Reduction of retrosternal and pericardial adhesions with rapidly resorbable polymer films

Fibrin Hydrogel Layer-Anchored Pericardial Matrix Prevents Epicardial Adhesion in the Severe Heart Adhesion-Induced Miniature Pig Model

Postoperative adhesion is a very common and serious complication that occurs frequently in cardiac surgery. The purpose of this study was to evaluate the efficacy of a fibrin hydrogel layer-anchored decellularized pericardial matrix in preventing pericardial adhesions in a miniature pig model with a myocardial injury. Fibrin hydrogel layer-anchored decellularized pericardial matrix was prepared by spraying a mixture of fibrinogen and thrombin on a fibrinogen-doped decellularized pericardium. Cardiac injury was generated by abrading and desiccating the epicardial surface of a miniature pig to induce severe postoperative adhesions. The adhesion between the epicardial surface and fibrin hydrogel layer-anchored decellularized pericardial matrix in three different regions (left outer, front, and right outer) was evaluated macroscopically one month after surgery. The fibrin hydrogel layer-anchored decellularized pericardial matrix showed significantly less adhesion than an autologous pericardium (0.2 ± 0.7 in DPM-FHG0.5 and 0.4 ± 0.8 in DPM-FHG1, p < 0.01) and expanded polytetrafluoroethylene (ePTFE) (1.6 ± 0.5, p < 0.05). The fibrin hydrogel concentration had no effect on preventing postoperative adhesion. A thinner fibrin hydrogel layer was observed on the decellularized pericardial matrix one month after surgery; however, the inside of the matrix was filled with fibrin hydrogel. Fibrin hydrogel layer-anchored decellularized pericardial matrix prevented postoperative epicardial adhesions in a miniature pig model. Our findings suggest that pericardial closure using a fibrin hydrogel layer-anchored decellularized pericardial matrix is a promising method for preventing adverse outcomes in reoperative surgeries.

A review of animal models for post-operative pericardial adhesions

Post-operative pericardial adhesions remain a serious complication after cardiac surgery that can lead to increased morbidity and mortality. Fibrous adhesions can destroy tissue planes leading to injury of surrounding vasculature, lengthening of operation time, and increased healthcare costs. While animal models are necessary for studying the formation and prevention of post-operative pericardial adhesions, a standardized animal model for inducing post-operative pericardial adhesions has not yet been established. In order to address this barrier to progress, an analysis of the literature on animal models for post-operative pericardial adhesions was performed. The animal model, method used to induce adhesions, and the time to allow development of adhesions were analyzed. Our analysis found that introduction of autologous blood into the pericardial cavity in addition to physical abrasion of the epicardium caused more severe adhesion formation in comparison to abrasion alone or abrasion with desiccation (vs. abrasion alone p = 0.0002; vs. abrasion and desiccation p = 0.0184). The most common time frame allowed for adhesion formation was 2 weeks, with the shortest time being 10 days and the longest being 12 months. Finally, we found that the difference in adhesion severity in all animal species was similar, suggesting the major determinants for the choice of model are animal size, animal cost, and the availability of research tools in the particular model. This survey of the literature provides a rational guide for researchers to select the appropriate adhesion induction modality, animal model, and time allowed for the development of adhesions.

Prevention of Post-Operative Adhesions: A Comprehensive Review of Present and Emerging Strategies

Post-operative adhesions affect patients undergoing all types of surgeries. They are associated with serious complications, including higher risk of morbidity and mortality. Given increased hospitalization, longer operative times, and longer length of hospital stay, post-surgical adhesions also pose a great financial burden. Although our knowledge of some of the underlying mechanisms driving adhesion formation has significantly improved over the past two decades, literature has yet to fully explain the pathogenesis and etiology of post-surgical adhesions. As a result, finding an ideal preventative strategy and leveraging appropriate tissue engineering strategies has proven to be difficult. Different products have been developed and enjoyed various levels of success along the translational tissue engineering research spectrum, but their clinical translation has been limited. Herein, we comprehensively review the agents and products that have been developed to mitigate post-operative adhesion formation. We also assess emerging strategies that aid in facilitating precision and personalized medicine to improve outcomes for patients and our healthcare system.

Advancement of Biomaterial-Based Postoperative Adhesion Barriers

Postoperative peritoneal adhesion (PPA) is a prevalent incidence that generally happens during the healing process of traumatized tissues. It causes multiple severe complications such as intestinal obstruction, chronic abdominal pain, and female infertility. To prevent PPA, several antiadhesion materials and drug delivery systems composed of biomaterials are used clinically, and clinical antiadhesive is one of the important applications nowadays. In addition to several commercially available materials, like film, spray, injectable hydrogel, powder, or solution type have been energetically studied based on natural and synthetic biomaterials such as alginate, hyaluronan, cellulose, starch, chondroitin sulfate, polyethylene glycol, polylactic acid, etc. Moreover, many kinds of animal adhesion models, such as cecum abrasion models and unitary horn models, are developed to evaluate new materials' efficacy. A new animal adhesion model based on hepatectomy and conventional animal adhesion models is recently developed and a new adhesion barrier by this new model is also developed. In summary, many kinds of materials and animal models are studied; thus, it is quite important to overview this field's current progress. Here, PPA is reviewed in terms of the species of biomaterials and animal models and several problems to be solved to develop better antiadhesion materials in the future are discussed.

Bioresorbable electrospun gelatin/polycaprolactone nanofibrous membrane as a barrier to prevent cardiac postoperative adhesion

Post-cardiac surgical sternal and epicardial adhesions increase the risk and complexity of cardiac re-operative surgeries, which represent a significant challenge for patients with the congenital cardiac disease. Bioresorbable membranes can serve as barriers to prevent postoperative adhesions. Herein, we fabricated a bioresorbable gelatin/polycaprolactone (GT/PCL) composite membrane via electrospinning. The membrane was characterized in terms of morphology, mechanical properties, and biocompatibility. We then evaluated its efficacy as a physical barrier to prevent cardiac operative adhesions in a rabbit model. Our results showed that the membrane had a nanofibrous structure and was sturdy enough to be handled for the surgical procedures. In vitro studies with rabbit cardiac fibroblasts demonstrated that the membrane was biocompatible and inhibited cell infiltration. Further application of the membrane in a rabbit cardiac adhesion model revealed that the membrane was resorbed gradually and effectively resisted the sternal and epicardial adhesions. Interestingly, six months after the operation, the GT/PCL membrane was completely resorbed with simultaneous ingrowth of host cells to form a natural barrier. Collectively, these results indicated that the GT/PCL membrane might be a suitable barrier to prevent sternal and epicardial adhesions and might be utilized as a novel pericardial substitute for cardiac surgery. STATEMENT OF SIGNIFICANCE: Electrospinning is a versatile method to prepare nanofibrous membranes for tissue engineering and regenerative medicine applications. However, with the micro-/nano-scale structure and high porosity, the electrospun membrane might be an excellent candidate as a barrier to prevent postoperative adhesion. Here we prepared an electropun GT/PCL nanofibrous membrane and applied it as a barrier to prevent sternal and epicardial adhesions. Our results showed that the membrane had sufficient mechanical strength, good biocompatibility, and effectively resisted the sternal and epicardial adhesions. What's more, the membrane was bioresorbable and allowed simultaneous ingrowth of host cells to form a natural barrier. We believe that the current will inspire more research on nanomaterials to prevent postoperative adhesion applications.

Polymer materials for prevention of postoperative adhesion

Postoperative adhesion (POA) is a common complication that often occurs after a variety of surgeries, such as plastic surgery, repair operations of abdominal, pelvic, and tendon, and so forth. Moreover, POA leads to chronic abdominal pain, secondary infertility in women, intestinal obstruction, and other severe complications, which significantly reduce the life quality of patients. In order to prevent the formation of POA, a number of strategies have been developed, among which an emerging method is physical barriers consisting of polymer materials. This review highlights the most commonly used natural and synthetic polymer materials in anti-adhesion physical barriers. The specific features of polymer materials are analyzed and compared, and the possible prospect is also predicted.

STATEMENT OF SIGNIFICANCE

Postoperative adhesion (POA) is a serious complication accompanied with various surgeries. Polymer material-based physical barriers have attracted a large amount of attention in POA prevention. The polymer barriers can effectively avoid the formation of fibrous tissues among normal organs by reducing the interconnection of injured tissues. In this review, specific features of the natural and synthetic polymer materials for application in POA prevention were presented, and the possible prospects were predicted. All in all, our work can provide inspiration for researchers to choose proper polymer materials for preclinical and even clinical anti-adhesion studies.

No Effect of Rapamycin on Cardiac Adhesion Formation: A Drug-Loaded Bioresorbable Polylactone Patch in a Porcine Cardiac Surgical Model

Background: The fusing of the epicardium and sternum due to adhesion is a common problem during repeated cardiac surgery and carries with it an increased risk of bleeding. The use of barriers and patches has been tested to prevent the formation of adhesions, but the very presence of a patch can provoke adhesion formation. The objective of this study was, therefore, to investigate both biodegradable and bioresorbable polylactone patches [(polycaprolactone-poly(ethylene oxide)-polycaprolactone tri-block copolymer (PCE)]. The patches were also tested with a controlled release of rapamycin, which prevents cell migration and extracellular matrix deposition. The clinical effectiveness of rapamycin in pericardial patches has not previously been examined. Materials and Methods: Three groups of 6 female Danish Landrace pigs underwent sternotomy and abrasion of the epicardium, before being randomized to either group 1 - the control group (with no patch), group 2 - PCE patch implanted between the sternum and epicardium, or group 3 - PCE patch and slow-release 1.6-mg rapamycin. After a median time period of 26 days, the pigs were euthanized and their hearts removed en bloc with the sternum, for macroscopic, histological and pathological examination. Results: Upon macroscopic examination, a significantly lower degree of adhesion in group 2, as compared to group 1 (p < 0.05), was found. Histological analysis of the tissues showed significantly more fibrosis, inflammation and foreign body granulomas (p < 0.05) in both group 2 and group 3, when compared to group 1. Conclusion: A PCE patch following sternotomy in animal subjects reduces postoperative macroscopic adhesions without reducing microscopic fibrosis or inflammation. Loading the patch with rapamycin was found not to increase the antifibrotic effect.

Bonding behavior of hydrophobically modified gelatin films on the intestinal surface

The bonding behavior was determined for hydrophobically modified alkaline-treated gelatin on wet porcine intestinal surfaces. The modified gelatin films were obtained by reacting the amino groups of alkaline-treated gelatin with fatty acid chlorides of different alkyl chain lengths, namely, hexanoyl (Hx: C6) chloride, decanoyl (Dec: C10) chloride, and stearoyl (Ste: C18) chloride. Three kinds of the films were prepared, 32HxAlGltn, 24DecAlGltn, and 26SteAlGltn that had substitution ratios of hydrophobic groups to the amino groups of 32HxAlGltn, 24DecAlGltn, and 26SteAlGltn of 32%, 24%, and 26%, respectively. The 32HxAlGltn film had the strongest bonding to porcine intestinal surfaces. A thick 32HxAlGltn film remained on the intestinal surface even after the bonded film was scraped off for the measurement of bonding strength. In addition, the burst strength increased with an increase in the substitution ratio of the Hx group. Thus, the HxAlGltn film with the higher Hx modification ratio has a potential as a sealant material to prevent agglutination of intestinal surfaces.

European clinical experience with REPEL-CV®

The objective of the feasibility study was to gain European clinical experiences with REPEL-CV for reducing postoperative adhesions in pediatric patients undergoing cardiovascular surgery. The pediatric patient population included patients requiring staged cardiovascular sternotomy procedures where it was anticipated that the second sternotomy procedure would be performed 2-8 months subsequent to the initial procedure. At the time of the second sternotomy procedure, 13 out of 15 (86.7%) patients had no Grade 3 ('severe') adhesions. The mean percentage of the investigational surgical site with severe adhesions was 11%. There were five serious adverse events. All were anticipated (identified in the protocol and the investigator's brochure) and were considered by the investigators to be 'definitely not related' to the study device. Based on the incidence and extent of 'severe' adhesions and the safety profile for REPEL-CV as demonstrated in this study, the effectiveness and safety of REPEL-CV have been further demonstrated.

Surgical application of fascia lata as a pericardial substitute in rabbits

PURPOSE

To use fascia lata instead of pericardium and observe the presence of adhesions.

METHODS

Twenty rabbits were divided into two group of ten. In group A, a 1×1 cm segment of pericardium was excised and resutured. In group B excised pericardium was substituted for autologous fascia lata.

RESULTS

In the comparison of microscopic adhesion rate between two groups A, B after eight weeks, there was no significant statistical difference.

CONCLUSION

Fascia lata is safe and it can be substituted for pericardium especially in repeat sternotomy in repairing congenital heart defects to avoid heart injury.

Current strategies and future perspectives for intraperitoneal adhesion prevention

INTRODUCTION

The formation of peritoneal adhesions still is a relevant clinical problem after abdominal surgery. Until today, the most important clinical strategies for adhesion prevention are accurate surgical technique and the physical separation of traumatized serosal areas. Despite a variety of barriers which are available in clinical use, the optimal material has not yet been found.

DISCUSSION

Mesothelial cells play a crucial physiological role in friction less gliding of the serosa and the maintenance of anantiadhesive surface. The formation of postoperative adhesions results from a cascade of events and is regulated by various cellular and humoral factors. Therefore, optimization or functionalization of barrier materials by developments interacting with this cascade on a structural or pharmacological level could give an innovative input for future strategies in peritoneal adhesion prevention. For this purpose, the proper understanding of the formal pathogenesis of adhesion formation is essential. Based on the physiology of the serosa and the pathophysiology of adhesion formation, the available barriers in current clinical practice as well as new innovations are discussed in the present review.

Intraperitoneal adhesions--an ongoing challenge between biomedical engineering and the life sciences

Peritoneal adhesions remain a relevant clinical problem despite the currently available prophylactic barrier materials. So far, the physical separation of traumatized serosa areas using barriers represents the most important clinical strategy for adhesion prevention. However, the optimal material has not yet been found. Further optimization or pharmacological functionalization of these barriers could give an innovative input for peritoneal adhesion prevention. Therefore, a more complete understanding of pathogenesis is required. On the basis of the pathophysiology of adhesion formation the main barriers currently in clinical practice as well as new innovations are discussed in the present review. Physiologically, mesothelial cells play a decisive role in providing a frictionless gliding surface on the serosa. Adhesion formation results from a cascade of events and is regulated by a variety of cellular and humoral factors. The main clinically applied strategy for adhesion prevention is based on the use of liquid or solid adhesion barriers to separate physically any denuded tissue. Both animal and human trials have not yet been able to identify the optimal barrier to prevent adhesion formation in a sustainable way. Therefore, further developments are required for effective prevention of postoperative adhesion formation. To reach this goal the combination of structural modification and pharmacological functionalization of barrier materials should be addressed. Achieving this aim requires the interaction between basic research, materials science and clinical expertise.

Bioresorbable adhesion barrier for reducing the severity of postoperative cardiac adhesions: Focus on REPEL-CV(®)

Treatment of a number of congenital heart defects often necessitates staged surgical intervention. In addition, substantial improvements in postoperative cardiac care and more liberal use of biological valve substitutes have resulted in many adult patients surviving to become potential candidates for reoperations to repair or replace valves or to undergo additional revascularization procedures. In all these scenarios, surgeons are confronted with cardiac adhesions, leading to an increased surgical risk. Thus, bioresorbable adhesion barriers had become of increasing interest because they are easy to use, and safe and effective. This review focuses on the mechanisms by which REPEL-CV^® prevents adhesive processes, as well as the development, design, and materials used, and also summarizes efficacy studies, clinical data, safety, and current role in therapy.

Mechanism of paradoxical ventricular septal motion after coronary artery bypass grafting

Paradoxical septal motion is commonly noted on echocardiography after coronary artery bypass grafting (CABG), but its mechanism is unclear. Cardiac magnetic resonance imaging was performed before and 3 months after CABG in 23 patients. On a mid-left ventricular short-axis cine image, the motion of myocardial landmarks during the cardiac cycle was ascertained relative to a stationary anterior reference point. Before CABG, the movement of the ventricular septum in systole was either posterior or neutral (median -2 mm) in 19 patients, whereas after CABG, the septum moved anteriorly in all 23 patients (+4 mm; p<0.001). (A positive sign indicates anterior motion in ventricular systole, and a negative sign denotes posterior motion.) The motion of the right ventricular free wall was reduced after CABG (-5 vs -3 mm; p=0.002), whereas anterior movement of the lateral left ventricular wall in systole increased (+4 vs +9 mm; p<0.001). There was a positive correlation between degree of anterior movement of the ventricular septum and right ventricular ejection fraction (r=0.47, p=0.023). In conclusion, after CABG, the entire left ventricle translocated anteriorly in systole. Despite preserved right ventricular function, there was restricted motion of the right ventricular free wall suggestive of postoperative adhesions. The pattern of movement observed offers a sound explanation for postoperative paradoxical septal motion.

Bioabsorbable Gelatin Sheets Latticed With Polyglycolic Acid Can Eliminate Pericardial Adhesion

BACKGROUND

As an extension of our previous studies on bioabsorbable pericardial substitutes, we have created a new form of gelatin sheets latticed with bioabsorbable polyglycolic acid (PGA). This study was undertaken to evaluate the biomechanical property of the sheet and the preventive effect on pericardial adhesions after pericardial replacement in a canine model before its clinical applications.

METHODS

The mechanical property was assessed by measuring tension of suture pull-out at first break test. Fifteen dogs underwent partial pericardial replacement with the bioabsorbable sheets through a left thoracotomy. Macroscopic assessment for severity of adhesions and microscopic evaluation for histologic changes were made at 2, 4, 12, and 24 weeks postoperatively.

RESULTS

The latticed sheets exhibited tenfold higher tension of disruption at the suturing margin compared to our previously developed gelatin sheets (619 +/- 141 versus 62 +/- 7 gf, p < 0.001), and demonstrated equivalent strength to that of clinically available expanded polytetrafluoroethylene membrane. During rethoracotomy, adhesions between the epicardium and the pericardial substitutes were moderate at the 4-week interval and resolved completely after 12 weeks postoperatively. Inflammatory reaction scores graded into 4 scales on histologic assessment were 2 +/- 0.0, 1.6 +/- 0.6, and 0.3 +/- 0.5 at 4, 12, and 24 weeks, respectively. Inflammatory reaction significantly decreased from the 4-week interval to the 24-week interval after the pericardial replacement (p < 0.05).

CONCLUSIONS

The bioabsorbable gelatin sheets latticed with PGA gained improved mechanical properties compared with the previously reported gelatin sheets without impairing its bioabsorbability. The bioabsorbable sheet could eliminate pericardial adhesions after being replaced with regenerated tissue.

BioGlue�: A Protective Barrier After Pericardiotomy

BACKGROUND

Repeat operation on the heart composes about 20% of procedures in contemporary practice of cardiac surgery. A sheet of material providing a barrier against cardiac adhesion to the sternum would be desirable.

METHODS

Anterior pericardiectomy was performed in rats. BioGlue milled to a 0.4 mm sheet was applied to the anterior surface of the heart in 16 rats; Surgicel plus liquid BioGlue in seven; Surgicel alone in three; and nothing (control) in eight. The operative site was reexamined for gross evidence of adhesion, scarring, and residual BioGlue 1, 3, and 6 months later.

RESULTS

There was formation of a loose connective tissue barrier containing blood vessels without scar formation in all animals treated with milled BioGlue. Surgicel plus BioGlue resulted in a barrier containing more denser connective tissue with collagen fibers. Surgicel alone resulted in a similar barrier. No barrier formed in the control experiments.

CONCLUSIONS

A sheet of milled BioGlue applied over the surface of the heart but not attached to it after partial pericardiectomy has been shown to stimulate formation of a loose connective tissue barrier containing blood vessels. This barrier is unique compared to dense fibrous scar which usually forms after opening the pericardium for cardiac operations.

Autologous platelet gel and fibrin sealant enhance the efficacy of total knee arthroplasty: improved range of motion, decreased length of stay and a reduced incidence of arthrofibrosis

In this study we describe the potential role of autologous platelet gel and fibrin sealant in unilateral total knee arthroplasty to improve the postoperative range of motion and to reduce the incidence of arthrofibrosis. Total knee arthroplasty is often associated with a considerable amount of post-operative blood loss. Persistent limited motion directly after surgery may ultimately result in arthrofibrosis. To counteract these effects we investigated whether the use of autologous derived platelet gel and fibrin sealant would reduce postoperative blood loss, decrease the impaired range of motion and the incidence of arthrofibrosis. All patients were consecutively operated and assigned to the study or control groups. Study group patients (n = 85) were treated with the application of autologous platelet gel and fibrin sealant at the end of surgery. Eighty patients were operated without the use of platelet gel and fibrin sealant, and served as the control group. The postoperative hemoglobin decrease, range of motion and length of hospitalization were recorded. During a 5-month postoperative period patients were followed to observe the incidence of arthrofibrosis. In patients in the treatment group the hemoglobin concentration in blood decreased significantly less when compared to the control group. They also showed a superior postoperative range of motion when compared to those of the control group (P < 0.001). The incidence of arthrofibrosis and subsequent forced manipulation was significantly less (P < 0.001) in patients managed with platelet gel and fibrin sealant. We conclude that peri-operatively applied platelet gel and fibrin sealant may improve the range of motion after total knee arthroplasty, decreases the length of stay and may reduce the incidence of arthrofibrosis.

Postoperative Pericardial Adhesion Prevention Using Carbylan-SX in a Rabbit Model

INTRODUCTION

The presence of dense adhesions within the pericardial space complicates reoperative cardiac surgery. Prior attempts to reduce adhesion formation after primary cardiac surgery using medications or biomaterials have had variable success. Carbylan-SX (Carbylan Biosurgery Inc., Palo Alto, CA) is a hyaluronan-based biomaterial, which has been shown to be effective at reducing adhesions in a nonthoracic rat model. This study evaluates whether Carbylan-SX can effectively reduce postoperative adhesions within the pericardial cavity.

METHODS

Thirty-eight New Zealand white rabbits underwent a left lateral thoracotomy. A pericardiotomy was made and epicardial adhesions were induced on the anterior surface of the heart using a Dremel device (Racine, WI). The rabbits were divided into four groups: controls with abrasions only receiving no treatment (n=10), Carbylan-SX films (n=10), Carbylan-SX aerosolized hydrogel (n=10), and Seprafilm (n=8). The pericardial sac and chest were subsequently closed. Rabbits were sacrificed at a mean of 15 days. For histological analysis, each heart was divided into 12 separate 1 mm sections. Computer imaging software was used to measure the adhesion thickness and the mean of 12 random measurements for each animal was recorded and statistical analysis performed.

RESULTS

Histological analysis revealed all treatment groups to be significantly better than the control (2159 mum thickness, P<0.0001) at preventing adhesions. The Carbylan-SX film and Carbylan-SX aerosolized hydrogel both proved to be better at preventing adhesions than Seprafilm (Genzyme Corp., Cambridge, MA) with an average adhesion thickness of 454 and 577 microm, respectively, compared with 1319 microm for Seprafilm (P<0.0001 and P<0.0005, respectively). The Carbylan-SX film and Carbylan-SX aerosolized hydrogel were equally effective at preventing adhesion formation.

CONCLUSION

Carbylan-SX film and Carbylan-SX aerosolized crosslinkable hydrogel are equally effective methods of reducing postoperative pericardial adhesions within the pericardial cavity. Both the Carbylan-SX film and aerosolized hydrogel showed a significantly greater reduction in adhesions than Seprafilm. Clinical application of Carbylan-SX could have significant therapeutic implications in the future.

Site-specific delivery of dexamethasone from biodegradable implants reduces formation of pericardial adhesions in rabbits

Repeated sternotomy often leads to serious complications in patients due to the formation of cardiac adhesions. In this study we characterized dexamethasone-loaded biodegradable poly(lactide)-poly(ethyleneglycol) copolymer films for site-specific drug delivery and examined their efficacy in the rabbit model of postoperative cardiac adhesions. Tritiated dexamethasone-loaded films were used to determine the in vitro release and in vivo drug distribution. Dexamethasone release in serum was biphasic with 69% drug released after 72 hr. The implants produced sustained drug levels at the implantation site with low distribution into the peripheral tissues. The matrices were implanted in rabbits between the epicardium and the sternum following sternotomy, pericardiectomy and epicardium abrasion, with the drug-releasing surface facing the epicardium. The tenacity and density of the adhesions was examined 21 days post procedure in comparison to both groups of untreated and rabbits implanted with blank matrices. Similarly tenacious and dense adhesions were observed in both control groups. In contrast, epicardial adhesions' formation was significantly reduced and the anatomy was preserved in the treated animals. It is concluded that local delivery of dexamethasone from biodegradable implants provides a promising approach for the prevention of pericardial adhesions while potentially minimizing the systemic adverse effects inherent to systemic therapy or high blood levels of the drug.

Closure of the Pericardium Using Synthetic Bioabsorbable Polymers

BACKGROUND

Pericardial substitutes are known to ensure safer resternotomy at reoperation. A synthetic sheet made from expanded-polytetrafluoroethylene (e-PTFE) has been most commonly used as a pericardial substitute. The e-PTFE sheet, however, can induce severe inflammatory reaction and diffuse fibrosis. This study was designed to investigate the absorption rate and tissue reaction associated with two absorbable pericardial substitutes: a gelatin sheet and L-lactic acid-epsilon-caprolactone copolymer (L-C copolymer). In addition, e-PTFE sheet and autologous pericardium were used as controls.

METHODS

Sixty dogs were divided into four groups of 15. In group A, a 3 x 3 cm segment of pericardium was excised, and the autologous pericardium was resutured. In group B, the pericardial defect was replaced with gelatin sheet. In group C, the defect was replaced with L-C copolymer sheet. In group D, the defect was replaced with e-PTFE sheet. For each group, the implanted membranes were retrieved at 2 weeks (n = 1), 4 weeks (n = 3), 12 weeks (n = 5), and 24 weeks (n = 6) after implantation.

RESULTS

The e-PTFE sheet produced severe adhesions to the heart and pleura and a more prominent inflammatory reaction, as compared with the gelatin sheet. The absorbable pericardial substitutes were completely absorbed by 24 weeks after implantation, and were replaced with fibrous membrane.

CONCLUSIONS

Gelatin sheet may involve less adhesion and a reduced inflammatory reaction compared with e-PTFE.

Histological evaluation of the effects of angiotensin peptides on wound repair in diabetic mice

Recent studies have shown that angiotensin peptides accelerate dermal repair. Histological observation of samples taken at the termination of studies showed that the wounds treated with peptides were mature and organized by day 25 after full thickness excision in diabetic mice. However, the mechanisms by which this acceleration occurs has not been determined. In the experiments described here, the effect of angiotensin peptides (AII, A(1-7) and NorLeu (3)-A(1-7) on the quality of the healing wound was evaluated histologically. Administration of the peptides accelerated collagen deposition, re-epithelialization and new blood vessels formation. By day 4, the percentage of the wound with collagen increased two- to six-fold depending upon the peptide. The increase by angiotensin peptides continued throughout the experimental period. On days 4 and 7 9 (only) after injury, exposure to angiotensin peptides increased the number of blood vessels at wound site two-to three-fold. Finally, the percentage of the wound site covered with new epithelium increased after administration of angiotensin peptides. Re-epithelialization was observed as early as day 4 in wounds treated ith angiotensin peptides. The increase was greater at later time points (up to 8-fold ar day 14 with NorLeu(3)-A(1-7) had an increase in neutrophils and macrophages on day 4 after wounding. Overall, administration of these peptides resulted in a healing site that was more mature, including reorganization of the collagen into a basket-weave appearance. Further, these studies confirm the superiority of NorLeu(3)-A(1-7) to AII and A(1-7) in wound healing evaluated at a microscopic level.

Evaluation of a bioabsorable polylactide film in a large animal model for the reduction of retrosternal adhesions

OBJECTIVES

An adult pig model of retrosternal adhesion formation via an inferior hemisternotomy was used to evaluate the formation and development of pericardial and retrosternal adhesions, as well as adhesion reduction using two thicknesses of a bioabsorbable polylactide film.

MATERIALS AND METHODS

Twenty-five adult female pigs (70 kg) were allocated to either a control group or four different treatments using two thicknesses (0.02 or 0.05 mm) of a polylactide film. In each animal, the film was placed either inside the pericardium or inside and outside the pericardium.

RESULTS

All animals demonstrated adhesions between the posterior and lateral surfaces of the heart and pericardium. Thick fibrous retrosternal adhesions and pericardial adhesions were noted in the control animals with complete obliteration of the anatomical plane. The polylactide films preserved the anatomical planes and reduced the adhesion response.

CONCLUSIONS

A reproducible animal model was used to examine the formation and reduction of retrosternal and pericardial adhesions. A polylactide film placed inside the pericardium or between the heart and sternum was able to limit adhesion formation and maintain the anatomical planes, which would facilitate reentry.

Next-Generation HydroGel Films as Tissue Sealants and Adhesion Barriers

BACKGROUND

The development of conveniently sprayed, tissue-adherent, inert hydrogel films has made possible the creation of novel products that can serve a dual function, as a surgical sealant to achieve immediate hemostasis, and as a barrier to prevent adhesion formation over time.

METHODS

A sprayable, in situ formed absorbable hydrogel film was evaluated as a tissue sealant in a heparinized canine carotid artery graft model. PTFE grafts with leaking end-to-side anastomoses were treated with the synthetic sealant, and hemostasis was evaluated upon restoration of blood flow. Also, the hydrogel films were evaluated as an adhesion barrier in a rabbit pericardial abrasion model.

RESULTS

The sprayable, in situ forming hydrogel film was shown to immediately seal carotid-PTFE anastomoses in six of six applications. Hydrogel application in a rabbit pericardial abrasion model resulted in a statistically significant reduction in the number and tenacity of adhesions.

CONCLUSIONS

This novel in situ formed sprayable hydrogel film has demonstrated a dual function as an effective tissue sealant and as an adhesion barrier in cardiovascular preclinical models. These next generation synthetic biomaterials are currently undergoing clinical investigations.