deterioration and scar formation were notably attenuated by injection of strontium ion-containing composite hydrogels into murine infarcted myocardium at 20 minutes of reperfusion following 60 minutes of ischemia. These beneficial effects were accompanied by reduced cardiomyocyte apoptosis and increased angiogenesis. The effects of strontium ions were further confirmed by the enhanced viability of cardiomyocytes and stimulated angiogenesis in vitro. These findings are the first to reveal the cardioprotective effects of strontium ions against I/R injury, which may provide a new therapeutic approach to ischemic heart disease at a lower cost, with higher stability, and with potentially greater safety.

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.

Surgical applications of intracorporal tissue adhesive agents: current evidence and future development

Introduction: Traditional mechanical closure techniques pose many challenges including the risk of infection, tissue reaction, and injury to both patients and clinicians. There is an urgent need to develop tissue adhesive agents to reform closure technique. This review examined a variety of tissue adhesive agents available in the market in an attempt to gain a better understanding of intracorporal tissue adhesive agents as medical devices.Areas covered: Fundamental principles and clinical determinants of the tissue adhesives were summarized. The available tissue adhesives for intracorporal use and their relevant clinical evidence were then presented. Lastly, the perspective of future development for intracorporal tissue adhesive were discussed. Clinical evidence shows current agents are efficacious as adjunctive measures to mechanical closure and these agents have been trialed outside of clinical indications with varied results.Expert opinion: Despite some advancements in the development of tissue adhesives, there is still a demand to develop novel technologies in order to address unmet clinical needs, including low tensile strength in wet conditions, non-controllable polimerization and sub-optimal biocompatibility. Research trends focus on producing novel adhesive agents to remit these challenges. Examples include the development of biomimetic adhesives, externally activated adhesives, and multiple crosslinking strategies. Economic feasibility and biosafety are limiting factors for clinical implementation.

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.

Bioglass Activated Albumin Hydrogels for Wound Healing

In this study, a novel Bioglass/albumin composite hydrogel with controllable injectability, good adhesiveness, and bioactivity, is developed by utilizing dual-functional bioactive ions released from Bioglass, which on one side controls the gelling time by creating an alkaline environment to regulate the cross-linking reaction between human serum albumin and succinimidyl succinate modified poly(ethylene glycol), and on the other side stimulates wound healing. The composite hydrogel exhibits adhesive property that is superior to clinically used fibrin and cyanoacrylate glues. The gelation time of the composite hydrogel could be regulated via changing the amounts of Bioglass which endows the hydrogel with good injectability. The in vivo experiment confirms that this composite hydrogel has good bioactivity to stimulate angiogenesis and enhance chronic wound healing. Moreover, for the first time, the concentrations of the bioactive ions released from the composite hydrogel in situ are quantified during wound healing using a microdialysis technique, and a correlation of the in vitro and in vivo concentration of ions released from the hydrogel is determined, which is extremely important for understanding the bioactivity mechanisms of Bioglass/bioceramic-based biomaterials and designing biomaterials for tissue regeneration.

Engineering a highly elastic human protein-based sealant for surgical applications

Surgical sealants have been used for sealing or reconnecting ruptured tissues but often have low adhesion, inappropriate mechanical strength, cytotoxicity concerns, and poor performance in biological environments. To address these challenges, we engineered a biocompatible and highly elastic hydrogel sealant with tunable adhesion properties by photocrosslinking the recombinant human protein tropoelastin. The subcutaneous implantation of the methacryloyl-substituted tropoelastin (MeTro) sealant in rodents demonstrated low toxicity and controlled degradation. All animals survived surgical procedures with adequate blood circulation by using MeTro in an incisional model of artery sealing in rats, and animals showed normal breathing and lung function in a model of surgically induced rat lung leakage. In vivo experiments in a porcine model demonstrated complete sealing of severely leaking lung tissue in the absence of sutures or staples, with no clinical or sonographic signs of pneumothorax during 14 days of follow-up. The engineered MeTro sealant has high potential for clinical applications because of superior adhesion and mechanical properties compared to commercially available sealants, as well as opportunity for further optimization of the degradation rate to fit desired surgical applications on different tissues.

A highly adhesive and naturally derived sealant

Conventional surgical techniques to seal and repair defects in highly stressed elastic tissues are insufficient. Therefore, this study aimed to engineer an inexpensive, highly adhesive, biocompatible, and biodegradable sealant based on a modified and naturally derived biopolymer, gelatin methacryloyl (GelMA). We tuned the degree of gelatin modification, prepolymer concentration, photoinitiator concentration, and crosslinking conditions to optimize the physical properties and adhesion of the photocrosslinked GelMA sealants. Following ASTM standard tests that target wound closure strength, shear resistance, and burst pressure, GelMA sealant was shown to exhibit adhesive properties that were superior to clinically used fibrin- and poly(ethylene glycol)-based glues. Chronic in vivo experiments in small as well as translational large animal models proved GelMA to effectively seal large lung leakages without the need for sutures or staples, presenting improved performance as compared to fibrin glue, poly(ethylene glycol) glue and sutures only. Furthermore, high biocompatibility of GelMA sealant was observed, as evidenced by a low inflammatory host response and fast in vivo degradation while allowing for adequate wound healing at the same time. Combining these results with the low costs, ease of synthesis and application of the material, GelMA sealant is envisioned to be commercialized not only as a sealant to stop air leakages, but also as a biocompatible and biodegradable hydrogel to support lung tissue regeneration.

Prospective evaluation of biodegradable polymeric sealant for intraoperative air leaks

Background

A biodegradable polymeric sealant has been previously shown to reduce postoperative air leaks after open pulmonary resection. The aim of this study was to evaluate safety and efficacy during minimally invasive pulmonary resection.

Methods

In a multicenter prospective single-arm trial, 112 patients with a median age of 69 years (range 34–87 years) were treated with sealant for at least one intraoperative air leak after standard methods of repair (sutures, staples or cautery) following minimally invasive pulmonary resection (Video-Assisted Thoracic Surgery (VATS) or Robotic-Assisted). Patients were followed in hospital and 1 month after surgery for procedure-related and device-related complications and presence of air leak.

Results

Forty patients had VATS and 72 patients had Robotic-Assisted procedures with the majority (80/112, 71%) undergoing anatomic resection (61 lobectomy, 13 segmentectomy, 6 bilobectomy). There were no device-related adverse events. The overall morbidity rate was 41% (46/112), with major complications occurring in 16.1% (18/112). In-hospital mortality and 30-day mortality were 1.9% (2/103). The majority of intraoperative air leaks (107/133, 81%) were sealed after sealant application, and an additional 16% (21/133) were considered reduced. Forty-nine percent of patients (55/112) were free of air leak throughout the entire postoperative study period. Median chest tube duration was 2 days (range 1 – 46 days), and median length of hospitalization was 3 days (range 1 – 20 days).

Conclusions

This study demonstrated that use of a biodegradable polymer for closure of intraoperative air leaks as an adjunct to standard methods is safe and effective following minimally invasive pulmonary resection.

Trial registration

ClinicalTrials.gov: NCT01867658. Registered 3 May 2013.

A Decision-Theoretic Comparison of Treatments to Resolve Air Leaks After Lung Surgery Based on Nonparametric Modeling

We propose a Bayesian nonparametric utility-based group sequential design for a randomized clinical trial to compare a gel sealant to standard care for resolving air leaks after pulmonary resection. Clinically, resolving air leaks in the days soon after surgery is highly important, since longer resolution time produces undesirable complications that require extended hospitalization. The problem of comparing treatments is complicated by the fact that the resolution time distributions are skewed and multi-modal, so using means is misleading. We address these challenges by assuming Bayesian nonparametric probability models for the resolution time distributions and basing the comparative test on weighted means. The weights are elicited as clinical utilities of the resolution times. The proposed design uses posterior expected utilities as group sequential test criteria. The procedure's frequentist properties are studied by extensive simulations.

Surgical sealants with tunable swelling, burst pressures, and biodegradation rates

We developed two types of polyethylene glycol (PEG)-based surgical sealants, which we have termed the PER and PRO series. In one, the PRO series, an 8-arm PEG containing activated carbonyl end-groups was reacted with a 4-armed amino-PEG. In the second, the PER series, a 4-arm PEG containing bi-functional end groups with four azides and four activated esters was reacted by strain-promoted alkyne-azide cycloaddition with a 4-arm cyclooctyne-PEG to give a near-ideal Tetra-PEG hydrogel. The sealants showed predictably tunable strength, swelling, adhesion, and gelation properties. The gels were compared to commercially available PEG-based sealants and exhibit physical properties equivalent to or better than the standards. Variants of each gel-format were prepared that contained a β-eliminative cleavable linker in the crosslinks to control degradation rate. Linkers of this type self-cleave with half-lives spanning from hours to years, and offer the unique ability to precisely tune the degradation to match the healing process. In addition, these linkers could serve as cleavable tethers for controlled drug release. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 1602-1611, 2017.

Elastic sealants for surgical applications

Sealants have emerged as promising candidates for replacing sutures and staples to prevent air and liquid leakages during and after the surgeries. Their physical properties and adhesion strength to seal the wound area without limiting the tissue movement and function are key factors in their successful implementation in clinical practice. In this contribution, the advances in the development of elastic sealants formed from synthetic and natural materials are critically reviewed and their shortcomings are pointed out. In addition, we highlight the applications in which elasticity of the sealant is critical and outline the limitations of the currently available sealants. This review will provide insights for the development of novel bioadhesives with advanced functionality for surgical applications.

Adhesive and sealant interfaces for general surgery applications

The main functions of biological adhesives and sealants are to repair injured tissues, reinforce surgical wounds, or even replace common suturing techniques. In general surgery, adhesives must match several requirements taking into account clinical needs, biological effects, and material features; these requirements can be fulfilled by specific polymers. Natural or synthetic polymeric materials can be employed to generate three-dimensional networks that physically or chemically bind to the target tissues and act as hemostats, sealants, or adhesives. Among them, fibrin, gelatin, dextran, chitosan, cyanoacrylates, polyethylene glycol, and polyurethanes are the most important components of these interfaces; various aspects regarding their adhesion mechanisms, mechanical performance, and resistance to body fluids should be taken into account to choose the most suitable formulation for the target application. This review aims to describe the main adhesives and sealant materials for general surgery applications developed in the past decades and to highlight the most important aspects for the development of future formulations.

Treatment of the degenerated intervertebral disc; closure, repair and regeneration of the annulus fibrosus

Degeneration of the intervertebral disc (IVD) and disc herniation are two causes of low back pain. The aetiology of these disorders is unknown, but tissue weakening, which primarily occurs due to inherited genetic factors, ageing, nutritional compromise and loading history, is the basic factor causing disc degeneration. Symptomatic disc herniation mainly causes radicular pain. Current treatments of intervertebral disc degeneration and low back pain are based on alleviating the symptoms and comprise administration of painkillers or surgical methods such as spinal fusion. None of these methods is completely successful. Current research focuses on regeneration of the IVD and particularly on regeneration of the nucleus pulposus. Less attention has been directed to the repair or regeneration of the annulus fibrosus, although this is the key to successful nucleus pulposus, and therewith IVD, repair. This review focuses on the importance of restoring the function of the annulus fibrosus, as well as on the repair, replacement or regeneration of the annulus fibrosus in combination with restoration of the function of the nucleus pulposus, to treat low back pain.

Pleural tissue repair with cord blood platelet gel

BACKGROUND

Prolonged air leak is the major cause of morbidity after pulmonary resection. In this study we used in vitro and in vivo experiments to investigate an innovative approach based on the use of human umbilical cord blood platelet gel.

MATERIALS AND METHODS

In vitro, a scratch assay was performed to test the tissue repair capability mediated by cord blood platelet gel compared to the standard culture conditions using human primary mesothelial cells. In vivo, an iatrogenic injury was made to the left lung of 54 Wistar rats. Cord blood platelet gel was placed on the injured area only in treated animals and at different times histological changes and the presence of pleural adhesions were evaluated. In addition, changes in the pattern of soluble inflammatory factors were investigated using a multiplex proteome array.

RESULTS

In vitro, mesothelial cell damage was repaired in a shorter time by cord blood platelet gel than in the control condition (24 versus 35 hours, respectively). In vivo, formation of new mesothelial tissue and complete tissue recovery were observed at 45±1 and 75±1 hours in treated animals and at 130±2.5 and 160±6 hours in controls, respectively. Pleural adhesions were evident in 43% of treated animals compared to 17% of controls. No complications were observed. Interestingly, some crucial soluble factors involved in inflammation were significantly reduced in treated animals.

DISCUSSION

Cord blood platelet gel accelerates the repair of pleural damage and stimulates the development of pleural adhesions. Both properties could be particularly useful in the management of prolonged air leak, and to reduce inflammation.

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.

The experimental use of N-butyl cyanoacrylate tissue adhesive in pulmonary wedge resections

BACKGROUND

In this experimental study, the effectiveness of N-butyl cyanoacrylate tissue adhesive on preventing air leakage after pulmonary wedge resection was observed.

METHODS

Twenty pairs of sheep lungs were used. Before initiating the study, the sheep lungs were ventilated to identify any air leakage from the parenchyma. On positive results, those sheep lungs were then excluded from the study. Wedge resection was performed on the right and left lower lobes of sheep lungs by clamping the edges forming a triangle of 5 cm × 5 cm × 5 cm. One side of parenchyma was sutured by 3/0 vicryl (Group A) while the other side of parenchyma was sealed by N-butyl cyanoacrylate (Group B). After waiting for 5 min for N-butyl cyanoacrylate to dry, the sheep lungs were intubated by 6F endotracheal tubes. The lungs were soaked in a bath tub filled with 10 cm deep water and inflated by 40 mmHg pressure to record any air leakage from the parenchyma partially sutured by vicryl and sealed by N-butyl cyanoacrylate.

RESULTS

Air leakages were observed on the parenchyma surfaces of group of lungs (100%) sutured by vicryl (minimal 30%, mild 50% or massive 20% levels), while only on four of (20%) the other group of lungs sealed by N-butyl cyanoacrylate, minimal air leakage was observed on the parenchymal surface. There was an extremely significant difference between Group A and Group B in terms of the development of air leakage (p=000).

CONCLUSION

We consider that, N-butyl cyanoacrylate could be used effectively and safely to prevent air leakage from the pulmonary wedge resection surface.

A novel approach to control air leaks in complex lung surgery: a retrospective review

Background

Intra-operative air leaks (IOAL) are common complications of pulmonary surgery. The post-operative management of air leaks requires a chest tube which may lead to longer hospitalization, further medical complications, and increased costs. Sealants have been shown to help control intra-operative air leaks and studies have demonstrated a reduction in chest tube duration and/or length of hospital stay. Nevertheless, systematic reviews have not presented sufficient evidence to recommend their general use in lung resection.

Methods

One hundred and twenty-one consecutive patients who underwent pulmonary surgery with and without Progel® Pleural Air Leak Sealant were reviewed retrospectively. Intra-operative and 3-months postoperative data were assessed for the presence and persistence of air leaks, chest tube duration, the length of hospital stay, and complications.

Results

Seventy patients (57.9%) had IOAL. Thirty-six were treated with Progel in addition to standard intra-operative technique (pleural-sealant group; PSG) and 34 patients were treated only with standard technique (control group; CG). The percentage of post-operative air leaks in the PSG was 11% (1.2% >Grade 2 air leak) compared with 58.8% (6% >Grade 2 air leak) in the CG (p <0.0001, Leaks graded from 1 = small air leak to 7 = large air leak). The median chest tube duration was significantly shorter in the PSG compared with the controls (1.0 versus 2.5 days; p < 0.0001). The median length of hospital stay was 50% lower in the PSG compared with the control group (1.5 versus 3.0 days; p = 0.047). There were no significant differences in complications between the two groups.

Conclusions

The results of this single-center, single surgeon, retrospective review demonstrate a significant reduction in IOAL, chest tube duration, and length of hospital stay in the in patients treated with Progel when compared with standard intra-operative closure management alone. They suggest that the use of a pleural sealant is more effective in reducing alveolar air leaks associated with lung resection compared with standard closure techniques alone and may result in both an improved surgical outcome and a reduction in costs associated with prolonged hospital stay.

In situ gelable interpenetrating double network hydrogel formulated from binary components: thiolated chitosan and oxidized dextran

In situ gelable interpenetrating double-network hydrogels composed of thiolated chitosan (Chitosan-NAC) and oxidized dextran (Odex), completely devoid of potentially cytotoxic small molecule cross-linkers and that do not require complex maneuvers or catalysis, have been formulated. The interpenetrating network structure is created by Schiff base formations and disulfide bond inter-cross-linkings through exploiting the disparity of their reaction times. Compared with the autogelable thiolated chitosan hydrogels that typically require a relatively long time span for gelation to occur, the Odex/Chitosan-NAC composition solidifies rapidly and forms a well-developed 3D network in a short time span. Compared with typical hydrogels derived from natural materials, the Odex/Chitosan-NAC hydrogels are mechanically strong and resist degradation. The cytotoxicity potential of the hydrogels was determined by an in vitro viability assay using fibroblast as a model cell, and the results reveal that the hydrogels are noncytotoxic. In parallel, in vivo results from subdermal implantation in mice models demonstrate that this hydrogel is not only highly resistant to degradation but also induces very mild tissue response.

Delivery of rosiglitazone from an injectable triple interpenetrating network hydrogel composed of naturally derived materials

An in situ gelable and biodegradable triple-interpenetrating network (3XN) hydrogel, completely devoid of potentially cytotoxic extraneous small molecule crosslinkers, is formulated from partially oxidized dextran (Odex), teleostean and N-carboxyethyl chitosan (CEC). Both the rheological profile and mechanical strength of the 3XN hydrogel approximate the combined characteristics of the three individual hydrogels composed of the binary partial formulations (i.e., Odex/CEC, Odex/teleostean, and CEC/teleostean). The 3XN hydrogel is considerably more resistant to fibroblast-mediated degradation compared to each partial formulation in cell culture models; this is attributable to the interpenetrating triple-network structure. The presence of teleostean in the 3XN hydrogel imparts cell affinity, constituting an environment amenable to fibroblast growth. in vivo subdermal injection into mouse model shows that the 3XN hydrogel does not induce extensive inflammatory response nor is there any evidence of tissue necrosis, further confirming the non-cytotoxicity of the hydrogel and its degradation byproducts. Importantly, the capability of the 3XN hydrogel to serve as a sustained drug delivery vehicle is confirmed using rosiglitazone as a model drug. The presence of rosiglitazone profoundly changes the cell/tissue interactions with the subdermally injected 3XN hydrogel. Rosiglitazone suppresses both the inflammatory response and tissue repair in a dose-dependent manner and considerably moderated the hydrogel degradation.

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.

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.

Dynamic sealing of lung air leaks by the transplantation of tissue engineered cell sheets

Current methods including the use of various biological and synthetic sealants are ineffective in the closure of intraoperative air leaks that often occur during cardiothoracic surgeries, resulting in a decreased quality of life for patients. We present the development of a novel lung air leak sealant using tissue engineered cell sheets. In contrast to previous materials such as fibrin glue, these bioengineered cell sheets immediately and permanently seal air leaks in a dynamic fashion that allows for the extensive tissue contraction and expansion involved in respiration, without any postoperative recurrences. Additionally, we demonstrate that mesothelial cells migrate to cover the transplanted cells sheets, thereby confirming excellent biocompatibility and integration with the host tissues. Finally, we present the use of skin fibroblasts as an effective and readily available autologous cell source that can be easily applied. This study shows for the first time, the development of an immediate and permanent lung air leak sealant, suitable for future clinical applications.

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.

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.

Prospective randomized study evaluating a biodegradable polymeric sealant for sealing intraoperative air leaks that occur during pulmonary resection

BACKGROUND

To evaluate the safety and effectiveness of a new biodegradable polymeric sealant to close intraoperative air leaks after pulmonary resection.

METHODS

In a multicenter prospective randomized trial, 161 patients with a median age of 67 years old (range 18-85 years old), were randomized in a 2:1 ratio to receive sealant or control for at least one significant air leak (> or = 2.0 mm in size) after pulmonary resection. In the sealant group, all significant air leaks underwent attempted repair by standard methods (sutures, staples, or cautery) prior to the application of sealant. The control group underwent only standard methods. Blood was analyzed for immunologic response. Patients were followed up 1 month after surgery.

RESULTS

Intraoperative air leaks were sealed in 77% of the sealant group compared with 16% in the control group (p < 0.001). The sealant group had significantly fewer patients with postoperative air leaks compared with the control group (65% vs 86%, p = 0.005). Median length of hospitalization was 6 days (range, 3-23 days) for the sealant group compared with 7 days (range 4-38 days) for controls (p = 0.028). There was no difference in mortality, morbidity, duration of chest tubes, or immune responses between the two groups.

CONCLUSIONS

This study demonstrates the effectiveness of a biodegradable polymer when used as an adjunct to standard closure methods for sealing significant intraoperative air leaks that develop from pulmonary surgery. Use of the sealant led to a reduction in postoperative air leaks, which may have decreased the length of hospitalization.

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.