The Use of Hyaluronic Acid Polymers to Reduce Postoperative 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.

Biodegradable Zwitterionic Cream Gel for Effective Prevention of Postoperative Adhesion

Postoperative peritoneal adhesions were frequent complications for almost any types of abdominal and pelvic surgery. This led to numerous medical problems and huge financial burden to the patients. Current anti-adhesion strategies focused mostly on physical barriers including films and hydrogels. However, they can only alleviate or reduce adhesions to certain level and their applying processes were far from ideal. This work reported the development of a biodegradable zwitterionic cream gel presenting a series of characters for an idea anti-adhesion material, including unique injectable yet malleable and self-supporting properties, which enabled an instant topical application, no curing, waiting or suturing, no hemostasis requirement, protein/cell resistance and biodegradability. The cream gel showed a major advancement in anti-adhesion efficacy by completely and reliably preventing a primary and a more severe recurrent adhesion in rat models.

Chitosan-g-hematin: enzyme-mimicking polymeric catalyst for adhesive hydrogels

Phenol derivative-containing adhesive hydrogels has been widely recognized as having potential for biomedical applications, but their conventional production methods, utilizing a moderate/strong base, alkaline buffers, the addition of oxidizing agents or the use of enzymes, require alternative approaches to improve their biocompatibility. In this study, we report a polymeric, enzyme-mimetic biocatalyst, hematin-grafted chitosan (chitosan-g-hem), which results in effective gelation without the use of alkaline buffers or enzymes. Furthermore, gelation occurs under mild physiological conditions. Chitosan-g-hem biocatalyst (0.01%, w/v) has excellent catalytic properties, forming chitosan-catechol hydrogels rapidly (within 5 min). In vivo adhesive force measurement demonstrated that the hydrogel formed by the chitosan-g-hem activity showed an increase in adhesion force (33.6 ± 5.9 kPa) compared with the same hydrogel formed by pH-induced catechol oxidation (20.6 ± 5.5 kPa) in mouse subcutaneous tissue. Using the chitosan-g-hem biocatalyst, other catechol-functionalized polymers (hyaluronic acid-catechol and poly(vinyl alcohol)-catechol) also formed hydrogels, indicating that chitosan-g-hem can be used as a general polymeric catalyst for preparing catechol-containing hydrogels.

Polymers in the prevention of peritoneal adhesions

Peritoneal adhesions are serious complications of surgery, and can result in pain, infertility, and potentially lethal bowel obstruction. Pharmacotherapy and barrier devices have reduced adhesion formation to varying degrees in preclinical studies or clinical trials; however, complete prevention of adhesions remains to be accomplished. We and others have hypothesized that the limitations of the two approaches could be overcome by combining their strengths in the context of controlled drug delivery. Here we review the role of polymeric systems in the prevention of peritoneal adhesions, with an emphasis on our recent work in developing and applying polymeric drug delivery systems such as nano- or microparticles, hydrogels, and hybrid systems for peritoneal use.

In situ cross-linkable hyaluronic acid hydrogels prevent post-operative abdominal adhesions in a rabbit model

We studied the efficacy of an in situ cross-linked hyaluronic acid hydrogel (HAX) in preventing post-surgical peritoneal adhesions, using a rabbit sidewall defect-cecum abrasion model. Two cross-linkable precursors were prepared by modifying hyaluronic acid with adipic dihydrazide and aldehyde, respectively. The hydrogel precursors cross-linked to form a flexible hydrogel upon mixing. The hydrogel was biodegradable and provided a durable physical barrier, which was highly effective in reducing the formation of post-operative adhesions. Ten out of 12 animals in the untreated control group developed fibrous adhesions requiring sharp dissection, while only 2 out of 8 animals treated with HAX gels showed such adhesions, and those occurred in locations that were not covered by the hydrogel. We also studied means by which gel degradation time can be modulated by varying the precursor concentration and molecular weight.

Adhesion reduction after knee surgery in a rabbit model by Hyaloglide, a hyaluronan derivative gel

A randomized controlled experimental trial was performed in a rabbit model of surgical adhesions to investigate the anti-adhesive effects of Hyaloglide, a highly viscous hyaluronan derivative absorbable gel after knee surgery. Twenty New Zealand white rabbits were prepared and randomly divided into two groups of 10 animals each. An intra-articular fibro-adhesive scar was created in the right knee joint of the hind paw of each rabbit using a standardized surgical procedure, and Hyaloglide was administered into the joint cavity of the knee at the end of intervention in the animals belonging to the treatment group. No anti-adhesive treatment was applied in the control group. Additionally, immobilization using a Kirschner wire was applied in order to increase the risk of adhesions. Six weeks after surgery the animals were euthanized and after removal of the immobilization system, adhesions were evaluated both macroscopically and histologically. Results of gross observations using a specific adhesion scoring system showed a significant reduction (p<0.01) of both incidence and severity of adhesions in the hyaluronan-treated group compared to the control group. Histologically, adhesions in the treated group were thinner with less collagenic fibers. In conclusion, Hyaloglide may be considered as a promising absorbable barrier for prevention of post-operative fibrotic adhesions after knee surgery.

Hyaluronic acid prevents peripheral nerve adhesion

The purpose of this study was to clarify the effectiveness of hyaluronic acid (HA) in the prevention of scar formation after neurolysis using a rabbit model. In the first stage, the left sciatic nerve was exposed and elevated along a 3 cm section. Then, the surface of the neural bed was coagulated using a bipolar coagulator. Finally, the sciatic nerve was replaced and fixed to the neural bed with 8/0 nylon sutures, and the wound was closed. In the second stage, the adherent sciatic nerve was re-exposed after 6 weeks. In the neurolysis group, a simple neurolysis was performed. In the HA group, the neurolysis was performed in a surgical field coated with HA from the beginning to the end of the operation. In the steroid group, methyl prednisolone acetate was infiltrated at the end of the neurolysis. In the third stage, electrophysiological, histological and biomechanical measurements were taken 6 weeks after the second stage. While there was no significant difference between the HA and the steroid groups, the electrophysiological functions of the HA and steroid groups were significantly better than that of the neurolysis group. Histology showed that the formation of intraneural and extraneural scar tissue was lowest in the HA group, followed by the steroid and neurolysis groups. The tensile strength required to strip the sciatic nerve from the neural bed of the HA group was significantly less than that of the neurolysis group. However, there was no significant difference between the steroid and neurolysis groups. In conclusion, HA effectively reduced scar formation after neurolysis.

Prevention of postsurgical adhesions with an autocrosslinked hyaluronan derivative gel

BACKGROUND

ACP gel is a new crosslinked derivative of hyaluronic acid (HA) that displays the biocompatibility properties of its original polymer but has a higher viscosity. It has been demonstrated in an animal model that the gel reduces adhesions after gynecological surgery. The aim of the present study was therefore to investigate the efficacy of ACP gel in increasing viscosity for the prevention of adhesions after abdominal surgery.

METHODS

The antiadhesive effect of ACP gel was tested in a controlled randomized study using a standardized animal model of abdominal surgery involving the creation of defects in the parietal peritoneum and muscular fascia and cecal abrasion. The animals (100 female New Zealand white rabbits) were randomly allocated into five treatment groups to receive: ACP gel (1, 2, 4, and 6%) on the injured area or no ACP gel (control). The incidence of adhesions and their grade (score 0-11) were blindly evaluated 10 weeks after surgery.

RESULTS

The percentages of adhesion-free animals were 60, 84, 90, and 84% in the 1, 2, 4, and 6% ACP gel concentration groups, respectively, versus 15% in the control group (P = 0.001). The mean adhesion scores were 3.00 +/- 0.91, 1.37 +/- 0.75, 0.65 +/- 0.45, and 1.16 +/- 0.64 in the 1, 2, 4, and 6% ACP gel groups, respectively, versus 7.70 +/- 0.83 in the control group (P < 0.001).

CONCLUSION

ACP gel prevents postsurgical abdominal adhesions even at a 1% concentration. This finding may be of clinical importance in situations in which large volumes of antiadhesive solution are required.

Reduction of adhesion formation with cross-linked hyaluronic acid after peritoneal surgery in rats

OBJECTIVE

To examine the effectiveness of a cross-linked hyaluronan solution (auto-cross-linked polysaccharide [ACP] gel) for the prevention of postsurgical adhesions.

DESIGN

A randomized blinded study using a rat model of laparotomy.

SETTING

Surgical Research Laboratory in a university medical school.

ANIMAL(S)

Sixty-seven sexually mature rats.

INTERVENTION(S)

Standardized surgical trauma was induced in the rat uterine horn to induce adhesion formation. After trauma, group-1 animals (n = 23) received no treatment, group 2 (n = 21) received noncross-linked hyaluronic acid (HA), and group 3 (n = 23) received cross-linked HA applied on the lesion.

MAIN OUTCOME MEASURE(S)

Six weeks after laparotomy, repeat laparotomy was performed and the adhesions were scored according to Blauer's scoring system.

RESULT(S)

Overall, 84% of the untreated animals and 65% of the animals treated with noncross-linked HA presented with severe adhesions. The mean (+/-SEM) increase in the adhesion score was 2.46+/-0.23 in the untreated group, 2.23+/-0.29 in the group receiving noncross-linked HA, and 1.27+/-0.12 in the ACP gel group.

CONCLUSION(S)

ACP gel holds promise as a novel resorbable biomaterial for the reduction of postoperative adhesions after laparotomy.

Reduction of postsurgical adhesion formation in the rabbit uterine horn model with use of hyaluronate/carboxymethylcellulose gel

OBJECTIVE

To assess the efficacy of a bioabsorbable gel for reducing primary postoperative adhesions.

DESIGN

A randomized, prospective, blinded study.

SETTING

Academic research environment.

ANIMALS

Forty-one New Zealand Rabbits.

INTERVENTION(S)

A chemically modified hyaluronate and carboxymethylcellulose (HA/CMC) gel formulation was applied to a bilateral uterine horn injury. Postoperative adhesions were assessed at a second-look laparoscopy.

MAIN OUTCOME MEASURE(S)

The uterine horn model was shown to be adhesiogenic, with 29 (70%) of 42 untreated uterine horns found to have adhesions. After gel treatment, 22 (55%) of 40 uterine horns were free of adhesions compared with 12 (30%) of 42 controls.

RESULT(S)

Animals treated with HA/CMC gel had significantly reduced postsurgical adhesion scores when compared with controls.

CONCLUSION(S)

Treatment of injured uterine horn with HA/CMC gel resulted in a significant reduction in postoperative surgical adhesions.

A novel hyaluronan-based gel in laparoscopic adhesion prevention: preclinical evaluation in an animal model

OBJECTIVE

To evaluate the effectiveness of a crosslinked hyaluronan solution (ACP gel) in the prevention of postsurgical adhesions in laparoscopic surgery.

DESIGN

A randomized blinded study using a rabbit model in laparoscopic surgery.

SETTING

A standardized surgical trauma in the rabbit uterine horn to induce adhesion formation.

ANIMALS

Sixty-four sexually matured female New Zealand white rabbits weighing 2.5 to 3.0 kg and aged 3-4 months.

INTERVENTION(S)

After trauma, group 1 (n = 22) received no treatment, group 2 animals (n = 20) received oxidized-regenerated cellulose (Interceed [TC7]) in group 3 (n = 22) 5 mL of ACP gel were applied on the lesion.

MAIN OUTCOME MEASURE(S)

Six weeks after laparoscopy, a laparotomy was performed and the adhesions were scored according to Blauer's scoring system.

RESULT(S)

66% of the untreated animals and 85% of the animals treated with Interceed presented with severe adhesions, whereas only 35% of the ACP gel treatment group had significant adhesions. The mean ( +/- SEM) increased adhesion score was 2.24 +/- 0.26 in the untreated group, 2.45 +/- 0.22 in the Interceed group, and was 1.25 +/- 0.28 in the ACP gel group.

CONCLUSION(S)

This study revealed that ACP gel holds promise as a novel resorbable biomaterial for the reduction of postoperative adhesions after laparoscopic surgery.

Reduction of adhesion formation with hyaluronic acid after peritoneal surgery in rabbits

OBJECTIVE

To examine the effect of hyaluronic acid, a high-molecular-weight glucosaminoglycan found in the extracellular matrix, on the formation of adhesions, a major source of postoperative complications.

DESIGN

The ability of hyaluronic acid to reduce adhesion formation was evaluated using a standardized rabbit model. The material was administered i.p. at the end of surgery.

SETTING

University laboratory.

ANIMAL(S)

New Zealand White female rabbits.

INTERVENTION(S)

Intraperitoneal administration of various formulations of hyaluronic acid at the end of surgery.

MAIN OUTCOME MEASURE(S)

One week after surgery, a second laparotomy was performed and the extent of adhesion formation was determined.

RESULT(S)

Five separate molecular weight ranges of hyaluronic acid representing eight viscosities between 1,000 and 12,000 centipoise (CPS) were shown to reduce adhesion formation in this model. All volumes, 1 to 30 mL, of hyaluronic acid tested reduced adhesion formation. In addition, the low-viscosity, low-molecular-weight hyaluronic acid significantly reduced adhesion formation when added to the trauma site or when injected at a site remote from the trauma area.

CONCLUSION(S)

This study showed that hyaluronic acid administered at the end of surgery reduced adhesion formation.

Prevention of postoperative pericardial adhesions using tissue-protective solutions

Repeat cardiac surgical procedures are associated with increased technical difficulty and risk because of the previous formation of dense adhesions between the heart and the surrounding tissues. Dilute solutions of sodium hyaluronic acid (NaHA) and carboxymethyl cellulose (CMC) have been shown to prevent postoperative abdominal and pelvic adhesions and could therefore potentially inhibit adhesion formation following cardiac surgery. Adhesion prevention using 0.1% NaHA, 0.4% NaHA, or 0.1% CMC solutions was examined in a canine abrasion/desiccation pericardial adhesion model (5 animals/group) and compared to 10 animals treated with Ringer's lactate (RL) solution alone. The pericardium and heart were coated with 25 ml of test or control solution prior to and after pericardiotomy, after controlled gauze abrasion, after 30 min of desiccation, and prior to closure. At 6 weeks, animals were reexplored and adhesions were scored in a blinded manner by three to four surgeons using a 0-4 scale. Scores of 2 or greater were considered clinically significant. Mean adhesion scores from the left epicardium were 0.0 in animals treated with 0.1% NaHA, 0.6 in animals treated with 0.4% NaHA or 1% CMC, and 2.3 in animals treated with RL (P < 0.05 Duncan's ANOVA). In addition, none of the animals treated with 0.1% NaHA, 20% of the animals treated with 0.4% NaHA, and 20% of the animals treated with 1% CMC had clinically significant adhesions, whereas 80% of animals treated with RL had such adhesions. Sodium hyaluronic acid and CMC solutions, used as tissue coatings during cardiac surgery, inhibit the formation of undesired postoperative adhesions. Application of these biocompatible polymer solutions during surgery could reduce the technical difficulty and risk of repeat cardiac surgical procedures.

Trends in the development of bioresorbable polymers for medical applications

The gradual shift from biostable prostheses to degradable, temporary implants represents one of the most significant trends in biomaterials research. In view of this trend, medical applications of degradable implant materials were reviewed with special emphasis on orthopedic polymeric implants. Among the polymeric implant materials derived from natural sources, collagen, various polysaccharides such as cellulose, and microbial polyesters have been intensively investigated. Among the synthetic, degradable polymers, aliphatic polyesters such as poly(glycolic acid), poly(lactic acid), poly(caprolactone) and polydioxanone, are most commonly investigated. Only recently, several new classes of polymers such as poly(ortho esters), polyanhydrides, and degradable polycarbonates have been introduced as potential implant materials. A particularly versatile group of new biomaterials with promising engineering properties are the "pseudo"-poly(amino acids), amino acid derived polymers in which conventional peptide bonds have been replaced by various chemical linkages.