Polysaccharide-based films for the prevention of unwanted postoperative adhesions at biological interfaces

Abstract

Postoperative adhesions protect, repair, and supply nutrients to injured tissues; however, such adhesions often remain permanent and complicate otherwise successful surgeries by tethering tissues together that are normally separated. An ideal adhesion barrier should not only effectively prevent unwanted adhesions but should be easy to use, however, those that are currently available have inconsistent efficacy and are difficult to handle or to apply. A robust hydrogel film composed of alginate and a photo-crosslinkable hyaluronic acid (HA) derivative (glycidyl methacrylate functionalized hyaluronic acid (GMHA)) represents a solution to this problem. A sacrificial porogen (urea) was used in the film manufacture process to impart macropores that yield films that are more malleable and tougher than equivalent films produced without the sacrificial porogen. The robust mechanical behavior of these templated alginate/GMHA films directly facilitated handling characteristics of the barrier film. In a rat peritoneal abrasion model for adhesion formation, the polysaccharide films successfully prevented adhesions with statistical equivalence to the leading anti-adhesion technology on the market, Seprafilm®.

Statement of Significance

Postoperative adhesions often remain permanent and complicate otherwise successful surgeries by tethering tissues together that are normally separated and pose potentially significant challenges to patients. Therefore, the generation of adhesion barriers that are easy to deploy during surgery and effectively prevent unwanted adhesions is a big challenge. In this study robust hydrogel films composed of alginate and a photo-crosslinkable hyaluronic acid (HA) derivative (glycidyl methacrylate functionalized HA, GMHA) were fabricated and investigated for their potential to act as a solution to this problem using a rat peritoneal abrasion model for adhesion formation. We observed the polysaccharide films successfully prevented adhesions with statistical equivalence to the leading anti-adhesion technology on the market, Seprafilm®, suggesting that such films represent a promising strategy for the prevention of postoperative adhesions.

Introduction

Postoperative adhesions are a major complication to otherwise successful surgeries [1], [2], [3], [4], [5], [6], [7], [8]. Despite tremendous efforts to resolve this unwanted scar formation, there exists no consistently efficacious and safe solution [2,4,9,10]. Adhesions form in the normal, acute phase of injury, and resolve in an equilibrium state between fibrin deposition and fibrinolysis until the injury site has healed [11], [12], [13]. However, these fibrinous strands may remain well beyond the healing period and tether tissues that are normally separated, causing chronic pain and even loss of function, such as secondary female infertility and bowel obstruction affecting the quality of life of the patients [2,5,10,[14], [15], [16], [17]]. Adhesion formation occurs in up to 90% of abdominopelvic procedures [8], requiring additional surgical interventions in over 33% of patients [18] which presents huge costs to the healthcare system (in excess of $3.45 billion (US) annually in the USA) [19], [20], [21], [22].

Efforts to resolve unwanted adhesions have included improvements in surgical techniques [23], pharmaceutical methods [24], and barrier devices to mechanically separate tissues [3]. Mechanical devices have had the greatest success of any adhesion prevention method [13,25]. These devices include sprays, gels, solutions, in situ gelling polymers, and pre-formed membranes made from natural and synthetic polymers [10,26].

A variety of adhesion prevention devices made from natural and synthetic polymeric materials have reached the Food and Drug Administration (FDA) approval. One of which is Seprafilm® (Sanofi, Paris, France), a pre-formed hydrogel membrane consisting of carboxymethylcellulose (CMC) and chemically modified HA. Despite its efficacy, the use of Seprafilm® is limited owing to its handling issues [27], [28], [29]. A dry Seprafilm is too brittle, sticks to tools, and is not repositionable; and the wet film has poor mechanical integrity and cannot be manipulated [2,10]. Interceed® (Gynecare, Ethicon, Somerville, NJ) made from oxidized regenerated cellulose has mixed reviews with some studies indicating adhesion induction [30] and limited efficacy in incomplete hemostasis [4]. Liquid based antiadhesion formulations like Adept™ (Baxter, Unterschleissheim, Germany) made of 4% icodextrin, is sutureless and can be administered laparoscopically, but its fluidity causes leakage from the surgical site with limited adherence to designated regions [31]. Some gels and in situ gelling formulations as adhesion barriers initially received much enthusiasm because of their ability to conform to tissue geometries and delivery via laparoscopy. However, injectable gels that are cross-linkable in situ were less favorable because of long gelling times and assistance required from external devices [2,[32], [33], [34], [35]]. The liquid based anti-adhesion agents are limited in their scope because they require complicated procedures to spray at the targeted site [31] and have failed due to dilution with bodily fluids and migration from the injury site [13], and crosslinked injectable gels such as Hyalobarrier^Ⓡ (Anika Therapeutics, S.r.l., Abano Terme, Italy) may be hindered by uneven distribution at the injury site [36].

An ideal anti-adhesion barrier should have the following attributes: be pliable, robust enough to withstand operating room procedures including laparoscopic delivery; maintain mechanical integrity to facilitate repositioning within the surgical field; conform to delicate tissue geometries; be mucoadhesive to avoid the need for sutures and staples; and have appropriate retention time to effectively prevent unwanted adhesions during the critical healing period of 3–7 days [37], [38], [39].

In this study, we present a pre-formed hydrogel membrane composed of HA and alginate, both are natural polysaccharides well established for wound healing and anti-adhesion [40], [41], [42], [43], [44], [45], [46]. The distinguishing feature of this membrane is a fibrillar ultrastructure attained by use of a sacrificial porogen (urea crystals) that imparts toughness and elasticity to the films. This ultrastructure is obtained by combining a photoreactive HA derivative, glycidyl methacrylate-hyaluronic acid (GMHA), alginate, and urea in aqueous solution. The solution is then cast into thin films, dried and nucleated with a urea seed crystal to initiate the growth of microscopic, branch-like urea crystals throughout the membrane. This in situ crystallization process compresses the polymers into microfibers [47], which are then stabilized by crosslinking with UV light and calcium chloride. Thoroughly rinsing the films with water washes away the urea crystals, leaving behind an interconnected porous network running alongside the fibers. This simple processing method does not require expensive equipment, software programming and is readily scalable. Furthermore, the resulting toughness and elasticity can be modified by tuning the membrane composition and crosslink density.

The alginate component in this membrane undergoes a gradual gel-to-mucoadhesive transition. Calcium ions responsible for gelation of the alginate are replaced with sodium ions, causing dissolution of the alginate into a mucous material [46]. This dissolution permits brief repositioning of the membranes in the surgical field, as well as subsequent mucous adherence to tissues.

The proposed innovative membrane solves the limitations of the existing anti-adhesion devices. This pre-formed membrane is easy to handle, can be manipulated while wet, is mucoadhesive, and can successfully prevent unwanted adhesions at a biological interface. Additionally, this membrane can be laparoscopically delivered, and requires no additional equipment or suturing. The unique fibrillar ultrastructure contributes to better mechanical and handling properties. In addition, the porosity within the membrane facilitates the diffusion of water, nutrients and oxygen through the large surface area [48]. The form and mechanical characteristics of this adhesion barrier provide the foundation for excellent product efficacy.