A new poly(1,3-trimethylene carbonate) film provides effective adhesion reduction after major abdominal surgery in a rat model

Evaluation of the Effect of an Intraperitoneal Cytostatic-Loaded Supramolecular Hydrogel on Intestinal Anastomotic Healing in an Animal Model

The prognosis of colorectal cancer patients with peritoneal metastases is very poor. Intraperitoneal drug delivery systems, like supramolecular hydrogels, are being developed to improve local delivery and intraperitoneal residence time of a cytostatic such as mitomycin C (MMC). In this study, we evaluate the effect of intraperitoneal hydrogel administration on anastomotic healing. Forty-two healthy Wistar rats received a colonic end-to-end anastomosis, after which 6 animals received an intraperitoneal injection with saline, 18 with unloaded hydrogel and 18 with MMC-loaded hydrogel. After 7 days, animals were euthanized, and the anastomotic adhesion and leakage score were measured as primary outcome. Secondary outcomes were bursting pressure, histological anastomosis evaluation and body weight changes. Twenty-two rats completed the follow-up period (saline: n = 6, unloaded hydrogel: n = 10, MMC-loaded hydrogel: n = 6) and were included in the analysis. A trend towards significance was found for anastomotic leakage score between the rats receiving saline and unloaded hydrogel after multiple-comparison correction (p = 0.020, α = 0.0167). No significant differences were found for all other outcomes. The main reason for drop-out in this study was intestinal blood loss. Although the preliminary results suggest that MMC-loaded or unloaded hydrogel does not influence anastomotic healing, the intestinal blood loss observed in a considerable number of animals receiving unloaded and MMC-loaded hydrogel implies that the injection of the hydrogel under the studied conditions is not safe in the current rodent model and warrants further optimalisation of the hydrogel.

The Controlled Release and Prevention of Abdominal Adhesion of Tannic Acid and Mitomycin C-Loaded Thermosensitive Gel

Postoperative abdominal adhesion is one of the most common complications after abdominal surgery. A single drug or physical barrier treatment does not achieve the ideal anti-adhesion effect. We developed a thermosensitive hydrogel (PPH hydrogel) consisting of poloxamer 407 (P407), poloxamer (P188), and hydroxypropyl methylcellulose (HPMC) co-blended. An injectable thermosensitive TA/MMC-PPH hydrogel was obtained by loading tannic acid (TA) with an anti-inflammatory effect and mitomycin C (MMC), which inhibits fibroblast migration or proliferation. The optimal prescriptions of PPH hydrogels with a suitable gelling time (63 s) at 37 °C was 20% (w/v) P407, 18% (w/v) P188, and 0.5% (w/v) HPMC. The scanning electron microscopy (SEM) revealed that the PPH hydrogel had a three-dimensional mesh structure, which was favorable for drug encapsulation. The PPH hydrogel had a suitable gelation temperature of 33 °C, a high gel strength, and complicated viscosity at 37 °C, according to the rheological analysis. In vitro release studies have shown that the PPH hydrogel could delay the release of TA and MMC and conform to the first-order release rate. Anti-adhesion tests performed on rats in vivo revealed that TA/MMC-PPH hydrogel significantly reduced the risk of postoperative adhesion. In conclusion, the TA/MMC-PPH hydrogel prepared in this study showed an excellent performance in both controlled drug release and anti-adhesive effects. It can be used as a protocol to prevent or reduce postoperative abdominal adhesion.

Temperature-responsive biodegradable injectable polymers with tissue adhesive properties

Injectable polymers (IPs) exhibiting in situ hydrogel formation have attracted attention as vascular embolization and postoperative adhesion prevention materials. While utilizing hydrogels for such purposes, it is essential to ensure that they have appropriate and controllable tissue adhesion property, as it is crucial for them to not detach from their deposited location in the blood vessel or abdominal cavity. Additionally, it is important to maintain gel state in vivo for the desired period at such locations, where large amounts of body fluid exist. We had previously reported on a biodegradable IP system exhibiting temperature-responsive gelation and subsequent covalent cross-link formation. We had utilized triblock copolymers of aliphatic polyester and poly(ethylene glycol) (tri-PCGs) and its derivative containing acrylate group at the termini (tri-PCG-Acryl), exhibiting a longer and more controllable duration time of the gel state. In this study, the introduction of aldehyde groups by the addition of aldehyde-modified Pluronic (PL-CHO) was performed for conferring controllable and appropriate tissue adhesive properties on these IP systems. The IP systems containing PL-CHO, which were not covalently incorporated into the hydrogel network, exhibited tissue adhesive properties through Schiff base formation. The adhesion strength could be controlled by the amount of PL-CHO added. The IP system showed good vascular embolization performance and pressure resistance in the blood vessels. The IP hydrogel remained at the administration site in the abdominal space for 2 days and displayed effective adhesion prevention performance. STATEMENT OF SIGNIFICANCE: Injectable polymers (IPs), which exhibit in situ hydrogel formation, are expected to be utilized as vascular embolization and postoperative adhesion prevention materials. The tissue adhesion properties of hydrogels are important for such applications. We succeeded in conferring tissue adhesion properties onto a previously reported IP system by mixing it with Pluronic modified with aldehyde groups (PL-CHO). The aldehyde groups allowed for the formation of Schiff bases at the tissue surfaces. The tissue adhesion property could be conveniently controlled by altering the amount of PL-CHO. We revealed that the in vitro embolization properties of IPs in blood vessels could be substantially improved by mixing with PL-CHO. The IP system containing PL-CHO also exhibited good in vivo performance for postoperative adhesion prevention.

Use of hypertonic glucose (10%) in the prevention of postoperative adhesions in rats

Purpose

To evaluate the efficacy of hypertonic glucose (10%), alone or in combination with the corticoid dexamethasone, to prevent peritoneal adhesion following hysterectomy in rats.

Methods

Forty-two adult rats underwent hysterectomy with peritoneal lavage: G1 – glucose (10%); G2 – glucose (10%) and dexamethasone 3 mg·kg^–1; and G3 – physiological saline (PS) 0.9%.

Results

In the macroscopic analysis after 14 days, G1 had a median score of 1, G2 of 1, and G3 of 2.5 (p < 0.0001), G3 compared to G1 and G2. There was no difference between groups after 28 days. In the microscopic analysis, the median vascular proliferation after 14 days was 2 for G1, 1 for G2, and 3 for G3 (p = 0.0037, G3 vs. G1 and G2). After 28 days, G1 showed a median vascular proliferation score of 2, G2 of 2.5, and G3 of 3 (p < 0.0001, G3 vs. G1 and G2). Regarding the inflammatory reaction after 14 days, G1 had a median score of 2, G2 of 1, and G3 of 3 (p = 0.7916). After 28 days, G1 had a median score of 0.5 (0–1.75), G2 of 1.5, and G3 of 2.5 (p < 0.0001, G3 vs. the others and G2 vs. G1). In the evaluation of fibrosis after 14 days, G1 had a median score of 1, G2 of 1, and G3 of 2.5 (p < 0.0001, G3 vs. G1and G2). After 28 days, G1 had a median fibrosis score of 1, G2: 2, and G3: 2.5 (p < 0.0001), G3 vs. the others andG2 vs. G1).

Conclusions

The use of hypertonic glucose (10%) solution seems to reduce macroscopic and microscopic pelvic adhesions.

Nintedanib, a multitarget tyrosine kinase inhibitor, suppresses postoperative peritoneal adhesion formation in a rat model

BACKGROUND

Nintedanib is an antifibrotic agent approved by the United States Food and Drug Administration for the treatment of lung fibrosis. This study aimed to evaluate the efficacy of nintedanib for the prevention of postoperative peritoneal adhesion formation in a rat model.

METHODS

Eighteen female Sprague-Dawley rats underwent peritoneal ischemic button creation to induce peritoneal adhesion formation and were randomly allocated to receive 1 mL saline, 50 mg/kg nintedanib, or 100 mg/kg nintedanib by gavage once daily for 7 days. Peritoneal adhesion evaluation and histological and immunochemical examinations were performed on postoperative day 7. Twelve additional Sprague-Dawley rats underwent ileal resection and anastomosis and were randomized to receive saline or 100 mg/kg nintedanib by gavage once daily for 7 days. Anastomotic bursting pressure was assessed on postoperative day 7.

RESULTS

All rats survived until death 7 days after surgery without complications. Peritoneal adhesion incidence, quality, and tenacity were lower in both nintedanib groups than in the saline group (P < .01), but no differences were found between the 2 nintedanib groups (P > .05). Histological and immunochemical results demonstrated less inflammation, fibrosis, collagen, and cell proliferation and fewer myofibroblasts in the ischemic buttons treated with 50 mg/kg or 100 mg/kg nintedanib than in those treated with saline (P < .01), but no difference was found between the 2 nintedanib groups (P > .05). Anastomotic bursting pressures were not significantly different between the saline and nintedanib groups (P > .05).

CONCLUSION

Nintedanib is effective for the prevention of postoperative peritoneal adhesion formation in a rat model.

Postoperative Adhesion Prevention Using a Biodegradable Temperature-Responsive Injectable Polymer System and Concomitant Effects of the Chymase Inhibitor

Postoperative adhesion remains a problem in surgery and causes postoperative complications. Laparoscopic surgery is now common, making it increasingly important to develop injectable formulations of adhesion barriers that can be applied during such surgeries. Temperature-responsive injectable polymer (IP) systems exhibiting a sol-to-gel transition in response to temperature are promising candidates as effective adhesion barriers that can be applied conveniently during laparoscopic surgery. We previously developed IP systems exhibiting temperature-responsive irreversible gelation based on a triblock copolymer of poly(ε-caprolactone-co-glycolic acid) (PCGA) and poly(ethylene glycol) (PEG) (PCGA-b-PEG-b-PCGA: tri-PCG) and a tri-PCG derivative with acrylate groups at the termini (tri-PCG-acryl). A mixture of tri-PCG-acryl micelle solution and tri-PCG micelle solution containing polythiol exhibited an irreversible sol-to-gel transition in response to a temperature increase. The gel contains partial covalent cross-linking, and the degradation and physical properties of these IP hydrogels can easily be controlled by changing the mixing ratio of tri-PCG-acryl in the formulation. In this study, we investigated the effect of physical properties of the IP hydrogel on the efficacy of adhesion prevention using our IP system containing various amounts of tri-PCG-acryl. Our results show that an IP system with lower physical strength and rapid degradation reduces adhesion more effectively. Chymase plays a crucial role in exacerbating adhesion formation, and a peptide derivative-type chymase inhibitor (CI), Suc-Val-Pro-Phe^P(OPh)₂, was previously reported to prevent adhesion. We thus investigated the concomitant use of this CI with our IP system using two methods: separate administration of the CI and IP and entrapping the CI in the IP hydrogel. IP systems with separately administrated CI provided better results than the administration of an IP system entrapping the CI or sole IP systems. These findings suggest that the pharmacological effect of the CI and a physical barrier generated by our IP system effectively prevents adhesion.

Dual dynamically crosslinked thermosensitive hydrogel with self-fixing as a postoperative anti-adhesion barrier

Tissue adhesion is a severe postoperative complication. Various strategies have been developed to minimize postoperative adhesion, but the clinical efficacy is still far from satisfactory. Herein, we present a dual dynamically crosslinked hydrogel to serve as a physical postoperative anti-adhesion barrier. The hydrogel was generated by dynamic chemical oxime bonding from alkoxyamine-terminated Pluronic F127 (AOP127) and oxidized hyaluronic acid (OHA), as well as hydrophobic association of AOP127. Rheological analysis demonstrated that the hydrogel exhibits temperature sensitivity. At 37 °C, it shows much higher modulus and higher stability than the Pluronic F127 hydrogel. Hemolytic assays suggested that the hydrogel undergoes low hemolysis. In addition, it exhibited anti-adhesion to blood cells in blood cell adhesion tests. It also showed an anti-attachment effect to fibroblasts and biocompatibility in vitro cell studies. Macroscopic evaluation and lap-shear tests revealed that the hydrogel has a moderate adhesive capacity to tissue, which is important for self-fixation. A rat model of sidewall defect-bowel abrasion was established to evaluate the anti-adhesion effect in vivo. The gross observation and pathological analysis revealed a significant reduction in postoperative peritoneal adhesion in the AOP127/OHA hydrogel-treated group than those treated with normal saline or Pluronic F127 hydrogel. Hence, the dual dynamically crosslinked hydrogel with self-fixable capacity may be suitable as a physical barrier for postoperative adhesion prevention. STATEMENT OF SIGNIFICANCE: Despite the development of numerous postoperative anti-adhesion barriers, their anti-adhesion efficacy is still limited in clinical trials due to poor tissue adhesion and rapid clearance from injured areas. Herein, we have developed a dual dynamic crosslinked hydrogel, generated by dynamic oxime bonds and hydrophobic interactions. The hydrogel is temperature-sensitive and demonstrates moderate tissue adhesion capacity, which allows for self-fixation when applied to defects. The introduction of dynamic covalent bonds improves the stability of the hydrogel. Moreover, the hydrogel not only displays appropriate hemocompatibility, cytocompatibility and anti-adhesion of blood cells and fibroblasts, but it also effectively contributes to preventing postoperative peritoneal adhesions in vivo. Hence, this dual dynamic crosslinked hydrogel may have potential applications as a physical barrier in clinical practice.

Baseline performance of the ischaemic button model for induction of adhesions in laboratory rats

The ischaemic button model is frequently used for the induction of adhesions in laboratory rats. Male rats are often used because of the common belief that the peritesticular (intra-abdominal) fat in males facilitates adhesion formation, although this theory is not evidence based. Comparing the model’s performance in both sexes is an important aspect of refining animal experiments. The aim of this study is to compare baseline performance of the modified ischaemic button model in both male and female rats. Follow-up was 1 week and noted endpoints were intra-abdominal adhesion formation and differences in welfare assessment. A total of 192 ischaemic buttons (96 male/96 female) were created in 24 Wistar Han rats (12 male/12 female). After 1 week of follow-up, 93 buttons survived in the male group (96.9%) compared with 91 in the female group (94.8%) (p = 0.409). In the male group, 85 out of 93 (91.4%) buttons induced adhesions compared with 84 out of 91 (92.3%) in the female group (p = 0.881). All but one animal had a Zühlke score of 3. There were no clinically relevant differences in welfare scores. Male animals increased in weight significantly faster compared to females (p < 0.001), after correcting for physiological growth. The ischaemic button model resulted in equal quality and quantity of intra-abdominal adhesions in both male and female Wistar Han rats. Both male and female Wistar Han rats are suitable for the induction of experimental adhesions in the ischaemic button model.

Comparison of Poly(l-lactide-co-ɛ-caprolactone) and Poly(trimethylene carbonate) Membranes for Urethral Regeneration: An In Vitro and In Vivo Study

Urethral defects are normally reconstructed using a patient's own genital tissue; however, in severe cases, additional grafts are needed. We studied the suitability of poly(l-lactide-co-ɛ-caprolactone) (PLCL) and poly(trimethylene carbonate) (PTMC) membranes for urethral reconstruction in vivo. Further, the compatibility of the materials was evaluated in vitro with human urothelial cells (hUCs). The attachment and viability of hUCs and the expression of different urothelial cell markers (cytokeratin 7, 8, 19, and uroplakin Ia, Ib, and III) were studied after in vitro cell culture on PLCL and PTMC. For the in vivo study, 32 rabbits were divided into the PLCL (n = 15), PTMC (n = 15), and control or sham surgery (n = 2) groups. An oval urethral defect 1 × 2 cm in size was surgically excised and replaced with a PLCL or a PTMC membrane or urethral mucosa in sham surgery group. The rabbits were followed for 2, 4, and 16 weeks. After the follow-up, urethrography was performed to check the patency of the urethra. The defect area was excised for histological examination, where the epithelial integrity and structure, inflammation, and fibrosis were observed. There was no notable difference on hUCs attachment on PLCL and PTMC membranes after 1 day of cell seeding, further, the majority of hUCs were viable and maintained their urothelial phenotype on both biomaterials. Postoperatively, animals recovered well, and no severe strictures were discovered by urethrography. In histological examination, the urothelial integrity and structure developed toward a normal urothelium with only mild signs of fibrosis or inflammation. According to these results, PLCL and PTMC are both suitable for reconstructing urethral defects. There were no explicit differences between the PLCL and PTMC membranes. However, PTMC membranes were more flexible, easier to suture and shape, and developed significant epithelial integrity.

Work of separation - A method to assess intraperitoneal adhesion and healing of parietal peritoneum in an animal model

BACKGROUND

Adhesion grades and adhesion breaking strength are widely used to assess severity of intraperitoneal adhesion in animal models. However, the results of adhesion grades have the large deviations due to vary personal experience. Adhesion breaking strength ignores the details of adhesion. This study introduced work of separation, the energy consumption during breakage of adhesion, to better evaluate intraperitoneal adhesion.

METHODS

The intraperitoneal adhesion was induced by traumas created at rat cecum and adjacent abdominal wall. The wounds were coated with or without sodium hyaluronate. On day 14 after surgery, the intraperitoneal adhesion was assessed by adhesion density grade, adhesion area grade, adhesion breaking strength and work of separation. The healing of parietal peritoneum was evaluated with histology, adhesion breaking strength and work of separation.

FINDINGS

The severity of adhesion evaluated with work of separation was consistent with those obtained from the grades of adhesion density, adhesion area and adhesion breaking strength. Work of separation had a linear correlation with adhesion breaking strength. Furthermore, the results of histological examination and work of separation demonstrated that adhesion significantly delayed healing process of abdominal wall muscles.

INTERPRETATION

Work of separation can quantify all intraperitoneal adhesions rather than the major one by other methods. It is a more precise method to evaluate postoperative adhesions, especially those including adipose tissue. This study proved that work of separation could be a reliable method to assess intraperitoneal adhesion and tissue healing.

Comparison of three different application routes of butyrate to improve colonic anastomotic strength in rats

INTRODUCTION

Despite extensive research, anastomotic leakage (AL) remains one of the most dreaded complications after colorectal surgery. Since butyrate enemas are known to enhance anastomotic healing, several administration routes have been explored in this study.

METHODS

Three intraluminal approaches involving butyrate were investigated: (1) butyrin-elucidating patch, (2) a single injection of hyaluronan-butyrate (HA-But) prior to construction of the proximal anastomosis and (3) rectal hyaluronan-butyrate (HA-But) enemas designed for distal anastomoses. The main outcome was AL and secondary outcomes were bursting pressure, histological analysis of the anastomosis, zymography to detect MMP activity and qPCR for gene expression of MMP2, MMP9, MUC2 and TFF3.

RESULTS

Neither the patches nor the injections led to a reduction of AL in experiments 1 and 2. In experiment 3, a significant reduction of AL was accomplished with the (HA-But) enema compared to the control group together with a higher bursting pressure. Histological analysis detected only an increased inflammation in experiment 2 in the hyaluronan injection group compared to the control group. No other differences were found regarding wound healing. Zymography identified a decreased proenzyme of MMP9 when HA-But was administered as a rectal enema. qPCR did not show any significant differences between groups in any experiment.

CONCLUSION

Butyrate enemas are effective in the enhancement of colonic anastomosis. Enhanced butyrate-based approaches designed to reduce AL in animal models for both proximal and distal anastomoses were not more effective than were butyrate enemas alone. Further research should focus on how exogenous butyrate can improve anastomotic healing after gastrointestinal surgery.