A narrative review on pathophysiology and the trends in A narrative review on pathophysiology and the trends in preventing colon anastomotic leakage in animals preventing colon anastomotic leakage in animals

Intestinal healing normally proceeds through three stages: the in ﬂ ammatory, proliferative, and maturation stages. Dehiscence, a disastrous outcome of intestinal anastomosis surgery, usually happens during the in ﬂ ammatory stage of recovery, when the anastomotic technique (suture or staple line) has the greatest in ﬂ uence on the biomechanical strength of the anastomosis. Because of the severe systemic abnormalities and ﬁ nancial load brought on by septic peritonitis and the need for a second surgery, the ensuing septic peritonitis is linked to a staggering morbidity rate of up to 85%. Despite the relatively high frequency of anastomosis surgeries, anastomotic leaks pose a deadly risk to colon anastomosis surgery due to increased morbidity and mortality. Several therapies have been developed to reduce the possibility of colon anastomotic leaks and to facilitate the healing of anastomotic wounds. Many treatments have been described to address these unfortunate circumstances and speed up the healing process because anastomotic leakages might have potentially lethal effects. We have produced a combined evaluation that includes some of the most excellent and recent methods for using various materials for colonic anastomotic leaking and the healing process in order to better understand the procedures taken to treat this issue. This article aims to provide a general overview of colonic anastomotic leakage, as well as new approaches to prevent and manage the problem. It also aims to improve anastomotic healing for a broader readership, with a focus on biomedical engineers.


Introduction
W ithin the field of general and gastrointes- tinal surgery, one of the most common performed surgical operations is intestinal anastomosis [1].Colon anastomoses are more difficult gastrointestinal surgical procedures than anastomoses of the stomach and small intestine [2].In terms of the equilibrium between the creation and destruction of collagen and the intestinal flora, anastomoses of the gastrointestinal system in other localizations are not like those of the large bowel [3].
After colorectal anastomosis, anastomotic insufficiency is a potentially dangerous clinical complication that occurs 3e20% of the time and increases postoperative morbidity and mortality [4].In the small intestine, anastomosis leakage occurs at a rate of 1%, whereas in the large intestine, it can reach a rate of 30% [5e7].Preventing gastrointestinal anastomotic leakage is the primary aim of gastrointestinal surgery.The most significant factor influencing hospital stay duration, morbidity, and mortality is anastomotic leak [8].Regretfully, the problem still exists now and probably will for some time.Managing anastomotic leaks can be challenging and can irritate surgeons.Nonetheless, this review focuses on colonic anastomotic leakage and its therapies because a significant portion of anastomotic leakage cases occur in the colon-related region of the gastrointestinal system [9].
A colon resection, also known as a colectomy, is a surgical surgery used to treat or prevent diseases and disorders that affect the colon by removing all or part of the large intestine.These disorders could be Crohn's disease, diverticulitis, cancer, or intestinal blockages.Open colectomy was once seen to be the gold standard procedure; but, less invasive laparoscopic colectomy has gained popularity recently [10].
Anastomotic leakage (AL) is one of the deadliest side effects that results in a higher rate of morbidity and mortality after surgery.After colonic resection surgeries, an artificial connection must be created via a process known as anastomosis.This process can result in anastomotic dehiscence, or AL, which has occurred at different rates in the past.However, historical investigations have documented leak rates of up to 30% [11].'Leak of luminal contents from a surgical join between two hollow viscera' is the definition of a colonic anastomotic leak [12].If the luminal contents were to spill into the abdominal cavity, patients may suffer from multiple organ failure, fever, abscess, septicemia, and metabolic problems [12].This may lead to a more frequent need for follow-up procedures, a higher chance of local recurrence, higher rates of morbidity and mortality, and overall worse quality of life [13].

Are colorectal affections being interesting in veterinary medicine?
In cats and dogs, colonic affection are very common condition.Veterinary Medicine states that the most common etiologies in young animals are parasitic (infectious), alimentary (food intolerance, fiberresponsive colopathy), or breed-related (granulomatous colitis) [14].
Anastomoses are frequently needed after colorectal surgery, for benign illnesses such as diverticulitis or inflammatory bowel disease as well as malignancy operations.Thus, the emergence of an AL is the most feared consequence for colorectal surgeons.Since AL is still an unsolved issue, it is crucial to lessen its manifestation or clinical impact [15].
Due to the higher rate of leakage, slower pace of healing, and lower collagen content in repaired tissue, the large intestine and the rectum are the most troublesome portions of the gastrointestinal tract [16,17].Reduced collagen content in healed anastomoses results in decreased mechanical strength and a higher risk of leaking [18].

Definition and different methods
The process of joining two intestinal segments to restore intestinal continuity is known as intestinal anastomosis [19].Since the early 1800s, intestinal anastomoses have been used in surgical procedures [20].The most frequent procedure for gut reconstruction is called gastrointestinal anastomosis [21,22].To complete intestinal anastomoses, a variety of methods, supplies, and tools have been created and tested.These methods include sutureless anastomosis, stapled procedures, and handsewn suture techniques [23].The continuous and interrupted suture techniques are used during manual bowel anastomosis.Intestinal anastomosis currently typically involves interrupted sutures [24,25].Anastomoses problems persist, and the consequences are unsatisfactory, regardless of the technique used for the patients or the variety of these procedures [26].

Large bowel anastomosis
In terms of the balance between the creation and destruction of collagen and the intestinal flora, anastomoses of the gastrointestinal system in other localizations are not like those of the large bowel.The large intestine has a higher risk of anastomosis leakage than the other locations because of a higher concentration of pathogenic bacteria and a higher level of collagenase enzyme activity.In the small intestine, anastomosis leakage is seen at a rate of 1%, whereas in the large intestine, it can reach a rate of 30% [5e7].

The physiology of colon anastomosis healing process
There are four layers that make up the colon's intestine wall: the mucosa, submucosa, muscularis propria, and serosa.Because it has the highest tensile strength among these four layers, the submucosadwhich is primarily made up of collagen and elastin fibersdhas long been considered to be the most crucial layer in the healing of wounds.After gastrointestinal surgery, submucosa fibroblasts become active and begin to deposit collagen during the first three to four days [27].
The surrounding healthy tissue's strength and resilience have already been absorbed by the newly formed tissue after just five days.About 90% of the wound has healed and the collagen has nearly completely reorganized after four weeks following surgery.Thus, for healthy individuals, the first few days following surgery have the highest risk for AL [28,29].But since the other layers are as important to the healing process of wounds, their contribution should not be overlooked.While the relationship between bacteria, mucus, and the mucosal layer appears crucial to maintain homeostasis in which anastomotic healing can proceed, the serosa seems to be important in providing a matrix for fibroblasts [27].
Normal wound healing also requires the production of granulation tissue, which contains fibro vascular tissue made up of collagen, fibroblasts, and blood vessels [30].The process of wound healing depends on angiogenesis since the wound needs to be supplied with nutrients, oxygen, and immune cells.Wastes also need to be taken out of the area where injuries occurred.Three days after an injury, new blood arteries and capillaries often develop, ensuring adequate tissue perfusion.Furthermore, normal gut function, which involves the transfer of nutrients from the mucosa into the bloodstream, depends on capillary development.
A number of coordinated and integrated physiological regenerative mechanisms involving cells, their environment, and the extracellular matrix are necessary for the dynamic process of anastomotic wound healing [31e33].Successful anastomosis healing has been linked to a number of systemic and local variables [34].A crucial component in regulating the following perfusion is the surgical mobility of the intestine [35,36] and the development of anastomotic leakage is significantly influenced by disturbance of the blood supply.
A healthy blood supply plays a crucial role in anastomotic healing locally because it is necessary for the production of collagen and the development of infection resistance [37].When compared with normal mucosa, colonic anastomoses have less blood flow along the suture line [35].One of the essential elements of anastomotic healing is the angiogenesis or development of new vessels [38].However since morbidity and death are so high, no matter what kind of treatment is used, the avoidance of anastomotic leakage is more crucial than any kind of treatment [39].

The associated factors related to poor bowel anastomosis healing
One of the biggest challenges in gastrointestinal tract surgery for older and co-morbid patients is poor intestinal anastomosis recovery [40,41].Poor healing and subsequent problems were caused by the leakage at the intestinal anastomotic lesion.Poor bowel anastomosis healing can result from a variety of local and systemic factors, such as malnutrition, blood transfusion, hypovolemic shock, immune deficient state, poorly managed diabetes, jaundice, or local infections.Anastomotic tension, poor apposition of wound edges, radiation injury, and distal obstruction are examples of local factors [42,43].
Inadequate wound healing at intestinal anastomotic sites may result in more severe and potentially fatal consequences, more surgeries, longer hospital stays and costs, discomfort, and a higher death rate [44e48].
An unresolved intestinal surgery issue is the failure of an intestinal anastomosis.Nonetheless, a lot of research is being done to reduce these possibly fatal consequences [49], patients with low nutritional status are more likely to experience problems, according to several research.Healing is further hampered by inadequate blood flow, excessive resection, high strain at the anastomotic site, and insufficient mobility of the anastomosis.Our search of the 'perfect' colon anastomosis requires exacting technique with subtle adjustments based on our knowledge of surgical principles as well as the use of pertinent new technologies [50].

Complications of bowel anastomosis healing
Although the topic of intestinal anastomosis healing is still of interest for research, anastomotic problems are still widespread, especially in elderly patients with co-morbid conditions or in emergency situations [51].When healing is insufficient, local anastomosis problems include dehiscence, leaks, and fistulas; when healing is excessive, they include stricture development and lumen stenosis [26].
Leakage, hemorrhage, and stenosis are the three main consequences of intestinal anastomosis.Leakage is the most serious and frequent complication among them, and it also has the highest fatality rate.Leakage is 1% likely to occur following small intestine proximal anastomoses, but 16% likely to occur following low anterior colonic resections [6,7].One of the most feared side effects following colorectal surgery is an anastomotic leak, which can occur anywhere from three to 5 days after surgery and have disastrous results [52].Anastomosis-induced sepsis is responsible for about 50% of postoperative deaths [53,54].
The frequency of anastomosis leakage after colonic resection was reported to range from 0.5% to 30% in a multi-center research [1,5,39].According to a different study, anastomotic leak deaths usually occur in the range of 10e15% [41].Although the surgical technique has continuously improved, the described incidence of gastrointestinal anastomosis leakage ranges from 2 to 10% and is related to increased morbidity (20e30%) and mortality (7e12%) [55,56].Furthermore, the creation of gastrointestinal fistulas is a common consequence following gastrointestinal anastomosis, with an incidence that may reach 17.4% [57].
Colonic anastomosis leakage, as previously mentioned, is caused by several factors and this problem raises mortality rates [58].Anastomotic leakage following colorectal resections occurs in 3e23% of cases [59].This anastomotic dehiscence is a significant obstacle to anastomotic repair for a variety of reasons.It has been attempted to minimize this difficulty by reinforcing the anastomosis using synthetic or biological materials.One of the main issues that persists after abdominal procedures is the production of peritoneal adhesions as a result of tissue ischemia, inflammation, fibrin organization, and collagen synthesis [60].Various agents have been used to reduce each of these steps [61].

New treatment modalities for preventing anastomotic leakage and promotion the healing process
Treatment alone, however, is insufficient because of the extremely high rates of morbidity and death; therefore, preventing anastomotic leaking is more crucial than receiving treatment [39].The key components of a successful anastomosis include tension-free anastomosis, superior sutures, and refined surgical methods.The anastomosis healing process is directly impacted by unchangeable patient characteristics, such as advanced age, underlying disease, co-morbid diseases, and emergency patients.These factors are still quite significant.For these patients at high risk, new treatment approaches are required to stop anastomosis leaking [26].
Injection the anastomotic wound by growth factors [52], soaking suture material with promoted healing agent [62] and wrapping anastomotic wound with shielding materials [20,26,63] are now the best techniques applied for prevention of anastomotic leakage and amelioration its healing process.
The study done by Ref. [52] concluded that, by stimulating angiogenesis at the anastomosis, VEGF injection to colonic anastomosis strengthens the anastomosis and speeds up wound healing.In light of this, local VEGF administration is thought to reduce the possibility of anastomotic leakage, Ref. [62] shown that the environment created by AgNPs-coated suture may be perfect for fostering intestinal anastomotic recovery, for its therapeutic potential to be realized, more research is required [63].Effectively shown that using nano-fibrous scaffolds made of polycaprolactone (PCL) and polylactic acid (PLCL) to reinforce an anastomosis on the GI tract is safe.Sulu and colleagues found that giving rabbits oral shark cartilage accelerated anastomotic healing and had no negative effects, such as bacterial translocation [3].The study done by Ref. [20] demonstrated that the use of polypropylene mesh wrapped around anastomotic intestinal incisions can significantly lower the risk of leaking, as well omentoplasty appears to reduce the rate of overall and clinical anastomotic leakage [64] the most frequent and serious complication of intestinal anastomoses.
The rates of gastrointestinal anastomotic complications have not yet decreased to a minimal degree despite current medical advancements in surgical procedures and postoperative care [65].Therefore, new methods of avoiding anastomotic problems are deemed necessary and eagerly awaited.
A number of variables, such as the anastomotic technique and the existence of septic peritonitis, might affect how the intestines heal after surgery [66,67].Additionally, a number of systemic and local variables can interfere with the healing of wounds, increasing pain and suffering as well as occasionally causing a threat to life.Thankfully, a variety of methods, including tissue transplantation, gene therapy, growth factors, and stem cell therapy, can be employed to either avoid the disruption of wound healing or to encourage the healing and regeneration of injured tissues [33].
The majority of researchers working today focus on cellular aspects of wound repair.Growth factors (GFs) are recognized to play a significant role in controlling the various cellular processes involved in wound healing.GFs promote poor wound repair and speed up the healing of normal tissues, according to a plethora of clinical studies [68,69].In surgical practice, regeneration of the intestinal anastomosis is unquestionably important because a break in the continuity of the intestinal anastomosis results in wound disruption and a high rate of morbidity and mortality [70].
Studies have shown that using a range of naturally occurring biological regeneration materials such as platelet capabilities [26] can enhance the healing process, in addition, some of bioactive molecules like chitosan (CS) [71] and nanomaterial such silver nanoparticles (AgNPs) [72].Fibrin sealant, collagen patches, and omentoplasty are the most studied biomaterials [15].
We have applied an effective method to prevent leakages from anastomoses, diminish adhesions, and provide external mechanical support to the anastomotic outline in which the anastomotic wound is completely encircled with L-PRF that loaded with CS and CS-AgNPs.We have tried this performance in rabbits after the routine of a single layer of standard anastomosis to the ascending colon.In addition, we aimed to explain the possible expected bio-stimulatory synergistic effects between L-PRF and CS.AgNPs on colon anastomosis healing in rabbits.

The most studied biomaterials for regeneration of bowel anastomosis
The most crucial element in blood coagulation is platelets, which accelerate the healing process by releasing certain cytokines [73].The inflammatory cells and platelets release cytokines that stimulate the production of new blood vessels and collagen, which determine the healing response in a dynamic balance with collagen breakdown [74].As the first blood cells to respond to a wound, platelets stimulate tissue regeneration by releasing growth factors (GFs) such as insulin-like growth factor (IGF), vascular endothelial growth factor, fibroblast growth factor (FGF), platelet-driven growth factor (PDGF), and transforming growth factor (TGF-b), among other active agents that are well-known sources of healing [65,75].These factors are wellknown for their mitogenic and chemotactic qualities, which stimulate angiogenesis and encourage growth and vascular fibroblast proliferation, which in turn increases collagen production.This process promotes wound healing [76e78].
To promote the production of granulation tissue and epithelialization, platelet concentration must be greater than four to five times the usual intravascular platelet amount [79e82].Different methods of platelet concentrates could have an effective role in wound healing [83].When exposed to injured tissues, platelets naturally become more driven.It has been found that platelets play a major and noticeable part in the initiation and maintenance of wound healing [84].
Numerous preparations high in platelets have been tested to accelerate tissue repair, with promising outcomes.Platelets are trapped in PRF, a fibrin matrix that has the potential to function as a resorbable membrane [85].The fibrin matrix may first aid in the exterior anastomosis.It then promotes angiogenesis, aids in immunity, directs the covering of wounded tissues, and influences the metabolism of fibroblasts and epithelial cells.Fibrin also functions as the angiogenesis's natural regulator.Hemostasis, wound sealing, graft stabilization, and wound healing can all be aided by it [85,86].
The solid fibrin biomaterial known as Leukocyte Platelet-Rich Fibrin (L-PRF) contains leukocytes.Nearly all of the platelets and over 50% of the leukocytes (monocytes, lymphocytes, and granulocytes) from the original blood harvest are present in the L-PRF clot, which also has a distinct three-dimensional distribution of the platelets and leukocytes and a robust fibrin architecture [85].According to reports, these cells' interactions with the fibrin matrix cause a gradual release of growth factors, which in the early stages of the process may improve wound healing [87,88].
In reconstruction surgery, the L-PRF has been widely used as a viable fibrin biomaterial to promote tissue repair.In addition to several adhesion factors, it contains a significant amount of platelets, leukocytes, stem cells, cytokines, and growth factors like PDGF, TGF-b, IGF, EGF, VEGF, and interleukins-1b, 4 and 6.This solid fibrin preserves the morphological features and characteristics of these cytokines and growth factors, which can be released gradually over up to 15 days [70,89].We have designed a unique performance in which the anastomotic outline is completely wrapped with L-PRF to stop leaks from anastomoses as coating of intestinal anastomoses helps for prevention of postoperative leakage [90].We have experimented with this method on rabbits that were given a single layer of conventional anastomosis to the ascending colon.The purpose of this technique was to provide the anastomotic contour with external mechanical support.Furthermore, our goal was to clarify how L-PRF affects the repair of colon anastomoses in rabbits.
We seek to identify some of these effects on colon anastomosis healing in rabbits based on the idea that there may be synergistic or potentiation effects between certain biological preparations and nanoparticles, such as L-PRF, chitosan, and AgNPs).
Chitosan is a copolymer comprising glucosamine and N-acetyl glucosamine units connected by 1e4 glucosidic linkages.It is the main derivative of chitin, a naturally occurring polysaccharide [91].Because of its exceptional biocompatibility, chitosan is a biopolymer that is highly recommended for use as a revolutionary biomatrix in clinical applications, including drug delivery devices, tissue engineering scaffolds, and bioactive dressings.Additional intriguing features include superior biodegradability, antibacterial activity, and rapid wound-healing capabilities.It is also nontoxic and non-immunogenic [92,93].
Chitosan has a special group of biological characteristics.Because the biopolymer is biocompatible, the main draws are acceptable biodegradation products and biocompatibility [94,95].Chitosan possess excellent antimicrobial properties [96].Numerous studies have shown that chitosan possesses antimicrobial and analgesic qualities, accelerates wound healing, and promotes connective tissue regeneration [73,97].In the realms of medicine, cosmetics, tissue engineering, biochemical separation systems, and wound dressings, chitosan and its derivatives are widely utilized [98].
Chitosan and its derivatives have been the subject of recent publications that have shown off several special qualities, including hemostatic qualities, appropriate biodegradability, good biocompatibility, and promising microbial activities.As a result, chitosan has been utilized in numerous vital domains, including biotechnology, pharmaceuticals, the food and medical industries, and environmental protection [99e101].Chitosan and its derivatives can activate immunological regulatory responses, stimulate phagocytes, and cause natural killer cells to produce cytokines [102].
Chitosan can be made into gel, sheets, and solutions of nanoparticles, among other forms.The discipline of biomedicine has been paying more and more attention to nanomaterials in recent years [103].Chitosan nanoparticles enhance the stability of the loaded medications and regulate the speed of drug release while retaining the biological characteristics of chitosan [104].When used as a possible gene delivery technology, chitosan nanoparticles are safe, biodegradable, and simple to produce DNA or protein complexes [105].When combined with other materials, chitosan nanoparticles maintain the biocompatibility and biodegradability of chitosan, which is a valuable characteristic and a prospective therapeutic method in targeted therapy.
Since ancient times, silver has been recognized as a natural antibacterial agent.Due to its exceptional broad-spectrum antimicrobial power, which has been proved at the Nano meter level, its use in the biomedical area is growing nowadays [106].AgNPs are the best known Nano products [107] have attracted considerable attention as antimicrobial agents [108].
The development of nanotechnology has allowed for the engineering of some traditional materials to display novel physiochemical and biological capabilities at the nanoscale [72].Numerous prior investigations have demonstrated the potential for using metal nanoparticle-based antibacterial formulations as potent bactericidal agents [106].A novel class of bactericidal materials against both Gram-positive and Gram-negative bacteria was introduced recently in the form of extremely reactive metal oxide nanoparticles.Silver nanoparticles, or AgNPs, have been the subject of the most research lately out of all the nanomaterials.AgNPs have long been demonstrated in numerous studies to have broad-spectrum antibacterial properties [109,110].Additionally, earlier research demonstrated that AgNPs showed anti-inflammatory properties in models of burn wounds and peritoneal adhesions [111,112].Apart from the aforementioned models, other models such as contaminated wounds also demonstrate the anti-inflammatory impact mediated by AgNPs [113], ulcerative colitis [114], and chronic venous leg ulcers [115], as well contact dermatitis model [116].In contrast to current antibiotic-coated sutures, immobilizing AgNPs on sutures may have antibacterial, anti-inflammatory, and pro-healing effects [62,72].
AgNPs have distinct chemical and physical characteristics [117] and have been used in a wide variety of applications [118].One typical side effect of intraperitoneal surgery is postoperative surgical adhesion, which can result in a number of problems, including adhesive minor and large bowel blockages and chronic abdominopelvic pain that has a major negative financial impact on medical expenses [119e121].Numerous attempts have been made to use anti-inflammatory drugs to lower the rate of postoperative surgical adhesion formation [122], fibrinolytic [123], anti-coagulants [124], mechanical barriers [125] and anti-biotic [126].There have also been reports of the effectiveness of silver nanoparticles with antibacterial qualities on the formation of surgical adhesions following surgery [127].Wound-bursting strength with elevated intestinal pressure is defined by a number of experimental studies pertaining to the strength of the developed intestinal anastomoses [47,128,129].
In order to compare the effects of L-PRF alone, L-PRF with chitosan, and L-PRF with chitosan & silver nanoparticle application on colon anastomosis regeneration and adhesion development, we conducted experimental research.We used immunohistochemical analysis, histopathological inspection, and clinical data to assess some of these promoters in the rabbit healing process.

Conclusion
Colon anastomosis is one of the most common surgical procedures in the field of gastrointestinal surgery.Poor wound healing at intestinal anastomotic sites could lead to severe and life-threatening complications.Anastomotic leakage is the most serious one that may reach up to 30% for colon anastomosis.New treatment modalities and materials are continuously needed to ameliorate colon anastomosis healing such as wrapping anastomotic sites by L-PRF alone or in combination with chitosan or AgNPs.

Ethics approval
All experiments were performed following relevant guidelines and regulations.The Welfare and Ethics Committee approved this study of the Faculty of Veterinary Medicine, Mansoura University, Egypt.All procedures in this study were performed following ARRIVE guidelines.