The new adhesion prophylaxis membrane A-part--from in vitro testing to first in vivo results

Standard Biocompatibility Studies Do Not Predict All Effects of PVA/CMC Anti-Adhesive Gel in vivo

Purpose: PVA/CMC (polyvinyl alcohol/carboxymethyl cellulose) hydrogel fulfills various physiochemical properties required for an adhesion barrier and has shown good anti-adhesion properties in previous in vivo studies. In this investigation, we assessed the in vitro and in vivo biocompatibility of PVA/CMC gel and compared this to the functionality and promotion of wound healing for two surgical indications. Methods: Standardized ISO10993 in vitro and in vivo biocompatibility studies, comprising cytotoxicity, genotoxicity, acute systemic toxicity, delayed contact and maximization sensitization test, intracutaneous reactivity and local muscle implantation, were performed on PVA/CMC gel. In the functional studies, PVA/CMC gel was applied - on the one hand - to a rabbit abdominal wall model enforced with a polypropylene mesh for testing the anti-adhesion properties and - on the other hand - to an end- to-end anastomosis model that was selected for surveying potential influences of different dosages of PVA/CMC gel on anastomotic wound healing. Results: The ISO10993 methods indicated generally good biocompatibility properties, such as the absence of cytotoxic and mutagenic effects as well as no signs of systemic toxicity and sensitization potentials. No irritation effects were observed after the intracutaneous injection of lipophilic PVA/CMC sesame oil extract. However, the injection of hydrophilic PVA/CMC physiologic saline extract induced slight irritation. Following rabbit muscle implantation of the PVA membrane for 2, 4, 12, 26 and 52 weeks, a slight irritant effect was observed at 12 weeks due to the peak of phagocytosis. In the functionality tests, PVA/CMC gel showed good anti-adhesive effects in the abdominal wall model enforced with the mesh, with significantly lower and less tense adhesions compared to the untreated control. However, moderate signs of inflammation, especially in the spleen were observed after the intra-abdominal implantation of 3.3 ml PVA/CMC gel per kg body weight. In the end-to-end anastomosis model, PVA/CMC gel had no influence on wound healing. For dosages of 1-6 ml gel per treatment, no signs of intestinal leaks were detected, and tensile strength was equal to that of the untreated control, but again more moderate signs of inflammation in the spleen were observed at a dosage >3 ml. Conclusion: Comparing the standardized ISO10993 methods, anti-adhesive PVA/CMC gel displays good biocompatibility. However, those methods do not seem to be sensitive enough because the rabbit abdominal wall and the end-to-end anastomosis models display more effects with respect to the dosage and routes of the intra-abdominal resorption of PVA/CMC gel - with the recommended <2 ml PVA/CMC gel per kg body weight as a secure dosage.

A-Part Gel, an adhesion prophylaxis for abdominal surgery: a randomized controlled phase I-II safety study [NCT00646412]

Background

Intra-abdominal surgical intervention can cause the development of intra-peritoneal adhesions. To reduce this problem, different agents have been tested to minimize abdominal adhesions; however, the optimal adhesion prophylaxis has not been found so far. Therefore, the A-Part^® Gel was developed as a barrier to diminish postsurgical adhesions; the aim of this randomized controlled study was a first evaluation of its safety and efficacy.

Methods

In this prospective, controlled, randomized, patient-blinded, monocenter phase I–II study, 62 patients received either the hydrogel A-Part-Gel^® as an anti-adhesive barrier or were untreated after primary elective median laparotomy. Primary endpoint was the occurrence of peritonitis and/or wound healing impairment 28 ± 10 days postoperatively. As secondary endpoints anastomotic leakage until 28 days after surgery, adverse events and adhesions were assessed until 3 months postoperatively.

Results

A lower rate of wound healing impairment and/or peritonitis was observed in the A-Part Gel^® group compared to the control group: (6.5 vs. 13.8 %). The difference between the two groups was −7.3%, 90 % confidence interval [−20.1, 5.4 %]. Both treatment groups showed similar frequency of anastomotic leakage but incidence of adverse events and serious adverse events were slightly lower in the A-Part Gel^® group compared to the control. Adhesion rates were comparable in both groups.

Conclusion

A-Part Gel^® is safe as an adhesion prophylaxis after abdominal wall surgery but no reduction of postoperative peritoneal adhesion could be found in comparison to the control group. This may at least in part be due to the small sample size as well as to the incomplete coverage of the incision due to the used application.

Trial Registration: NCT00646412

Effects of new anti-adhesion polyvinyl alcohol gel on healing of colon anastomoses in rats

BACKGROUND

Adhesions follow abdominal surgery with an incidence as high as 95%, resulting in invalidating complications such as bowel obstruction, female infertility, and chronic pain. Searches have been performed for a safe and effective adhesion barrier; however, such barriers have impaired anastomotic site healing. The primary aim of this study was to investigate the effect of a new adhesion barrier, polyvinyl alcohol gel, on healing of colonic anastomoses using a rat model.

METHODS

Thirty-two Wistar rats were divided in two groups. In all animals, an anastomosis was constructed in the ascending colon. The first group received no adhesion barrier, whereas in the second group, 2 mL of polyvinyl alcohol gel (A-Part Gel(®); Aesculap AG, Tuttlingen, Germany) was applied circularly around the anastomosis. All animals were sacrificed on the seventh post-operative day, and the abdomen was inspected for signs of anastomotic leakage. The anastomotic bursting pressure, the adhesions around the anastomosis, and the collagen content of the excised anastomosis were measured.

RESULTS

No significant differences were observed between the two groups in the incidence of anastomotic leakage, the anastomotic bursting pressure (p=0.08), or the collagen concentration (p=0.91). No significant reduction in amount of adhesions was observed in the rats receiving polyvinyl alcohol gel.

CONCLUSIONS

This experimental study showed no significant differences in anastomotic leakage, anastomotic bursting pressure, or collagen content of the anastomosis when using the adhesion barrier polyvinyl alcohol around colonic anastomoses. The barrier did not prevent adhesion formation.

A hydrogel for adhesion prevention: characterization and efficacy study in a rabbit uterus model

OBJECTIVE

Postoperative peritoneal adhesions following gynaecological surgery remain a clinically relevant problem. One approach to prevent adhesion formation is to apply physical barriers such as hydrogels.

STUDY DESIGN

A physically crosslinked polyvinyl alcohol and carboxymethylcellulose (PVA/CMC) hydrogel (A-Part) was characterized in vitro. Three different traumatization methods were evaluated in a rabbit uterine study. To determine its anti-adhesion efficacy, the hydrogel was first tested in an in vivo pilot study and then in a larger trial to compare it with icodextrin 4% solution (Adept) and controls.

RESULTS

Rheological measurements showed an increased elasticity of the hydrogel after freezing. In vivo experiments revealed a clear reduction in incidence, extent and severity of adhesions compared to the icodextrin 4% solution and the untreated control group.

CONCLUSIONS

These results warrant further investigation of the PVA/CMC A-Part hydrogel in clinical trials focused on gynaecological procedures.

A prospective, randomised, controlled, double-blind phase I-II clinical trial on the safety of A-Part Gel as adhesion prophylaxis after major abdominal surgery versus non-treated group

Background

Postoperative adhesions occur when fibrous strands of internal scar tissue bind anatomical structures to one another. The most common cause of intra-abdominal adhesions is previous intra-abdominal surgical intervention. Up to 74% of intestinal obstructions are caused by post surgical adhesions. Although a variety of methods and agents have been investigated to prevent post surgical adhesions, the problem of peritoneal adhesions remains largely unsolved. Materials serving as an adhesion barrier are much needed.

Methods/Design

This is a prospective, randomised, controlled, patient blinded and observer blinded, single centre phase I-II trial, which evaluates the safety of A-Part^® Gel as an adhesion prophylaxis after major abdominal wall surgery, in comparison to an untreated control group. 60 patients undergoing an elective median laparotomy without prior abdominal surgery are randomly allocated into two groups of a 1:1- ratio. Safety parameter and primary endpoint of the study is the occurrence of wound healing impairment or peritonitis within 28 (+10) days after surgery. The frequency of anastomotic leakage within 28 days after operation, occurrence of adverse and serious adverse events during hospital stay up to 3 months and the rate of adhesions along the scar within 3 months are defined as secondary endpoints. After hospital discharge the investigator will examine the enrolled patients at 28 (+10) days and 3 months (±14 days) after surgery.

Discussion

This trial aims to assess, whether the intra-peritoneal application of A-Part^® Gel is safe and efficacious in the prevention of post-surgical adhesions after median laparotomy, in comparison to untreated controls.

Trial registration

NCT00646412