Wound Healing/Plastic Surgery
Novel Macromolecular Crosslinking Hydrogel to Reduce Intra-Abdominal Adhesions

https://doi.org/10.1016/j.jss.2008.09.035Get rights and content

Background

The aim of this study was to compare the anti-adhesion efficacy of a biodegradable, in situ, macromolecular cross-linking hydrogel made from oxidized dextran/N-carboxyethyl chitosan (Odex/CEC) with a commercially available carboxymethylcellulose/modified hyaluronan barrier film (Seprafilm; Genzyme Corporation, Cambridge, MA) in a rat cecum abrasion model.

Methods

The rat model utilized a cecal abrasion and abdominal wall insult surgical protocol. The 2% Odex/CEC hydrogel treatment was applied by syringe to coat both the cecal and the abdominal wall insults, while other animals were treated with Seprafilm applied to the cecal injury only. Control animals did not receive any treatment. Animals were sacrificed after post operative day 21 and adhesion severity was quantitatively graded using a whole number scale from 0 – 3. Histological analysis was also performed for animals receiving Odex/CEC hydrogel treatment and no treatment (control).

Results

Mean adhesion score was 2.09 ± 1.22 for control animals, 1.00 ± 1.00 for 2% Odex/CEC hydrogel animals, and 1.25 ± 1.22 for Seprafilm animals. Hydrogel treated animals showed significantly lower adhesion scores than control animals (P < 0.05), while Seprafilm demonstrated a marginally lower adhesion score (P < 0.1) compared with the controls. Histological analysis of an Odex/CEC treated rat showed tissue repair and small fragments of hydrogel inside both healed abdominal and cecal surfaces.

Conclusions

Both Seprafilm and the 2% Odex/CEC hydrogel showed a significantly decreased adhesion score compared with the control. However, the hydrogel, compared with Seprafilm, offers ease of application and ability to conform to complex tissue geometries that could provide surgeons with another prophylactic treatment to prevent abdominal adhesions.

Introduction

In the United States, more than 90% of patients undergoing abdominal surgery experience some form of adhesions, from minimal to extreme. These adhesions are induced by prolonged inflammation of injured tissues, fibroblast in-growth, and neovascularization leading to fibrous tissue formations [1]. The impact of complications from adhesions includes severe pain, bowel obstruction, and infertility [2]. Adhesions most commonly develop 12 h to 3 d after abdominal surgery and are likely initiated when organs are handled during the operation or temporarily shifted from their normal positions [3]. Additionally, insoluble fibrin from blood coagulation becomes a provisional matrix that can form the initial bridging between tissue surfaces in the abdomen and later could provide a structure for fibroblasts to remodel into strong, fibrotic tissue 2, 4, 5. In about 10% of adhesion cases, part of the bowel may twist tightly around the bands of fibrous tissue leading to ischemia, tissue infarction, and eventual tissue necrosis [6].

The research area in prevention or reduction of abdominal adhesions has manifested many different clinical products. These products generally fall into two categories: non-absorbable and absorbable. Preclude (W.L. Gore and Associates, Flagstaff, AZ) membranes are made of non-biodegradable polytetrafluoroethylene are highly efficacious in preventing adhesions over a long period after surgery; however, these membranes must be surgically removed at a later time. Biodegradable barriers, in contrast, are appealing as additional surgery for later removal could be circumvented, thus minimizing patient discomfort and hospitalization costs. Seprafilm (Genzyme Corporation, Cambridge, MA), also approved for abdominal and gynecological surgeries, is a type of absorbable barrier film composed of un-crosslinked, carboxymethylcellulose/sodium hyaluronate [7]. Upon deployment, the dry film develops into a gel consistency over 24 h as it absorbs moisture from the application site and surrounding tissues. It acts as an occlusive barrier between damaged tissue sites to reduce the incidence of adhesion formation while also allowing the damaged tissues to repair under the barrier 8, 9, 10. However, these films are brittle and relatively difficult to apply as they aggressively adhere to any moisture on the surgeon's gloves during placement; thus, their use is limited primarily to open surgical proceedures 9, 11.

The rigidity issue of a barrier film could be addressed by a fluidly applied, self-crosslinking hydrogel barrier capable of fully conforming to any complex geometries/folds inside the abdomen, serve as an effective barrier for several d, and also allow either endoscopic or laparotomy application. Several studies have introduced such hydrogel barriers with both synthetic and natural polymer components. A purely synthetic, poly(ethylene glycol)-based hydrogel (SprayGel, Confluent Surgical, Waltham, MA) is currently in clinical trials in the United States. A possible drawback to the wide adoption of this treatment may be the additional need for an air supply set-up to propel the gel onto the wounded tissue in the surgical field. Self-crosslinking hyaluronan-based hydrogels have also reported good efficacy in both large bowel trauma models 12, 13 and pelvic surgical models 14, 15. However, consistency across different hyaluronan formulations has been elusive so far. Intergel (Ethicon, Somerville, NJ), consisting of a ferric hyaluronate-based, ionically crosslinked solution, initially showed promise in pelvic surgical clinical studies [16]; however, it was removed from the market after occurrences of severe complications. Another possible setback to a hyaluronan-based hydrogel barrier is cost: medical-grade hyaluronan is expensive and could increase the price of the hydrogel above re-imbursement caps imposed by a third party.

Other natural polymers have also been modified to initiate gelation without the addition of third crosslinking agent. In a previously published study by Weng et al., a novel hydrogel formulation composed of partially oxidized dextran (Odex) and N-carboxyethyl chitosan (CEC) was developed [17]. There are two major advantages for usage of this system as an adhesion barrier: 1) both chitosan 18, 19 and dextran [20] are FDA GRAS materials and have been widely investigated with demonstrated excellent biocompatibility; 2) Odex and CEC cross-link at physiological pH/temperature by electrostatic interaction, hydrogen bonding and eventually stabilization by Schiff base formation between aldehyde and amine groups located on the two molecules [17]. Specifically, the Odex component serves as a macromolecular cross-linker to bind CEC to form a macromolecular network, thereby obviating the need for potentially cytotoxic small molecule cross-linking agents, which decreases toxicity concerns directly after application/during in situ degradation [21]. In vitro cytotoxicity studies have demonstrated that the Odex/CEC hydrogel formulation has excellent biocompatibility with dermal fibroblast cells in direct contact and encapsulated inside crosslinked hydrogel [22].

The purpose of this study was to evaluate the anti-adhesion efficacy of a 2% Odex/CEC hydrogel in a 21-d, rat cecum abrasion model. In parallel, the hydrogel was benchmarked against Seprafilm, a widely utilized anti-adhesion product. This comparison allowed us to assess the adhesion prevention quality of the Odex/CEC hydrogel against a current and proven standard of care used clinically.

Section snippets

Synthesis of N-Carboxyethyl Chitosan (CEC)

The CEC was synthesized by a method previously described by us 17, 23. About 1 g of chitosan (deacetylation degree 85%, Mw = 750,000) was dissolved in 50 mL of water containing 1.88 mL acrylic acid under constant stirring at 50 °C for 3 d. Afterwards, a 10 N NaOH solution was added to the reaction mixture to increase the pH to 10-12. This step converted the CEC into its sodium salt. The mixture was then dialyzed extensively for 3 d until pure CEC was obtained by lyophilization.

Synthesis of Oxidized Dextran (Odex)

The Odex was synthesized

Results

The raw adhesion severity scores can be found in Table 1. The mean adhesion score for the control animals was 2.09 ± 1.22. Animals treated with Seprafilm and the 2% Odex/CEC hydrogel had adhesion scores of 1.25 ± 0.707 and 1.00 ± 1.00, respectively. The Odex/CEC hydrogel treatment had a significantly lower adhesion score (P = 0.029) than the control. Animals treated with Seprafilm also demonstrated a significantly lower adhesion score (P = 0.056). There was no statistical difference between the two

Discussion

Studies have shown that the window for efficacy of an adhesion barrier occurs between 12 and 36 h after surgery 29, 30. The rats in this study were sacrificed 21 d after surgery to observe the adhesion severity. In many comparable rat cecum abrasion models, the typical post-operative sacrifice time range for a solid or hydrogel barrier is 7-14 d 31, 32. Since adhesions typically manifest within the first few d after surgery, it is between 5-7 d that the adhesion fibrosis becomes more organized,

Acknowledgments

This research was supported by a grant from the New York State Foundation of Science, Technology and Innovation (NYSTAR) administered through the Center for Biotechnology of the State University of New York-Stony Brook. Partial support was also provided by the National Institutes of Health (DK068401). We also gratefully acknowledge the assistance of Wei Zhu, Ph.D., with the data and statistical analysis and Sharon Liang, M.D., Ph.D., for her expertise and assessment of the histological slides.

References (37)

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